Patent Application
20230097051
The present invention relates to a fixing apparatus that fixes an image to a recording medium and an image forming apparatus that forms an image on a recording medium.
An image forming apparatus of an electrophotographic system or the like includes a fixing apparatus of a thermal fixation system that heats and fixes a toner image transferred onto a recording material. Japanese Patent Laid-Open No. 2001-102150 discloses a fixing apparatus of a film heating system including a heater in which a heat-generating resistor is formed on a ceramic substrate, a holder member that holds the heater, a tubular film fitted on the heater, and a pressurizing roller in pressure contact with the heater with the film therebetween. In addition, this document discloses efficiently heating the film by dispersing particles having a low thermal conductivity in the holder member.
However, in the case where the fixing apparatus is used for a long period, the holder member creeps in some cases by being continuously subjected to heat and load. For example, in the case where the holder member creeps in the configuration of the above-described document, the rotation trajectory of the film rotating around the holder member changes, and an influence thereof can appear as deterioration of the fixing performance caused by reduction of the contact area between the film and the heater or the like.
The present invention provides a fixing apparatus and an image forming apparatus that can achieve stable fixing performance for a long period.
According to one aspect of the invention, a fixing apparatus includes a first rotary member configured to rotate, a nip forming unit including a heater and a holder member and disposed in an inner space of the first rotary member, the heater having a length in a longitudinal direction thereof larger than a length thereof in a short direction orthogonal to the longitudinal direction, the holder member being configured to hold the heater, a second rotary member configured to be in a pressure contact with the nip forming unit with the first rotary member therebetween to form a nip portion between the second rotary member and the nip forming unit, the first rotary member and the second rotary member being configured to nip a recording material at the nip portion and convey the recording material from a first side toward a second side in the short direction, and a support member disposed in the inner space of the first rotary member and configured to support the nip forming unit, wherein the holder member includes a first surface configured to support the heater and provided on the nip portion side of the holder member in an orthogonal direction orthogonal to both of the longitudinal direction and the short direction, a second surface provided on a side of the holder member opposite to the first surface in the orthogonal direction and configured to abut a first abutting portion of the support member on the first side in the short direction with respect to the first surface and abut a second abutting portion of the support member on the second side in the short direction with respect to the first surface, and a rib portion provided to project from the second surface and extend in the short direction throughout at least a range in the short direction where the first surface is provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments according to the present disclosure will be described below with reference to drawings.
An image forming apparatus according to a first embodiment will be described with reference to a schematic view illustrated in
The image forming apparatus 50 includes, as an image forming portion, an electrophotographic unit including a photosensitive drum 1, a charging unit 2, an exposing unit 3, a developing unit 5, a transfer roller 10, and a drum cleaner 16. The photosensitive drum 1 serving as an image bearing member is an electrophotographic photoconductor formed in a drum shape, that is, a cylindrical shape. The charging unit 2, the exposing unit 3, the developing unit 5, the transfer roller 10, and the drum cleaner 16 are arranged around the photosensitive drum 1 in this order in a rotation direction of the photosensitive drum 1 indicated by an arrow R1.
When an image formation request is input to the image forming apparatus 50 from an external computer, the photosensitive drum 1 is rotationally driven in the arrow R1 direction, and the surface of the photosensitive drum 1 is charged to a predetermined polarity, which is a negative polarity in the present embodiment, by the charging unit 2. Then, the charged surface of the photosensitive drum 1 is irradiated with laser light L from the exposing unit 3, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. The developing unit 5 accommodates black toner serving as developer of the present embodiment, and supplies negatively-charged black toner to the photosensitive drum 1 via a developing roller. As a result of this, toner attaches to the electrostatic latent image region on the photosensitive drum 1, and thus a toner image is formed on the surface of the photosensitive drum 1.
A feed tray on which recording materials P are supported is provided in a lower portion of the image forming apparatus 50. As the recording materials P, various sheet materials of different sizes and materials can be used. Examples of the various sheet materials include paper sheets such as plain paper sheets and cardboards, plastic films, cloths, surface-treated sheet materials such as coated paper sheets, and sheet materials of irregular shapes such as envelops and index paper sheets.
The recording materials P supported on the feed tray are fed one by one by a feed roller 4, and are conveyed by conveyance rollers 6 to a transfer nip Ntr serving as a transfer portion where a toner image is transferred onto the recording material P. The transfer nip Ntr is a nip portion between the photosensitive drum 1 and the transfer roller 10. Then, a voltage of a positive polarity, which is a polarity opposite to the normal charging polarity of the toner, is applied to the transfer roller 10 from an unillustrated power source, and thus the toner image on the photosensitive drum 1 is transferred onto the recording material P in the transfer nip Ntr. Attached matter such as transfer residual toner and paper dust attaching to the surface of the photosensitive drum having passed the transfer nip Ntr is removed by the drum cleaner 16 including an elastic blade.
The recording material P on which the toner image has been transferred is conveyed to a fixing apparatus 100 of a thermal fixation system that will be described below, and the toner image is subjected to a fixing process. The recording material P having passed the fixing apparatus 100 is discharged as a product to the outside of the image forming apparatus 50 by a discharge roller pair.
To be noted, although an image forming apparatus of a direct transfer system has been described as an example, an image forming apparatus of a different system may be used as long as the image forming apparatus includes a fixing apparatus that heats and fixes a toner image formed on the recording material P For example, a fixing apparatus that will be described below may be applied to an image forming apparatus of an intermediate transfer system in which a toner image formed on an image bearing member is transferred onto an intermediate transfer member such as an intermediate transfer belt through primary transfer and then the toner image is transferred from the intermediate transfer member onto a recording material. In addition, the fixing apparatus that will be described below may be applied to an image forming apparatus that forms a color image on a recording material by using toner of a plurality of colors.
Summary of the fixing apparatus 100 of the present embodiment will be described with reference to
In the description below, the shapes and positional relationships of members in the fixing apparatus 100 will be described by using a recording material conveyance direction A, a longitudinal direction B, and an orthogonal direction C. The recording material conveyance direction A is a conveyance direction of the recording material P in a fixing nip Nf that is a nip portion of the fixing apparatus 100. The longitudinal direction B is a width direction of the recording material P in the fixing nip Nf. The longitudinal direction B is orthogonal to the recording material conveyance direction A, and also serves as a main scanning direction in image formation. The orthogonal direction C is an orthogonal direction orthogonal to both the recording material conveyance direction A and the longitudinal direction B.
As illustrated in
The heater holder 130 serves as a holder member or a holding member in the present embodiment. The pressurizing stay 119 serves as a support member or a reinforcing member in the present embodiment. The pressurizing roller 110 serves as a second rotary member in the fixing apparatus 100 of the present embodiment. In addition, the pressurizing roller 110 serves as a pressurizing member in the present embodiment.
The fixing film 112 serves as a first rotary member in the fixing apparatus 100 of the present embodiment. The fixing film 112 is a flexible tubular film member, that is, an endless belt member. The fixing film 112 of the present embodiment has an outer diameter of 18 mm in a cylindrical shape that is not deformed, and has a multilayer structure in the thickness direction. The layer configuration of the fixing film 112 at least includes a base layer for the strength of the film, and a release layer for reducing attachment of soiling to the surface thereof.
The material of the base layer preferably has a heat resistance to endure the heat of the heater 113 and a strength high enough to slide on the heater 113. Preferable examples of the base layer include metals such as stainless steel and nickel, and heat-resistant resins such as polyimide resin. In the present embodiment, polyimide resin to which carbon-based filler is added to improve the thermal conductivity and the strength is used as the material of the base layer of the fixing film 112. The thickness of the base layer is preferably 15 μm to 100 μm because the smaller the thickness of the base layer is, the more it is likely for the heat of the heater 113 to be transmitted to the surface of the recording material P but the lower the strength thereof becomes. In the present embodiment, the thickness of the base layer is set to 60 μm.
Preferable examples of the material of the release layer of the fixing film 112 include fluorine resins such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), and tetrafluoroethylene-hexafluoropropylene resin (FEP). In the present embodiment, PFA, which is excellent in the releasing property and heat resistance among the fluorine resins, is used. The release layer may be formed by covering the base layer with a tube, or may be formed by coating the surface of the base layer with a coating liquid. In the present embodiment, the release layer is formed by the coating method that is excellent in formation of a thin layer. The thinner the release layer is, the more it is likely for the heat of the heater 113 to be transmitted to the surface of the fixing film 112, but it becomes difficult to secure the durability if the release layer is too thin. Therefore, the thickness of the release layer is preferably about 5 μm to 30 μm, and is set to 10 μm in the present embodiment. In addition, although it is not used in the present embodiment, an elastic layer may be provided between the base layer and the release layer. In this case, silicone rubber, fluorine rubber, or the like is used as the material of the elastic layer.
The heater holder 130 is provided on the inner circumferential side of the fixing film 112. The heater holder 130 has an approximately semicircular gutter shape in transverse section view, which is a section view taken along a plane orthogonal to the longitudinal direction B. That is, in the heater holder 130, a surface opposing the fixing nip Nf is curved in a convex shape protruding toward the pressurizing roller 110 side in the orthogonal direction C, and a heater holding portion serving as a fitting portion that holds the heater 113 is provided at an approximate center portion of the curved surface in the recording material conveyance direction A. The heater holding portion has a thin elongated groove shape that opens toward the pressurizing roller 110 side in the orthogonal direction C and is longer in the longitudinal direction B. The heater holder 130 is formed from liquid crystalline polymer resin having high heat resistance to satisfy requirements for heat resistance and stiffness. To be noted, in the present embodiment, as the liquid crystalline polymer resin, Sumika Super E5204L (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. is used.
The heater holder 130 includes a heater seating surface S1 that supports the heater 113, an upstream projection portion 131 and a downstream projection portion 132 that are adjacent to the heater seating surface S1, and a stay contact surface S3 provided on the opposite side to the heater seating surface S1 in the orthogonal direction C. The heater seating surface S1 is a first surface of the heater holder 130 that is provided on the pressurizing roller 110 side in the orthogonal direction C orthogonal to both the recording material conveyance direction A and the longitudinal direction B. The heater seating surface S1 supports a surface of the heater 113 opposite to the pressurizing roller 110 in the orthogonal direction C, that is, a surface opposite to a sliding surface S2.
The upstream projection portion 131 is provided on the upstream side of the heater seating surface S1 in the recording material conveyance direction A, and projects toward the pressurizing roller 110 side in the orthogonal direction C with respect to the heater seating surface S1. The downstream projection portion 132 is provided on the downstream side of the heater seating surface S1 in the recording material conveyance direction A, and projects toward the pressurizing roller 110 side in the orthogonal direction C with respect to the heater seating surface S1. The heater seating surface S1 is a bottom portion of a groove shape serving as a heater holding portion formed between the upstream projection portion 131 and the downstream projection portion 132. In addition, the upstream projection portion 131 and the downstream projection portion 132 each include a sliding surface that slides on the inner surface of the fixing film 112 on the upstream side or downstream side of the sliding surface S2 of the heater 113 in the recording material conveyance direction A.
Further, the heater holder 130 includes an upstream guide 126 that guides the fixing film 112 on the upstream side of the fixing nip Nf in the recording material conveyance direction A, and a downstream guide 127 that guides the fixing film 112 on the downstream side of the fixing nip Nf. That is, the heater holder 130 has a function of holding the heater 113 and guiding the rotation of the fixing film 112.
The upstream guide 126 and the downstream guide 127 both extend to the side opposite to the pressurizing roller 110 in the orthogonal direction C with respect to the stay contact surface S3 of the heater holder 130. More specifically, as illustrated in
To be noted, instead of the configuration in which the fixing film 112 is guided by the guide ribs 129 projecting from the wall portions 124, a configuration in which the wall portions 124 themselves are formed in the same sectional shape as the guide ribs 129 of the present embodiment and the fixing film 112 is guided by the outer surface of the wall portions 124 may be employed. In this case, the guide ribs 129 may be formed to be continuous with the outer surface of the wall portions 124 and guide the fixing film 112 on the upstream side or the downstream side of the outer surface of the wall portions 124 in the rotation direction of the fixing film 112, or the guide ribs 129 may be omitted.
The heater 113 and the heater holder 130 are disposed in an inner space of the fixing film 112, and functions as a nip forming unit that is in pressure contact with the pressurizing roller 110 with the fixing film 112 therebetween to form the fixing nip Nf. To be noted, although a configuration in which the heater 113 directly slides on the inner surface of the fixing film 112 will be described in the present embodiment, a configuration in which a sliding member is provided between the heater 113 and the fixing film 112 may be employed. As the sliding member, a material having high thermal conductivity and high slidability on the inner surface of the fixing film 112 is used, and for example, a sheet member formed from ferroalloy or aluminum can be used. That is, the nip forming unit may have a configuration in which the heater 113 indirectly heats the fixing film 112 via the sliding member.
The pressurizing stay 119 is provided along the longitudinal direction B of the heater holder 130. The pressurizing stay 119 is formed by performing a bending process on a metal plate of a material having high rigidity such as stainless steel to uniformly pressurize the heater holder 130 in the longitudinal direction B. The pressurizing stay 119 is formed in an angular C shape opening toward the pressurizing roller 110 side in the orthogonal direction C as viewed in the longitudinal direction B. That is, the pressurizing stay 119 includes a first portion 91 extending in the recording material conveyance direction A, and a second portion 92 and a third portion 93 that respectively extend in the orthogonal direction C toward the heater holder 130 from the upstream end and the downstream end of the first portion 91 in the recording material conveyance direction A.
One end portion 119a of the pressurizing stay 119 is a first abutting portion that abuts the stay contact surface S3 of the heater holder 130 on the upstream side of the heater seating surface S1 in the recording material conveyance direction A, that is, on the first side of the heater 113 in the short direction. The other end portion 119b of the pressurizing stay 119 is a second abutting portion that abuts the stay contact surface S3 of the heater holder 130 on the downstream side of the heater seating surface S1 in the recording material conveyance direction A, that is, on the second side of the heater 113 in the short direction. That is, the pressurizing stay 119 abuts the stay contact surface S3 serving as a second surface of the heater holder 130 at the end portions 119a and 119b that respectively serve as distal ends of the second portion 92 and the third portion 93.
The pressurizing stay 119 presses the stay contact surface S3 toward the pressurizing roller 110 side in the orthogonal direction C at the end portion 119a, and thus supports the heater holder 130 against the nip pressure of the fixing nip Nf. That is, the pressurizing stay 119 functions as a support member that supports the nip forming unit including the heater 113 and the heater holder 130.
The pressurizing roller 110 of the present embodiment has an outer diameter of 20 mm, and is constituted by forming an elastic layer 116 having a thickness of 3.0 mm on the outer circumferential surface of a core metal 117 having a diameter of 14 mm and formed from iron. As the material of the elastic layer 116, solid rubber, foam rubber, or the like is used. The foam rubber has a low heat capacity and a low thermal conductivity, and is thus less likely to absorb the heat of the surface of the pressurizing roller 110 to the inside, thus the surface temperature thereof is likely to rise, and therefore the foam rubber is advantageous in shortening the activation time of the fixing apparatus 100. In the present embodiment, foam rubber obtained by foaming silicone rubber is used for the elastic layer 116. As the release layer, a release layer 118 formed from perfluoroalkoxy resin (PFA) is formed on the elastic layer 116. The release layer 118 may be formed by covering the elastic layer 116 with a tube similarly to the release layer of the fixing film 112, or formed by coating the surface of the elastic layer 116 with a coating liquid. In the present embodiment, the release layer 118 is formed by covering the outer circumferential surface of the elastic layer 116 with a tube having excellent durability. As the material of the release layer 118 other than PFA, fluorine resins such as PTFE and FEP, fluorine rubbers, silicone rubbers, and the like that have good releasability, and the like may be used. The width of the fixing nip Nf can be achieved at a lower pressure if the surface hardness of the pressurizing roller 110 is lower, but the surface hardness is also determined in consideration of the durability. In the present embodiment, a material having an Asker-C hardness (load: 4.9 N) of 50° is used. To be noted, a belt unit including a belt member stretched over a plurality of rollers may be used as the pressurizing member instead of the pressurizing roller 110.
As the heater 113 of the present embodiment, a heater formed by providing a heat-generating resistor on a ceramic substrate is used. Specifically, as the substrate of the heater 113, an alumina substrate having a width of 6 mm in the recording material conveyance direction A and a thickness of 1 mm in the orthogonal direction C is used. The heater 113 is formed by coating the surface of this substrate with an Ag/Pd (silver palladium) heat-generating resistor to a thickness of several μm by screen printing, and forming a glass layer having a thickness of 60 μm thereon for protection of the heat-generating resistor and improvement in the slidability.
The fixing apparatus 100 is configured such that the temperature of the heater 113 can be adjusted by appropriately controlling the current flowing in the heat-generating resistor in accordance with a signal of a temperature detection element (heat sensor) that will be described later and that detects the temperature of the substrate of the heater 113 or the fixing film 112. The heater 113 is supported in a fixed manner by being fit in the groove portion provided in the heater holder 130. In the present embodiment, the center of the heater 113 in the recording material conveyance direction A is positioned 0.4 mm upstream of the center (rotation axis) of the pressurizing roller 110.
As illustrated in
The core metal 117 of the pressurizing roller 110 includes shaft portions 117a penetrating both the side plates 134, and the shaft portions 117a are each held by a bearing member 135 engaged with the side plate 134. As a result of this, the pressurizing roller 110 is rotatably supported by the frame 133.
Further, pressurizing springs 122 are respectively provided, in a compressed form, between pressurizing portions 120b of the fixing flanges 120 and spring support portions 121 fixed to the frame 133. As a result of this, the urging force of the pressurizing springs 122 is transmitted to the heater 113 via the fixing flanges 120 on both sides, the pressurizing stay 119, and the heater holder 130, and the heater 113 is pressed against the pressurizing roller 110 by a predetermined pressing force with the fixing film 112 therebetween.
In the present embodiment, the spring constant and the compression amount of the pressurizing springs 122 are set such that the pressing force by which the fixing film 112 and the pressurizing roller 110 press each other in the orthogonal direction C in the fixing nip Nf is 15 kgf. In the fixing nip Nf, the fixing film 112 is nipped between the heater 113 and the pressurizing roller 110 and is thus warped along the sliding surface S2 that is a flat front surface of the heater 113, and thus the inner surface of the fixing film 112 is in firm contact (surface contact) with the sliding surface S2. To be noted, film regulating portions 120a of the fixing flanges 120 are each formed in a shape following the natural shape that is formed when the fixing film 112 is pressurized in the fixing nip Nf as illustrated in
When a driving force transmitted from an unillustrated drive source is input to a drive gear 117g provided on one of the shaft portions 117a of the pressurizing roller 110 illustrated in
When fixing the image, the pressurizing roller 110 is driven while supplying power to the heater 113, and thus the recording material is nipped and conveyed between the pressurizing roller 110 and the fixing film 112 in the fixing nip Nf. At the same time as this, the image on the recording material is heated by the fixing film 112 heated by the heater 113, and thus the image is thermally fixed.
To be noted, a heat-resistant lubricant is applied on the inner surface of the fixing film 112, and thus slidability of the inner surface of the fixing film 112 on the heater 113 and the heater holder 130 is secured. In the present embodiment, a fluorine-based grease is used as the lubricant. Specifically, a grease including a perfluoropolyether (PFPE) oil as a base oil and polytetrafluoroethylene (PTFE) powder as a thickener is used.
As a specific example of the crown shape of the heater seating surface S1, the shape of the heater seating surface S1 is set to a shape of a gentle quadratic curve as viewed in the recording material conveyance direction A in a region CR having a longitudinal width of 225 mm and corresponding to a range in the longitudinal direction B where the heater 113 opposes the pressurizing roller 110. The projection amount by which the center portion of the heater seating surface S1 projects in the orthogonal direction C with respect to the end portions thereof is, for example, 0.4 mm.
By providing a crown shape like this, the fixing nip Nf having a constant width throughout approximately the entire region in the longitudinal direction B can be formed. That is, when the film unit 101 is pressed against the pressurizing roller 110 by the urging force of the pressurizing springs 122, the pressurizing stay 119 and the core metal 117 of the pressurizing roller 110 are slightly warped. In the case where the heater seating surface S1 is not formed in a crown shape, the heater 113 is strongly pressed by the pressurizing roller 110 at end portions thereof in the longitudinal direction B, and thus the nip width of the fixing nip Nf increases at the end portions. In contrast, the nip width of the fixing nip Nf is reduced at the center portion in the longitudinal direction B. However, by providing the crown shape of the present embodiment, the difference in the nip width of the fixing nip Nf between the center portion and the end portions in the longitudinal direction B can be reduced. The width of the fixing nip Nf in the recording material conveyance direction A in the present embodiment is about 6.2 mm throughout the entirety of the region CR in the longitudinal direction B.
Next, an opening portion O of the heater holder 130 will be described.
As illustrated in
By using a temperature fuse or a thermoswitch as the temperature detection element T, a controller 51 of the image forming apparatus 50 can control a power supply circuit 52 for the heater 113 on the basis of the signal of the temperature detection element T to block the power supply to the heater 113. The power supply circuit 52 includes a blocking circuit such as a relay capable of blocking the power supply to the heater 113 on the basis of a command from the controller 51. In this case, the controller 51 and the blocking circuit functions as a blocking portion (safety device) that detects an abnormal temperature rise of the heater 113 and blocks the power supply to the heater 113. In addition, by using a thermistor as the temperature detection element T, the controller 51 can control the amount of power supplied from the power supply circuit 52 to the heater 113 on the basis of the signal of the temperature detection element T. In this case, the controller 51 functions as a temperature controller (temperature adjusting device) that controls the temperature of the heater 113 to a predetermined target temperature.
Here, a peripheral portion of the opening portion O of the heater holder 130 has a lower rigidity than the other portion of the heater holder 130. Therefore, in the present embodiment, as will be described later, reinforcing ribs 123 are provided in the vicinity of the opening portion O on the stay contact surface S3 opposite to the heater seating surface S1.
Next, a rotation trajectory of the fixing film 112 regulated by the heater holder 130 will be described.
As described above, the heater holder 130 includes an upstream projection portion 131 projecting toward the pressurizing roller 110 side with respect to the heater seating surface S1 at a position upstream of the heater 113 in the recording material conveyance direction A. The projection height H of the upstream projection portion 131 with respect to the sliding surface S2 of the heater 113 is preferably of a sufficient value for regulating the trajectory of the fixing film 112 such that the fixing film 112 does not contact an edge portion of the heater 113 on the upstream side in the recording material conveyance direction A. However, if the projection height H is set to be too large, the upstream projection portion 131 presses the fixing film 112, and thus the contact width between the inner surface of the fixing film 112 and the heater 113, that is, an inner surface nip width Nn decreases. In this case, heat transmission from the heater 113 to the fixing film 112 is reduced, which can lead to occurrence of a fixation failure.
The projection height H of the upstream projection portion 131 with respect to the sliding surface S2 of the heater 113 is, for example, preferably about 0.1 mm to 0.7 mm, and is 0.2 mm in the present embodiment. In addition, the inner surface nip width Nn is preferably 4 mm or larger, and is 4.2 mm in the present embodiment.
Next, the shape and positional relationship with the pressurizing stay 119 of the reinforcing ribs 123 provided on the heater holder 130 according to the present embodiment will be described.
Incidentally, the reinforcing ribs 123 have shapes projecting from the stay contact surface S3 of the heater holder 130 to the side opposite to the pressurizing roller 110 in the orthogonal direction C. Therefore, the end portions 119a and 119b of the pressurizing stay 119 opposing the heater holder 130 are each provided with a cutout portion 119c avoiding the reinforcing ribs 123 as illustrated in
In the present embodiment, the height Hr of the reinforcing rib 123 in the orthogonal direction C is set to 1.5 mm, and the width Wr of the reinforcing rib 123 in the longitudinal direction B is set to 2.0 mm. In addition, the height of the cutout portion 119c of the pressurizing stay 119 in the recording material conveyance direction A is set to 2.0 mm, and the width of the cutout portion 119c in the longitudinal direction B is set to 2.5 mm. As a result of this, contact between the reinforcing ribs 123 and the pressurizing stay 119 is avoided, and thus the pressurizing stay 119 can press the heater holder 130 by a force that is substantially uniform in the longitudinal direction B even in a state in which the reinforcing ribs 123 are provided.
Reduction of creep deformation of the heater holder 130 according to the configuration of the present embodiment will be described with reference to
As a result of this, a bending moment that displaces the heater seating surface S1 toward a side opposite to the pressurizing roller 110 in the orthogonal direction C acts on the heater holder 130 between the contact portions between the pressurizing stay 119 and the heater holder 130, that is, between a first position P1 and a second position P2. In other words, a bending moment that warps the heater holder 130 such that the upstream projection portion 131 and the downstream projection portion 132 are displaced toward the pressurizing roller 110 side in the orthogonal direction C is generated on the heater 113.
If the heater holder 130 is deformed by such a bending moment, the fixing performance of the fixing apparatus 100 can deteriorate.
Next, a case where the heater holder 130 is deformed by the bending moment will be described with reference to a reference example.
As a result of a sheet passing test in which an image is formed on a paper sheet of an LTR (Letter) size by using the image forming apparatus 50 including the fixing apparatus 100 of the reference example, damage to the heater holder 130 and wrinkling of the recording material did not occur. If the mechanical strength or dimensional precision of the heater holder 130 is insufficient, there is a possibility that the heater holder 130 is damaged, or the rotation of the fixing film 112 becomes unstable, which can lead to biased movement of the fixing film 112 and wrinkles of the recording material. Regarding this, it can be considered that sufficient values of mechanical strength and dimensional precision of the heater holder 130 were secured in the fixing apparatus 100 of the reference example.
However, in this reference example, in the case where an endurance test in which images were repeatedly performed on a large number of paper sheets was performed, fixation failures increasingly occurred as the total number of passed sheets increased, and the result gradually became worse. This can be considered to be because the bending moment described above caused creep deformation of the heater holder 130, and thus the inner surface nip width Nn, which was the contact width between the inner surface of the fixing film 112 and the heater 113, decreased. That is, it can be considered to be because the upstream projection portion 131 and the downstream projection portion 132 were displaced toward the pressurizing roller 110 side in the orthogonal direction C with respect to the heater 113, and thus the fixing film 112 was separated from part of the heater 113. When the inner surface nip width Nn decreases, the surface temperature of the fixing film 112 is reduced, and when the surface temperature of the fixing film 112 becomes lower than the lower limit of a temperature range suitable for image fixation, this appears as a fixation failure.
In addition, in the endurance test, the fixation failures occurred at positions corresponding to the vicinity of the opening portion O of the heater holder 130 in the longitudinal direction B. This can be considered to be because the creep deformation of the heater holder 130 was caused by the bending moment described above mainly in the vicinity of the opening portion O where the rigidity was relatively low.
Next, the case of the present embodiment will be described with reference to
Particularly, in the present embodiment, the reinforcing ribs 123 are disposed in the vicinity of the opening portion O of the heater holder 130 in the longitudinal direction B. As a result of this, the flexural rigidity in the vicinity of the opening portion O having a lower rigidity than a portion where the opening portion O is not provided can be improved, and the creep deformation of the heater holder 130 can be effectively reduced.
The reinforcing ribs 123 are preferably provided throughout at least a range where the heater seating surface S1 serving as a first surface is provided in the recording material conveyance direction A. As a result of this, the flexural rigidity of the portion where the thickness of the heater holder 130 in the orthogonal direction C is small due to the space for receiving the heater 113 can be improved by the reinforcing ribs 123, and thus the creep deformation can be reduced.
More preferably, the reinforcing ribs 123 are provided throughout at least a range from the first position P1 to the second position P2 of
Further preferably, as in the present embodiment, the reinforcing ribs 123 are formed to be continuous in the recording material conveyance direction A from the upstream guide 126 serving as a first guide portion to the downstream guide 127 serving as a second guide portion of the heater holder 130. As a result of this, the flexural rigidity of the heater holder 130 can be further improved, and the creep deformation can be further reduced.
As a result of a sheet passing test in which an image is formed on a paper sheet of an LTR size by using the image forming apparatus 50 including the fixing apparatus 100 of the present embodiment, damage to the heater holder 130 and wrinkling of the recording material did not occur. In addition, also in the case of conducting the endurance test, abnormal images such as fixation failures did not occur, and a state in which fixed images that were uniform throughout the entire region in the longitudinal direction B could be obtained was maintained for a long period. This can be considered to be because the creep deformation of the heater holder 130 was reduced by the reinforcing ribs 123 provided in the vicinity of the opening portion O of the heater holder 130.
To be noted, as a substitute means for reducing the creep deformation by improving the flexural rigidity of the heater holder 130, increasing the thickness of the portion of the heater holder 130 where the heater seating surface S1 and the stay contact surface S3 are provided can be also considered. However, according to this configuration, the heat capacity of the heater holder 130 increases, and thus the activation time of the fixing apparatus 100 becomes longer. In contrast, by using the reinforcing ribs 123 as in the present embodiment, the flexural rigidity of the heater holder 130 can be improved while suppressing the increase in the heat capacity of the heater holder 130. That is, according to the configuration of the present embodiment, the creep deformation of the heater holder 130 can be reduced while reducing the influence on the activation time of the fixing apparatus 100.
A second embodiment of the present disclosure will be described below. As a result of checking an image on a paper sheet of the LTR size after performing the sheet passing test on a paper sheet of an A4 size by using the image forming apparatus 50 including the fixing apparatus 100 of the first embodiment, a slight fixation failure was observed at left and right end portions of the image in some cases. The present embodiment enables further reducing the occurrence of a fixation failure like this.
In the present embodiment, more reinforcing ribs 123 are added to the heater holder 130 used in the first embodiment. The other elements are substantially the same as in the first embodiment. In the description below, elements denoted by the same reference signs as in the first embodiment are assumed to have substantially the same configurations and effects as in the first embodiment, and parts different from the first embodiment will be mainly described.
Reinforcing rib 123 of the heater holder 130 according to the present embodiment will be described with reference to
In the present embodiment, the reinforcing ribs 123 are added to respective positions at 107.5 mm from a position serving as a standard for a center position in the longitudinal direction B of the recording material passing the fixing nip Nf on both sides in the longitudinal direction B. The position serving as the standard for the center position of the recording material will be hereinafter referred to as a conveyance center of the recording material. These positions are set in consideration of the fact that, from the conveyance center of the recording material in the longitudinal direction B, the distance to end portion positions of the paper sheet of the A4 size is 105 mm, and the distance to end portion positions of the heat-generating resistor on the heater 113 is 110 mm.
The reinforcing ribs 123 added in the present embodiment are formed to interconnect the upstream guide 126 and the downstream guide 127 on the heater holder 130 similarly to the reinforcing ribs 123 described in the first embodiment. In the present embodiment, the height Hr of the reinforcing ribs 123 in the orthogonal direction C is set to 1.5 mm, and the width Wr is set to 2.0 mm.
In addition, in accordance with the addition of the reinforcing ribs 123, cutout portions for accepting the reinforcing ribs 123 are added to the pressurizing stay 119. The height of the cutout portions provided in the pressurizing stay 119 in the recording material conveyance direction A is set to 2.0 mm, and the width thereof in the longitudinal direction B is set to 2.5 mm such that the reinforcing ribs 123 do not contact the pressurizing stay 119.
The fixing apparatus 100 and the image forming apparatus 50 of the present embodiment are capable of performing image formation on at most a paper sheet of the LTR size, which has a width in the longitudinal direction B of 216 mm, similarly to the first embodiment. That is, the paper sheet of the LTR size is a paper sheet of the maximum passable size in the present embodiment. In accordance with this, the width in the longitudinal direction B of the heat-generating resistor on the heater 113 is set to include an effective image region in which an image can be formed on the paper sheet of the maximum passable size.
Here, in the case of performing image formation on a recording material having a smaller width in the longitudinal direction B than the paper sheet of the maximum passable size, that is, in the case of a paper sheet of a small size, there is a region in the fixing nip Nf that the recording material does not pass through and that is heated by the heat-generating resistor. This region will be hereinafter referred to as a non-sheet passing region. Therefore, in the case of successively performing image formation on paper sheets of a small size such as the A4 size, there is a possibility that the surface temperature of the fixing film 112 and the pressurizing roller 110 in the non-sheet passing region becomes higher than in a sheet passing region that the paper sheets of the small size pass through. This is because in the non-sheet passing region, heat is not transmitted to the recording material in the fixing nip Nf, and thus the heat generated by the heat-generating resistor is gradually accumulated. This phenomenon is called “temperature rise in a non-sheet passing portion”.
As a result of the temperature rise in the non-sheet passing portion, in the case of successively performing image formation on paper sheets of a small size, the heater holder 130 has a thermal peak in the non-sheet passing region, that is, in a region that is outside the sheet passing region and in a heat-generating region of the heater 113. That is, if the state in which the temperature of heater holder 130 in the non-sheet passing region is higher than in the sheet passing region due to the temperature rise in the non-sheet passing portion continues, there is a possibility that the creep deformation of the heater holder 130 occurs in the non-sheet passing region.
Reduction of the creep deformation of the heater holder 130 in the non-sheet passing region according to the present embodiment will be described. In the present embodiment, since the reinforcing ribs 123 are disposed in the non-sheet passing region of the heater holder 130, the flexural rigidity of the heater holder 130 in the non-sheet passing region is improved. Therefore, in the non-sheet passing region, the creep deformation of the heater holder 130 is not likely to occur even in the case where the forces F1 and F2 and the heat from the temperature rise in the non-sheet passing portion simultaneously act on the heater holder 130 as illustrated in
As a result of a sheet passing test in which an image is formed on a paper sheet of the A4 size by using the image forming apparatus 50 including the fixing apparatus 100 of the present embodiment, damage to the heater holder 130 and wrinkling of the recording material did not occur. In addition, also in the case of conducting the endurance test, abnormal images such as fixation failures did not occur, and a state in which fixed images that were uniform throughout the entire region in the longitudinal direction B could be obtained was maintained for a long period.
Further, as a result of conducting the sheet passing test of the paper sheet of the LTR size after the endurance test using the paper sheets of the A4 size, the fixation failure neither occurred. This can be considered to be because the reinforcing ribs 123 added in the present embodiment reduced the creep deformation of the heater holder 130 in the non-sheet passing region.
To be noted, although a configuration in which the reinforcing ribs 123 are disposed in the non-sheet passing region in addition to the reinforcing ribs 123 described in the first embodiment has been described as an example in the present embodiment, a configuration in which only the reinforcing ribs 123 in the non-sheet passing region described in the first embodiment are provided may be employed.
In the first and second embodiments, the reinforcing ribs 123 are provided to project from the stay contact surface S3 that is flat and provided between the upstream guide 126 and the downstream guide 127 in the recording material conveyance direction A. The configuration is not limited to this, and the reinforcing ribs 123 may be provided also in the case where the surface opposite to the heater seating surface S1 serving as a first surface of the heater holder 130 has recesses and projections as viewed in the longitudinal direction B. For example, as illustrated in
In addition, as illustrated in
As another modification example, as illustrated in
The reinforcing ribs 123 illustrated in
In addition, in the first and second embodiments, the reinforcing ribs 123 disposed in the vicinity of the opening portion O of the heater holder 130 in the longitudinal direction B or in the non-sheet passing region at end portions of the heater holder 130 in the longitudinal direction B have been described above as an example. The arrangement of the reinforcing ribs 123 is not limited to this. For example, a plurality of reinforcing ribs 123 may be disposed at predetermined intervals in the longitudinal direction B. In addition, it suffices as long as at least one reinforcing rib 123 is provided. In any of the modification examples, the flexural rigidity of the heater holder 130 is improved by the reinforcing ribs 123, and therefore the creep deformation of the heater holder 130 can be reduced.
In the first and second embodiments described above, a configuration in which a ceramic heater in which a heat-generating resistor is formed on a ceramic substrate is used as the heating portion, that is, the heater of the fixing apparatus, and the fixing film 112 is heated by non-radiant heat of the ceramic heater has been described as an example. The configuration is not limited to this, and a configuration in which a halogen lamp is used as the heater may be employed. That is, a configuration in which a halogen lamp disposed in an inner space of a first rotary member and a sliding member serving as a nip forming portion that is in contact with the inner surface of the first rotary member and receives radiant heat from the halogen lamp to heat the first rotary member are provided as a nip forming unit may be employed. Also in this case, the creep deformation can be reduced by providing a rib portion, that is, a reinforcing rib on a holder member holding the nip forming unit.
In addition, although a configuration in which a film is used as the first rotary member and a roller is used as the second rotary member has been described in the first and second embodiments described above, the combination of the first rotary member and the second rotary member is not limited to this. For example, a roller member may be used as the first rotary member.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2021-159605, filed on Sep. 29, 2021, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-159605 | Sep 2021 | JP | national |
