JP2007034068A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device having a structure capable of preventing disorder of an image by eliminating flaws or lines generated in a fixing member. <P>SOLUTION: The fixing device capable of fixing an unfixed image to a recording medium which passes through an opposite position between a fixing object 64 and a pressurization object 63 is characterized that surface roughness Ra1 of a contact member 65 which abuts on the fixing object 64 is larger than surface roughness Ra2 of the fixing object. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly, to a configuration for preventing scratches and streaks of members used for fixing from being transferred to an image.

  As is well known, in an image forming apparatus using an electrophotographic system or an electrostatic system, an electrostatic latent image corresponding to image information is formed on a photoconductor which is a uniformly charged latent image carrier. Then, the electrostatic latent image is subjected to visible image processing by the toner supplied from the developing device.

  The toner image carried on the photosensitive member is transferred to a recording paper which is one of the recording media, and then fixed on the recording paper by melting and permeating action by receiving heat and pressure from a fixing device.

The fixing device includes a heat roller system (for example, Patent Document 1) including a heating roller and a pressure roller that can sandwich and convey the recording paper, and a belt fixing system using a belt having a small heat capacity ( For example, there is Patent Document 2).
The configuration used for the belt fixing system includes a fixing belt wound around a heating roller incorporating a heat source and a fixing roller facing the pressure roller (for example, Patent Document 2), or a pressure roller. There is a configuration (for example, Patent Document 3) in which a heat source is also built in the opposing fixing roller.

By the way, in the fixing belt system, there is a case where the main idea is not to simply use a belt having a small heat capacity but to make the temperature rise in the belt faster.
As a configuration in this case, in order to increase the amount of heat transfer to the belt, a configuration is proposed in which a tension roller that presses the belt itself from its surface side is provided, and the amount of winding on the heating roller is increased by this tension roller. (For example, Patent Document 4).

  FIG. 8 shows a configuration using the tension roller. In FIG. 8, the fixing device A is wound around a heating roller B incorporating a heat source BH and a fixing roller D facing the pressure roller C. The fixing belt E is provided with a tension roller F that can be pressed from the outside of the fixing belt E to increase the amount of heat received by increasing the winding amount of the fixing belt E around the heating roller B. . Further, the thermistor G is provided in contact with the fixing belt E so as to detect the temperature, and energization control to the heat source BH is performed according to the detection result.

Japanese Patent No. 3243143 JP 2003-131505 A JP 2002-123111 A JP-A-9-218601

  In a conventionally known fixing device, a release agent is applied to a member located on the side in direct contact with the toner in order to prevent toner offset. However, in recent years, an oil-less tendency has been increasing, and instead of applying a release agent, there is a tendency that the surface of the fixing member is made of a highly releasable material. In particular, as a highly releasable material, a fluororesin such as perfluoroalkoxy (PFA) or polytetrafluoroethylene (PTF), for example, Teflon (registered trademark) manufactured by DuPont is used.

However, Teflon (registered trademark) and PFA are easily damaged because of their low surface hardness. When these are used on the surface of the fixing member, scars and streaks generated on the surface of the fixing member are transferred to the image surface after fixing. May cause image defects.
FIG. 9 shows this case. In the same figure, traces of the scratches generated on the surface of the fixing belt E used as a fixing member are transferred into the image after fixing and exhibit gloss lines different from the image portions. Part of the image may be disturbed.

On the other hand, when passing recording paper of different sizes, or when passing the paper in different transport forms even if it is the same size, the paper width edge of the recording paper that is passed in the width direction of the fixing belt If the streak is transferred to the image, it may appear as a streak with a different gloss.
FIG. 10 is a diagram showing this case. In FIG. 10, a case where an image forming apparatus capable of using A4 size paper and A3 size paper is targeted is shown.
In FIG. 10, when fixing is repeated in the state of A4 size recording paper in the state of longitudinal paper, streaks may occur in the fixing belt E, which is a fixing member, at the end of the paper width during A4 longitudinal paper. This streak may be transferred to the image surface when A4 landscape paper or A3 portrait paper is carried out after A4 portrait paper.
Such streaks at the end of the paper width are caused by the fact that the amount of paper represented by calcium carbonate is exposed when the recording paper is cut to a desired size. For this reason, the surface of the fixing belt E, which is a fixing member, is roughened by the paper dust on the end surface of the paper in the nip portion that sandwiches and conveys the recording paper. A part of the image is disturbed by being transferred inside. In other words, the gloss of a part of the image appears as a streak different from the other parts.

  Therefore, as a measure for preventing such a problem, the pressure between the fixing member and the pressure member at the nip portion is reduced, or the above-mentioned Teflon (registered trademark) or PFA constituting the fixing member surface layer is used as a filler. Although it is conceivable to increase the hardness of the fixing member surface layer by adding a pressure, it is difficult to obtain heat transfer necessary for image fixing at the fixing nip portion when the pressure is reduced. A new problem occurs that the moldability deteriorates.

  An object of the present invention is to provide a fixing device and an image forming apparatus having a configuration capable of preventing the image from being disturbed by eliminating scratches and streaks generated in the fixing member in view of the problems in the fixing device. It is to provide.

  According to the first aspect of the present invention, in a fixing device capable of fixing an unfixed image to a recording medium passing through a position where the fixing member and the pressure member are opposed to each other, the surface roughness Ra1 of the contact member that contacts the fixing member. Is larger than the surface roughness Ra2 of the fixing member.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the surface hardness of the contact member is greater than the surface hardness of the fixing body.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, a contact width between the contact member and the fixing body is equal to or greater than an A4 sheet vertical width.

  According to a fourth aspect of the present invention, in the fixing device according to one of the first to third aspects, the surface layer of the contact member is made of foamed silicone rubber.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the surface layer of the contact member is made of a blasted and rough metal.

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the contact member is formed of a rotating body.

  According to a seventh aspect of the present invention, in the fixing device according to the fourth aspect, the contact member follows the fixing body.

  The invention according to claim 8 is characterized in that the fixing device according to one of claims 1 to 7 is used in an image forming apparatus.

  According to the first aspect of the present invention, the surface of the fixing member is roughened because the surface roughness of the abutting member is larger than the surface roughness of the fixing member. It is possible to prevent the contrast of the glossiness between the medium edge position and other than the edge position from changing significantly. As a result, only the edge position of the recording medium is roughened, and the gloss at that position is different from the gloss at other positions, thereby preventing the occurrence of stripes having different glossiness in the image. It is possible to prevent the part from being disturbed. In particular, it is possible to prevent the surface of the fixing body, which was initially roughened over time, from being smoothed by maintaining the above relationship, so that the appearance of streaks due to the difference in glossiness in the image is almost eliminated. It becomes possible to maintain the state.

  According to the second aspect of the present invention, it is possible to prevent the surface layer of the fixing member from being smoothed over time by making the surface hardness of the contact member larger than that of the fixing member. In particular, in the case of a metal, unlike a resin such as silicone rubber, by continuing the roughness utilizing the relationship of surface hardness, unlike a foamed resin, it is less likely to cause wear and deformation, and the fixing body It is possible to prevent the difference in contrast between the two.

  According to the third aspect of the present invention, since the contact width between the contact member and the fixing member is equal to or greater than the A4 sheet vertical width, when a sheet of less than A4 vertical width is fixed, it corresponds to the end of the sheet. Since the surface of the fixing body is roughened, it is possible to suppress the occurrence of contrast marks, and to make the lines less noticeable.

  According to the fourth aspect of the invention, the surface can be efficiently roughened by using foamed silicone rubber for the surface layer of the contact member, so that the surface roughness relationship between the contact member and the fixing member can be maintained. It becomes.

  According to the fifth aspect of the present invention, the surface layer of the fixing body is prevented from being smoothed over time while maintaining the surface hardness in the rough state by using the metal whose surface layer is blasted as the contact member. It becomes possible to do. Unlike metals such as silicone rubber, it is possible to continue the roughness using the surface height due to being a metal.

  According to the sixth aspect of the present invention, since the contact member is a rotating body, there is no friction between the fixing body and the minute foreign matter generated from the recording medium is not blocked. It is possible to prevent damage to the surface layer of the fixing body due to the accumulation of minute foreign matter, and it is possible to suppress the generation of streaks on the image. In particular, by rotating while abutting paper, it is possible to prevent the minute foreign matter from being deposited by scraping the minute foreign matter while maintaining the roughness of the surface of the fixing body.

  According to the seventh aspect of the present invention, since the contact member can slide with respect to the movement of the fixing member, the material used for the fixing member that contacts the contact member is relatively soft. It becomes possible to easily roughen the surface layer.

  According to the eighth aspect of the present invention, it is possible to obtain an image having no gloss streak.

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

  FIG. 1 shows a color printer which is one of image forming apparatuses in which a fixing device according to an embodiment of the present invention is used. The present invention is not limited to a printer as an image forming apparatus, but includes a copying machine, a facsimile machine, a printing machine, and an apparatus that combines these functions.

In FIG. 1, an image forming apparatus 100 includes photosensitive drums 20Y, 20C, and 20M as image carriers capable of forming images as images corresponding to colors separated into yellow, magenta, cyan, and black, respectively. , 20BK is used in parallel.
In the image forming apparatus 100 having the configuration shown in FIG. 1, the visible images formed on the photosensitive drums 20Y, 20C, 20M, and 20BK face the photosensitive drums 20Y, 20C, 20M, and 20BK, and are in the direction of arrow A1. A transfer sheet S on which an image is superimposed and transferred by performing a primary transfer process on an intermediate transfer body (hereinafter referred to as a transfer belt) 11 using a movable endless belt, and thereafter a recording sheet or the like is used. On the other hand, batch transfer is performed by executing a secondary transfer process.

  Around each photosensitive drum, an apparatus for performing image forming processing is arranged according to the rotation of the photosensitive drum. Now, the photosensitive drum 20BK that performs black image formation will be described as an object. A charging device 30BK, a developing device 40BK, a primary transfer roller 12BK, and a cleaning device 50BK that perform image forming processing along the rotation direction are arranged. As described later, the optical scanning device 8 is used for writing performed after charging.

  In the superimposing transfer to the transfer belt 11, the visible image formed on each photoconductive drum 20 </ b> Y, 20 </ b> C, 20 </ b> M, 20 </ b> BK is transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A <b> 1 direction. As described above, voltage application by the primary transfer rollers 12Y, 12C, 12M, and 12BK arranged to face the photosensitive drums 20Y, 20C, 20M, and 20BK across the transfer belt 11 causes the upstream side in the A1 direction. The timing is shifted toward the downstream side.

  The photosensitive drums 20Y, 20C, 20M, and 20BK are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 20Y, 20C, 20M, and 20BK is provided in an image station for forming yellow, cyan, magenta, and black images.

The image forming apparatus 100 is disposed so as to face four image stations that perform image forming processing for each color and above each of the photosensitive drums 20Y, 20C, 20M, and 20BK, and the transfer belt 11 and the primary transfer roller 12Y. , 12C, 12M, and 12BK, a secondary transfer roller 5 that is a transfer roller as a transfer member that is arranged to face the transfer belt 11 and is driven by the transfer belt 11 and rotated. An intermediate transfer belt cleaning device 13 disposed opposite to the transfer belt 11 for cleaning the transfer belt 11, and an optical scanning device 8 serving as an optical writing device disposed below these four image stations. have.
The optical scanning device 8 in this embodiment is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a mirror, a rotary polygon mirror, and the like, and each of the photosensitive drums 20Y, 20C, 20M, and 20BK. On the other hand, writing light Lb corresponding to each color (in FIG. 1, for convenience, the reference is applied only to the image station of the black image, but the same applies to the other image stations), and the photosensitive drum 20Y is emitted. , 20C, 20M, and 20BK, an electrostatic latent image is formed.

  The image forming apparatus 100 includes a sheet feeding device 61 serving as a sheet feeding cassette on which transfer sheets S transported between the photosensitive drums 20Y, 20C, 20M, and 20BK and the transfer belt 11 are stacked. A transfer section between the photosensitive drums 20Y, 20C, 20M, and 20BK and the transfer belt 11 at a predetermined timing that matches the timing of toner image formation by the image station with the recording sheet S conveyed from the feeding device 61. And a sensor (not shown) for detecting that the leading edge of the transfer sheet S has reached the registration roller pair 4.

  In the image forming apparatus 100, the fixing device 6 as a fixing unit for fixing the toner image onto the transfer paper S to which the toner image is transferred, and the fixed transfer paper S are discharged to the outside of the main body of the image forming apparatus 100. A paper discharge roller 7, a paper discharge tray 17 disposed on the upper part of the main body of the image forming apparatus 100 and loaded with the transfer paper S discharged to the outside of the main body of the image forming apparatus 100 by the discharge roller 7, Toner bottles 9Y, 9C, 9M, and 9BK that are filled with toner of each color of yellow, cyan, magenta, and black are provided.

  The transfer belt unit 10 includes a drive roller 72 and a driven roller 73 around which the transfer belt 11 is wound, in addition to the transfer belt 11 and the primary transfer rollers 12Y, 12C, 12M, and 12BK.

  The driven roller 73 also has a function as a tension urging unit for the transfer belt 11. For this reason, the driven roller 73 is provided with an urging unit using a spring or the like. Such a transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12BK, the secondary transfer roller 5, and the cleaning device 13 constitute a transfer device 71.

  The sheet feeding device 80 is disposed at the lower part of the main body of the image forming apparatus 100, and includes a feeding roller 3 as a feeding roller that comes into contact with the upper surface of the uppermost transfer sheet S. The uppermost transfer sheet S is fed toward the registration roller pair 4 by being rotationally driven 3 in the counterclockwise direction.

  The fixing device 6 uses a belt fixing system. As a configuration for this, a fixing belt 61, a heating roller 62 around which the belt 61 is wound and a heat source, a pressure roller 63, and a pressure roller 63 are provided. A fixing roller 64 around which the fixing belt 61 is wound is provided. Details of the fixing device 6 will be described later.

  Although not shown in detail, the cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade disposed so as to face and contact the transfer belt 11. The transfer belt 11 is cleaned by scraping and removing foreign matter such as residual toner on the top with a cleaning brush and a cleaning blade. The cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the residual toner removed from the transfer belt 11. In the image forming apparatus 100 having the configuration shown in FIG. 1, the images formed on the photosensitive drums are sequentially transferred onto the transfer belt 11, and the color images superimposed are transferred by the secondary transfer roller 5. In this method, the transfer sheet S is transferred to the sheet S. Alternatively, the transfer sheet S is carried on the transfer belt 11 and the transfer sheet S is opposed to each photosensitive drum so that each color image is directly transferred onto the transfer sheet S. It is also possible to use a superposition method.

FIG. 2 is a diagram illustrating a configuration of the fixing device 6 according to the present embodiment.
In the figure, a fixing device 6 includes a pressure roller 63 as a pressure member, a fixing belt 61 as a fixing member, a heating roller 62 around which the fixing belt 61 is wound, and the pressure belt 61 facing the pressure roller. Is composed of a fixing roller 64 and a tension roller 65 that applies tension to the fixing belt 61.

The pressure roller 63 is provided with an elastic layer such as silicone rubber on a core metal such as aluminum or iron, and a surface layer is provided with a release layer of PFA or PTFE.
The fixing belt 61 is configured by a base material such as nickel or polyimide having a release layer such as PFA or PTFE, or an intermediate layer provided with an elastic layer such as silicone rubber. The fixing belt 61 is wound around a fixing roller 64 and a heating roller 62, and is maintained at an appropriate tension by a tension roller 65 from the outside.
The fixing roller 64 has a metal core and silicone rubber.
The heating roller 62 is a hollow aluminum or iron roller and has a heat source H such as a halogen heater inside.
The fixing device 6 configured by including such a member is not shown in the figure, but toward the nip portion formed by the fixing roller 64 and the pressure roller 63 and capable of nipping and conveying. The image on the recording paper is fixed by applying predetermined pressure and heat in the section.

In this embodiment, the following relationship is set for the surface roughness of the tension roller 65 that is a contact member with the fixing belt 61 as a fixing body.
When the surface roughness of the tension roller 65 is Ra1 and the surface roughness of the fixing belt 61 is Ra2, the relationship Ra1> Ra2 is set.
By setting such a relationship, the surface layer of the fixing belt 61 is always roughened by the tension roller 65. As a result, it is possible to prevent the occurrence of a line portion having a low glossiness, that is, a so-called vertical streak, in the image due to a difference in glossiness between this portion and other portions caused by the fact that only the paper width end portion of the recording paper is roughened. . The reason is as follows.
FIG. 3 is a diagram for explaining a state in which a streak is formed at the paper width end portion of the recording paper on the assumption of the case shown in FIG. 10, and FIG. 3A shows the state shown in FIG. (B) shows a case according to the present embodiment.
In this embodiment, the entire surface layer of the fixing belt 61 is roughened by the tension roller 65 by setting the above relationship. For this reason, as shown in FIG. 3B, the difference in gloss between the portion where the streaks are generated and the portion where the streaks are not generated, that is, the difference in contrast, is reduced over the entire fixing belt 61. Therefore, in other words, there is no difference between the streak portion and the other portions, and only the streak portion is not transferred to the image.

  In particular, by setting the above relationship, even if there is a possibility that both surfaces may be smoothed over time, the surface will always be roughened, so smoothing is prevented and the difference in contrast is noticeable. (As shown by the broken line in FIG. 3B, the contrast between the streak portion and the other portions becomes inconspicuous).

  On the other hand, as a configuration for roughening the surface, in this embodiment, the surface layer of the tension roller 65 that is a contact member to the fixing belt 61 is formed of foamed silicone rubber. As a result, the foamed portion comes into contact and scrapes the surface of the fixing belt 61, so that the surface of the fixing belt 61 can be efficiently roughened.

  Further, as a configuration for roughening the surface, it is also possible to use a metal having a surface layer blasted with a surface hardness higher than that of the fixing belt 61 instead of the foamed silicone rubber. In this case, for example, by using a metal whose surface has been roughened by sandblasting, the surface roughness can be maintained, and the amount of streaking on the fixing belt 61 can be reduced to the extent that wear and deformation do not occur as with foamed silicone rubber. It is possible to prevent the difference in contrast between the part and the other part from occurring over time.

  In this embodiment, since the tension roller 65 that contacts the fixing belt 61 as a fixing body is a rotating body, for example, minute foreign matters such as paper dust generated from the recording paper are not blocked. As a result, it is possible to prevent scratches other than the streaks that occur when the minute foreign matter is blocked, and the fine foreign matter can be scraped backward, so that the fine line due to the occurrence of scratches can be eliminated. The streak can be eliminated. Further, when the tension roller surface is made of the above-described metal, the surface layer of the fixing belt 61 can be prevented from being scraped off by rotation, so that it is possible to prevent the surface of the fixing belt from being scratched by grinding. It becomes.

  By the way, when the tension roller 65, which is a member in contact with the fixing belt 61, is made of foamed silicone rubber, the surface layer is relatively soft if the rotation is configured to slide with respect to the movement of the fixing belt 61. Even an object can be efficiently destroyed by rubbing, and the difference in contrast due to the generation of streaks and scratches can be eliminated without providing a special drive system.

  On the other hand, as shown in FIG. 4, the surface temperature of the fixing belt 61 is detected by the thermistor 66, but when the thermistor 66 is in contact with the fixing belt 61, as described above. Even when the surface roughness relationship between the fixing belt 61 and the tension roller 65 is established, the portion of the fixing belt 61 in contact with the thermistor 66 is different from the other portions as shown in FIG. It will be smoothed and the glossiness will be different. Therefore, in this embodiment, as shown in FIG. 5, a thermistor (indicated by reference numeral 66 ′ for convenience) is configured so as not to contact the fixing belt 61. As such a thermistor 66 ', an infrared detection method or the like is used. FIG. 4A shows the state of streaks generated at the end of the paper width when the surface roughness relationship is not set.

  Further, in this embodiment, as in the case of the thermistor, the configuration of the separation claw that causes a flaw or a line on the fixing belt 61 is also locally shown in the width direction of the fixing belt 61 as shown in FIG. By using the plate member, that is, the separation plate 90 instead of the opposing configuration, it is possible to eliminate the generation of scratches and streaks that occur when the fixing belt 61 contacts the local portion.

  The inventor conducted experiments on the number of sheets to be passed and the occurrence of traces using the fixing device based on the above-described embodiment, and obtained the results shown in FIG. In FIG. 7, trace ranks 1 to 5 were set, and the results obtained with respect to this rank in terms of the number of sheets passed were observed.

  As is clear from the results shown in FIG. 7, according to this example, the generation of traces could be efficiently suppressed.

1 is a schematic diagram illustrating a configuration of an image forming apparatus to which a fixing device according to an embodiment of the present invention is applied. FIG. 3 is a diagram for explaining a main configuration of a fixing device according to an embodiment. FIG. 3 is a diagram for explaining the operation of the fixing device shown in FIG. 2 in comparison with the operation of a conventional fixing device. FIG. 10 is a diagram for explaining a problem in a conventional fixing device. It is a figure for demonstrating the other principal part of the fixing device by a present Example. FIG. 10 is a diagram for explaining still another main part of the fixing device according to the present embodiment. It is a figure which shows the experimental result for demonstrating the effect | action of the fixing device by a present Example. It is a figure which shows the prior art example of a fixing device. It is a figure for demonstrating the malfunction which generate | occur | produces with the conventional fixing device. FIG. 10 is a diagram for explaining a problem that occurs due to a difference in a sheet passing state in a conventional fixing device.

Explanation of symbols

6 Fixing Device 61 Fixing Belt 62 Heating Roller 63 Pressure Roller 64 Fixing Roller 65 Tension Roller 66 ′ Non-Contact Thermistor 100 Image Forming Apparatus

Claims (8)

In a fixing device capable of fixing an unfixed image on a recording medium passing through a position where the fixing body and the pressure body are opposed to each other,
The fixing device according to claim 1, wherein a surface roughness Ra1 of the contact member contacting the fixing body is larger than a surface roughness Ra2 of the fixing body. The fixing device according to claim 1.
A fixing device, wherein the surface hardness of the contact member is larger than the surface hardness of the fixing member. The fixing device according to claim 1 or 2,
A fixing device, wherein a contact width between the contact member and the fixing body is equal to or greater than an A4 sheet vertical width. The fixing device according to any one of claims 1 to 3,
A fixing device in which a surface layer of the contact member is made of foamed silicone rubber. The fixing device according to any one of claims 1 to 4, wherein:
A fixing device, wherein a surface layer of the contact member is made of a metal that has been blasted and roughened. The fixing device according to any one of claims 1 to 5,
The fixing device, wherein the contact member is constituted by a rotating body. The fixing device according to claim 4.
The fixing device according to claim 1, wherein the contact member is driven by the fixing body.   An image forming apparatus using the fixing device according to claim 1.

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