JP2006330253A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where a transferred image on transfer material is not affected even though a fixing roller or a fixing belt comes into contact with recording material to cause change in terms of physical properties on the surface of a fixing member when paper passes consecutively. <P>SOLUTION: By making the peripheral length of the fixing member longer than the size of the recording material and changing a position where the recording material comes into contact with the fixing member in the midst of consecutive fixing operation by prescribed amount, the history of defective image quality caused on the surface of the fixing member is restrained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a FAX.

  In general, an electrophotographic image forming apparatus is provided with a charging unit, an exposure unit, and a developing unit at the periphery of an image carrier, and forms a toner image on the image carrier by charging, exposing and developing, and a recording material. Fixing means for fixing a toner image by sandwiching and transporting an unfixed toner image on a recording material formed by transfer onto a heated roller and a pressure roller pressed against the heating roller are widely used. .

  In such a fixing device, when the length in the recording material conveyance direction is longer than the circumferential length of the heating roller, the recording material is rotated with a heating roller that rotates after the leading end of the recording material in the conveyance direction contacts the heating roller. Although it is nipped and conveyed by the pressure roller, the second rotation heating roller comes into contact again with the rear end portion of the recording material that is still in contact with the heating roller (not yet passed through the nip portion). This portion is referred to as an overlap portion (see FIG. 3d).

  The heating roller temperature of this overlap portion is lower than the normal fixing temperature because heat is taken away while in contact with the recording material, so-called fixing under which the fixing is not performed completely, or on the heating roller There arises a problem that the unfixed toner is transferred to the pressure roller so as to stain the back surface of the recording material, so-called back surface contamination. Further, even if such a significant defect does not occur, the gloss of the overlap portion is lower than that of the preceding portion and the boundary is clear, resulting in a difference in gloss and lowering the image quality.

In order to solve the above problem, a method has been proposed in which the circumferential length of the heating roller is set to a length obtained by adding the length of the recording material and the interval length of the next recording material, or an integral multiple thereof. (For example, Patent Document 1)
In addition, a method has been proposed in which the peripheral length of the fixing member is set to be equal to or greater than the length in the conveyance direction of the standard size having the highest use frequency, or to the length of the short size of the standard size. (For example, Patent Document 2)
JP-A-8-146797 JP 2002-49264 A

However, in the methods described in Patent Document 1 and Patent Document 2, when the sheet is continuously passed, the recording material always comes into contact with the surface of the fixing member, and the wax contained in the toner, the toner itself, and the paper that comes out of the paper Differences occur in the roughness of the surface of the fixing member and in chemical and electrostatic characteristics due to powder and the like.
In this way, changes in physical properties remain as a history on the surface of the fixing member, causing a difference in image quality in the next job.

  In view of the above problems, the object of the present invention is to make a sharp boundary change due to an end face in the conveyance direction of a physical recording material on the surface of the fixing member when a specific position of the fixing roller or the fixing belt comes into contact with the recording material during continuous paper feeding. It is an object of the present invention to provide an image forming apparatus that prevents the occurrence of the above-described problem and does not affect the transferred image on the transfer material.

(Claim 1)
A fixing unit configured to nipping and conveying an unfixed toner image on a recording material by a heated fixing member and a pressure member to heat and fix the fixing member, wherein the fixing member has a circumferential length longer than a recording material size. In an image forming apparatus having
An image forming apparatus comprising means for changing the position of a recording material in contact with the fixing member by a predetermined amount during a continuous fixing operation.

(Claim 2)
The image forming apparatus according to claim 1, wherein the predetermined amount for shifting the position of the recording material is equal to or shorter than a length of the non-image forming area.

(Claim 3)
A fixing unit configured to nipping and conveying an unfixed toner image on a recording material by a heated fixing member and a pressure member to heat and fix the fixing member, wherein the fixing member has a circumferential length longer than a recording material size. In an image forming apparatus having
An image forming apparatus comprising means for making the position of the recording material in contact with the fixing member different between a continuous fixing operation and a next continuous fixing operation.

  According to the first aspect of the present invention, by making the peripheral length of the fixing member longer than the recording material size, the history of the previous print does not come into contact with the subsequent prints (does not overlap). Further, during a continuous fixing operation, the boundary of the change occurring on the surface of the fixing member can be made ambiguous by changing the position of the recording material in contact with the fixing member by a predetermined amount.

  According to the second aspect of the present invention, the predetermined amount for shifting the position of the recording material is the same as or shorter than the length of the non-image forming area. Has no effect.

  According to the third aspect of the present invention, since the position of the recording material in contact with the fixing member is changed between the continuous fixing operation and the next continuous fixing operation, printing or printing can be performed in advance in the job. Unaffected by previous prints. Since the position changes between jobs, there is no permanent history.

  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. Further, the following assertive description in the embodiment of the present invention shows the best image forming mode, and does not limit the meaning or technical scope of the terms of the present invention.

  An image forming apparatus including the fixing device according to the present invention will be described below with reference to FIG. The fixing means according to the present invention will be described 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 17.

  An image reading device YS including an automatic document feeder 301 and a document image scanning exposure device 302 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 301 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 302, 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 material P as a transfer material accommodated in the paper feeding cassette 20 is fed by the paper feeding means 21 and conveyed to the transfer means 7A via the paper feeding rollers 22A, 22B, 22C, the registration rollers 23, and the like. A color image is transferred onto the recording material P (secondary transfer). The recording material P to which the color image has been transferred is formed in the fixing device 17, and is formed in the auxiliary nip portion Na (see FIG. 2, not shown in FIG. 1) and the fixing device 17 positioned prior to the fixing position. The recording material P is sandwiched at the main nip portion Nb (see FIG. 2, not shown in FIG. 1), and the color toner image (or toner image) on the recording material P is fixed by applying heat and pressure to record. The sheet P is fixed on the material P, sandwiched between the sheet discharge rollers 24 on the sheet discharge path side, and placed on the sheet 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 (front surface), and the recording material P discharged from the fixing device 17 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 material P that has been reversed (circulated and reversed) is again conveyed to the secondary transfer roller 7A via the timing roller 23, and a color image (color toner image) is formed on the other surface (back surface) of the recording material P. Batch transfer. The recording material P onto which the color image has been transferred is subjected to fixing processing by the fixing device 17, 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 material 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 material P is separated by curvature.

  FIG. 2A shows a fixing belt 27 made of an endless belt member, a fixing roller 17 a that supports and stretches the fixing belt 27 on one of the inner peripheral surfaces of the fixing belt 27, and the other of the inner peripheral surfaces of the fixing belt 27. A fixing nip portion Nb is formed between a heating roller 17c that supports and stretches the fixing belt 27 and has a heater 173c therein and a pressure roller 17b that contacts and presses the fixing roller 17a via the fixing belt 27. In addition, the toner image on the recording material P is fixed and fixed by heating and pressing at the fixing nip portion Nb.

  Further, the pressure applied by the pressure roller that presses the fixing roller is desirably 800 N to 1200 N in consideration of gloss after transfer, curl of the transfer material, and the like. At this time, the rotation shaft on the fixing roller side is fixed (does not move up and down), and a pressure release mechanism (not shown) is provided on the pressure roller side.

  Here, the fixing belt 27 uses a heat-resistant resin belt such as polyimide as a base, an outer diameter of about 150 to 170 mm, a peripheral length of 500 to 550 mm, a width of 350 to 400 mm, a thickness of 50 to 200 μm, and the outer side (outer peripheral surface) of the base. In addition, a silicon rubber having a thickness of about 100 to 500 μm is coated with PFA (perfluoroalkoxy) or a fluorine-based resin having a thickness of about 30 to 50 μm as a release layer, or a PFA tube is coated. It is configured. The silicon rubber layer is preferable as a condition for obtaining good fixability and thermal responsiveness in a rubber hardness range of 20 to 40 degrees (JIS-A hardness meter).

  The fixing roller 17a includes, for example, a metal pipe 171a using a steel material such as STKM (carbon steel pipe for mechanical structure), and a thickness of 5 to 15 mm and a hardness of 5 to 30 degrees (JIS-A hardness) on the outer peripheral surface of the metal pipe 171a. A total of silicon rubber layer 172a is provided, and is configured as a soft roller having an outer diameter of about 20 to 50 mm.

  The pressure roller 17b is made of, for example, a metal pipe 171b having a thickness of about 2 to 5 mm using a steel material such as STKM (carbon steel pipe for mechanical structure) or an aluminum material, and a thickness of 1 to 1 on the outer peripheral surface of the metal pipe 171b. A 3 mm silicon rubber layer 172 b is provided, and a release layer 173 b using a PFA (perfluoroalkoxy) tube having a thickness of about 20 to 50 μm on the outside of the silicon rubber layer 172 b, and having an outer diameter of about 40 to 80 mm. It is configured as a soft roller and has a pressure roller heater 174b made of a halogen heater inside. The silicone rubber layer has a rubber hardness of 5 to 30 degrees (JIS-A hardness meter), and is provided with a pressure roller temperature sensor 175b that is in contact with or not in contact with the pressure roller 17b. It is possible.

  The heating roller 17c includes a cylindrical metal pipe 171c having a thickness of about 1 to 5 mm using, for example, an aluminum material as a base, and a PFA (perfluoroalkoxy) having a thickness of about 10 to 30 μm on the outer peripheral surface of the metal pipe 171c. It is configured as a roller member having an outer diameter of about 40 to 80 mm formed with a coating 172c, and has a heating roller heater 173c made of a halogen heater inside. Further, a heating roller temperature sensor 174c is provided so as to be in contact with or not in contact with the heating roller 17c, and the temperature of the heating roller 17c can be controlled.

  Here, the fixing means is a belt fixing system, but a cylindrical roller fixing system having a diameter larger than the maximum length of the recording material as shown in FIG.

  In FIG. 2B, the fixing heating roller 17d is a metal pipe 171c having a thickness of about 1 to 10 mm using, for example, an aluminum material as a base, and a silicon rubber layer having a thickness of 1 to 5 mm on the outer peripheral surface of the metal pipe 171c. And a roller member having an outer diameter of about 160 to 175 mm, in which a PFA (perfluoroalkoxy) coating 172c having a thickness of about 10 to 30 μm is formed on the outer peripheral surface of the silicon rubber layer, and is composed of a halogen heater inside. It has a heat source 173d. The pressure roller has the same configuration as the pressure roller 17b.

  FIG. 3 shows the positional relationship when the circumference of the fixing belt 27 and the recording material are shifted by a predetermined amount. FIG. 3e shows that an overlap portion is generated when the circumferential length of the fixing roller is shorter than the recording material size.

In FIG. 3a, the circumference of the fixing belt 27 is longer than the recording material size. That is, when paper size + paper interval = belt circumference, there is no overlap portion of the conventional method, so that fixing can be performed without causing a temperature boundary due to the paper leading edge. However, since the recording material contacts the fixing member at the same position during continuous fixing operation, the fixing member surface roughness, chemical and electrostatic characteristics are increased by the wax contained in the toner, the toner itself, and paper dust from the paper. A difference occurs and a fixing history occurs.

Therefore, as shown in FIG. 3b, the distance between sheets is set so as to satisfy the following equation.
Paper size + paper interval = belt circumference ± predetermined amount predetermined amount ≦ non-image forming area width. If the predetermined amount is positive, the position of the recording material on the belt gradually shifts backward, and if it is negative, it shifts forward.

  In this way, the position of the recording material in contact with the fixing member is gradually changed, and the fixing failure such as the roughness of the fixing member surface or chemical change is made uniform, and the difference in image quality can be suppressed. Also, by making the predetermined amount smaller than the non-image area width, it is possible to avoid the boundary history of the previous print from affecting the image.

  Here, the non-image forming area refers to a portion where an image is not formed at the front and rear end portions in the conveyance direction of the recording material.

  Further, in the above embodiment, the recording material position on the belt is changed during the job, but the position of the recording material relative to the fixing member may be different between the continuous fixing operation and the next continuous fixing operation. In this case, the fixing history is more disadvantageous than the means for changing the position of the recording material of the belt for every belt rotation, but the printing before and further before the printing history does not affect the image in the job.

  The above is a measure for printing paper such as coated paper whose fixing quality is affected by the fixing history, but it is related to the fixing belt rotation cycle when printing continuously on plain paper that does not require high image quality, such as A4 size. In addition, it is possible to improve the print productivity by performing continuous printing in a cycle of a length obtained by adding the length in the A4 conveying direction and the distance between the sheets (FIG. 3c).

Example 1
The fixing device shown in FIG. 2A was attached to the image forming apparatus shown in FIG. 1 to form an image, and the fixing glossiness was visually determined. In this example, Konica Minolta copy paper NR-A80 was used as the plain paper, and POD128 g / m ² paper made from Oji Paper was used as the coated paper.

  In this embodiment, the maximum paper size is A3 (paper transport direction 420 mm × width 297 mm). The predetermined amount was 2 mm (in the spreading direction). The design dimension of the paper interval is 110 mm.

The configuration of the fixing device is as follows.
Fixing belt: Inner diameter 165 mm (circumference length 520 mm)
Base material Polyimide
Base thickness 0.07mm
Elastic layer thickness 0.2mm
Material of elastic layer Silicon rubber (hardness JIS-A 30 degrees)
0.03mm PFA tube coated fixing roller: Outer diameter 40mm
Base material Carbon steel pipe for machine structure
Base thickness 2mm
The outer diameter of the substrate 26mm
Elastic layer thickness 7mm
Material of elastic layer Silicone sponge (hardness Asker-C30 degree)
Heating roller: 50mm outer diameter
Base material Aluminum pipe PFA coating thickness 10μm
Thickness of substrate 3mm
Pressure roller: 50mm outer diameter
Base material Carbon steel pipe for machine structure
Base thickness 2mm
Base diameter 46mm
Elastic layer thickness 2mm
Elastic layer material Silicon rubber (hardness JIS-A 10 degrees)
0.05mm PFA tube coating system speed: 300mm / sec Nip pressure contact force: 900N
Number of copies: 1000 continuous sheets of plain A3 size paper
Coated paper A3 size continuous 1000 sheets In Example 1 above, the difference in the amount of release agent contained in or applied to the toner on the surface of the fixing belt and a slight amount of offset toner, the difference in surface wear, and contact with the paper Long-term deformation of the belt rubber due to the paper step in the region did not occur. After that, even when an A4 size image is passed in the productivity priority mode, no history boundary is generated.
(Comparative Example 1)
After passing the A4 size image in the productivity priority mode after passing the paper under the same conditions with the predetermined amount = 0, the boundary between the place where the paper touches the belt and the place where it does not is recognized as a gloss difference. It was necessary to pass about 300 sheets until the difference in gloss was resolved.
(Example 2)
The paper was passed under the same conditions as in Example 1 except that the paper to be passed was A4 size, and then A3 size paper was passed, but no history of A4 size paper was found.
(Comparative Example 2)
Except that the paper to be passed is A4 size, the paper is passed under the same conditions as in Comparative Example 1 and then A3 size paper is passed. The history of A4 size paper is recognized in the image, and the visual history is not understood. It was necessary to pass about 300 sheets.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus including a fixing device according to the present invention. 1 is a schematic sectional view of a fixing device according to the present invention. FIG. 6 is a diagram illustrating a relationship between a circumferential length of a fixing belt according to the present invention, a length in a conveyance direction of each recording material, and a circumferential length of a fixing roller of a conventional method.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 2Y, 2M, 2C, 2K Charging unit 3Y, 3M, 3C, 3K Exposure unit 4Y, 4M, 4C, 4K Developing device 27 Fixing belt 101 System control unit 102 Reading control unit 103 Image Processing unit 104 Conveyance drive control unit 105 Image formation control unit 106 Display operation control unit 107 Memory 108 Fixing control unit 17 Fixing device 17a Fixing roller 17b Pressure roller 17c Heating roller 173c Heating heater Nb Main nip portion P Recording material

Claims (3)

A fixing unit configured to nipping and conveying an unfixed toner image on a recording material by a heated fixing member and a pressure member to heat and fix the fixing member, wherein the fixing member has a circumferential length longer than a recording material size. In an image forming apparatus having
An image forming apparatus comprising means for changing the position of a recording material in contact with the fixing member by a predetermined amount during a continuous fixing operation. The image forming apparatus according to claim 1, wherein the predetermined amount for shifting the position of the recording material is equal to or shorter than a length of the non-image forming area. A fixing unit configured to nipping and conveying an unfixed toner image on a recording material by a heated fixing member and a pressure member to heat and fix the fixing member, wherein the fixing member has a circumferential length longer than a recording material size. In an image forming apparatus having
An image forming apparatus comprising means for making the position of the recording material in contact with the fixing member different between a continuous fixing operation and a next continuous fixing operation.

Images