JP2002091220A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simply constituted fixing device capable of always forming an image of high glossiness without causing the deterioration of image quality due to dust and wax by surely cleaning the surface of a fixing belt. SOLUTION: As for the fixing device provided with a 1st fixing roll, a single or plural rotating rolls arranged at a prescribed interval from the 1st fixing roll, an endless fixing belt which is stretched to be laid between the 1st fixing roll and the rotating roll and which is rotatably supported, a 2nd fixing roll which faces the 1st fixing roll and which is brought into contact with the 1st fixing roll across the fixing belt, and a cleaning means for removing foreign materials on the surface of the fixing belt, the cleaning sheet having a thermoplastic surface is brought into contact with a part of the fixing belt surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile, and a printer, and more particularly to an image forming apparatus using a belt type fixing device.

[0002]

2. Description of the Related Art In recent years, a method of creating a color image using a digital electrophotographic method has been widely used. In general, four colors of yellow, magenta, cyan, and black toners obtained by mixing a pigment with a thermoplastic binder are irradiated on a photoreceptor with a laser beam modulated based on image information. A toner image is formed by attaching the toner image to a latent image, the toner image is transferred onto a recording medium, and then fused and fixed with a heating roll or the like to form an image.

As a fixing device for fixing a toner image recording medium, a heating roll system as shown in FIG. 4 is widely used.

In this method, a heating source 10 is provided inside a cylindrical cored bar.
2, a fixing roll 101 in which a heat-resistant rubber layer or a heat-resistant release layer (not shown) is coated on the outer periphery of the cylindrical core metal, and a pressure roll 105 which is pressed against the fixing roll 101 and has the same configuration as the fixing roll 101. In the meantime, the unfixed toner image 107 is passed through the recording medium 108 formed on the surface, and the toner image 107 is heated and pressurized and fixed. In order to increase the gloss of the image after fixing and improve the appearance of the color image, the molecular weight of the thermoplastic binder in the toner is reduced and the viscosity at the time of heating and melting is designed to reduce the toner image surface. Is used to make the surface smooth.

A color image obtained by such a method is as follows.
Although the gloss is high, the toner is not completely embedded in the fibers of the paper as the recording medium, so irregularities due to the thickness of the toner remain, irregular reflection of the incident light on the image surface occurs, and the micro unevenness of the gloss In this case, the color reproducibility is reduced.

[0006] The use of full-color electrophotographic printers as outputs for digital still cameras, which have been actively introduced in recent years, is increasing. In this case, since the output image is compared with a silver halide photographic image as a photograph, the above-described irregularities are particularly conspicuous, and are immediately judged to be different from the photograph.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 63-92965 discloses a method in which a transparent resin layer is provided on a recording medium, and at the time of fixing, the transparent resin layer is melted simultaneously with the toner to make the toner transparent. A method of embedding in the inside has been proposed. According to this method, although an image having a high gloss is obtained over the entire surface including the background portion, when the recording medium is released from the heating and pressing region, the viscosity of both the toner and the transparent resin layer is low, so that As a result, the toner image portion remains in a convex shape, and the high frequency irregularities of the transparent resin become conspicuous. Furthermore, when a heating roll type fixing device shown in FIG. 4 is used, since the releasing property of the releasing layer on the fixing roll surface to the toner is not sufficient, a releasing agent such as silicone oil is separately supplied by the oil supply unit 103. It is necessary to prevent the toner from being applied to the fixing roll 101 by being applied. However, in a system using oil, it is difficult to uniformly apply the oil to the heating roll, so that oil streaks due to uneven oil application are likely to occur, such as disclosed in JP-A-63-92965. High gloss images are noticeable and may degrade image quality. Further, there is a problem that paper having oil adhered to the surface has poor writing performance with a ball-point pen, a felt-tip pen or the like.

Therefore, Japanese Patent Application Laid-Open Nos.
In the method disclosed in Japanese Patent No. 16322, a glossing sheet or belt is superimposed on a recording medium coated with a thermoplastic resin, and then heated and pressed, and after cooling, the recording medium is separated from the glossing sheet or belt. Discloses a high quality image output method in which the smoothness of the image surface is further improved as compared with the heating roll method, and the texture of a photographic paper is brought closer.

The gist of the operation of both publications will be described below with reference to FIG. In FIG. 5, 116 is a recording medium, 1
Reference numeral 17 denotes a toner image, and reference numeral 109 denotes a heating roll having a heating source 110 inside. An outer peripheral portion of the heating roll has an elastic layer made of rubber or the like (not shown). 112 is a pressure roll, 111 is a fixing belt, 114 is a peeling roll, and 115 is a peeling roll.

Recording medium 1 carrying unfixed toner image 117
16 is conveyed in the direction indicated by arrow C, heated by the heating roll 109 in a state where the toner image 117 and the fixing belt 111 are in contact with each other, and conveyed while both are kept in close contact with each other.
5 separates from the fixing belt 111. Here, since the recording medium 116 is provided with the transparent resin layer 116b made of a thermoplastic resin on the surface of the base material 116a, the action of heat and pressure of the heating roll 109 and the pressure roll 112 together with the toner image 117 The transparent resin layer 116b is melted while being kept in close contact with the fixing belt 111.

Then, before the recording medium 116 and the fixing belt 111 are separated from each other, the recording medium 116 and the fixing belt 111 are cooled while being in close contact with each other by natural cooling or forced cooling means. Therefore, the toner image 117
And the transparent resin layer 116b solidifies in a form following the smooth surface of the fixing belt 111, so that an image having very high smoothness and high gloss can be obtained as compared with JP-A-63-92965. Further, the recording medium 116 is fixed on the fixing belt with the cohesive force of the toner image 117 and the transparent resin layer 116b being higher than the adhesive force with the belt.
Since it is peeled off from the fixing belt 111, it is not necessary to apply silicone oil on the fixing belt, and the above-mentioned problems that occur when oil is used do not occur.

However, even in a system that does not use oil, such as JP-A-1-35452 and JP-A-5-216322, the releasability of the recording medium 116 and the fixing belt 111 does not cause any problem at first, but When fixing hundreds or thousands of sheets, minute irregularities are generated on the belt surface, and the releasability may be reduced. Therefore, as disclosed in JP-A-5-104868, in order to improve the peeling performance of the recording medium and the durability of the fixing belt, wax is mixed into the transparent resin layer of the recording medium, or a toner containing a wax component is used. A method is also disclosed.

[0013]

However, the above-mentioned known examples are not yet sufficient. In the methods disclosed in JP-A-1-35452 and JP-A-5-216322, the cleaning device is not provided, and dust adhered on the fixing belt 111, paper dust, a small amount of residual toner, or Since the toner at the time of paper jam is not removed, if any of these adheres, the next image is transferred and becomes unsightly. In particular, when the recording medium provided with the above-described transparent resin layer is used, dust and the like taken into the transparent resin in the background portion are remarkably conspicuous.

Therefore, even if a cleaner 106 using a web used in a fixing device of a heating roll system shown in FIG. In a system that does not use oil as disclosed in Japanese Unexamined Patent Publication No. 5-216322 or dust, paper dust cannot be removed because adhesion to the web does not work.

On the other hand, the surface of the fixing belt is made of silicone rubber, for the purpose of achieving both a releasability from the toner and a highly smooth surface.
Because a layer of a rubber-like substance such as fluoro rubber is provided,
It can easily be inferred that a blade cleaner generally used for a photoreceptor cannot be used because the friction between the two is large and the blade is turned up.

In a method of mixing wax into a transparent resin layer of a recording medium or using a toner containing a wax component as disclosed in Japanese Patent Application Laid-Open No. 5-104868,
As a result of the experiment, the following was found. That is, after the recording medium is fixed, when the recording medium is separated from the fixing belt, the wax that has permeated and solidified at the interface between the recording medium and the fixing belt is divided into the fixing belt and the recording medium, and the surface of the fixing belt and the surface of the recording medium are separated. Then, a very small amount of wax is attached.

There is no problem if the wax on the surface is not conspicuous even if the next image is fixed without removing the wax on the fixing belt as it is, but depending on the conditions as a result of an experiment using a toner containing the wax. When several tens to several hundreds of images are continuously fixed, wax gradually accumulates on the fixing belt, and when a certain number or more, wax becomes whitish on the surface, and gloss is reduced and cloudy It turned out to be an image.

Therefore, a method of removing the toner and wax by heating the surface of the pressure-sensitive adhesive roll provided with a thermoplastic resin, as disclosed in Japanese Patent Application Laid-Open No. 10-214010, can be considered. Therefore, as a result of melting of the wax, the wax is divided into the adhesive roll side and the belt side and cannot be completely removed. Furthermore, it is necessary to install a cleaner for the adhesive roll in order to keep the resin surface in a clean state so as to maintain a certain level of adhesive strength, but the apparatus becomes large-scale.

The present invention has been made to solve the above problems, and has a simple structure of the apparatus and can reliably clean the surface of the fixing belt, so that the glossiness is always reduced without deteriorating the image quality due to dust or wax. It is an object of the present invention to provide a fixing device capable of forming a high-quality image.

[0020]

SUMMARY OF THE INVENTION The present invention provides a first fixing roll, a single or a plurality of rotating rolls disposed at a predetermined distance from the first fixing roll, and a first fixing roll. And an endless fixing belt rotatably supported by being wound around a rotating roll, a second fixing roll sandwiching the fixing belt and pressed against the first fixing roll, and a surface of the fixing belt. With a cleaning means for removing foreign matter, a recording medium having a toner image corresponding to image information formed on the surface thereof is brought into close contact with the surface of the fixing belt at a pressure contact portion between the first fixing roll and the second fixing roll, In a fixing device configured to be separated from the surface of the fixing belt after being conveyed by a predetermined distance with the rotation of the fixing roll, the cleaning unit includes a cleaning sheet having a thermoplastic portion on its surface. It is intended to abut on a portion of the wear surface of the belt.

In order to minimize stress on the endless belt, it is preferable that the cleaning sheet has a structure in which the cleaning sheet does not have a relative speed with respect to the fixing belt in the partial area.

Further, as a specific configuration, the cleaning means includes an upstream contacting means for contacting the cleaning sheet with the fixing belt at a rotation direction upstream end of the fixing belt in the partial area; And a downstream abutting means for abutting the cleaning sheet against the fixing belt at the downstream end of the fixing belt in the rotation direction of the fixing area.

Further, the upstream abutting means can be provided with a heating member for heating and softening the thermoplastic portion on the surface of the cleaning sheet to such an extent that foreign substances can be taken into the thermoplastic portion, and from the viewpoint of simplification of the apparatus. The upstream contact means includes an upstream urging member for urging the cleaning sheet back surface toward the fixing belt, and an upstream backup member facing the upstream urging member from the back of the fixing belt,
During cleaning, the fixing belt is rotated in reverse,
The first fixing roll may function as an upstream backup member and the heating member. On the other hand, the downstream-side abutting means may be separated from the upstream-side abutting means by a predetermined distance so as to be cooled and hardened to such an extent that foreign matters taken in the thermoplastic portion of the cleaning sheet surface can be held. .

The cleaning means may cause the cleaning sheet to come into contact with the surface of the fixing belt during cleaning, and to separate the cleaning sheet during fixing. Further, the fixing belt may be driven to rotate at a lower speed during cleaning than at the time of fixing.

According to the present invention, a toner image forming surface on a recording medium on which a toner image corresponding to image information is formed, and a fixing belt rotatably supported by a plurality of rolls including at least a first heating roll. After the toner image is heated and melted at a pressure contact portion between the surface of the portion supported by the first heating roll and the pressure roll, the pressure contact is performed with the toner image forming surface in contact with the fixing belt surface. In the image forming apparatus, wherein the cleaning unit on the surface of the fixing belt contacts a fixing sheet provided with a thermoplastic resin on the surface of the fixing belt. It is also possible to express that the cleaning sheet is peeled off from the fixing belt after being heated in a state and moved a predetermined distance while both are in contact with each other. Kill.

Here, when a silicone rubber or fluorine rubber layer is provided on the surface of the fixing belt that contacts the recording medium, such a configuration is effective. here,
The heating means for the cleaning sheet may be a second heating roll, but from the viewpoint of simplification of the apparatus, the first heating roll may be used.
The heating roller may also function as a heating unit for the cleaning sheet, and may rotate the fixing belt in a direction opposite to that in fixing the recording medium during cleaning.

The recording medium may be provided with a thermoplastic resin layer on the surface. Further, the thermoplastic resin on the surface of the cleaning sheet and the thermoplastic resin layer on the surface of the recording medium may be made of the same material. At least one of the toner and the thermoplastic resin layer on the recording medium may contain a release agent such as wax.

The cleaning may be performed after a predetermined number of images have been formed, may be performed based on an output value of an optical sensor for detecting the state of the fixing belt surface, or may be a recording medium. May be performed at the time of conveyance jam, or may be performed according to an instruction from a control panel of the image forming apparatus main body or a computer.

Further, when the fixing unit cleans the fixing belt, the rotation speed of the fixing belt may be lower than that when the recording medium is fixed.

[0030]

FIG. 9 is a side sectional view showing an embodiment of an image forming apparatus according to the present invention. Hereinafter, the operation of the present image forming apparatus will be described with reference to the drawings.

First, the photosensitive member 24 rotating in the direction of the arrow is charged by the charger.
After being uniformly charged at 25, a light beam subjected to color separation and modulation according to image information is irradiated onto a photoreceptor 24 by a light beam exposure device 23 to form an electrostatic latent image. In the vicinity of the photoconductor 24,
Developing units 22Y, 22M, 22C, and 22K each containing a toner of each color of yellow, magenta, cyan, and black are arranged, and develop an electrostatic latent image corresponding to each color to form a toner image. The toner image of each color is electrostatically transferred to the intermediate transfer belt 27 by the primary transfer roll 30, and by repeating this four times,
A color toner image is formed on the intermediate transfer belt 27.

Next, the toner image on the intermediate transfer belt 27 is
The image is transferred onto the recording medium 8 sent from the paper tray 26 by a transfer electric field formed by the secondary transfer roll 29 and the opposing roll 28. Then, by fixing the recording medium 8 on which the unfixed toner image is formed by a belt-type fixing device,
A high gloss color image is formed.

Then, the surface of the fixing belt 3 after the image is fixed is cleaned by the cleaner 11.

The image forming apparatus according to the present invention has the following features.
In addition to the apparatus using the photoreceptor, the present invention can be applied to a so-called tandem type electrophotographic type in which four photoreceptors are arranged in series for each color for speeding up. Further, in the above-described embodiment, a method using a known intermediate transfer belt has been described. However, a method using an intermediate transfer roll, or a method in which a toner image is directly transferred from a photoconductor to a recording medium without using an intermediate transfer body. Of course, the method can also be used.

As the recording medium, not only plain paper used in a general electrophotographic system, but also high gloss coated paper, art paper, overhead transparency and the like can be used. In particular, when a photographic image is desired to be output by an output of a digital camera or the like, a base material coated with a colorless and transparent thermoplastic resin is preferable. Here, the material used for the base material is not particularly limited, and a conventionally known base material of a recording medium can be arbitrarily selected and used, but in the case of outputting a photographic image, High whiteness to give a sense of quality, basis weight 150
Those having about 220 g / m2 are preferred.

As the thermoplastic resin, styrene- (meth)
Acrylic copolymer, polyester resin, epoxy resin,
Styrene butadiene copolymer, polyurethane and the like can be used alone or in a mixed form. Among them,
It is preferable to use a polyester resin in consideration of transparency and mechanical strength. The transparent resin is melted at the same time as the toner at the time of fixing, and the toner is embedded in the transparent resin, and at the same time, the entire image surface is made to conform to the surface of the fixing belt, thereby obtaining a high gloss image.

The thickness of these transparent resins ranges from 2 μm to 20 μm.
m is preferred. Below this range, the toner cannot be sufficiently embedded in the transparent resin layer, resulting in an image having irregularities on the surface. On the other hand, when the thickness exceeds this range, cracks are easily generated in the transparent resin layer, and the image durability is reduced. Using such a recording medium, the transparent resin on the recording medium, the melt viscosity of the binder resin of the toner,
Further, by properly controlling the fixing conditions, the toner can be buried in the transparent resin layer, so that an image having a surface more similar to a photograph can be formed.

Further, when a recording medium provided with a transparent resin layer is used, a release agent may be contained in the transparent resin layer in order to improve releasability from the fixing belt. Examples of the release agent include low molecular weight polyolefins, silicones, carboxylic acid esters, carboxylic acid amides, vegetable waxes, animal waxes, petroleum waxes, and modified products thereof. In particular, paraffin wax and low molecular weight polyolefin wax are suitable. It is preferable to mix these release agents with 0.5 to 10% by weight in the transparent resin.

The toner used in the present image forming apparatus is not particularly limited. Examples of the binder resin include a styrene- (meth) acryl copolymer, a polyester resin, and a styrene (meth) acrylic resin similar to the transparent resin formed on the recording medium. Epoxy resins, styrene-butadiene copolymers, polyurethanes and the like can be used alone or in a mixture. Further, a release agent may be contained in the transparent resin layer in order to improve the releasability from the fixing belt. As the release agent, for example,
Examples include low molecular weight polyolefins, silicones, carboxylic esters, carboxylic amides, vegetable waxes, animal waxes, petroleum waxes, and modified products thereof. In particular, paraffin wax and low molecular weight polyolefin wax are suitable. It is preferable to mix these release agents in the binder resin in an amount of 0.5 to 10% by weight.

As the colorant to be mixed with the binder resin of these toners, known pigments and dyes can be used. Further, conventionally known external additives for toner can be used for the purpose of controlling charging and improving transferability.

Next, details of the belt-type fixing device will be described below.

FIG. 1 is a side sectional view showing the operation of a belt-type fixing device used in the present image forming apparatus.

The heating fixing roll 1 and the endless fixing belt 3
A main part is constituted by a pressure roll 5 pressed against the heat-fixing roll 1 via the fixing belt 3 and a peeling roll 6.

As shown in FIG. 7, the fixing belt 3 preferably has a structure in which a heat-resistant elastic layer 3b is provided on the surface of a base layer 3a to improve the adhesion to the toner 10 on the recording medium 8. In consideration of heat resistance, strength and surface smoothness, the material of the base layer 3a is preferably made of a heat-resistant resin such as polyimide, polyamide, or polyamideimide, or a metal such as aluminum or stainless steel. 15-250μm
It is preferred that it is about.

The heat-resistant elastic layer 3b is appropriately selected from silicone rubber, fluorine rubber and the like in consideration of the releasability of the toner, and preferably has a thickness of about 5 to 100 μm. Above all, silicone rubber has a very high surface smoothness after application, and when combined with a recording medium provided with a transparent resin layer, the surface gloss of the output image becomes JISZ87.
It is more preferable because a 75-degree specular gloss value according to 41-1997 is about 100, which is almost the same as photographic paper.

Further, carbon black, metal oxide powder, and the like are contained in the heat resistant resin and the heat resistant elastic layer 3b of the base layer 3a.
A conductivity adjusting agent such as graphite powder may be contained. This is because if the resistance of the fixing belt 3 is too high, the surface is easily charged, and the recording medium 8 is electrostatically attracted or the toner is scattered to disturb the toner image before fixing. . The overall thickness of this fixing belt 3 is 20 to 300
μm, more preferably in the range of 50 to 200 μm. This is because if the thickness is too thin, the strength of the belt will be low or the stiffness will be weak.On the other hand, if the thickness is 300 μm or more, the heat capacity will be large, so the energy at the time of heating will be large, and the fixing speed will be low. This is because an adverse effect is caused.

Further, the fixing belt 3 is endless, is stretched between the heat fixing roll 1 and the peeling roll 6, and is driven to rotate by the heat fixing roll 1.

As shown in FIG. 6, the heat fixing roll 1 is provided with a heating source 2 such as a halogen lamp in a metal core 1a (cylindrical core), and heats the fixing belt 3 and the recording medium 8. I do. As a material of the core, a material having high thermal conductivity such as iron, aluminum, and stainless steel can be used. Further, an elastic layer 1b made of a rubber-like substance or the like can be appropriately provided on the outer periphery thereof. This is because the heat-resistant elastic layer 3b of the fixing belt 3 has insufficient cushioning properties, and also prevents the fixing belt 3 and the heat fixing roll 1 from slipping during driving. Further, in order to prevent the abrasion of the fixing belt 3 with the heat fixing roll 1, a fluororesin 1c such as PFA may be provided on the outermost surface with a thickness of several tens of μm.

The pressure roll 5 applies a pressure to the recording medium 8 at the time of fixing, and at the same time, a heating source 4 such as a halogen lamp.
And the recording medium can be heated from the back side.
In particular, when a recording medium having a large basis weight is used, it is necessary to supply a large amount of heat, and the amount of heat from the heat fixing roll 1 alone is insufficient. It is preferable that an elastic layer and a fluororesin for preventing adhesion of toner and the like be provided around the metal core in substantially the same manner as the heat fixing roll 1.

Here, the elastic layer 1b used for the heat fixing roll 1 and the pressure roll 5 is optimally made of silicone rubber. Its thickness is preferably about 0.5 to 4 mm. If both rolls are below this range, the width of the heating and pressing region 18 is narrow, that is, the heating time is short, and the surface of the image is not sufficiently smooth. On the other hand, if it is more than this range, the heat capacity of the roll is too large, so that the standby time increases, which is not preferable.

Further, it is desirable that the pressure in the heating and pressurizing region 18 is in the range of 2 to 20 kg / cm 2 as a result of the experiment. It was found that when the pressure was lower than this range, the toner was not sufficiently embedded in the transparent resin layer. Further, if the pressure is set to 20 kg / cm 2, the core 1a needs to be thickened and the roll diameter itself needs to be increased because the roll is bent, which is not preferable.

Further, the heating device and the pressing device are not limited to the above-described configuration of the heating fixing roll 1 and the pressing roll 5, but a planar or linear heating element can be used as a heating source. is there.

The peeling roll 6 is made of a metal such as aluminum, stainless steel, iron, or brass in consideration of the effect of cooling the fixing belt 3 and the recording medium 8 by contact and reducing the wear on the fixing belt 3. Is preferred. Also, considering that the fixing belt 3 has a curvature and peels off the recording medium 8, the diameter is desirably 50 mm or less. Further, the fixing member is not limited to a roll-shaped member as in the present embodiment, and may be a fixed member as long as stable movement of the fixing belt is not hindered.

Next, a series of operations of the belt-type fixing device will be described by taking a case where a photographic image is output as an example.

The recording medium 8 on which the toner image 10 is formed is sent to the fixing device in the direction indicated by arrow C, and is heated and rotated in the direction of arrow A by a motor (not shown). The transparent resin layer 8b is heated and melted together with the toner image 10 by the heating / pressing unit 18 formed by the fixing belt 3 and the pressure roll 5 to be heated. Here, when the fixing belt 3 and the recording medium 8 are separated immediately after the heating and melting, the gloss is high but the surface smoothness is inferior, and a high-quality image may not always be obtained and offset may occur.

On the other hand, in the present embodiment, after the heating and melting, the fixing belt 3 and the recording medium 8 are driven and conveyed by the heating roll 1 while keeping the recording medium 8 in close contact with each other, so that the toner image 10 and the transparent resin layer 8b are cooled and the viscosity is increased. Is separated from the fixing belt 3. This allows
The image surface follows the surface of the fixing belt 3 which is smooth, and a smooth image as if the surface was laminated can be obtained. If the fixing speed is high,
Since there is a case where the cooling cannot be sufficiently performed until the fixing belt 8 is separated from the fixing belt 3, a known cooling device that cools the fixing belt 3 and the recording medium 8 between the heating / pressing unit 18 and the separation roll 6 is used. You may. As the cooling device, a blower that cools the two without contacting them, a heat sink or a heat pipe that contacts the back surface of the fixing belt 3 or the back surface of the recording medium 8 to take heat can be used.

The recording medium 8 cooled while being in contact with the fixing belt 3 is forcibly peeled off by means of a peeling claw or the like.
The film is naturally peeled off from the peeling roll 6 without being brought into contact with the sheet. This is because the peeling force due to the curvature of the peeling roll 6 and the stiffness of the recording medium 8 exceed the adhesive force between the fixing belt 3 and the recording medium 8. However, as a result of the experiment, in some cases, the leading end portion of the recording medium 8 was naturally peeled off, but the trailing end portion was not peeled off and was taken to the fixing belt 3 as it was. Is held in a non-contact state, so that the recording medium 8 after peeling
I was able to run stably along 9. Also in this case, since the peeling member does not come into contact with the fixing belt 3, its durability does not decrease.

Next, the operation of the cleaner 11 will be described.

In the fixing device of the present image forming apparatus, since the recording medium 8 is separated from the fixing belt 3 after cooling without using a release agent such as oil, dust and paper dust adhere to the surface of the fixing belt 3. In this case, an image portion or a recording medium provided with a transparent resin layer on the entire surface is also taken into a non-image portion.
When the image mainly composed of characters is output on plain paper, it is not so noticeable, but when using the recording medium 8 having the transparent resin layer 8b provided on the surface for the purpose of outputting a photographic image as described above, fixing is performed. Since the gloss of the subsequent image is very high, even a small amount of dust becomes a noticeable defect that cannot be ignored.

On the other hand, the heat-resistant elastic layer 3
Since b is provided and oil is not used, it is difficult to clean the belt surface by a conventionally known method. Further, in order to improve the releasability between the fixing belt 3 and the recording medium 8, the toner or the transparent resin layer 8 of the recording medium 8 is used.
If wax is mixed in b, the wax accumulates on the surface of the fixing belt 3, and if the accumulation progresses to a certain extent, a wax layer is formed on the output image surface, resulting in a cloudy image with reduced gloss. I understood.

In order to avoid these phenomena, a cleaner 11 as shown in FIG. 1 has been used.

The cleaner 11 includes a cleaning sheet 12,
Two take-up rolls 15 and 16, and two press rolls 1
It consists of 3,14. These are integrated as a unit by a frame (not shown), and are installed so as to be able to approach and separate from the fixing belt 3 in the direction shown by arrow D.

As shown in FIG. 8, the cleaning sheet 12
In the same manner as the recording medium provided with the transparent resin layer, a thermoplastic resin 12a is provided on a base material 12b, the thermoplastic resin 12a is melted by heat, and then separated from the fixing belt after cooling. In addition, all of the offset toner or wax can be taken in. The substrate 12b is not particularly limited, and a conventionally known substrate material of a recording medium can be arbitrarily selected and used, but preferably has a smooth surface. Specifically, the material is selected from heat-resistant paper and a polymer film, but is preferably thinner in order to increase the amount of winding on the winding rolls 15 and 16. Specifically, the range of 20 to 150 μm is suitable.

Further, a thermoplastic resin 12a provided thereon is provided.
For example, a styrene- (meth) acrylic copolymer, a polyester resin, an epoxy resin, a styrene-butadiene copolymer, a polyurethane or the like can be used alone or in a mixed form. Above all, it is preferable to use a polyester resin in consideration of transparency and mechanical strength. In particular, it is desirable to use the same type of resin as the recording medium because it is not necessary to change the fixing temperature between image output and cleaning. The thickness of the thermoplastic resin 12a is 2 to 20 μm, considering that the heat capacity is not so large and that a certain thickness is required for repeated use.
It is desirable that Then, when not in use, the winding roll 16 is mostly wound.

As the winding rolls 15 and 16, existing metal rolls and resin rolls can be used, and a resin or rubber layer may be provided on the surface for improving grip force. Both rolls are rotated in the same direction by a motor (not shown). Further, it also serves to apply tension so that the cleaning sheet 12 does not sag.

The pressing rolls 13 and 14 are pressed by the heating roll 2 and the opposing roll 17 during cleaning. Since it is necessary to heat the cleaning sheet 12, a metal roll is preferable. Further, in order to increase the heating time of the cleaning sheet 12, the pressing roll 13 is preferably provided with an elastic layer of silicone rubber or the like with a thickness of several mm on its surface. Further, when the pressing pressure of the cleaning sheet 12 in the heating area is 0.1 to 5 kg / cm 2, the cleaner efficiency is increased, which is good.

In the case of the configuration shown in FIG. 1, cleaning is performed by rotating the fixing belt 3 in a direction reverse to that at the time of fixing an image. The following five cleaning timings are conceivable. After the main power of the apparatus is turned on, after outputting a predetermined number of images, the optical sensor 34 on the surface of the fixing belt 3 is output.
When the light reflected by the controller becomes equal to or less than a predetermined threshold value, when the operator determines, there is an instruction from the control panel of the apparatus main body or a computer, and when a transport jam occurs. In particular,-can be used alone or in combination as needed.

FIG. 2 is a diagram showing the cleaning operation by the reverse rotation method. When any of the above-described cleaning instructions is detected, the operation of the fixing belt 3 is temporarily stopped, and the cleaning sheet 12 of the cleaner 11 is brought into close contact with the fixing belt 3. At this time, if it is between image output,
Since the heat-fixing roll 1 is sufficiently heated so that the thermoplastic resin on the surface of the cleaning sheet 12 melts, the heat-fixing roll 1 is melted in a contact area between the pressure roll 13 and the heat-fixing roll 1.

At the same time when the fixing belt 3 is brought into close contact with the fixing belt 3, the heating / pressing roll is rotated in the direction indicated by the arrow F. After rotating in the direction of G, the take-up roll 15 takes up the sent cleaning sheet 12. At this time, the fixing belt 3 of the cleaning sheet 12
The thermoplastic resin, which is provided on the surface in contact with and is melted by heat, passes through the contact area with the heating and pressing roll 1 and is cooled by heat radiation, so that toner, dust, wax, etc. adhered to the surface of the fixing belt 3 It solidifies in a form that incorporates extraneous matter. Then, since the fixing roller 3 is peeled off from the fixing belt 3 by the pressing roller 14, the attached matter is taken to the cleaning sheet, and the surface of the fixing belt 3 becomes a clean surface without the attached matter.

Here, in order to allow sufficient time for the cleaning sheet 12 to be sufficiently cooled, it is desirable that the rotation speed of the fixing belt 3 be lower than that during image output. If you want to increase the cleaning speed, use the cleaning sheet
A well-known cooling device for cooling the fixing belt 3 and the cleaning sheet 12 on the back side of the fixing belt 3 that does not contact the fixing belt 3 may be used. As the cooling device, a blower that cools the two without contacting them, a heat sink or a heat pipe that contacts the back surface of the cleaning sheet 12 to remove heat can be used.

When the above operation is performed at least for one rotation of the fixing belt 3 to complete the cleaning, the cleaner 11 is separated from the fixing belt 3 and at the same time, the rotation of the fixing belt 3 is stopped, and the image output operation is started. The cleaning sheet 12 can be reused several times to several tens of times, instead of being discarded when the new cleaning sheet 12 has been wound up by the winding roll 15. In that case, after winding up with the winding roll 15,
Next, the take-up roll 16 may be rotated to rewind.
And for those with reduced cleaning ability,
Replace only the cleaning sheet 12 with a new one.

FIG. 10 shows a flow chart of the above-described series of cleaning operations.

On the other hand, as shown in FIG. 3, the present cleaner can act simultaneously with image output. in this case,
A heat source such as a halogen lamp is inserted into the pressing roll 14, and the cooling fixing belt 3 is heated in a state in which the fixing belt 3 is in close contact with the cleaning sheet 12, and the cleaning sheet 12 is moved in the H direction. 3 and the cleaning sheet 12 are peeled off. Also in this case, the cleaner 11 does not keep the fixing belt 3 in close contact with the fixing belt 3.
As in the case of the reverse rotation, it is preferable to make contact and separation as needed. In addition, it goes without saying that a cooling device for the cleaning sheet 12 can be used. Furthermore, although a belt provided with a heat-resistant elastic layer has been described, it goes without saying that the present invention can be applied to a belt having a hard coat release layer such as PFA or silicone-modified polyimide.

[0074]

As described above in detail, according to the present invention, according to the image forming apparatus of the present invention, since the structure of the apparatus is simple and the surface of the fixing belt can be reliably cleaned, dust and wax Therefore, it is possible to always form an image having a high gloss level without deterioration in image quality.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an operation of a belt-type fixing device used in the present image forming apparatus.

FIG. 2 is a diagram illustrating an operation of cleaning by a reverse rotation method in FIG. 2;

FIG. 3 is a diagram illustrating a case where the present cleaner is operated simultaneously with image output.

FIG. 4 illustrates an example of a heating roll type fixing device.

FIG. 5 is a view for explaining the essential points of the operation of the fixing device disclosed in the conventional publication.

FIG. 6 illustrates a configuration of the heat fixing roll 1.

FIG. 7 illustrates the configuration of the fixing belt 3.

FIG. 8 illustrates a configuration of a cleaning sheet.

FIG. 9 is a side sectional view showing an embodiment of the image forming apparatus according to the present invention.

FIG. 10 is a flowchart of a series of cleaning operations.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heat fixing roll, 2 ... Pressure roll, 3 ... Fixing belt, 12 ... Cleaning sheet, 8 ... Recording medium, 6 ... Peeling roll, 11 ... Cleaner

Claims (8)

[Claims] 1. A first fixing roll, a single or a plurality of rotating rolls arranged at a predetermined distance from the first fixing roll, and a first fixing roll and a rotating roll wound around the first fixing roll and the rotating roll. An endless fixing belt rotatably supported, a second fixing roll sandwiching the fixing belt and pressed against the first fixing roll, and a cleaning unit for removing foreign matter on the surface of the fixing belt. The recording medium on which the toner image corresponding to the image information is formed is brought into close contact with the surface of the fixing belt at the pressure contact portion between the first fixing roll and the second fixing roll, and is conveyed by a predetermined distance with the rotation of the fixing roll. The fixing device is configured to be separated from the surface of the fixing belt after the fixing, and the cleaning unit applies a cleaning sheet having a thermoplastic portion on the surface to a partial area of the fixing belt surface. A fixing device for causing the abutment. 2. The cleaning sheet according to claim 1, wherein the cleaning sheet has no relative speed to the fixing belt in the partial area.
3. The fixing device according to claim 1. 3. The fixing device according to claim 1, wherein the cleaning unit includes an upstream contact unit configured to contact a cleaning sheet with the fixing belt at an upstream end of the fixing belt in a rotation direction of the partial region, and a rotation of the fixing belt in the partial region. 3. The fixing device according to claim 1, further comprising a downstream contact unit configured to contact the cleaning sheet with the fixing belt at a downstream end in the direction. 4. The fixing device according to claim 3, wherein the upstream abutting means includes a heating member for heating and softening the thermoplastic portion on the surface of the cleaning sheet to such an extent that foreign matter can be taken into the thermoplastic portion. 5. An upstream biasing member for biasing the back surface of the cleaning sheet toward the fixing belt,
An upstream backup member facing the upstream biasing member from the back side of the fixing belt, the fixing belt is reversely rotated during cleaning, and the first fixing roll acts as an upstream backup member and the heating member. The fixing device according to claim 4. 6. The downstream abutting means is separated from the upstream abutting means by a predetermined distance so that the downstream abutting means is cooled and hardened to such an extent that foreign matter taken in the thermoplastic portion on the cleaning sheet surface can be held. The fixing device according to claim 4. 7. The fixing device according to claim 1, wherein the cleaning unit contacts the cleaning sheet with a surface of the fixing belt during cleaning and separates the cleaning sheet during fixing. 8. The fixing belt according to claim 1, wherein the fixing belt is rotated at a lower speed during cleaning than at the time of fixing.
8. The fixing device according to any one of items 7.