JP2008020577A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently improve peeling performance while reducing image shift and paper sheet load by causing local deformation of a heating roller elastic layer within a nip part region and optimizing a paper sheet protrusion posture of a nip output section. <P>SOLUTION: The fixing device includes: a heat fixing roller 1 of an inverted crown shape having an elastic layer 3 and a heat source 6; and a pressure means having an endless heating member 5 and a pressure member 21 and having elasticity thereby being formable to a crown shape, and fixes an unfixed toner image on the paper sheet P by making the endless heating member 5 pass through the nip section formed of the heating means by conveying the paper sheet P while being held fixed with the unfixed toner image. The pressure member 21 which is the elastic layer has the rubber hardness different in the central part and end part in its thrust direction, the rubber hardness in the end part being greater than the rubber hardness in the central part. When forming the nip, the pressure member 21 is prevented from being elongated in the thrust direction and the nip can be uniformly assured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device used for thermal fixing of a toner image in an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and an image forming apparatus using the same.

  A heating unit having an elastic layer and a heat source; and a pressing unit having an endless member and a pressing member. The recording medium is transported with an unfixed toner image attached to the endless member by the heating unit. Various proposals have been made regarding a fixing device that passes through a nip portion to be formed and fixes an unfixed toner image on the recording medium. However, the conventional technology is a rotatable fixing device whose surface is elastically deformed. This is a belt nip method in which a pressure member that locally elastically deforms the outlet portion is pressed against a heating roller, a nip portion is formed, and a toner image on the recording medium fed therebetween is pressed and heated to be fixed. . However, this belt nip type fixing device has a problem that image misalignment is likely to occur due to a speed difference due to local deformation of the exit portion. Furthermore, the elastic layer of the heating roller is pressed with a hard member to locally strain the elastic layer and create a nip shape with a small curvature, which increases the load on the paper (paper damage and curl amount). .

  Therefore, Patent Document 1 discloses a pressure member having an inverted crown shape, in which the density of foaming is changed so that the end of the elastic layer is harder than the center. Patent Document 2 discloses a fixing device in which a heating body has a crown shape, an endless film is provided on the outer periphery together with a plurality of rollers, and a pressure rotating body having an inverted crown shape is pressed against the heating body. Further, Patent Document 3 discloses a heating roller having a rubber layer thickness of 0.5 to 10 mm, a hardness of 8 (JIS-A) or less and an outer diameter of 28 mm or less. Further, Patent Document 4 discloses a roller having an elastic layer having a hardness of 15 to 55 degrees (Asker-C) and a permanent set (compression) of 0.5 to 5%.

JP 09-251252 A Japanese Patent Laid-Open No. 03-233586 JP 2001-296691 A JP 2002-25713 A

  In view of the above-described conventional problems, the present invention is a fixing device including at least a heating unit, a pressure member, and an endless member, which simplifies the configuration of the device and does not apply a large load to the recording medium. In addition, a fixing device and an image forming apparatus capable of improving the separation of the recording medium from the heating means and forming a uniform nip by pressing the elastic layer of the pressing member to improve the image quality formed on the recording medium. The purpose is to do.

  The fixing device of the present invention according to claim 1 is a fixing device that has a heat source and performs heat fixing, wherein the opposing roller is bent in an inverted crown shape, and a pressure unit that forms a nip with the opposing roller is provided. A central portion of the pressurizing unit is pressed toward the counter roller so as to have a crown shape corresponding to the reverse crown shape of the counter roller, and an elastic layer forming the pressurizing unit in the nip region is The central portion and the end portion in the thrust direction of the pressure means have different rubber hardness, and the rubber hardness of the end portion is larger than the rubber hardness of the central portion.

  The fixing device of the present invention according to claim 2 is characterized in that, in the fixing device according to claim 1, the ratio of the end portion of the elastic layer to the entire volume of the elastic layer is 20% or less. .

  The fixing device of the present invention according to claim 3 is the fixing device according to claim 1 or 2, wherein the thickness of the end portion of the elastic layer is not less than 100% and not more than 130% with respect to the central portion. And

  The fixing device of the present invention according to claim 4 is the fixing device according to any one of claims 1 to 3, wherein a material of an end portion of the elastic layer is less in thermal expansion than a material of the central portion. It is used.

  The fixing device according to the fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein a coating agent is applied to the surface of the elastic layer, and the thickness of the coating agent on the surface of the end portion. Is made larger than the thickness of the coating agent on the surface of the central portion.

  The fixing device of the present invention according to claim 6 is the fixing device according to claim 5, wherein the hardness after application of the coating agent on the surface of the end portion of the elastic layer is after application of the coating agent on the surface of the central portion. It is characterized by being larger than the hardness.

  The fixing device of the present invention according to claim 7 is the fixing device according to any one of claims 1 to 6, wherein a rubber hardness of a central portion of the elastic layer is 8Hs (JIS-A) or less, and a rubber load direction. The thickness is 2 mm or less.

  The fixing device of the present invention according to claim 8 is the fixing device according to any one of claims 1 to 7, wherein the elastic layer has a permanent strain of 4% or less at a center portion thereof and a thickness in a rubber load direction of 2 mm. It is characterized by the following.

  The fixing device of the present invention according to claim 9 is the fixing device according to any one of claims 1 to 8, wherein an outer diameter of the opposing roller serving as a heat fixing roller is 28 mm or less, and an elastic layer is provided. The rubber hardness at the center in the thrust direction is 8 Hs (JIS-A) or less, and the rubber thickness is 0.8 mm or more.

  The fixing device according to the tenth aspect of the present invention is the fixing device according to any one of the first to ninth aspects, wherein the elastic layer of the counter roller has a permanent strain of 4% or less.

  The fixing device of the present invention according to claim 11 is the fixing device according to any one of claims 1 to 10, wherein an elastic coefficient K = EA / t (E = Young's modulus, A) of the elastic layer of the pressing means. = Nip area, t = thickness in the load direction) in the thrust direction of the pressurizing means is higher at the end than at the center.

  The fixing device of the present invention according to claim 12 is the fixing device according to any one of claims 1 to 11, wherein the heating unit includes a plurality of rotatable rollers each having the elastic layer and the heat source, And an endless heating member wound around a plurality of rotatable rollers.

  The image forming apparatus of the present invention according to claim 13 comprises a plurality of developing means for forming toner images of different colors, a photosensitive means for adhering the toner image of the developing means to the surface, and a toner image of the photosensitive means. An intermediate transfer means for transferring and a transfer means for transferring a toner image of the intermediate transfer means to a recording medium, comprising the fixing device according to any one of claims 1 to 12.

  According to the present invention, it is possible to prevent the pressing member from extending in the thrust direction at the time of forming the nip and to ensure a uniform nip.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 100 includes a photoconductor 110 that rotates in the direction of arrow A, a scorotron charging device 112 that charges the surface of the photoconductor 110, and an exposure light R that modulates the surface of the charged photoconductor 110 with image information. A ROS (laser output unit) 113 that forms an electrostatic latent image on the photosensitive member 110 by exposure, and a developing device that develops the electrostatic latent image on the photosensitive member 110 with toner to form a toner image on the photosensitive member 110 114, a transfer device 115 that transfers the toner image on the photoconductor 110 to the paper P, a fixing device 116 that fixes the toner image transferred to the paper P, a paper tray 117 that stores the paper P, and the surface of the photoconductor 110. A cleaner 118 for removing residual charges on the surface of the photosensitive member 110, and a charge eliminating device 119 for removing residual charges on the surface of the photoreceptor 110.

Next, an image forming operation in the image forming apparatus will be described with reference to FIG.
First, an original image signal read from an original by an image reading unit (not shown) or an original image signal created by an external computer (not shown) or the like is input to an image processing unit (not shown). Appropriate image processing is performed. The input image signal obtained in this way is input to a ROS (laser output unit) 113 to modulate the laser beam R. The laser beam R modulated by the input image signal is irradiated on the surface of the photoreceptor 110 uniformly charged by the scorotron charging device 112 as a raster. When the surface of the photoconductor 110 is irradiated with the laser beam R, an electrostatic latent image corresponding to the input image signal is formed on the photoconductor 110.

  The electrostatic latent image formed on the photoconductor 110 is developed with toner by the developing device 114 to form a toner image on the photoconductor 110. The toner image formed on the photoconductor 110 is conveyed toward the transfer device 115 disposed opposite to the photoconductor 110 as the photoconductor 110 rotates in the direction of arrow A.

  On the other hand, the paper P stored in the paper tray 7 is supplied toward the nip portion between the photoconductor 110 and the transfer device 115, and the toner image on the photoconductor 110 is transferred onto the paper P by the transfer device 115. The The toner image transferred onto the paper P is conveyed and fixed by the fixing device 116 to obtain a desired image.

  Adhered matter such as residual toner adhering to the surface of the photoconductor 110 after the transfer of the toner image onto the paper P is cleaned by the cleaner 8, and the residual charge on the surface of the photoconductor 110 is removed by the static eliminator 9. Thus, one image forming operation is completed.

  FIG. 2 is a configuration diagram of the fixing device 116 employed in the image forming apparatus 100 shown in FIG. The fixing device shown in FIG. 2 corresponds to an embodiment of the fixing device of the present invention.

  In FIG. 2, reference numeral 1 denotes a heat fixing roller. The heat fixing roller 1 has a surface coating layer 2, an elastic layer 3, a cored bar 4, and a heat source 6, is bent in an inverted crown shape, and is driven to rotate. Has been. In the figure, 32 is a recording medium, and 31 is unfixed toner adhering to the surface of the recording medium 32. The recording medium 32 is conveyed in the direction of the arrow in FIG. A pressure unit is provided opposite to the heat fixing roller 1 with the recording medium 32 interposed therebetween.

  The pressurizing means forms a heat insulating layer and an elastic layer (in the present application document, including not only the case where the heat insulating layer and the elastic layer are all formed but also part of the heat insulating layer and the elastic layer). A supporting member 22 that supports the pressing member 21, a pressing spring 11 that pressurizes the pressing member 21 and the supporting member 22 toward the recording medium 32, an endless member 23 that is driven, and an endless member 23. A low-friction member 25 for reducing the friction between the pressure members 21 and a guide 24 for defining a conveyance path of the endless member 23 are provided. In the figure, 27 is a lubricating oil supply member that supplies lubricating oil for further reducing the friction between the endless member 23 and the pressure member 21. Generally, lubricating oil containing silicon oil or fluorine oil is used. In the figure, reference numeral 33 denotes a fixed image on the recording medium 32 after passing through the nip portion between the heat fixing roller 1 and the endless member 23. As the surface coating layer 2 of the heat fixing roller 1, a PFA layer or the like is used so that the unfixed toner 31 does not easily adhere. In addition, as the elastic layer 3, silicone rubber, fluorine rubber, or the like is generally used. When silicone rubber is used, a fluorine layer or the like may be coated to improve swelling resistance. The endless member 23 is made of PFA and polyimide. The pressure member 21 uses a pressure pad with a flat surface in the pressure direction, and has a rubber layer of silicone rubber or fluorine rubber. Here, examples of the recording medium 32 include sheets such as cut sheets.

  FIG. 3 shows the nip width in the thrust direction of the pressure member 21 in the nip portion region obtained when the pressure member 21 is brought into pressure contact with the heat fixing roller 1. In the graph of FIG. 3, the vertical axis indicates the nip width, and the horizontal axis indicates the thrust direction of the pressure member 21 (the direction perpendicular to the paper surface of FIG. 2). The conventional nip width relationship is represented by curve A. In the conventional example (curve A), a cold offset occurs because the nip width at the end of the pressure member 21 is extremely small compared to the center portion. However, in the case of the embodiment of the present invention (curve B), the pressure member 21. It can be seen that the nip width as large as the central portion can be secured even at the end of this, and the drawbacks of the conventional example are eliminated.

  FIG. 4 shows a second embodiment of the present invention. The same parts as those in FIG. 2 are described with the same reference numerals. In the figure, reference numeral 5 denotes an endless heating member which is provided on the image surface side of the recording medium 32 to which the unfixed toner 32 adheres. In the figure, 8 is a heating member forming an elastic layer. Reference numeral 9 denotes a pressure support member that supports the pressure member 8. Furthermore, in the figure, 6 is a heat source, and 7 is a heating roller that stretches or heats the endless heating member 5 at the same time. When the amount of heat is insufficient, a method of heating the endless heating member 5 from the outside by bringing the heating roller 71 or 73 into contact with it can be used. In the figure, reference numeral 72 denotes a driven roller that rotates without having a heat source therein. Although the drive source for driving the endless heating member 5 is provided or arranged on the heating roller 7, it may be provided or arranged on the driven roller 72 side. This configuration uses the endless heating member 5 rather than the configuration using the heat fixing roller 1 as shown in FIG. It has the characteristic that it can. However, in this configuration, it is necessary to set the width of the pressure member 21 to be equal to or smaller than the width of the heating member 8.

FIG. 5 shows the fixing device of the embodiment shown in FIGS. 2 and 4 (Shower Electric Heating Roller: outer diameter φ27 mm, pressure member 21 rubber thickness 1.0 mm, rubber hardness 8 Hs (JIS-A) , Rubber permanent strain 4%, rubber axial length 230 mm), a load of 40 kgf is applied, and the configuration of the pressure member 21 is variously changed. It is a figure which shows the result of having tested the occurrence condition of offset. All the experiment settings were performed under the same conditions, and only the configuration of the pressure member 21 was changed. A cut sheet was used as the recording medium 32. In this experiment, a full-color image was adhered to a general sheet having a basis weight of 55 g / cm ^{2 with} a solid front face, and the experiment was performed using the fixing device shown in FIG. As a result, when the hardness and thickness at the end portion B of the pressure member 21 were larger than the central portion A, the nip width could be secured at the end portion, and no cold offset occurred. Here, the nip width is an OHP film (OHP film CG3700 manufactured by 3M), the power is turned off when the OHP film passes through the nip area of the fixing part, and the OHP film is sandwiched in the nip area for 12 seconds. Thereafter, the pressure of the fixing device is released, the OHP film is taken out, and the area where the nip is formed by heat is measured. In addition, the cold offset was performed by checking whether there is unfixed toner on the white cloth when the fixed cut sheet is rubbed with a white cloth (Hanicot # 440 manufactured by Sakata Inx Corporation). The case where there was no cold offset is indicated by ◯, and the case where it occurred is indicated by ×.

  When the pressure member 21 had the same hardness as the central portion A or a small thickness, the nip width was small because the thickness of the end portion due to pressing was smaller than the central portion, and a cold offset occurred. Moreover, the same result that the nip width | variety was made uniform was obtained by apply | coating the surface coating agent C to the surface, and changing hardness, thickness, and volume in a center part and an edge part. However, the end portion B is 20% or less with respect to the central portion A, and when this is larger than 20%, the end portion B has a higher hardness, which is disadvantageous for separation. It is preferable to improve the separability by reducing the rubber hardness of the central portion A to the last. Moreover, the thickness of the center part A and the edge part B shows an average value, and the center part A and the edge part B need to be a nip of a smooth curve. Naturally, when there is an extreme difference in thickness between the central portion A and the end portion B, uneven gloss and vertical stripes occur in terms of image quality.

  In this experiment, although not shown in FIG. 5, compared with a fixing device using a pressure member 21 having a rubber hardness of 8Hs (JIS-A), a rubber permanent strain of 4%, and a rubber load direction thickness of 4 mm, It was confirmed that the separation performance was improved by changing the thickness in the rubber load direction to 2 mm. Further, when the rubber permanent distortion of the elastic layer 3 on the heat fixing roller 1 side is large, the surface shape of the heat fixing roller 1 is locally deformed, which causes image deterioration such as uneven gloss of the image. It has been found that when the rubber permanent strain is 5% or more, uneven glossiness is conspicuous and the rubber permanent strain is preferably 4% or less. Further, the outer diameter of the heat-fixing roller 1 is also determined from the idea that if the clearance between the surface of the heat-fixing roller 1 after the nip exit and the surface of the recording medium 32 is large, the sheet is easily separated. It can be seen that this is one of the parameters that determine the clearance. It has been confirmed that when the outer diameter of the heat fixing roller 1 is φ28 mm or more, the separation performance is deteriorated. Therefore, it is natural that the outer diameter of the heat fixing roller 1 is desirably 28 mm or less. Further, it can be seen that the thickness of the elastic layer 3 of the heat fixing roller 1 is also one of the parameters that determine the clearance between the surface of the heat fixing roller 1 and the surface of the paper. It has been found that the separation performance decreases when the rubber thickness is 0.8 mm or less. This is presumably because the amount of deformation becomes smaller as the thickness of the elastic layer 3 of the heat-fixing roller 1 becomes thinner, and the sheet protruding posture at the nip outlet cannot be set to an appropriate state. Therefore, the thickness of the elastic layer 3 of the heat fixing roller 1 is desirably 0.8 mm or more. Similarly, it can be seen that the rubber hardness of the elastic layer 3 of the heat-fixing roller 1 is one of the parameters that determine the clearance during separation. It has been found that when the rubber hardness is 8Hs (JIS-A) or higher, the separation performance is lowered. This is presumably because the amount of deformation becomes smaller as the hardness of the elastic layer 3 of the heat-fixing roller 1 becomes higher, and the paper protruding posture at the nip outlet cannot be brought into an appropriate state. Accordingly, the rubber hardness of the elastic layer 3 of the heat fixing roller 1 is desirably 8 Hs (JIS-A) or less. Further, when the rubber permanent distortion of the pressure member 21 is large, the nip shape may be deformed with time, and the fixing characteristics and separation characteristics may become unstable. It was confirmed that when the rubber permanent strain of the pressure member 21 is 5% or more, the separation characteristics after heating and idling for 100 hours or more are deteriorated. Accordingly, the rubber permanent strain of the pressure member 21 is desirably 4% or less.

  FIG. 6 is a view showing a configuration example in the central portion A and the end portion B in the pressure member 21 used in the above-described experiment or its elastic layer. FIG. 7 is a view showing a configuration of an example in which a surface coating agent is similarly applied to the surface. In both the examples of FIGS. 6 and 7, from the experimental results of FIG. 5, it was possible to keep the nip uniform and to prevent the occurrence of cold offset by using the end of the pressure member 21 having a high hardness.

  That is, according to the present invention, it is possible to prevent the pressing member 21 from extending in the thrust direction due to pressing during nip formation, and to ensure a uniform nip, thereby preventing a cold offset of the end portion during continuous paper feeding. Moreover, local deformation | transformation of an edge part is prevented by optimizing the ratio which occupies for the whole heat insulation layer of the edge part B with respect to the center part A and the edge part B of the pressurization member 21, and it is in the thrust direction of a pressure member. On the other hand, a nip can be ensured uniformly, and a cold offset at the end can be prevented. In addition, the change rate of the elastic deformation may be optimized by increasing the thickness of the end portion B with respect to the central portion A.

  Furthermore, it is possible to prevent the central portion A from extending in the thrust direction by using an elastic material with little thermal expansion as the end portion B, and so to speak, as a stopper. And by apply | coating a surface coating agent to the surface, since the edge part B is thick with respect to the center part A, a uniform nip can be ensured. Moreover, if the hardness of the part which forms the heat insulation layer of the edge part B is enlarged with respect to the center part A, the change of a deformation rate can be optimized. Also, by optimizing rubber hardness and rubber thickness, optimizing permanent distortion, optimizing rubber hardness and rubber thickness, etc. Can be secured. By using a pressure belt instead of the pressure member as the pressure means, it is possible to cope with high speed.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention. Configuration diagram of a fixing device employed in the image forming apparatus shown in FIG. The figure which shows the nip width in the thrust direction of a pressure member in the nip part area | region obtained when a pressure member is press-contacted to a heat fixing roller with the structure of FIG. The figure which shows Example 2 of this invention The figure which shows the result of the experiment example regarding the Example shown in FIG.2 and FIG.4 FIG. 5 is a diagram of a configuration example at the center and end of the pressure member used in the experiment whose result is shown in FIG. The figure which showed the composition of the example which applied the surface coating agent to the surface of the pressurizing member similarly

Explanation of symbols

1: Heat fixing roller 2: Surface coating layer 3: Elastic layer 4: Core metal 5: Endless heating member 6: Heat source 7: Heating roller 8: Heating member 9: Pressure support member 10, 11: Pressure spring 21: Pressure member 22: Support member 23: Endless member 24: Guide 25: Low friction member 27: Lubricating oil supply member 31: Unfixed toner 32: Recording medium 33: Fixed image 71, 73: Heating roller 72: Driven roller 100 : Image forming apparatus 110: Photoconductor 112: Scorotron charging device 113: ROS (laser output unit)
114: Developing device 115: Transfer device 116: Fixing device 117: Paper tray 118: Cleaner 119: Neutralizing device A: Central portion in the thrust direction of the pressure member or its elastic layer B: Same end C: Surface coating agent P: Paper R: Exposure light

Claims (13)

A fixing device that has a heat source and performs heat-fixing, wherein the opposing roller is bent in an inverted crown shape, and a pressure unit that forms a nip with the opposing roller corresponds to the inverted crown shape of the opposing roller The elastic layer forming the pressurizing means in the nip portion region is pressed against the opposite roller side so that the central part of the pressurizing means and the end part in the thrust direction of the pressurizing means Has a different rubber hardness, and the rubber hardness of the end portion is larger than the rubber hardness of the central portion. 2. The fixing device according to claim 1, wherein the ratio of the end portion of the elastic layer to the entire volume of the elastic layer is 20% or less. 3. The fixing device according to claim 1, wherein a thickness of an end portion of the elastic layer is 100% or more and 130% or less with respect to the central portion. 4. The fixing device according to claim 1, wherein a material having a smaller thermal expansion than a material of the central portion is used as a material of an end portion of the elastic layer. 5. 5. The fixing device according to claim 1, wherein a coating agent is applied to a surface of the elastic layer, and a thickness of the coating agent on the surface of the end portion is larger than a thickness of the coating agent on the surface of the central portion. A fixing device characterized by that. The fixing device according to claim 5, wherein the hardness of the end surface of the elastic layer after application of the coating agent is greater than the hardness of the central surface after application of the coating agent. 7. The fixing device according to claim 1, wherein a rubber hardness at a central portion of the elastic layer is 8 Hs (JIS-A) or less and a thickness in a rubber load direction is 2 mm or less. apparatus. 8. The fixing device according to claim 1, wherein the elastic layer has a permanent distortion of 4% or less at a center portion thereof and a thickness in a rubber load direction of 2 mm or less. 9. The fixing device according to claim 1, wherein the opposed roller serving as the heat fixing roller has an outer diameter of 28 mm or less, an elastic layer, and a rubber hardness at a central portion in the thrust direction of 8 Hs (JIS−). A) A fixing device having a rubber thickness of 0.8 mm or more. 10. The fixing device according to claim 1, wherein the elastic layer of the opposing roller has a permanent strain of 4% or less. 11. 11. The fixing device according to claim 1, wherein an elastic coefficient K = EA / t (E = Young's modulus, A = nip area, t = thickness in a load direction) of an elastic layer of the pressurizing unit, A fixing device characterized in that an end portion is made higher than a central portion in a thrust direction of the pressing means. 12. The fixing device according to claim 1, wherein the heating unit includes a plurality of rotatable rollers each having the elastic layer and the heat source, and endless heating around the plurality of rotatable rollers. And a fixing device. A plurality of developing means for forming toner images of different colors, a photosensitive means for attaching the toner image of the developing means to the surface, an intermediate transfer means for transferring the toner image of the photosensitive means, and a toner image of the intermediate transfer means An image forming apparatus comprising: a transfer unit that transfers the image to a recording medium, and comprising the fixing device according to claim 1.