HEATING DEVICE, FIXING DEVICE, AND IMAGE FORMING APPARATUS

Abstract

A heating device includes a rotator having an internal space, a heater heating the rotator, lubricant applied to the rotator, a rotator support supporting the rotator, and a cover. The rotator support has a first opening communicating with the internal space of the rotator, penetrating through the rotator support, and extending in the longitudinal direction. The cover covers the first opening and has a face facing the first opening and a second opening communicating with the internal space of the rotator and an exterior of the cover. The cover maintains a temperature of the face of the cover at 40° C. or higher.

Description

BACKGROUND

Technical Field

Embodiments of the present disclosure generally relate to a heating device, a fixing device, and an image forming apparatus.

Related Art

One type of image forming apparatus such as a copier or a printer includes a fixing device that is a heating device heating a recording medium such as a sheet bearing an unfixed image to fix the unfixed image onto the recording medium.

Such a fixing device typically includes a rotator such as a belt and lubricant such as oil or grease applied to the inner face of the rotator in order to reduce sliding friction when the rotator rotates. The lubricant refers to a substance that is interposed between components to reduce frictional resistance between the components.

SUMMARY

This specification describes an improved heating device that includes a rotator, a heater, lubricant, a rotator support, and a cover. The rotator has an internal space inside a loop of the rotator. The heater heats the rotator. The lubricant is applied to an inner circumferential surface of the rotator. The rotator support supports an end of the rotator in a longitudinal direction of the rotator. The rotator support has a first opening communicating with the internal space of the rotator, penetrating through the rotator support, and extending in the longitudinal direction. The cover covers the first opening and has a face facing the first opening and a second opening communicating with the internal space of the rotator and an exterior of the cover. The cover maintains a temperature of the face of the cover at 40° C. or higher.

This specification also describes a fixing device including the heating device and an image forming apparatus including the heating device.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a configuration of an image forming apparatus according to an embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of a center portion of a fixing device according to an embodiment of the present disclosure;

FIG. 3 is a perspective view of the fixing device of FIG. 2;

FIG. 4 is a plan view of a heater according to an embodiment of the present disclosure;

FIG. 5 is a cross-sectional view of an end portion of a fixing device in the longitudinal direction of the fixing device according to a first embodiment of the present disclosure;

FIG. 6 is a side view of the fixing device illustrated in FIG. 5, as viewed from the left side of FIG. 5;

FIG. 7 is a perspective view of a cover of the fixing device according to the first embodiment of the present disclosure;

FIG. 8 is a table listing the results of tests in which generation rates of fine particles including ultrafine particles (FP/UFP), lowest temperatures of covers, and highest temperatures of covers were measured from two minutes after the start of continuous printing to ten minutes after the start of continuous printing in different conditions;

FIG. 9 is a cross-sectional view of an end portion of a fixing device in the longitudinal direction of the fixing device according to a second embodiment of the present disclosure;

FIG. 10 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2 and 5 but applicable to the above-described embodiments;

FIG. 11 is an exploded perspective view of the fixing device illustrated in FIG. 10;

FIG. 12 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, and 10 but applicable to the above-described embodiments;

FIG. 13 is an exploded perspective view of the fixing device illustrated in FIG. 12;

FIG. 14 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, 10, and 12 but applicable to the above-described embodiments;

FIG. 15 is an exploded perspective view of the fixing device illustrated in FIG. 14;

FIG. 16 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, 10, 12, and 14 but applicable to the above-described embodiments;

FIG. 17 is a cross-sectional view of the fixing device illustrated in FIG. 16, taken along the longitudinal direction of a fixing belt included in the fixing device;

FIG. 18 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, 10, 12, 14, and 16 but applicable to the above-described embodiments;

FIG. 19 is an exploded perspective view of the fixing device illustrated in FIG. 18;

FIG. 20 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, 10, 12, 14, 16, and 18 but applicable to the above-described embodiments;

FIG. 21 is a schematic cross-sectional view of a holding structure to hold a pressure roller illustrated in FIG. 20;

FIG. 22 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, 10, 12, 14, 16, 18, and 20 but applicable to the above-described embodiments;

FIG. 23 is a perspective view of a part of the fixing device illustrated in FIG. 22;

FIG. 24 is a cross-sectional view of a fixing device that is different from the fixing devices of FIGS. 2, 5, 10, 12, 14, 16, 18, 20, and 22 but applicable to the above-described embodiments;

FIG. 25 is an exploded perspective view of the fixing device illustrated in FIG. 24;

FIG. 26 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 27 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 28 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 29 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 30 is a cross-sectional view of an image forming apparatus having a configuration different from an image forming apparatus according to the above embodiments of the present disclosure;

FIG. 31 is a cross-sectional view of the fixing device illustrated in FIG. 30;

FIG. 32 is a plan view of the heater illustrated in FIG. 31;

FIG. 33 is a partial perspective view of the heater and a nip formation pad illustrated in FIG. 31;

FIG. 34 is a view to illustrate a method of attaching a connector to the heater illustrated in FIG. 31;

FIG. 35 is a diagram illustrating an arrangement of temperature sensors and thermostats included in the fixing device illustrated in FIG. 30;

FIG. 36 is a schematic diagram illustrating a groove of a flange illustrated in FIG. 34;

FIG. 37 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 38 is a perspective view of the heater, the first high thermal conductor, and the nip formation pad that are illustrated in FIG. 37;

FIG. 39 is a plan view of a heater 11 to illustrate an arrangement of a first high thermal conductor, according to an embodiment of the present disclosure;

FIG. 40 is a schematic diagram illustrating an arrangement of first high thermal conductors in a heater, according to an alternative embodiment of the present disclosure;

FIG. 41 is a plan view of a heater to illustrate an arrangement of a first high thermal conductor according to another alternative embodiment of the present disclosure;

FIG. 42 is a plan view of a heater to illustrate enlarged separation areas, according to an embodiment of the present disclosure.;

FIG. 43 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 44 is a perspective view of the heater, the first high thermal conductor, the second high thermal conductor, and the nip formation pad illustrated in FIG. 43;

FIG. 45 is a plan view of a heater to illustrate an arrangement of second high thermal conductors on a first high thermal conductor, according to an embodiment of the present disclosure.;

FIG. 46 is a schematic diagram of another arrangement of first high thermal conductors and second high thermal conductors;

FIG. 47 is a plan view of a heater to illustrate an arrangement of a second high thermal conductor, according to still another alternative embodiment of the present disclosure.;

FIG. 48 is a cross-sectional view of a fixing device having a configuration different from fixing devices according to the above embodiments of the present disclosure;

FIG. 49 is a schematic diagram illustrating a two-dimensional atomic crystal structure of graphene;

FIG. 50 is a schematic diagram illustrating a three-dimensional atomic crystal structure of graphite;

FIG. 51 is a schematic cross-sectional view of an inkjet image forming apparatus including a drying device, according to an embodiment of the present disclosure;

FIG. 52 is a schematic cross-sectional view of the drying device of FIG. 51;

FIG. 53 is a schematic cross-sectional view of an image forming apparatus including a laminating device according to an embodiment of the present disclosure;

FIG. 54 is a cross-sectional view of an end portion of a fixing device in the longitudinal direction of the fixing device according to a comparative example;

FIG. 55 is a block diagram including a controller connected to a temperature sensor, a heater, and a fan;

FIG. 56 is a flowchart illustrating a control according to an embodiment of the present disclosure; and

FIG. 57 is a flowchart illustrating a control according to an embodiment of the present disclosure.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

With reference to the accompanying drawings, descriptions are given below of embodiments of the present disclosure. In the drawings for illustrating embodiments of the present disclosure, like reference signs denote like elements, and overlapping description may be simplified or omitted as appropriate.

FIG. 1 is a schematic diagram of a configuration of an image forming apparatus according to an embodiment of the present disclosure. In the following description, the “image forming apparatus” includes a printer, a copier, a facsimile machine, or a multifunction peripheral having at least two of printing, copying, scanning, and facsimile functions. “Image formation” means the formation of images with meanings such as characters and figures and the formation of images with no meanings such as patterns. Initially, with reference to FIG. 1, a description is given below of the overall configuration and operation of an image forming apparatus 100 according to the present embodiment.

As illustrated in FIG. 1, the image forming apparatus 100 according to the present embodiment includes an image forming section 200 to form an image on a sheet-shaped recording medium such as a sheet, a fixing section 300 to fix the image onto the recording medium, a recording medium feeder 400 to feed the recording medium to the image forming section 200, and a recording medium ejection section 500 to eject the recording medium to an outside of the image forming apparatus 100.

The image forming section 200 includes four process units 1Y, 1M, 1C, and 1Bk as image forming units, an exposure device 6 to form an electrostatic latent image on a photoconductor 2 in each of the process units 1Y, 1M, 1C, and 1Bk, and a transfer device 8 to transfer an image onto the recording medium.

The process units 1Y, 1M, 1C, and 1Bk have the same configuration except for containing different color toners (developers), i.e., yellow (Y), magenta (M), cyan (C), and black (Bk) toners, respectively, corresponding to decomposed color separation components of a full-color image. Specifically, each of the process units 1Y, IM, 1C, and 1Bk includes the photoconductor 2 serving as an image bearer bearing the image on the surface of the image bearer, a charger 3 to charge the surface of the photoconductor 2, a developing device 4 to supply the toner as the developer to the surface of the photoconductor 2 to form a toner image, and a cleaner 5 to clean the surface of the photoconductor 2.

The transfer device 8 includes an intermediate transfer belt 11, primary transfer rollers 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt stretched by a plurality of support rollers. Four primary transfer rollers 12 are disposed inside the loop of the intermediate transfer belt 11. Each of the primary transfer rollers 12 is in contact with the corresponding photoconductor 2 via the intermediate transfer belt 11 to form a primary transfer nip between the intermediate transfer belt 11 and each photoconductor 2. The secondary transfer roller 13 is in contact with the outer circumferential surface of the intermediate transfer belt 11 to form a secondary transfer nip.

The fixing section 300 includes a fixing device 20 as a heating device that heats the recording medium bearing the transferred image. The fixing device 20 includes a fixing belt 21 and a pressure roller 22. The fixing belt 21 heats the image on the recording medium. The pressure roller 22 contacts the fixing belt 21 to form an area of contact, called a fixing nip, between the fixing belt 21 and the pressure roller 22.

The recording medium feeder 400 includes a sheet tray 14 to store sheets P as recording media and a feed roller 15 to feed the sheet P from the sheet tray 14. Although a “recording medium” is described as a “sheet of paper” (referred to simply as “sheet”) in the following description, the “recording medium” is not limited to the sheet of paper. Examples of the “recording medium” include not only a sheet of paper but also an overhead projector (OHP) transparency sheet, a fabric, a metallic sheet, a plastic film, and a prepreg sheet including carbon fibers previously impregnated with resin. Examples of the “sheet” include thick paper, a postcard, an envelope, thin paper, coated paper (e.g., coat paper and art paper), and tracing paper, in addition to plain paper.

The recording medium ejection section 500 includes an output roller pair 17 to eject the sheet P to the outside of the image forming apparatus 100 and an output tray 18 to place the sheet P ejected by the output roller pair 17.

To provide a fuller understanding of the embodiments of the present disclosure, a description is now given of the printing operation of the image forming apparatus 100 according to the present embodiment, with continued reference to FIG. 1.

When the image forming apparatus 100 starts the printing operation, the photoconductors 2 in the process units 1Y, 1M, 1C, and 1Bk and the intermediate transfer belt 11 in the transfer device 8 start rotating. The feed roller 15 starts rotating to feed the sheet P from the sheet tray 14. The sheet P fed from the sheet tray 14 is brought into contact with a timing roller pair 16 and temporarily stopped until the image forming section 200 forms the image to be transferred to the sheet P.

In each of the process units 1Y, 1M, 1C, and 1Bk, the charger 3 uniformly charges the surface of the photoconductor 2 at a high electric potential. Based on image data of a document read by a document reading device or print data instructed to print by a terminal, the exposure device 6 exposes the charged surface of each of the photoconductors 2. As a result, the electric potential at an exposed portion on the surface of each of the photoconductors 2 is decreased. Thus, an electrostatic latent image is formed on the surface of each of the photoconductors 2. The developing device 4 supplies toner to the electrostatic latent image formed on the photoconductor 2 to form the toner image on the photoconductor 2. The toner images formed on the photoconductors 2 reach the primary transfer nips defined by the primary transfer rollers 12 with the rotation of the photoconductors 2 and are transferred onto the intermediate transfer belt 11 rotated counterclockwise in FIG. 1 successively such that the toner images are superimposed on the intermediate transfer belt 11, forming a full-color toner image thereon. Thus, the full-color toner image is formed on the intermediate transfer belt 11. The image forming apparatus 100 can form a monochrome toner image by using any one of the four process units 1Y, 1M, 1C, and 1Bk, or can form a bicolor toner image or a tricolor toner image by using two or three of the process units 1Y, 1M, 1C, and 1Bk. After the toner image is transferred to the intermediate transfer belt 11, the cleaner 5 removes the residual toner that remains on the photoconductor 2 from the surface of the photoconductor 2.

In accordance with the rotation of the intermediate transfer belt 11, the toner image transferred onto the intermediate transfer belt 11 is conveyed to the secondary transfer nip (the position of the secondary transfer roller 13) and is transferred onto the sheet P conveyed by the timing roller pair 16. The sheet P bearing the toner image is conveyed to the fixing device 20. In the fixing device 20, the fixing belt 21 and the pressure roller 22 apply heat and pressure to the toner image on the sheet P to fix the toner image onto the sheet P. Then, the sheet P bearing the fixed toner image is conveyed to the recording medium ejection section 500. In the recording medium ejection section 500, the output roller pair 17 ejects the sheet P onto the output tray 18. Thus, a series of printing operations is completed.

Subsequently, with reference to FIGS. 2 and 3, a description is given of a basic configuration of the fixing device 20 according to the present embodiment. FIG. 2 is a cross-sectional view of a center portion of the fixing device 20 according to the present embodiment, taken along a line Mx-Xm of FIG. 3 at the center of the fixing belt 21 in the longitudinal direction of the fixing belt 21. FIG. 3 is a perspective view of the fixing device 20 in the present embodiment. In the following description, the “longitudinal direction” of the fixing belt 21 means a direction orthogonal to the rotation direction of the fixing belt and along the outer circumferential surface of the fixing belt.

The above-described “longitudinal direction” of the fixing belt 21 is a direction indicated by a two-headed arrow X in FIG. 3 and a direction parallel with the rotation axis direction of the pressure roller 22 or the width direction of the sheet passing through the fixing nip between the fixing belt 21 and the pressure roller 22. The width direction of the sheet is a direction intersecting a sheet conveyance direction in which the sheet is conveyed.

As illustrated in FIG. 2, the fixing device 20 according to the present embodiment includes a heater 23, a heater holder 24, a stay 25, and temperature sensors 26 in addition to the fixing belt 21 and the pressure roller 22.

The fixing belt 21 is a rotator (specifically, a first rotator or a fixing rotator) that contacts a surface of the sheet P bearing unfixed toner to fix the unfixed toner (in other words, an unfixed image) onto the sheet P.

The fixing belt 21 is an endless belt including a base layer, an elastic layer, and a release layer successively layered from the inner circumferential surface to the outer circumferential surface. The base has, for example, a thickness of 30 μm to 50 μm and is made of metal such as nickel or stainless steel or resin such as polyimide. The elastic layer has a thickness of 100 μm to 300 μm and is made of rubber such as silicone rubber, silicone rubber foam, or fluorine rubber. The elastic layer of the fixing belt 21 eliminates slight surface asperities of the fixing belt 21 at the fixing nip, thus facilitating uniform conduction of heat to the toner image on the sheet P. The release layer of the fixing belt 21 has a thickness of 10 μm to 50 μm and is made of, for example, tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), polyimide, polyetherimide, or polyether sulfide (PES). The release layer of the fixing belt 21 facilitates the separation of toner contained in the toner image on the sheet P from the fixing belt 21. In other words, the release layer of the fixing belt 21 facilitates the release of the toner from the fixing belt 21. To reduce the size and thermal capacity of the fixing belt 21, the fixing belt 21 preferably has a total thickness equal to or less than 1 mm and a loop diameter equal to or less than 30 mm.

Belt holders 27 illustrated in FIG. 3 are a pair of rotator holders and rotatably hold both end portions of the fixing belt 21 in the longitudinal direction. Both end portions of the fixing belt 21 in the longitudinal direction described above are not limited to both edges of the fixing belt 21, which are the most ends in the longitudinal direction of the fixing belt 21. Similarly, an “end portion” of the fixing belt 21 in the longitudinal direction, which is described below, is not limited to a longitudinal edge of the fixing belt 21, which is the most end in the longitudinal direction of the fixing belt 21. The end portion of the fixing belt 21 in the longitudinal direction includes, in addition to the longitudinal edge of the fixing belt 21, a position within a range having one-third of the length of the fixing belt 21 from the edge of the fixing belt 21 in the longitudinal direction of the fixing belt 21. Accordingly, the belt holder 27 may hold a portion of the fixing belt 21 that is not the longitudinal edge of the fixing belt 21 as the end portion of the fixing belt 21 in addition to the longitudinal edge of the fixing belt 21.

Specifically, the belt holder 27 includes an insertion 27a, a restraint 27b, and a fixed portion 27c. The insertion 27a has a C-shaped cross-section and is inserted into the longitudinal end portion of the fixing belt 21. The restraint 27b has an outer diameter greater than that of the insertion 27a. The fixed portion 27c is fixed to a side plate described later. The restraint 27b has an outer diameter greater than that of at least the fixing belt 21 to restrain the deviation or movement of the fixing belt 21 in the longitudinal direction X. The insertion 27a has an outer diameter equal to or smaller than the inner diameter of the fixing belt 21 and is inserted into the longitudinal end portion of the fixing belt 21 to hold the inner circumferential surface of the fixing belt 21 such that the fixing belt 21 can rotate.

The pressure roller 22 is a rotator (specifically, a second rotator or counter rotator) disposed to face the outer circumferential surface of the fixing belt 21. The pressure roller 22 is a pressure rotator pressed against the outer circumferential surface of the fixing belt 21.

The pressure roller 22 is in contact with the outer circumferential surface of the fixing belt 21 to form the nip N between the pressure roller 22 and the fixing belt 21 to pass the sheet P.

Specifically, the pressure roller 22 includes a solid iron core, an elastic layer on an outer circumferential surface of the core, and a release layer resting on an outer circumferential surface of the elastic layer. The core may be hollow. The elastic layer is made of, for example, silicone rubber, silicone rubber foam, or fluorine rubber. The release layer is made of a fluororesin such as PFA or PTFE.

The heater 23 heats the fixing belt 21. The heater 23 in the present embodiment as a heat source is a planar heater having a plate shape and including resistive heat generators 31. The heater 23 is disposed to contact the inner circumferential surface of the fixing belt 21. Power is supplied to the heater 23, and the resistive heat generators 31 generate heat. The heat is transferred to the fixing belt 21 to heat the fixing belt 21.

The heater holder 24 is a heat source holder to hold the heater 23 inside the loop of the fixing belt 21. Since the heater holder 24 is subject to temperature increase by heat from the heater 23, the heater holder 24 is made of a heat-resistant material. The heater holder 24 made of heat-resistant resin having low thermal conduction, such as a liquid crystal polymer (LCP), reduces heat transfer from the heater 23 to the heater holder 24 and provides efficient heating of the fixing belt 21. The heater holder 24 in the present embodiment includes a guide 28 to guide the fixing belt 21. The guide 28 has a guide face having an arc or a projected curve curving along the inner circumferential surface of the fixing belt 21. When the fixing belt 21 rotates, the guide face guides the fixing belt 21, and the fixing belt 21 slides on the guide face. In the present embodiment, the guide 28 is formed integrally with the heater holder 24 but may be formed separately.

The stay 25 is a reinforcement to reinforce the heater holder 24. The stay 25 supports a stay side face of the heater holder 24 opposite a nip side face of the heater holder 24. The nip side face faces the pressure roller 22. Accordingly, the stay 25 prevents the heater holder 24 and the heater 23 from being bent, in a direction orthogonal to the longitudinal direction of the fixing belt 21 in particular, by the pressing force of the pressure roller 22. As a result, the fixing nip N having a uniform width is obtained. The stay 25 is preferably made of iron-based metal such as steel use stainless (SUS) or steel electrolytic cold commercial (SECC) to enhance the rigidity.

The temperature sensor 26 is a temperature detector that contacts the heater 23 and detects the temperature of the heater 23. The temperature sensor 26 in the present embodiment is disposed so as to be in contact with a surface of the heater 23 opposite a surface of the heater 23 facing the nip N. The temperature sensor 26 is not limited to the contact-type temperature sensor that contacts the heater 23. The temperature sensor 26 may be a non-contact-type temperature sensor that is disposed not to be in contact with the heater 23. The temperature sensor 26 may be, for example, a thermopile, a thermostat, a thermistor, or a non-contact-type (NC) temperature sensor.

FIG. 4 is a plan view of the heater 23 according to the present embodiment.

As illustrated in FIG. 4, the heater 23 according to the present embodiment includes a base 30 having a plate shape, multiple resistive heat generators 31 disposed on the base 30, an insulation layer 32 covering the multiple resistive heat generators 31, and a pair of electrodes 33 connected to multiple heat generators 31 via power supply lines 34.

The base 30 is formed of a longitudinal plate extending in the lateral direction in FIG. 4. The base 30 is disposed such that the longitudinal direction of the base 30 is substantially parallel with the longitudinal direction X of the fixing belt 21 illustrated in FIG. 3. The material of the base 30 is preferably a nonmetallic material having excellent thermal resistance and insulating properties, such as glass, mica, or ceramic such as alumina or aluminum nitride. Interposing another insulation layer between the base 30 and the resistive heat generators 31 enables using a conductive material such as a metal material as the material of the base 30. Low-cost aluminum or stainless steel is favorable as the metal material of the base 30. To enhance the thermal uniformity of the heater 23 and image quality, the base 30 may be made of a material having high thermal conductivity, such as copper, graphite, or graphene.

The multiple resistive heat generators 31 function as a heat generation part to which the power is supplied to generate heat. The multiple resistive heat generators 31 are arranged at intervals in the longitudinal direction of the base 30. A gap between neighboring resistive heat generators 31 is preferably 0.2 mm or more, and is more preferably 0.4 mm or more, from the viewpoint of maintaining the insulation between the neighboring resistive heat generators 31. In addition, the gap between the resistive heat generators 31 adjacent to each other is preferably 5 mm or less, and is more preferably 1 mm or less, from the viewpoint of reducing temperature unevenness across an area in the longitudinal direction because a too large gap between the resistive heat generators 31 adjacent to each other easily causes a temperature drop in the gap. The resistive heat generator 31 is, for example, produced as below. Silver palladium (AgPd) and glass powder are mixed to make paste. The paste is screen-printed on the surface of the base 30. After the paste is screen-printed, the base 30 is subject to firing. Thus, the resistive heat generator 31 is produced. The material of the resistive heat generator 31 may contain a resistance material, such as silver alloy (e.g., AgPt) or ruthenium oxide (RuO₂).

Each of the resistive heat generators 31 is coupled to the pair of electrodes 33 via the power supply lines 34.

In the present embodiment, one of the pair of electrodes 33 is disposed on one end of the base 30 in the longitudinal direction of the base 30, and the other one of the pair of electrodes 33 is disposed on the other end of the base 30 in the longitudinal direction. The resistive heat generators 31 are electrically coupled in parallel to the pair of electrodes 33. Connecting the connector as a power supply component to each of the electrodes 33 enables supplying power from a power supply to each resistive heat generator 31.

The insulation layer 32 covers the resistive heat generators 31 and power supply lines 34 to enhance durability and insulate the resistive heat generators 31 and power supply lines 34 from other parts. However, the insulation layer 32 does not cover the electrode 33 to expose the electrode 33 so as to be connected to the connector. The insulation layer 32 may be made of, for example, heat-resistant glass. Although the resistive heat generators 31, the electrodes 33, the power supply lines 34, and the insulation layer 32 are disposed on the side of the base 30 facing the fixing belt 21 (that is, the fixing nip N) in the present embodiment (see FIG. 2), the resistive heat generators 31, the electrodes 33, the power supply lines 34, and the insulation layer 32 may be disposed on the opposite side of the base 30, that is, the side facing the heater holder 24. In this case, since the heat of the resistive heat generators 31 is transmitted to the fixing belt 21 through the base 30, it is preferable that the base 30 be made of a material with high thermal conductivity such as aluminum nitride.

The heat source to heat the fixing belt 21 may be a radiant heat type heater such as a halogen heater, a carbon heater, or a ceramic heater, or an electromagnetic induction heating system, in addition to the planar heater 23 having the plate shape as in the present embodiment.

The fixing device 20 according to the present embodiment operates as follows.

When the printing operation starts, a driver drives and rotates the pressure roller 22 in a direction indicated by an arrow in FIG. 2, and the rotation of the pressure roller 22 rotates the fixing belt 21. The power is supplied to the heater 23, and the heater 23 generates heat to heat the fixing belt 21. At this time, the temperature sensors 26 detect the temperatures of the heater 23, and a controller controls the heat generation amount of the heater 23 based on the detected temperatures so that the fixing belt 21 keeps a predetermined fixing temperature that can fix the toner image onto the sheet. The sheet P bearing the unfixed toner image is conveyed to the fixing nip N between the fixing belt 21 and the pressure roller 22, and the fixing belt 21 and the pressure roller 22 apply heat and pressure to the sheet P to fix the unfixed toner image onto the sheet P.

Incidentally, Japanese Unexamined Patent Application Publication No. H08262903 discloses a fixing device including a rotatable heating and fixing roller, an endless belt (that is the fixing belt) contacting the heating and fixing roller, and a pressure pad (that is the nip formation pad) in pressure contact with the heating and fixing roller (that is the pressure roller) via the endless belt. The pressure pad is disposed inside the loop of the endless belt, does not rotate, and presses the endless belt against the heating and fixing roller so that the endless belt is in pressure contact with the heating and fixing roller. As a result, the surface of the heating and fixing roller is elastically deformed to form a belt nip between the endless belt and the heating and fixing roller to pass a recording sheet (that is a recording medium or a recording material, holding a toner image). Japanese Unexamined Patent Application Publication No. H08262903 suggests that the above configuration of the image fixing device reduces heat loss in the belt nip and can prevent the occurrence of a speed difference between the recording sheet and the heating and fixing roller and the disturbance of the toner image due to air or water vapor in the belt nip.

However, a large friction coefficient between the inner circumferential surface of the endless belt and the pressure pad serving as the nip formation pad increases the driving torque of the heating and fixing roller and the stress acting on the gear receiving portion, which may damage a gear and a core. In addition, the frictional force between the endless belt and the pressure pad that is too large as compared with the driving force of the heating and fixing roller to drive the endless belt causes a slip between the heating and fixing roller and the endless belt, which may cause shifting the unfixed toner image on the recording sheet.

In order to solve the above disadvantages, Japanese Patent Application Publication No. H10213984 proposes a fixing device including modified silicone oil as lubricant interposed between the pressure pad (in other words, a pressing pad) and the endless belt. Japanese Patent Application Publication No. H10213984 suggests that the above-described fixing device can have a stable running performance (in other words, a stable rotation performance) of the endless belt without deteriorating the releasing property of the recording sheet from the heating and fixing roller.

However, Japanese Patent Application Publication No. H10213984 discloses only reducing the friction coefficient of a low-friction sheet to form a low-friction surface of the pressure pad on which the endless belt slides in the fixing device. The above document does not consider the surface wetting characteristics of the modified silicone oil with respect to the low-friction sheet or the endless belt. As a result, the technology disclosed in the above document has problems that stably holding the modified silicone oil is difficult, and maintenance is difficult.

In order to solve the problems, Japanese Unexamined Patent Application Publication No. 2010-211220 proposes a configuration including a slide sheet interposed between the pressure pad as the pressing member and the endless belt that is a resin film tube, and the slide sheet is a non-porous sheet including a base having irregularities, a slide face formed on the base, and a heat-resistant resin contained in at least the slide face. Japanese Unexamined Patent Application Publication No. 2001-249588 proposes another fixing device including the pressure pad serving as the pressing member having the slide face, and a portion including the slide face is made of a fluororesin subjected to lipophilization treatment or a lipophilization agent used in combination with a fluororesin. The above-described documents suggest that the disclosed technology can improve wettability with respect to the lubricant and hardly causes oil shortage. As a result, the above-described documents suggest that the disclosed technology can stabilize sliding performance and maintain a good quality of a fixed image and a good fixing property.

The fixing device including the nip formation pad (that is the pressure pad), the fixing belt (that is the endless belt), and the lubricant such as silicone oil is interposed between the slide face of the nip formation pad and the inner circumferential surface of the fixing belt has an advantage that energy efficiency is high and energy saving is easily achieved. For this reason, many image forming apparatuses include the above-described fixing devices, respectively.

Japanese Unexamined Patent Application Publication No. 2019-8159 discloses a configuration including a sheet impregnated with lubricant such as fluorine grease, silicone grease, or silicone oil and interposed between the nip formation pad and the fixing belt in order to reduce sliding friction between the nip formation pad and the fixing belt.

In the fixing device 20 according to the present embodiment illustrated in FIG. 2, rotating the fixing belt 21 generates sliding friction between the fixing belt 21 and the heater 23 and the heater holder 24 (that is a guide 28) which are in contact with the fixing belt 21. To reduce the sliding friction, lubricant such as silicone oil, silicone grease, fluorine oil, or fluorine grease is applied to the inner circumferential surface of the fixing belt 21 according to the present embodiment. The lubricant is interposed between the fixing belt 21 and the heater 23 and between the fixing belt 21 and the heater holder 24 (that is the guide 28) to reduce the sliding friction between the fixing belt 21 and the heater 23 and between the fixing belt 21 and the heater holder 24.

In the fixing device 20 according to the present embodiment in which the pair of belt holders 27 holds the fixing belt 21, rotating the fixing belt 21 also causes sliding friction between the fixing belt 21 and the belt holders 27. For this reason, the same lubricant as described above is interposed between each belt holder 27 and the fixing belt 21.

Applying the lubricant to the inner circumferential surface of the fixing belt 21 can reduce the sliding friction between the fixing belt 21 and the above-described members in contact with the fixing belt 21. In contrast, heat generated by the heater 23 causes a temperature rise of the lubricant adhered to the inner circumferential surface of the fixing belt 21, and fine particles may be generated from the lubricant. Specifically, the temperature rise of the lubricant on the inner circumferential surface of the fixing belt 21 volatilizes a part of the low-molecular components of the lubricant, and the volatilized components are cooled by air and aggregated. As a result, fine particles are generated. The “fine particles” described above and below mean fine particles including ultrafine particles (that are referred to as “FP/UFP ” below) measured by an apparatus and conditions in conformity with the fine particles standard of Blue Angel DE-UZ219 and mean particles having a particle size of 5.6 nm or more and 560 nm or less.

Currently, due to an increase in the awareness of environmental issues, the reduction of FP/UFP discharged from products has been desired. The image forming apparatuses that reduce the generation of FP/UFP are also to be developed.

However, the pair of belt holders holding both ends of the fixing belt in the longitudinal direction of the fixing belt typically has the C-shape in the cross section of the belt holder or the tube shape. As a result, the belt holder 27 has an opening 27d penetrating the inside of the belt holder 27 and extending in the longitudinal direction X of the fixing belt 21

In this case, the FP/UFP generated from the lubricant inside the loop of the fixing belt 21 are discharged to the outside through the opening 27d of the belt holder 27 as indicated by arrows in FIG. 54.

In the embodiments of the present disclosure, the following countermeasures are taken to reduce the amount of FP/UFP discharged to the outside. A configuration of a first embodiment of the present disclosure is described below with reference to FIGS. 5 to 7.

FIG. 5 is a cross-sectional view of an end portion of the fixing device 20 in the longitudinal direction of the fixing device 20 according to the first embodiment of the present disclosure. FIG. 6 is a side view of the fixing device 20 illustrated in FIG. 5 as viewed from the left side of FIG. 5, and FIG. 7 is a perspective view of a cover 40 included in the fixing device 20 according to the first embodiment.

As illustrated in FIGS. 5 and 6, the fixing device 20 according to the first embodiment includes a side plate 29 as a support to support the belt holder 27. In the first embodiment, the side plate 29 supports the fixing belt 21 via the belt holder 27. The belt holder 27 and the side plate 29 function as a rotator support 10 that rotatably supports the end portion of the fixing belt 21 in the longitudinal direction of the fixing belt 21. In the present embodiment, the belt holder 27 and the side plate 29 are configured as separate parts, but may be configured integrally as one part.

Since the belt holder 27 has the C-shape in the cross section or the tube shape, the opening 27d of the belt holder 27 penetrates the inside of the belt holder 27 and extends in the longitudinal direction X of the fixing belt 21. As a result, an internal space of the fixing belt 21 is opened to the outside through the opening 27d of the belt holder 27.

The fixing device 20 according to the first embodiment includes the cover 40 that covers the opening 27d of the belt holder 27 to prevent the FP/UFP generated inside the loop of the fixing belt 21 from being discharged to the outside. As illustrated in FIG. 5, the cover 40 is disposed outside from the side plate 29 in the longitudinal direction X of the fixing belt 21 and covers the outside of the opening 27d.

Although FIG. 5 illustrates the cover 40 disposed on one side plate 29 adjacent to one end portion of the fixing belt 21 in the longitudinal direction, the cover 40 is also disposed on the other side plate adjacent to the other end portion of the fixing belt 21 in the longitudinal direction.

Subsequently, the configuration of the cover 40 according to the first embodiment is described below with reference to FIG. 7.

As illustrated in FIG. 7, the cover 40 is a box-shaped component having a rectangular opening 40a. The cover 40 has a bottom wall 41 disposed so as to face the opening 40a and four side walls 42 to 45 extending from the bottom wall 41 in a direction intersecting or orthogonal to the bottom wall 41. The bottom wall 41 and the side walls 42 to 45 are connected to each other and form the cover 40 as one component.

The cover 40 includes an attachment plate 46 attached to an outer face of the side plate 29 in the longitudinal direction X of the fixing belt 21. The attachment plate 46 protrudes from one side wall 45 of the four side walls 42 to 45. The attachment plate 46 has a hole 46a through which a screw as a fastener is inserted. Inserting the screw into the hole 46a and fastening the screw to the side plate 29 attaches the cover 40 to the outer face of the side plate 29.

As illustrated in FIGS. 5 and 6, the cover 40 is attached to and placed on the side plate 29 such that the side plate 29 covers the opening 40a of the cover 40, and the cover 40 covers the entire opening 27d of the belt holder 27 (in other words, overlays the entire opening region of the opening 27d) when viewed from the longitudinal direction X of the fixing belt 21 (see FIG. 6).

As illustrated in FIGS. 5 and 6, the bottom wall 41 of the cover 40 attached to the side plate 29 faces the opening 27d in the longitudinal direction X of the fixing belt 21, and the side walls 42 to 45 are disposed to surround the periphery of the opening 27d. In other words, the cover 40 includes a first wall (the bottom wall 41), a second wall (the side wall 42), a third wall (the side wall 43), a fourth wall (the side wall 44), and a fifth wall (the side wall 45). The first wall faces the opening 27d in the longitudinal direction X of the fixing belt 21. The second wall and the third wall are closer to the opening 27d than the first wall in the longitudinal direction X of the fixing belt 21. The second wall and the third wall face each other across the opening 27d in a direction Y (see FIG. 6) perpendicular to the longitudinal direction X. The fourth wall and the fifth wall are closer to the opening 27d than the first wall in the longitudinal direction X of the fixing belt 21. The fourth wall and the fifth wall face each other across the opening 27d in a direction Z (see FIG. 6) perpendicular to the longitudinal direction X and the direction Y.

As described above, since the cover 40 in the first embodiment covers the entire opening 27d, the cover 40 prevents the FP/UFP generated from the lubricant inside the loop of the fixing belt 21 by the temperature rise of the lubricant from being discharged to the outside of the image forming apparatus 100 through the opening 27d. In other words, the FP/UFP generated inside the loop of the fixing belt 21 move to the outside of the image forming apparatus 100 through the opening 27d of the belt holder 27, but the cover 40 regulates the movement of the FP/UFP to prevent the FP/UFP from being discharged to the outside.

Since the cover 40 prevents the FP/UFP from being discharged to the outside, the FP/UFP stay in the cover 40. As a result, the concentration of the FP/UFP in the cover 40 increases, the gas component of the FP/UFP condenses, and the FP/UFP is likely to aggregate. The aggregation of the FP/UFP increases the particle diameter and decreases the number of FP/UFP. As a result, the number of FP/UFP discharged to the outside can be decreased.

The material of the cover 40 may be any material having heat resistance. Specifically, the cover 40 may be made of heat-resistant resin such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), and polyether ether ketone (PEEK) or metal such as iron, aluminum, copper, and nickel, alloy such as stainless steel or bronze; and composite of above materials. Among these materials, metal or alloy is particularly preferable because the temperature of the cover made of metal or alloy is easily controlled. Further, in consideration of thermal conductivity and cost, aluminum, iron, or bronze is preferable.

In order to completely prevent the FP/UFP from being discharged from the internal space of the fixing belt to the outside, preferably, the cover 40 completely blocks the opening 27d. However, completely blocking the opening 27d prevents, in addition to the FP/UFP, hot air in the internal space of the fixing belt 21 from being discharged to the outside. As a result, continuous printing causes a temperature rise in the internal space of the fixing belt 21, which may cause disadvantages such as disconnection of the heater 23 and deterioration of components.

To countermeasure the above-described disadvantage, the cover 40 in the first embodiment has another opening 40d (see FIG. 5). In the following description, the opening 27d of the belt holder 27 is referred to as a first opening 27d, and the opening 40d is referred to as a second opening 40d. As illustrated in FIG. 7, the second opening 40d is formed by cutting out a part of the lower side wall 43. Forming the second opening 40d as described above causes the internal space of the fixing belt 21 to communicate with an external space of the cover 40 (in other words, an exterior of the cover 40) through the second opening 40d.

As a result, the fixing device according to the first embodiment can discharge the hot air in the internal space of the fixing belt 21 to the outside through the second opening 40d. Air in the external space of the cover 40 can also flow into the internal space of the fixing belt 21 through the second opening 40d and the first opening 27d. As a result, the air in the internal space of the fixing belt 21 can be replaced with the air in the external space of the cover 40 through the second opening 40d, which enables reducing the temperature rise in the air in the internal space of the fixing belt 21 and avoiding the occurrence of the disadvantages such as the disconnection of the heater 23 and the deterioration of the components due to the temperature rise.

Since the FP/UFP are generated in the internal space of the fixing belt 21 and are discharged together with the hot air in the internal space of the fixing belt 21, the FP/UFP tend to move upward together with the updraft of the hot air. Accordingly, the second opening 40d is preferably disposed below the first opening 27d as illustrated in FIGS. 5 and 6. Locating the second opening 40d below the first opening 27d causes the FP/UFP to be less likely to be discharged from the second opening 40d. Locating the second opening 40d below the first opening 27d causes the FP/UFP to stay in the cover 40 for a long time, which promotes the aggregation of the FP/UFP in the cover 40. The number of the second opening 40d is not limited to one, and multiple second openings may be disposed.

The present inventors considered that the cover 40 cooled the gaseous FP/UFP to condense the FP/UFP and reduce the number of FP/UFP discharged as described above in the fixing device according to the present embodiment. In order to further promote the condensation of the gaseous FP/UFP, the present inventors cooled the cover to decrease the temperature of the cover 40. However, the number of discharged FP/UFP was not reduced as expected.

In contrast, the present inventors increased the temperature of the cover 40. Contrary to expectation, the number of discharged FP/UFP decreased. The present inventors examined the particle size of the FP/UFP discharged at this time and found that the particle size increased. This means that so-called aggregation growth of FP/UFP occurred. In the aggregation growth, a gas component of FP/UFP aggregates on the surface of other FP/UFP.

For example, many cyclic siloxanes, which are cited as one of the causative substances of FP/UFP, become solid when the temperature is low, and become liquid when the temperature is high. The liquid FP/UFP are integrated at the moment when the liquid FP/UFP contact each other, and aggregation occurs quickly. However, maintaining the temperature of the cover 40 to be high increases the time during which the gas component of the FP/UFP in the cover 40 is in a gaseous state. The present inventors considered that the above-described environment is likely to cause the aggregation (aggregation growth) of the FP/UFP. In contrast, maintaining the temperature of the cover 40 to be low causes the gas component of the FP/UFP to be less likely to maintain the gaseous state. The present inventors considered that a part of the FP/UFP adheres to the cover 40 before the gas component of FP/UFP aggregates on the surface of other FP/UFP, which causes the concentration of the FP/UFP in the cover 40 to be low. As a result, it is considered that the aggregation of FP/UFP is not promoted.

As described above, the present inventors found that maintaining the temperature of the cover 40 to be high is important to promote the aggregation of the FP/UFP in the cover 40.

In particular, the FP/UFP of the cyclic siloxane having large particle diameters have chemical affinity with the FP/UFP of higher alcohol or paraffin, are easily aggregated in the image forming apparatus, and can reduce the number of FP/UFP discharged from the entire image forming apparatus. Further, since the FP/UFP having large particle diameters are easily collected by a filter, the image forming apparatus equipped with the filter can effectively reduce the number of the FP/UFP to be discharged.

The present inventors investigated the temperature of the cover 40 to promote the aggregation of the FP/UFP. As a result, the present inventors found that the temperature of the cover 40 that is 40° C. or higher effectively promoted the aggregation of the FP/UFP. In other words, the present inventors found that the temperature of the cover 40 that is 40° C. or higher effectively promoted the aggregation of the FP/UFP and reduced the generation rate of the FP/UFP (in other words, the number of the FP/UFP discharged from the image forming apparatus). The following describes experimental results which are the basis of such findings.

The present inventors performed four experiments under different conditions as described below. In the following description, the experiments are referred to as a first example, a second example, a first comparative example, and a second comparative example. In the experiments, fixing devices having different structures were installed in the image forming apparatuses. Each image forming apparatus was placed in a test room conforming to Blue Angel DE UZ219. Each image forming apparatus performed continuous printing for ten minutes, and the FP/UFP were measured by the measuring method conforming to Blue Angel DE UZ219. Generation rates of the FP/UFP (that is, the number of particles of the FP/UFP discharged from the image forming apparatus performing the continuous printing for ten minutes), lowest temperatures of covers, and highest temperatures of covers were measured. The generation rate of the FP/UFP was measured by a measuring device (FAST MOBILITY PARTICLE SIZER (FMPS) Model 3091 manufactured by TSI Incorporated). The temperature of the cover 40 was measured at a face 40e (an inner face) of the cover 40. The face 40e faces the first opening 27d (see FIG. 5).

Since the FP/UFP are hardly discharged from the internal space of the fixing belt in less than two minutes after the start of the continuous printing, the measurements of the generation rate of the FP/UFP and the temperature of the cover were started at two minutes after the start of the continuous printing. The measurements are to be completed ten minutes after the start of the continuous printing because the image forming apparatuses in the market generally perform the continuous printing within several minutes and rarely perform the continuous printing of 5 minutes or more. During the measurements, the image forming apparatuses formed no image on the sheets. Other than that, the measurements were performed with apparatuses and under conditions compliant with the FP/UFP (fine particles) standards specified by the Blue Angel.

FIRST EXAMPLE

In the first example, the fixing device had the same structure as that of the first embodiment of the present disclosure illustrated in FIGS. 2 to 7. The cover was made of stainless steel and fastened to the side plate of the fixing device with a screw, and the temperature of the cover was maintained to be 40° C. or higher.

SECOND EXAMPLE

In the second example, the cover was made of aluminum, and other conditions were the same as those in the first example.

First Comparative Example

In the first comparative example, the measurements were performed in the fixing device illustrated in FIG. 54 including no cover.

Second Comparative Example

In the second comparative example, the measurements were performed in the fixing device having the same structure as that of the first example including the cover made of stainless steel, but the temperature of the cover was controlled to be in a range of 25° C. or higher and 35° C. or less. Other than the temperature of the cover, the configuration and conditions were the same as those of the first example.

FIG. 8 is a table listing the results of experiments in which generation rates of the FP/UFP, lowest temperatures of covers, and highest temperatures of covers were measured from two minutes after the start of continuous printing to ten minutes after the start of continuous printing in the first example, the second example, the first comparative example, and the second comparative example that have different conditions and configurations as described above. FIG. 8 lists the generation rates of the FP/UFP that were relative values when the generation rate of the FP/UFP in the first comparative example was assumed to be “100%”.

According to the results in FIG. 8, the generation rate of the FP/UFP in the fixing device according to the first comparative example including no cover was the highest (the generation rate: 100%). Although the fixing device according to the second comparative example includes the cover, the generation rate of the FP/UFP was not reduced so much (the generation rate: 90%). The present inventors considered that maintaining the temperature of the cover to be low, that is, 25° C. or higher and 35°7 C. or lower in the second comparative example prevented the aggregation of FP/UFP. In contrast, maintaining the temperature of the cover to be high, that is, 40° C. or higher as in the first example and the second example reduced the generation rate of the FP/UFP to be equal to or smaller than half of the generation rate of the FP/UFP in the first comparative example (the generation rates: 49% and 44%). As a result, the present inventors considered that maintaining the temperature of the cover to be high effectively promoted the aggregation of the FP/UFP.

From the above-described experimental results, maintaining the temperature of the cover to be 40° C. or higher from 2 minutes after the start of continuous printing to 10 minutes after the start of continuous printing effectively promotes the aggregation of FP/UFP and reduces the discharge amount (the generation rate) of the FP/UFP. Based on the above, in the embodiments of the present disclosure, the temperature of the face 40e of the cover 40 facing the first opening 27d is maintained to be 40° C. or higher from 2 minutes after the start of continuous printing to 10 minutes after the start of continuous printing. The face 40e may be referred to as an “opening facing face”. As a result, the aggregation of the FP/UFP in the cover 40 is effectively promoted to effectively reduce the number of FP/UFP discharged to the outside of the image forming apparatus.

In order to maintain the temperature of the opening facing face 40e of the cover 40 to be 40° C. or higher, the cover 40 may be made of a material having good thermal conductivity such as metal or alloy. In this case, transferring heat from the side plate 29 to the cover 40 increases the temperature of the cover 40 and enables maintaining the temperature of the cover 40 at 40° C. or higher from two minutes after the start of continuous printing to ten minutes after the start of continuous printing without using a heat source such as a heater.

Alternatively, the fixing device according to the first embodiment may include a temperature sensor 49 to detect the temperature of the opening facing face 40e of the cover 40 and a cover heater 47 disposed on the outer face of the cover 40 or the inner face of the cover 40. A controller 101 that is circuitry controls the cover heater 47 based on the temperature of the cover 40 to maintain the temperature of the opening facing face 40e of the cover 40 to be 40° C. or higher.

Alternatively, the cover heater 47 may be removed from the fixing device according to the first embodiment, and the fixing device may include the cover 40 made of a material having good thermal conductivity such as metal or alloy and the temperature sensor 49. In this case, after transferring heat from the side plate 29 to the cover 40 increases the temperature of the cover 40, the controller 101 starts the printing operation based on the temperature detected by the temperature sensor 49 to maintain the temperature of the cover 40 at 40° C. or higher from two minutes after the start of continuous printing to ten minutes after the start of continuous printing.

Maintaining the temperature of the opening facing face 40e of the cover 40 to be 40° C. or higher reduces the number of the FP/UFP discharged to the outside of the image forming apparatus as described above, but too high temperature of the opening facing face 40e, which exceeds 130° C., may damage or deteriorate the conductive wire connected to the heater 23 inside the loop of the fixing belt 21. To avoid the above-described disadvantage, the temperature of the opening facing face 40e of the cover 40 from 2 minutes after the start of continuous printing to 10 minutes after the start of continuous printing is preferably 40° C. or higher and 130° C. or lower.

Specifically, the fixing device according to the first embodiment further includes a fan 104 to cool the cover 40. As illustrated in FIG. 55, the controller 101 is connected to the temperature sensor 49, the cover heater 47, and the fan 104.

As illustrated in FIG. 56, after the controller 101 receives a print instruction (YES in step S1), the controller 101 determines whether the temperature of the cover 40 is 40° C. or higher in step S2. If the temperature of the cover 40 is equal to or higher than 40° C. (YES in step S2), the controller 101 starts the printing operation in step S4. If the temperature of the cover 40 is lower than 40° C. (NO in step S2), the controller 101 turns on the cover heater 47 in step S3 and starts the printing operation.

Until the printing operation is completed (NO in step S17), the temperature sensor 49 detects the temperature of the cover 40, and the controller 101 determines whether the temperature of the cover is 40° C. or higher at a predetermined interval based on the output of the temperature sensor 49 in step S5. If the temperature of the cover 40 is equal to or higher than 40° C. (YES in step S5), the controller 101 turns off the cover heater 47 in step S6.

Subsequently, The controller 101 determines whether the temperature of the cover is 130° C. or lower at a predetermined interval based on the output of the temperature sensor 49 in step S7. If the temperature of the cover exceeds 130° C. (YES in step S7), the controller 101 drives the fan 104 to lower the temperature of the cover in step S8. In this case, the controller 101 further checks the temperature of the cover to see if the temperature of the cover exceeds 130° C. for one minute or more in step S9. If the temperature of the cover exceeds 130° C. for one minute or more (YES in step S9), the controller 101 stops the printing operation and performs abnormality display in step S10. If the temperature of the cover is lowered (NO in step S9), the controller continues the printing operation. The controller 101 performs the above-described control until the printing operation is completed (YES in step S17).

Alternatively, the cover heater 47 and the fan 104 may be removed from the fixing device according to the first embodiment, and the controller 101 may perform the following control.

As illustrated in FIG. 57, after the controller 101 receives a print instruction (YES in step S11), the controller 101 determines whether the temperature of the cover 40 is 40° C. or higher in step S12. If the temperature of the cover 40 is equal to or higher than 40° C. (YES in step S12), the controller 101 starts the printing operation in step S14. If the temperature of the cover 40 is lower than 40° C. (NO in step S12), the controller 101 waits starting the printing operation in step S13 and, after the temperature of the cover 40 is equal to or higher than 40° C. (YES in step S12), starts the printing operation in step S14.

Until the printing operation is completed (NO in step S17), the temperature sensor 49 detects the temperature of the cover 40. The controller 101 determines whether the temperature of the cover is 130° C. or lower at a predetermined interval based on the output of the temperature sensor 49 in step S15. If the temperature of the cover exceeds 130° C. (YES in step S15), the controller 101 stops the printing operation and performs abnormality display in step S16. If the temperature of the cover is equal to or lower than 130° C. (NO in step S15), the controller continues the printing operation. The controller 101 performs the above-described control until the printing operation is completed (YES in step S17).

As a result, the above-described structures can prevent the damage or the deterioration of the conductive wire and effectively reduce the number of the FP/UFP discharged to the outside of the image forming apparatus.

Subsequently, other embodiments different from the above-described first embodiment are described. Differences from the above-described embodiment are mainly described, and descriptions of the same portions are appropriately omitted.

FIG. 9 is a view of the configuration of the fixing device 20 according to a second embodiment of the present disclosure.

In the second embodiment illustrated in FIG. 9, the fixing device 20 includes a halogen heater 38 as the heat source to heat the fixing belt 21. The halogen heater 38 is disposed inside the loop of the fixing belt 21. The halogen heater 38 is a non-contact-type heat source that irradiates the inner circumferential surface of the fixing belt 21 with infrared light to heat the fixing belt 21. Each of both ends of the halogen heater 38 in the longitudinal direction of the halogen heater is inserted through an opening 29a of the side plate 29, exposed to the outside of the side plate 29, and supported by a bracket 39 as a heat source support fixed to the outer face of the side plate 29.

As described above, the fixing device 20 according to the second embodiment has the opening 29a to expose the end of the halogen heater 38 in the longitudinal direction to the outside of the side plate 29, and thus the internal space of the fixing belt 21 is opened to the outside through the opening 29a. To reduce the FP/UFP discharged from the opening 29a to the outside of the image forming apparatus, the fixing device 20 according to the second embodiment includes the cover 40 disposed outside from the bracket 39 in the longitudinal direction X of the fixing belt 21 to cover the entire opening 29a.

In the second embodiment illustrated in FIG. 9, the cover 40 covering the entire opening 29a of the side plate 29 can reduce the FP/UFP discharged from the internal space of the fixing belt 21 to the outside of the image forming apparatus.

In addition, also in the second embodiment, maintaining the temperature of the opening facing face 40e of the cover 40 to be 40° C. or higher from 2 minutes after the start of continuous printing to 10 minutes after the start of continuous printing can effectively promote the aggregation of the FP/UFP in the cover 40.

As a result, the number of FP/UFP discharged to the outside of the image forming apparatus can be effectively reduced.

In the second embodiment, the internal space of the fixing belt 21 is opened to the outside through the opening 27d of the belt holder 27 in addition to the opening 29a of the side plate 29. Accordingly, the opening (the first opening) of the rotator support 10 that supports the fixing belt 21 includes the opening 27d of the belt holder 27 in addition to the opening 29a of the side plate 29. In other words, the rotator support 10 has two openings 29a and 27d having different sizes and disposed at different positions. The opening (that is the first opening) covered with the cover 40 in the present disclosure means an opening formed in the face of a component facing the cover 40.

Since the face of the component facing the cover 40 in the second embodiment is the outer face of the side plate 29, the cover 40 covers the entire opening 29a formed on the outer face of the side plate 29.

In addition, the cover 40 in the second embodiment also has the second opening 40d in order to generate preferable air flows between the internal space of the fixing belt 21 and the external space of the cover 40. The cover 40 having the second opening 40d as described above enables replacing the air in the internal space of the fixing belt 21 with the air in the external space of the cover 40 through the second opening 40d, reducing the temperature rise in the air in the internal space of the fixing belt 21.

In addition, the fixing device in the second embodiment includes a harness 37 that is a conductive wire to electrically connect the halogen heater 38 to an external power supply. The harness 37 is exposed to the outside through the second opening 40d and connected to the external power supply. As described above, the second opening 40d may be used as the opening through which the harness 37 extending from the halogen heater 38 passes.

As described above, the fixing device according to the second embodiment includes the cover covering the entire first opening of the rotator support, and the temperature of the opening facing face of the cover is maintained at 40° C. or higher at least from 2 minutes after the start of continuous printing to 10 minutes after the start of continuous printing, which promotes the aggregation of the FP/UFP and reduces the number of FP/UFP discharged to the outside of the image forming apparatus. According to one aspect of the present disclosure, performing the temperature control and adding simple components (the cover) without a significant design change enables providing the fixing device and the image forming apparatus that can reduce the amount of FP/UFP discharged and avoid increases in the size and cost of the fixing device and the image forming apparatus.

Although the fluorine grease, the fluorine oil, the silicone oil, and the silicone grease have been described as example substances that generate the FP/UFP in the above embodiments, another liquid or semi-solid lubricating substance (i.e., liquid or semi-solid substance having lubricity) besides these substances may be used in another embodiment of the present disclosure. In the embodiments of the present disclosure, the lubricating substance (i.e., the substance having lubricity) refers to a substance that is interposed between components to reduce frictional resistance between the components. Even when the liquid or semi-solid substance having lubricity other than silicone oil, silicone grease, fluorine oil, and fluorine grease is used, the configuration according to one aspect of the present disclosure can reduce the discharge of FP/UFP generated from the substance having lubricity.

According to the embodiments of the present disclosure, the configuration of the fixing device is not limited to the configuration described above. The embodiments of the present disclosure may be applied to fixing devices having various configurations. A description is now given of some examples of the configuration of the fixing device to which the embodiments of the present disclosure are applicable.

A fixing device 130 illustrated in FIGS. 10 and 11 includes a fixing belt 131 as the first rotator, a pressure roller 132 as the second rotator, a heater 133 as the heat source, a heater holder 134 as the heat source holder, a pressure stay 135 as the reinforcement, flanges 137 (see FIG. 11) as rotator holders, and a thermistor 138 as the temperature detector.

Functions and configurations of the fixing belt 131, the pressure roller 132, the heater 133, the heater holder 134, the pressure stay 135, and the flanges 137 illustrated in FIGS. 10 and 11 are basically the same as those of the fixing belt 21, the pressure roller 22, the heater 23, the heater holder 24, the stay 25, and the belt holders 27 illustrated in FIG. 2. Similar to the above-described belt holder 27, the flange 137 has a backup portion 137a as the insertion portion to be inserted into the fixing belt 131 and a flange portion 137b as the restraint to restrain the movement of the fixing belt 131 in the longitudinal direction of fixing belt 131. A biasing member such as a spring presses the flange 137 against the end of the fixing belt 131 to hold the flange 137 inserted into the loop of the fixing belt 131.

The thermistor 138 disposed on the pressure stay 135 is a contact-type temperature detector that is in contact with the inner circumferential surface of the fixing belt 131 to detect the temperature of the inner circumferential surface of the fixing belt 131. In this case, the amount of heat to be generated by the heaters 133 is controlled based on the temperature of the fixing belt 131 detected by the thermistor 138 to achieve a given fixing temperature of the fixing belt 131 at which the image can be fixed.

Subsequently, a fixing device 50 illustrated in FIGS. 12 and 13 is described. Similar to the fixing device 130 illustrated in FIGS. 10 and 11, the fixing device 50 includes the ceramic heater (that is a heater 53). Specifically, the fixing device 50 illustrated in FIGS. 12 and 13 includes a fixing belt 51 as the first rotator, a pressure rotator 52 as the second rotator, the heater 53 as the heat source, a heater holder 54 as the heat source holder, a reinforcement 55, belt holders 57 as the rotator holders (see FIG. 13), heat-sensitive members 58 (see FIG. 13) as the temperature detector, and covers 59 (see FIG. 13).

Functions and configurations of the fixing belt 51, the pressure rotator 52, the heater 53, the heater holder 54, the reinforcement 55, and the belt holders 57 illustrated in FIGS. 12 and 13 are basically the same as those of the fixing belt 131, the pressure roller 132, the heater 133, the heater holder 134, the pressure stay 135, and the flanges 137 illustrated in FIGS. 10 and 11.

The heat-sensitive members 58 are disposed on a side of the heater holder 54 opposite a side of the heater holder 54 to hold the heater 53 and detect the temperature of the heater 53 via the heater holder 54. Based on temperatures detected by the heat-sensitive members 58, heat generation of the heater 53 is controlled so that the fixing belt 51 is maintained at a predetermined fixing temperature.

The covers 59 are box-shaped members made of heat-resistant resin. Each cover 59 is disposed so as to face the heater holder 54 via the heat-sensitive member 58 inside the loop of the fixing belt 51 to cover the corresponding heat-sensitive member 58.

Subsequently, a fixing device 60 illustrated in FIGS. 14 and 15 is described below. The fixing device 60 includes a halogen heater (i.e., a heater 63) as the heat source. Specifically, the fixing device 60 illustrated in FIGS. 14 and 15 includes a fixing belt 61 as the first rotator, a pressure roller 62 as the second rotator, the heater 63 as the heat source, a nip formation pad 64, a support 65 as the reinforcement, a reflective plate 66 as a reflector, retention frames 67 as the rotator holders (see FIG. 15), and rings 68 as slide aids (see FIG. 15).

Functions and configurations of the fixing belt 61, the pressure roller 62, and the retention frames 67 illustrated in FIGS. 14 and 15 are basically the same as those of the fixing belt 21, the pressure roller 22, and the belt holders 27 illustrated in FIG. 2.

The heater 63 is the halogen heater and is disposed inside the loop of the fixing belt 61. The heater 63 irradiates the inner circumferential surface of the fixing belt 61 with infrared light to heat the fixing belt 61.

The nip formation pad 64 is disposed inside the loop of the fixing belt 61. The nip formation pad 64 forms a nip N between the fixing belt 61 and the pressure roller 62 under pressure from the pressure roller 62. The nip formation pad 64 has one side pressed by the pressure roller 62 and the other side opposite the one side, and the support 65 supports the other side of the nip formation pad 64. The support 65 prevents the nip formation pad 64 from being bent by the pressure of the pressure roller 62. As a result, the nip N having a uniform width is obtained. The nip formation pad 64 includes a metal base pad 640 and a fluororesin sliding sheet 641 that is interposed between the base pad 640 and an inner circumferential surface of the fixing belt 61. The sliding sheet 641 interposed between the base pad 640 and the fixing belt 61 reduces the sliding friction of the fixing belt 61 with respect to the base pad 640.

The reflective plate 66 is disposed inside the loop of the fixing belt 61 to face the heater 63. In this configuration, the reflective plate 66 reflects a part of the infrared light emitted from the heater 63 to the inner circumferential surface of the fixing belt 61. As a result, the fixing belt 61 is heated by the infrared light reflected by the reflective plate 66 in addition to the infrared light directly emitted from the heater 63.

The ring 68 is mounted on an outer circumferential surface of a cylindrical portion 67a as an insertion portion of the retention frame 67 that is inserted into the loop formed by the fixing belt 61. The ring 68 is interposed between a longitudinal edge of the fixing belt 61 and a fixing plate 67b as a restraint of the retention frame 67. As the fixing belt 61 rotates, the ring 68 rotates together with the fixing belt 61, or the fixing belt 61 slides over the low-friction ring 68. Thus, the sliding friction that is generated between the fixing belt 61 and the retention frame 67 is reduced.

Subsequently, a fixing device 70 illustrated in FIGS. 16 and 17 is described below. The fixing device 70 includes a fixing belt 71 as the first rotator, a pressure roller 72 as the second rotator, a halogen heater 73 as the heat source, a nip formation pad 74, a reflector 76, belt supports 77 (see FIG. 17) as rotator holders, a temperature sensor 78 as the temperature detector, and guides 79.

Functions of the fixing belt 71, the pressure roller 72, and the belt supports 77 illustrated in FIGS. 16 and 17 are basically the same as those of the fixing belt 21, the pressure roller 22, and the belt holders 27 illustrated in FIG. 2.

The temperature sensor 78 is a non-contact-type temperature detector that is disposed not to be in contact with the outer circumferential surface of the fixing belt 71 and detects the temperature of the fixing belt 71.

The nip formation pad 74 is disposed inside the loop of the fixing belt 71 and sandwiches the fixing belt 71 together with the pressure roller 72, to form the nip N.

The reflector 76 is disposed inside the loop of the fixing belt 71 and has a U-shape in a cross section so as to surround the halogen heater 73. The inner face of the reflector 76 includes a reflecting surface 76a having a high reflectivity and facing the halogen heater 73. When the infrared light is emitted from the halogen heater 73, the reflecting surface 76a of the reflector 76 reflects the infrared light to the nip formation pad 74. As a result, the nip formation pad 74 is heated by the infrared light directly emitted from the halogen heater 73 to the nip formation pad 74 and the infrared light reflected by the reflector 76 to the nip formation pad 74. The heat is conducted from the nip formation pad 74 to the fixing belt 71 at the nip N to heat the fixing belt 71. The nip formation pad 74 forms the nip N and, in addition, functions as a heat conductor that conducts heat to the fixing belt 71 at the nip N. To function as described above, the nip formation pad 74 is made of metal having good thermal conductivity such as copper or aluminum.

The reflector 76 also functions as a reinforcement (in other words, a stay) that supports and reinforces the nip formation pad 74. Since the reflector 76 supports the nip formation pad 74 throughout the length of the fixing belt 71, the bending of the nip formation pad 74 is prevented and the nip N having a uniform width is formed between the fixing belt 71 and the pressure roller 72. The reflector 76 is preferably made of metal having relatively high rigidity such as SUS or SECC to have the function as the reinforcement.

The guides 79 are disposed inside the loop of the fixing belt 71 to guide the inner circumferential surface of the fixing belt 71 rotating. Each of the guides 79 has a guide face 79a curving along the inner circumferential surface of the fixing belt 71. As the fixing belt 71 is guided along the guide face 79a, the fixing belt 71 smoothly rotates without being largely deformed.

Subsequently, a fixing device 80 illustrated in FIGS. 18 and 19 is described below. The fixing device 80 includes a ceramic heater (i.e., a heater 83) as the heat source. The fixing device 80 illustrated in FIGS. 18 and 19 includes a fixing belt 81 as the first rotator, a pressure roller 82 as the second rotator, the heater 83 as the heat source, a holder 84 as the heat source holder, a stay 85 as the reinforcement, arc-shaped guides 87 (see FIG. 19) as the rotator holders, a heat diffuser 88 as the heat conductor, and a heat retaining plate 89 as the heat insulator.

Functions and configurations of the fixing belt 81, the pressure roller 82, the heater 83, the holder 84, the stay 85, and the arc-shaped guides 87 illustrated in FIGS. 18 and 19 are basically the same as those of the fixing belt 21, the pressure roller 22, the heater 23, the heater holder 24, the stay 25, and the belt holders 27 illustrated in FIG. 2. In addition to the heater 83, the holder 84 holds the heat diffuser 88 and the heat retaining plate 89 that are overlaid.

The heat diffuser 88 is made of metal such as stainless steel, aluminum alloy, or iron. The heat diffuser 88 is disposed so as to be in contact with the inner circumferential surface of the fixing belt 81, transmits heat generated by the heater 83 to the fixing belt 81, and is in contact with the pressure roller 82 via the fixing belt 81 to form the nip N. Thermal conductive grease is applied between the heater 83 and the heat diffuser 88 to enhance heat transfer efficiency from the heater 83 to the heat diffuser 88. On the other hand, the heat retaining plate 89 is disposed on a side of the heater 83 opposite a side of the heater 83 facing the heat diffuser 88 to prevent the heat of the heater 83 from being transmitted to the holder 84 and the stay 85.

Since the fixing belt 81 rotates and slides on the heat diffuser 88, lubricant is applied between the fixing belt 81 and the heat diffuser 88 to enhance sliding performance. A sliding surface of the heat diffuser 88 in contact with the fixing belt 81 is formed with a surface layer such as a glass coating layer or a hard chromium plating layer each having low friction and wear resistance.

Subsequently, a fixing device 90 illustrated in FIGS. 20 and 21 is described below. The fixing device 90 includes an endless belt 91 as the first rotator, a heating roller 96 as a heating member, a heater 93 as the heat source, a pressure roller 92 as the second rotator, a nip formation pad 94, a support 95 as the reinforcement, a guide 98, a lubricant applicator 99 as a lubricant supplier, and bearings 97 (see FIG. 21).

As illustrated in FIG. 20, the belt 91 is wound around the heating roller 96, the nip formation pad 94, and the guide 98. As illustrated in FIG. 21, the heating roller 96 is rotatably held by a pair of bearings 97 disposed on the outer circumferential surface of both ends of the heating roller 96 in the axial direction (longitudinal direction) of the heating roller 96. In addition, a biasing member such as a spring presses the heating roller 96 in a direction away from the nip formation pad 94 to apply a predetermined tension to the belt 91. In this state, rotating the pressure roller 92 rotates the belt 91.

The nip formation pad 94 includes a pressing member 940 and a low-friction sliding sheet 941 that is interposed between the pressing member 940 and the inner circumferential surface of the fixing belt 91. The pressing member 940 is supported by the support 95 to receive the pressing force of the pressure roller 92 and form the nip N.

The heater 93 is the halogen heater and is disposed in the heating roller 96. The heater 93 generating heat heats the heating roller 96, and the heat of the heating roller 96 is transmitted to the belt 91.

The lubricant applicator 99 comes into contact with the inner circumferential surface of the belt 91 and supplies the lubricant to enhance slidability with respect to the inner circumferential surface of the belt 91. The lubricant supplied to the inner circumferential surface of the belt 91 is interposed between the guide 98 and the belt 91 and between the nip formation pad 94 and the belt 91 as the belt 91 rotates, so that the belt 91 can smoothly rotate.

Subsequently, a fixing device 110 illustrated in FIGS. 22 and 23 is described below. The fixing device 110 includes a fixing belt 111 as the first rotator, a fixing roller 116, a pressure roller 112 as the second rotator, a heater 113 as the heat source, a pressing pad 114 as the nip formation pad, a guide 115, a support 117 as the reinforcement, a temperature sensor 118 as the temperature detector, a heat transferor 119, and belt holders 122 (see FIG. 23) as the rotator holders.

The fixing belt 111 is wound around the fixing roller 116, the pressure pad 114, the guide 115, and the heat transferor 119. The pressure roller 112 is at a position opposite the pressure pad 114 and pressed against the outer circumferential surface of the fixing belt 111. In such a configuration, rotating the pressure roller 112 rotates the fixing roller 116.

The heater 113 is a planar heater or a plate-shaped heater such as a ceramic heater and disposed in the heat transferor 119. The heat transferor 119 is interposed between the heater 113 and the fixing belt 111 to transfer the heat of the heater 113 to the fixing belt 111. A spring 120 attached to the support 117 biases the heat transferor 119 against the fixing belt 111 so that the heat transferor 119 comes into contact with the inner circumferential surface of the fixing belt 111.

Another spring 121 attached to the support 117 biases the pressing pad 114 against the fixing belt 111 so that the pressing pad 114 comes into contact with the inner circumferential surface of the fixing belt 111. As a result, the pressing pad 114 is pressed against the pressure roller 112 via the fixing belt 111 to form the nip N between the fixing belt 111 and the pressure roller 112.

The guide 115 is attached to and supported by the support 117. A temperature sensor 118 is attached to the guide 115 and detects the temperature of the fixing belt 111.

Subsequently, a fixing device 140 illustrated in FIGS. 24 and 25 is described below. The fixing device 140 includes a fixing belt 141 as the first rotator, a pressure roller 142 as the second rotator, a heater 143 as the heat source, a nip formation pad 144, a stay 145 as the reinforcement, and a reflector 146 as the reflector. The nip formation pad 144 includes a metal supporter 147 and a pad 148.

The fixing belt 141 is an endless belt having a predetermined inner diameter and a width larger than the width of the sheet P. The fixing belt 141 is made of a flexible material, and includes, for example, a base layer, an elastic layer on the outer circumferential face of the base layer, and a release layer on the outer circumferential face of the elastic layer.

The base layer is made of metal such as SUS or nickel (Ni). The elastic layer is made of, for example, silicone rubber. The release layer is made of, for example, a PFA tube. A fixing housing as the rotator support rotatably supports both ends of the fixing belt 141 in the longitudinal direction of the fixing belt 141.

A stay 145 penetrates through a lower portion of a space extending in the longitudinal direction of the fixing belt 141 inside the loop of the fixing belt 141. The stay 145 is a channel-shaped component having side walls projecting upward and longer than the length of the fixing belt 141 in the longitudinal direction X of the fixing belt 141. The fixing housing supports both ends of the stay 145 in the longitudinal direction.

The stay 145 has a bottom plate having three positioning holes 145a (see FIG. 24) arranged at predetermined intervals in the longitudinal direction X of the fixing belt 141. Upper ends of the side walls of the stay 145 support the reflector 146.

The heater 143 (for example, the halogen heater) has a length equivalent to the length of the fixing belt 141 in the longitudinal direction X. The heater 143 is disposed in an upper portion of the space inside the loop of the fixing belt 141 (in other words, above the stay 145), and the fixing housing supports both ends of the heater 143 in the longitudinal direction.

The heater 143 radiates radiant heat (including infrared light) to the inner circumferential surface of the fixing belt 141 (mainly a portion slightly narrower than the upper half circumferential surface of the fixing belt 141) to heat the fixing belt 141. The radiant heat radiated downward from the heater 143 is reflected by the reflector 146 to the inner circumferential surface of the fixing belt 141. The heater 143 is controlled by a controller.

The pressure roller 142 includes a core, an elastic layer on the outer circumferential face of the core, and a release layer on the outer circumferential face of the elastic layer. The elastic layer is made of, for example, silicone rubber.

The release layer is made of, for example, a PFA tube.

The pressure roller 142 is disposed below the fixing belt 141 and is supported by the fixing housing. The pressure roller 142 is in contact with the outer circumferential surface of the fixing belt 141 to form the nip N between the pressure roller 142 and the fixing belt 141. The pressure roller 142 is coupled to, for example, a motor, and the motor rotates the pressure roller 142. The controller controls the motor. The fixing belt 141 is driven by the pressure roller 142. Rotating the pressure roller 142 counterclockwise in FIG. 24 rotates the fixing belt 141 in a clockwise direction reverse to the rotation direction of the pressure roller 142. The rotating pressure roller 142 and the rotating fixing belt 141 convey the sheet P after the sheet P enters the nip N, and the sheet P passes through the nip N.

The metal supporter 147 has a flat rectangular parallelepiped shape extending in the longitudinal direction X of the fixing belt 141 and is made of, for example, metal. The metal supporter 147 includes multiple (eighteen) projections 147a, multiple (seven) fixing pins 147b, and multiple (three) positioning pins 147c that project upward from predetermined positions on the upper face of the metal supporter 147.

The pad 148 is a rectangular sheet having a width equal to the width of the metal supporter 147 and a length that allows the pad to be wound around the metal supporter 147 once and, for example, made by weaving PTFE fibers and PPS fibers.

The pad 148 is wound around the metal supporter 147 by one turn, and both ends of the pad 148 are overlapped on the upper face of the metal supporter 147. Both ends of the pad 148 have openings 148a, fixing holes 148b, and positioning holes 148c, and the projections 147a, the fixing pins 147b, and the positioning pins 147c on the metal support 147 are fitted into the openings 148a, the fixing holes 148b, and the positioning holes 148c, respectively.

Fitting the positioning pins 147c of the metal supporter 147 into the positioning holes 145a of the stay 145 positions the nip formation pad 144 with respect to the stay 145.

Lubricant such as oil or grease may be applied to the pad 148. In this case, the pad 148 is in contact with the inner circumferential surface of the fixing belt 141 via the lubricant.

The above-described fixing devices to which the embodiments according to the present disclosure are applicable each include a rotator such as the fixing belt and a component inside the loop of the rotator, and the rotator slides on the component. Accordingly, the lubricant is used to reduce the sliding friction between the component and the rotator. Heating the rotator increases the temperature of the lubricant applied to the inner circumferential surface of the rotator which generates the FP/UFP from the lubricant and may cause the discharge of the FP/UFP from the opening of the rotator support supporting the rotator. Applying any one of the embodiments of the present disclosure to these fixing devices, covering the opening of the rotator support with the cover, and maintaining the temperature of the cover to be equal to or higher than 40° C. from 2 minutes after the start of the continuous printing to 10 minutes after the start of the continuous printing can reduce the discharge of FP/UFP to the outside, similarly to the fixing device according to any one of the above-described embodiments.

The embodiments of the present disclosure are also applicable to fixing devices as illustrated in FIGS. 26 to 29, respectively, in addition to the fixing devices described above. The configurations of fixing devices illustrated in FIGS. 26 to 29 are described below.

A different point between the fixing device 20 illustrated in FIG. 26 and the fixing device 20 illustrated in FIG. 2 is the position of the temperature sensor 26 to detect the temperature of the heater 23. Other than that, the configuration illustrated in FIG. 26 is the same as that in FIG. 2. In the fixing device 20 illustrated in FIG. 26, the temperature sensor 26 is disposed upstream from the center M of the nip N in the sheet conveyance direction (that is, near a nip entrance). In the fixing device 20 illustrated in FIG. 2, the temperature sensor 26 is disposed in the center M of the nip N in the sheet conveyance direction. The temperature sensor 26 disposed upstream from the center M of the nip N in the sheet conveyance direction as illustrated in FIG. 26 can accurately detect the temperature near the nip entrance. Since the sheet P entering the nip N particularly easily takes the heat of the fixing belt 21 away in a portion near the nip entrance, the temperature sensor 26 that accurately detects the temperature at the portion near the nip entrance enables enhancing the fixing property of the image and effectively preventing the occurrence of fixing offset (that is, a state in which the toner image cannot be sufficiently heated).

Subsequently, the fixing device 20 in the present embodiment is described with reference to FIG. 27. The fixing device 20 illustrated in FIG. 38 has a heating nip N1 in which the heater 23 heats the fixing belt 21 and a fixing nip N2 through which the sheet P passes, and the heating nip N1 and the nip N2 are formed at different positions. Specifically, the fixing device 20 in the present embodiment includes a nip formation pad 150 inside the loop of the fixing belt 21 in addition to the heater 23. A pressure roller 151 presses the heater 23 via the fixing belt 21 to form the heating nip N1 between the heater 23 and the pressure rollers 151. A pressure roller 152 presses the nip formation pad 150 to form the fixing nip N2 between the nip formation pad 150 and the pressure roller 152. In the above-described fixing device 20, the heater 23 heats the fixing belt 21 in the heating nip N1, and the fixing belt 21 applies heat to the sheet P in the fixing nip N2 to fix the unfixed image onto the sheet P.

Subsequently, the fixing device 20 illustrated in FIG. 28 is described. The fixing device 20 illustrated in FIG. 28 omits the above-described pressure roller 151 adjacent to the heater 23 from the fixing device 20 illustrated in FIG. 27 and includes the heater 23 formed to be arc having a curvature of the fixing belt 21. The other configuration is the same as the configuration illustrated in FIG. 27. In this case, the arc-shaped heater 23 surely maintains a length of the contact between the fixing belt 21 and the heater 23 in a belt rotation direction to efficiently heat the fixing belt 21.

Subsequently, the fixing device 20 illustrated in FIG. 29 is described. The fixing device 20 illustrated in FIG. 29 includes a roller 163 between a pair of belts 161 and 162. The fixing device 20 includes the heater 23 disposed inside the loop of the belt 161 on the left side in FIG. 29 and a nip formation pad 153 disposed inside the loop of the belt 162 on the right side in FIG. 29. The heater 23 is in contact with the roller 163 via the left belt 161 to form the heating nip N1. The nip formation pad 153 is in contact with the roller 163 via the right belt 162 to form the fixing nip N2.

Applying any one of the embodiments of the present disclosure to the above-described fixing devices illustrated in FIGS. 26 to 29 can reduce the discharge of FP/UFP to the outside of the image forming apparatus, similarly to the fixing device according to any one of the above-described embodiments.

The image forming apparatus to which the embodiments of the present disclosure are applied is not limited to the color image forming apparatus illustrated in FIG. 1, and the embodiments of the present disclosure may be applied to an image forming apparatus having a configuration illustrated in FIG. 30. The following describes another embodiment of the image forming apparatus to which the present embodiments may be applied.

The image forming apparatus 100 illustrated in FIG. 30 includes an image forming device 170 including a photoconductor drum, a sheet conveyer including a timing roller pair 171, a sheet feeder 172, a fixing device 173, a sheet ejection device 174, and a reading device 175. The sheet feeder 172 includes a plurality of sheet feeding trays, and the sheet feeding trays store sheets of different sizes, respectively.

The reading device 175 reads an image of a document Q. The reading device 175 generates image data from the read image. The sheet feeder 172 stores the sheets P and feeds the sheet P to the conveyance path. The timing roller pair 171 conveys the sheet P on the conveyance path to the image forming device 170.

The image forming device 170 forms a toner image on the sheet P. Specifically, the image forming device 170 includes the photoconductor drum, a charging roller, the exposure device, the developing device, a supply device, a transfer roller, the cleaning device, and a discharger. The fixing device 173 heats and presses the toner image to fix the toner image on the sheet P. Conveyance rollers convey the sheet P on which the toner image has been fixed to the sheet ejection device 174. The sheet ejection device 174 ejects the sheet P to the outside of the image forming apparatus 100.

Subsequently, a fixing device 173 according to the present embodiment is described with reference to FIG. 31. In the configuration illustrated in FIG. 31, components common to those of the fixing device 20 of the above-described embodiment illustrated in FIG. 2 are denoted by like reference signs, and overlapping description may be simplified or omitted as appropriate.

As illustrated in FIG. 31, the fixing device 173 includes the fixing belt 21, the pressure roller 22, the heater 23, the heater holder 24, the stay 25, and the temperature sensors 26.

The nip N is formed between the fixing belt 21 and the pressure roller 22. The nip width of the nip N is 10 mm, and the linear velocity of the fixing device 173 is 240 mm/s.

The fixing belt 21 includes a polyimide base layer and the release layer and does not include the elastic layer. The release layer is made of a heat-resistant film material made of, for example, fluororesin. The outer loop diameter of the fixing belt 21 is about 24 mm.

The pressure roller 22 includes the core, the elastic layer, and the release layer. The pressure roller 22 has an outer diameter of 24 mm to 30 mm, and the elastic layer has a thickness of 3 mm to 4 mm.

The heater 23 includes the base, a thermal insulation layer, a conductor layer including the resistive heat generators, and the insulation layer, and is formed to have a thickness of 1 mm as a whole. The width of the heater 23 in the sheet conveyance direction is, for example, 13 mm.

As illustrated in FIG. 32, the conductor layer of the heater 23 includes the resistive heat generators 31, the power supply lines 34, and electrodes 33A to 33C. The resistive heat generators 31 are arranged at intervals in the longitudinal direction of the heater 23 (that is, the direction indicated by the arrow X). In the following description, a portion between the neighboring resistive heat generators 31 is referred to as a separation area B. As illustrated in an enlarged view of FIG. 32, the separation area B is formed between the neighboring resistive heat generators of the resistive heat generators 31. The enlarged view of FIG. 32 illustrates two separation areas B, but the separation area B is formed between neighboring resistive heat generators of all the resistive heat generators 31. In FIG. 32, a direction indicated by an arrow Y is a direction intersecting or orthogonal to the longitudinal direction X of the heater 23, which is referred to as a longitudinal intersecting direction. The longitudinal intersecting direction is different from the thickness direction of the base 30.

In addition, the direction indicated by the arrow Y is the same as a direction intersecting an arrangement direction of the resistive heat generators 31, a short-side direction of the heater 23 along a surface of the base 30 on which the resistive heat generators 31 are disposed, and the sheet conveyance direction of the sheet passing through fixing device.

The heater 23 includes a central heat generation portion 35B and end heat generation portions 35A and 35C at both sides of the central heat generation portion 35B. The central heat generation portion 35B and the end heat generation portions 35A and 35C are configured by the resistive heat generators 31. The end heat generation portions 35A and 35C can generate heat separately from the central heat generation portion 35B. For example, choosing a left electrode 33A and a central electrode 33B of the three electrodes 33A to 33C and applying a voltage between the left electrode 33A and the central electrode 33B in FIG. 32 causes the end heat generation portions 35A and 35C adjacent to both sides of the central heat generation portion 35B to generate heat. Applying the voltage between the left electrode 33A and the right electrode 33C causes the central heat generation portion 35B to generate heat. To fix the image onto a small sheet, the central heat generation portion 35B alone can generate heat. To fix the image onto a large sheet, all the heat generation portions 35A to 35C can generate heat. As a result, the heater in the fixing device can generate heat in accordance with the size of the sheet.

As illustrated in FIG. 33, the heater holder 24 according to the present embodiment includes a recessed portion 24a to receive and hold the heater 23. The recessed portion 24a is formed on the side of the heater holder 24 facing the heater 23. The recessed portion 24a has a bottom 24f formed in a rectangular shape substantially the same size as the heater 23, and four side walls 24b, 24c, 24d, and 24e disposed on four sides of the bottom 24f, respectively. In FIG. 33, the right side wall 24e is omitted. The recessed portion 24a may have an opening that opens toward one end in the longitudinal direction of the heater 23. The opening is configured by removing one of a pair of the left side wall 24d and the right side wall 24e that intersect the longitudinal direction X of the heater 23 (that is, the arrangement direction of the resistive heat generators 31).

As illustrated in FIG. 34, a connector 36 holds the heater 23 and the heater holder 24 according to the present embodiment. The connector 36 includes a housing made of resin such as LCP and multiple contact terminals fixed to the inner face of the housing.

To attach to the heater 23 and the heater holder 24, the connector 36 is moved in the direction intersecting the longitudinal direction X of the heater 23 that is the arrangement direction of the resistive heat generators 31 (see a direction indicated by an arrow extending from the connector 36 in FIG. 34). The connector 36 is attached to one end of the heater 23 and one end of the heater holder 24 in the longitudinal direction X of the heater 23 that is the arrangement direction of the resistive heat generators 31. The one end of the heater 23 and the one end of the heater holder 24 are farther from a portion in which the pressure roller 22 receives a driving force from a drive motor than the other end of the heater 23 and the other end of the heater holder 24, respectively. The connector 36 and the heater holder 24 may have a convex portion and a recessed portion to attach the connector 36 to the heater holder 24. The convex portion disposed on one of the connector 36 and the heater holder 24 engages with the recessed portion disposed on the other and relatively move in the recessed portion to attach the connector 36 to the heater holder 24.

After the connector 36 is attached to the heater 23 and the heater holder 24, the heater 23 and the heater holder 24 are sandwiched and held by the connector 36. In this state, the contact terminals contact and press against the electrodes of the heater 23, respectively, and the resistive heat generators 31 are electrically coupled to the power supply disposed in the image forming apparatus via the connector 36. As a result, the power supply can supply electric power to the resistive heat generators 31.

A pair of flanges 48 one of which is illustrated in FIG. 34 is a pair of belt holders contacting the inner circumferential surface of the fixing belt 21 at both ends of the fixing belt 21 in the longitudinal direction of the fixing belt 21 to hold the fixing belt 21. The flanges 48 are inserted into both ends of the stay 25 and fixed to a pair of side plates that are frame members of the fixing device, respectively.

FIG. 35 is a diagram illustrating an arrangement of temperature sensors 26 and thermostats 19 included in the fixing device according to the present embodiment. Each of the thermostats 19 cuts off a current flowing through the resistive heat generators under a certain condition.

As illustrated in FIG. 35, one of the temperature sensors 26 according to the present embodiment is disposed to face the inner circumferential surface of the fixing belt 21 near the center Xm of the fixing belt 21 in the longitudinal direction X of the fixing belt 21, and the other one of the temperature sensors 26 is disposed to face the inner circumferential surface of the fixing belt 21 near the end of the fixing belt 21 in the longitudinal direction X. One of the temperature sensors 26 is disposed at a position corresponding to the separation area B (see FIG. 32) between the resistive heat generators of the heater 23.

In addition, one of the thermostats 19 is disposed to face the inner circumferential surface of the fixing belt 21 near the center Xm of the fixing belt 21, and the other one of the thermostats 19 is disposed to face the inner circumferential surface of the fixing belt 21 near the end of the fixing belt 21. Each thermostat 19 detects the temperature of the inner circumferential surface of the fixing belt 21 or the ambient temperature in the vicinity of the inner circumferential surface of the fixing belt 21. The thermostat 19 cuts off the current flowing to the heater 23 in response to detecting the temperature that exceeds a preset threshold value.

As illustrated in FIGS. 35 and 36, flanges 48 to hold both ends of the fixing belt 21 each have a slide groove 48a. The slide groove 48a extends in a direction in which the fixing belt 21 moves toward and away from the pressure roller 22. An engaging portion of the housing of the fixing device engages with the slide groove 48a. The relative movement of the engaging portion in the slide groove 48a enables the fixing belt 21 to move toward and away from the pressure roller 22.

The embodiments of the present disclosure are also applicable to the fixing devices having the following configurations.

FIG. 37 is a schematic diagram illustrating a fixing device to which the above-described embodiments of the present disclosure can be applied.

The fixing device 20 illustrated in FIG. 37 includes the fixing belt 21 as the first rotator or the fixing rotator, the pressure roller 22 as the second rotator or the pressure rotator, the heater 23 as the heat source, the heater holder 24 as the heat source holder, the stay 25 as the reinforcement, the temperature sensor 26 (that is the thermistor) as the temperature detector, and a first high thermal conductor 181 as a thermal equalizer (in other words, a thermal conduction aid). The fixing belt 21 is the endless belt.

The pressure roller 22 is in contact with the outer circumferential surface of the fixing belt 21 to form the nip N between the pressure roller 22 and the fixing belt 21. The heater 23 heats the fixing belt 21. The heater holder 24 holds the heater 23 and the first high thermal conductor 181. The stay 25 supports the heater holder 24. The temperature sensor 26 detects the temperature of the first high thermal conductor 181. The direction orthogonal to the surface of the paper on which FIG. 37 is drawn is the longitudinal direction of the fixing belt 21, the pressure roller 22, the heater 23, the heater holder 24, the stay 25, and the first high thermal conductor 181, and this direction is referred to simply as the longitudinal direction below. The longitudinal direction is also the width direction of the conveyed sheet, the longitudinal direction of the fixing belt 21, and the axial direction of the pressure roller 22.

Like the heater illustrated in FIG. 32, the heater 23 illustrated in FIG. 37 includes the resistive heat generators 31 that are spaced from each other in the longitudinal direction of the heater 23.

In the heater 23 including the multiple resistive heat generators 31 arranged at intervals, the temperature of the heater 23 in the separation area B corresponding to the interval between the resistive heat generators 31 tends to be lower than the temperature of the heater 23 in a portion entirely occupied by the resistive heat generator 31. For this reason, the temperature of the fixing belt 21 corresponding to the separation area B also becomes low, which may cause an uneven temperature distribution of the fixing belt 21 in the longitudinal direction.

To prevent the above-described temperature drop in the separation area B and reduce the temperature unevenness in the longitudinal direction of the fixing belt 21, the heater 23 illustrated in FIG. 37 includes the first high thermal conductor 181. A detailed description is given below of the first high thermal conductor 181.

As illustrated in FIG. 37, the first high thermal conductor 181 is disposed between the heater 23 and the stay 25 in the lateral direction of FIG. 37 and is particularly sandwiched between the heater 23 and the heater holder 24. In other words, the first high thermal conductor 181 has one face in contact with the back side of the base 30 of the heater 23 and the other face (opposite the one face) in contact with the heater holder 24.

The stay 25 has two rectangular portions 25a extending in a thickness direction of the heater 23 and each having a contact surface 25a1 in contact with the back side of the heater holder 24 to support the heater holder 24, the first high thermal conductor 181, and the heater 23. In the direction intersecting the longitudinal direction that is the vertical direction in FIG. 37, the contact surfaces 25a1 are outside the resistive heat generators 31. The above-described structure prevents heat transfer from the heater 23 to the stay 25 and enables the heater 23 to effectively heat the fixing belt 21.

As illustrated in FIG. 38, the first high thermal conductor 181 is a plate having a certain thickness such as 0 3 mm and having, for example, a length of 222 mm in the longitudinal direction, and a width of 10 mm in the direction intersecting the longitudinal direction. Although the first high thermal conductor 181 is a single plate according to the present embodiment, the first high thermal conductor 181 may have multiple parts. In FIG. 38, the guide 28 illustrated in FIG. 37 is omitted.

The first high thermal conductor 181 is fitted into the recessed portion 24a of the heater holder 24. The heater 23 is attached onto the first high thermal conductor 181. Thus, the first high thermal conductor 181 is sandwiched and held between the heater holder 24 and the heater 23. In FIG. 49, the length of the first high thermal conductor 181 in the longitudinal direction is substantially the same as the length of the heater 23 in the longitudinal direction. Both side walls 24d and 24e extending in a direction intersecting the longitudinal direction of the recessed portion 24a restrict movement of the heater 23 and movement of the first high thermal conductor 181 in the longitudinal direction and work as longitudinal direction regulators. Since the longitudinal displacement of the first high thermal conductor 181 in the fixing device is regulated, the thermal conduction efficiency is enhanced with respect to the target range in the longitudinal direction. Both side walls 24b and 24c extending in the longitudinal direction of the recessed portion 24a restrict movement of the heater 23 and movement of the first high thermal conductor 181 in the direction intersecting the longitudinal direction and work as direction-intersecting-arrangement-direction regulators.

The range in which the first high thermal conductor 181 is disposed in the longitudinal direction indicated by the arrow X is not limited to the range illustrated in FIG. 38. For example, as illustrated in FIG. 39, the first high thermal conductor 181 may be disposed in only a longitudinal range in which the resistive heat generators 31 are disposed (see a hatched portion in FIG. 39).

As illustrated in FIG. 40, the first high thermal conductors 181 may be disposed in only the entire separation areas at positions corresponding to the separation areas B (in other words, gap areas between the resistive heat generators) in the longitudinal direction indicated by the arrow X. Although the resistive heat generators 31 and the first high thermal conductor 181 are shifted in the vertical direction in FIG. 40 for convenience, the resistive heat generators 31 and the first high thermal conductor 181 are disposed at substantially the same position in the direction (indicated by double-head arrow Y) intersecting the longitudinal direction. The direction intersecting the longitudinal direction may be referred to simply as the direction Y in the following description. In addition, the first high thermal conductor 181 may be disposed over a part of the resistive heat generator 31 in the direction intersecting the longitudinal direction (the direction indicated by the arrow Y), or as in the example illustrated in FIG. 41, may be disposed so as to cover all the resistive heat generator 31 in the direction intersecting the longitudinal direction (the direction indicated by the arrow Y). As illustrated in FIG. 41, the first high thermal conductor 181 may be disposed to face a part of each of the neighboring resistive heat generators 31 in addition to the gap area between the neighboring resistive heat generators 31. The first high thermal conductor 181 may be disposed to face all separation areas B in the heater 23, one separation area B as illustrated in FIG. 41, or some of the separation areas B. At least a part of the first high thermal conductor 181 may be disposed to face the separation area B.

Due to the pressing force of the pressure roller 22, the first high thermal conductor 181 is sandwiched between the heater 23 and the heater holder 24 and is brought into close contact with the heater 23 and the heater holder 24. The first high thermal conductor 181 in contact with the heater 23 enhances the thermal conduction efficiency of the heater 23 in the longitudinal direction. The first high thermal conductor 181 facing the separation area B enhances the heat conduction efficiency of a part of the heater 23 facing the separation area B in the longitudinal direction, transmits heat to the part of the heater 23 facing the separation area B, and raise the temperature of the part of the heater 23 facing the separation area B. Thus, the first high thermal conductor 181 reduces the temperature unevenness of the heater 23 in the longitudinal direction and the temperature unevenness of the fixing belt 21 in the longitudinal direction. As a result, the above-described structure can prevent uneven fixing and uneven gloss in the image fixed on the sheet. Since the heater 23 does not need to generate additional heat to obtain a sufficient fixing performance in the part of the heater 23 facing the separation area B, energy consumption of the fixing device can be saved. In particular, the first high thermal conductor 181 disposed over the entire area in which the resistive heat generators 31 are arranged in the longitudinal direction enhances the heat transfer efficiency of the heater 23 over the entire area of a main heating region of the heater 23 (that is, an area facing an image formation area of the sheet passing through the fixing device) and reduces the temperature unevenness of the heater 23 and the temperature unevenness of the fixing belt 21 in the longitudinal direction.

In addition, the combination of the first high thermal conductor 181 and the resistive heat generator 31 having a Positive Temperature Coefficient (PTC) characteristic effectively prevents an overheating of the non-sheet passing region (that is the region of the fixing belt that is not in contact with the small sheet) of the fixing belt 21 when small sheets pass through the fixing device 20. The PTC characteristic is a characteristic in which the resistance value increases as the temperature increases, for example, a heater output decreases under a constant voltage. The resistive heat generator 31 having the PTC characteristic effectively reduces the amount of heat generated by the resistive heat generator 31 in the non-sheet passing region, and the first high thermal conductor 181 effectively transfers heat from the non-sheet passing region in which the temperature rises to a sheet passing region that is a region of the fixing belt contacting the sheet. As a result, the overheating of the non-sheet passing region is effectively prevented.

The first high thermal conductor 181 may be disposed opposite an area around the separation area B because the small heat generation amount in the separation area B decreases the temperature of the heater 23 in the area around the separation area B. For example, the first high thermal conductor 181 facing an enlarged separation area C that includes the separation area B and an area around the separation area B as illustrated in FIG. 42 enhances the heat transfer efficiency of the separation area B and the area around the separation area B in the longitudinal direction and effectively reduces the temperature unevenness in the longitudinal direction of the heaters 23. The first high thermal conductor 181 facing the entire region in which all the resistive heat generators 31 are arranged in the longitudinal direction reduces the temperature unevenness of the heater 23 (and the fixing belt 21) in the longitudinal direction.

FIG. 43 is a cross-sectional view of a fixing device having a configuration different from the fixing devices according to the above embodiments of the present disclosure.

The fixing device 20 illustrated in FIG. 43 includes a second high thermal conductor 182 between the heater holder 24 and the first high thermal conductor 181. The second high thermal conductor 182 is disposed at positions different from the position of the first high thermal conductor 181 in the lateral direction in FIG. 43 that is a direction in which the heater holder 24, the stay 25, and the first high thermal conductor 181 are layered. Specifically, the second high thermal conductor 182 is disposed so as to overlap the first high thermal conductor 181. The fixing device in the present embodiment includes the temperature sensor 26 (that is, the thermistor), which is the same as the fixing device illustrated in FIG. 37. FIG. 43 illustrates a cross section in which the temperature sensor 26 is not disposed.

The second high thermal conductor 182 is made of a material having thermal conductivity higher than the thermal conductivity of the base 30, such as graphene or graphite. In the present embodiment, the second high thermal conductor 182 is made of a graphite sheet having a thickness of 1 mm. Alternatively, the second high thermal conductor 182 may be a plate made of aluminum, copper, or silver.

As illustrated in FIG. 44, multiple second high thermal conductors 182 are arranged on the recessed portion 24a of the heater holder 24 at intervals in the longitudinal direction. The heater holder 24 has recesses deeper than the other portion. The second high thermal conductors 182 are disposed at the recesses. Clearances are formed between the heater holder 24 and both sides of the second high thermal conductor 182 in the longitudinal direction. The clearance prevents heat transfer from the second high thermal conductor 182 to the heater holder 24, and the heater 23 efficiently heats the fixing belt 21. In FIG. 44, the guide 28 illustrated in FIG. 43 is omitted.

As illustrated in FIG. 45, each of the second high thermal conductors 182 (see the hatched portions) is disposed at a position corresponding to the separation area B in the longitudinal direction indicated by the arrow X and faces at least a part of each of the neighboring resistive heat generators 31 in the longitudinal direction. In particular, each of the second high thermal conductors 182 in the present embodiment faces the entire separation area B. FIG. 45 (and FIG. 47 described below) illustrates the first high thermal conductor 181 facing the entire region in which all the resistive heat generators 31 are arranged in the longitudinal direction. The range in which the first high thermal conductor 181 is disposed in the longitudinal direction is not limited to the above.

The fixing device according to the present embodiment includes the second high thermal conductor 182 disposed at a position corresponding to the separation area B in the longitudinal direction and the position at which at least a part of each of the neighboring resistive heat generators 31 faces the second high thermal conductor 182 in addition to the first high thermal conductor 181. The above-described structure further enhances the heat transfer efficiency in the separation area B in the longitudinal direction and more efficiently reduces the temperature unevenness of the heater 23 in the longitudinal direction. As illustrated in FIG. 46, the first high thermal conductor 181 and the second high thermal conductor 182 may be disposed opposite the entire gap area between resistive heat generators 31. The above-described structure enhances the heat transfer efficiency of the part of the heater 23 corresponding to the gap area to be higher than the heat transfer efficiency of the other part of the heater 23. In FIG. 46, for the sake of convenience, the resistive heat generators 31, the first high thermal conductors 181, and the second high thermal conductors 182 are shifted in the vertical direction of FIG. 57 but are disposed at substantially the same position in the direction intersecting the longitudinal direction indicated by the arrow Y. However, the present disclosure is not limited to the above. The first high thermal conductor 181 and the second high thermal conductor 182 may be disposed opposite a part of the resistive heat generators 31 in the direction intersecting the longitudinal direction or may be disposed so as to cover the entire resistive heat generators 31 in the direction intersecting the longitudinal direction.

Both the first high thermal conductor 181 and the second high thermal conductor 182 may be made of a graphene sheet. The first high thermal conductor 181 and the second high thermal conductor 182 made of the graphene sheet have high thermal conductivity in a predetermined direction along the plane of the graphene, that is, not in the thickness direction but in the longitudinal direction. Accordingly, the above-described structure can effectively reduce the temperature unevenness of the fixing belt 21 in the longitudinal direction and the temperature unevenness of the heater 23 in the longitudinal direction.

Graphene is a flaky powder. Graphene has a planar hexagonal lattice structure of carbon atoms, as illustrated in FIG. 49. The graphene sheet is typically a single layer. The graphene sheet may contain impurities in a single layer of carbon or may have a fullerene structure. The fullerene structures are typically recognized as compounds including an even number of carbon atoms, which form a cage-like fused ring polycyclic system with five and six membered rings, including, for example, C60, C70, and C80 fullerenes or other closed cage structures having three-coordinate carbon atoms.

Graphene sheets are artificially made by, for example, a chemical vapor deposition (CVD) method.

The graphene sheet is commercially available. The size and thickness of the graphene sheet or the number of layers of the graphite sheet described below are measured by, for example, a transmission electron microscope (TEM).

Graphite obtained by multilayering graphene has a large thermal conduction anisotropy. As illustrated in FIG. 50, the graphite has a crystal structure formed by layering a number of layers each having a condensed six membered ring layer plane of carbon atoms extending in a planar shape. Among carbon atoms in this crystal structure, adjacent carbon atoms in the layer are coupled by a covalent bond, and carbon atoms between layers are coupled by a van der Waals bond. The covalent bond has a larger bonding force than a van der Waals bond. Therefore, there is a large anisotropy between the bond between carbon atoms in a layer and the bond between carbon atoms in different layers. In other words, the first high thermal conductor 181 and the second high thermal conductor 182 that are made of graphite each have the heat transfer efficiency in the arrangement direction larger than the heat transfer efficiency in the thickness direction of the first high thermal conductor 181 and the second high thermal conductor 182 (that is, the stacking direction of these components), reducing the heat transferred to the heater holder 24. Accordingly, the above-described structure can efficiently decrease the temperature unevenness of the heater 23 in the longitudinal direction and can minimize the heat transferred to the heater holder 24. Since the first high thermal conductor 181 and the second high thermal conductor 182 that are made of graphite are not oxidized at about 700 degrees or lower, the first high thermal conductor 181 and the second high thermal conductor 182 each have an excellent heat resistance.

The physical properties and dimensions of the graphite sheet may be appropriately changed according to the function required for the first high thermal conductor 181 or the second high thermal conductor 182. For example, the anisotropy of the thermal conduction can be increased by using high-purity graphite or single-crystal graphite or by increasing the thickness of the graphite sheet. Using a thin graphite sheet can reduce the thermal capacity of the fixing device so that the fixing device can perform high speed printing. When the fixing nip N and the heater 23 are large in width, the first high thermal conductor 181 or the second high thermal conductor 182 may be increased in dimension along the width of the fixing nip N and the heater 23.

From the viewpoint of increasing mechanical strength, the number of layers of the graphite sheet is preferably 11 or more. The graphite sheet may partially include a single layer portion and a multilayer portion.

As long as the second high thermal conductor 182 faces a part of each of neighboring resistive heat generators 31 and at least a part of the gap area between the neighboring resistive heat generators 31, the configuration of the second high thermal conductor 182 is not limited to the configuration illustrated in FIG. 45. For example, as illustrated in FIG. 47, a second high thermal conductor 182A may be longer than the base 30 in the direction intersecting the longitudinal direction indicated by the arrow Y, and both ends of the second high thermal conductor 182A in the direction intersecting the longitudinal direction may be outside the base 30 in FIG. 58. A second high thermal conductor 182B may be disposed in a range in which the resistive heat generators 31 are provided in the direction Y. A second high thermal conductor 182C may be disposed to face a part of the gap area and a part of each of neighboring resistive heat generators 31.

The fixing device according to an embodiment illustrated in FIG. 48 has a gap between the first high thermal conductor 181 and the heater holder 24 in the thickness direction that is the lateral direction in FIG. 48. In other words, the fixing device has a gap 24g serving as a thermal insulation layer in a part of a region of the recessed portion 24a (see FIG. 44) of the heater holder 24 in which the heater 23, the first high thermal conductor 181, and the second high thermal conductors 182 are disposed. The gap 24g is in the part of the region of the recessed portion 24a in the longitudinal direction, and the second high thermal conductor 182 is not in the part. For this reason, FIG. 48 does not include the second high thermal conductor 182. The gap 24g has a depth deeper than the depth of the recessed portion 24a of the heater holder 24. Since the gap 24g reduces the area of contact between the heater holder 24 and the first high thermal conductor 181, the thermal conduction from the first high thermal conductor 181 to the heater holder 24 is reduced and the heater 23 can efficiently heat the fixing belt 21. In the cross section of the fixing device at a longitudinal position in which the second high thermal conductor 182 is disposed, the second high thermal conductor 182 is in contact with the heater holder 24 as illustrated in FIG. 43 of the above-described embodiment.

The gap 24g in the present embodiment is in an entire area in which the resistive heat generators 31 are disposed in the direction intersecting the longitudinal direction that is the vertical direction in FIG. 48. The above-described configuration efficiently prevents heat transfer from the first high thermal conductor 181 to the heater holder 24, and the heater 23 efficiently heats the fixing belt 21. The fixing device may include a thermal insulation layer made of heat insulator having a lower thermal conductivity than the thermal conductivity of the heater holder 24 instead of a space like the gap 24g serving as the thermal insulation layer.

In the present embodiment, the second high thermal conductor 182 is different from the first high thermal conductor 181, but the present embodiment is not limited to this. For example, the first high thermal conductor 181 may have a thicker portion than the other portion so that the thicker portion faces the separation area B and functions as the second high thermal conductor 182.

In the above, various configurations of the fixing device and the image forming apparatus in which the embodiments of the present disclosure can be applied are described. Applying the embodiments to the various configurations of the fixing device and the image forming apparatus gives effects similar to the above-described effects in the embodiments. Applying any one of the above-described embodiments of the present disclosure to any one of the above-described fixing devices can reduce the discharge of FP/UFP to the outside of the image forming apparatus. As a result, the environmentally friendly image forming apparatus reducing the discharge of FP/UFP can be provided.

In the above description, the embodiments of the present disclosure are applied to the fixing device incorporated in the electrophotographic image forming apparatus as illustrated in FIG. 1. However, the present disclosure is not limited to this. The embodiments of the present disclosure may be applied to a heating device other than the fixing device, such as a drying device that is included in an inkjet image forming apparatus and dries liquid such as ink applied to a sheet.

FIG. 51 is a schematic cross-sectional view of an inkjet image forming apparatus including a drying device according to an embodiment of the present disclosure.

An inkjet image forming apparatus 2000 illustrated in FIG. 51 includes an image reading device 202, an image forming device 203, a sheet supplying device 204, a drying device 206, and an output section 207. A sheet aligning apparatus 3000 is disposed beside the inkjet image forming apparatus 2000.

In response to an instruction to start a printing operation, the sheet supplying device 204 feeds a sheet such as a sheet of paper as a recording medium in the inkjet image forming apparatus 2000. When the sheet is conveyed to the image forming device 203, the image forming device 203 discharges ink from a liquid discharge head 214 to the sheet according to the image data of a document read by the image reading device 202 or print data instructed to print by a terminal, to form an image on the sheet.

The sheet bearing the image is selectively guided to a conveyance passage 222 or a conveyance passage 223. When the sheet is guided to the conveyance passage 222, the sheet passes through the drying device 206. When the sheet is guided to the conveyance passage 223, the sheet does not pass through the drying device 206. When the sheet is guided to the drying device 206, the drying device 206 accelerates the drying of the ink on the sheet. The sheet is then guided to the output section 207 or the sheet aligning apparatus 3000. By contrast, when the sheet is guided to the conveyance passage 223 along which the sheet does not pass through the drying device 206, the sheet is directly guided to the output section 207 or the sheet aligning apparatus 3000. The sheet aligning apparatus 3000 aligns and places the sheets guided to the sheet aligning apparatus 3000.

FIG. 52 is a schematic cross-sectional view of the drying device 206 installed in the inkjet image forming apparatus 2000.

As illustrated in FIG. 52, the drying device 206 includes a heating belt 291 as the first rotator, a heating roller 292 as the second rotator, a first heater 293 as the heat source that heats the heating belt 291, a second heater 294 as the heat source that heats the heating roller 292, a nip formation pad 295, a stay 296 as the reinforcement, a reflector 297, and belt holders 298 as the rotator holders that hold the heating belt 291 such that the heating belt 291 can rotate.

The nip formation pad 295 contacts an outer peripheral surface of the heating roller 292 via the heating belt 291 to form a nip N between the heating belt 291 and the heating roller 292. As illustrated in FIG. 52, when a sheet 250 bearing an image formed by the ink I is conveyed to the nip N of the drying device 206, the sheet 250 is heated while being conveyed by the heating belt 291 and the heating roller 292 rotating in the directions indicated by arrows in FIG. 63. Thus, the drying of the ink I on the sheet 250 is accelerated.

In the drying device 206 installed in the inkjet image forming apparatus 2000, since the heating belt 291 is rotatably held by the pair of belt holders 298 disposed at both ends of the heating belt 291 in the longitudinal direction of the heating belt 291, the lubricant is used to reduce sliding friction between the heating belt 291 and the belt holder 298. As a result, heating the heating belt 291 causes the temperature rise of the belt holder 298, which may generate the FP/UFP from the lubricant adhering to the belt holder 298. Accordingly, applying any one of the embodiments of the present disclosure to the drying device 206, placing the cover covering the opening of the rotator holder (that is the belt holder 298) supporting the heating belt 291, and maintaining the temperature of the cover 40 to be 40° C. or higher from 2 minutes after the start of the continuous printing to 10 minutes after the start of the continuous printing can reduce the discharge of the FP/UFP from the heating belt 291 to the outside of the image forming apparatus.

FIG. 53 is a schematic cross-sectional view of an image forming apparatus including a laminating device to which any one of the embodiments of the present disclosure is applicable.

An image forming apparatus 4000 that is illustrated in FIG. 53 includes a laminator 401, an image forming device 402, a fixing device 403, and a sheet feeding device 404 as a recording-medium supplier. The image forming device 402 includes multiple image forming units 411C, 411M, 411Y, and 411Bk, an exposure device 412, and a transfer device 413.

The laminator 401 is a heating device that applies heat and pressure to two sheets between which another sheet is inserted, to fix said another sheet between the two sheets under the heat and the pressure. Specifically, the laminator 401 includes a sheet supplier 420, a sheet separator 430, and heat and pressure rollers 440. The sheet supplier 420 supplies a sheet 450. The sheet separator 430 separates the sheet supplied from the sheet supplier 420 into two sheets. The heat and pressure rollers 440 as rotators convey the two separated sheets between which said another sheet is inserted, while applying heat and pressure to the sheets and said another sheet. The thermal pressure roller 440 is heated by a heat source such as the heater. A pair of rotator holders such as a pair of bearings rotatably holds both ends of the heat and pressure roller 440 in the longitudinal direction of the heat and pressure roller 440.

The sheet feeding device 404 supplies the sheet P as the recording medium to the image forming device 402, and the image forming device 402 forms an image on the sheet P. Subsequently, the sheet P is conveyed to the fixing device 403 to fix the image onto the sheet P. Since the image forming operation in the image forming device 402 and the fixing process in the fixing device 403 are basically the same as those described in the above embodiments, a redundant description is omitted.

The sheet P subjected to the fixing process is conveyed to the laminator 401 and inserted between two sheets separated from each other. Then, the heat and pressure rollers 440 apply heat and pressure to the sheet P sandwiched between the two sheets to fix the sheet P between the sheets. The sheets and the sheet P thus thermally pressed and fixed are ejected to the outside of the image forming apparatus 4000.

The heat source such as the heater heats the heat and pressure roller 440, which may cause the temperature rise of the lubricant inside the heat and pressure roller 440. As a result, the FP/UFP may be generated. Accordingly, applying any one of the embodiments of the present disclosure to the laminator 401 including the above-described heat and pressure roller 440, placing the cover covering the opening of the rotator holder supporting the heat and pressure roller 440, and maintaining the temperature of the cover 40 to be 40° C. or higher from 2 minutes after the start of the continuous printing to 10 minutes after the start of the continuous printing can reduce the discharge of the FP/UFP from the heat and pressure roller 440 to the outside.

The embodiments described above are given by way of example, and unique advantageous effects are achieved for each of the following aspects given below.

First Aspect

In a first aspect, a heating device includes a rotator, a heater, lubricant, a rotator support, and a cover. The rotator has an internal space inside a loop od the rotator. The heater heats the rotator. The lubricant is applied to an inner circumferential surface of the rotator. The rotator support supports an end of the rotator in a longitudinal direction of the rotator. The rotator support has a first opening communicating with the internal space of the rotator, penetrating through the rotator support, and extending in the longitudinal direction. The cover covers the first opening and has a face facing the first opening and a second opening communicating with the internal space of the rotator and an exterior of the cover. The cover maintains a temperature of the face of the cover at 40° C. or higher.

Second Aspect

In a second aspect, the cover in the heating device according to the first aspect maintains the temperature of the face of the cover at 40° C. or higher and 130° C. or lower from two to ten minutes after a start of continuous printing.

Third Aspect

In a third aspect, the cover in the heating device according to the first aspect or the second aspect is made of any one of metal and alloy.

Fourth Aspect

In a fourth aspect, a fixing device includes the heating device according to any one of the first to third aspects.

Fifth Aspect

In a fifth aspect, the fixing device according to the fourth aspect further includes a pressure rotator pressing an outer circumferential face of the rotator and a nip formation pad disposed inside the loop of the rotator and pressed by the pressure rotator to form a nip between the rotator and the pressure rotator, and the rotator has a belt shape.

Sixth Aspect

In a sixth aspect, an image forming apparatus includes the heating device according to any one of the first to third aspects.

Seventh Aspect

In a seventh aspect, the cover in the heating device according to the first aspect or the second aspect includes a cover heater to heat the face of the cover.

Eighth Aspect

In an eighth aspect, the heating device according to the seventh aspect further includes a controller configured to cause the cover heater to heat the face of the cover at 40° C. or higher and 130° C. or lower from two to ten minutes after a start of continuous printing. The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.

The functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, application specific integrated circuits (ASICs), digital signal processors (DSPs), field programmable gate arrays (FPGAs), conventional circuitry and/or combinations thereof which are configured or programmed to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein. In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein or otherwise known which is programmed or configured to carry out the recited functionality. When the hardware is a processor which may be considered a type of circuitry, the circuitry, means, or units are a combination of hardware and software, the software being used to configure the hardware and/or processor.

Claims

1. A heating device comprising: a rotator having an internal space inside a loop of the rotator:a heater to heat the rotator:lubricant applied to an inner circumferential surface of the rotator:a rotator support to support an end of the rotator in a longitudinal direction of the rotator, the rotator support having a first opening: communicating with the internal space of the rotator;penetrating through the rotator support: andextending in the longitudinal direction: and a cover covering the first opening, the cover having:a face facing the first opening: anda second opening communicating with the internal space of the rotator and an exterior of the cover,wherein the cover maintains a temperature of the face of the cover at 40° C. or higher.

2. The heating device according to claim 1, wherein the cover maintains the temperature of the face of the cover at 40° C. or higher and 130° C. or lower from two to ten minutes after a start of continuous printing.

3. The heating device according to claim 1, wherein the cover is made of any one of metal and alloy.

4. A fixing device comprising the heating device according to claim 1.

5. The fixing device according to claim 4, further comprising: a pressure rotator pressing an outer circumferential face of the rotator: anda nip formation pad disposed inside the loop of the rotator and pressed by the pressure rotator to form a nip between the rotator and the pressure rotator,wherein the rotator has a belt shape.

6. An image forming apparatus comprising the heating device according to claim 1.

7. The heating device according to claim 1, wherein the cover includes a cover heater to heat the face of the cover.

8. The heating device according to claim 7, further comprising circuitry configured to cause the cover heater to heat the face of the cover at 40° C. or higher and 130° C. or lower from two to ten minutes after a start of continuous printing.