Patent Application
20250208548
This patent application is based on and claims priority pursuant to 35 U.S.C. § 119 (a) to Japanese Patent Application No. 2023-217577, filed on Dec. 25, 2023, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
Embodiments of the present disclosure relate to a fixing device and an image forming apparatus incorporating the fixing device.
An electrophotographic image forming apparatus such as a copier or a printer includes a fixing device to fix a toner image onto a recording medium such as a sheet. Various types of fixing devices are used, and a sliding belt type is known as a typical type.
This specification describes an improved fixing device that includes a fixing rotator, a heat conductor, a pressure rotator, a heater, a pressure-receiving portion, and a heat insulator. The heat conductor contacts an inner circumferential surface of the fixing rotator to uniform temperature distribution in a rotation axis direction of the fixing rotator. The pressure rotator presses the fixing rotator against the heat conductor to form a nip and presses a recording medium passing through the nip. The heater is disposed inside a loop of the fixing rotator. The pressure-receiving portion contacts the heat conductor to receive pressure from the pressure rotator via the fixing rotator. The heat insulator is between the pressure-receiving portion and the heat conductor and includes a sheet-shaped silica aerogel.
This specification also describes an image forming apparatus that includes the fixing device.
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:
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.
Referring to the drawings, embodiments of the present disclosure are described below. Like reference signs are assigned to identical or equivalent components and a description of those components may be simplified or omitted.
The image forming apparatus 1 includes an image forming section 100 to form an image on a sheet P as a recording medium. The image forming apparatus 1 is a tandem-type image forming apparatus. The image forming section 100 includes image forming devices 10Y, 10M, 10C, and 10K for respective colors of yellow (Y), magenta (M), cyan (C), and black (K), an intermediate transfer belt 20 as an intermediate transferor, and an optical writing device 9 as an electrostatic-latent-image forming device. The image forming devices 10Y, 10M, 10C, and 10K are arranged along a rotation direction of the intermediate transfer belt 20 on the intermediate transfer belt 20. The image forming devices 10Y, 10M, 10C, and 10K include photoconductors 11Y, 11M, 11C, and 11K as latent image bearers, respectively.
Each of the image forming devices 10Y, 10M, 10C, and 10K includes a charging device as a charger and a developing device around each of the photoconductors 11Y, 11M, 11C, and 11K. In addition, each of the image forming devices 10Y, 10M, 10C, and 10K includes a primary transfer device as a primary transferor and a cleaning device as a cleaner around each of the photoconductors 11Y, 11M, 11C, and 11K.
The charging device uniformly charges the surface of the photoconductor to a predetermined potential. The optical writing device 9 irradiates the surface of the photoconductor uniformly charged by the charging device with light based on image data to form an electrostatic latent image. The developing devices develop the electrostatic latent images on the photoconductors to form toner images of toners of respective colors (yellow, magenta, cyan, and black), respectively, which is referred to as a developing process. The primary transfer device transfers the toner image on the photoconductor onto the intermediate transfer belt 20. The cleaning device removes residual toner that is not transferred onto the intermediate transfer belt and remains on the photoconductor to clean the surface of the photoconductor.
The respective color toner images formed on the photoconductors 11Y, 11M, 11C, and 11K are primarily transferred to the intermediate transfer belt 20 by the primary transfer devices to overlap each other, thereby forming a full-color toner image on the intermediate transfer belt 20. The full-color toner image on the intermediate transfer belt 20 is conveyed to a region (secondary transfer region) opposite a secondary transfer device 30 as the intermediate transfer belt 20 rotates.
The image forming apparatus includes a sheet tray 60 below the image forming section 100. The sheet tray 60 holds sheets P and serves as a feeding section for feeding the sheet P. A pickup roller 61 feeds the sheets P one by one from the sheet tray 60 to a conveyance path. A registration roller pair 62 conveys the sheet P to the secondary transfer region along the conveyance path.
The registration roller pair 62 conveys the sheet P to the secondary transfer region at a specified timing at which the full-color toner image on the intermediate transfer belt 20 reaches the secondary transfer region, and the secondary transfer device 30 secondarily transfers the full-color toner image from the intermediate transfer belt 20 onto the sheet P. The sheet P on which the full-color toner image is formed is then conveyed to a fixing device 40, and the fixing device 40 applies heat and pressure to the sheet P to fix the full-color toner image onto the sheet P. After the full-color toner image is fixed onto the sheet P, the sheet Pis conveyed along the conveyance path, and an output roller pair 63 ejects the sheet P to an output tray 50.
The fixing device 40 includes a stay 44 and a nip formation pad 45 held by the stay 44 that are disposed inside the loop of the fixing belt 42. The nip formation pad 45 sandwiches the fixing belt 42 together with the pressure roller 41 to form a nip.
The nip formation pad 45 includes a heat conductor 45a and a resin-pad 45b. The heat conductor 45a faces a nip face and serves as a heat transferor and a slide. The resin-pad 45b supports the heat conductor 45a. One of the functions of the resin-pad 45b is thermal insulation to reduce heat transferred from the fixing belt 42 to the stay 44 via the nip formation pad 45 and prevent warm-up time and a Typical Electricity Consumption (TEC) value from increasing.
The heat conductor 45a has, for example, a pad shape extending in a width direction of the fixing belt 42. The heat conductor 45a is disposed to equalize temperature distribution in the fixing belt 42 in a rotation axis direction of the fixing belt 42. The heat conductor 45a transfers heat from a high-temperature portion of the fixing belt 42 to a low-temperature portion of the fixing belt 42 to equalize the temperature distribution in the fixing belt 42 in the rotation axis direction.
In
The heat conductor 45a is made of metal such as aluminum or copper and has a high thermal conductivity of 50 [W/m·K] or more, and the surface of the heat conductor 45a is coated with a coating having an excellent sliding property. Examples of the material for the coating include resin-based materials such as polyimide resin, fluororesin, polyphenylene sulfide resin, and saturated polyester resin. The above-described resin-based coating material may be mixed with glass fiber, carbon, graphite, graphite fluoride, carbon fiber, molybdenum disulfide, and fluororesin.
Alternatively, metal-based coating material may be used. Examples of the metal-based coating materials include molybdenum disulfide, nickel, and composite plating of nickel and fluorine resin. In addition, the metal-based coating material may be anodized aluminum or anodized aluminum impregnated with resin or metal. Ceramics may also be used as the coating material. Examples of the ceramic used as the coating material include silicon carbide ceramic, silicon nitride ceramic, alumina ceramic, and mixtures thereof with molybdenum disulfide or fluorine resin.
Alternatively, forming an anodized aluminum layer on the surface layer of the heat conductor 45a made of aluminum or aluminum alloys and filling the fine pores of the anodized aluminum layer with molybdenum disulfide generated by secondary electrolysis from the deepest portions of the fine pores to the outermost surface layer forms the excellent coating.
The heat conductor 45a having a high thermal conductivity in the present embodiment is made of a material having a thermal conductivity equal to or higher than the thermal conductivity of aluminum and is processed as described above. Thus, the heat conductor 45a having a high thermal conductivity is produced.
The pressure roller 41 is in contact with the outer circumferential surface of the fixing belt 42 to form the nip and applies pressure to the recording medium passing through the nip. The pressure roller 41 includes a metal roller, a silicone rubber layer on the outer in circumferential face of the metal roller, and a release layer on the outer circumferential face of the silicone layer. The release layer is made of perfluoroalkoxy alkane (PFA) or polytetrafluoroethylene (PTFE) to obtain releasability. A spring presses the pressure roller 41 against the fixing belt 42 to deform the silicone rubber layer. As a result, the nip has a predetermined nip width.
A driver such as a motor is disposed in the image forming apparatus 1 and transmits driving force to the pressure roller 41 through gears to rotate the pressure roller 41. The pressure roller 41 transmits the driving force to the fixing belt 42 at the nip to rotate the fixing belt 42.
The pressure roller 41 may be a solid roller but is preferably hollow because the hollow roller has a small thermal capacity. The pressure roller 41 may include a heater such as the halogen heater. The silicone rubber layer of the pressure roller 41 may be made of solid rubber. Alternatively, if no heater is situated inside the pressure roller 41, the silicone rubber layer of the pressure roller 41 may be made of sponge rubber. The sponge rubber enhances the thermal insulation of the pressure roller 41, preferably causing the pressure roller 41 to draw less heat from the fixing belt 42.
The fixing belt 42 is an endless belt or film and includes a base layer made of metal such as nickel or steel use stainless (SUS) or resin such as polyimide. The surface layer of the fixing belt 42 has a release layer. The release layer is made of PFA or PTFE to facilitate the separation of toner of the toner image on the sheet P from the fixing belt 42, thus preventing the toner of the toner image from adhering to the fixing belt 42.
An elastic layer made of, e.g., silicone rubber may be interposed between the base layer and the release layer in the fixing belt 42. Omitting the elastic layer made of silicone rubber reduces thermal capacity and enhances a fixing performance. However, the slight surface roughness of the fixing belt 42 may be transferred onto the toner image while the toner image is pressed and fixed onto the recording medium, causing an orange-peel image, which is an image having uneven gloss in a solid part of the image. To prevent the uneven gloss or the orange peel image, the elastic layer made of silicone rubber has a thickness of 100 μm or more. Deformation of the elastic layer made of silicone rubber absorbs the slight surface roughness of the fixing belt 42, preventing the formation of the orange-peel image.
The stay 44 has a hollow pipe-shaped metal body made of metal such as aluminum, iron, or stainless steel. In the present embodiment, a cross-sectional shape of the stay 44 has right angles but may have another cross-sectional shape. The stay 44 prevents bending of the nip formation pad 45 that receives pressure from the pressure roller 41 and uniformly forms the nip width in the axial direction of the pressure roller 41.
Two heaters 43 are disposed inside the loop of the fixing belt 42 to raise the temperature of the fixing belt 42. The heaters 43 in the present embodiment are halogen heaters and directly heat the inner circumferential surface of the fixing belt 42 with radiant heat. As long as the heater 43 can heat the fixing belt 42, the heater 43 may be one of various types of heaters such as a heater including an induction heating (IH) coil, a resistive heat generator, or a carbon heater.
The fixing device 40 includes a reflector 48 inside the loop of the fixing belt 42. The reflector 48 reflects the radiant heat from the heater 43 to the fixing belt 42 to reduce the loss of the radiant heat. The reflector 48 is made of a high-luminance aluminum, which includes a base made of a high-purity aluminum material as a metal member to obtain a high reflectance, for example, a reflectivity of 95% or more. The base has a surface layer including a plurality of reflection-enhancing films and protective films. Depending on the configuration, silver may be deposited on an aluminum plate by vapor deposition to further increase the reflectance.
The reflectance of the reflector 48 in the present embodiment is measured using the spectrophotometer that is the ultraviolet visible infrared spectrophotometer UH4150 manufactured by Hitachi High-Technologies Corporation in which the incident angle is set to 5°.
The reflector 48 according to the present embodiment includes a reflecting portion 48a and a pressure-receiving portion 48b. The reflecting portion 48a reflects the radiant heat toward the inner circumferential surface of the fixing belt 42. The pressure-receiving portion 48b receives the pressure from the pressure roller 41. The reflecting portion 48a is disposed between the heater 43 and the stay 44. The pressure-receiving portion 48b is interposed between the heat conductor 45a as the slide and the resin-pad 45b.
The reflector 48 includes the pressure-receiving portion 48b extending to a region between the heat conductor 45a and the resin-pad 45b, and the region receives the pressure from the pressure roller 41. The reflector 48 made of metal having good thermal conductivity such as aluminum quickly transfers heat absorbed in the reflecting portion 48a to the entire reflector 48. In other words, the reflecting portion 48a is connected to the pressure-receiving portion 48b to transfer heat from the reflecting portion 48a to the pressure-receiving portion 48b.
The heat transferred to the pressure-receiving portion 48b transfers to the heat conductor 45a in contact with the pressure-receiving portion 48b, and as a result, the temperature rise of the reflector 48 can be reduced. The heat transferred to the heat conductor 45a is subsequently transferred to the fixing belt 42 and used for melting the toner.
The above-described configuration can more effectively use the heat of the reflector 48 than a configuration in which another member such as the stay 44 dissipates the heat of the reflector 48. As a result, the above-described configuration can shorten a lighting time of the heater 43 and reduce power consumption.
The pressure-receiving portion 48b is located in a pressure region that receives the pressure from the pressure roller 41. The pressure causes the heat conductor 45a to be in close contact with the pressure-receiving portion 48b to enhance heat transfer performance. As a result, the pressure-receiving portion 48b can effectively dissipate the heat of the reflector 48. In addition, the heat conductor 45a and the reflector 48 made of metal having good thermal conductivity can effectively dissipate the heat of the reflector 48 to the fixing belt 42.
As illustrated in
The above-described structure enables the fixing device to prevent the temperature increase in the reflector 48, effectively using the heat of the reflector 48 to melt the toner and achieve energy saving.
Since the heat conductor 45a is coated with the above-described coating having the excellent sliding property, the friction coefficient of the heat conductor 45a with respect to the inner circumferential surface of the fixing belt 42 is smaller than the friction coefficient of the surface of the pressure-receiving portion 48b with respect to the inner circumferential face of the fixing belt 42.
Thus, the sliding resistance of the fixing belt 42 can be reduced as compared with a case in which the pressure-receiving portion 48b of the reflector 48 is brought into contact with the inner circumferential face of the fixing belt 42 to dissipate the heat of the reflector 48 to the fixing belt 42 without passing through the heat conductor 45a. The above-described structure prevents an increase in torque for rotating the fixing belt 42 and abrasion of the inner circumferential face of the fixing belt 42.
If the pressure-receiving portion 48b of the reflector 48 is coated with the coating having the excellent sliding property to be in contact with the inner circumferential surface of the fixing belt 42, the following disadvantage may be expected. If the coating material having the excellent sliding property adheres to the reflecting portion 48a of the reflector 48, the reflectance of the reflecting portion 48a may decrease.
To avoid adhesion of the coating material having the excellent sliding property to the reflecting portion 48a, for example, it is necessary to apply masking to the reflecting portion 48a. Applying the masking to the reflecting portion 48a needs processes such as a process to apply the masking, a process to remove the masking, and a process to remove an adhesive for masking adhered to the reflecting portion 48a. It is very difficult for a machine to perform these processes. If the machine that performs these processes can be made, the machine will be expensive.
In contrast, transmitting the heat of the reflector 48 to the fixing belt 42 via the heat conductor 45a as described in the present embodiment does not need the excellent slidability of the reflector 48 with respect to the inner circumferential surface of the fixing belt 42. Accordingly, it is not necessary to apply the coating having the excellent sliding property to the pressure-receiving portion 48b, which prevents manufacturing difficulty and an increase in cost.
The heat conductor 45a is disposed between the pressure-receiving portion 48b of the reflector 48 and the fixing belt 42. However, a member disposed between the pressure-receiving portion 48b and the fixing belt 42 may be a member having a better sliding property with respect to the inner circumferential surface of the fixing belt 42 than the pressure-receiving portion 48b.
For example, although a property to dissipate the heat to the fixing belt 42 is inferior to a property of the heat conductor 45a, a sliding sheet as the sliding member may be disposed between the pressure-receiving portion 48b and the fixing belt 42. The sliding sheet is made of fibers such as PTFE impregnated with a lubricant such as silicone oil. The sliding sheet is, for example, disposed so as to be wound around the resin-pad 45b and fixed by a screw on a back side of the resin-pad 45b, the back side facing the stay 44.
A description is given below of a characteristic configuration according to the present embodiment of the present disclosure.
The reflector 48 contacting the heat conductor 45a as described above reduces the temperature rise in the non-sheet passing region when small sheets pass through the fixing device, which enhances the productivity, and utilizing the heat of the reflector 48 enables achieving energy saving. However, on the other hand, the reflector 48 contacting the heat conductor 45a causes a disadvantage that the heat of the fixing belt 42 escapes to the heat conductor 45a and the reflector 48 when temperatures of the reflector 48 and the heat conductor 45a are low, for example, during warming-up.
To countermeasure the disadvantage, the fixing device in the present embodiment includes a heat insulator that is a sheet (or a thin plate) containing silica aerogel between the reflector 48 and the heat conductor 45a.
The fixing device 40 illustrated in
The heat insulator 49 blocks the heat transfer from the fixing belt 42 to the pressure-receiving portion 48b of the reflector 48 through the heat conductor 45a, preventing the temperature rise of the fixing belt 42 from being delayed.
The following describes the silica aerogel. Liquid crystal polymer has a thermal conductivity of 0.4 [W/m·K] and is used as a known material of heat insulator. However, even if the liquid crystal polymer is disposed between the heat conductor 45a and the pressure-receiving portion 48b, an amount of heat transferring from the heat conductor 45a to the pressure-receiving portion 48b is still large, and as a result, setting the liquid crystal polymer in the fixing device cannot sufficiently shorten the time that the temperature of the fixing belt 42 reaches the target temperature.
On the other hand, the silica aerogel has a thermal conductivity of 0.012 to 0.027 [W/m·K]. The silica aerogel has a high porosity and a low density that is typically about 0.06 to 0.2 [g/cm3]. The ratio of a solid portion in the silica aerogel is small, and therefore, the conductive heat transfer through the silica skeleton is small. The mean pore diameter of the silica aerogel is about several ten nanometers that is below the mean free path of the main gas molecules in the air at around room temperature and atmospheric pressure, which prevents the convective heat transfer of the air.
Using the heat insulator having the thin plate shape and synthesized from the silica aerogel and fibers (or cellulose) enables sufficiently blocking heat escaping from the fixing belt 42 to the reflector 48 via the heat conductor 45a and, as a result, accelerating the temperature rise of the fixing belt 42.
The fiber of the heat insulator is preferably a heat-resistant material such as polyphenylene sulfide (PPS) or aramid. The heat insulator may be a rigid body.
A description is given below of an advantageous configuration of the heat insulator.
The larger the thickness of the heat insulator 49, the smaller the amount of heat transferring (escaping) from the fixing belt 42 to the heat conductor 45a and the pressure-receiving portion 48b that contacts the heat conductor 45a. As a result, the temperature rise of the fixing belt 42 is accelerated. However, on the other hand, increasing the thickness of the heat insulator 49 reduces the heat equalizing effect of the heat conductor 45a and the pressure-receiving portion 48b, and therefore, the productivity of printing small recording media is reduced.
In addition, increasing the thickness of the heat insulator 49 reduces an amount of heat transferring from the reflector 48 to the fixing belt 42 via the heat conductor 45a in the above-described configuration, which reduces the energy saving performance. The temperature rise property and the productivity and energy saving property with respect to the thickness of the heat insulator 49 are in a trade-off relationship.
The thickness of the heat insulator 49 is preferably in a range of 0.1 mm to 1.0 mm so that the temperature rise property, the productivity, and the energy saving property are suitable values for products.
The thickness of the heat insulator 49 may be adjusted to provide a superior temperature rise property (or a superior productivity and energy saving property) depending on the use of the product.
The embodiments of the present disclosure have been described in detail above. The above-described embodiments are examples and can be modified within the scope not departing from the gist of the present disclosure. For example, any embodiment and any modification may be combined.
The effects obtained by the above-described embodiment are examples. The effects according to the present disclosure are not limited to the above-described effects.
Aspects of the present disclosure are, for example, as follows.
In a first aspect, a fixing device includes a fixing rotator, a heat conductor, a pressure rotator, a heater, a pressure-receiving portion, and a heat insulator. The heat conductor contacts an inner circumferential surface of the fixing rotator to uniform temperature distribution in a rotation axis direction of the fixing rotator. The pressure rotator presses the fixing rotator against the heat conductor to form a nip and presses a recording medium passing through the nip. The heater is disposed inside a loop of the fixing rotator. The pressure-receiving portion contacts the heat conductor to receive pressure from the pressure rotator via the fixing rotator. The heat insulator is between the pressure-receiving portion and the heat conductor and includes a sheet-shaped silica aerogel.
In a second aspect, the fixing device according to the first aspect further includes a reflector including a reflecting portion to reflect radiant heat radiated by the heater toward an inner circumferential surface of the fixing rotator, and the pressure-receiving portion connected to the reflecting portion to transfer heat from the reflecting portion to the pressure-receiving portion.
In a third aspect, a thermal conductivity of the heat insulator in the fixing device according to the first aspect or the second aspect is in a range from 0.012 to 0.027 W/m·K.
In a forth aspect, a thickness of the heat insulator in the fixing device according to any one of the first to third aspects is in a range from 0.1 to 1.0 mm.
In a fifth aspect, an image forming apparatus includes the fixing device according to any one of the first to fourth aspects.
In a sixth aspect, the sheet-shaped silica aerogel in the fixing device according to any one of the first to fourth aspects includes a sheet synthesized from silica aerogel and fibers.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-217577 | Dec 2023 | JP | national |
