Image forming system

Abstract

To provide an image forming system capable of effectively preventing image unevenness while minimizing layout restrictions of conveying members.SOLUTION: An image forming system is provided, comprising: a fixing unit for thermally fixing a toner image on a recording medium; and low-thermal-conductivity conveyor rollers having a lower thermal conductivity than one or more other conveyor rollers downstream of the fixing unit, the low-thermal-conductivity conveyor rollers being provided in a given region downstream of the fixing unit where a thermally fixed toner image reaches a glass transition temperature and configured to sandwich and convey the recording medium by means of a nip formed thereby.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming system. [Background technology]

[0002] In an electrophotographic image forming apparatus, for example, an electrostatic latent image formed by exposing a charged photosensitive member to light is developed with toner to form a toner image on the surface of the photosensitive member, and the toner image is then transferred to an intermediate transfer member, which then transfers the toner image to paper.The toner image on the paper is then heated and pressurized to form a fixing process that fixes the toner image to the paper, thereby forming an image on the paper.

[0003] When transporting paper with a fixed toner image, if the toner image comes into contact with the transport roller at the time the toner reaches its glass transition temperature, the cooling state of the wax contained in the toner may differ between the contacting and non-contacting areas, which may result in unevenness in the image.

[0004] The following prior art is disclosed in Patent Document 1: A transport roller is provided downstream of a fixing unit that fixes a toner image to a sheet. The transport roller rotates in contact with the toner fixing surface of the sheet being transported with the fixed toner image. The transport roller is located upstream in the sheet transport direction from the point where the toner image reaches its glass transition temperature. The transport roller is composed of a core material and a surface layer member made of a resin material that covers the core material. This reduces the thermal conductivity of the transport roller's surface, thereby reducing the temperature difference between the area where the transport roller comes into contact with toner at a temperature higher than the toner's glass transition temperature and other areas, thereby suppressing the generation of roller marks caused by the transport roller. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-129091 Summary of the Invention [Problem to be solved by the invention]

[0006] However, because the toner state becomes more unstable when the toner image reaches its glass transition temperature, temperature differences in the toner image at the glass transition temperature increase the likelihood of image unevenness. In the configuration of the above-mentioned prior art, it is necessary to avoid installing a transport roller or transport rollers in the area where the toner image reaches its glass transition temperature, which places restrictions on the layout of the transport components. Furthermore, although the above-mentioned prior art reduces the thermal conductivity of the transport roller surface, the transport rollers' contact with the paper is relatively unstable, so the possibility of image unevenness still remains. Furthermore, because the transport rollers do not have the driving force to transport the paper, the toner image on the paper must be cooled below its glass transition temperature before the paper is transported to the drive roller, which is the first to contact the paper downstream of the fixing unit.

[0007] The present invention has been made to solve such problems, and an object of the present invention is to provide an image forming system that can effectively prevent the occurrence of image unevenness while minimizing restrictions on the layout of the transport members. [Means for solving the problem]

[0008] The above-mentioned problems of the present invention are solved by the following means.

[0009] (1) An image forming system having a fixing unit that heat-fixes a toner image onto a recording medium, and a low-thermal conductivity transport roller that is provided in a predetermined area downstream of the fixing unit and has a lower thermal conductivity than one or more other transport rollers downstream of the fixing unit, and that transports the recording medium by nipping it with a nip formed therein, so that the toner image reaches its glass transition temperature after heat fixing.

[0010] (2) The image forming system according to (1), wherein the nip pressure of the low thermal conductivity transport roller is variable.

[0011] (3) The image forming system according to (1) above, wherein the low thermal conductivity transport roller has a roller surface made of a resin material with a porous structure.

[0012] (4) The image forming system according to (1) above, wherein the low thermal conductivity transport roller is a roller having a width wider than the maximum image width.

[0013] (5) The image forming system described in (1) above, wherein the low thermal conductivity transport roller is a plurality of rollers each having a width narrower than the maximum image width, spaced apart from one another in a direction perpendicular to the transport direction of the recording medium.

[0014] (6) The image forming system according to (1) above, further comprising a control unit that controls at least one of decelerating and stopping the low thermal conductivity transport roller.

[0015] (7) The image forming system according to (1), wherein the low thermal conductivity transport roller is provided at a position on the double-sided circulating transport path where the transport direction of the recording medium is reversed.

[0016] (8) The image forming system according to (1) above, further comprising a cooling unit that cools the recording medium, the cooling unit being disposed downstream of the fixing unit and upstream of the low thermal conductivity transport roller.

[0017] (9) An image forming system as described in (1) above, wherein the low thermal conductivity transport roller is the roller that contacts the toner image among the multiple rollers forming the nip, and has a lower thermal conductivity than one or more other transport rollers downstream of the fixing unit.

[0018] (10) The image forming system according to (1), wherein a plurality of the low thermal conductivity transport rollers are arranged consecutively in the transport direction of the recording medium. [Effects of the Invention]

[0019] A low-thermal-conductivity transport roller, which has a lower thermal conductivity than one or more other transport rollers downstream of the fixing unit, is provided in a predetermined area downstream of the fixing unit where the toner image reaches its glass transition point after heat fixing. This reduces restrictions on the layout of the transport members, suppresses heat absorption from the toner image by the transport roller, and maintains a constant contact state between the transport members and the toner image, thereby effectively preventing image unevenness. [Brief explanation of the drawings]

[0020] Advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for purposes of illustration only and are not intended to be limiting. [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [Figure 2] FIG. 1 is a block diagram showing a configuration of an image forming apparatus. [Figure 3] FIG. 10 is an explanatory diagram showing the state of toner on a graph of the relationship between toner temperature and hardness; [Figure 4] FIG. 2 is a partial enlarged view of a paper transport unit including an ADU transport path. [Figure 5] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [Figure 6] FIG. 2 is a schematic diagram illustrating the configuration of an image forming apparatus and a charge adjusting device. DETAILED DESCRIPTION OF THE INVENTION

[0021] An image forming system according to an embodiment of the present invention will be described below with reference to the drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the drawings, identical elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0022] (First embodiment) Fig. 1 is a schematic diagram showing the configuration of an image forming apparatus 100. Fig. 2 is a block diagram showing the configuration of the image forming apparatus 100. The image forming apparatus 100 constitutes an image forming system 1. In other words, the image forming system 1 can be constituted by only the image forming apparatus 100.

[0023] Image forming apparatus 100 includes a control unit 110, a storage unit 120, a communication unit 130, an operation display unit 140, an image reading unit 150, an image control unit 160, and an image forming unit 170. These components are communicably connected to one another via a bus 180. Image forming apparatus 100 may be configured as an MFP (Multi Function Peripheral).

[0024] The control unit 110 includes a CPU (Central Processing Unit) and various memories, and controls the above-mentioned units and performs various arithmetic processing according to a program.

[0025] The storage unit 120 is configured by a solid state drive (SDD) or a hard disk drive (HDD), and stores various programs and various data.

[0026] The communication unit 130 is an interface for communicating between the image forming apparatus 100 and an external device. A network interface conforming to standards such as Ethernet (registered trademark), SATA, or IEEE1394 is used as the communication unit 130. Alternatively, various local connection interfaces such as wireless communication interfaces such as Bluetooth (registered trademark) or IEEE802.11 are used as the communication unit 130.

[0027] The operation display unit 140 includes a touch panel, a numeric keypad, a start button, a stop button, and the like, and is used to display various information and input various instructions.

[0028] Image reading unit 150 has a light source such as a fluorescent lamp and an imaging element such as a CCD (Charge Coupled Device) image sensor. Image reading unit 150 irradiates a document set at a predetermined reading position with light from the light source, photoelectrically converts the reflected light with the imaging element, and generates image data from the electrical signal.

[0029] The image control unit 160 performs layout processing and rasterization processing on the print data included in the print job or the like received by the communication unit 130, and generates image data in bitmap format.

[0030] A print job is a general term for a print command to image forming apparatus 100, and includes print data and print settings. Print data is document data to be printed, and may include various types of data, such as image data, vector data, and text data. Specifically, print data may be PDL (Page Description Language) data, PDF (Portable Document Format) data, or TIFF (Tagged Image File Format) data. Print settings are settings related to image formation on paper 900, and may include various settings such as the number of pages, number of copies, paper type, selection of color or monochrome, double-sided printing, and page layout.

[0031] Image forming section 170 includes an image creating section 40, a fixing section 50, a paper feeding section 60, and a paper transport section 70. Paper transport section 70 forms a transport path for transporting paper 900 by a plurality of transport rollers 72.

[0032] The image forming unit 40 has image forming units 41Y, 41M, 41C, and 41K corresponding to the toners of the respective colors of Y (yellow), M (magenta), C (cyan), and K (black). Each image forming unit 41Y, 41M, 41C, and 41K forms a toner image on the photosensitive drum 42 through processes of charging, exposure, and development based on image data. Exposure is performed by scanning the photosensitive drum 42 with a laser beam. The toner images formed on the photosensitive drum 42 are sequentially superimposed and primarily transferred onto the intermediate transfer belt 43 by electrostatic force generated by a constant-voltage-controlled transfer voltage applied to the primary transfer roller 44. This results in a color toner image being held on the intermediate transfer belt 43. The color toner images on the intermediate transfer belt 43 are then secondarily transferred onto the paper 900 by the secondary transfer roller 45.

[0033] Fixing unit 50 includes fixing roller 51a and pressure roller 52, and fixing roller 51a and pressure roller 52 are pressed against each other to form a nip between fixing roller 51a and pressure roller 52. Fixing unit 50 heats and presses paper 900 conveyed to the nip at the nip, and rotates fixing roller 51a and pressure roller 52, thereby heat-fixing the toner image on paper 900 to the surface of paper 900.

[0034] The paper 900 on which the toner image has been heat-fixed is discharged onto the paper discharge tray 90 by the transport rollers 72 .

[0035] If the print setting of the print job is double-sided printing, the paper transport unit 70 transports the paper 900, on whose front side a toner image has been heat-fixed, to an ADU (Auto Duplex Unit) transport path 80. The paper 900 transported to the ADU transport path 80 is turned over in a switchback path, and then merges with the transport path 71, where an image is formed again on the back side of the paper by the image forming unit 170. The ADU transport path 80 constitutes a double-sided circulating transport path.

[0036] The temperature of the toner image that has been heat-fixed to the surface of paper 900 by fixing unit 50 decreases over time and reaches the glass transition point. More specifically, the temperature of the wax contained in the toner that forms the toner image decreases, and the wax reaches the glass transition point.

[0037] FIG. 3 is an explanatory diagram showing the state of the toner on a graph showing the relationship between the temperature and hardness of the toner.

[0038] Toner becomes liquid at temperatures above its melting point Tm. At this time, the toner is fluid, the wax crystals are broken, and the molecules are actively moving. Toner becomes rubbery at temperatures below its melting point and above its glass transition temperature Tg. At this time, the toner is solid, but as the temperature drops, it grows from highly mobile amorphous to crystalline. Toner becomes glassy at temperatures below its glass transition temperature Tg. At this time, the toner is solid, and both the crystalline and amorphous parts have low mobility.

[0039] Since the state of the toner becomes more unstable when the toner image reaches its glass transition temperature, if a temperature difference occurs in the toner image that has reached its glass transition temperature, the possibility of image unevenness increases. Therefore, in order to prevent the occurrence of image unevenness, it is important to prevent a temperature difference from occurring in the toner image when the toner image reaches its glass transition temperature.

[0040] After the toner image is heat-fixed to the paper 900, if the paper 900 is sandwiched in the nip of the transport rollers 72 when the temperature of the toner image reaches its glass transition temperature, the toner image on the paper 900 may come into contact with the transport roller 72, causing heat to be locally removed. This can result in a temperature difference between the portion of the toner image on the paper 900 that is in contact with the transport roller 72 and the portion that is not. Even if the transport roller 72 is wider than the maximum image width, the contact state between the transport roller 72 and the paper 900 can be partially different due to bending of the roller's rotation axis when the nip is formed, etc. Therefore, the above-mentioned temperature difference can occur even if the transport roller 72 is wider than the maximum image width.

[0041] FIG. 4 is a partially enlarged view of the paper transport section 70 including the ADU transport path 80. As shown in FIG.

[0042] In Figure 4, a glass transition temperature reaching region 81 where the toner image on the transported paper 900 reaches its glass transition temperature is indicated by a dashed line. The glass transition temperature reaching region 81 may include the point where the toner image reaches its glass transition temperature. The glass transition temperature reaching region 81 constitutes a "predetermined region." The glass transition temperature reaching region 81 may change depending on the transport speed of the paper 900, etc.

[0043] In the example of FIG. 4, the position on the ADU transport path 80 where the paper 900 is transported with its transport direction reversed is the glass transition temperature reaching region 81.

[0044] The transport roller 72 located in the glass transition temperature reaching region 81 is a low-thermal conductivity transport roller 73 having a lower thermal conductivity than the other transport roller or rollers 72 downstream of the fixing unit 50. Specifically, the low-thermal conductivity transport roller 73 is located in a predetermined region downstream of the fixing unit 50 where the toner image reaches its glass transition temperature and nip the paper 900 between the transport roller 72 and the nip. This minimizes limitations on the layout of the transport members, suppresses heat absorption from the toner image by the transport roller 72, and ensures consistent contact between the transport member and the toner image, effectively preventing image unevenness. The low-thermal conductivity transport roller 73 is preferably the roller with the lowest thermal conductivity among the transport rollers 72 downstream of the fixing unit 50.

[0045] The low thermal conductivity transport roller 73 is configured, for example, by a roller whose roller surface is made of a porous resin material. In this case, the transport rollers 72 downstream of the fixing unit 50 other than the low thermal conductivity transport roller 73 are configured, for example, by a roller whose roller surface is made of a rubber material such as urethane.

[0046] The low thermal conductivity transport roller 73 may be such that only the roller that contacts the toner image among the multiple rollers forming the nip has a lower thermal conductivity than the other one or more transport rollers 72 downstream of the fixing unit 50. This makes it possible to prevent image unevenness while suppressing an increase in the cost of the device.

[0047] As described above, in the example of FIG. 4 , the glass transition temperature reaching region 81 is the position on the ADU transport path 80 where the paper 900 is transported after the transport direction has been reversed. Therefore, the low thermal conductivity transport roller 73 is provided at the position on the ADU transport path 80 where the paper 900 is transported after the transport direction has been reversed. The low thermal conductivity transport roller 73 provided at the position on the ADU transport path 80 where the paper 900 is transported after the transport direction has been reversed is controlled to slow down and stop by the control unit 110. If the toner image on the paper 900 is held between the rollers for a long time after reaching its glass transition temperature, the temperature difference between the portion of the toner image that contacts the roller and the portion that does not contact the roller may increase. Therefore, by using the low thermal conductivity transport roller 73 as the transport roller 72 provided at the position on the ADU transport path 80 where the paper 900 is transported after the transport direction has been reversed and controlled to slow down and stop, the occurrence of image unevenness can be more effectively prevented.

[0048] The low thermal conductivity transport roller 73 may be a roller with a width wider than the maximum image width, which eliminates any areas that do not come into contact with the toner image, thereby preventing unevenness in the image.

[0049] The low thermal conductivity transport roller 73 may be a roller in which a plurality of rollers, each having a width narrower than the maximum image width, are arranged at a distance from each other in a direction perpendicular to the transport direction of the paper 900. In this case, using the low thermal conductivity transport roller 73 as the roller can increase the effect of preventing the occurrence of image unevenness.

[0050] The low-thermal conductivity transport roller 73 may be a roller with variable nip pressure. The nip pressure can be changed, for example, by changing the distance between the shafts of each roller of the pair of rollers that make up the low-thermal conductivity transport roller 73 using a cam or the like. If the low-thermal conductivity transport roller 73 is not effective in preventing image unevenness, the nip pressure of the low-thermal conductivity transport roller 73 can be reduced. This narrows the nip width where the paper 900 contacts the low-thermal conductivity transport roller 73, thereby improving the low-thermal conductivity transport roller 73's effectiveness in preventing image unevenness. Separating the rollers that form the nip of the low-thermal conductivity transport roller 73 to set the nip pressure to zero also improves the low-thermal conductivity transport roller 73's effectiveness in preventing image unevenness.

[0051] A plurality of low thermal conductivity transport rollers 73 can be arranged consecutively in the transport direction of the paper 900. In the example of FIG. 4, three low thermal conductivity transport rollers 73 are arranged consecutively in the transport direction of the paper 900. At temperatures around the glass transition point of the toner, the toner undergoes a relatively gradual transition from a rubbery state to a glassy state, and the hardness also transitions relatively gradual. Therefore, by arranging a plurality of low thermal conductivity transport rollers 73 consecutively in the transport direction of the paper 900, the effect of preventing image unevenness can be further improved.

[0052] (Second embodiment) A second embodiment will be described. The present embodiment differs from the first embodiment in the following respects. In this embodiment, a cooling unit 74 (see FIG. 5) is provided downstream of the fixing unit 50 and upstream of the low thermal conductivity transport roller 73. In other respects, this embodiment is similar to the first embodiment, and therefore a duplicated description will be omitted.

[0053] FIG. 5 is a schematic diagram showing the configuration of the image forming apparatus 100. As shown in FIG.

[0054] 5, a cooling unit 74 is provided downstream of the fixing unit 50 and upstream of the low thermal conductivity transport roller 73. When different paper materials such as coated paper and synthetic paper are used as the paper 900, when paper 900 with different basis weights such as thin paper and thick paper is used, or when the amount of toner in the toner image is different, the glass transition temperature reaching region 81 may vary.

[0055] In this embodiment, the temperature of the paper 900 is controlled by a cooling unit 74 provided downstream of the fixing unit 50 and upstream of the low thermal conductivity transport roller 73. This prevents fluctuations in the glass transition temperature reaching region 81. The cooling unit 74 may be configured, for example, by a fan. The temperature of the paper 900 is controlled by the control unit 110 controlling the power supplied to the fan, which is the cooling unit 74, so that the glass transition temperature reaching region 81 becomes a predetermined region.

[0056] (Third embodiment) A third embodiment will now be described. The present embodiment differs from the first embodiment in the following respects. In this embodiment, a charge adjustment device 200 is provided that adjusts the charge of paper 900 on which an image has been formed by image forming apparatus 100, and a charging roller 220 of the charge adjustment device 200 serves as a low thermal conductivity transport roller 73. In other respects, this embodiment is similar to the first embodiment, and therefore a duplicated description will be omitted.

[0057] FIG. 6 is a schematic diagram showing the configuration of image forming apparatus 100 and charge adjustment device 200. As shown in FIG.

[0058] Image forming apparatus 100 and charge adjustment apparatus 200 constitute an image forming system 1 .

[0059] The charge adjustment device 200 includes a control unit 210, a charging roller 220, and a paper discharge roller 230. The paper discharge roller 230 also functions as the transport roller 72 to transport the paper 900.

[0060] The charging roller 220 charges the paper 900 on which an image has been formed by the image forming apparatus 100 to prevent the paper 900 from sticking together. When the paper 900 passes through the nip of the charging roller 220, the paper 900 is charged. This adjusts the charge on the paper 900. A charge adjustment power supply (not shown) is connected to the charging roller 220. The charging roller 220 also serves as the transport roller 72 to transport the paper 900.

[0061] When the charge adjustment device 200 is provided, a roller within the charge adjustment device 200 can be a roller provided in the glass transition temperature reaching region 81. For this reason, in this embodiment, the charging roller 220 provided in the glass transition temperature reaching region 81 is the low thermal conductivity transport roller 73. The charging roller 220 is configured with a roller whose roller surface is made of a porous resin material. As a result, the charging roller 220 is configured as the low thermal conductivity transport roller 73 whose thermal conductivity is lower than that of the other one or more transport rollers 72 and the paper discharge roller 230 downstream of the fixing unit 50. In this case, the transport rollers 72 and the paper discharge roller 230 other than the low thermal conductivity transport roller 73 downstream of the fixing unit 50 can be configured with rollers whose roller surfaces are made of a rubber material such as urethane.

[0062] The embodiment has the following advantages.

[0063] A low-thermal-conductivity transport roller, which has a lower thermal conductivity than one or more other transport rollers downstream of the fixing unit, is provided in a predetermined area downstream of the fixing unit where the toner image reaches its glass transition point after heat fixing. This reduces restrictions on the layout of the transport members, suppresses heat absorption from the toner image by the transport roller, and maintains a constant contact state between the transport members and the toner image, thereby effectively preventing image unevenness.

[0064] In addition, the nip pressure of the low thermal conductivity transport roller can be made variable. This allows the nip width to be narrowed, improving the effectiveness of the low thermal conductivity transport roller in preventing image unevenness. Furthermore, by separating the rollers that form the nip of the low thermal conductivity transport roller and setting the nip pressure to zero, the effectiveness of the low thermal conductivity transport roller in preventing image unevenness can be improved.

[0065] Furthermore, the low thermal conductivity transport roller is configured by a roller whose surface is made of a porous resin material, which can effectively improve the effect of preventing image unevenness.

[0066] Furthermore, the low thermal conductivity transport roller is a roller with a width wider than the maximum image width, which eliminates any areas that do not come into contact with the toner image, thereby suppressing the occurrence of image unevenness.

[0067] Furthermore, the low thermal conductivity transport roller is a roller in which a plurality of rollers each having a width narrower than the maximum image width are arranged at a distance from each other in a direction perpendicular to the transport direction of the recording medium, thereby increasing the effect of preventing image unevenness by using the roller as a low thermal conductivity transport roller.

[0068] The printer also includes a control unit that controls the low thermal conductivity transport rollers to at least either slow down or stop them, thereby increasing the effectiveness of preventing image unevenness by using low thermal conductivity transport rollers in areas where control is required to at least either slow down or stop them.

[0069] Furthermore, a low thermal conductivity transport roller is provided at a position on the double-sided circulating transport path where the recording medium is transported with the transport direction reversed, thereby preventing image unevenness simply and effectively.

[0070] The cooling unit is located downstream of the fixing unit and upstream of the low thermal conductivity transport roller, and cools the recording medium, thereby preventing fluctuations in the glass transition temperature range.

[0071] Furthermore, the low thermal conductivity transport roller is the only one of the multiple rollers forming the nip that comes into contact with the toner image, and has a thermal conductivity lower than that of the other transport roller or rollers downstream of the fixing unit, thereby preventing image unevenness while suppressing increases in the cost of the device.

[0072] Furthermore, by arranging a plurality of low thermal conductivity transport rollers in succession in the transport direction of the recording medium, the effect of preventing image unevenness can be further improved.

[0073] The present invention is not limited to the above-described embodiments.

[0074] For example, the low thermal conductivity transport roller 73 may be any roller having a lower thermal conductivity than the other one or more transport rollers 72 downstream of the fixing unit 50, and is not limited to a roller whose roller surface is made of a porous resin material. Therefore, by devising the material, structure, etc., the low thermal conductivity transport roller 73 can be configured as any roller whose thermal conductivity is lower than the other one or more transport rollers 72 downstream of the fixing unit 50.

[0075] While embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and are not intended to be limiting, and the scope of the present invention should be construed by the language of the appended claims. [Explanation of symbols]

[0076] 41Y, 41M, 41C, 41K imaging units, 42 photosensitive drum, 43 Intermediate transfer belt, 44 Primary transfer roller, 50 fixing section, 51a fuser roller, 52 pressure roller, 71 conveying route, 72 conveying roller, 73 Low thermal conductivity transport roller, 74 Cooling section, 80 ADU transport route, 81 Glass transition temperature range, 44 Primary transfer roller, 100 Image forming device, 110 control section, 120 storage section, 130 Communications Department, 140 Operation display section, 150 image reading unit, 160 Image control unit, 170 Image forming unit.

Claims

1. a fixing unit that heats and fixes the toner image onto the recording medium; a low-thermal-conductivity transport roller that is provided in a predetermined area downstream of the fixing unit and has a lower thermal conductivity than one or more other transport rollers downstream of the fixing unit, and that has a temperature at which the toner image reaches a glass transition temperature after heat fixing, and that transports the recording medium while nipping it with a nip formed therein; An image forming system having:

2. The image forming system according to claim 1 , wherein the nip pressure of the low thermal conductivity transport roller is variable.

3. 2. The image forming system according to claim 1, wherein the low thermal conductivity transport roller has a roller surface made of a resin material with a porous structure.

4. 2. The image forming system according to claim 1, wherein the low thermal conductivity transport roller is a roller having a width wider than a maximum image width.

5. 2. The image forming system according to claim 1, wherein the low thermal conductivity transport roller is a plurality of rollers each having a width narrower than a maximum image width and arranged at intervals in a direction perpendicular to the transport direction of the recording medium.

6. The image forming system according to claim 1 , further comprising a control unit that controls at least one of decelerating and stopping the low thermal conductivity transport roller.

7. The image forming system according to claim 1 , wherein the low thermal conductivity transport roller is provided at a position on the double-sided circulating transport path where the transport direction of the recording medium is reversed.

8. 2. The image forming system according to claim 1, further comprising a cooling unit that cools the recording medium, the cooling unit being provided downstream of the fixing unit and upstream of the low thermal conductivity transport roller.

9. 2. The image forming system of claim 1, wherein the low thermal conductivity transport roller is such that only the roller that contacts the toner image among the plurality of rollers forming the nip has a lower thermal conductivity than one or more other transport rollers downstream of the fixing unit.

10. The image forming system according to claim 1 , wherein a plurality of the low thermal conductivity transport rollers are arranged consecutively in the transport direction of the recording medium.

Images