JP2006030744A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of changing glossiness in a wide range in a state where image slurring is little with simple constitution. <P>SOLUTION: The image forming apparatus has a sliding member having elasticity, an endless fixing belt at least stretched and laid on the sliding member, and a pressure member provided to be opposed to the sliding member through the fixing belt, and a toner image on recording paper conveyed between the pressure member and the sliding member through the fixing belt is fixed. The apparatus has a pressing means for pressing the upstream side end and the downstream side end of the sliding member seen in a recording paper conveying direction linearly in a direction perpendicular to the recording paper conveying direction to the direction of the pressure member, and the pressing force of the pressing means to at least one end of the sliding member is varied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including a fixing device using a fixing belt used for image formation, such as an electrophotographic copying machine, a printer, and a FAX.

  When a color image is formed by a copying machine or the like, high gloss is preferred because the color gamut can be widened. However, when non-glossy paper is used, the glossiness differs between the image area and the paper and looks unnatural. .

  In this case, an image having a gloss level comparable to that of paper tends to be preferred.

  In addition, when printing a character image in monochrome, low gloss is preferred because the characters are glaring and difficult to see.

  As described above, in response to the demand for varying the glossiness according to the use situation, the following techniques for varying the glossiness using a belt fixing device capable of forming a wide nip width have been proposed.

  One is to heat-fix the toner image on the transfer paper by passing the transfer paper between an endless fixing belt rotatably supported by a plurality of rollers and a pressure roller in contact with the fixing belt. In this fixing device, the contact width between the fixing belt and the pressure roller is changed according to the type of transfer paper to be used to obtain a desired fixing condition (see, for example, Patent Document 1). .

One has a first heating source, forms a nip portion for nipping and conveying a recording material carrying unfixed toner, a fixing member for fixing the unfixed toner image by heat, and a second heating source A pre-fixing heating means that heats the recording material and the unfixed toner image in a non-contact manner, and is positioned in the upstream side of the nip portion with respect to the conveyance direction of the recording material. A fixing device having a guide member that guides the recording material to the nip portion in proximity, and fixing by changing a distance between the guide member and the second heating source based on a condition of an image to be created The amount of heat given to the recording material by the preheating means is controlled to obtain a desired gloss level (see, for example, Patent Document 2).
JP-A-5-165357 JP 2003-330299 A

  However, in the configuration described in Patent Document 1, the nip pressure generated between the fixing belt and the pressure roller is low, and there is a possibility that sufficient fixing properties and glossiness may not be obtained.

  Also, when the backup roller is placed at a position facing the pressure roller via the fixing belt to increase the nip pressure, the nip pressure varies within the contact width between the fixing belt and the pressure roller, and the fixing process is in progress. In other words, the image on the transfer paper is misaligned.

  Further, in the configuration described in Patent Document 2, the recording material is supplied with heat from a heating source in a non-contact manner. However, when the recording material is transported at a high speed or high glossiness is desired, it is desirable. The glossiness of may not be obtained.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an image forming apparatus capable of changing glossiness over a wide range with a simple configuration and little image displacement.

  The object of the present invention can be achieved by the following constitution.

  (1) An elastic sliding member, at least an endless fixing belt stretched around the sliding member, and a pressure member provided to face the sliding member via the fixing belt An image forming apparatus for fixing a toner image on a recording sheet conveyed between the pressure member and the sliding member via the fixing belt, the upstream of the sliding member in the recording sheet conveying direction. A pressing unit that presses the side end and the downstream end in a direction perpendicular to the recording paper conveyance direction in the direction of the pressing member, and the pressing unit includes at least one end of the pressing unit; An image forming apparatus characterized in that a pressing force to a sliding member is variable.

  (2) In the above (1), the pressing means is configured to simultaneously press an upstream end and a downstream end of the sliding member viewed in the recording paper conveyance direction. Image forming apparatus.

  (3) The pressing means presses the central portion of the sliding member viewed in the recording paper conveyance direction into a line perpendicular to the recording paper conveyance direction in the direction of the pressure member with a predetermined fixed pressure. The image forming apparatus according to (1) or (2), further including a central pressing member that performs the above operation.

  (4) The pressing unit is configured to make the pressing force at the upstream end or the downstream end as viewed in the recording paper conveyance direction of the sliding member constant (1). The image forming apparatus described in 1.

  (5) The sliding member comprises a rubber-like or sponge-like elastic sliding member that contacts the fixing belt and a supporting member that supports the elastic sliding member. The image forming apparatus according to any one of the above.

  (6) The image forming apparatus according to any one of (1) to (5), wherein the sliding member includes a fluororesin layer, and the fluororesin layer contacts the fixing belt. apparatus.

  According to the first aspect of the present invention, the elastic sliding member, at least the endless fixing belt stretched around the sliding member, and the sliding member are provided to face the sliding member. In the image forming apparatus for fixing a toner image on a recording sheet conveyed between the pressure member and the sliding member via the fixing belt, the recording of the sliding member is performed. A pressing means for pressing the upstream end and the downstream end in the paper transport direction in a direction perpendicular to the recording paper transport direction in the direction of the pressure member, and at least of the press means; By making the pressing force to the sliding member at one end variable, the nip width in which the sliding member is in contact with the pressure member via the fixing belt can be changed greatly, and the nip Even if the width is changed, the nip pressure is spread over the entire nip width. Since it takes with changes smoothly, with less of the image shift can be obtained glossiness corresponding to the various paper types.

  According to the second aspect of the present invention, the pressing means is configured to simultaneously press the upstream end and the downstream end of the sliding member as viewed in the recording paper conveyance direction. As a result, the pressure distribution is symmetrical, and a nip pressure with little change in the entire nip width can be obtained, so that image misalignment can be reduced for various paper types.

  According to a third aspect of the present invention, the pressing means applies the central portion of the sliding member viewed in the recording paper conveyance direction to a linear shape perpendicular to the recording paper conveyance direction at a predetermined fixed pressure. By having a central pressing member that presses in the direction of the pressure member, the center portion of the nip width is pressed at a predetermined fixed pressure, so that fixing ability can be ensured even if the nip width is narrowed and the glossiness is lowered. it can.

  According to a fourth aspect of the present invention, the pressing means is configured to vary the pressing force at the upstream end or the downstream end as viewed in the recording paper conveyance direction of the sliding member. The fixing conditions including the degree can be changed greatly.

  For example, by changing the pressing force at the upstream end and greatly changing the nip width, the fixing property can be secured by the pressing force at the downstream end and the gloss control range can be widened.

  Further, by changing the pressing force at the downstream end, the toner can be fixed at the upstream end, and the glossiness can be changed with less image displacement.

  According to a fifth aspect of the present invention, the sliding member comprises a rubber-like or sponge-like elastic sliding member that comes into contact with the fixing belt, and a support member that supports the elastic sliding member. Since the nip pressure is applied from the sliding member following the irregularities on the surface of the paper, uniform glossiness can be obtained over the entire area of the recording paper.

  According to the invention of claim 6, the sliding member has a fluororesin layer, and the fluororesin layer is configured to contact the fixing belt, whereby the frictional force between the fixing belt and the sliding member is increased. Accordingly, the life of the fixing belt and the sliding member can be extended.

  Hereinafter, an example of an embodiment of the present invention will be described. The description in this column does not limit the technical scope of the claims and the meaning of the terms, and the assertive explanation in the following embodiments of the present invention shows the best mode, It does not limit the meaning or technical scope of the terms of the present invention.

  First, an image forming apparatus using a fixing device according to the present invention will be described with reference to FIG.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus.

  In addition, in the following description including FIG. 1, the same number is attached | subjected to the member which has the same function and structure.

  According to FIG. 1, the image forming apparatus GS includes an image forming apparatus main body GH and an image reading apparatus SC provided on the upper part of the image forming apparatus main body GH.

  The image forming apparatus main body GH is called a tandem type color image forming apparatus, and arranges image forming units that form yellow, magenta, cyan, and black color toner images along the moving direction of the intermediate transfer member. The color toner images formed on the image carrier of each image forming unit are transferred onto the intermediate transfer member and superimposed, and then transferred onto the transfer material at once.

  In the figure, an analog signal scanned and exposed by an optical system on a document image placed on the image reading device SC, read into a line image sensor CCD, and photoelectrically converted by the line image sensor CCD is converted into an analog signal by an image processing unit. After processing, A / D conversion, shading correction, image compression processing, and the like are performed, the image is sent to an exposure optical system 3 serving as an image writing unit.

  In the figure, four sets of processes for forming images for each color of yellow (Y), magenta (M), cyan (C) and black (K) are provided on the peripheral edge of the intermediate transfer belt 6 as an intermediate transfer body. The unit 100 serves as a color toner image forming means in the order of Y, M, C, K in the vertical direction along the intermediate transfer belt 6 with respect to the rotation direction of the intermediate transfer belt 6 in the vertical direction indicated by the arrows in the drawing. Has been placed.

  Each of the four process units 100 has a common structure, and each includes a photosensitive drum 1 as an image carrier, a charger 2 as a charging unit, an exposure optical system 3 as an image writing unit, and development. It comprises a developing device 4 as a means and a photoreceptor cleaning device 190 as an image carrier cleaning means.

  The photosensitive drum 1 is an organic material having a layer thickness (film thickness) of about 20 to 40 μm as a photosensitive layer on the outer periphery of a cylindrical substrate formed of a metallic member such as aluminum having an outer diameter of about 40 to 100 mm. A photoconductive layer (OPC) is formed. The photosensitive drum 1 is rotated in the direction indicated by the arrow.

  Around the photosensitive drum 1, an image forming unit including a charger 2, an exposure optical system 3, and a developing device 4 as a set is arranged with respect to the rotation direction of the photosensitive drum 1 indicated by an arrow in the drawing. .

  The charger 2 is attached in close proximity to the photosensitive drum 1 in a direction orthogonal to the moving direction of the photosensitive drum 1 (in the direction perpendicular to the paper surface in the drawing). The charger 2 includes a discharge wire as a corona discharge electrode that applies a predetermined potential to the organic photosensitive layer of the photosensitive drum 1, and performs charging action by corona discharge having the same polarity as the toner. A uniform potential is applied.

  The exposure optical system 3 rotationally scans laser light emitted from a semiconductor laser (LD) light source (not shown) in the main scanning direction by a rotating polygon mirror (no symbol), an fθ lens (no symbol), and a reflection mirror (reference symbol). None), the photosensitive drum 1 is exposed to an electrical signal corresponding to the image signal (image writing), and an electrostatic latent image corresponding to the original image is formed on the photosensitive layer on the surface of the photosensitive drum 1. To do.

  The developing device 4 accommodates a two-component developer of each color of yellow (Y), magenta (M), cyan (C) or black (K) charged to the same polarity as the charging polarity of the photosensitive drum 1, A developing roller 4a which is a developer carrying member is provided. The developing roller 4a is kept in a predetermined gap from the photosensitive drum 1 by an abutment roller (not shown), and rotates in the forward direction and the rotational direction of the photosensitive drum 1. During development, the developing roller 4a On the other hand, by applying a DC voltage having the same polarity as the toner or a developing bias voltage that superimposes an AC voltage on the DC voltage, reversal development is performed on the exposed portion on the photosensitive drum 1.

  The intermediate transfer belt 6 is a semiconductive endless (seamless) resin belt member having a volume resistivity of about 1E + 7 to 1E + 9 Ω · cm and a surface resistivity of about 1E + 10 to 1E + 12 Ω / □. The intermediate transfer belt 6 is wound around a plurality of roller members including a tension roller 6a, and is supported rotatably in a vertical method. It is also possible to use a drum-shaped intermediate transfer member.

  The primary transfer roller 7 as a first transfer unit for each color is made of a roller-like conductive member using foamed rubber such as silicon or urethane, and a photosensitive drum for each color with the intermediate transfer belt 6 interposed therebetween. 1, and the back surface of the intermediate transfer belt 6 is pressed to form a transfer area with the photosensitive drum 1. A DC constant current having a polarity opposite to that of the toner is applied to the primary transfer roller 7 by constant current control, and the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by a transfer electric field formed in the transfer area. The

  The image forming process (image forming process) will be described below.

  When the image recording is started, the photosensitive drum drive motor (not shown) is rotated to rotate the Y photosensitive drum 1 in the direction indicated by the arrow in the figure, and a potential is applied to the Y photosensitive drum 1 by the Y charger 2. . After the Y photosensitive drum 1 is applied with a potential, the Y exposure optical system 3 performs exposure (image writing) with an electrical signal corresponding to the first color signal, that is, the Y image data. An electrostatic latent image corresponding to a yellow (Y) image is formed on the body drum 1. The latent image is reversely developed by the Y developing device 4 to form a toner image made of yellow (Y) toner on the Y photosensitive drum 1. The Y toner image formed on the Y photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by a primary transfer roller 7 as a primary transfer means.

  By a similar process, magenta (M), cyan (C), and black (K) toner images are sequentially formed on the intermediate transfer belt 6 in a superimposed manner.

  The toner remaining on the peripheral surface of each photoreceptor drum 1 after the transfer is cleaned by the photoreceptor cleaning device 190.

  On the other hand, the recording paper k as a transfer material accommodated in the paper feed cassettes 20A, 20B, and 20C is fed by the feed roller 21 and the paper feed roller 22A provided in the paper feed cassettes 20A, 20B, and 20C, respectively, and conveyed. The roller 22B, 22C, 22D and the registration roller 23 are conveyed to a secondary transfer roller 7A as a secondary transfer means to which a voltage having a polarity opposite to that of the toner is applied. In the transfer area of the secondary transfer roller 7A, intermediate transfer is performed. The superimposed color toner images formed on the belt 6 are collectively transferred onto the recording paper k.

  The recording sheet k on which the color image has been transferred is fixed by a fixing device 17 according to the present invention, which will be described later, and is sandwiched between paper discharge rollers 24 and placed on a paper discharge tray 25 outside the apparatus.

  Further, after the color image is transferred onto the recording paper k by the secondary transfer roller 7A, the residual toner is removed from the intermediate transfer belt 6 that has separated the curvature of the recording paper k by the intermediate transfer body cleaning device 190A.

  In the description of the image forming apparatus, the color image formation is described. However, the present invention includes a case where a monochrome image is formed.

  Next, details of the fixing device 17 according to the present invention will be described with reference to FIG.

  FIG. 2 is a central sectional view of the fixing device 17.

  Reference numeral 171 denotes an endless fixing belt, which is stretched around an elastic sliding member 172 and a heating roller 173, and is configured to have a constant tension by the action of compression springs 174 provided at both ends of the heating roller 173. Yes.

A pressure roller 175 is a pressure member and is provided to face the sliding member 172 with the fixing belt 171 interposed therebetween.
The sliding member 172 includes a rubber-like elastic sliding member 172A that contacts the fixing belt 171 and a leaf spring-like supporting member 172B that supports the elastic sliding member 172A.

  In the present embodiment, the elastic sliding member 172A is made of silicon rubber, but may be a rubber-like elastic member other than this, or a sponge-like material such as silicon sponge.

  The surface of the elastic sliding member 172A that contacts the fixing belt 171 is provided with a fluororesin layer such as PFA or PTFA to improve the slipping and durability of both.

  In addition to the above method, for example, oil application may be applied to the inner surface of the fixing belt 172 in order to improve the slipperiness.

  The elastic sliding member 172A and the support member 172B may be formed of an elastic member formed integrally.

  As shown in the figure, reference numeral 176 denotes a pressing member having a U-shaped cross section extending in the direction perpendicular to the conveyance direction indicated by the arrow of the recording paper k, and the upstream side of the support member 172B as viewed in the recording paper conveyance direction. The end part and the downstream end part are in contact with a line in a direction perpendicular to the recording paper conveyance direction.

  The term “contacting linearly in the direction perpendicular to the recording paper conveyance direction” here is wider than the width in the conveyance direction of the recording paper k, and the U-shaped tip of the pressing member 176 is the support member 172B. It is in contact with the upstream end and the downstream end as viewed in the recording paper conveyance direction.

  The pressing member 176 is guided by guide members 177 and 178 provided on a main body side plate (not shown) of the fixing device 17 so as to be movable in the direction of the pressure roller 175.

  Reference numeral 179 denotes an eccentric cam, and rotation is transmitted by a drive motor (not shown). FIG. 2 shows a state in which the pressing member 176 is pushed to the heating roller 175 side by the eccentric cam 179.

  As a result, the sliding member 172 is pushed toward the pressure roller 175 via the fixing belt 171 to form a nip width L1 when viewed in the recording paper conveyance direction.

  Since the sliding member 172 is made of an elastic body, when the eccentric cam 179 rotates by an arbitrary angle from the position shown in the figure, the upstream end and the downstream end of the sliding member 172 viewed in the recording paper conveyance direction are Moving away from the pressure roller 175, as shown in FIG. 3, a nip width L2 smaller than the nip width L1 is formed.

  As described above, the driving motor, the pressing member 176, the guide members 177 and 178, the eccentric cam 179, and the like constitute the pressing means 17A that makes the pressing force of the sliding member 172 in the direction of the pressure roller 175 variable. .

  The gloss level can be set from an operation unit (not shown) of the image forming apparatus. For example, when a desired gloss level is selected from the operation unit, correlation data between the gloss level and the pressing force is stored. With reference to the means (not shown), the control means (not shown) rotates the eccentric cam 179 to a predetermined position and applies a pressing force to the sliding member 172 by the pressing member 176.

  Reference numeral 180 denotes a central pressing member fixed to a main body side plate (not shown) of the fixing device 17, and a central portion of the sliding member 172 viewed in the recording paper conveyance direction is linearly formed in a direction perpendicular to the recording paper conveyance direction. The pressure is pressed at a predetermined fixed pressure. As a result, a fixed nip pressure is generated at the center of the nip width L1.

  Reference numeral 181 denotes a temperature sensor composed of a thermistor, which is arranged in contact with or non-contact with the surface of the heating roller 173, measures the surface temperature of the heating roller 173, and based on the measurement result, temperature control means (not shown). The heating roller 173 is controlled so as to maintain a constant temperature.

  The heating roller 173 is rotated in the direction of the arrow shown in the figure by driving means (not shown), and the fixing belt 171 is rotated, and the pressure roller 175 is rotated in a predetermined direction via the fixing belt 171.

  The heating roller 173 has a halogen lamp HLa inside and is made of, for example, an aluminum material, and has a cylindrical metal pipe 173A having a thickness of about 1 to 2 mm, and a PFA (about 15 to 50 μm thick) coated on the outer peripheral surface thereof. A roller having an outer diameter of about 40 to 60 mm, on which a release layer 173B made of a perfluoroalkoxy) coating is formed.

  The fixing belt 171 is an endless metal belt using, for example, a nickel electroformed belt having a thickness of about 20 to 80 μm as a substrate, or a heat-resistant resin belt using polyimide or polyamide having a thickness of about 40 to 150 μm. On the outside (peripheral surface), which is coated with insulating silicon rubber having a thickness of about 100 to 300 μm, a PFA (perfluoroalkoxy) tube having a thickness of about 30 to 50 μm is coated on the surface as a release layer, The one with PFA or PTFE coating is used.

  The pressure roller 175 is made of, for example, aluminum, a cylindrical metal pipe 175A having a thickness of about 2 to 5 mm, and a silicon material on the outer peripheral surface thereof, and is thin with a thickness (thickness) of 1 to 5 mm. , A rubber roller layer 175B composed of a rubber layer having a rubber hardness of 5Hs to 60Hs (JIS, A rubber hardness), and a release layer 175C covered with a PFA (perfluoroalkoxy) tube having a thickness of about 15 to 50 μm on the surface. A soft roller having an outer diameter of about 40 to 60 mm. Further, a halogen lamp HLa as a heating member may be provided inside the pressure roller 175.

  Next, the operation and action of the fixing device 17 having the above-described configuration will be described.

  When the operator selects a desired gloss level from the operation unit, as described above, the eccentric cam 179 rotates to a predetermined position, applies a pressing force to the sliding member 172 via the pressing member 176, and the sliding member 172 A predetermined nip width is formed by the pressure roller 175.

  Thereafter, the recording paper k carrying the toner image is conveyed by the sliding member 172 pressed by the pressing means 17A and the pressure roller 175, and a fixed image having a desired glossiness is obtained.

  Thus, the nip width between the sliding member 172 and the pressure roller 175 can be greatly changed by changing the pressing force of the pressing means 17A.

  However, even if the nip width is changed greatly, the nip pressure is symmetrical and is applied while changing smoothly over the entire nip width, so that various paper types can be maintained while maintaining a low image misalignment. Can be obtained.

  Further, since the central portion of the nip width is pressed by the central pressing member 180 with a predetermined fixed pressure, the fixing property can be secured even if the nip width is narrowed to reduce the glossiness.

  In addition, it is good also as a structure which does not provide the center press member 180, By such a structure, a nip width | variety can be changed more widely than the case where the center press member 180 exists.

  Since the elastic sliding member 172A is composed of a rubber-like elastic member, a pressing force is applied following the irregularities on the surface of the recording paper k, so that uniform glossiness can be obtained over the entire recording paper.

  Furthermore, since the fluororesin layer is provided on the contact surface of the elastic sliding member 172A with the fixing belt 171, both slipping and durability can be improved.

  In addition to the present embodiment, as a method for controlling the glossiness, for example, a configuration as shown in FIG. 4 can be used.

  The configuration described in FIG. 4 is such that the pressing force on the downstream side of the support member 172B in the recording paper conveyance direction is fixed, and only the upstream end is controlled by the eccentric cam 179 so that the pressing force can be varied. With such a configuration, the pressing force at the nip outlet can be maintained in a high state, so that a wide range of glossiness can be controlled while securing the fixing property.

  Contrary to the configuration of FIG. 4, the pressing force at the upstream end is fixed and only the downstream end is variable, so that the toner is fixed at the nip entrance. Glossiness control can be performed in a small state.

1 is a schematic configuration diagram of an image forming apparatus. FIG. 3 is a central sectional view of the fixing device 17. FIG. 6 is a central sectional view of the fixing device 17 when the nip width is narrowed. FIG. 6 is a central sectional view of the fixing device 17 in which the pressing force at the upstream end of the support member is variable.

Explanation of symbols

17 fixing device 17A pressing means 171 fixing belt 172 sliding member 172A elastic sliding member 172B support member 173 heating roller 174 compression spring 175 pressure roller 176 pressing member 177, 178 guide member 179 eccentric cam 180 central pressing member 181 temperature sensor k Recording paper L1, L2 Nip width

Claims (6)

An elastic sliding member, at least an endless fixing belt stretched over the sliding member, and a pressure member provided to face the sliding member via the fixing belt, In an image forming apparatus for fixing a toner image on a recording sheet conveyed between the pressure member and the sliding member via the fixing belt,
A pressing means for pressing the upstream end and the downstream end of the sliding member as viewed in the recording paper conveyance direction in a direction perpendicular to the recording paper conveyance direction in the direction of the pressure member; ,
An image forming apparatus characterized in that a pressing force to at least one end of the pressing means to the sliding member is variable. The image forming apparatus according to claim 1, wherein the pressing unit is configured to simultaneously press an upstream end and a downstream end of the sliding member as viewed in a recording paper conveyance direction. The pressing means presses the central portion of the sliding member as viewed in the recording paper conveyance direction in a line perpendicular to the recording paper conveyance direction in the direction of the pressure member with a predetermined fixed pressure. The image forming apparatus according to claim 1, further comprising a member. 2. The image according to claim 1, wherein the pressing unit is configured to make a pressing force at an upstream end or a downstream end as viewed in a recording paper conveyance direction of the sliding member constant. Forming equipment. 5. The slide member according to claim 1, wherein the slide member includes a rubber-like or sponge-like elastic slide member that contacts the fixing belt and a support member that supports the elastic slide member. The image forming apparatus described in the item. The image forming apparatus according to claim 1, wherein the sliding member includes a fluororesin layer, and the fluororesin layer is in contact with the fixing belt.

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