JP2006330556A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a fixing device without causing poor fixing image quality by gloss level difference to a transfer material. <P>SOLUTION: In the image forming apparatus provided with the fixing device which has a rotatable fixing member heated by a heating means and a rotatable pressurization member brought into pressure-contact with the fixing member to form a nip part and fixes unfixed toner on the transfer material by passing the transfer material through the nip part, it is provided with a cooling means for cooling the pressurization member and a preheating means for heating the transfer material before entering the nip part and a control means for controlling the cooling means and the preheating means so that temperature difference between the pressurization member and the transfer material becomes small. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a fixing device that fixes unfixed toner onto a transfer material by heating and pressing a transfer material carrying an unfixed toner image while being nipped and conveyed by a fixing member and a pressure member.

  In recent years, color electrophotographic image forming devices have come to be used in place of conventional printing devices, taking advantage of small lots, short delivery times, and low costs, resulting in higher speed and higher image quality. It has been demanded.

  In a fixing device in which a toner is melted and fixed on a transfer material by applying heat and pressure with a fixing member and a pressure member, a glossy image is required. Therefore, the toner surface is sufficiently melted to smooth the surface of the toner after fixing. .

  Hot offset is likely to occur when the temperature is high to sufficiently dissolve the toner. For this reason, the toner may contain WAX, oil may be applied to the surface of the fixing member, or the surface of the fixing member may be coated with a highly releasable material. Thus, the release property between the toner and the surface of the fixing member is improved.

  Further, if the surface of the fixing member is hard, the toner is not melted uniformly and an image with uneven glossiness is formed. Therefore, an elastic member such as silicon rubber is used to achieve uniform melting. In addition, in order to obtain a uniform glossy image, a coated paper whose transfer material surface is coated with a resin layer may be used.

  Further, as a recent trend, if characters and the like are too glossy, they are difficult to see and have been kept within an appropriate gloss range.

  As described above, various techniques for increasing or controlling the glossiness have been proposed, but as described in detail in “Problems to be Solved by the Invention”, when viewed in the transfer material conveyance direction, It was found that there was a step in the gloss on the transfer material.

  This is a new problem and there was no appropriate reference to solve this.

  As described above, the inventors have found that there is a problem of a gloss level difference that affects the high image quality while researching on a uniform glossy image.

  Hereinafter, the gloss level difference will be briefly described.

  For example, in a fixing device that fuses and fixes toner while sandwiching and transporting a transfer material between a fixing roller that includes a heating source and a pressure roller, the surface temperature of the fixing roller immediately after passing through the fixing nip is deprived of heat by the transfer material. A temperature difference is generated at a position corresponding to the paper passing portion and the inter-paper portion where heat is not removed.

  Silicone rubber on the surface of the fixing roller and polyimide used for the fixing belt substrate are poor in heat conduction compared to metal, and therefore remain at a high speed even after one rotation when the temperature difference is heated.

  Since the level of gloss corresponds to the fixing roller temperature, it is recognized as a gloss level difference at the boundary of the temperature difference.

  In a conventional high-gloss color image, the gloss with respect to the fixing temperature is saturated, and even if there is a temperature difference, it is difficult to recognize because the gloss difference is small.

  However, the difference in gloss has become more conspicuous in an image with a moderate gloss range.

  The temperature difference increases as the difference between the transfer material temperature and the pressure roller surface temperature increases.

  Normally, the transfer material temperature is substantially equal to and constant at room temperature (around 20 °), so that the higher the pressure roller temperature, the larger the temperature difference and the more noticeable gloss difference becomes.

  The pressure roller temperature changes depending on the conditions such as the sheet passing mode (double-sided / single-sided, continuous / intermittent), transfer material size, transfer material basis weight, etc., one of these conditions, or a combination of these conditions Depending on the direction, the temperature of the pressure roller becomes higher, and the gloss level difference becomes conspicuous.

  Examples of conditions for increasing the pressure roller temperature include the following.

  During continuous image formation, the shorter the transfer material length, the longer the distance between sheets with respect to the sheet passing distance, and the higher the pressure roller temperature.

  This is because the pressure roller temperature is determined by subtracting the temperature given from the fixing roller and the amount of heat taken by the transfer material.

  Even during double-sided image formation, the distance between the transfer materials is increased by the time of reversing the front and back, so that the pressure roller temperature increases.

  Even in the intermittent mode in which a small amount of image formation is repeated, the pressure roller temperature becomes high.

  Further, when the basis weight of the transfer material is small, that is, when the transfer material is thin, the amount of heat taken away by the transfer material is reduced, and the temperature of the pressure roller becomes high.

  As described above, when the fixing process is performed under the condition that the temperature of the pressure roller becomes high, the above-described problem of gloss level difference occurs.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus including a fixing device that does not cause a fixing image quality defect due to a gloss difference in a transfer material.

The object of the present invention can be achieved by the following constitution.
(Claim 1)
A fixing member that is heated and rotated by a heating means; and
A rotatable pressure member that presses against the fixing member to form a nip portion;
In an image forming apparatus provided with a fixing device for passing a transfer material through the nip portion and fixing unfixed toner on the transfer material,
Cooling means for cooling the pressure member;
Preheating means for heating the transfer material before entering the nip portion,
An image forming apparatus comprising: a control unit that controls the cooling unit and the preheating unit so that a temperature difference between the pressure member and the transfer material is reduced.
(Claim 2)
Information of temperature detection means for detecting the temperature of the pressure member, or at least one of image forming number, transfer material size, transfer material type, transfer material basis weight, and single-sided copy or double-sided copy paper passing mode The image forming apparatus according to claim 1, wherein the cooling unit and the preheating unit are controlled based on one piece of information.
(Claim 3)
3. The image forming apparatus according to claim 1, wherein the heat source of the preliminary heating unit is waste hot air when the pressure member is cooled. 4.

  According to the first aspect of the present invention, a fixing image quality defect due to a gloss level difference is generated in the transfer material by controlling the cooling unit and the preheating unit so that the temperature difference between the pressure member and the transfer material becomes small. It is possible to provide an image forming apparatus provided with a fixing device without any problem.

  In order to reduce the temperature difference between the pressure member and the transfer material, when only the pressure member is cooled and the temperature is lowered, the temperature difference between the fixing member and the pressure member becomes large. There is a risk that the temperature difference between the front and back of the transfer material will increase and curl will occur, causing jams in the paper discharge process, post-processing process, and duplex copying process.

  On the other hand, in order to reduce the temperature difference between the pressure member and the transfer material, when performing only the transfer material preheating, a large amount of electric power and a large preheating device are required, resulting in an increase in cost.

  However, as in the present invention, by performing both cooling of the pressure member and heating of the transfer material, it is possible to prevent the occurrence of a gloss step while suppressing curling of the transfer material and suppressing power consumption and the enlargement of the apparatus. .

  In addition, by preheating the transfer material, the moisture content of the transfer material can be reduced, and by lowering the temperature of the pressure member, the amount of moisture evaporation from the transfer material can be suppressed during fixing. It is possible to prevent toner blisters (blowing due to bubbles) from occurring on the fixed toner surface.

  A technique for cooling the pressure roller has been proposed in Japanese Patent Application Laid-Open No. 10-48881. In order to suppress the temperature rise at the non-sheet passing end portion of the fixing (heating) roller during the small width sheet passing, The non-sheet passing portion of the pressure roller is cooled. In the sheet passing portion, the temperature of the pressure roller rises, so that a gloss level difference occurs.

  A technique for heating a transfer material before fixing is proposed in Japanese Patent Application Laid-Open Nos. 2003-295648 and 2003-271007. In Japanese Patent Application Laid-Open No. 2003-295648, fixing (heating) is performed by passing paper. In order to reduce the amount of heat taken away from the roller and consequently suppress the temperature rise of the non-sheet passing portion, Japanese Patent Laid-Open No. 2003-271007 heats the transfer material in order to prevent the fixing strength from being lowered by the transfer material. Therefore, if the temperature increase of the pressure roller increases due to the increase in the temperature of the transfer material, and the temperature difference between the transfer material and the pressure roller does not decrease, a gloss level difference occurs.

  According to the invention of claim 2, information of the temperature detecting means for detecting the temperature of the pressure member, or the number of image formations, the transfer material size, the type of transfer material, the basis weight of the transfer material, single-sided copy or double-sided copy By controlling the cooling means and the preheating means based on at least one information in the sheet passing mode, it is possible to accurately reduce the temperature difference between the pressure member and the transfer material.

  According to the invention of claim 3, by using the waste heat air when the pressurizing member is cooled as the heat source of the preheating means, it is possible to reduce the size of the apparatus and save power.

  An example of an embodiment of the present invention will be described with reference to the drawings. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

  An image forming apparatus provided with a fixing device according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an image forming apparatus.

  In FIG. 1, the image forming apparatus GS includes an image forming apparatus main body GH and an image reading apparatus YS.

  The image forming apparatus main body GH is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 6, a sheet feeding and conveying unit, and a fixing unit to be described later. It consists of device 9 and the like.

  An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus main body GH. The document D placed on the document table of the automatic document feeder 201 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202, and the line image sensor CCD is scanned. Is read.

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to processing such as analog processing, A / D conversion, shading correction, and image compression processing in the image processing unit, and once stored in the memory, the image writing unit (Exposure means) 3Y, 3M, 3C, 3K.

  An image forming unit 10Y that forms a yellow (Y) image includes a photosensitive drum 1Y as an image carrier, a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 8Y disposed around the photosensitive drum 1Y. An image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 8M. An image forming unit 10C for forming a cyan (C) image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 8C. An image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 8K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  Each of the developing devices 4Y, 4M, 4C, and 4K includes a two-component developer composed of a toner having a small particle diameter and a carrier of yellow (Y), magenta (M), cyan (C), and black (K). .

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred (primary transfer) and synthesized on the rotating intermediate transfer body 6 by the transfer units 7Y, 7M, 7C, and 7K. A color image is formed. The recording paper P as a transfer material accommodated in the paper feed cassette 20 is fed by the paper feed means 21 and conveyed to the transfer means 7A via the paper feed rollers 22A, 22B, 22C, 22D, the registration rollers 23, and the like. Then, the color image is transferred onto the recording paper P (secondary transfer). The recording paper P onto which the color image has been transferred is sandwiched between the recording paper P in a nip portion N (see FIG. 2, not shown in FIG. 1) formed in the fixing device 9, and is recorded by applying heat and pressure. The color toner image (or toner image) on the paper P is fixed and fixed on the recording paper P, and is sandwiched between the paper discharge rollers 24 on the paper discharge path side and placed on the paper discharge tray 25 outside the apparatus. .

  At the time of double-sided image formation, a color image (color toner image) is formed on one side (first side), and the recording paper P fixed by the fixing device 9 is branched from the sheet discharge path by the branching unit 26, Through the lower circulating paper path 27A, which respectively constitutes the paper feeding and conveying means, the front and back are reversed by the reversing conveyance path 27B that is the refeed mechanism (ADU mechanism), and passes through the refeed conveyance section 27C. The paper feed roller 22D joins the transport path of the recording paper P supplied from the paper feed cassette 20.

  The recording paper P that has been reversed (circulated and reversed) is conveyed again to the secondary transfer roller 7A through the registration roller 23, and a color image (color toner image) is formed on the other surface (second surface) of the recording paper P. ) Is batch transferred. The recording paper P to which the color image has been transferred is fixed by the fixing device 9 and is sandwiched between the paper discharge rollers 24 on the paper discharge path side and placed on a paper discharge tray 25 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the transfer means 7A, the residual toner is removed by the cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  Reference numeral 200 denotes preheating means for the recording paper P, which is installed before the recording paper P supplied from the paper feed cassette 20 and the recording paper P supplied from the reverse conveyance path 27C merge. Only the recording paper P supplied from is heated. Details of the preheating means 200 will be described later.

  The preheating unit 200 is not limited to the above-mentioned place, and may be anywhere before fixing. For example, the preheating unit 200 may be provided between the transfer unit 7A and the fixing device 9.

  Reference numeral 300 denotes a control unit of the image forming apparatus GS, and 301 denotes an operation / display unit.

  Next, an example of an embodiment of a fixing device according to the present invention will be described with reference to FIG. FIG. 2 is a schematic sectional view of the fixing device 9.

  The fixing belt 91 as a fixing member is formed in an endless shape. For example, a heat-resistant resin belt made of PI (polyimide) or the like having a thickness of 70 μm is used as a base, and an outer peripheral surface of the base is 200 μm in thickness as an elastic layer. It is covered with heat-resistant silicon rubber (hardness JIS-A 30 °), and further covered with a 30 μm thick PFA (perfluoroalkoxy) tube as a surface layer. The outer diameter is 80 mm, for example.

  The heating roller 92 incorporates a halogen lamp 92A as a heating means for heating the fixing belt 91. For example, the outer peripheral surface of a cylindrical hollow rotating body 92B having a thickness of 2 mm formed of aluminum or the like is used as a surface layer 92C. A 30 μm heat-resistant PFA is coated to form a hard roller. The outer diameter is 47 mm, for example.

  The fixing roller 93 is, for example, a solid core metal 93A formed of a metal such as iron is covered with a heat-resistant silicone rubber and silicone sponge having a thickness of 10 mm as an elastic layer 93B, and is further thickened as a surface layer 93C. Covered with a 30 μm thick PFA tube and configured as a soft roller. In addition, an outer diameter dimension is 40 mm, for example.

  The pressure roller 94 as a pressure member incorporates a halogen lamp 94A as a heating means for heating the pressure roller 94, and has an outer peripheral surface of a cylindrical hollow rotating body 94B having a thickness of 3 mm formed of, for example, aluminum. Is coated with 3 mm thick heat-resistant silicon rubber (hardness JIS-A 30 °) as the elastic layer 94C, and further is coated with a 30 μm thick PFA tube as the release layer 94D to constitute a hard roller. . In addition, an outer diameter dimension is 50 mm, for example.

  The halogen lamp 94A built in the pressure roller 94 is used to quickly bring the pressure roller 94 to a predetermined temperature in order to shorten the warming time. However, the pressure roller 94 does not contain the halogen lamp 94A. It is also possible.

  The pressure roller 94 includes a pressure contact release motor 95A, a disk 95B, a pin 95C, a connecting rod 95D connected to a support shaft 94E of the pressure roller 94, and the like while the pressure roller 94 is stopped and warming up. The pressure is released by the pressure release means 95, and the pressure contact is made in conjunction with the start of image formation.

  S 1 and S 2 are temperature detection means for detecting the temperature of the heating roller 92 via the fixing belt 91 and temperature detection means for detecting the temperature of the pressure roller 94.

  Note that any heating means may be used as a heating means for heating the fixing belt 91 and the pressure roller 94, and for example, an induction heating heating element using an exciting coil may be used. Further, the heating means is not necessarily arranged in the heating roller 92 and the pressure roller 94, and may be arranged anywhere.

  Further, a fixing device provided with a tension roller for pressing the fixing belt 91 may be used.

  In the above configuration, when the fixing roller 93 is rotated clockwise by driving means (not shown), the fixing belt 91 and the heating roller 92 are also rotated clockwise, and the pressure roller 94 is rotated counterclockwise. Further, the fixing belt 91 in contact with the heating roller 92 is heated by the halogen lamp 92A, and the pressure roller 94 is also heated by the halogen lamp 94A. Since the pressure roller 94 is urged in the direction of the fixing roller 93 by an urging means (not shown), the nip portion N between the fixing belt 91 wound around the fixing roller 93 and the pressure roller 94. Thus, the fed recording paper P is heated and pressurized, and the toner image on the recording paper P is fixed.

  Next, the cooling means for the pressure roller 94 and the preheating means for the recording paper P, which are the features of the present invention, will be described with reference to FIGS.

  3 is an axial sectional view of the pressure roller of FIG. 2, and FIG. 4 is a sectional view of the preheating means.

  First, the cooling means 100 will be described with reference to FIG.

  Reference numeral 101 denotes a cooling fan with a motor, which is provided at a position where air is introduced from the outside of the image forming apparatus.

  Reference numeral 102 denotes an introduction duct that is installed between the cooling fan 101 and the pressure roller 94 and sends air taken in by the cooling fan 101 to the inner cylinder portion of the pressure roller 94.

  Reference numeral 103 denotes an intermediate duct that is installed at the end of the pressure roller 94 opposite to the introduction duct 102 and uses the air exhausted from the pressure roller 94 as a heat source of a preheating means described later.

  As described above, the cooling means 100 is configured by the cooling fan 101, the introduction duct 102, the intermediate duct 103, and the like.

  Next, the preheating means 200 will be described with reference to FIG. FIG. 4 is a perspective view of the preheating means 200.

  Reference numerals 201 and 202 denote conveyance guide plates for conveying the recording paper P, which are installed at a predetermined interval.

  Reference numerals 203 and 204 denote chambers connected to the intermediate duct 103, which are fixed to the conveyance guide plates 201 and 202, respectively.

  Reference numeral 205 denotes an exhaust duct, one end of which is connected to the side surface of the chambers 203 and 204 opposite to the intermediate duct 103, and the other end extends to the side surface of the image forming apparatus. Exhaust.

  Thus, the preheating means 200 is comprised by the conveyance guide plates 201 and 202, the chambers 203 and 204, the exhaust duct 205, and the like.

  With the above configuration, the air sucked from the outside of the apparatus by the cooling fan 101 is sent to the inner cylinder portion of the pressure roller 94 by the introduction duct 102 to cool the pressure roller 94. The air that has cooled the pressure roller 94 is sent to the intermediate duct 103, but the air that has risen in temperature due to the cooling of the pressure roller 94 (waste heat air) passes through the chambers 203 and 204 and passes through the conveyance guide plates 201 and 202. The recording paper P that is heated and conveyed in the meantime is heated.

  Next, the control configuration of the cooling means 100 will be described with reference to FIG.

  FIG. 5 is a control block diagram of the image forming apparatus GS and the cooling unit 100.

  In FIG. 5, the control unit 300 controls the image forming apparatus GS and the cooling unit 100, and includes a CPU that performs arithmetic processing, a ROM that is a storage unit, a RAM, and the like.

  The operation and display means 300A is connected to the control means 300, such as setting the number of copies, recording paper size, recording paper type, recording paper basis weight, and selection of the sheet passing mode for single-sided copying or double-sided copying. While performing the operation, the image forming state such as an abnormal part is displayed.

  The temperature detection means S1 and S2 are connected to the control means 300 and transmit temperature information of the heating roller 92 and the pressure roller 94, respectively.

  The control unit 300 controls the image reading device YS, the image forming units 10Y, 10M, 10C, and 10K, the fixing device 9, the pressure contact release unit 95, and the like according to the program stored in the storage unit ROM, and the cooling fan driving unit 101A. The driving of the cooling fan 101 is controlled via this.

  Next, control of the cooling means 100 in the above configuration will be described.

  First, an operation is performed by the operator, and the number of copies, recording sheet size, recording sheet type, basis weight of recording sheet, and selection of a sheet passing mode for single-sided copying or double-sided copying are performed from the display unit 300A.

  When at least one of the above settings and selections meets the conditions stored in the storage means ROM in advance, the cooling fan 101 is set so that the temperature difference between the pressure roller 94 and the recording paper P during fixing is small. The pressure roller 94 is activated and the recording paper P is preheated.

  Alternatively, apart from the setting and selection described above, when the temperature detected by the temperature detection means S2 of the pressure roller 94 exceeds a predetermined temperature, the temperature difference between the pressure roller 94 and the recording paper P during fixing is reduced. Then, the cooling fan 101 is operated to cool the pressure roller 94 and preheat the recording paper P.

  As described above, the gloss in the recording sheet conveyance direction that appears in the fixed image on the recording sheet P by controlling the temperature difference between the pressure roller 94 and the recording sheet P at the time of fixing by operating the cooling unit 100. The step can be prevented, and the details will be described with reference to FIGS.

  First, the generation mechanism of the gloss level difference in the recording paper conveyance direction will be described with reference to FIG. 6 schematically showing the generation mechanism.

  As shown in FIG. 6A, the surface temperature of the fixing belt 91 immediately after passing through the nip portion N is a position corresponding to a paper passing portion where heat is taken away by the recording paper P and an inter-paper portion where heat is not taken away. A temperature difference occurs at.

  That is, the surface temperature of the fixing belt 91 is higher at the position corresponding to the inter-paper portion than at the position corresponding to the paper passing portion.

  Since the polyimide used for the base of the fixing belt 91 is poor in heat conduction compared to metal, a temperature difference remains even after passing through the heating roller at a high speed as shown in FIG. 6B.

  Since the level of gloss corresponds to the temperature of the fixing belt 91, as shown in FIG. 6C, a gloss level difference is recognized at the boundary of the temperature difference.

  In the conventional high-gloss color image, the gloss with respect to the fixing temperature is saturated, so even if there is a temperature difference in the circumferential direction of the fixing belt 91, it is difficult to recognize because the difference in gloss is small, but it is limited to an appropriate gloss range. In the image, the gloss difference is more noticeable.

  The temperature difference increases as the difference between the temperature of the recording paper P and the surface temperature of the pressure roller 94 increases.

  Usually, the temperature of the recording paper P is substantially equal and constant at room temperature (around 20 °), so that the temperature difference becomes larger and the gloss difference becomes more conspicuous as the temperature of the pressure roller 94 is higher.

  The temperature of the pressure roller 94 varies depending on conditions such as a sheet passing mode (double-sided / single-sided, continuous / intermittent), a recording paper size, a recording paper basis weight, and the like. Depending on the combination, the temperature of the pressure roller 94 becomes high, and the gloss difference becomes conspicuous.

  Examples of conditions for increasing the temperature of the pressure roller 94 include the following.

  During continuous image formation, the shorter the recording paper length, the longer the interval between papers with respect to the paper passing distance, so the temperature of the pressure roller 94 increases.

  This is because the temperature of the pressure roller 94 is determined by subtracting the temperature given from the fixing belt 91 and the amount of heat taken by the recording paper P.

  Even when the double-sided image is formed, the recording paper interval is increased by the front and back reversal time, so the temperature of the pressure roller 94 is increased.

  Even in the intermittent mode in which a small amount of image formation is repeated, the temperature of the pressure roller 94 increases.

  Further, when the basis weight of the recording paper P is small, that is, when the recording paper P is thin, the amount of heat taken away by the recording paper P is reduced, so that the temperature of the pressure roller 94 is increased.

  As described above, when the fixing process is performed under the condition that the temperature of the pressure roller 94 is high, the above-described problem of gloss level difference occurs.

  On the other hand, if the temperature difference between the fixing belt 91 and the pressure roller 94 is large, this temperature difference appears as a temperature difference between the front surface and the back surface of the recording paper P and causes the recording paper P to curl.

  Thus, the gloss level difference and the curl are opposite to each other when viewed from the temperature difference between the pressure roller 94 and the recording paper P. Therefore, in order not to generate the gloss level difference and the curl, the pressure roller 94, It is necessary to appropriately control the temperature difference of the recording paper P, and this will be described with reference to FIG.

  FIG. 7 shows the cooling of the pressure roller 94 in an experiment in which A4 plain paper is used as the recording paper P and double-sided copying is repeated 100 times one by one with A4 short edge feeding in the image forming apparatus of the present embodiment. 4 is a diagram schematically showing changes in temperature of the pressure roller 94 and the recording paper P depending on whether or not the recording paper P is preheated. The temperature of the recording paper P was measured before the nip portion N.

  FIGS. 7A and 7C are the same, and when the pressure roller 94 is not cooled and the recording paper P is not preheated, FIG. FIG. 7D shows a case where the pressure roller 94 is cooled and the recording paper P is preheated.

  In order to prevent the gloss level difference of the fixed image from being recognized, the temperature difference between the pressure roller 94 and the recording paper P is within 100 ° C., and the curl amount is prevented from jamming in the paper passing path for paper discharge, post-processing, and double-sided copying. In some cases, the temperature difference between the fixing belt 91 and the pressure roller 94 must be within 80 ° C. in advance.

  As shown in FIGS. 7A and 7C, when the pressure roller 94 is not cooled and the recording paper P is not preheated, the temperature of the pressure roller 94 increases and reaches 170.degree. In this case, it is understood that the curl is within the allowable temperature of 80 ° C., but the gloss step is not within the allowable temperature of 100 ° C.

  As shown in FIG. 7B, when only the pressure roller 94 is cooled and lowered to 100 ° C., which is a temperature at which there is no gloss level difference, the temperature difference between the fixing belt 91 and the pressure roller 94 becomes 100 ° C. It can be seen that the allowable temperature is exceeded.

  As shown in FIG. 7D, when the recording paper P is preheated in addition to the cooling of the pressure roller 94, the temperature difference between the pressure roller 94 and the recording paper P is 80 ° C. and the fixing belt 91 is heated. It can be seen that the temperature difference from the pressure roller 94 is 70 ° C., there is no gloss step, and no curling jam occurs.

  As described above, by controlling the cooling means and the preheating means so that the temperature difference between the pressurizing member and the recording paper is reduced, the curling of the recording paper is suppressed and no gloss step is generated. An image forming apparatus provided with a fixing device can be provided.

  Further, at least one of information on temperature detecting means for detecting the temperature of the pressure member, or the number of images formed, transfer material size, transfer material type, transfer material basis weight, and single-sided copy or double-sided copy paper passing mode. By controlling the cooling means and the preheating means based on one piece of information, it is possible to more accurately prevent the occurrence of a gloss level difference.

  Furthermore, by using the waste heat air when the pressure member is cooled as the heat source of the preheating means, it is possible to reduce the size of the apparatus and save power.

  Although the present embodiment is a fixing device using a belt, the present invention is not limited to this, and other fixing devices such as a fixing roller as a fixing member and a pressure roller as a pressure member are used. A roller-type fixing device can also be used.

  Further, the basis weight of the recording paper may not be input from the operation and display means, but a basis weight measuring means may be provided on the recording paper conveyance path to control the cooling means and the preheating means based on this information.

  Further, although the preheating means uses waste heat air when the pressure member is cooled, the preheating means includes, for example, a heating member such as a halogen heater or a planar heating element. The recording paper may be preheated.

1 is a schematic configuration diagram of an image forming apparatus. FIG. 2 is a schematic sectional view of a fixing device. The axial direction sectional view of a pressure roller. The perspective view of a preheating means. 4 is a control block diagram of the image forming apparatus GS and the cooling unit 100. FIG. Schematic diagram of gloss level difference generation mechanism. FIG. 5 is a diagram schematically illustrating temperature changes of the fixing belt, the pressure roller, and the recording paper depending on whether the pressure roller is cooled and the recording paper is preheated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Fixing device 91 Fixing belt 92 Heating roller 92A Halogen lamp 92B Hollow rotating body 92C Surface layer 93 Fixing roller 93A Core metal 93B Elastic layer 93C Surface layer 94 Pressurizing roller 94A Halogen lamp 94B Hollow rotating body 94C Elastic layer 94D Release layer 94E Support shaft 95 pressure contact release means 95A pressure contact release motor 95B disk 95C pin 95D connecting rod 100 cooling means 101 cooling fan 101A cooling fan drive means 102 introduction duct 103 intermediate duct 200 preheating means 201, 202 transport guide plates 203, 204 chamber 205 exhaust duct 300 control means 300A operation, display means S1, S2 temperature detection means

Claims (3)

A fixing member that is heated and rotated by a heating means; and
A rotatable pressure member that presses against the fixing member to form a nip portion;
In an image forming apparatus provided with a fixing device for passing a transfer material through the nip portion and fixing unfixed toner on the transfer material,
Cooling means for cooling the pressure member;
Preheating means for heating the transfer material before entering the nip portion,
An image forming apparatus comprising: a control unit that controls the cooling unit and the preheating unit so that a temperature difference between the pressure member and the transfer material is reduced. Information on temperature detection means for detecting the temperature of the pressure member, or at least one of image forming number, transfer material size, transfer material type, transfer material basis weight, single-sided copy or double-sided copy paper passing mode The image forming apparatus according to claim 1, wherein the cooling unit and the preheating unit are controlled based on one piece of information. 3. The image forming apparatus according to claim 1, wherein the heat source of the preliminary heating unit is waste hot air when the pressure member is cooled. 4.

Images