JP2006145586A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a pair of conveyance rollers, disposed close to a fixing device, from forming a pressure mark or a slide scratch on a toner image on paper when holding and conveying the paper. <P>SOLUTION: The image forming apparatus includes: the fixing device 30 for applying heat and pressure to form S with an unfixed toner image transferred thereto, thereby fixing the unfixed toner image; and the pair of conveyance rollers 37 disposed downstream of the fixing nip area N of the fixing device 30 in the direction of paper conveyance and used to sandwich and convey the form S passed through the fixing nip area N. Of the pair of conveyance rollers 37, a plurality of microprotrusions 37B2 are formed on the peripheral face of the conveyance roller 37B that comes into contact with a toner image recorded on one side of the form S. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine. In particular, the toner image on a recording medium after being heated and melted by a fixing device is generated in the toner image by being pressed against a conveying roller. The present invention relates to an image forming apparatus that prevents indentation and scratches.

  In the image forming apparatus, a heating roller method, a heat fixing belt method, or the like is adopted as a fixing device that heats and fixes a recording medium carrying a toner made of a heat-meltable resin.

  The heat roller type fixing device is composed of a heating rotator having a heating element such as a halogen heater inside, and a pressure rotator that is in pressure contact with the heating rotator, and a fixing nip portion that is a pressure contact portion of the pair of rollers. By passing a recording medium such as paper, the toner image carried on the recording medium is heated and melted, and then discharged by a pair of conveying rollers.

In the image forming apparatus described in Patent Document 1, the pair of conveyance rollers closest to the downstream of the fixing nip portion of the fixing device is located on the upper roll positioned on the toner image side of the recording sheet and on the side opposite to the toner image of the recording sheet. The lower roll located is arranged in a non-contact state with a predetermined gap.
JP 2003-20149 A

  In an image forming apparatus, particularly a color image forming apparatus, generally, a multicolor toner image such as a photograph or a graph formed on a recording medium has a wider surface than a monochromatic toner image and a multicolor toner. The image formation thickness is larger than that of a monochromatic toner image.

  In a color image forming apparatus, a recording medium subjected to a special coating process may be used in order to make a color image clear. Furthermore, in order to add gloss to a color image, a high fixing temperature is set and a conveyance speed of a recording medium is reduced.

  In the fixing device that performs such color image processing, after the multicolor unfixed toner held on the recording medium is heated and melted by the fixing device, the toner on the recording medium is not completely solidified, When the recording medium is nipped and transported by the pair of transport rollers arranged in the vicinity of the fixing device, the transport roller pair causes indentations and scratches on the toner image on the recording medium.

  In the fixing device described in Patent Document 1, since the pressing force of the conveying roller pair is reduced in order to avoid the occurrence of indentation and scratches on the toner on the recording medium, the conveying force of the recording medium is reduced. , Transportation failure may occur. In particular, in a conveyance path in which a conveyance path switching member that reversely conveys the recording medium is arranged on the downstream side of the recording medium of the conveyance roller pair, when the recording medium discharged by the conveyance roller pair slides on the conveyance path switching member, There is a problem that when the recording medium is bent by the conveyance path switching member, it receives frictional resistance and causes a conveyance defect. If the conveyance path switching member is gently bent to reduce the frictional resistance, the conveyance path is extended and the image forming apparatus is enlarged.

  The present invention solves the above-described problems in the conventional fixing device, prevents the toner on the recording medium from being indented or scratched by the pair of conveying rollers, and ensures the conveying force of the recording medium, The object is to achieve downsizing of the forming apparatus.

  The object of the present invention is achieved by the following invention.

  (1) A fixing device that fixes a recording medium on which an unfixed toner image has been transferred by heating and pressing, and a fixing nip portion of the fixing device that is disposed downstream of the fixing nip portion in the recording medium conveyance direction and passes through the fixing nip portion. In the image forming apparatus provided with a pair of conveyance rollers for nipping and conveying the recording medium, a plurality of minute rollers are disposed on the outer circumferential surface of the conveyance roller that contacts the toner image of the recording medium after one-side recording. An image forming apparatus provided with a protrusion.

  (2) The image forming apparatus according to (1), wherein the minute protrusions are made of a member having an average particle diameter of 65 to 300 μm.

  (3) The image forming apparatus according to (1) or (2), wherein the material of the microprojections is formed of glass beads or ceramic powder.

  (4) The image forming apparatus according to any one of (1) to (3), wherein the toner image formed on the recording medium is a color toner image of a plurality of colors.

  (5) The image according to any one of (1) to (4), wherein a plurality of minute protrusions are provided on the outer peripheral surfaces of both of the conveyance rollers constituting the pair of conveyance rollers. Forming equipment.

  (6) a discharge conveyance path that conveys the recording medium toward the discharge section, and a reverse conveyance path branched from the discharge conveyance path, on the downstream side in the recording medium conveyance direction from the fixing device; 6. The apparatus according to any one of (1) to (5), wherein the pair of transport rollers is provided upstream of a branch point between the paper discharge transport path and the reverse transport path in the recording medium transport direction. Image forming apparatus.

  According to the fixing device of the present invention, the following excellent effects can be obtained.

  According to the first aspect of the present invention, when the recording medium is conveyed, it is completely solidified by providing a plurality of minute protrusions on the outer peripheral surface of the conveying roller that contacts the toner image of the recording medium after single-sided recording. By causing the toner on the recording medium in an unexposed state to come into point contact with the conveying roller, the toner image on the recording medium caused by the conveying roller pair is eliminated from being indented and scratched, and a high-quality image is provided. In addition, since the plurality of minute protrusions formed on the conveyance roller are brought into contact with the recording medium and conveyed by a pressing force necessary for conveyance, a sufficient conveyance force can be obtained.

  According to the second aspect of the present invention, the average particle diameter of the minute protrusions of the conveying roller that contacts the toner image is set to 65 to 300 μm to ensure the conveyance of the recording medium and to be formed on the recording medium. Generation of indentations and scratches on the toner image is eliminated, and a high-quality image is provided.

  According to the third aspect of the present invention, the minute protrusions of the conveying roller that are in contact with the toner image are formed of glass beads or ceramic powder, so that the indentation at the point contact portion becomes inconspicuous and a high-quality image is provided. .

According to the fourth aspect of the present invention, in the case of a color toner image in which the maximum toner adhesion amount of the toner image formed on the recording medium exceeds 7 g / m ² , the recording by the conveying roller pair increases as the toner adhesion amount increases. The present invention eliminates the problem of indentation and scratches on the toner image on the medium, and provides a high-quality image. In addition, even when the fixing temperature is raised to improve the glossiness of the color toner image or the conveyance speed of the recording medium is lowered, indentations and scratches are generated on the sufficiently melted color toner image. Things are resolved and high-quality images are provided.

  According to the fifth aspect of the present invention, a plurality of minute protrusions are provided on the outer peripheral surfaces of both the driving roller and the driven roller constituting the conveying roller pair, so that the two-sided image is formed on the recording medium. Generation of indentations and scratches on the toner image is eliminated, and a high-quality image is provided.

  According to the sixth aspect of the present invention, the recording medium that has passed through the nip position of the fixing device is sandwiched between the pair of transport rollers, passes through the branch point, and is transported along the curved surface having a small radius of curvature of the branch plate. Even in this case, since the conveying force against the frictional resistance with the curved surface is held by the conveying roller pair having the minute protrusions, the radius of curvature of the branch plate can be reduced and the apparatus can be miniaturized.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms.

[Image forming apparatus]
FIG. 1 is a configuration diagram of an image forming apparatus A including a fixing device according to the present invention.

  The image forming apparatus A 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 device 20, and a fixing device described later. 30 or the like.

  On the upper part of the image forming apparatus A, an image reading apparatus B is installed. The document placed on the document table is scanned and exposed by the optical system of the document image scanning exposure apparatus of the image reading apparatus B, and read by the line image sensor. The analog signal photoelectrically converted by the line image sensor is subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the image processing unit, and then input to the exposure means 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 5Y 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 5M. An image forming unit 10C for forming a cyan (C) color 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 5C. 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 5K. 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 contain a two-component developer composed of a small particle size toner 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 images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) and synthesized by the primary transfer units 7Y, 7M, 7C, and 7K on the rotating intermediate transfer body 6. A color image is formed.

  A recording medium (hereinafter referred to as “paper”) S stored in a paper storage unit (paper cassette) 21 of the paper supply device 20 is supplied by a paper supply unit (first paper supply unit) 22 and is supplied by a paper supply roller. 23, 24, 25A, 25B, registration rollers (second paper feed unit) 26, etc., are conveyed to secondary transfer means (transfer roller) 9, and a color image is transferred onto paper S (secondary transfer). .

  It should be noted that the three-stage paper storage units 21 arranged vertically in the vertical direction below the image forming apparatus A have substantially the same configuration, and thus are denoted by the same reference numerals. Also, the three-stage paper feeding means 22 has almost the same configuration, and therefore is given the same reference numeral. The paper storage unit 21 and the paper supply means 22 are collectively referred to as a paper supply device 20.

  The size and paper type of the paper S stored in the paper storage unit 21 are displayed on the display screen of the operation unit 11 and are arbitrarily selected and set. It is also possible to automatically set the size of the paper S according to the document size and the copy magnification.

  The sheet S on which the color image has been transferred is sandwiched by the fixing device 30, and the color toner image (or toner image) on the sheet S is fixed by applying heat and pressure, and is fixed on the sheet S. Then, the paper is nipped and transported between the pair of transport rollers 37, discharged from a paper discharge roller 27 provided in the paper discharge transport path, and placed on a paper discharge tray 28 outside the apparatus.

  On the other hand, after the color image is transferred to the sheet S by the secondary transfer unit 9, the residual toner is removed by the cleaning unit 8 from the intermediate transfer body 6 that has separated the curvature of the sheet S.

  In the case of reversely discharging the fixed sheet S, the sheet S passes through the conveyance path on the right side of the branch plate 29 arranged at the middle branch point between the fixing device 30 and the sheet discharge roller 27 and is conveyed downward. After being transported to the path r1 (reverse transport path), it is transported in reverse, passes through the transport path r2 on the left side of the branch plate 29, and is discharged out of the apparatus by the paper discharge roller 27.

  When copying on both sides of the paper S, after fixing the image formed on the first surface of the paper S, the paper S is branched from the paper discharge conveyance path by the branch plate 29, and the lower conveyance path r1 is further conveyed. After being introduced into the path r3, the sheet is conveyed in the reverse direction, conveyed to the conveyance path r4, detoured upward, and conveyed by the paper feed roller 25B.

  The sheet S is formed on both sides by the image forming means 10Y, 10M, 10C, and 10K with images of each color, heated and fixed by the fixing device 30, and discharged to the outside by the paper discharge roller 27.

  In the description of the image forming apparatus A, the color image formation has been described. However, the present invention includes a case of forming a monochrome image.

[Overall configuration of fixing device]
Hereinafter, the fixing device 30 of the image forming apparatus A will be described.

  FIG. 2 is a cross-sectional view showing an embodiment of the heating roller type fixing device 30.

  The fixing device 30 includes a fixing roller 31 heated by a heating source 33, a pressure roller 32 heated by a heating source 34, and the like.

  Around the fixing roller 31, a cleaning roller 35, a temperature detecting means (temperature sensor) TS1, a thermostat for preventing an abnormal temperature (not shown), and the like are arranged. Also around the pressure roller 32, a temperature detecting means (temperature sensor) TS2, a thermostat for preventing abnormal temperature, and the like are arranged.

[Fixing roller]
A halogen lamp, induction heating means, or the like is used for the heating sources 33 and 34.

  The fixing roller 31 includes a heat conductive substrate (core metal) 311, an elastic layer 312, a coating layer 313, and the like.

  The temperature sensor TS1 detects the surface temperature of the fixing roller 31. The control means controls the surface temperature of the fixing roller 31 to a predetermined temperature based on the detection signal of the temperature sensor TS1.

  When the sheet S is introduced into the fixing nip N where the fixing roller 31 and the pressure roller 32 are in pressure contact, the heat of the fixing roller 31 heated by the heating source 33 is applied to the sheet S, and the toner image on the sheet S is applied. t is fixed by heating.

  The fixing roller 31 is a cylindrical member having an outer diameter of 20 to 70 mm, which includes a heat conductive base 311, an elastic layer 312, and a coating layer 313. As the cylindrical heat conductive substrate 311, an aluminum material having good heat conductivity is mainly used, and a nonmagnetic stainless steel material, heat resistant glass, or the like is also used. The heat conductive substrate 311 has a required mechanical strength and a thickness (wall thickness) of 0.8 to 10 mm.

  The elastic layer 312 is formed of synthetic rubber such as silicone rubber or fluorine rubber, for example. Further, in order to cope with speeding up of image formation, a method of improving thermal conductivity by blending 5-30% by mass of a metal oxide powder such as silica, alumina, magnesium oxide or the like as a filler in the synthetic rubber is preferable. . The mixed filler is preferably a highly conductive one like the conductive carbon black. By doing so, the electrical resistance (volume resistivity) of the elastic layer 312 can be easily set low. The elastic layer 312 has a thickness (wall thickness) of 0.3 to 3 mm, preferably 1 to 3 mm, and a rubber hardness of 5Hs to 30Hs, which is a JIS-A rubber hardness.

  In order to improve the releasability from the toner on the outer side (outer peripheral surface) of the elastic layer 312, a 20 to 80 μm thick PFA (fluororesin) tube or a fluororesin (PFA or PTFE) paint is used. A heat-resistant coating layer 313 having a good thermal conductivity and a heat-resistant coating layer 313 is provided which is applied with 20 to 100 μm, or formed with silicone rubber or fluororubber having a layer thickness of 20 to 500 μm. The covering layer 313 improves the releasability with the toner and enhances the durability of the elastic layer 312.

[Pressure roller]
A pressure roller 32 as a lower cylindrical fixing member that forms a pair with the upper fixing roller 31 is a cylindrical member, and includes a heat conductive base 321, an elastic layer 322, and a coating layer 323. The constituent members of the pressure roller 32 are formed with substantially the same material, characteristics, and dimensions as the constituent members of the fixing roller 31.

  For example, a thermally conductive substrate 321 using STKM having a thickness of 1 to 3 mm, and a sponge-like thickness using, for example, a silicone rubber layer, a fluorine rubber layer, or a foamed material of silicone rubber on the outer peripheral surface of the thermally conductive substrate 321. (Thickness) A roller having an outer diameter of about 30 to 700 mm formed by an elastic layer 322 made of a thick rubber layer having a thickness of 0.3 to 5 mm and a rubber hardness of 30 Hs to 70 Hs (JIS-A rubber hardness). Is done. On the outer side (outer peripheral surface) of the elastic layer 322, a coating layer 323 is formed that covers a tube of heat-resistant fluororesin such as PFA or PTFA having releasability. A planar fixing nip portion N is formed between the upper fixing roller 31 rotatably supported at the fixed position and the lower pressure roller 32 pressed against the fixing roller 31 by being spring-biased. The image t is fixed.

  The sheet S that has passed through the fixing nip N of the fixing device 30 is separated from the outer peripheral surface of the fixing roller 31 by the separation claw 36. On the downstream side of the fixing nip N in the sheet conveyance direction, a conveyance roller pair 37 including a driving roller 37A and a driven roller 37B is disposed.

[Conveying roller pair]
FIG. 3A is a perspective view showing the configuration of the conveying roller pair 37 according to the embodiment of the present invention, and FIG. 3B is an enlarged cross-sectional view of the conveying roller pair 37.

  The conveyance roller pair 37 includes a driving roller 37A that is driven and rotated by being connected to a driving source (not shown), and a driven roller 37B that is driven to rotate by being pressed by the driving roller 37A by an urging means (not shown). The conveyance roller pair 37 is a pair of roller pairs in which a driving roller 37A and a driven roller 37B are in pressure contact with each other and fixed to a rotating shaft.

  The surface of the driving roller 37A fixed to a rotating shaft rotated by a driving means (not shown) is formed of heat resistant rubber.

  The length of pressure contact of the driven roller 37B with the driving roller 37A in the direction of the rotation axis is 16 mm when the pair of roller pairs is 8 mm. The pressing force of the conveying roller pair 37 per total length of 16 mm was set to 0.42 N to 0.96 N (N is Newton).

  The driven roller 37B is disposed above the paper conveyance path and contacts the toner image t. A plurality of minute protrusions 37B2 are formed in a convex shape on the outer peripheral surface of the roller base 37B1 of the driven roller 37B. The microprotrusion 37B2 has excellent wear resistance and can provide a stable point contact, or has a high rigidity and a uniform particle size to obtain a stable point contact and secure a uniform gap with the toner layer. Material is preferred.

  Table 1 shows the particle diameter of the microprojections 37B2 and the evaluation of the toner image t on the paper S that has been fixed by the fixing unit and discharged through the pair of conveying rollers. The evaluation of the toner image t is based on visual judgment.

  The average particle diameter of the microprojections 37B2 is in the range of 65 to 300 [mu] m, preferably 80 to 170 [mu] m, because it does not cause deterioration of image quality such as roller marks or scratches due to roller rubbing.

  In manufacturing the driven roller 37B, the paint layer 37B3 is formed by spraying the paint with an electrostatic coating device. Subsequently, fine protrusions 37B2 made of ceramic powder are sprayed by an electrostatic coating apparatus. The sprayed ceramic powder is uniformly distributed and attached to the outer peripheral surface of the roller base 37B1 in a state of being in contact with the coating layer 37B3.

  When a pressing force necessary for transporting the paper S is applied to the transport roller pair 37 and the paper S is transported in pressure contact with the opposing drive roller 37A, the toner on the paper S that is not completely solidified is driven roller 37B. Therefore, the toner image t on the paper S caused by the driven roller 37B is eliminated from being indented or scratched, and a high-quality image is provided.

  Further, since the plurality of minute protrusions 37B2 formed on the driven roller 37B are brought into contact with the sheet S and conveyed by a pressing force necessary for conveyance, the branch plate 29 (disposed on the sheet conveyance downstream side of the conveyance roller pair 37) When it is bent in sliding contact with (see FIG. 1), even if it receives a frictional resistance, it does not cause a conveyance failure.

In the color image forming apparatus shown in FIG. 1, when forming a multilayer color toner image t having a maximum toner adhesion amount of the toner image t formed on the paper S exceeding 7 g / m ² , for example, conventionally, toner adhesion The present invention eliminates the problem of indentation and scratches on the toner image t on the paper S caused by the conveying roller pair 37 that has been generated as the amount increases, and provides a high-quality image. Even when the fixing temperature is increased to improve the glossiness of the color toner image t or the conveyance speed of the recording medium is decreased, the sufficiently melted color toner image t may be indented or scratched. Occurrence is eliminated and a high-quality image is provided.

  Further, by providing a plurality of minute protrusions on the surface of the driving roller 37A constituting the conveying roller pair 37, it is possible to improve the image quality when forming a double-sided image.

  In the embodiment of the present invention, the fixing device mounted on the color image forming apparatus has been described. However, the present invention is also applicable to a single-color or multi-color copying machine, a facsimile, a printer, and a multifunction machine having these functions. .

1 is a configuration diagram of an image forming apparatus including a fixing device according to the present invention. FIG. 3 is a cross-sectional view showing an embodiment of a fixing device of a heating roller type. The perspective view which shows the structure of the conveyance roller pair which shows embodiment of this invention, and the expanded sectional view of a conveyance roller pair.

Explanation of symbols

30 Fixing device 31 Fixing roller 32 Pressure roller 33, 34 Heat source (heater)
37 Conveying roller pair 37A Driving roller 37B Driven roller 37B1 Roller base 37B2 Micro protrusion 37B3 Coating layer A Image forming apparatus S Recording medium (paper)
N Fixing nip

Claims (6)

The fixing device that fixes the recording medium on which the unfixed toner image has been transferred by heating and pressurizing, and the recording that is disposed downstream of the fixing nip portion of the fixing device in the recording medium conveyance direction and passes through the fixing nip portion. In an image forming apparatus provided with a pair of conveyance rollers for nipping and conveying a medium,
An image forming apparatus, comprising: a plurality of minute protrusions provided on an outer peripheral surface of a conveyance roller that contacts a toner image of the recording medium after one-side recording. The image forming apparatus according to claim 1, wherein the minute protrusions are made of a member having an average particle diameter of 65 to 300 μm. The image forming apparatus according to claim 1, wherein the material of the microprojections is formed of glass beads or ceramic powder. The image forming apparatus according to claim 1, wherein the toner image formed on the recording medium is a color toner image of a plurality of colors. 5. The image forming apparatus according to claim 1, wherein a plurality of minute protrusions are provided on outer peripheral surfaces of both of the transport rollers constituting the transport roller pair. A conveyance roller having a discharge conveyance path for conveying the recording medium toward the sheet discharge unit and a reverse conveyance path branched from the discharge conveyance path, on the downstream side in the recording medium conveyance direction from the fixing device; 6. The image forming apparatus according to claim 1, wherein the pair is provided on the upstream side in the recording medium conveyance direction with respect to a branch point between the discharge conveyance path and the reverse conveyance path.

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