JP2019101360A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus for reducing the degradation of the quality of a formed image.SOLUTION: An image forming apparatus 100 includes a fixing unit 30 which fixes a toner image formed on a paper sheet and a cooling unit 55 which cools a fixing paper to which the toner image is fixed. The cooling unit 55 includes a cooling roller 52 (cooling part) and an opposing roller 51 (opposing part) which faces the cooling roller 52. The cooling roller 52 includes a main body part and a surface part which is provided on the surface of the main body part and comes into press-contact with the fixing paper. The heat capacity of the surface part is lower than the heat capacity of the main body part. The heat conductivity of the surface part is lower than the heat conductivity of the main body part. When the number of paper sheets continuously cooled by the cooling unit 55 becomes a predetermined first threshold or more or the continuous cooling time of the cooling unit 55 becomes a predetermined second threshold or more, a control part 18 stops the image formation processing of the image forming apparatus 100.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, there is an image forming apparatus provided with a fixing device for fixing an image formed by unfixed toner or the like by heating or the like. For example, when performing double-sided printing, the image forming apparatus of Patent Document 1 cools the sheet on which the first side has been fixed by a cooling member after fixing the first side to prevent the outflow of moisture inside the sheet. As a result, transfer failure (hereinafter, image unevenness) on the second surface is reduced.

Unexamined-Japanese-Patent No. 2004-145160

  In the invention described in Patent Document 1, in the case of performing double-sided printing on a large number of sheets, the temperature of the cooling member itself rises because the cooling member absorbs heat from the large number of sheets. If it does so, the cooling effect of a cooling member will fall. Thus, if the cooling effect of the cooling member is reduced, for example, even if the cooling member cools the sheet on which the unfixed toner image is fixed on the first surface (surface) in double-sided printing, Since the cooling effect of the cooling member is reduced, the paper can not be cooled properly. As a result, when the unfixed toner image is fixed to the second surface (rear surface), the problem of image quality deterioration occurs due to the occurrence of image unevenness.

  The present disclosure has been conceived in view of the above-described circumstances, and an object thereof relates to an image forming apparatus that reduces the degradation of the quality of an image to be formed.

  According to an aspect of the present disclosure, a fixing unit configured to fix a toner image formed on a sheet, and a cooling unit configured to cool the fixing sheet on which the toner image is fixed, the cooling unit includes a main unit and There is provided an image forming apparatus including a surface portion provided on a surface of a main body portion, wherein a heat capacity of the surface portion is lower than a heat capacity of the main body portion.

Preferably, the thermal conductivity of the surface portion is lower than the thermal conductivity of the main body portion.
Preferably, the image forming process of the image forming apparatus is stopped when the number of the fixing sheets continuously cooled by the cooling unit becomes equal to or more than a first threshold.

  Preferably, the image forming process of the image forming apparatus is stopped when the time during which the cooling section continuously cools the fixing sheet is equal to or greater than a second threshold.

  Preferably, in the case where the fixing unit fixes the toner image formed on both sides of the sheet, the cooling unit cools the fixing sheet on which the toner image is fixed on the first side of the sheet. The fixing sheet on which the toner image is fixed to the second side of the sheet is not cooled.

  Preferably, the image forming apparatus further comprises an opposing portion facing the cooling portion and holding the cooling portion and the fixing sheet.

  Preferably, the facing portion includes a facing main body portion, and a facing surface portion provided on a surface of the facing main body portion and pressed against the fixing sheet.

Preferably, the thermal conductivity of the facing surface portion is higher than the thermal conductivity of the surface portion.
Preferably, the heat capacity of the surface portion is 1/10 or less of the heat capacity of the main body portion.

Preferably, the surface is a resin and the body is solid.
Preferably, the thickness of the surface portion is 0.1 mm to 1 mm.

  Preferably, the cooling unit is disposed at a position where it contacts within 0.5 seconds from the position where the toner image is fixed in the fixing unit.

  According to the present disclosure, it is possible to reduce the degradation of the quality of the formed image.

FIG. 1 is a diagram showing an entire configuration of an image forming apparatus. FIG. 2 is a diagram illustrating a hardware configuration of an image forming apparatus. It is a figure which shows the perspective view of a cooler and a fixing device. FIG. 6 is a cross-sectional view of a cooling roller 52. It is a figure showing a cooler and a fixing device. It is the figure which showed transition of the surface temperature of a cooling roller. It is the figure which showed the enlarged view of transition of the surface temperature of a cooling roller. It is a figure showing transition of temperature of paper which passed cooling roller. It is the figure which showed transition of the surface temperature of a cooling roller. It is a figure showing the physical relationship of a cooler and a fixing device. FIG. 6 is a view showing an example of a temperature change of a sheet after being heat-fixed by a fixing roller. It is a figure which shows an example of a change of the moisture content in a paper in the example of FIG. FIG. 6 is a view showing a temperature change of a sheet with respect to an elapsed time from discharge from a fixing roller nip portion. FIG. 6 is a graph showing a change in moisture content of a sheet with respect to an elapsed time from discharge of the fixing roller from a nip portion. FIG. 2 is a flowchart of the image forming apparatus. It is a figure which shows a 1st threshold value. It is a figure which shows a 2nd threshold value. It is the figure which showed the modification of a cooler and a fixing device. FIG. 2 is a flowchart of the image forming apparatus. It is the figure which showed the modification of a cooler and a fixing device. It is the figure which showed the modification of a cooler and a fixing device. It is the figure which showed the modification of a cooler and a fixing device. It is the figure which showed the modification of a cooler and a fixing device.

First Embodiment
First, the first embodiment will be described. Hereinafter, a fixing device and an image forming apparatus in an embodiment based on the present invention will be described with reference to the drawings. In the embodiments described below, when the number, the amount, and the like are mentioned, the scope of the present invention is not necessarily limited to the number, the amount, and the like unless otherwise specified. The same parts and corresponding parts are denoted by the same reference numerals, and duplicate descriptions may not be repeated. Moreover, it is planned from the beginning to use combining the structure in each embodiment suitably. Hereinafter, “forming an image” is also referred to as “printing”.

[Configuration of image forming apparatus]
The schematic configuration of the image forming apparatus 100 in the present embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an internal configuration of the image forming apparatus 100. As shown in FIG.

  FIG. 1 shows an image forming apparatus 100 as a color printer. Although the image forming apparatus 100 as a color printer will be described below, the image forming apparatus 100 is not limited to the color printer. For example, the image forming apparatus 100 may be a monochrome printer, or may be a monochrome printer, a color printer, and a multifunction peripheral (MFP: Multi-Functional Peripheral).

  The image forming apparatus 100 includes image forming units 1A to 1E as forming units, an intermediate transfer belt 11, a primary transfer roller 12, a secondary transfer roller 13, a cleaning unit 15, a paper discharge tray 16, and a cassette 17. And a control unit 18, an exposure control unit 19, a fixing unit 30 as a fixing unit, a sheet discharge roller 36, a reverse conveyance path 38, and the like.

  The image forming unit 1A forms a yellow (Y) toner image. The image forming unit 1B forms a toner image of magenta (M). The image forming unit 1C forms a cyan (C) toner image. The image forming unit 1D forms a black (BK) toner image.

  The intermediate transfer belt 11 is an endless belt, and is driven to rotate in the direction of the arrow 21 by rotating at least one of the plurality of support rollers. The image forming units 1A to 1E are arranged in order along the driving direction of the intermediate transfer belt 11, respectively.

  Each of the image forming units 1A to 1E includes a photosensitive member 2, a charging unit 3, a developing unit 4, a photosensitive member cleaning unit 5, and an exposure unit 9. The photosensitive member 2 is an image carrier that carries a toner image. As an example, for the photosensitive member 2, a photosensitive drum having a photosensitive layer formed on the surface thereof is used. The photosensitive member 2 rotates in a direction corresponding to the driving direction of the intermediate transfer belt 11.

  The charging unit 3 uniformly charges the surface of the photosensitive member 2. The exposure unit 9 irradiates the photosensitive member 2 with laser light in accordance with the control signal from the exposure control unit 19 and exposes the surface of the photosensitive member 2 in accordance with the designated image pattern. As a result, an electrostatic latent image corresponding to the designated image pattern is formed on the photosensitive member 2.

  The developing unit 4 develops the electrostatic latent image formed on the photosensitive member 2 as a toner image. As an example, the developing unit 4 develops the electrostatic latent image using a two-component developer composed of toner and carrier.

  The toner image formed on the surface of the photosensitive member 2 is transferred to the intermediate transfer belt 11 by the primary transfer roller 12. At this time, a toner image of yellow (Y), a toner image of magenta (M), a toner image of cyan (C), and a toner image of black (BK) are sequentially superimposed and transferred to the intermediate transfer belt 11. Thus, a color toner image is formed on the intermediate transfer belt 11.

  The photoreceptor cleaning unit 5 includes a cleaning blade. The cleaning blade is in pressure contact with the photosensitive member 2 and collects toner remaining on the photosensitive member 2 after transfer of the toner image.

  The primary transfer roller 12 transfers the toner image developed on the photosensitive member 2 to the intermediate transfer belt 11. The photosensitive member 2 and the intermediate transfer belt 11 are in contact with each other at a portion where the primary transfer roller 12 is provided. A predetermined transfer bias (voltage) is applied to the contact portion, and the toner image on the photosensitive member 2 is transferred to the intermediate transfer belt 11 by the transfer bias.

  The cassette 17 is provided at the lower part of the image forming apparatus 100. A sheet 14 such as paper is set in the cassette 17. The sheets 14 are sent to the secondary transfer roller 13 one by one from the cassette 17. By synchronizing the timing of delivery and conveyance of the sheet 14 with the position of the toner image on the intermediate transfer belt 11, the toner image is transferred to an appropriate position of the sheet 14. Thereafter, the sheet 14 is sent to the fixing device 30. Further, a portion where the secondary transfer roller 13 is in pressure contact with the fed sheet is also referred to as a “transfer nip portion 13A” or a “transfer portion”.

  The fixing unit 30 thermally fuses the toner image (unfixed toner image) transferred to the sheet 14 and fixes the toner image on the sheet 14. The fixing device 30 sandwiches the fixing roller 32 as a heating member heated by the heater 32 h as a heating device, and the sheet 14 on which the unfixed image is formed on the surface together with the fixing roller 32. , And a temperature detection unit 33 (see FIG. 2). Fixing temperature control is performed by the control unit 18 based on the detection result of the temperature detection unit 33.

  The image forming apparatus 100 can also receive an input from the user from the operation unit 50. The user can, for example, enter either a single-sided print job or a double-sided print job. The single-sided print job is a job for forming an image on one side of a sheet. The double-sided printing job is a job for forming an image on both sides of the sheet (the first side (front side) of the sheet and the second side (back side) of the sheet).

  When the single-sided print job is input by the user, the sheet 14 is discharged to the sheet discharge tray 16 by the sheet discharge roller 36 after the fixing process by the fixing device 30. When a double-sided print job is input by the user, the sheet 14 is sent to the reverse conveyance path 38 by the reverse rotation of the sheet discharge roller 36 after the fixing process by the fixing device 30. Thereafter, the sheet is sent to the secondary transfer roller 13 so that the toner image is transferred to the back surface (second side) of the sheet. The secondary transfer roller 13 transfers the toner image to an appropriate position on the back side of the sheet 14. Thereafter, the sheet is again sent to the fixing device 30, and the fixing device 30 fixes the toner image on the back surface of the sheet. Thus, when a double-sided printing job is input by the user, it is possible to print on both sides. The sheet fixed by the fixing unit 30 is also referred to as “fixing sheet”.

  The cleaning unit 15 includes a cleaning blade. The cleaning blade is in pressure contact with the intermediate transfer belt 11, and collects toner particles remaining on the intermediate transfer belt 11 after the transfer of the toner image. The toner particles are transported by a transport screw (not shown) and collected in a waste toner container (not shown).

  The control unit 18 controls an image forming process of the image forming apparatus 100. The control unit 18 controls the image forming units 1A to 1E, the secondary transfer roller 13, the fixing unit 30 (temperature control of the heater 32h, the rotation speed of the pressure roller 31, etc.), the exposure control unit 19 and the like.

  Further, a cooler 55 is provided downstream of the fixing device 30. The cooler 55 includes a cooling roller 52 (cooling unit) and an opposing roller 51 (opposing unit). The cooler 55 is controlled by the control unit 18. The opposing roller 51 opposes the cooling roller 52, and holds the sheet between the opposing roller 51 and the cooling roller 52.

  As described above, since the sheet is held by the opposing roller 51 and the cooling roller 52 to cool the sheet, the sheet can be stably cooled.

[Hardware configuration of image forming apparatus]
FIG. 2 is a diagram showing a hardware configuration of the image forming apparatus 100. As shown in FIG. Referring to FIG. 2, image forming apparatus 100 includes a central processing unit (CPU) 101 that executes a program, a read only memory (ROM) 102 that stores data in a nonvolatile manner, and a RAM that stores data in a volatile manner. (Random Access Memory) 103, a flash memory 104, a touch screen 105, a speaker 106, and a communication IF 108.

  The touch screen 105 includes a display 1051 as a display device and a touch panel 1052 as an input device. Specifically, the touch screen 105 is realized by positioning and fixing the touch panel 1052 on the display 1051 (for example, liquid crystal display). The touch screen is also referred to as a touch panel display, a display with a touch panel, or a touch panel monitor. In addition, in the touch screen 105, for example, a resistive film method or an electrostatic capacitance method can be used as a detection method of the touch position. A job is input by an operation of the touch screen 105 by the user.

  The flash memory 104 is a non-volatile semiconductor memory. The flash memory 104 stores an operating system and various programs executed by the CPU 101, various contents, and data. The flash memory 104 also stores various data such as data generated by the image forming apparatus 100 and data acquired from an external device of the image forming apparatus 100 in a volatile manner.

  The speaker 106 generates a sound in response to an instruction from the CPU 101. The CPU 101 specifies an input position based on an output from the touch panel 1052, and performs screen display based on the specified input position.

  The communication IF 108 is also connected to another external device (for example, a PC) through a network. When a user inputs a job from the other external device, the image forming apparatus 100 acquires the job via the communication IF.

  The processing in the image forming apparatus 100 is realized by each hardware and software executed by the CPU 101. Such software may be stored in advance in the flash memory 104. Each component constituting the image forming apparatus 100 shown in the figure is a general one. Therefore, the essential part of the present invention can be said to be software stored in the flash memory 104, memory card or other storage medium, or software downloadable via a network. The operation of each hardware of image forming apparatus 100 is well known, and therefore detailed description will not be repeated.

  The recording medium is not limited to a DVD-ROM, a CD-ROM, an FD (Flexible Disk), a hard disk, a magnetic tape, a cassette tape, an optical disk (MO (Magnetic OptiDal Disc) / MD (Mini Disc) / DVD (Digital It may be a medium that holds a program in a fixed manner, such as a Versatile Disc), an optical card, a mask ROM, an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a semiconductor memory such as a flash ROM. Also, the recording medium is a non-transitory medium in which the program etc. can be read by a computer.

  The program referred to here includes not only a program directly executable by the CPU but also a program of source program format, a program subjected to compression processing, an encrypted program and the like.

[Cooler and Fixer]
FIG. 3 shows a perspective view of the cooler 55 and the fixing device 30. As shown in FIG. As shown in FIG. 3, the widths of the cooling roller 52 and the opposing roller 51 of the cooler 55 are longer than the width of the sheet printed by the image forming apparatus 100. With such a configuration, the cooler 55 can be properly cooled regardless of the width of the sheet printed by the image forming apparatus 100. Further, in FIG. 3, the arrow A indicates the conveyance direction of the sheet P. In the example of FIG. 3, the distance between the cooler 55 and the fixing device 30 is shorter than the longitudinal direction of the sheet. However, the distance between the cooler 55 and the fixing device 30 may be longer than the longitudinal direction of the sheet.

[About the cooler]
Next, the cooler 55 will be described. FIG. 4 shows a cross-sectional view of the cooling roller 52 included in the cooler 55. As shown in FIG. Cooling roller 52 includes a surface portion 52A and a main portion 52B. The main body 52B has a cylindrical shape (roller shape). The surface portion 52A is provided on the surface of the main portion 52B. The surface portion 52A is a portion that contacts the sheet after fixing. In the example of FIG. 4, the surface portion 52A is a surface layer formed along the circumference of the main portion 52B. That is, the cooling roller 52 is configured by coating the surface portion 52A on the surface layer of the main body portion 52B having a roller shape.

  In the present embodiment, the cored bar as the main body 52B has a solid structure. That is, the cooling roller 52 has a structure without a gap. The heat capacity of the surface 52A is lower than the heat capacity of the main body 52B. Further, the thermal conductivity of the surface portion 52A is lower than the thermal conductivity of the main portion 52B.

  Moreover, as a material of surface part 52A, a metal material or a resin material may be sufficient. The material of the surface portion 52A is preferably resin. The surface 52A is made of, for example, polyethylene, polypropylene, polystyrene, acrylonitrile styrene, SAN resin, ABS resin, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polymethyl methacrylate (acrylic resin), polyamide, polyoxymethylene, polyethylene Material containing at least one of terephthalate, polysulfone, polyphenylene oxide, cellulose acetate, cellulose acetate butyrate, phenol resin, epoxy resin, unsaturated polyester resin, polyurethane resin, urea resin, and melamine resin (hereinafter referred to as “first material And so on) are preferable.

  In addition, the surface portion 52A may be made of a material (hereinafter, referred to as a "second material") which has a high specific heat and can prevent the contamination with the toner. The second material may be, for example, a fluorine-based resin. The fluorine-based resin may be, for example, a material including at least one of PTFE, PFA, FEP, ETFE, PVDF, ECTFE, PCTFE, and PVF. In addition, the surface portion 52A may be a material including both of the first material and the second material.

  In addition, it is preferable that the volume of the surface portion 52A be reduced so as to reduce the heat capacity of the surface portion 52A. As shown in FIG. 4, the thickness L of the surface portion 52A is preferably, for example, 0.1 to 1 mm.

  The material of the main body 52B (core) is preferably, for example, a material containing at least one of iron, aluminum and the like (hereinafter, also referred to as “third material”). As described above, the material of the surface 52A and the material of the main body 52B are preferably selected so that the heat capacity of the surface 52A is lower than the heat capacity of the main body 52B. The material of the surface 52A and the material of the main body 52B are preferably selected so that the thermal conductivity of the surface 52A is lower than the thermal conductivity of the main body 52B.

  The material of the surface 52A and the material of the main body 52B are preferably selected so that the specific heat of the surface 52A is lower than the specific heat of the main 52B.

  Further, as a result of the applicant's repeated experiments, it has been found that the heat capacity of the surface portion 52A is preferably 1/10 or approximately 1/10 of the heat capacity of the main portion 52B.

  Further, it is preferable that the heat capacity of the surface portion 52A be larger than the heat capacity of the outside air around the cooling roller 52. As a modification, the heat capacity of the outside air around the cooling roller 52 may be the same. Further, as a modification, the heat capacity of the surface 52A may be smaller than the heat capacity of the outside air around the cooling roller 52.

  FIG. 5 is a view showing the fixing roller 32 and the like. In the example of FIG. 5, the cooler 55 includes a biasing member 56 for biasing the cooling roller 52 against the opposing roller 51, and a biasing member 57 for biasing the opposing roller 51 against the cooling roller 52. . The biasing member 56 is provided on the cooling roller 52. Further, the biasing member 57 is provided on the opposing roller 51. In the example of FIG. 5, the biasing member 56 and the biasing member 57 are both springs. As a modification, at least one of the biasing member 56 and the biasing member 57 may use a member other than a spring.

  Thus, the cooler 55 of FIG. 5 biases the cooling roller 52 against the opposing roller 51 by having the biasing member 56 and the biasing member 57, and the opposing roller 51 is cooled by the cooling roller 52. Can be biased against. Therefore, the cooling efficiency to the paper P of the cooling roller 52 can be improved.

  Further, the cooling roller 52 is disposed so as to cool the surface heated by the fixing roller 32 of both sides of the sheet. That is, the cooling roller 52 is disposed on the same side as the fixing roller 32. Thereby, the cooling efficiency of the cooling roller 52 can be improved.

Next, the effects of the image forming apparatus 100 of the present embodiment will be described.
In the conventional cooler, when double-sided printing is performed on a large number of sheets, the cooling member absorbs heat from the large number of sheets, which causes a temperature rise of the cooling member itself. If it does so, the cooling effect of a cooling member will fall. Thus, if the cooling effect of the cooling member is reduced, for example, even if the cooling member cools the sheet on which the unfixed toner image is fixed on the first surface (surface) in double-sided printing, Since the cooling effect of the cooling member is reduced, the paper can not be cooled properly. As a result, the water is excessively released from the sheet. If the water is removed too much from the paper, the amount of water in the paper decreases, and the electrical resistance value of the paper may increase. For example, when double-sided printing is performed by image forming apparatus 100, the unfixed toner image may be fixed on the second surface (rear surface) of the sheet on which the unfixed toner image is fixed on the first surface. In such a case, there is a problem that the quality of the image formed on the back surface is degraded when the electric resistance value of the sheet becomes high (there is a problem that image unevenness occurs).

  In view of such a problem, it is conceivable to employ a cooling member for cooling a cooler (for example, a cooling roller). The cooling member is, for example, a cooling fan and a jetting member for jetting cooling water to a cooler. However, when such a cooling member is added, the size of the cooler is increased, and the configuration of the cooler is complicated.

  So, in this embodiment, the heat capacity of surface part 52A is constituted so that it may become lower than the heat capacity of main part 52B. Generally, a member having a large heat capacity is difficult to warm up and cool down. Moreover, a member having a small heat capacity is easy to warm and cool. Therefore, the heat stored in the member having a small heat capacity (in the present embodiment, the surface portion 52A) is difficult to transfer to the member having a large heat capacity (in the present embodiment, the main portion 52B), and this heat is transferred to the outside air Ru.

  Further, since the sheet passing through the fixing device 30 is heated by the fixing device 30, the temperature of the sheet is high. Therefore, the heat of the sheet which is in the high temperature state can be transferred to the outside (outside air) of the cooling roller 52 without transferring to the main body 52B as much as possible. Therefore, the decrease in the cooling effect of the cooler 55 can be appropriately suppressed without providing the cooling member in the cooler 55. Therefore, for example, even in the case where the unfixed toner image is fixed on the second surface, it is possible to suppress the occurrence of the image unevenness. As a result, degradation of the quality of the formed image can be reduced.

  6-8 is a figure which shows an experimental result. The horizontal axis of FIGS. 6 and 7 indicates the number of printed sheets (that is, the number of sheets cooled by the cooler 55), and the vertical axis indicates the temperature of the cooling roller 52. The horizontal axis in FIG. 8 indicates the number of printed sheets, and the vertical axis indicates the surface temperature of the sheet. FIG. 7 is an enlarged view of a period in which the first to fourth sheets of FIG. 6 are cooled. 6 to 8 are examples when the temperature of the sheet after fixing is 100 degrees and the temperature around the outside air (cooler 55) is 23 degrees.

  6-8, a solid line shows a cooling roller which has a surface part (it is assumed that it is PFA), and a broken line shows a cooling roller which does not have a surface part (that is, a cooling roller of only a main part). In FIG. 7, the sheet passing period refers to a period in which the sheet is passed through the cooler 55, that is, a period in which the sheet is cooled. The inter-paper period is a period in which the sheet is not passed through the cooler 55 (a period from when the sheet is passed through the cooler 55 until it is passed next), that is, a period in which the sheet is not cooled.

  As shown in FIG. 7A, during the first sheet passing period, from the sheet being cooled regardless of whether it is a cooling roller having a surface portion or a cooling roller having no surface portion. Since the heat is absorbed, the temperature of the cooling roller rises. Further, for the cooling roller having the surface portion, most of the heat is accumulated on the surface portion, and for the cooling roller not having the surface portion, the heat is accumulated on the main body portion.

  As shown in b of FIG. 7, the temperature of the main body hardly decreases because the heat is accumulated in the main body during the inter-paper period with the cooling roller having no surface. On the other hand, as shown to c of FIG. 7, about the paper interval period in the cooling roller which has a surface part, it is thermally stored by the surface part. As described above, the heat capacity of the surface portion is lower than the heat capacity of the main body portion, and the heat capacity of the outside air is lower than the heat capacity of the main body portion. Therefore, the cooler has a function of releasing the heat stored in the surface to the outside. Therefore, during the sheet passing period, the temperature of the surface portion (cooling roller) decreases.

  Thereafter, during the sheet passing period, the temperature of the cooling roller rises because heat is absorbed from the sheet being cooled regardless of whether it is the cooling roller having the surface portion or the cooling roller having no surface portion. . In the inter-paper period, the temperature of the cooling roller (main body) not having the surface portion does not decrease, but the temperature of the cooling roller (surface portion) having the surface portion decreases.

  In the example of FIG. 6, the temperature of the cooling roller converges to 100 degrees when approximately 19 sheets are printed for the cooling roller having no surface portion. On the other hand, with regard to the cooling roller having no surface portion, the temperature of the cooling roller converges to 100 ° when approximately 38 sheets are printed. As described above, the number of sheets that can be printed before the temperature of the cooling roller converges to 100 degrees is larger for the cooling roller having the surface portion than for the cooling roller having no surface portion.

  Further, in the example of FIG. 8, it is shown that the cooling effect of the cooling roller on the sheet is longer for the cooling roller having the surface portion than for the cooling roller having no surface portion.

  Further, in the present embodiment, the thermal conductivity of the surface portion 52A is lower than the thermal conductivity of the main portion 52B. Thereby, the temperature rise of the surface portion 52A can be suppressed by preventing the heat accumulated in the main portion 52B (the core metal inside the cooling roller) from being transferred to the surface portion 52A.

  FIG. 9 is a view comparing a cooling roller in which the main portion 52B is solid and a cooling roller in which the main portion 52B is hollow. The hollow configuration is different from the solid configuration in that the main body 52B has a space. In FIG. 9, a solid line indicates a cooling roller having a surface portion and a solid body configuration, and a broken line indicates a cooling roller having a surface portion and a hollow body configuration. In FIG. 9, the vertical axis indicates the temperature of the surface of the cooling roller, that is, the temperature of the surface portion. The horizontal axis indicates the number of printed sheets (that is, the number of sheets cooled by the cooler).

  As shown in FIG. 9, in the case of the cooling roller in which the main body portion is hollow, the number of sheets of paper printed until the surface portion reaches 100 degrees is 38 sheets. On the other hand, in the case of a cooling roller having a solid body portion, the number of sheets printed before the surface portion reaches 100 degrees is 50 or more. As apparent from FIG. 9, the cooling roller having a hollow main body portion can lower the temperature rise of the main body portion more than the cooling roller having a solid main body portion.

  Also, heat transfer is determined by the temperature difference and the thermal conductivity, not just the thermal conductivity. In the present embodiment, the temperature of the sheet> the temperature of the surface portion 52A> the temperature of the outside air is in the ideal state. As a method for that purpose, the heat capacity of the surface 52A is made lower than the heat capacity of the main body 52B, thereby making it difficult to raise the temperature of the surface 52A, and the thermal conductivity of the surface 52A to be the thermal conductivity of the main 52B. By making the temperature lower than that, it is difficult to move the heat accumulated in the main body 52B to the surface 52A.

  Moreover, it is preferable that the heat capacity of surface part 52A shall be 1/10 or less of the heat capacity of main part 52B. Thereby, the heat of the surface portion 52A can be released to the outside air without being transferred to the main body portion 52B as much as possible.

  Moreover, it is preferable that surface part 52A is resin, and the main-body part 52B is solid. Thereby, the heat capacity of surface part 52A can be made lower than the heat capacity of main part 52B from a viewpoint of material.

  Further, in the present embodiment, the cooler 55 (cooling roller 52) is disposed at a position where the sheet to be conveyed contacts the position heated by the fixing unit 30 within 0.5 seconds. In this way, it is possible to prevent the water from being excessively released from the sheet. Therefore, it can suppress that the electrical resistance value of paper becomes high, and can suppress that the quality of the image formed in the back surface falls.

  FIG. 10 is a diagram showing this positional relationship. The fixing roller 32 heats the sheet P by sandwiching the sheet P with the pressure roller 31. In FIG. 2, the cooling roller 52 cools the sheet P by sandwiching the sheet P with the opposing roller 51. The opposing roller 51 not only sandwiches the cooling roller 52 and the sheet P, but also plays a role as a conveyance guide for the sheet P.

  A point X represents a position (nip portion) where the fixing roller 32 and the pressure roller 31 sandwich the sheet P. Point Y represents a position where the cooling roller 52 and the opposing roller 51 sandwich the sheet P. The distance R represents the distance by which the sheet P is transported from the point X to the point Y.

  In the image forming apparatus, the cooling roller 52 and the opposing roller 51 are disposed at positions where the sheet P heated by the fixing roller 32 is conveyed to the cooling roller 52 within 0.5 seconds. More specifically, assuming that the conveyance speed of the sheet P by the conveyance unit is V, the cooling roller 52 and the opposing roller 51 are disposed such that the distance R satisfies the relationship of the following formula (1).

R / V ≦ 0.5 (seconds) (1)
By arranging the opposing roller 51 so as to satisfy the condition according to the equation (1), the time during which the sheet P is in the high temperature state is 0.5 seconds or less. As a result, it is possible to avoid that the water is excessively drained from the sheet P. When the water content in the paper P decreases, the electrical resistance value in the paper P may increase. The sheet P on which an image is formed on the first side (hereinafter also referred to as “front side”) may subsequently form an image on the second side (hereinafter also referred to as “back side”). In such a case, when the electric resistance value of the sheet P becomes high, the quality of the image formed on the back surface may be degraded. When the condition according to the equation (1) is satisfied, the change in the electrical properties of the sheet P can be suppressed, whereby the deterioration of the image quality formed on the back surface can be avoided.

  FIG. 11 is a view showing an example of the temperature change of the sheet P after being heat-fixed by the fixing roller 32. As shown in FIG. The result shown in FIG. 11 is the case where the sheet P heated by the fixing roller 32 is left without being cooled by the cooling roller 52.

  In FIG. 11, a line L11 and a line L12 indicate the case where the fixing temperature of the fixing roller 32 is 190 degrees and 130 degrees, respectively. In FIG. 11, the horizontal axis represents the elapsed time after being discharged from the nip portion of the fixing roller 32, and the vertical axis represents the temperature of the sheet P (recording medium).

  Immediately after the sheet P is discharged from the nip portion of the fixing roller 32, the temperature of the sheet P rapidly drops in any of the line L11 and the line L12. At both fixing temperatures of 190 ° and 130 ° C., the degree of temperature decrease becomes low after about 0.6 seconds after discharge.

  FIG. 12 is a diagram showing an example of the change in the moisture content of the sheet P in the example of FIG. The moisture content is a percentage of the weight of the moisture contained in the paper P.

  In FIG. 12, lines L21 and L22 respectively indicate cases where the fixing temperature at the fixing roller 32 is 190 degrees and 130 degrees. A line L21 indicates a change in moisture content of the sheet represented by a line L11 in FIG. A line L22 indicates a change in moisture content of the sheet represented by the line L12 in FIG. In FIG. 12, the horizontal axis represents the elapsed time after being discharged from the nip portion of the fixing roller 32, and the vertical axis represents the moisture content of the sheet P.

  As indicated by the lines L21 and L22, the moisture content of the sheet P rapidly increases immediately after being discharged from the nip portion of the fixing roller 32 regardless of whether the fixing temperature is 190 degrees or 130 degrees. Decrease. Overall, the moisture content is lower at 190 degrees than at 130 degrees.

  As shown in both the line L21 and the line L22, the sheet is discharged from the nip portion of the fixing roller 32 to the sheet P by 0.6 seconds regardless of whether the fixing temperature is 190 degrees or 130 degrees. The reduction of the water content ends. Therefore, it can be said that cooling before the lapse of 0.6 seconds after the heating and fixing in the fixing roller 32 is effective in suppressing the loss of water from the sheet P.

  Therefore, in the present disclosure, the sheet P is cooled by bringing the cooling member into contact within 0.5 seconds after being discharged from the nip portion. Thereby, it can be efficiently avoided that moisture is released from the heated sheet P. The time during which the sheet P is at high temperature can be shortened by shortening the time from the discharge from the nip portion to the cooling by the cooling member. As a result, the time in which the paper P is in a state in which water is easily evaporated can be shortened, and the evaporation amount of water from the paper P can be suppressed. From this, the image forming apparatus may be designed such that the sheet P comes into contact with the cooling member in a shorter time (for example, within 0.2 seconds) after discharging from the nip portion.

  13 and 14 are diagrams showing the behavior of the sheet P cooled by the cooling member after the heating and fixing in the image forming apparatus according to the present disclosure. More specifically, FIG. 13 shows the temperature change of the sheet P with respect to the elapsed time from the discharge of the fixing roller 32 from the nip portion. FIG. 14 shows the change in moisture content of the sheet P with respect to the elapsed time from the discharge from the nip portion of the fixing roller 32.

  The examples shown in FIGS. 13 and 14 show the results when the sheet P is cooled by being brought into contact with the cooling member 0.2 seconds after the discharge from the nip portion. As shown in FIG. 13, due to the contact with the cooling member, the temperature of the sheet P drops rapidly, regardless of whether the fixing temperature is 190 degrees (line L31) or 130 degrees (line L32). As shown in FIG. 14, when the fixing temperature is 190 degrees (line L41) or 130 degrees (line L42), 0.2 from the discharge from the nip portion to correspond to the rapid drop in temperature. After the second, the drop in the moisture content of the paper P is dramatically suppressed. According to the result shown in FIG. 14, the release of the moisture from the sheet P is suppressed by cooling by the cooling member after the heating and fixing.

Second Embodiment
Next, a second embodiment will be described. In the second embodiment, when double-sided printing is performed, the image forming process of the image forming apparatus is performed when the number of sheets continuously cooled by the cooler 55 becomes equal to or greater than a predetermined first threshold. It is what makes it stop. The unit of the first threshold is the number of sheets, which will be described later with reference to FIG.

  FIG. 15 is a diagram showing a processing flow of the second embodiment. The process of FIG. 15 is a process executed by the control unit 18 when one job is input. In S2, the control unit 18 determines whether the job to be executed is a double-sided printing job. If it is determined NO in S2, the process ends. On the other hand, if it is determined YES in S2, the process proceeds to S4.

  In S4, it is determined whether the number of sheets continuously cooled by the cooler 55 (hereinafter referred to as "the number of continuous cooling sheets") has become equal to or greater than a first threshold. Here, “continuously cooling” means “cooling to paper by the cooler 55 in one job”, and “a period from the one job to the next job is a predetermined period (for example, 1 second) And the cooling by the cooler 55 to the last sheet in the one job and the cooling by the cooler 55 to the first sheet in the next job.

  When it is judged as NO in S4, it progresses to S12. When it is determined YES in S4, the process proceeds to S6. The case where YES is determined in S4 means that the continuous cooling period is long. In response to the determination that the continuous cooling period is long, in S6, the control unit 18 stops the printing operation. Next, in S8, the printing operation is stopped until the waiting period has elapsed. As described above, by stopping the printing operation until the waiting period has elapsed, the fixing unit 30 is not fixed and the cooling unit 55 is not cooled. Therefore, the cooling roller 52 of the cooler 55 can be prevented from absorbing heat from the sheet, and the cooling roller 52 can be cooled because the heat is radiated from the cooling roller 52 during the waiting period. The waiting period is a predetermined period, and may be, for example, 30 seconds. This waiting period may be set freely by the user, for example.

  If it is judged as YES at S8, it will progress to S10. In S10, the control unit 18 resumes the printing operation of the image forming apparatus 100. Next, in step S12, the control unit 18 determines whether one job that has triggered the start of the process of FIG. 15 has ended. If it is determined YES in S12, the process of FIG. 15 is ended. On the other hand, when it is judged as NO by S12, it returns to S2.

  Next, the first threshold described in S4 will be described. FIG. 16 is a diagram showing an example of a first threshold value table of the number of continuously cooled sheets. In the example of FIG. 16, the first threshold is a value according to the type of sheet, the print mode (print mode), and the environment of the image forming apparatus 100. In the example of FIG. 16, the sheet type includes the sheet thickness and the sheet width. Also, the printing mode includes which one of the printing mode (color mode and monochrome mode) and the coverage. Further, the environment of the image forming apparatus 100 is an in-machine temperature of the image forming apparatus 100. The coverage means the toner use ratio per sheet.

  In the example of FIG. 16, the first threshold is set to be smaller as the sheet is thicker. The thicker the paper, the more fixing heat required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the first threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  Further, the first threshold is set to be smaller in the full color mode than in the monochrome mode. In the full color mode, the toner layer is thicker than in the monochrome mode. The thicker the toner layer, the more heat of fixing needed. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the first threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  Further, the first threshold is set to be smaller when the coverage is a predetermined value (50% in the example of FIG. 16) or more than when the coverage is less than the predetermined value. The greater the coverage, the more fixing heat is required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the first threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  The first threshold is set to be smaller when the sheet width to be cooled is equal to or greater than a predetermined value (210 mm in the example of FIG. 16) than when the sheet width is less than the predetermined value. The larger the paper width, the more fixing heat required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the first threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  Further, the lower the in-machine temperature of the image forming apparatus 100 (the temperature around the cooling roller 52) is, the larger the first threshold is set. This is because the lower the in-machine temperature, the more fixing heat required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the first threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  The control unit 18 obtains the sheet thickness, the print mode, the coverage, the sheet width, and the in-machine temperature, and obtains the first threshold from these parameters with reference to the table of FIG. The table of FIG. 16 is stored in a predetermined storage area (for example, the ROM 102) of the image forming apparatus 100.

For example, the control unit 18 acquires information that the thickness of the sheet is 120 g / m ³ or more, acquires information that the printing mode is full color mode, and acquires information that the coverage is less than 50%. If the information that the width of the sheet is less than 210 mm is acquired and the in-machine temperature is acquired less than 10 degrees, 500 is acquired as the first threshold.

  As a modification, in S4, it may be determined whether a period (hereinafter referred to as a "continuous cooling period") in which the cooler 55 continuously cools the sheet has become equal to or greater than the second threshold. Good. This modification is described in parentheses in S4 of FIG. The unit of the second threshold is, for example, seconds or minutes.

  FIG. 17 is a diagram showing an example of a table of the second threshold value of the continuous cooling period. In the example of FIG. 17, the second threshold is set to be smaller as the sheet is thicker. The thicker the paper, the more fixing heat required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the second threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  Further, the second threshold is set to be smaller in the full color mode than in the monochrome mode. In the full color mode, the toner layer is thicker than in the monochrome mode. The thicker the toner layer, the more heat of fixing needed. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the second threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  Further, the second threshold is set to be smaller when the coverage is a predetermined value (50% in the example of FIG. 16) or more than when the coverage is less than the predetermined value. The greater the coverage, the more fixing heat is required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the second threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  Further, the second threshold is set to be smaller when the width of the sheet to be cooled is a predetermined value (210 mm in the example of FIG. 16) or more than when it is less than the predetermined value. The larger the paper width, the more fixing heat required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the second threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  The second threshold is set to be larger as the in-machine temperature of the image forming apparatus 100 (the temperature around the cooling roller 52) is lower. This is because the lower the in-machine temperature, the more fixing heat required. Therefore, since the control unit 18 raises the heating temperature by the fixing unit 30, the temperature of the sheet after fixing becomes high. When the temperature of the sheet after fixing is high, the amount of heat received by the cooling roller 52 also increases. Therefore, by decreasing the second threshold, it is possible to increase the frequency at which the printing operation is stopped (execution frequency of S6). Thus, the temperature of the cooling roller 52 can be prevented from rising excessively.

  The control unit 18 obtains the sheet thickness, the print mode, the coverage, the sheet width, and the in-machine temperature, and obtains the second threshold from these parameters with reference to the table of FIG. The table of FIG. 16 is stored in a predetermined storage area (for example, the ROM 102) of the image forming apparatus 100.

For example, the control unit 18 acquires information that the thickness of the sheet is 120 g / m ³ or more, acquires information that the printing mode is full color mode, and acquires information that the coverage is less than 50%. If the information that the width of the sheet is less than 210 mm is acquired and the in-machine temperature is acquired less than 10 degrees, 400 is acquired as the second threshold.

  According to the second embodiment, when the number of sheets continuously cooled by the cooler 55 (the number of continuous cooling sheets) becomes equal to or more than the first threshold, the image forming process (printing process) of the image forming apparatus 100 Stop. Therefore, the cooling roller 52 is cooled during the standby period even if the cooling effect of the cooling roller 52 is reduced due to the increase in the number of sheets of paper continuously cooled by the cooling roller of the cooler 55. The cooling effect of the lowered cooling roller 52 can be improved.

  Further, as a modification, when the period (continuous cooling period) in which the cooler 55 continuously cools the sheet becomes equal to or more than the second threshold, the image forming process (printing process) of the image forming apparatus 100 is stopped. . Therefore, the cooling roller 52 is cooled during the standby period even if the cooling effect of the cooling roller 52 is reduced by the prolonged period in which the cooling roller of the cooler 55 continuously cools the sheet. The cooling effect of the lowered cooling roller 52 can be improved.

  Further, both the first threshold and the second threshold are values according to the type of sheet, the print mode, and the environment of the image forming apparatus 100. Therefore, the determination process of S4 can be executed according to the type of paper, the print mode, and the environment of the image forming apparatus 100.

  Further, since the surface portion 52A of the cooling roller 52 has a low heat capacity, the temperature lowering characteristics of the cooling roller are also higher than when the cooling roller 52 is configured not to have a surface portion. Since the surface portion 52A of the cooling roller 52 has a low heat capacity, the waiting period (see S8) required to lower the same temperature is shorter than when the cooling roller 52 has a configuration without a surface portion. I'm sorry.

  As a modification, the control unit 18 may execute the determination process of S4 using the first threshold and the second threshold. In this case, for example, when the number of continuous coolings is equal to or larger than the first threshold and the continuous cooling period is equal to or larger than the second threshold, the control unit 18 determines YES in S4, and proceeds to S6. do it.

Third Embodiment
Next, a third embodiment will be described. In the third embodiment, the cooler 55 cools the sheet on which the toner image is fixed on the first side of the sheet. On the other hand, the sheet on which the toner image is fixed on the second side of the sheet is not cooled.

  FIG. 18 shows an example of the structure of the cooler 55 of the third embodiment. In the example of FIG. 18, the cooling roller is supported by the spacer 61. The separating member 61 is a member capable of pressing the cooling roller 52 against the opposing roller 51 and separating the same. The spacing member 61 includes a pointing member 60 and a biasing member 62 (in the example of FIG. 18, a spring). Further, the opposing roller 51 is provided with a biasing member 62 (a spring in the example of FIG. 18) for biasing the cooling roller 52.

  When the control unit 18 executes control for applying a force in the direction of arrow A in FIG. 18, the cooling roller 52 is urged against the opposing roller 51 by the biasing force of the biasing member 62 and the biasing force of the biasing member 62. It can be pressure-welded. On the other hand, when the control unit 18 executes control for applying a force in the direction of arrow B in FIG. 18, the cooling roller 52 is separated from the opposing roller 51.

  As described above, in the third embodiment, under the control of the control unit 18, it is possible to execute either the pressing process for pressing the cooling roller 52 against the sheet or the separation process for spacing the cooling roller 52 away. That is, by the control of the control unit 18, the sheet can be cooled or not cooled.

  FIG. 19 is a diagram illustrating a flowchart of processing performed by the control unit 18 according to the third embodiment. The process of FIG. 19 is a process executed by the control unit 18 when one job is input. First, in S102, the control unit 18 determines whether the job to be executed is a double-sided printing job. When it is judged as NO in S102, it progresses to S112. On the other hand, if it is determined YES in S102, the process proceeds to S104.

  Next, in step S104, the control unit 18 determines whether the first surface (surface) is to be cooled. When it is judged as NO by S104, it progresses to S112. On the other hand, when it is judged as YES by S104, it progresses to S106.

  In S106, the control unit 18 cools the sheet by executing the pressure contact process. As a result, by cooling the sheet in preparation for fixing the second side of the sheet, it is possible to prevent the deterioration of the quality of the image formed on the second side as much as possible.

  Next, in S108, the control unit 18 determines whether a sheet (a sheet determined as YES in S104) has passed through the cooler 55 on which the pressure contact process of S106 is being performed. In S108, the control unit 18 stands by until the sheet passes through the cooler 55 (NO in S108). If the control unit 18 determines in S108 that the sheet has passed the cooler 55, the process proceeds to S110.

  In S110, the control unit 18 executes separation processing. Thereby, the cooling roller 52 and the opposing roller 51 are separated. Then, in step S108, an unfixed toner image is formed on the second side (back side) of the sheet determined to have passed, and the unfixed toner image is fixed by the fixing device 30. The sheet on which the second side is fixed is conveyed to the cooler 55. However, since separation processing is performed in the cooler 55, the sheet is hardly cooled. That is, heat can be prevented from transferring to the cooling roller 52.

  When the process of S110 is completed (for example, when the sheet passes through the cooler 55 in which the separation process is performed), the process proceeds to S112. In S112, the control unit 18 determines whether one job that has triggered the start of the process of FIG. 19 has ended. If it is determined YES in S112, the process of FIG. 19 is ended. On the other hand, when it is judged as NO by S112, it returns to S102.

  According to the third embodiment, the cooler 55 cools the sheet on which the toner image is fixed on the first side of the sheet, but does not cool the sheet on which the toner image is fixed on the second side of the sheet. Therefore, the heat accumulated in the cooling roller 52 of the cooler 55 can be released while the cooler 55 is not cooling the sheet. Therefore, it is possible to prevent the cooling effect of the cooling roller 52 of the cooler 55 from being reduced. Further, the fixing process by the fixing device 30 is not performed on the sheet on which the toner image is fixed on the second side. Therefore, even when the sheet on which the toner image is fixed on the second side is cooled, no particular problem occurs.

Fourth Embodiment
Next, a fourth embodiment will be described. In the fourth embodiment, the opposite roller has a main body, and a surface provided on the surface of the main body and absorbing heat from the sheet. FIG. 20 is a diagram for explaining the fourth embodiment.

  The description of FIG. 20 differs from that of FIG. 18 in that the opposing roller 51 of FIG. 18 is replaced by the opposing roller 512. The opposing roller 512 includes a surface portion 512A (opposite surface portion) and a main body portion 512B (opposite main body portion). The main body 512B has a cylindrical shape (roller shape). The surface portion 512A is a surface layer formed along the circumference of the main portion 512B. That is, the opposing roller 512 is configured by coating the surface portion 512A on the surface layer of the main body portion 512B having a roller shape.

  In addition, the surface portion 512A may be a material including at least one of the first material and the second material. Further, the main body portion 512B may be a third material. It is preferable that the heat capacity of the surface portion 512A be configured to be lower than the heat capacity of the main portion 512B by the selection of such a material. Therefore, it is possible to transfer the heat of the sheet whose temperature is high to the outside (the outside air) of the opposing roller 512 without transferring the heat to the main body portion 521B as much as possible.

  Further, the thermal conductivity of the surface portion 512A is preferably lower than the thermal conductivity of the main portion 512B. Thereby, the temperature rise of the surface portion 52A can be suppressed by preventing the heat accumulated in the main body portion 512B (the cored bar inside the opposing roller) from being transferred to the surface portion 512A.

  The thermal conductivity of the surface portion 512A of the opposing roller 512 is preferably higher than the thermal conductivity of the surface portion 52A of the cooling roller 52. With such a configuration, the heat accumulated in the cooling roller 52 can be conducted to the opposing roller 512.

  Further, the heat capacity of the surface portion 512A of the opposing roller 512 is preferably lower than the heat capacity of the surface portion 52A of the cooling roller 52. With such a configuration, the heat of the surface portion 52A of the cooling roller 52 can be transferred not only to the outside air but also to the surface portion 512A of the opposing roller 512. Further, in the present embodiment (the example of FIG. 20), the cooling roller 52 is disposed on the side where the toner image is fixed by the fixing device 30. That is, the cooling roller 52 cools the surface on which the toner image is fixed by the fixing device 30. Therefore, even if the temperature of the surface portion 512A of the opposing roller 512 is increased, the first surface on which the toner image is fixed can be cooled by the surface portion 52A (the surface portion from which heat is released) of the cooling roller 52. Therefore, the quality of the image formed on the second side can be prevented as much as possible.

  Further, the material of the cooling roller 52 and the material of the opposing roller 512 may be the same. Thereby, compared with the image forming apparatus in which the material of the cooling roller 52 and the material of the facing roller 512 are different, the manufacturing cost of the cooler can be reduced.

  Moreover, it is preferable that the shape of the cooling roller 52 and the shape of the opposing roller 512 are the same. Thereby, compared with the image forming apparatus in which the material of the cooling roller 52 and the shape of the opposing roller 512 are different, the manufacturing cost of the cooler can be reduced.

Fifth Embodiment
Next, a fifth embodiment will be described. FIG. 21 is a diagram for explaining the fifth embodiment. In the example of FIG. 21, compared with the description of FIG. 20, both figures differ in the point by which the opposing roller 512 is substituted by the opposing pad 63. As shown in FIG.

  The opposing pad 63 is a pad different from the roller shape, for example, a shape having a rectangular cross section (for example, a plate shape), unlike a counter roller having a cylindrical shape. The opposing pad 63 also has a function of a conveyance guide for conveying the sheet P.

  In the example of FIG. 21, the facing pad 63 has a surface portion 62A (facing surface portion) and a main body portion 62B (facing main body portion).

  In addition, the surface portion 62A may be made of the same material as the surface portion 512A (see the fourth embodiment). Further, the main body portion 62B may be made of the same material as the surface portion 512B. With the cooler shown in FIG. 21, it is not necessary to use a roller member such as the opposing roller 512 shown in FIG. 20, while achieving the same effect as the image forming apparatus of the fourth embodiment. Can also reduce costs.

  As a modification, the shape of the above-mentioned cooling roller may be the same as that of the facing pad 63 shown in FIG. Even with such a configuration, the same effect as that of the above-described embodiment can be obtained.

  In addition, the facing pad 63 may not have the surface portion 62A (the facing surface portion). In this case, for example, the facing pad 63 is formed of a metal plate made of iron, aluminum or the like.

Sixth Embodiment
Next, a sixth embodiment will be described. FIG. 22 is a diagram for explaining the sixth embodiment. In the example of FIG. 22, the two figures are different in that the fixing device 30 is replaced with the fixing device 75 as compared with the description of FIG.

  The fixing device 75 includes a first fixing roller 70, a second fixing roller 72, a heat source 72h provided inside the second fixing roller 72, and an endless fixing belt 74. The fixing belt 74 is wound (tensioned) around the first fixing roller 70 and the second fixing roller 72. When the second fixing roller 72 rotates, the power of the rotation is transmitted to the first fixing roller 70 by the fixing belt 74. The power is transmitted to the first fixing roller 70, whereby the first fixing roller 70 rotates.

  Further, the heat generated from the heat source 72 h is transmitted to the second fixing roller 72. The heat transferred to the second fixing roller 72 is transferred to the first fixing roller 70 via the fixing belt 74. The sheet P is heated by the heat transferred to the first fixing roller 70. Thus, the unfixed toner image formed on the sheet P can be fixed.

Seventh Embodiment
A seventh embodiment will now be described. FIG. 23 is a diagram for explaining the seventh embodiment. In the example of FIG. 23, both inventions are different in that the first fixing roller 70 is replaced with the fixing pad 76 in comparison with the description of FIG.

  The fixing pad 76 has an abutting surface 76A that is in contact with the sheet P to be fixed. The contact surface 76A is curved. The heat generated from the heat source 72 h is transmitted to the second fixing roller 72. The fixing belt 75 is wound with a fixing pad 76 and a second fixing roller 72. The heat transferred to the second fixing roller 72 is transferred to the fixing pad 76 via the fixing belt 74.

  The sheet P is heated by the heat transferred to the fixing pad 76. Thus, the unfixed toner image formed on the sheet P can be fixed. Moreover, in the example of FIG. 23, although the shape of contact surface 76A is a curved shape, it is good also as another shape. For example, the abutment surface 76A may have a planar shape. Such a seventh embodiment can achieve the same effect as that of the previous embodiment.

Note that, as a modification, the pressure roller 31 may also be in a pad shape.
[Others]
The essential part of the present invention can be said to be software stored in a flash memory or other storage medium, or software downloadable via a network. The recording medium is not limited to DVD-ROM, CD-ROM, FD, hard disk, and may be a fixed type of semiconductor memory such as magnetic tape, cassette tape, optical disk, optical card, mask ROM, EPROM, EEPROM, flash ROM, etc. May be a medium that carries the program. Also, the recording medium is a non-transitory medium in which the program and the like can be read by a computer. Further, the program referred to here includes not only a program directly executable by the CPU but also a program of source program format, a compressed program, an encrypted program and the like.

  Further, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In addition, the invention described in the embodiment and each modification is intended to be implemented as much as possible, alone or in combination.

  51 opposing roller, 52 cooling roller, 52A surface, 52B body, 55 cooler.

Claims (12)

A fixing unit for fixing a toner image formed on a sheet;
And a cooling unit configured to cool the fixing sheet on which the toner image is fixed.
The cooling unit includes a main body, and a surface provided on a surface of the main body and pressed against the fixing sheet.
The image forming apparatus, wherein the heat capacity of the surface portion is lower than the heat capacity of the main body portion.   The image forming apparatus according to claim 1, wherein a thermal conductivity of the surface portion is lower than a thermal conductivity of the main body portion.   The image forming apparatus according to claim 1 or 2, wherein the image forming process of the image forming apparatus is stopped when the number of the fixing sheets continuously cooled by the cooling unit becomes equal to or more than a first threshold. .   4. The image forming apparatus according to claim 1, wherein the image forming process of the image forming apparatus is stopped when the time during which the cooling unit continuously cools the fixing sheet becomes equal to or greater than a second threshold. Image forming device. In the case where the fixing unit fixes the toner image formed on both sides of the sheet,
The cooling unit cools the fixing sheet on which the toner image is fixed on the first side of the sheet, but does not cool the fixing sheet on which the toner image is fixed on the second side of the sheet. The image forming apparatus according to claim 4.   The image forming apparatus according to any one of claims 1 to 5, further comprising: a facing portion facing the cooling portion and holding the cooling portion and the fixing sheet.   The image forming apparatus according to claim 6, wherein the facing portion includes a facing main body portion, and a facing surface portion provided on a surface of the facing main body portion and pressed against the fixing sheet.   The image forming apparatus according to claim 6, wherein a thermal conductivity of the facing surface portion is higher than a thermal conductivity of the surface portion.   The image forming apparatus according to any one of claims 1 to 8, wherein a heat capacity of the surface portion is 1/10 or less of a heat capacity of the main body portion.   The image forming apparatus according to any one of claims 1 to 9, wherein the surface portion is a resin, and the main body portion is solid.   The image forming apparatus according to any one of claims 1 to 10, wherein a thickness of the surface portion is 0.1 mm to 1 mm.   The image forming apparatus according to any one of claims 1 to 11, wherein the cooling unit is disposed at a position where it contacts within 0.5 seconds from a position where the toner image is fixed in the fixing unit. .

Images