JP2012082037A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a cooling effect of a toner image for a long period of time.SOLUTION: An image forming apparatus includes: an image forming unit for forming the toner image on a sheet; a fixing unit for heating and fixing the toner image on the sheet; and a conveying roller pair for holding the sheet passing the fixing unit, and for cooling the sheet while being conveyed. In the apparatus, at least one cooling roller 31 of the conveying roller pair is cylindrically formed while being extended in the width direction perpendicular to the sheet conveying direction, and a phase change material 33 which reacts endothermically when changing from solid into liquid is encapsulated. A paper passing area 31A for conveying the sheet is cylindrically formed, and an inside radius R of a cylindrical portion of non-sheet passing area 31b not conveying the sheet is set larger than an inside radius r of the sheet passing area (R>r).

Description

  The present invention relates to an image forming apparatus that forms a toner image on a sheet using an electrophotographic system.

  Image forming apparatuses such as copiers, printers, fax machines, and multi-function machines having a plurality of these functions that form a toner image on a sheet (recording material) are generally provided with a fixing device that fixes the toner image on the sheet. Yes. The fixing device heats the sheet and fixes the toner image on the sheet. The toner temperature when the fixing device fixes the toner image on the sheet is about 170 ° C., although it varies depending on the type of toner, and the surface temperature of the sheet immediately after fixing the toner image is about 100 ° C. Therefore, the toner of the toner image fixed on the sheet immediately after fixing is in an adhesive state without being solidified.

  As described above, when a subsequent sheet is discharged on a sheet discharged in a state where the toner is not solidified, the sheets may stick to each other with the toner, and the sheet may not be peeled off. Even if the toner image can be removed, the toner image may be scratched and the quality of the toner image may be lowered. Such a phenomenon becomes more prominent as the image forming speed of the image forming apparatus increases.

  Patent document 1 and patent document 2 describe image forming apparatuses that deal with such problems. The former image forming apparatus is provided with a cooling roller pair that cools the sheet by fixing the toner image downstream of the fixing unit, and the cooling roller pair is cooled by a fan to cool the toner of the toner image. It has become. In the latter image forming apparatus, a rotatable heat pipe pair is provided downstream of the fixing device, and the sheet is conveyed by the heat pipe, thereby absorbing heat from the sheet and absorbing the absorbed heat at the end of the heat pipe pair. Heat is dissipated by the provided fins.

JP-A-6-75490 JP-A-10-207155

  However, since the image forming apparatus described in Patent Document 1 uses a fan to cool the cooling roller, electric power for rotating the fan is required, and the rotation sound of the fan causes noise. Etc. are provided.

  Further, in the image forming apparatus described in Patent Document 2, when the temperature inside the image forming apparatus becomes high due to continuous operation or a temperature rise around the place where the image forming apparatus is installed, the heat dissipation efficiency due to the fins at the end portion decreases. As a result, the temperature of the heat pipe may increase. In such a case, there exists a subject that the cooling effect by a heat pipe pair falls. Therefore, if the fins are cooled by a fan, the image forming apparatus described in Patent Document 2 is required to have electric power for rotating the fan, and the rotation noise of the fan causes noise. The same problem as that of the image forming apparatus disclosed in Patent Document 1 occurs.

  In addition, the image forming apparatuses of both patent documents also have a problem that requires a space such as a fan or a heat radiating fin.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can maintain a cooling effect for lowering the toner temperature of a toner image on a sheet that has passed through a fixing device for a long period of time by a pair of conveying rollers in which a heat absorbing material is enclosed.

  The image forming apparatus of the present invention includes an image forming unit that forms a toner image on a sheet, and a fixing device that heat-fixes the toner image on the sheet, and further sandwiches and conveys the sheet that has passed through the fixing device. A pair of conveying rollers for cooling, and at least one roller of the pair of conveying rollers is formed in a cylindrical shape extending in the width direction orthogonal to the sheet conveying direction and absorbs heat when changing from solid to liquid. The material is enclosed, the portion for conveying the sheet is formed in a cylindrical shape, and the inner method of the cylindrical portion outside the width direction of the portion for conveying the sheet is set larger than the inner diameter of the cylindrical portion. It is characterized by that.

  In the image forming apparatus of the present invention, the inner method of the portion that does not contact the sheet is set larger than the inner diameter of the portion that contacts the sheet of the conveying roller pair, and even if air enters the conveying roller pair, Air accumulates inside the portion that does not contact the sheet.

  For this reason, in the image forming apparatus of the present invention, the endothermic material is always in contact with the portion of the conveyance roller pair that contacts the sheet, and the sheet on which the toner image is fixed by the fixing device is quickly cooled, The toner can be solidified. In addition, in the image forming apparatus, since the endothermic material is always in contact with the sheet contact portion of the conveying roller pair, the sheet can be cooled for a long period of time, and the cooling effect can be maintained for a long period of time.

  Further, the image forming apparatus of the present invention does not use a fan or a heat radiating fin unlike the conventional one, so that no electric power is required, no noise is generated, and no installation space for the fan or the heat radiating fin is required. The effect of.

FIG. 3 is a cross-sectional view of the image forming apparatus according to the embodiment of the present invention along the sheet conveyance direction. It is an external appearance perspective view of a roller cooling device. It is sectional drawing of a cooling roller. (A) is sectional drawing along an axial direction. (B) is AA arrow sectional drawing of FIG. 3 (A). It is a temperature change graph of a phase change material. It is a temperature change graph of a cooling roller. It is sectional drawing of a cooling roller. It is sectional drawing of the other cooling roller corresponded in the shape shown to FIG. 3 (B). It is sectional drawing of a cooling roller at the time of making it an air gap generate | occur | produce at both ends.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of the image forming apparatus according to the embodiment of the present invention along the sheet conveying direction.

  An image forming apparatus will be schematically described. The image forming apparatus 20 is a four-color image forming apparatus, and includes yellow, magenta, cyan, and black primary forming portions Pa, Pb, Pc, and Pd. Each of the primary forming portions Pa, Pb, Pc, and Pd forms toner images of different colors on a sheet through a latent image, development, and transfer process. The primary forming portions Pa, Pb, Pc, and Pd are respectively provided with dedicated image carriers, in this example, electrophotographic photosensitive drums 3a, 3b, 3c, and 3d, and each of the photosensitive drums 3a, 3b, 3c, and 3d includes A toner image of each color is formed. An intermediate transfer member 130 is installed adjacent to each photosensitive drum 3a, 3b, 3c, 3d. The intermediate transfer member 130 is a belt that is guided and circulated by the rollers 13, 14, and 16. The toner images of the respective colors formed on the photosensitive drums 3 a, 3 b, 3 c, 3 d are primarily transferred to the intermediate transfer body 130 and transferred to the sheet (recording material) P by the secondary transfer roller 11. Further, the sheet P on which the toner image is transferred is heated and pressurized by the fixing device 9 to fix the toner image. Finally, the sheet is discharged out of the apparatus.

  The image forming apparatus will be described in detail.

  Drum chargers 2a, 2b, 2c, and 2d, developing devices 1a, 1b, 1c, and 1d, primary transfer chargers 24a, 24b, 24c, and 24d, and a cleaner 4a are disposed on the outer periphery of the photosensitive drums 3a, 3b, 3c, and 3d, respectively. , 4b, 4c, 4d are provided. A light source device and a polygon mirror (not shown) are further installed in the upper part of the device.

  The laser light emitted from the light source device becomes scanning light by the rotating polygon mirror, the light beam is deflected by the reflection mirror, and is condensed on the buses of the photosensitive drums 3a, 3b, 3c, and 3d by the fθ lens, and the photosensitive drum. To expose. A latent image corresponding to an image signal is formed on the exposed photosensitive drums 3a, 3b, 3c, and 3d.

  The developing devices 1a, 1b, 1c, and 1d are filled with predetermined amounts of yellow, magenta, cyan, and black toners as developers, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images formed on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images, and black toner images. .

  The intermediate transfer member 130 circulates in the direction of the arrow at the same peripheral speed as the photosensitive drum 3. The first color yellow toner image formed and supported on the photosensitive drum 3 a passes through the nip between the photosensitive drum 3 and the intermediate transfer body 130, and the electric field formed by the primary transfer bias applied to the intermediate transfer body 130. And the pressure are transferred to the intermediate transfer body 130. Similarly, the second color magenta toner image, the third color cyan toner image, and the fourth color black toner image are sequentially superimposed and transferred onto the intermediate transfer body 130 to correspond to the target color image. A toner image is formed.

  The secondary transfer roller 11 is supported in parallel with the intermediate transfer member 130 and is disposed in contact with the outer peripheral surface of the intermediate transfer member 130. A desired secondary transfer bias is applied to the secondary transfer roller 11 by a secondary transfer bias source.

  On the other hand, the sheet P passes through the registration roller 12 and the pre-transfer guide from the paper feed cassette 10 and is fed to the nip between the intermediate transfer body 130 and the secondary transfer roller 11 at a predetermined timing, and at the same time, the secondary transfer bias. Is applied from a bias power source. By this secondary transfer bias, the composite color toner image superimposed and transferred onto the outer peripheral surface of the intermediate transfer member 130 is transferred from the intermediate transfer member 130 to the sheet P.

  In addition, the photosensitive drums 3a, 3b, 3c, and 3d after the primary transfer have been completed, the transfer residual toner adhering to the photosensitive drum is removed by the respective cleaners 4a, 4b, 4c, and 4d, and the next latent image is continuously formed. Provided. The intermediate transfer member 130 is also prepared for the next transfer by wiping off the toner and other foreign matters remaining on the intermediate transfer member 130 with a cleaning web (nonwoven fabric) 19 in contact with the surface of the intermediate transfer member 130.

  The sheet P that has received the transfer of the toner image is conveyed to a fixing device 9 that heats and fixes the toner image on the sheet, and is heated to fix the toner image, and is then conveyed while being cooled by the roller cooling device 30. It is discharged outside the image forming apparatus 20.

  The primary forming portions Pa, Pb, Pc, Pd, the intermediate transfer member 130, the secondary transfer roller 11, and the like constitute an image forming portion 15 that forms a toner image on a sheet.

  The above image forming apparatus has been described by taking an example of a so-called tandem type image forming apparatus, but is not limited to such an image forming apparatus. For example, an image forming apparatus having a rotary developing device may be used. Of course, the image forming apparatus is not limited to a color image forming apparatus, and may be a monochrome image forming apparatus.

(Roller cooling device)
Next, the roller cooling device 30 will be described. In addition, a numerical value is a reference numerical value, Comprising: It is not a numerical value which limits this invention.

  FIG. 2 is an external perspective view of the roller cooling device 30. The roller cooling device 30 includes a conveyance roller pair 35 including a cooling roller 31 and a pressure roller 32. The conveyance roller pair 35 cools the sheet that has passed through the fixing device 9 while nipping and rotating the sheet.

  The pressure roller 32 is a roller formed by covering the periphery of a metal shaft with a silicon foam material. The pressure roller 32 is pressed against the cooling roller 31 by a spring (not shown) and forms a nip N with the cooling roller 31. The cooling roller 31 is a driving roller that rotates with a driving force from a driving source (not shown) and conveys the sheet P through a nip formed between the pressure roller 32.

  FIG. 3 is a cross-sectional view of the cooling roller 31. The cooling roller 31 is a hollow tube member formed in a cylindrical shape made of an aluminum alloy material having an outer diameter of 20 mm and a basic thickness of 1.5 mm. The cooling roller 31 is formed of a sheet passing area 31A, a non-sheet passing area 31B, and the like. The sheet passing area 31 </ b> A is a portion that extends in a direction orthogonal to the sheet conveying direction and is formed in a cylindrical shape, and conveys the sheet in contact with the sheet. The non-sheet passing region 31B is a portion that is formed in a cylindrical shape or a non-cylindrical shape outside a portion (sheet passing region 31A) that conveys the sheet and that does not contact the sheet (portion that does not convey the sheet). The sheet passing area 31A is formed by an original sheet passing area 31C through which a non-skewed sheet passes and an escape area 31D through which an edge of the skewed sheet passes.

  The inner diameters of the hollow portions 31e and 31f of the cooling roller 31 are different between the sheet passing area 31A and the non-sheet passing area 31B. The inner method (inner radius R) of the hollow portion 31f of the non-sheet passing region 31B is set larger (r <R) than the inner diameter (inner radius r) of the hollow portion 31e of the sheet passing region 31A.

  About 100 g of phase change material 33 as an endothermic material is placed in the hollow portions 31e and 31f. Both ends of the cooling roller 31 are sealed so that the phase change material 33 does not leak. The phase change material 33 is sealed so that an air gap 34 is formed in a portion on the upper side of the hollow portion 31f of the non-sheet passing region 31B.

  The phase change material 33 is generally used as a heat storage material, a cold insulation material, or the like by using latent heat generated at the time of phase change between a solid and a liquid or at the time of phase change between a liquid and a gas. . The phase change material 33 in the present embodiment is made of polyethylene glycol as a main raw material, and is not limited to this, and may be made of sodium acetate, sodium sulfate, paraffin or the like as a main raw material.

  The phase change material 33 changes phase from a solid to a liquid at about 50 ° C. Since the phase change material 33 is a polymer material, it is difficult to clearly define the temperature at which the phase change material 33 changes from a solid to a liquid, that is, the melting point. The phase change material 33 in this embodiment has a freezing point of 50 ° C. as a predetermined temperature (phase change temperature) at which a phase changes from a liquid to a solid.

  FIG. 4 is a graph showing a change in temperature of the phase change material 33 when 100 g of the phase change material 33 is solidified at 0 ° C. and then placed in a constant temperature bath at 80 ° C. The vertical axis indicates the temperature (° C.) of the phase change material 33, and the horizontal axis indicates the time (hr) that has elapsed since being placed in the thermostatic chamber. The phase change material 33 has a state in which the temperature change per unit time is reduced during the phase change from solid to liquid. In FIG. 4, the temperature of the phase change material 33 changes from solid to liquid between about 35 ° C. and about 55 ° C. In this state, the phase change material 33 absorbs a lot of heat as latent heat of fusion.

  When the image forming apparatus is on standby (when no image is formed), the temperature around the cooling roller 31 is lower than the phase change temperature of the phase change material 33 (freezing point, about 50 ° C.). The surface temperature of the sheet P that has passed through the fixing device 9 is about 75 ° C. or higher, and the toner on the sheet P is in a viscous state. When the sheet P is conveyed by contact with the cooling roller 31, the phase change material 33 in the cooling roller 31 absorbs the heat of the sheet P. As a result, the surface temperature of the sheet P that has passed through the roller cooling device 30 becomes 60 ° C. or less, which is the glass transition point of the toner, and the toner on the sheet P is in a solidified state.

  FIG. 5 is a graph showing changes in the surface temperature of the cooling roller 31 on which image formation has been continuously performed from a state where the image forming apparatus is on standby. A solid line indicates a change in the surface temperature of the cooling roller in which the phase change material 33 is enclosed inside in the present embodiment. The broken line indicates the surface temperature of the cooling roller when water is enclosed as an endothermic material. The vertical axis represents the surface temperature (° C.) of the cooling roller 31. The horizontal axis indicates the time (hr) that has elapsed since the start of continuous image formation.

  When the image formation is repeated continuously, the phase change material 33 continues to absorb heat from the sheet P through the surface of the cooling roller 31. As described above, in the process in which the phase change material 33 changes from solid to liquid, the temperature change per unit time is small. In the process of changing the surface temperature of the cooling roller 31 from about 35 ° C. to about 55 ° C., the internal phase change material 33 is a process of changing from solid to liquid. On the other hand, since the water is liquid from 0 ° C. to 100 ° C., no latent heat is generated. Therefore, the change in the surface temperature of the cooling roller 31 per unit time from the start of continuous image formation to about 3.5 hours is included in the phase change material 33 rather than in the case where water is sealed in the cooling roller. Less if you did.

  Therefore, the surface temperature difference of each sheet P after passing through the roller cooling device 30 is reduced, and the image glossiness is stabilized.

  The phase change temperature of the phase change material is selected by changing the ambient temperature around the roller cooling device 30 and the toner image surface temperature of the sheet P before and after the sheet P passes through the roller cooling device 30. This can be done in consideration. If the time during which the surface temperature change of the cooling roller can be reduced is made longer even if image formation is continuously repeated, a phase change material having a higher latent heat of fusion is selected or the internal capacity of the cooling roller 31 is increased. Thus, the amount of the phase change material 33 to be enclosed can be increased or coped with.

  By the way, the volume of the phase change material 33 used in the present embodiment changes when it changes from solid to liquid by endothermic reaction. If this volume change cannot be allowed due to deformation of the cooling roller 31, the phase change material 33 may leak out from the seal portion of the cooling roller 31. Therefore, in order to prevent the phase change material 33 from leaking out of the cooling roller 31 due to a volume change, the air gap 34 is provided instead of filling the hollow portion of the cooling roller 31 with the phase change material 33. Is preferred. As a result, since the volume of the air in the air gap 34 is changed by the amount of the phase change material 33 changed in volume, the pressure fluctuation inside the cooling roller 31 is reduced, and the phase change material 33 does not leak to the outside.

  Further, it is difficult to fill the inside of the cooling roller with the phase change material and to seal it, from the viewpoint of manufacturing the cooling roller, compared to the case where an air gap is provided inside. Therefore, from the viewpoint of manufacturing the cooling roller, it is easier to manufacture the cooling roller if an air gap is formed inside the cooling roller.

  Depending on the manufacturing method, the cooling roller 31 can have a sealed structure in which the phase change material 33 does not leak outside, so an air gap is not necessarily required.

  Here, FIG. 6 shows a cross-sectional view when the inside diameter of the hollow portion of the cooling roller is made uniform. When the hollow portion inner diameter 36e of the cooling roller 36 is made uniform, an air gap 34 is generated in the sheet passing area 36A. In this case, the portion of the air gap 34 is a portion where the heat absorption efficiency from the sheet P is low because the phase change material 33 is not in contact with the inside of the cooling roller 36. As a result, the heat absorption from the sheet P is uneven, which causes a temperature unevenness on the surface of the toner image. Note that the sheet passing area 36A in FIG. 6 is also formed by an original sheet passing area 36C through which a non-skewed sheet passes and an escape area 36D through which the edge of the skewed sheet passes.

  Therefore, the phase change material 33 in the cooling roller 31 of the present embodiment is sealed so that an air gap 34 is formed in the non-sheet passing region 31B having the inner radius R of the cooling roller 31. As a result, the air gap 34 does not exist in the portion of the inner radius r of the paper passing area 31A of the cooling roller 31. Therefore, temperature unevenness due to the air gap 34 does not occur in the paper passing area 31A of the cooling roller 31. Therefore, unevenness in heat absorption from the sheet P is less likely to occur, and occurrence of temperature unevenness on the toner image surface can be reduced.

  In addition, although the cooling roller 31 demonstrated above is formed in the circular tube shape (cylindrical shape) as a whole, it is not limited to a circular tube shape. That is, the non-sheet passing region 31B in FIG. 3 is cylindrical, but the non-sheet passing region shown in FIG. 7 corresponding to the shape shown in FIG. 3B, which is a cross-sectional view taken along the line AA in FIG. As in the region 31E, it may be formed in a rectangular cylinder shape.

  In this case, the minimum distance Rmin from the rotation center C of the non-sheet passing region 31E to the hollow inner wall at the end of the cooling roller 31 is larger than the maximum distance rmax from the rotation center C to the hollow inner wall in the sheet passing region 31A. Set. By doing so, even if it is a quadrangular cylindrical shape, the air gap 34 can be generated in the non-sheet passing area 31E without being generated in the sheet area 31A. Further, the cross-sectional shape of the non-sheet passing region 31E is not limited to a quadrangular cylinder, and may be a polygonal or elliptical cylindrical shape, or a circular or noncircular cylindrical shape. .

  That is, the cooling roller 31 is formed in a cylindrical shape extending in the width direction orthogonal to the sheet conveyance direction, and encloses a phase change material that undergoes an endothermic reaction when changing from a solid to a liquid at a predetermined temperature. A part of the paper passing area 31A for conveying the sheet is formed in a cylindrical shape. The inner method (2R) of the cylindrical portions of the non-sheet passing regions 31B and 31E that do not convey the sheet is set to be larger (2R> 2r) than the inner diameter (2r) of the cylindrical portion of the sheet passing region 31A. That's fine.

  As described above, the image forming apparatus 20 according to the present embodiment uses the conveyance roller pair 35 having the cooling roller 31 in which the phase change material is sealed. Therefore, it is possible to save power and reduce noise from toner on the sheet. It absorbs heat and can be cooled to a temperature at which the toner is solidified. In addition, since a fan for cooling the cooling roller and an active heat radiating portion of the cooling roller 31 are not required, the toner on the sheet can be cooled in a small space.

  Further, an air gap 34 that is enlarged at the end of the cooling roller 31 and is not filled with the phase change material is formed at the end of the cooling roller 31. Therefore, in the sheet passing area 31 </ b> A of the cooling roller 31, the phase change material is in a state of being filled in the cooling roller 31, that is, in a state of being always in close contact with the entire inner area of the cooling roller 31. Therefore, it is possible to suppress unevenness of the surface temperature in the sheet passing area 31A of the cooling roller 31. As a result, the image forming apparatus 20 can suppress uneven cooling of the toner image due to uneven surface temperature of the cooling roller 31 and suppress uneven gloss of the image.

  In addition, the temperature at which the phase change material 33 changes between the solid and the liquid is higher than the peripheral temperature of the pair of conveying rollers when the image forming apparatus is on standby, and is below the glass transition point of the toner on the sheet. is there. For this reason, even when the image forming apparatus continuously repeats the image forming operation, it is possible to reduce the change in the surface temperature of the cooling roller 31, and to cool the toner of the toner image on the sheet more stably. Can do.

  In the above description, the phase change material is taken up as the endothermic material, but is not limited to the phase change material and may be water.

(Cooling roller of other embodiment)
The cooling roller of the above embodiment is configured to generate the air gap 34 at one end, but may be configured to be generated at both ends.

  FIG. 8 shows a cross-sectional view of the cooling roller 131 in another embodiment. The cooling roller 131 has an air gap 134 in the non-sheet passing area 131B at both ends. In FIG. 8, the same parts as those in FIG. 3 are denoted by reference numerals in the 100s, and description of those parts is omitted. The shape of the non-sheet passing region 131B may be either a circular shape or a non-circular cylindrical shape as described with reference to FIG.

  The volume of the air gap 34 is determined in consideration of the volume change amount of the phase change material sealed inside the cooling roller, the sealing strength of the cooling roller, the shape change of the cooling roller due to the pressure variation inside the cooling roller, and the like. The Therefore, as in the cooling roller 131 shown in FIG. In particular, when the air gap 34 is provided at one end, if the peripheral space cannot be sufficiently secured, the air gap 34 is dispersed so that the air gap 34 is generated at both ends as in the cooling roller 131 shown in FIG. Can be used effectively.

  The cooling roller 131 and the image forming apparatus provided with the cooling roller in FIG. 8 can obtain the same effects as the cooling roller 31 and the image forming apparatus provided with the cooling roller.

  In the above description, the phase change material is enclosed in the cooling rollers 31 and 131 as drive rollers that are rotated by a drive source. However, the pressure roller 32 as a driven roller is cylindrical and enclosed in the pressure roller 32. May be.

  Further, the phase change material may be enclosed in both the cooling rollers 31 and 131 and the pressure roller 32. However, in this case, as shown in FIG. 8, when the non-sheet passing area is formed so that an air gap is formed at both ends of the roller, the non-sheet passing areas of both rollers interfere with each other to form a nip between both rollers. Cannot be formed. For this reason, it is necessary to form the non-sheet-passing area only on one side of the opposite end portions of both rollers so that the non-sheet-passing areas do not interfere with each other so that a nip formed by both rollers can be formed. There is.

  P: sheet, r: radius of the sheet passing area of the cooling roller, R: radius of the non-sheet passing area of the cooling roller, C: rotation center of the cooling roller, 9: fixing unit, 15: image forming unit, 20: image forming Device: 30: Roller cooling device, 31: Cooling roller, 31A: Paper passing area (portion where sheet is conveyed), 31B: Non-paper passing area (portion where sheet is not conveyed), 31E: Non-paper passing area (sheet conveying) 32: pressure roller, 33: phase change material (endothermic material), 34: air gap, 35: transport roller pair, 131: cooling roller, 131A: paper passing area, 131B: non-paper passing area, 131E : Non-sheet passing region, 131e: hollow portion of the sheet passing region, 131f: hollow portion of the non-sheet passing region 131B,

Claims (3)

An image forming unit for forming a toner image on a sheet;
An image forming apparatus comprising: a fixing device that heat-fixes the toner image on a sheet;
A pair of conveyance rollers that clamp the sheet that has passed through the fixing device and cool while conveying the sheet,
At least one roller of the pair of conveying rollers is formed in a cylindrical shape extending in the width direction orthogonal to the sheet conveying direction, and encloses an endothermic material that absorbs heat when changing from solid to liquid, and conveys the sheet. The portion to be formed in a cylindrical shape, the inner method of the cylindrical portion outside the width direction of the portion conveying the sheet is set larger than the inner diameter of the cylindrical portion,
An image forming apparatus. An air gap is formed inside the outer cylindrical portion in the width direction of the one roller,
The image forming apparatus according to claim 1. The endothermic material has a temperature at which a phase change between a solid and a liquid exceeds a peripheral temperature of the pair of conveying rollers when the image forming apparatus is on standby, and is equal to or lower than a glass transition point of the toner on the sheet. A phase change material,
The image forming apparatus according to claim 1, wherein:

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