JP2006227157A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the phenomenon of a toner blister occurring in image formation. <P>SOLUTION: An image forming apparatus includes: a fixing apparatus 9, which has a heat fixing member and a pressurized contact member in pressurized contact with the fixing member and fixes a recording paper sheet, on which an unfixed toner image is stuck, passed through a fixing nip part formed by being the heat fixing member and the pressurized contact member in pressurized contact with each other; and a double-sided image forming means for forming and fixing the unfixed toner image again on a backside of the recording paper sheet to which the toner image is fixed once. The image forming apparatus is characterized in that it has an operation mode for forming the toner image on one side of the recording paper sheet and ejecting the paper sheet after being passed through the fixing apparatus 9 twice. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying apparatus or a printer that forms an image by electrophotography, and more particularly to an image forming apparatus that enables double-sided image formation.

  In an image forming apparatus, a toner image formed on an image carrier (photosensitive member) or an intermediate transfer member is transferred onto a recording paper (also referred to as a transfer material) by a transfer unit, and the recording paper holding the toner image is fixed. Heat and pressure are applied while passing through a fixing nip formed by the heat fixing member and the pressure contact member in the pressure contact state of the apparatus, and the toner is fused and fixed on the recording paper.

  A fixing device used in a color image forming apparatus that performs high-speed processing is required to have excellent separation from a heat-fixing member and a nip width of a fixing nip portion as long as possible. A low-hardness fixing roller is used. In the fixing device having such a configuration, there is a problem that the average nip surface pressure of the fixing nip portion becomes small and toner blisters are easily generated.

  Toner blister is a phenomenon that occurs remarkably when coated paper with a small amount of soot is used as recording paper, and it is a phenomenon that occurs when air between toner particles does not escape to the outside and forms bubbles inside the toner layer. Then, the gloss of the toner layer portion is low, and the image quality is deteriorated while the surface of the toner is rough.

  In order to avoid this toner blister phenomenon, it is necessary to increase the nip surface pressure or to increase the nip time.

  In order to increase the nip surface pressure, it is necessary to increase the roller hardness of the fixing roller. If the roller hardness is increased, it becomes difficult to ensure the nip width. To increase the nip surface pressure and secure the nip width, it is necessary to increase the diameter of the fixing roller. However, if the diameter is increased, there is a problem that the separation of the recording paper after fixing cannot be ensured. Come on.

  In order to increase the nip time, it is necessary to reduce the system speed to about 1/3 to 1/4. However, if the system speed is decreased, the productivity is lowered.

Patent Document 1 or Patent Document 2 discloses a technique in which two fixing units are provided in parallel to increase the nip time to control the gloss of an image and improve the OHT light projecting property.
JP 2002-304072 A JP 2004-139039 A

  In both proposals of Patent Documents 1 and 2 in which two fixing units are provided in parallel, the nip time becomes long, but an increase in the size of the apparatus is inevitable.

  An object of the present invention is to provide an image forming apparatus capable of obtaining a good fixed image by preventing the occurrence of toner blisters without particularly changing the apparatus.

In order to solve the above problems and achieve the object, the present invention is configured as follows.
(Claim 1)
The recording sheet having the unfixed toner image is passed through a fixing nip portion formed by pressing the heat fixing member and the pressure fixing member. An image forming apparatus having a double-sided image forming unit for forming and fixing an unfixed toner image again on the back surface of the recording paper on which the toner image is fixed once.
An image forming apparatus having an operation mode in which a toner image is formed on one side of a recording sheet, and discharged after passing through the fixing device twice.
(Claim 2)
The fixing device includes a heating roller having a heating unit, a support roller disposed in parallel and spaced apart from the heating roller, and a fixing that is endlessly stretched between the heating roller and the support roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is a belt fixing device including an external pressure roller that is in pressure contact with the support roller via the fixing belt.
(Claim 3)
The image forming apparatus according to claim 1, wherein the operation mode is executed for a selected type of recording paper.

  According to the first aspect of the present invention, there is provided an operation mode in which the recording sheet holding the toner image on one side is discharged twice after passing through the fixing device by using the reverse conveyance path of the double-sided image forming unit. Therefore, when performing the printing operation in this operation mode, the toner image on the recording paper is remelted, the bubbles inside the toner layer escape, and the surface becomes smooth, so that no toner blister is generated. Good image quality is guaranteed.

  According to the second aspect of the present invention, since a belt fixing device suitable for color image formation is used as the fixing device, it is possible to prevent the occurrence of toner blisters for color images.

  According to the third aspect of the present invention, since there is a paper type in which toner blisters are likely to be generated depending on the paper type of the recording paper, the operation of passing the fixing device twice only when forming an image of the type of paper that is likely to occur. By executing the mode, toner blisters can be efficiently prevented.

  (1) An embodiment of the present invention will be described. 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 capable of forming a double-sided image according to the present invention will be described below with reference to FIG.

  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 type 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. Device 9.

  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. At this time, the document D conveyed from the document table is subjected to glossiness level detection sensor PKa used as a gloss level selection unit to determine the glossiness of the document image, monochrome and color of the document image, and double-sided image discrimination. Done.

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

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 8Y disposed around a photosensitive drum 1Y as an image carrier. The 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. The image forming unit 10C that forms 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. The 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.

  4Y, 4M, 4C, and 4K are developing devices that include 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) by the transfer means 7Y, 7M, 7C, and 7K onto the rotating intermediate transfer body 6 and synthesized. 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 is conveyed to the transfer means 7A via the paper feed rollers 22A, 22B, 22C, the registration rollers 23, etc. A 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 by a pressure nip portion N (see FIG. 2; not shown in FIG. 1) formed in the fixing device 9, and heat and pressure are applied. As a result, the color toner image (or toner image) on the recording paper P is fixed and fixed on the recording paper P, and is sandwiched between the discharge rollers 24 on the discharge path side and placed on the discharge tray 25 outside the apparatus. Is done.

At the time of double-sided image formation, a color image (color toner image) is formed on one side (front surface), and the recording paper P discharged from the fixing device 9 is branched from the sheet discharge path by the branching unit 26 and is fed respectively. Through the lower circulating paper path 27A constituting the conveying means, the front and back are reversed by the reverse conveying path 27B which is a refeeding mechanism (ADU mechanism), and passes through the refeeding conveying section 27C to be fed by the feed roller. Merge at 22D. The recording paper P that has been reversely conveyed (circulated and reversed) is conveyed again to the secondary transfer roller 7A via the timing roller 23, and a color image (color toner image) is formed on the other side (back surface) of the recording paper P. Batch transfer. 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.

  (2) A belt fixing device used in the image forming apparatus of the present invention will be described below with reference to FIG.

  The fixing device 9 includes a fixing belt 91 in which a metal substrate or a heat-resistant resin substrate and silicon rubber are molded into a belt shape, and supports and conveys the fixing belt 91 with the transfer material and the fixing belt 91 sandwiched therebetween. It comprises a roller 92, an external pressure roller 93 opposed thereto, and a support heating roller 94 incorporating a heater 94a that supports and conveys the fixing belt 91. Further, in order to maintain the surface temperature of the external pressure roller 93 at a temperature suitable for fixing, an external heating roller 95 that contacts the outer periphery of the external pressure roller 93 may be provided. In the belt fixing device 9 configured as described above, the pressure nip portion N is formed by the support pressure roller 92 and the external pressure roller 93.

  The supporting pressure roller 92 includes a rotating shaft 921 using a cylindrical metal pipe having a thickness of 2 to 5 mm or a metal shaft, and an outer surface of the rotating shaft 921 having a 7 mm thick Si sponge elastic layer 922 fixed thereto. A soft roller with a diameter of 40 mm.

  The external pressure roller 93 has a rotating shaft 931 using a cylindrical metal pipe having a thickness of 2 to 5 mm, and a 3 mm thick Si rubber elastic layer 932 fixed to the outer peripheral surface of the rotating shaft 931, and further to the outside. And a soft roller having an outer diameter of 50 mm covered with a PFA (perfluoroalkoxy) tube 933 as a release layer.

  The elastic layer 922 of the support pressure roller 92 uses a softer material than the elastic layer 932 of the external pressure roller 93, and the elastic layer is thicker. 92 is mainly deformed to maintain the pressure contact state. In the embodiment, a nip portion of 16 mm is formed by applying a load of 900 N.

  The fixing belt 91 wound around the supporting pressure roller 92 is an endless belt having a diameter of 80 mm having a 200 μm Si rubber layer and a 30 μm PFA (perfluoroalkoxy) tube layer outside a 70 μm thick polyimide substrate. The fixing belt 91 is heat-transferred and heated through a heating roller by a heater 94a built in a support heating roller 94 that is also wound around.

  The support heating roller 94 is a roller having an outer diameter of 50 mm in which a fluororesin layer is provided on the outer periphery of an aluminum core having a thickness of 2 mm, and a fixing belt is provided at the end of the roller so that the fixing belt extends in the axial direction. The position is regulated so as not to slip.

  (3) FIG. 3 shows an outline of the electric control system. Reference numeral 110 denotes a CPU that performs arithmetic control processing, and is connected to a RAM 111 and a ROM 112. The ROM 112 stores calculation basic data, a single-sided image formation mode program, a double-sided image formation mode program, a single-sided image twice fixing mode program of the present invention, and the CPU 110 is connected to an external device via an interface 120. ing.

  Connected to the interface 120 are an image exposure means 121 such as a charging means 2, an exposure means 3 and a developing device 4, a developing device 9, and a recording paper conveying means 122 for feeding, conveying, reversing and discharging the recording paper. Has been.

  Further, the image forming apparatus shown in FIG. 1 is provided with an operation / display unit 30, and includes a start button for instructing the start of a printing operation, a size selection button for selecting the size of recording paper to be used, and printing of recording paper. In addition to a numeric keypad for instructing the number of sheets, an image density selection button for selecting the image density, etc., a selection button for single-sided image / double-sided image printing is provided.

  When the user selects single-sided image printing on the operation / display unit 30 and turns on the start button, the CPU 110 calls a single-sided image formation mode program from the ROM 112 and controls image formation according to the called program. That is, the CPU 110 controls the recording paper conveying means 122 to carry out the recording paper P from the corresponding paper feed cassette 20, and controls the image forming means 121 to form the toner image formed on the intermediate transfer member 6 with the recording paper. Control is performed so that the recording paper P transferred onto P and holding the toner image on one side is fixed by passing through the fixing device 9 and then discharged out of the apparatus through the paper discharge path.

  When the user selects double-sided image printing on the operation / display unit 30 and turns on the start button, the CPU 110 calls a double-sided image formation mode program from the ROM 112 and controls image formation according to the called program. That is, the CPU 110 controls the recording paper conveying means 122 to carry out the recording paper P from the corresponding paper feed cassette 20, and controls the image forming means 121 to transfer the toner image formed on the intermediate transfer member 6 to the recording paper. After the recording paper P, which has been transferred onto one surface (front surface) of P and the toner image is held on one surface (front surface), is fixed by passing through the fixing device 9, it is transferred again through the reverse conveyance path. 7A, the image forming means 121 is controlled to transfer the next toner image formed on the intermediate transfer body 6 onto the other surface (back surface) of the recording paper P, and the recording paper after transfer is completed. After P passes through the fixing device 9 and is fixed, control is performed so that the recording paper P having images on both sides is discharged out of the apparatus through the discharge path.

  The single-sided image twice fixing according to the present invention will be described.

  The toner blister phenomenon described above has a paper type that easily occurs and a paper type that hardly occurs. For example, the coated paper for printing (special paper) such as OS coat 127 (trade name) and OK top coat 104 (trade name). ) Causes toner blisters due to poor air permeability.

  In the present invention, it has been clarified through experiments that toner blisters generated when single-sided image printing is performed using such special paper are passed through the fixing device twice. A single-sided image twice fixing mode, which is applied when performing single-sided image printing, is provided.

  When the user performs single-sided image printing of special paper such as coated paper for printing, the user loads the special paper into the designated paper feed cassette 20 in which normal paper is normally loaded, and the special of the operation / display unit 30. Press the paper selection button to select special paper and turn on the start button.

  Upon detecting this, the CPU 110 calls a single-sided image twice fixing mode program from the ROM 112 and controls image formation according to the called program. That is, the CPU 110 controls the recording paper conveying means 122 to carry out the special paper PS from the designated paper feeding cassette 20, and controls the image forming means 121 to specialize the toner image formed on the intermediate transfer body 6. The special paper PS, which is transferred onto one surface (front surface) of the paper PS and holds the toner image on the one surface, passes through the fixing device 9 and is fixed, and then passes through the reverse conveyance path to the transfer means 7A again. And carry. On the other hand, the CPU 110 controls the image forming means 121 to rotate only the intermediate transfer body 6 without forming a toner image on the intermediate transfer body 6, and the special paper PS is also subjected to a transfer operation by the transfer means 7A. After passing through the fixing device 9 and passing through the fixing device 9 and being pressurized and heated, the special paper PS having an image on one side is discharged out of the machine through the paper discharge path. To control.

  By performing such control, the toner blister phenomenon is not recognized at all in the image on the discharged special paper PS.

  (4) The present inventors perform printing operations in various image forming modes on images having a uniform matte surface using coated paper (special paper) that is liable to generate toner blisters, and are discharged. The image on the special paper is visually evaluated from the toner blister generation state. The table below shows the relationship between the number of fixings and image evaluation based on these test results.

  In the table, “image” indicates that a surface having a toner image is fixed, and “blank” indicates that a surface in a blank state without a toner image is fixed.

  In the image evaluation, “good” indicates that no toner blisters are recognized, “good” indicates that almost no toner blisters are recognized, and “bad” indicates that toner blisters are recognized and image quality is poor. It shows that it is decreasing.

  This test result shows that when the toner image surface passes through the fixing device twice, the toner is remelted and bubbles in the toner layer escape, and the generation of toner blisters is improved. In the case of fixing the single-sided image twice (2), the special paper in a blank state once passes through the fixing device, so that the moisture content in the special paper is lowered, and the air in the toner layer is changed to the special paper. It is understood that the image quality is improved as a result of toner blisters being less likely to occur for toner images that are easily absorbed and subsequently transferred.

1 is a schematic sectional view of an image forming apparatus. Sectional drawing of a belt fixing device. 1 is a schematic block diagram of an electric control system.

Explanation of symbols

6 Intermediate transfer body 7A Transfer means 9 Fixing device 20 Paper feed cassette 30 Operation / display unit 100 Control unit 110 CPU
112 ROM

Claims (3)

The recording sheet having the unfixed toner image is passed through a fixing nip portion formed by pressing the heat fixing member and the pressure fixing member. An image forming apparatus having a double-sided image forming unit for forming and fixing an unfixed toner image again on the back surface of the recording paper on which the toner image is fixed once.
An image forming apparatus having an operation mode in which a toner image is formed on one side of a recording sheet, and discharged after passing through the fixing device twice. The fixing device includes a heating roller having a heating unit, a support roller disposed in parallel and spaced apart from the heating roller, and a fixing that is endlessly stretched between the heating roller and the support roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is a belt fixing device including an external pressure roller that is in pressure contact with the support roller via the fixing belt. The image forming apparatus according to claim 1, wherein the operation mode is executed for a selected type of recording paper.

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