JP4714902B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus in which compressed air is injected to separate a recording material that has passed through a nip portion of a fixing device, and the recording material is cooled with compressed air to prevent blocking or the like.

  2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive member, and toner is applied to the latent image. Thus, the visualized toner image is transferred onto the recording paper, and then the toner image transferred onto the recording paper is fixed and discharged.

  As a fixing device for fixing a toner image in this manner, a recording sheet onto which a toner image is transferred is sandwiched between a fixing roller having a built-in halogen heater and a pressure roller that presses the fixing roller. There is a fixing device of a heat roller fixing system that heats and pressurizes while conveying, and such a fixing device is widely used because of its simple configuration.

  In addition, an endless fixing belt is stretched between a heating roller incorporating a halogen heater or the like and a fixing roller, and has a pressure roller that presses the fixing roller through the fixing belt. There is a belt-fixing type fixing device that heats and pressurizes while pinching and transporting the recording paper onto which the toner image is transferred at the formed nip part. Such a fixing device has a small heat capacity of the fixing belt, so it warms up. It has the advantage of reducing time and saving energy.

  Here, since the recording paper after fixing is heated, the toner image on the recording paper is not sufficiently solidified and has adhesiveness. When such recording sheets are continuously conveyed and placed one after another on the paper discharge tray, a so-called blocking phenomenon occurs in which the recording sheets stick to each other and the toner image is peeled off.

  In addition, depending on the layout in the image forming apparatus, the temperature of the photosensitive member, the developing device, and the like may increase due to the recording paper having the remaining heat after fixing, and adversely affect unfixed toner.

  Furthermore, when performing double-sided copying, the fixed surface is also heated again when fixing the back surface, so that only the front surface becomes more glossy until it is naturally cooled. There is also a problem that a difference occurs.

  In order to prevent such a problem, there is known an image forming apparatus that cools recording paper having residual heat by disposing a cooling device including a fan and a heat pipe on the downstream side of the fixing device (for example, Patent Document 1). , 2).

  Further, since the toner of the toner image on the recording paper is heated when passing through the nip portion, the toner acts like an adhesive, and the recording paper that has passed through the nip portion does not separate without fixing the fixing roller or the fixing belt. There is a risk of wrapping around the surface and causing jamming. In particular, when a small amount of paper (thin paper) and a small amount of coated paper for printing are used as the recording paper, the separation performance is further deteriorated.

  For this purpose, a release claw coated with a fluorinated resin with good releasability is provided on the recording paper discharge side with respect to the nip, and the tip is brought into contact with the outer surface of the fixing roller so that the recording paper is peeled off from the fixing roller. There is a way to make it.

  However, since the sharp tip of the peeling claw is in contact with the surface of the fixing roller, the release layer formed from a fluororesin or the like that covers the surface of the fixing roller with a relatively short period of use is scuffed. There is a problem that wrinkles are also transferred to the image. In particular, in the case of a color image, since a glossy image is required, the surface roughness of the image tends to be remarkably apparent.

  Also known is a method of applying oil to the fixing roller, etc. to improve the separation of the recording paper and ensure the slidability of the peeling claw so that the fixing roller is not wrinkled. Therefore, there is a problem of enlargement and cost increase. Further, since oil adheres to the image, there is a problem that the image is liable to be caused by oil and writing with a ballpoint pen or the like is difficult.

  Also known is a self-stripping method that increases the curvature or increases the compression of the rubber near the exit of the nip to ensure the separability. In many cases, it cannot be secured.

In order to solve such a problem, compressed air is jetted onto the fixing roller on the recording paper discharge side with respect to the nip portion, and the leading end of the recording paper wound around the fixing roller is peeled off by the wind pressure of the compressed air. A fixing device is known (see, for example, Patent Document 3).
Japanese Patent Application Laid-Open No. 9-171311 JP-A-10-207155 Japanese Patent Application Laid-Open No. 2004-212954

  The remaining heat of the recording paper after fixing causes problems such as blocking, adverse effects on unfixed toner, and difference in glossiness between the front and back surfaces. In Patent Documents 1 and 2, fixing is performed as a countermeasure for this problem. A cooling device is arranged on the downstream side of the device. However, the arrangement of the cooling device has a problem that the image forming apparatus is increased in size and cost.

  Patent Document 3 is only a recording paper separation technique, and does not describe any countermeasures against the above-described problems.

  The present invention has been made in view of such problems, and after jetting compressed air to separate the recording material from the fixing member, the compressed recording material is further jetted to rapidly cool the recording material after fixing, blocking, toner It is an object of the present invention to propose an image forming apparatus that does not cause problems such as adverse effects on the image quality and difference in glossiness between the front and back surfaces during double-sided copying, and does not increase in size or cost.

  The object is achieved by the invention described below.

An image forming apparatus according to the present invention includes a fixing device that fixes a toner image to a recording material by heating and pressing a recording material on which the toner image is formed at a nip formed by a fixing member and a pressure member. In the image forming apparatus, the compressed air is jetted and the jetting direction is switchable , and the recording material is separated from the fixing member by jetting the compressed air to the leading end of the recording material that has passed through the nip portion. And a jetting direction switching means for switching the jetting direction of the compressed air and jetting the compressed air toward the surface portion of the recording material to be conveyed.

  According to the image forming apparatus of the present invention, after the compressed air is ejected from the compressed air ejecting device and the recording material is separated from the fixing member, the compressed air is further ejected from the same compressed air ejecting device and the recording material is fixed. Since the recording medium is rapidly cooled, the recording material is surely separated, and problems such as blocking, a bad influence on the toner, and a difference in glossiness between the front and back surfaces during double-sided copying do not occur. Since the compressed air injection device is used for two purposes, there is no increase in size and cost as in the prior art.

  Embodiments of the image forming apparatus according to the present invention will be described below with reference to the drawings.

  First, an example of an image forming apparatus will be described based on the configuration diagram of FIG.

  The image forming apparatus 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 type color image forming apparatus, and 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, a fixing device 9, and the like. Consists of.

  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.

  A signal formed by photoelectric conversion by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit, and then exposure means 3Y, 3M, 3C, 3K. Sent to.

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

  The developing units 4Y, 4M, 4C, and 4K include a two-component developer composed of a toner having a small particle size of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier.

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

  The fixing device 9 fixes the toner image on the recording paper (recording material) P by heating and pressing at a nip portion formed between the heated fixing roller 91 and the pressure roller 92.

  Thus, each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred onto the rotating intermediate transfer body 6 by the transfer means 7Y, 7M, 7C, and 7K (primary transfer). A toner image synthesized with a color image is formed. The recording paper P stored in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the transfer means 7A via the paper feeding rollers 22A, 22B, 22C, 22D, the registration rollers 23, etc. A color image is transferred onto P (secondary transfer). The recording paper P to which the color image has been transferred is heated and pressurized by the fixing device 9 and the color toner image on the recording paper P is fixed. Thereafter, the sheet is sandwiched between the sheet discharge rollers 24 and placed on the sheet 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.

  The image forming apparatus for forming a color image has been described above. However, an image forming apparatus for forming a monochrome image may be used, or an intermediate transfer member may or may not be used.

  Next, the fixing device according to the present invention will be described with reference to the sectional view of FIG.

  In FIG. 2, the fixing device 9 includes a fixing roller 91 (fixing member) heated by a halogen heater H, a pressure roller 92 (pressure member) that presses the fixing roller 91 from below.

  The fixing roller 91 includes a halogen heater H built in the center, a cored bar 91A formed in a cylindrical shape with aluminum, iron, or the like, a heat-resistant elastic layer 91B formed of silicone rubber, fluorine rubber, or the like, and PFA ( The release layer 91C is made of a fluororesin such as perfluoroalkoxy) or PTFE (polytetrafluoroethylene) and covers the elastic layer 91B with a coating or a tube.

  The pressure roller 92 is formed of a core metal 92A formed of a stainless steel or the like, an elastic layer 92B made of a foam of silicon rubber and positioned on the outer peripheral surface of the core metal 92A, a PFA tube, and the like. It is comprised from the mold release layer 92C which coat | covers the outer peripheral surface of 92B. The pressure roller 92 is urged by a urging member (not shown) to press the fixing roller 91 from below.

  In some cases, an induction heating method may be used in place of the halogen heater H as a heating member for heating the fixing roller 91.

  Further, a cleaning unit 95 for cleaning toner or the like adhering to the fixing roller 91 is provided. And a winding shaft 95D for winding the web 95A after use. The web 95A is made of a non-woven fabric and is wound up intermittently every predetermined number of sheets.

  With the above configuration, when the fixing roller 91 heated by the halogen heater H and driven by a motor (not shown) rotates in the clockwise direction, the pressure roller 92 rotates in the counterclockwise direction. Accordingly, the recording paper P on which the toner image is formed by the image forming apparatus as shown in FIG. 1 is sandwiched and conveyed by the nip portion N formed by the fixing roller 91 and the pressure roller 92, and is heated and pressurized. As a result, the toner image on the recording paper P is fixed.

  Here, an air nozzle 101 that ejects compressed air is provided on the paper discharge side of the recording paper P with respect to the nip portion N.

  As shown in the perspective view of FIG. 3, the air nozzle 101 includes an ejection unit 101A that ejects compressed air toward the leading end of the recording material P that has passed through the nip N, and a compressed air toward the surface of the recording paper P being conveyed. It has two injection parts which inject in two directions with injection part 101B which injects, and it is constituted so that compressed air may be injected only from any one injection part by external operation.

  As shown in FIG. 3, the length in the width direction of the opening portion 101 </ b> C from which the compressed air is jetted in the jet portion 101 </ b> A of the air nozzle 101 is larger than the length in the axial direction of the fixing roller 91 and the pressure roller 92. Therefore, even if the recording paper has the maximum size, the compressed air can be ejected over the entire region in the width direction. The injection unit 101B also has a similar opening.

  In order to prevent the toner image on the recording paper P from being pressed onto the surface of the fixing roller 91 and preventing the recording paper P from being wound around the fixing roller 91 due to the adhesiveness of the softened toner, the recording paper P is in the nip portion N. , Compressed air is ejected from the ejecting portion 101A of the air nozzle 101, and the leading end portion of the recording paper P wound around the fixing roller 91 is peeled off from the fixing roller 91 by the wind pressure of the compressed air.

  Further, since the guide member 96 is provided so as to protrude from the air nozzle 101 toward the nip portion N, the separated recording paper P is conveyed along the guide member 96 without contacting the air nozzle 101.

  Since the recording paper P is in sliding contact with the guide member 96, it is desirable that the sliding contact surface of the guide member 96 is formed as a smooth surface and a release layer is applied.

  When the recording paper P is separated, the ejection of the compressed air from the ejecting unit 101A is stopped, and the recording paper P is rapidly cooled by ejecting the compressed air toward the surface portion of the recording material P conveyed from the ejecting unit 101B. Let

  Accordingly, the recording paper P is separated from the fixing roller 91 by using one compressed air ejecting device, and the recording paper P is rapidly cooled to block, adversely affect unfixed toner, and the front and back surfaces of the two-sided copy. It is possible to prevent problems such as a difference in glossiness from occurring. Therefore, the image forming apparatus is not increased in size and cost as in the prior art.

  When separating the recording paper P, it is necessary to increase the jet pressure of the compressed air, but when cooling the recording paper P, the jet pressure may be low, and the jet pressure from the jet section 101B is the jet pressure of the jet section 101A. About 1/3 to 1/10.

  As the air nozzle, as shown in FIG. 4, the air nozzle 121 has only one injection portion 121A, and the injection portion 121A moves to a position drawn by a two-dot chain line by rotation or the like so that the injection direction is switched. It may be.

  Further, there is a case where a toner containing wax is used with the fixing device oilless. In this case, the toner image after fixing may be rapidly cooled by coming into contact with a conveying roller or the like, and a rubbing trace may be generated. However, as described above, it is possible to prevent such rubbing traces from being generated by rapidly ejecting the recording paper P by ejecting the compressed air from the ejection unit 101B.

  As waxes contained in the toner, known waxes such as paraffin waxes, polyolefin waxes, oxides and grafted products thereof, higher fatty acids, higher fatty acid metal salts, higher fatty acid amide waxes and ester waxes. In particular, higher fatty acid ester waxes are preferred.

  Next, the configuration for switching the injection direction of the compressed air will be described by adding FIG. 2 to the flowchart of FIG. 5 and the block diagram of FIG.

  5 and 6, when image formation is started by the operation of the operator and feeding of the recording paper is started (S1), the paper feeding sensor 111 located on the upstream side of the fixing device passes the leading edge of the recording paper P. (S2), the control unit 110 causes the timer 113 to start measuring time (S3), and the timer 113 is the time until the leading edge of the recording paper P passes through the nip N of the fixing device 9. Time. Since this time is constant, if this time has elapsed (Y in S4), the control means 110 opens the control valve 102 consisting of an electromagnetic valve or the like widely, opens the injection unit 101A of the air nozzle 101, and the injection unit. 101B is closed, high-pressure compressed air is jetted from the jetting part 101A, and the leading end of the recording paper P wound around the fixing roller 91 is peeled off from the fixing roller 91 (S5). When the paper discharge sensor 112 that is disposed downstream of the fixing device 9 and detects that the recording paper P after separation has passed passes through the recording paper P and detects the passage of the leading end of the recording paper P (S6), The control means 110 opens the control valve 102 small, switches the injection direction of the air nozzle 101, opens the injection unit 101B, closes the injection unit 101A, and injects low-pressure compressed air from the injection unit 101B (S7). When the paper discharge sensor 112 detects the trailing edge of the conveyed recording paper P and is turned off (S8), the control unit 110 closes the control valve 102 and stops all injection of compressed air. (S9).

  In the compressed air injection means, the compressed air is stored in the air tank 103 from the compressor 104 and is injected from the air nozzle 101 when the control valve 102 is opened.

  In addition, the present invention is not limited to the above-described heat roller fixing type fixing device, and can also be applied to a belt fixing type fixing device as shown in FIG. An example of a belt fixing type fixing device using the present invention will be described below with reference to FIG.

  The fixing belt 201 (fixing member) is formed in an endless shape. For example, a heat-resistant resin belt made of PI (polyimide) or the like is used as a base, and the outer peripheral surface of the base is covered with heat-resistant silicon rubber. The release layer is covered with a PFA (perfluoroalkoxy) tube.

  The heating roller 202 incorporates a halogen heater H1 as a heating member for heating the fixing belt 201. For example, the outer peripheral surface of a cylindrical hollow rotating body 202A formed of aluminum or the like is covered with a heat-resistant PFA tube 202B. And it is configured as a hard roller.

  The fixing roller 203 is configured as a soft roller by covering a solid core metal 203A formed of a metal such as iron with a heat-resistant silicone rubber 203B and further covering with a sponge 203C.

  The pressure roller 204 (pressure member) incorporates a halogen heater H2, covers the outer peripheral surface of a cylindrical hollow rotating body 204A made of, for example, aluminum or the like with heat-resistant silicon rubber 204B, and further releases the mold. The layer is covered with a PFA (perfluoroalkoxy) tube 204C and configured as a soft roller.

  Note that any heating member may be used as a heating member for heating the fixing belt 201, for example, an induction heating heating element using an exciting coil may be used. Further, the heating member is not necessarily arranged in the heating roller 202 or the like, and may be arranged anywhere.

  In addition, a cleaning unit 205 for cleaning the toner and the like attached to the fixing belt 201 is provided, and the web 205A, the original winding shaft 205B for winding the web 205A before use, and the web 205A are pressure-bonded to the fixing belt 201 on the heating roller 202. It comprises a pressure roller 205C to be wound and a winding shaft 205D for winding the web 205A after use. The web 205A is made of non-woven fabric and is wound up intermittently every predetermined number of sheets.

  In the above configuration, when the fixing roller 203 is rotated clockwise by a driving unit (not shown), the fixing belt 201 and the heating roller 202 are rotated clockwise, and the pressure roller 204 is rotated counterclockwise. Further, since the heating roller 202 can be heated by the halogen heater H1, the fixing belt 201 in contact with the heating roller 202 is also heated, and the pressure roller 204 is also heated by the halogen heater H2. Since the pressure roller 204 is urged in the direction of the fixing roller 203 by an urging means (not shown), a nip portion N between the fixing belt 201 wound around the fixing roller 203 and the pressure roller 204 is used. Thus, the fed recording paper P is heated and pressurized, and the toner image on the recording paper P is fixed.

  2, an air nozzle 101 that ejects compressed air is provided on the paper discharge side of the recording paper P with respect to the nip portion N, and the recording paper is compressed by the compressed air ejected from the ejecting unit 101A. After peeling P, the entire recording paper P is rapidly cooled by the compressed air jetted from the jetting part 101B.

1 is a configuration diagram of an image forming apparatus. FIG. 3 is a cross-sectional view of a fixing device. It is a perspective view of an air nozzle. It is a perspective view of the air nozzle of other composition. It is a flowchart which injects compressed air. It is a block diagram of the member which comprises a compressed air injection apparatus. FIG. 4 is a cross-sectional view of a belt fixing type fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Fixing device 91,203 Fixing roller 202 Heating roller 92,204 Pressure roller 96 Guide member 101,121 Air nozzle 101A, 101B, 121A Injection part 102 Control valve 110 Control means 111 Paper feed sensor 112 Paper discharge sensor 113 Timer 201 Fixing belt P Recording paper (recording material)
N Nip part

Claims (5)

An image forming apparatus including a fixing device that fixes a toner image on a recording material by heating and pressing a recording material on which the toner image is formed at a nip formed by a fixing member and a pressure member.
Compressed air injection means that injects compressed air and is capable of switching the injection direction ;
After the recording material is peeled from the fixing member by jetting compressed air to the leading end of the recording material that has passed through the nip portion, the jetting direction of the compressed air is switched, and the compressed air is directed toward the surface portion of the recording material to be conveyed. Injection direction switching means for injecting;
An image forming apparatus comprising: It said compressed air injection means have a two injection unit for injecting in different directions,
The image forming apparatus according to claim 1, wherein the ejection direction switching unit switches the ejection unit from one to the other after the recording material is separated from the fixing member . The compressed air injection means has an injection unit that switches the injection direction of the compressed air by switching the direction,
The image forming apparatus according to claim 1, wherein the ejection direction switching unit switches the direction of the ejection unit after separating the recording material from the fixing member . After the recording material is peeled off from the member forming the nip portion, it is provided with a control means for controlling the jetting direction of the compressed air to be switched and the jetting pressure of the compressed air to be lowered by the jetting direction switching means. images forming device according to any one of claims 1 to 3.   The image forming apparatus according to claim 1, wherein the compressed air ejecting unit ejects the compressed air over an entire region in a width direction orthogonal to the conveyance direction of the recording material.

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