JP2007079234A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce toner blister to form a successful image. <P>SOLUTION: The fixing device is characterized in that a fixing belt has a mold release layer and hardness D1 of the mold release layer of the fixing belt and surface roughness Ry (the maximum height) of a support member satisfies a relation of 35°≤D1≤76°, 0.5μm≤Ry≤100μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device such as a copying machine, a printer, and a facsimile, and an image forming apparatus.

  An electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile machine transfers a toner image from a surface of an image carrier such as a photosensitive member or an intermediate transfer member onto a recording material, and fixes the transferred toner image. An image is formed on the recording material.

  Current image forming apparatuses are required to reduce power consumption and shorten warm-up time. In this respect, power consumption is high, and it is important to improve the fixing device most related to warm-up time. Under such circumstances, a fixing device that uses a fixing belt having a small heat capacity and rapidly heats to shorten the warm-up time has been proposed (see Patent Documents 1 and 2).

  In addition, electrophotographic image forming apparatuses are required to form images on various recording materials. For example, there is a growing need to output images such as color photographs with high quality using coated paper (coated paper, art paper, etc.) having a coating layer coated on the surface.

  A situation in which a color image is formed on coated paper by an electrophotographic image forming apparatus will be described with reference to FIG. FIG. 4 is a diagram illustrating a state where coated paper is interposed in the nip region of the fixing device, wherein 1000 is a toner (developer), 1001 is a fixing belt, and 1002 is coated paper. The color image transferred onto the coated paper has a toner layer thicker than the monochrome image because the toner images of yellow, magenta, etc. overlap each other. Accordingly, the total amount of air contained in the gap between the toner and the toner is increasing. In FIG. 4, the part A (the part indicated by a black circle) is the air contained in the gap between the toner. Since the fixing device is at a high temperature, the air contained in the gap between the toner and the toner expands thermally. Since the coated paper has poor air permeability, there is no escape space for the thermally expanded air. As a result, bubbles are generated in the toner layer, and a phenomenon that the color image on the coated paper is disturbed, so-called “toner blister”, occurs.

  The toner blister is also generated by the thermal expansion of air (portion B in FIG. 4) contained in the gap between the fixing belt and the toner layer.

Further, it is conceivable that the toner blister is affected by moisture contained in the toner and moisture contained in the coated paper. This is because the moisture contained in the toner or the like is heated by the fixing device to become water vapor, and the diffusion of the water vapor is hindered by the coating layer of the coated paper so that there is no escape and bubbles are generated in the toner layer.
JP 2004-226815 A JP 2004-226819 A

  Conventionally, a fixing device using a fixing belt and an image forming apparatus using the fixing device have been proposed, but sufficient countermeasures have not been taken against the above-described toner blister that occurs remarkably in coated paper. .

  Accordingly, an object of the present invention is to provide a fixing device and an image forming apparatus that reduce toner blisters.

  In order to achieve the above object, in the present invention, the hardness of the release layer of the fixing belt and the surface roughness Ry (maximum height) of the support member that supports the fixing belt are optimized.

That is, in the fixing device of the present invention,
A fixing belt that is heated and rotated by a heat source;
A support member for supporting the fixing belt;
A pressure member facing the support member via the fixing belt;
A fixing device comprising:
The fixing belt has a release layer;
The mold release layer has a hardness D1 (hardness measured by MicroDurometer MD-1 manufactured by Asker) and a surface roughness Ry (maximum height) of the support member as follows.
35 ° ≦ D1 ≦ 76 °
0.5μm ≦ Ry ≦ 100μm
In the image forming apparatus of the present invention,
An image forming apparatus for forming an image on a recording material by fixing a toner image transferred from an image carrier,
A fixing device according to any one of claims 1 to 5 is provided.

  According to the fixing device and the image forming apparatus according to the present invention, it is possible to reduce toner blisters and form a good image.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram showing an internal configuration of a digital color image forming apparatus.

  A digital color image forming apparatus (hereinafter simply referred to as “image forming apparatus”) 1 has a plurality of recording material storage portions 20 at the bottom. An image forming unit 40 and an intermediate transfer belt 50 are installed above the recording material storage unit 20, and a document reading unit 30 is installed at the upper part of the apparatus main body.

  The recording material storage unit 20 can be pulled out to the front side of the apparatus (the front side in FIG. 1).

  The image forming unit 40 includes four sets of image forming units 400Y, 400M, 400C, and 400K for forming toner images for each color of Y, M, C, and K. The image forming units 400Y, 400M, 400C, and 400K are linearly arranged from top to bottom in this order, and have the same configuration. The configuration of the image forming unit 400Y will be described as an example. The image forming unit 400Y includes a photoreceptor 410 that rotates counterclockwise, a scorotron charging unit 420, an exposure unit 430, and a developing unit 440.

  The cleaning unit 450 is disposed to include a region facing the lowermost part of the photoconductor 410.

  The intermediate transfer belt 50 located at the center of the apparatus main body is endless and has an appropriate volume resistivity. Further, the intermediate transfer belt 50 is formed on the outside of a semiconductive film substrate in which a conductive material is dispersed in an engineering plastic such as knitted polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, etc. It consists of two layers with fluorine coating. Further, there may be a conductive material dispersed in silicon rubber or urethane rubber.

  The primary transfer electrode 510 is installed at a position facing the photoconductor 410 with the intermediate transfer belt 50 interposed therebetween.

  Next, a process for forming a color image will be described.

  The photoconductor 410 is driven by a main motor (not shown), the surface of the photoconductor 410 is supplied with a voltage by a power source (not shown), and is charged positively by the discharge of the scorotron charging means 420 (in this embodiment). + 800V). Next, optical writing according to image information is performed by the exposure unit 430, and an electrostatic latent image is formed on the photoreceptor 410. When the formed electrostatic latent image passes through the developing unit 440, the toner charged positively in the developing unit adheres to the portion of the latent image by application of the positive developing bias, and the toner image is formed on the photoreceptor 410. Is formed. The formed toner image is transferred to the intermediate transfer belt 50 that is pressure-bonded to the photoreceptor 410. The toner on the photoreceptor 410 remaining after the transfer is cleaned by the cleaning means 450. A toner image formed by each of the image forming units 400Y, 400M, 400C, and 400K is transferred to the intermediate transfer belt 50 so that a color image is formed on the intermediate transfer belt 50. The recording material P is discharged one by one by the recording material storage unit 20 and conveyed to the position of the registration roller 60. After the leading edges of the recording material P are aligned by the registration roller 60, the recording material P is fed from the registration roller 60 at a timing when the toner image on the intermediate transfer belt 50 matches the image position. The recording material P fed by the registration roller 60 is guided by a guide plate and fed to a transfer nip portion formed by the intermediate transfer belt 50 and the transfer portion 70. The transfer unit 70 composed of rollers presses the recording material P toward the intermediate transfer belt 50 side. By applying a bias (−500 V) having a polarity opposite to that of the toner to the transfer unit 70, the toner image on the intermediate transfer belt 50 is transferred to the recording material P by the action of electrostatic force. The recording material P is neutralized by a separating means (not shown) composed of a neutralizing needle, separated from the intermediate transfer belt 50, and sent to a fixing device 80 composed of a roller pair of a heating roller and a pressure roller. As a result, the toner image is fixed on the recording material P, and the recording material P on which the image has been formed is discharged out of the apparatus.

  FIG. 2 is a detailed view of the fixing device 80.

  The fixing device 80 passes the recording material through a nip region formed by the pressure member 801 and the fixing belt 803 to fix the toner image on the recording material.

  The pressure member 801 is, for example, coated on the outer periphery of a hollow aluminum core (thickness 2 mm) with silicon rubber (thickness 2 mm, hardness 10 ° (measured with a JIS K 6253 type A durometer (A type))). A φ50 mm roller coated with PFA (perfluoroalkoxy) (30 μm) thereon. What coated PTFE (polytetrafluoroethylene) instead of PFA may be used. A halogen heater 802 is provided inside the pressure member 801 in FIG. 2 to prevent a rapid temperature drop of the pressure member 801. Of course, the pressure member 801 may not be provided with the halogen heater 802 inside.

  The fixing belt 803 is stretched around a support member 804 and a heating roller 806, and is rotated in the direction of the arrow shown in FIG. The fixing belt 803 is a three-layered belt made of, for example, polyimide (110 μm), silicon rubber (200 μm), and PTFE coating (30 μm). The PTFE coating of the fixing belt 803 is a release layer and functions so that the recording material can be separated from the fixing belt.

  A support member 804 that presses the fixing belt 803 in the direction of the pressure member 801 is, for example, a φ40 mm roller in which a solid SUS mandrel is coated with silicon rubber (7 mm) and coated with PFA or the like. .

  The heating roller 806 is, for example, a hollow aluminum core (thickness 2 mm) coated with PFA (30 μm), and has a halogen heater 805 inside.

  Reference numerals 807 and 808 denote non-contact temperature sensors. The temperature sensor 807 detects the temperature of the pressure member 801, and the temperature sensor 808 detects the temperature of the heating roller 806.

  When the toner image is fixed on the coated paper, the above-described toner blister is likely to occur. Again, let us examine the phenomenon of toner blisters using FIG.

  As described above, the toner blister is considered to be generated mainly when the air (portion A in FIG. 4) contained in the gap between the toner and the toner expands thermally and the escape space of the thermally expanded air disappears. Since a color image has a thicker toner layer than a monochrome image, the total amount of air contained in the gap between the toner and the toner increases.

  The air contained in the gap between the surface of the fixing belt and the toner layer (the portion B in FIG. 4) is also considered as a factor of the toner blister. This air decreases if the fixing belt can follow the unevenness of the toner layer, and increases if it cannot follow. From the viewpoint of the toner blister, if the fixing belt can follow the unevenness of the toner layer, the air in the portion B in FIG. 4 is reduced, and the toner blister can be reduced. Therefore, paying attention to the hardness of the release layer of the fixing belt, it was examined using 9 types of fixing belts having different hardnesses to determine the hardness to reduce the toner blister (Table 1). reference). The hardness D1 of the release layer of the fixing belt is a hardness measured by MicroDurometer MD-1 manufactured by Asker.

  Further, it is considered that the toner blister is related to the surface roughness Ry (maximum height) of the support member in addition to the hardness of the release layer of the fixing belt. If the support member has a rough surface such as a sponge, unevenness is generated in the pressing force that presses the fixing belt from the back surface toward the pressing member, and air contained in the gap between the fixing belt and the toner layer (FIG. 4). B portion) cannot be reduced. Therefore, paying attention to the surface roughness Ry (maximum height) of the support member, how much surface roughness Ry (maximum height) should be used in order to reduce toner blisters, surface roughness Ry ( Investigation was made using 12 types of support members having different maximum heights (Table 2). The surface roughness Ry represents the maximum height of the surface roughness defined by JIS.

  FIG. 3 shows the results of experiments using nine types of fixing belts shown in Table 1 and 12 types of support members shown in Table 2. In FIG. 3, the horizontal axis represents the surface roughness Ry (μm) of the support member, and the vertical axis represents the hardness D1 (°) of the release layer of the fixing belt. In FIG. 3, “◯” indicates that the toner blister did not occur and the image was good, and “Δ” indicates that the toner blister was slightly generated and the image was slightly defective. "" Indicates that a toner blister occurred and the image was defective. As a result of the experiment, it is preferable that the hardness of the release layer of the fixing belt is 76 ° or less and the surface roughness Ry (maximum height) of the support member is 100 μm or less from the viewpoint of toner blister reduction.

  When the hardness of the release layer of the fixing belt is examined from another viewpoint, if the hardness of the release layer of the fixing belt is too low, there is a problem in durability of the fixing belt. Further, in an oilless fixing device that does not apply oil for ensuring releasability, if the hardness of the release layer of the fixing belt is too low, the adhesion with the coated paper increases and the releasability is not good. Therefore, the durability and separability of the fixing belt were examined using eight types of fixing belts having different hardnesses (see Table 3). The hardness here is also the hardness measured with MicroDurometer MD-1 manufactured by Asker.

  From the results of the experiment. The hardness of the release layer of the fixing belt is preferably 35 ° or more.

  The surface roughness Ry (maximum height) of the support member is preferably 0.5 μm or more for reasons of production of the fixing belt.

  Accordingly, it is desirable that the hardness D1 of the release layer of the fixing belt is 35 ° ≦ D1 ≦ 76 °, and the surface roughness Ry (maximum height) of the support member is 0.5 μm ≦ Ry ≦ 100 μm.

  The surface of the support member is preferably polished or has a release layer such as a PTFE coating or a PFA tube. Those not polished or having no release layer have high adhesion between the support member and the fixing belt. As a result, the fixing belt is not driven well or abnormal noise is generated when the fixing belt rotates. Therefore, it is preferable that the surface of the support member is polished or has a release layer.

  When the support member has an elastic layer, if the hardness of the elastic layer is too low, there is a problem in durability of the support member. On the other hand, if the hardness is too high, a sufficient nip region of the fixing device cannot be ensured, and an image with good fixability cannot be formed. When the support member has a roller shape, even if the elastic layer of the support member has a high hardness, a large nip area can be secured by increasing the roller diameter of the support member and the fixing property is good. If it is increased, the recording material cannot be satisfactorily separated from the fixing belt. Further, when the roller diameter of the support member is too small, the support member bends, and there is a problem that a uniform nip region cannot be secured over the longitudinal direction of the support member and the fixing property is not good.

  Considering these points, the relationship between the hardness D2 of the elastic layer of the support member and the roller diameter X of the support member was examined through experiments. In the experiment, the hardness D2 of the support member is set to 11 steps of 3 °, 5 °, 8 °, 15 °, 18 °, 20 °, 25 °, 30 °, 32 °, 34 °, and 38 °, and the roller diameter X of the support member. Were examined in 11 stages of 26 mm, 28 mm, 30 mm, 32 mm, 34 mm, 36 mm, 37 mm, 39 mm, 40 mm, 41 mm and 43 mm. The experimental results are shown in FIG. The hardness D2 of the elastic layer of the support member is measured with a JIS K 6253 type A durometer (A type). The horizontal axis in FIG. 5 indicates the hardness D2 of the elastic layer of the support member, and the vertical axis indicates the roller diameter X of the support member. In the figure, “◯” indicates that the support member has good durability, fixing properties, and separation properties, and “△” indicates any of the support member durability, fixing properties, and separation properties. The mark “x” indicates that the support member was defective in any of durability, fixing property, and separation property. As a result of the experiment, the hardness D2 of the elastic layer of the support member is preferably 5 ° or more from the viewpoint of durability of the support member, and is preferably 30 ° or less from the viewpoint of fixability. On the other hand, the roller diameter X of the support member is preferably 30 mm or more from the viewpoint of fixability, and is preferably 40 mm or less from the viewpoint of separability.

From the above results, it can be said that it is preferable that the hardness D2 of the elastic layer of the support member (measured with a JIS K 6253 type A durometer (A type)) and the roller diameter X of the support member have the following relationship.
5 ° ≦ D2 ≦ 30 °
30mm ≦ X ≦ 40mm

1 is a cross-sectional configuration diagram of an image forming apparatus showing an example of an embodiment of the present invention. 2 is an explanatory diagram of a fixing device. It is a figure showing the relationship between the hardness D1 of the release layer of the fixing belt and the surface roughness Ry (maximum height) of the support member. FIG. 6 is a diagram illustrating a state when coated paper is interposed in a nip region of the fixing device. FIG. 6 is a diagram illustrating a relationship between a hardness D2 of a release layer of a fixing belt and a roller diameter X of a support member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Recording material accommodating part 30 Document reading part 40 Image forming part 50 Intermediate transfer belt 60 Registration roller 70 Transfer part 80 Fixing apparatus 105 Recording material conveyance part 400Y, 400M, 400C, 400K Image forming means 410 Photosensitive body 420 Scorotron Charging unit 430 Exposure unit 440 Development unit 450 Cleaning unit 801 Pressure member 802 Halogen heater 803 Fixing belt 804 Support member 805 Halogen heater 806 Heating roller 807, 808 Temperature sensor

Claims (6)

A fixing belt that is heated and rotated by a heat source;
A support member for supporting the fixing belt;
A pressure member facing the support member via the fixing belt;
A fixing device comprising:
The fixing belt has a release layer;
The fixing device, wherein the release layer hardness D1 (the hardness measured by MicroDurometer MD-1 manufactured by Asker) and the surface roughness Ry (maximum height) of the support member have the following relationship.
35 ° ≦ D1 ≦ 76 °
0.5μm ≦ Ry ≦ 100μm The fixing device according to claim 1, wherein the support member includes an elastic layer. The support member has a roller shape,
The fixing device according to claim 2, wherein a hardness D2 of the elastic layer (measured with a type A durometer (A type) of JIS K 6253) and a roller diameter X of the support member have the following relationship.
5 ° ≦ D2 ≦ 30 °
30mm ≦ X ≦ 40mm The fixing device according to claim 1, wherein a surface of the support member is polished. The fixing device according to claim 1, wherein the support member has a release layer. An image forming apparatus for forming an image on a recording material by fixing a toner image transferred from an image carrier,
An image forming apparatus comprising the fixing device according to claim 1.

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