JP2008040279A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely remove the offset toner sticking to the surface of a fixing means even if the capacity reduction of the heating means within a fixing device accompanying the miniaturization of an image forming apparatus and speeding up of an image forming speed are performed and to prevent the occurrence of image staining when fixing of the toner image to a recording medium. <P>SOLUTION: A cleaning system 70 including a first cleaning means 71 and a second cleaning means 72 are arranged on the surface of a fixing roller 50 and a first web 73 included in the first cleaning means 71 and a second web 80 included in the second cleaning means 72 are brought into pressurized contact with the surface of the fixing roller 50 in such a manner that the second web 80 comes into contact with the rear face of the first web 73. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus.

  An electrophotographic image forming apparatus is widely used as a copying machine, a printer, a facsimile machine, a multifunction machine, and the like because it can form a high-quality image with good reproducibility and operability at low cost. The electrophotographic image forming apparatus includes, for example, a photoreceptor, a charging unit, an exposure unit, a developing unit, a transfer unit, and a fixing unit. The photoreceptor is a roller-like member that can form an electrostatic latent image corresponding to image information on the surface thereof. The charging means charges the surface of the photoreceptor. The exposure means irradiates the charged photoreceptor surface with signal light to form an electrostatic latent image. The developing means supplies toner to the electrostatic latent image on the surface of the photoreceptor to form a toner image. The transfer unit transfers the toner image on the surface of the photoreceptor to a recording medium. The fixing unit fixes the toner image on the recording medium to the recording medium to form an image. Here, as the fixing unit, a fixing device including a fixing roller and a pressure roller is generally used. The fixing roller is a roller member that has a heating means inside thereof and heats and melts the toner constituting the unfixed toner image on the recording medium to fix it on the recording medium. The pressure roller is provided so as to be in pressure contact with the fixing roller, and promotes fixing of the toner to the recording medium by pressing the toner against the recording medium when the toner is heated and melted by the fixing roller. The pressure contact portion between the fixing roller and the pressure roller is called a fixing nip portion. A recording medium carrying an unfixed toner image is introduced into the fixing nip so that the toner image carrying surface of the recording medium is in contact with the surface of the fixing roller, and the unfixed toner image is fixed by heating and pressing. The toner of the unfixed toner image or the offset toner may adhere to the surface of the fixing roller. The toner adhering to the fixing roller is fixed to another recording medium and recognized as image contamination. Therefore, various measures are conventionally taken in order to prevent the toner from adhering to the surface of the fixing roller or to remove the toner adhering to the surface of the fixing roller.

  In conventional fixing devices, the toner adhering to the surface of the fixing roller is removed by bringing a cleaning web impregnated with oil for preventing toner adhesion (hereinafter simply referred to as “web” unless otherwise specified) into contact with the surface of the fixing roller. In addition, a toner adhesion preventing oil is applied to the surface of the fixing roller. As a specific example of using the web, for example, the fixing device 100 shown in FIG. FIG. 5 is a cross-sectional view schematically showing a configuration of the fixing device 100 using a web. The fixing device 100 includes a fixing roller 101, a pressure roller 102, and a cleaning device 103. The fixing roller 101 has heating means 101 a and 101 b inside, and is provided so as to be rotatable in the direction of an arrow 106. The pressure roller 102 is provided so as to be in pressure contact with the fixing roller 101 and to be rotatable in the direction of an arrow 107. A pressure-contact portion between the fixing roller 101 and the pressure roller 102 is a fixing nip portion 108. The recording medium 104 carrying the toner image 105 is introduced into the fixing nip portion 108 so that the toner image 105 contacts the surface of the fixing roller 101. The toner image 105 is heated and pressurized at the fixing nip portion 108 and fixed on the recording medium 104. The cleaning device 103 includes a web 109, a delivery roller 110, a winding roller 111, and a pressure roller 112. The web 109 is impregnated with oil. The feed roller 110 is rotatably provided and feeds the web 109 in the direction of the arrow 113. The take-up roller 111 is rotatably provided, is sent out in the direction of the arrow 113 from the feed roller 110, and takes up the web 109 after coming into contact with the fixing roller 101. The pressure roller 112 is rotatably provided so as to be in pressure contact with the surface of the fixing roller 101 via the web 109. Accordingly, the web 109 is sandwiched between the fixing roller 101 and the pressure roller 112. A pressure contact portion between the fixing roller 101 and the web 109 is a cleaning nip portion 114. The web 109 is fed from the feed roller 110 in the direction of the arrow 113, passes through the cleaning nip 114, and is taken up by the take-up roller 111. When the web 109 passes through the cleaning nip portion 114, the toner attached to the surface of the fixing roller 101 is removed and oil is applied to the surface of the fixing roller 101. The cleaning effect of the surface of the fixing roller 101 by the cleaning device 103 in the fixing device 100 is good.

  By the way, along with the generalization of electrophotographic image forming apparatuses, the performance improvement requirements imposed on the image forming apparatuses are becoming more and more severe. Recently, as the image forming apparatus has been downsized, the heater for supplying heat to the fixing roller and the pressure roller has also been downsized, and the heat supply performance is inevitably reduced. On the other hand, the demand for an image forming apparatus extends to an increase in image forming speed. In recent image forming apparatuses, the number of recording media in contact with the fixing roller and the pressure roller is increasing per unit time. For this reason, although the amount of heat transferred from the fixing roller and the pressure roller to the recording medium is remarkably increased, the heat amount replenishment performance of the heater is reduced, so that the surface temperature of the fixing roller and the pressure roller is lowered and appropriate. Is not maintained in the correct range. As a result, there is a problem that the offset amount of the toner is increased more than usual and the fixing roller is contaminated. This problem is particularly noticeable when a large number of images with a high halftone printing ratio are copied. Even in the cleaning device 103, the toner offset amount may be larger than the cleaning ability of the web 109. In this case, the offset toner that cannot be removed is blocked by the pressure roller 112 and accumulated at the cleaning nip 114 or a downstream point 115 of the nip 114 in the rotation direction of the fixing roller 101 (hereinafter simply referred to as “downstream point 115”). To do. Since the fixing roller is sufficiently warm while the image operation continues, the offset toner stays at the cleaning nip 114 or the downstream point 115. However, the accumulated offset toner leaks from the cleaning nip 114 or the downstream point 115 when the image forming operation is finished and a predetermined time has passed and the image forming operation is resumed. The leaked offset toner moves to the surface of the pressure roller 102 that rotates idly before the recording medium 104 passes through the fixing nip portion 108, and adheres to the surface opposite to the toner image carrying surface of the recording medium 104. Since the toner adhering to the opposite surface is not sufficiently fixed, when continuously forming images, the image forming surface of the next recording medium is also soiled.

  In the cleaning device 103, since the web 109 is in contact with the fixing roller 101 only once, it is necessary to reliably remove the toner and apply oil in the single contact. The cleaning ability including the toner removing ability and the oil application ability is correlated with the feed amount of the web 109 per unit time, the thickness of the web 109, and the like. Therefore, in order to perform sufficient cleaning, it is necessary to determine the feeding speed, thickness, and the like of the web 109 according to the high-density halftone image or solid image having the largest amount of toner to be removed. However, it is extremely rare to form a high-density halftone image or a solid image. When the feeding speed and thickness of the web 109 are determined in accordance with this, the number of windings of the web 109 is increased, the feeding roller 110 and the winding roller. The diameter of 111 is increased, and an increase in the size of the apparatus is inevitable. In addition, there is a problem that it is time to replace the web 109 before the ability of the web 109 is fully utilized.

  In view of such a problem, a cleaning device is proposed in which the web is doubled and brought into contact with the surface of the fixing roller (see, for example, Patent Document 1). FIG. 6 is a cross-sectional view schematically showing the configuration of the cleaning device 120 of Patent Document 1. Hereinafter, the contact surface of the web with the surface of the fixing roller is referred to as “web surface”, and the surface opposite to the contact surface of the web with the surface of the fixing roller is referred to as “web back surface”. The cleaning device 120 includes a web 121, a delivery roller 122, a take-up roller 123, and a pressure roller 124. According to the cleaning device 120, the web 121 is first fed from the feed roller 122 in the direction of the arrow 125, wound so as to contact the outer peripheral surface of the pressure roller 124, and then directed from the pressure roller 124 toward the feed roller 122. Returned. This web 121 is called return web 121. The return web 121 is wound along the outer periphery of the web 121 that is newly fed out from the feed roller 122, and is sent out toward the press roller 124 again. That is, the back surface of the return web 121 comes into contact with the surface of the web 121 to be newly fed out, and subsequently the surface comes into contact with the surface of the fixing roller 101, and then is wound up and collected by the take-up roller 123. In the cleaning device 120, the pressure roller 124 is provided so as to contact the fixing roller 101. Accordingly, the web 121 is doubled at the cleaning nip portion 114. In this configuration, when a large amount of offset toner is generated, toner that cannot be sufficiently removed only by the web 121 on the side in contact with the fixing roller 101 is adhered to the web 121 on the side in contact with the pressure roller 124 and removed. With the goal. However, in this configuration, when the return web 121 comes into contact with the surface of the fixing roller 101, the toner adhering to the surface of the return web 121 reattaches to the surface of the fixing roller 101, and is fixed on the recording medium and recognized as image contamination. There is a fear. Further, the problem that toner accumulates in the cleaning nip portion 114 and the vicinity thereof is not sufficiently solved. Furthermore, when the toner accumulated in the cleaning nip portion 114 and the vicinity thereof is restarted after a lapse of a certain time from the end of the operation, there is a problem that the back surface of the recording medium is contaminated by the pressure roller. There is also a problem that is likely to occur.

Japanese Patent Laid-Open No. 9-80958

  The object of the present invention is to cope with the reduction in the capacity of the heating unit and the increase in the image forming speed accompanying the downsizing of the image forming apparatus, and even when a large amount of offset toner is generated, the offset toner is reliably removed from the fixing unit. An image forming apparatus including the fixing device and a fixing device capable of stably fixing a high-quality image free from image smearing on a recording medium.

The present invention
Fixing means provided so as to be rotatable around an axis, heating a recording medium carrying an unfixed toner image, and melting and fixing the toner constituting the unfixed toner image on the recording medium;
A pressure unit that presses against the fixing unit and forms a pressure contact portion with the fixing unit, and pressurizes a recording medium carrying an unfixed toner image conveyed to the pressure contact unit;
A first cleaning means comprising a first cleaning web provided to abut on the surface of the fixing means on the downstream side in the rotational driving direction of the fixing means with respect to the pressure contact portion between the fixing means and the pressure means;
And a second cleaning means comprising a second cleaning web provided so as to abut on the first cleaning web on the surface opposite to the abutment surface of the first cleaning web on the fixing means. This is a fixing device.

The fixing device of the present invention is
The first cleaning web is provided so as to be capable of being fed and wound, and the second cleaning web is provided so as to be rotatable in a loop shape.

Furthermore, the fixing device of the present invention is
The second cleaning web is provided so as to come into contact with the first cleaning web again in a state where the toner adhering to the first cleaning web is not fixed.

Furthermore, the fixing device of the present invention is
The second cleaning means is
A pressure roller that is rotatably supported and causes the second cleaning web to abut on the surface of the fixing unit via the first cleaning web;
A relay roller that is rotatably supported and applies tension to the second cleaning web;
And an endless belt-like second cleaning web that is stretched by a pressure roller and a relay roller to form a loop-like movement path.

Furthermore, the fixing device of the present invention is
The first cleaning means is
A delivery roller for delivering the first cleaning web;
A winding roller for winding the first cleaning web after coming into contact with the fixing unit;
And a first cleaning web that is sandwiched between the fixing unit and the pressure roller via the second cleaning web and contacts the fixing unit.

Furthermore, the fixing device of the present invention is
The second cleaning web is characterized in that it is thicker than the first cleaning web.

Furthermore, the fixing device of the present invention is
The first cleaning web and the second cleaning web are characterized by being impregnated with different oils.

The present invention also provides
An electrostatic latent image is formed by irradiating a photosensitive drum having a photosensitive layer on the surface thereof, charging means for charging the surface of the photosensitive drum, and signal light corresponding to image information on the charged photosensitive drum surface. Exposure means; developing means for supplying toner to the electrostatic latent image on the surface of the photosensitive drum to form a toner image; transfer means for transferring the toner image to a recording medium with or without an intermediate transfer medium; An image forming apparatus comprising: a fixing unit that fixes an unfixed toner image on a recording medium; and a cleaning unit that removes toner remaining on the surface of the photosensitive drum after the transfer of the toner image.
The fixing means is
An image forming apparatus characterized by being one of the fixing devices described above.

  The present invention relates to a first cleaning means comprising a fixing means, a pressure means, a first cleaning web (hereinafter referred to as “first web” unless otherwise specified), and a second cleaning web (hereinafter particularly referred to as “first cleaning web”). A second cleaning means provided with a second web) unless otherwise specified, and the first web is fixed on the downstream side in the rotational driving direction of the fixing means with respect to the pressure contact portion between the fixing means and the pressure means. There is provided a fixing device provided so as to abut on the surface of the means, and provided so that the second web abuts on a surface opposite to the abutting surface of the first web on the fixing means. In the fixing device according to the present invention, as in the conventional fixing device, the first web and the second web are doubly pressed against the surface of the fixing unit, but the second web is fixed to the first web. A configuration is adopted in which only the surface opposite to the contact surface with the means (hereinafter referred to as the “back surface of the first web”) is contacted. Also in the developing device of the present invention, when the amount of offset toner on the fixing roller is large, the offset toner is removed by the cooperation of the first web and the second web, and the toner also adheres to the second web. To do. However, since the second web contacts only the back surface of the first web, the contact surface of the first web to the fixing device is not contaminated by the toner. For this reason, the first web can be brought into contact with the fixing unit in a state where the cleaning ability is not lowered. Further, the toner adhering to the second web is gradually adhered to the back surface of the first web and removed from the second web when the amount of offset toner on the fixing unit is small. Can be used over a long period of time. Therefore, according to the fixing device of the present invention, it is possible to cope with the reduction in the capacity of the heating unit and the increase in the image forming speed accompanying the downsizing of the image forming apparatus, and even when a large amount of offset toner is generated, the offset from the fixing unit. The toner can be reliably removed, and a high-quality image free from image smearing can be stably fixed on the recording medium.

  According to the present invention, the basic operation in the fixing device of the present invention is more reliably performed by providing the first web so that it can be fed and wound and providing the second web so as to be rotatable in a loop. . The basic operation is that the offset toner on the fixing roller is mainly removed by the first web, and when the first web alone cannot completely remove the toner, the second web also cooperates to remove the toner. Is the action. In particular, by providing the second web so as to be rotatable in a loop shape and configuring it as a long-term durability member, the basic operation of the present invention can be performed with the web usage almost the same as that of a conventional cleaning device.

  According to the present invention, the second web is provided so as to come into contact with the first web again in a state where the toner adhering to the second web is not fixed due to contact with the first web and thus the fixing roller. When the amount of offset toner on the fixing roller is not large, the toner adhering to the second web is surely removed by the first web, so that the second web can be used for a longer period of time.

  According to the present invention, the pressure roller which is supported so as to be rotationally driven and makes the second web contact the surface of the fixing means via the first web, and the tension roller is supported so as to be rotationally driven and tension is applied to the second web. It is preferable to use a second cleaning means including a relay roller to be applied, and an endless belt-shaped second web that is stretched by the pressure contact roller and the relay roller to form a loop-shaped movement path. By using the second cleaning means, it is possible to easily realize a configuration in which the second web is in contact with the first web only by the contact surface of the fixing means. Further, the toner on the fixing unit is removed by the cooperation of the first web and the second web, the toner adhering to the second web is efficiently removed by the first web, and the surface of the fixing unit is cleaned. The effect is very high.

  According to the present invention, the first web feed roller, the first web take-up roller, the fixing means, and the pressure roller between the second web and the first web are in contact with the fixing means. It is preferable to use a first cleaning means including a web. By using the first cleaning unit, it is easy to change the design of the second cleaning unit, and the degree of freedom in designing the entire image forming apparatus is remarkably increased. This is particularly advantageous for downsizing the image forming apparatus.

  According to the present invention, by making the thickness of the second web larger than the thickness of the first web, the cleaning performance of the second cleaning unit can be improved without increasing the size of the second cleaning unit. Can be improved. In addition, since the second web can be impregnated with a large amount of oil, more oil can be applied to the surface of the fixing member than usual. As a result, the amount of offset toner adhering to the surface of the fixing member at the time of fixing the toner image can be reduced. Further, the offset toner adhering to the surface of the fixing member can be more reliably removed. Further, the present invention can be applied to an image forming system that requires use of a large amount of oil, for example, a system in which the surface of the fixing roller is made of silicone rubber or fluorine rubber.

  According to the present invention, by impregnating the first web and the second web with oil having different characteristics, the characteristics of the oil applied to the fixing member can be appropriately changed by combining two kinds of oils. For example, the first web is impregnated with oil having a relatively good affinity for the material constituting at least the surface layer of the fixing roller, and is inexpensive and relative to the material constituting the at least surface layer of the fixing roller. If the second web is impregnated with oil having a low affinity, the oil can be applied to the surface of the fixing roller at a relatively low price and with an appropriate affinity.

  According to the present invention, an electrophotographic image forming apparatus including the fixing device of the present invention is provided. According to the image forming apparatus, even if the heating capability of the heating unit during fixing is reduced and the image forming speed is increased due to the downsizing of the apparatus, the image due to poor fixing of the image or adhesion of the offset toner to the recording medium. Occurrence of contamination, contamination on the back surface of the recording medium (the back surface of the image forming surface), and the like are prevented, and a high-quality image can be formed stably over a long period of time. Moreover, there is almost no increase in device manufacturing costs.

  FIG. 1 is a cross-sectional view schematically showing a configuration of an image forming apparatus 1 which is another embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a configuration of a main part (a toner image forming unit 2 described later) of the image forming apparatus 1 shown in FIG. FIG. 3 is a cross-sectional view schematically showing the configuration of the fixing device 6 according to the first embodiment of the present invention. The image forming apparatus 1 is an electrophotographic image forming apparatus having a tandem configuration in which toner images of four colors of yellow, magenta, cyan, and black are sequentially superimposed and transferred. The image forming apparatus 1 includes a toner image forming unit 2, an intermediate transfer unit 3, a secondary transfer unit 4, a recording medium supply unit 5, a fixing device 6, and a scanner unit 7.

  The toner image forming unit 2 includes image forming units 10y, 10m, 10c, and 10b. The image forming units 10y, 10m, 10c, and 10b are arranged in a line in this order from the upstream side in the rotational driving direction (sub-scanning direction) of the intermediate transfer belt 21, which will be described later, that is, in the direction of the arrow 27, and input as digital signals or the like. An electrostatic latent image corresponding to the image information of each color is formed, toner of a color corresponding to the electrostatic latent image is supplied, and developed to form a toner image of each color. That is, the image forming unit 10y forms a toner image corresponding to yellow image information, the image forming unit 10m forms a toner image corresponding to magenta image information, and the image forming unit 10c corresponds to cyan image information. A toner image is formed, and the image forming unit 10b forms a toner image corresponding to black image information. The image forming unit 10y includes a photosensitive drum 11y, a charging roller 12y, an optical scanning unit 13, a developing device 14y, and a drum cleaner 15y.

  The photosensitive drum 11y is a roller-like member having a photosensitive layer on which an electrostatic latent image and thus a toner image is formed. Examples of the photosensitive drum 11y include those including a conductive base (not shown) and a photosensitive layer (not shown) formed on the surface of the conductive base. As the conductive substrate, a conductive substrate having a cylindrical shape, a columnar shape, a sheet shape or the like can be used, and among them, the cylindrical conductive substrate is preferable. Examples of the photosensitive layer include an organic photosensitive layer and an inorganic photosensitive layer. The organic photosensitive layer includes a laminate of a charge generation layer which is a resin layer containing a charge generation material and a charge transport layer which is a resin layer containing a charge transport material, and the charge generation material and the charge transport material in one resin layer And a resin layer containing. Examples of the inorganic photosensitive layer include a layer containing one or more selected from zinc oxide, selenium, amorphous silicon and the like. A base layer may be interposed between the conductive substrate and the photosensitive layer, and a surface layer (protective layer) for mainly protecting the photosensitive layer may be provided on the surface of the photosensitive layer. In the present embodiment, a photosensitive drum having a diameter of 30 mm including an aluminum base tube (conductive base) connected to the ground potential (GND) and an organic photosensitive layer having a thickness of 20 μm formed on the surface of the aluminum base tube. Is used. In the present embodiment, the photosensitive drum 11y is rotationally driven at a peripheral speed of 225 mm / s in the clockwise direction.

  The charging roller 12y is a roller-like member that is rotatably supported around an axis by a driving unit (not shown) and charges the surface of the photosensitive drum 11y to a predetermined polarity and potential. A power source (not shown) is connected to the charging roller 12y, and the surface of the photosensitive drum 11y is charged by discharging a voltage applied from the power source. In the present embodiment, a voltage of −1200 V is applied to the charging roller 12y, and the surface of the photosensitive drum 11y is charged to −600V. Instead of the charging roller 12y, a brush type charger, a charger type charger, a corona charger such as a scorotron, or the like can be used. The optical scanning unit 13 irradiates the charged surface of the photosensitive drum 11y with laser light 13y corresponding to yellow image information, and forms an electrostatic latent image corresponding to yellow image information on the surface of the photosensitive drum 11y. . A semiconductor laser or the like can be used for the optical scanning unit 13. In the present embodiment, an electrostatic latent image having an exposure potential of −70 V is formed on the surface of the photosensitive drum 11 y charged to −600 V.

  The developing device 14y includes a developing roller 17y, a developing blade 18y, a developing tank 19y, and stirring rollers 20y and 30y. The developing roller 17y carries the yellow toner 16y on its surface, and supplies the yellow toner 16y to the electrostatic latent image on the surface of the photosensitive drum 11y at a proximity portion (developing nip portion) between the developing roller 17y and the photosensitive drum 11y. To do. The developing roller 17y is supported by the developing tank 19y. A part of the developing roller 17y projects outward from an opening formed on the surface of the developing tank 19y facing the photosensitive drum 11y, and is close to the surface of the photosensitive drum 11y. This is a roller-like member that includes a fixed magnetic pole that is not to be rotated and is rotatably driven about an axis. The developing roller 17y is driven to rotate in the direction opposite to that of the photosensitive drum 11y. Accordingly, in the developing nip portion, the developing roller 17y and the photosensitive drum 11y are rotationally driven in the same direction. In the present embodiment, the developing roller 17y rotates at a peripheral speed of 338 mm / s, which is 1.5 times the peripheral speed of the photosensitive drum 11y. Further, a power source (not shown) is connected to the developing roller 17y, and a DC voltage (developing voltage) is applied from the power source. As a result, the yellow toner 16y on the surface of the developing roller 17y is smoothly supplied to the electrostatic latent image. In the present embodiment, a developing voltage of −420 V is applied to the developing roller 17y. The yellow toner layer on the surface of the developing roller 17y comes into contact with the photosensitive drum 11y in the developing nip portion, and the yellow toner 16y is supplied to the electrostatic latent image. The developing blade 18y is a plate-like member having one end supported by the developing tank 19y and the other end spaced apart from the surface of the developing roller 17y. The yellow is carried on the surface of the developing roller 17y. Uniform toner layer (layer regulation). The developing tank 19y is a container-like member having an internal space with an opening formed on the surface facing the photosensitive drum 11y as described above. The developing tank 19y contains a developing roller 17y and stirring rollers 20y and 30y in its internal space, and stores yellow toner 16y. The developing tank 19y is replenished with yellow toner 16y from a toner cartridge (not shown) according to the consumption state of the yellow toner 16y. In the present embodiment, the developing tank 19y is filled with a magnetic carrier in advance. The yellow toner 16y supplied to the developing tank 19y is mixed with the magnetic carrier and used in the form of a yellow two-component developer, but is not limited thereto, and is also used in the form of a one-component developer containing only the yellow toner 16y. it can. The stirring rollers 20y and 30y are screw-like members that are supported so as to be rotatable around an axis in the internal space of the developing tank 19y. The stirring roller 20y is provided so as to be in pressure contact with the surface of the developing roller 17y. The agitating rollers 20y and 30y feed yellow toner 16y supplied from a toner cartridge (not shown) into the developing tank 19y to the periphery of the surface of the developing roller 17y by their rotational driving. According to the developing device 14y, the developer in a form in which the yellow toner 16y adheres to the magnetic carrier in the developing tank 19y is supplied to the surface of the developing roller 17y by the stirring rollers 20y and 30y, and a developer layer is formed on the surface. . The developer layer is made uniform by the developing blade 18y, and then yellow toner 16y is selectively supplied from the developer layer to the electrostatic latent image on the surface of the photosensitive drum 11y by using a potential difference or the like. A yellow toner image corresponding to the image information is formed.

  As described later, the drum cleaner 15y removes and collects the yellow toner 16y remaining on the surface of the photosensitive drum 11y after the yellow toner image on the surface of the photosensitive drum 11y is transferred to the intermediate transfer belt 21. According to the image forming unit 10y, the surface of the photosensitive drum 11y charged by the charging roller 12y is irradiated with signal light 13y corresponding to yellow image information from the optical scanning unit 13 to form an electrostatic latent image. Then, yellow toner 16y is supplied from the developing device 14y to the electrostatic latent image to develop the electrostatic latent image, thereby forming a yellow toner image. As will be described later, this yellow toner image is transferred to the intermediate transfer belt 21 that is pressed against the surface of the photosensitive drum 11 y and is rotationally driven in the direction of the arrow 29. The yellow toner 16y remaining on the surface of the photosensitive drum 11y is removed and collected by the drum cleaner 15y. This image (toner image) forming operation is repeatedly executed. Since the image forming units 10m, 10c, and 10b have a structure corresponding to the image forming unit 10y except that magenta toner 16m, cyan toner 16c, or black toner 16b is used instead of the yellow toner 16y, the same reference numerals are used. In addition, “m” indicating magenta, “c” indicating cyan, and “b” indicating black are added to the end of each reference symbol, and description thereof is omitted.

  The toners 16y, 16m, 16c, and 16b (hereinafter collectively referred to as “toner 16” unless otherwise specified) contain a binder resin, a colorant, and a release agent. As the binder resin, those commonly used in this field can be used. For example, polystyrene, styrene-substituted homopolymer, styrene copolymer, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane Etc. Binder resin can be used individually by 1 type, or can use 2 or more types together. Among these binder resins, for color toners, a binder resin having a softening point of 100 to 150 ° C. and a glass transition point of 50 to 80 ° C. is preferable from the viewpoint of storage stability and durability. Polyester having a glass transition point is particularly preferred. Polyester exhibits high transparency in a softened or molten state. When the binder resin is polyester, when a multicolor toner image in which toner images of yellow, magenta, cyan and black are superimposed on each other is fixed on the recording medium 8, the polyester itself becomes transparent. Is obtained. As the colorant, pigments and dyes for toners conventionally used for electrophotographic image formation can be used. Examples of the pigment include azo pigments, benzimidazolone pigments, quinacridone pigments, phthalocyanine pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, anthraquinone pigments, perylene pigments, and perinone pigments. , Organic pigments such as thioindigo pigments, quinophthalone pigments, metal complex pigments, inorganic pigments such as carbon black, titanium oxide, molybdenum red, chrome yellow, titanium yellow, chromium oxide, Berlin blue, metals such as aluminum powder Examples include powder. A pigment can be used individually by 1 type or can use 2 or more types together. As the release agent, for example, wax can be used. As the wax, those commonly used in this field can be used, and examples thereof include polyethylene wax, polypropylene wax, and paraffin wax. In addition to the binder resin, the colorant, and the release agent, the toner 16 contains one or more general toner additives such as a charge control agent, a fluidity improver, a fixing accelerator, and a conductive agent. Can be contained.

  The toner 16 includes a pulverization method in which a colorant, a release agent, and the like are melt-kneaded and pulverized with a binder resin, a colorant, a release agent, a binder resin monomer, and the like are uniformly dispersed, and then a binder resin monomer. It can be produced according to a known method such as a suspension polymerization method for polymerizing a polymer, a binder resin particle, a colorant, a release agent and the like with an aggregating agent and heating the resulting fine particles of the aggregate. The volume average particle diameter of the toner 16 is not particularly limited, but is preferably 2 to 7 μm. When the volume average particle size of the toner 16 is less than 2 μm, the fluidity of the toner 16 is lowered, and during the developing operation, the supply, stirring and charging of the toner 16 become insufficient, the toner amount is insufficient, An increase or the like may occur, and a high-quality image may not be obtained. On the other hand, when the volume average particle diameter exceeds 7 μm, the toner particles having a large particle diameter that is difficult to be softened to the central portion increase, so that the fixability of the image to the recording medium 8 is lowered and the color of the image is deteriorated. In particular, in the case of fixing to OHP, the image becomes dark.

In the present embodiment, the toner 16 has the same configuration shown below except for the pigment. The toner 16 is a negatively chargeable insulating nonmagnetic toner having a glass transition point of 60 ° C., a softening point of 120 ° C., and a volume average particle size of 6 μm. A toner amount of 5 g / m ² is required to obtain an image density with a reflection density measurement value of 1.4 by X-Rite 310 using this toner. The toner 16 includes a polyester (binder resin) having a glass transition point of 60 ° C. and a softening point of 120 ° C., a low molecular weight polyethylene wax (release agent) having a glass transition point of 50 ° C. and a softening point of 70 ° C., and pigments of various colors. The content is 7% by weight of the total amount of the toner, the pigment content is 12% by weight of the total amount of the toner, and the balance is the binder resin polyester. The low molecular weight polyethylene wax contained in the toner 16 is a wax having a glass transition point and a softening point lower than that of the polyester of the binder resin.

  The intermediate transfer unit 3 includes an intermediate transfer belt 21, intermediate transfer rollers 22y, 22m, 22c, and 22b, support rollers 23, 24, and 25, and a belt cleaner 26. The intermediate transfer belt 21 is an endless belt-shaped toner image carrier that is stretched between support rollers 23, 24, and 25 to form a loop-shaped movement path. The intermediate transfer belt 21 includes photosensitive drums 11y, 11m, 11c, and 11b. It rotates in the direction of the arrow 27 at substantially the same peripheral speed. For the intermediate transfer belt 21, for example, a polyimide film having a thickness of 100 μm can be used. The material of the intermediate transfer belt 21 is not limited to polyimide, and films made of synthetic resins such as polycarbonate, polyamide, polyester, and polypropylene, and various rubbers can be used. In the film made of synthetic resin or various rubbers, a conductive material such as furnace black, thermal black, channel black, and graphite carbon is blended in order to adjust the electric resistance value as the intermediate transfer belt 21. The toner image carrying surface 21a of the intermediate transfer belt 21 is pressed against the photosensitive drums 11y, 11m, 11c, and 11b in this order from the upstream side in the rotational driving direction of the intermediate transfer belt 21. The positions where the intermediate transfer belt 21 is in pressure contact with the photosensitive drums 11y, 11m, 11c, and 11b are the intermediate transfer positions of the respective color toner images. Intermediate transfer rollers 22y, 22m, 22c, and 22b are disposed at positions facing the photosensitive drums 11y, 11m, 11c, and 11b with the intermediate transfer belt 21 interposed therebetween.

  The intermediate transfer rollers 22y, 22m, 22c, and 22b are opposed to the photosensitive drums 11y, 11m, 11c, and 11b through the intermediate transfer belt 21, and are opposite to the toner image carrying surface 21a of the intermediate transfer belt 21, respectively. It is a roller-like member provided in pressure contact and capable of being driven to rotate about its axis by driving means (not shown). For the intermediate transfer rollers 22y, 22m, 22c, and 22b, for example, a roller-shaped member that includes a metal shaft body and a conductive layer that covers the surface of the metal shaft body is used. The shaft body is formed of a metal such as stainless steel, for example. The diameter of the shaft body is not particularly limited, but is preferably 8 to 10 mm. The conductive layer is formed of a conductive elastic body or the like. As the conductive elastic body, those commonly used in this field can be used, and examples thereof include EPDM, foamed EPDM, foamed urethane and the like containing a conductive agent such as carbon black. A high voltage is uniformly applied to the intermediate transfer belt 21 by the conductive layer. The intermediate transfer rollers 22y, 22m, 22c, and 22b are opposite to the charging polarity of the toner in order to transfer the toner images formed on the surfaces of the photosensitive drums 11y, 11m, 11c, and 11b onto the intermediate transfer belt 21. A polar intermediate transfer bias is applied by constant voltage control. As a result, yellow, magenta, cyan, and black toner images formed on the photoconductive drums 11y, 11m, 11c, and 11b are sequentially superimposed and transferred onto the toner image carrying surface 21a of the intermediate transfer belt 21, thereby transferring a multicolor toner image. Is formed. However, when image information of only a part of yellow, magenta, cyan, and black is input, the image forming unit corresponding to the color of the input image information among the image forming units 10y, 10m, 10c, and 10b. Only a toner image is formed.

  The support rollers 23, 24, and 25 are provided so as to be rotatable around an axis by driving means (not shown), and the intermediate transfer belt 21 is stretched and rotated in the direction of an arrow 27. For the support rollers 23, 24, 25, for example, an aluminum cylinder (pipe-shaped roller) having a diameter of 30 mm and a wall thickness of 1 mm is used. The support roller 24 is pressed against a later-described secondary transfer roller 28 via the intermediate transfer belt 21 to form a secondary transfer nip portion, and is electrically grounded. The support roller 24 has a function of stretching the intermediate transfer belt 21 and a function of secondarily transferring the toner image on the intermediate transfer belt 21 to the recording medium 8.

  The belt cleaner 26 removes the toner remaining on the toner image carrying surface 21 a after transferring the toner image on the toner image carrying surface 21 a of the intermediate transfer belt 21 to the recording medium 8 in the secondary transfer fixing unit 4 described later. It is a member and is provided so as to face the support roller 25 with the intermediate transfer belt 21 interposed therebetween. The belt cleaner 26 includes a cleaning blade 26a and a toner storage container 26b. The cleaning blade 26a is a plate-like member that is pressed against the toner image carrying surface 21a of the intermediate transfer belt 21 by a pressing unit (not shown) and scrapes off residual toner on the toner image carrying surface 21a. For example, a blade made of a rubber material having elasticity (for example, urethane rubber) can be used as the cleaning blade 26a. The toner storage container 26b temporarily stores toner scraped off by the cleaning blade 26a.

  According to the intermediate transfer means 3, the toner images formed on the photosensitive drums 11y, 11m, 11c, and 11b are superimposed and transferred onto a predetermined position of the toner image carrying surface 21a of the intermediate transfer belt 21, and the toner image is transferred. It is formed. As will be described later, this toner image is secondarily transferred to the recording medium 8 at the secondary transfer nip portion. The toner, offset toner, paper dust, and the like remaining on the toner image carrying surface 21a of the intermediate transfer belt 21 after the secondary transfer are removed by the belt cleaner 26, and the toner image is transferred again to the toner image carrying surface 21a.

  The secondary transfer unit 4 includes a support roller 24 and a secondary transfer roller 28. The secondary transfer roller 28 is a roller-like member that is in pressure contact with the support roller 24 via the intermediate transfer belt 21 and is rotatably driven in the axial direction. The secondary transfer roller 28 includes, for example, a metal shaft body and a conductive layer coated on the surface of the metal shaft body. The metal shaft body is formed of a metal such as stainless steel, for example. The conductive layer is formed of a conductive elastic body or the like. As the conductive elastic body, those commonly used in this field can be used, and examples thereof include EPDM, foamed EPDM, foamed urethane and the like containing a conductive agent such as carbon black. A power supply (not shown) is connected to the secondary transfer roller 28, and a high voltage having a polarity opposite to the charging polarity of the toner 16 is uniformly applied. A pressure contact portion between the support roller 24, the intermediate transfer belt 21, and the secondary transfer roller 28 is a secondary transfer nip portion.

  According to the secondary transfer unit 4, the toner image on the intermediate transfer belt 21 is conveyed to the secondary transfer nip portion, and the recording medium 8 fed from a recording medium supply unit 5 (described later) is secondary-transferred in synchronization therewith. The toner image and the recording medium 8 are superposed at the secondary transfer nip portion, and the toner image is secondarily transferred to the recording medium 8. In this way, an unfixed toner image is carried on the recording medium 8. The recording medium 8 carrying the unfixed toner image is conveyed to the fixing device 6.

  The recording medium supply means 5 includes a recording medium cassette 42, a pickup roller 43, and registration rollers 44a and 44b. The recording medium cassette 42 stores the recording medium 8. Examples of the recording medium 8 include plain paper, coated paper, color copy dedicated paper, OHP (overhead projector) film, and postcards. The size includes A4, A3, B5, B4, postcard size, and the like. The pickup roller 43 feeds the recording medium 8 to the transport path P one by one. The registration rollers 44a and 44b are a pair of roller-like members provided so as to come into pressure contact with each other, and in synchronization with the transfer of the multicolor toner image on the intermediate transfer belt 21 to the transfer fixing nip portion, the transfer fixing nip portion. The recording medium 8 is fed to According to the recording medium supply means 6, the recording medium 8 stored in the recording medium cassette 42 is fed to the conveyance path P one by one by the pickup roller 43, and is further transferred to the transfer fixing nip portion by the registration rollers 44 a and 44 b. To be sent to.

  The fixing device 6 includes a fixing roller 50, a pressure roller 60, and a cleaning device 70. The fixing roller 50 is a roller-like member that is rotatably supported by a support unit (not shown) and rotates at a predetermined speed in the direction of an arrow 56 by a drive unit (not shown). The fixing roller 50 heats and melts the toner 16 constituting the toner image carried on the recording medium 8 and fixes the toner 16 on the recording medium 8. In the present embodiment, a roller-like member including a cored bar 51, an elastic body layer 52, and a surface layer 53 is used as the fixing roller 50. As the metal forming the cored bar 51, a metal having high thermal conductivity can be used, and examples thereof include aluminum and iron. Examples of the shape of the core metal 51 include a cylindrical shape and a columnar shape, but a cylindrical shape with a small amount of heat released from the core metal 51 is preferable. The material constituting the elastic layer 52 is not particularly limited as long as it has rubber elasticity, but is preferably superior in heat resistance. Specific examples of such materials include silicone rubber, fluorine rubber, fluorosilicone rubber, and the like. Among these, silicone rubber having particularly excellent rubber elasticity is preferable. The material constituting the surface layer 53 is not particularly limited as long as it is excellent in heat resistance and durability and has weak adhesion to the toner 16. For example, PFA (tetrafluoroethylene and perfluoroalkyl vinyl ether copolymer) ), Fluororesin materials such as PTFE (polytetrafluoroethylene), fluororubber, and the like. In the present embodiment, the surface layer 53 is a PFA layer having a thickness of about 30 μm. Two heating means 54 are provided inside the fixing roller 50. This is because the start-up time from when the image forming apparatus 1 is turned on until the image can be formed is shortened, and the surface temperature of the fixing roller 50 is reduced due to the transfer of heat to the recording medium 8 when fixing the toner image. This is to prevent it. In the present embodiment, a halogen lamp is used as the heating means 54.

  The pressure roller 60 is a roller-like member that is rotatably provided in a state of being pressed against the fixing roller 50 by a pressure mechanism (not shown) on the downstream side in the rotation direction of the fixing roller 50 with respect to the lowest vertical point of the fixing roller 50. It is. A pressure-contact portion between the fixing roller 50 and the pressure roller 60 is a fixing nip portion 55. The pressure roller 60 is rotated by the rotation of the fixing roller 50. The pressure roller 60 fixes the toner image on the recording medium 8 by pressing the toner 16 in a molten state against the recording medium 8 when the fixing roller 50 heat-fixes the toner image on the recording medium 8. Facilitate. In the present embodiment, a roller-like member having a diameter of 50 mm including a cored bar 61, an elastic body layer 62, and a surface layer 63 is used as the pressure roller 60. As a material for forming the cored bar 61, the elastic body layer 62, and the surface layer 63, the same metal or material as that for forming the cored bar 51, the elastic body layer 52, and the surface layer 53 of the fixing roller 50 can be used. Further, the shape of the cored bar 61 is the same as that of the fixing roller 50. A heating unit 64 is provided inside the pressure roller 60. This is because the start-up time from when the power of the image forming apparatus 1 is turned on until the image can be formed is shortened, and the surface temperature of the pressure roller 60 is abrupt due to the transfer of heat to the recording medium 8 when fixing the toner image. This is to prevent a decrease or the like. In the present embodiment, a halogen lamp is used as the heating means 64.

  The fixing mechanism including the fixing roller 50 and the pressure roller 60 is controlled by a CPU (Central Processing Unit) (not shown) that controls the entire operation of the image forming apparatus 1. When the CPU receives an image formation instruction, it sends a control signal to a power supply (not shown) that supplies power to the heating means 54 and 64 provided inside the fixing roller 50 and the pressure roller 60. The image forming instruction is input from an operation panel (not shown) provided on the upper surface in the vertical direction of the image forming apparatus 1 or an external device such as a computer connected to the image forming apparatus 1. Upon receipt of the control signal, the power supply supplies power to the fixing roller 50 and the pressure roller 60 to activate the heating means 54 and 64. The heating units 54 and 64 heat the surfaces of the fixing roller 50 and the pressure roller 60 so as to have respective set temperatures. When a temperature detection sensor (not shown) provided in the vicinity of the fixing roller 50 and the pressure roller 60 detects that the set temperature has been reached and the detection result is input to the CPU, the CPU rotates the fixing roller 50. A control signal is sent to the drive means that does not, and the fixing roller 50 is rotated in the direction of the arrow 55. Along with this, the pressure roller 60 is driven to rotate. In this state, the recording medium 8 carrying the unfixed toner image is conveyed from the secondary transfer unit 4 to the fixing nip portion, and the toner image is fixed to the recording medium 8 when the recording medium 8 passes through the fixing nip portion. The

  The cleaning device 70 includes a first cleaning unit 71 and a second cleaning unit 72, and removes offset toner and the like attached to the surface of the fixing roller 50.

The first cleaning means 71 includes a first web 73, a delivery roller 74, a relay roller 75, and a take-up roller 76. The surface of the first web 73 is provided so that the surface thereof is in pressure contact with the surface of the fixing roller 50 by a pressure roller 82 in a second cleaning unit 72 described later. The press contact portion between the first web 73 and the fixing roller 50 is a cleaning nip portion 77. For the first web 73, for example, a heat-resistant nonwoven fabric can be used. Although it does not restrict | limit especially as a heat resistant nonwoven fabric, For example, the nonwoven fabric etc. which have a moderate softness | flexibility and mechanical strength including an aromatic polyamide fiber and the polyester fiber softened at high temperature are mentioned. Such heat-resistant nonwoven fabrics are commercially available, and examples thereof include Nomex (trade name) and Himeron (trade name). Moreover, although the thickness of the 1st web 73 is not restrict | limited in particular, Preferably it is 30-100 micrometers. In the present embodiment, a first web 73 having a thickness of 40 μm is used. Further, the first web 73 can be impregnated with oil. Oils commonly used in this field can be used as the oil, and examples thereof include silicone oils such as dimethyl silicone oil, amino-modified silicone oil, mercapto-modified silicone oil, and fluorine-modified silicone oil. In the present embodiment, the first web 73 was impregnated with silicone oil having a viscosity of about 0.01 m ² / s (10000 centistokes, 25 ° C.). The feed roller 74 is supported so as to be driven to rotate around its axis, and the first web 73 is wound around and held on the surface thereof. The relay roller 75 is supported so as to be driven to rotate around the axis, and applies tension to the first web 73 fed from the feed roller 74. The take-up roller 76 is provided so as to be rotatable around an axis by a driving means (not shown), and takes up the first web 73 after contacting the fixing roller 50.

  According to the first cleaning means 71, the first web 73 fed out from the feed roller 74 in the direction of the arrow 78 is stretched by the relay roller 75 and the second cleaning means 72 described later, so that the second cleaning is performed. After being brought into contact with the surface of the fixing roller 50 by a pressure roller 81 which is one member of the means 72, it is partially wound around the fixing roller 50 and displaced in the direction of the arrow 79 in the conveying direction. Is taken up by a take-up roller 76 provided on the downstream side in the transport direction, away from the cleaning means 72. The operation of the first cleaning means 71 is controlled by a CPU (not shown). The CPU detects that a predetermined number of recording media 8 have passed through the fixing nip portion 55 by using a sensor, the number of rotations of the fixing roller 50, and the like, and then driving means (not shown here) that rotates the winding roller 76. A control signal is sent to a motor provided inside the main body of the apparatus 1. Upon receiving the control signal, the driving means rotates the take-up roller 76 to take up the first web 73 in the direction of the arrow 79 by a certain amount. By this winding, the first web 73 that is fed from the feed roller 74 in the direction of the arrow 78 and reaches the cleaning nip 77 (the pressure contact portion between the fixing roller 50 and the first web 73) is the surface of the fixing roller 50. The offset toner adhering to the toner is taken in and oil is supplied to the fixing roller 50. Although an example of the operation of intermittently winding by the winding roller 76 has been shown, the present invention is not limited to this, and the winding may be performed continuously in accordance with the timing when the recording medium 8 passes through the fixing nip portion 55. Good.

  The second cleaning unit 72 includes a second web 80, a pressure roller 81, and a relay roller 82. The second web 80 is an endless belt-like member that is stretched by the pressure contact roller 81 and the relay roller 82 to form a loop-shaped movement path and is rotatably driven in the direction of the arrow 83. The second web 80 is driven to rotate in the direction of the arrow 83 with the winding operation of the first web 73 by the winding roller 76. The surface of the second web 80 rotates in contact with the back surface of the first web 73 from the peripheral surface of the relay roller 82 to the separation point 84 via the cleaning nip 81. The second web 80 only contacts the back surface of the first web 73 and does not contact the surface of the first web 73. Therefore, toner or the like does not adhere to the surface of the first web 73, and the cleaning performance of the first web 73 is hardly deteriorated. Note that the position of the separation point 84 can be changed to an arbitrary position by adjusting the installation position, installation interval, and the like of each component member, but is preferably closer to the cleaning nip portion 77. When a position that is moderately separated from the cleaning nip 77 is set as the separation point 84, the toner adhering to the second web 80 is cooled, so that it is between the first web 73 and the second web 80. There is a risk that the two webs 73 and 80 may be bonded together. When the webs 73 and 80 are bonded, it is difficult to peel them off, which is not preferable because the torque of the motor for winding the first web 73 is increased and the webs 73 and 80 are damaged.

  For the second web 80, a heat-resistant non-woven cloth similar to the first web 73 can be used. The thickness of the second web 80 may be the same as the thickness of the first web 73, but is preferably thicker than the first web 73 from the viewpoint of absorbing more offset toner. The second web 80 can also be impregnated with oil. Oils commonly used in this field can be used as the oil, and examples thereof include silicone oils such as dimethyl silicone oil, amino-modified silicone oil, mercapto-modified silicone oil, and fluorine-modified silicone oil. The oil impregnated in the second web 80 may be the same as the oil impregnated in the first web 73, but may be different. For example, when at least the surface of the fixing roller 50 is made of fluororubber, the first web 73 is impregnated with amino-modified silicone oil or mercapto-modified silicone oil having good affinity with the fluororubber, and the second web 80. May be impregnated with inexpensive dimethyl silicone oil. In this way, a mixture of two types of oil is applied to the surface of the fixing roller 50. The two oil mixtures have a relatively good affinity for the surface material of the fixing roller 50 and are advantageous in terms of cost.

The pressure roller 81 is pivotally supported at both longitudinal ends by a bearing (not shown) so as to be driven to rotate, and is pressed against the surface of the fixing roller 50 via a first web 73 and a second web 80 by a pressing means (not shown). It is a roller-shaped member provided. The pressure roller 81 is driven to rotate together with the second web 80 during the winding operation of the first web 73 by the winding roller 76. A pressure contact portion between the pressure roller 81 and the fixing roller 50 is a cleaning nip portion 77. For the pressure roller 81, for example, a roller-shaped member including a metal core and an elastic layer formed on the surface of the metal core is used. As an elastic material which comprises an elastic layer, heat resistant rubbers, such as silicone rubber, its foam etc. are mentioned, for example. The surface hardness of the elastic layer is not particularly limited, but is preferably 20 ° to 30 ° (Asker-c, Asker C hardness). The pressing force to the fixing roller 50 is preferably 3793.6 Pa (0.039 kgf / cm ² ) to 18967.9 Pa (0.19 kgf / cm ² ). If it is less than 3793.6 Pa, the offset toner may leak into the image forming apparatus 1. If it exceeds 18967.9 Pa, the surface layer of the fixing roller 50 is liable to be damaged, and there is a risk of image fixing failure or the like. For example, a spring member or the like is used as the pressing means. The width in the longitudinal direction of the pressure roller 81 may be larger than the maximum width of the image forming area to be formed in the image forming apparatus 1. Further, the width of the cleaning nip portion 77 (cleaning nip width) has a great influence on the cleaning performance of the cleaning device 70, so it is preferable to design the width within the appropriate range. The cleaning nip width is mainly determined by the pressing force of the pressure roller 81 against the fixing roller 50, the roller diameter of the pressure roller 81, and the like. In this embodiment, the longitudinal width of the pressure roller 81 is 310 mm longer than the image forming area, the roller diameter is 20 mm, and the fixing nip width is 5 mm.

  The relay roller 82 is supported so as to be able to be driven and rotated about its axis, and applies tension to the second web 80 so that the second web 80 rotates in the direction of the arrow 83 along the loop-shaped movement path. The relay roller 82 is driven to rotate together with the second web 80 during the winding operation of the first web 73 by the winding roller 76. The interval between the pressure roller 81 and the relay roller 82 is the second interval until the second web 80 to which the toner adheres in the cleaning nip portion 77 comes into contact with the first web 73 again on the peripheral surface of the relay roller 82. The toner adhering to the web 80 is set so as not to adhere to the second web 80. As a result, the second web 80 can be used for a long time.

  According to the second cleaning means 72, the second web 80 stretched by the pressure roller 81 and the relay roller 82 is driven to rotate during the winding operation of the first web 73. Then, when the amount of offset toner generated by large-scale printing of a halftone image exceeds the cleaning ability of the first web 73, the second offset toner that passes through the first web 73 or passes through a minute hole is added to the second toner. By adsorbing the web 80, the surface of the fixing roller 50 is cleaned. At the same time, when a large amount of offset toner is generated, the amount of oil supplied to the fixing roller 50 by the first web 73 decreases, so that the oil impregnated in the second web 80 is fixed via the first web 73. Supplied to the roller 50. The second web 80 to which the offset toner has adhered in the cleaning nip portion 77 is moved to the separation point 84 along with the winding operation of the first web 73, and then the second web 80 having the offset toner cleaned is moved to the second web 80. 1 moves away from the web 73, that is, in the direction of the arrow 83, and again passes through the peripheral surface of the relay roller 82 toward the cleaning nip 77. The offset toner adhering to the second web 80 moves to the back surface of the first web 73 between the peripheral surface of the relay roller 82 and the separation point 84 when the occurrence of the offset toner is small. Since the web 80 is cleaned, the second web 80 can be used for a long time. According to the cleaning device 70, the surface of the fixing roller 50 is cleaned by the cooperation of the first web 73 and the second web 80.

  In the present embodiment, the fixing device 6 including the cleaning device 70 shown in FIG. 3 is used. However, the present invention is not limited to this, and the second web 80 is the back surface of the first web 73 (opposite to the pressure contact surface with the fixing roller 50). Any fixing device including a cleaning device configured to contact only the side surface) can be used without particular limitation. FIG. 4 is a cross-sectional view schematically showing the configuration of another type of fixing device 90. The fixing device 90 is similar to the fixing device 6, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. The fixing device 90 includes a cleaning device 91. The cleaning device 91 includes a first cleaning unit 92 and a second cleaning unit 72.

  The first cleaning unit 92 includes a first web 73, a feed roller 74, and a take-up roller 76. The first web 73 is brought into pressure contact with the surface of the fixing roller 50 by a pressure roller 81 in a second cleaning unit 72 described later. The press contact portion between the first web 73 and the fixing roller 50 is a cleaning nip portion 77. The first web 73 enters a contact state with the second web 80 at a contact start point 93 on the peripheral surface of the pressure roller 81, passes through the cleaning nip 77, and then at the separation point 94, the second web 80. Get away from. When the CPU detects that a predetermined number of recording media 8 have passed through the fixing nip portion 55, the CPU is connected to a driving means (not shown) that rotates the winding roller 76 (here, a motor disposed in the main body of the image forming apparatus 1). A control signal is sent, the take-up roller 76 is rotated, and the first web 73 is taken up by a certain amount. Along with the winding operation by the winding roller 76, the feeding roller 73 feeds the cleaning nip portion 77 in the direction of the arrow 95 and passes through the cleaning nip portion 77 under contact with the second web 80. The first web 73 takes in the offset toner adhering to the fixing roller 50 at the cleaning nip portion 73 and supplies oil impregnated therein to the surface of the fixing roller 50. Further, the first web 73 moves in the direction of the arrow 96 and is taken up by the take-up roller 76 after being separated from the second web 80. Here, a configuration is employed in which the winding operation by the winding roller 76 is intermittently performed. However, the present invention is not limited to this, and a configuration in which the winding operation is continuously performed in synchronization with the passage of the recording medium 8 through the fixing nip portion 55. May be taken.

  The second cleaning unit 72 includes a second web 80, a pressure roller 81, and a relay roller 82, except that the relay roller 82 is provided at a position facing the fixing roller 50 via the pressure roller 81. The configuration is the same as that of the second cleaning means 72 in the cleaning device 70. The second web 80 is in pressure contact with the fixing roller 50 with the pressure roller 81 passing through the first web 73 and in contact with the back surface of the first web 73. The second web 80 is driven and rotated in the direction of the arrow 97 in synchronization with the movement of the first web 73 in the direction of the arrow 95 accompanying the winding operation by the winding roller 76, and the surface of the fixing roller 50 is rotated. Remove the offset toner. In particular, when the amount of offset toner adhering to the surface of the fixing roller 50 exceeds the allowable intake amount of the first web 73 due to large-scale printing such as a halftone image, the first web 73 is transmitted or the first web 73 The second web 80 takes in the offset toner slipped through the minute holes. When the amount of oil supplied from the first web 73 is small, the oil impregnated in the second web 80 is supplied to the fixing roller 50. After passing through the cleaning nip 77, the second web 80 passes through the peripheral surface of the relay roller 82 and comes into contact with the first web 73 from the contact start point 93 toward the cleaning nip 77. In the present embodiment, since the time for the second web 80 that has taken in the offset toner in the cleaning nip 77 to contact the first web 73 is set short, the toner take-in capability of the first web 73 is improved. Only when there is a margin, the cleaning operation for attaching the offset toner adhering to the second web 80 to the back surface of the first web 73 is performed. Therefore, the second web 80 can be used over a long period of time. In this embodiment, the cleaning device 91 is disposed on the surface of the fixing roller 50. However, the present invention is not limited to this. The cleaning device 91 may be disposed on the pressure roller 60 or both the fixing roller 50 and the pressure roller 60. Good.

  The scanner unit 7 includes a document table 41, a light source (not shown), and a CCD sensor 9. A document to be copied is placed on the upper surface of the document table 41. A plate-like member made of a transparent material such as transparent glass is used for the document table 41. The light source illuminates the document placed on the document table 41. The CCD sensor 9 converts the reflected light into image information (image signal) by photoelectrically converting the reflected light from the original illuminated by the light source. The CCD sensor 9 includes a conversion unit, a transfer unit, and an output unit. The conversion unit converts an optical signal that is reflected light into an electric signal, and the transfer unit sequentially transfers the electric signal to the output unit in synchronization with a clock pulse. The output unit converts the electric signal into a voltage signal, amplifies it, lowers the impedance, and outputs it. The analog signal thus obtained is converted into a digital signal by performing known image processing. The image information of the original read by the scanner unit 7 is sent to a CPU (not shown) that controls the entire operation of the image forming apparatus, and after various image processing is performed, the image information is temporarily stored in the memory and stored in the memory according to an output instruction. The image is read out and transferred to the optical scanning unit 13 to form an image on the recording paper as the recording medium 8.

  The image forming apparatus 1 is provided with a control unit (not shown). The control means is, for example, a processing circuit that is provided in the upper part of the internal space of the image forming apparatus 1 and is realized by a microcomputer that includes a central processing unit (CPU) that includes a control unit, a calculation unit, a storage unit, and the like (not shown). including. The CPU storage unit stores image formation commands via an operation panel (not shown) arranged on the upper surface of the image forming apparatus 1, detection results from sensors (not shown) arranged at various locations inside the image forming apparatus 1, and from external devices. Image information, etc. are input, and the determination by the calculation unit is performed based on various types of input data (image formation command, detection result, image information, etc.), and a control signal is sent from the control unit according to the determination result of the calculation unit The whole operation of the image forming apparatus 1 is controlled. As the storage unit, those commonly used in this field can be used, and examples thereof include a read only memory (ROM), a random access memory (RAM), and a hard disk drive (HDD). As the external device, an electric / electronic device that can form or acquire image information and can be electrically connected to the image forming apparatus can be used. For example, a computer, a digital camera, a television, a video recorder, a DVD recorder, For example, a facsimile machine. The control unit includes a power source together with the processing circuit described above, and the power source supplies power not only to the control unit but also to each device in the image forming apparatus 1.

It is sectional drawing which shows schematically the structure of the image forming apparatus which is another embodiment of this invention. FIG. 2 is an enlarged cross-sectional view illustrating a configuration of main parts of the image forming apparatus illustrated in FIG. 1. 1 is a cross-sectional view schematically showing a configuration of a fixing device according to a first embodiment of the present invention. FIG. 6 is a cross-sectional view schematically illustrating a configuration of a fixing device according to another embodiment. FIG. 6 is a cross-sectional view schematically illustrating a configuration of a conventional fixing device that uses a cleaning web. It is sectional drawing which shows the structure of the cleaning apparatus of patent document 1 typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Toner image forming means 3 Intermediate transfer means 4 Secondary transfer means 5 Recording medium supply means 6, 90 Fixing device 7 Scanner unit 8 Recording medium 10y, 10m, 10c, 10b Image forming units 11y, 11m, 11c, 11b Photosensitive drum 12y, 12m, 12c, 12b Charging roller 13 Optical scanning unit 14y, 14m, 14c, 14b Developing device 15y, 15m, 15c, 15b Drum cleaner 16, 16y, 16m, 16c, 16b Toner 21 Intermediate transfer belt 28 Secondary transfer roller 50 Fixing roller 54, 64 Heating means 60 Pressure roller 70, 91 Cleaning device 71, 92 First cleaning means 72 Second cleaning means 73 First web 77 Cleaning nip 80 Second web

Claims (8)

Fixing means provided so as to be rotatable around an axis, heating a recording medium carrying an unfixed toner image, and melting and fixing the toner constituting the unfixed toner image on the recording medium;
A pressure unit that presses against the fixing unit and forms a pressure contact portion with the fixing unit, and pressurizes a recording medium carrying an unfixed toner image conveyed to the pressure contact unit;
A first cleaning means comprising a first cleaning web provided to abut on the surface of the fixing means on the downstream side in the rotational driving direction of the fixing means with respect to the pressure contact portion between the fixing means and the pressure means;
And a second cleaning means comprising a second cleaning web provided so as to abut on the first cleaning web on the surface opposite to the abutment surface of the first cleaning web on the fixing means. Fixing device to do. The fixing device according to claim 1, wherein the first cleaning web is provided so as to be fed out and wound up, and the second cleaning web is provided so as to be rotatable in a loop shape. The second cleaning web
3. The fixing device according to claim 1, wherein the fixing device is provided so as to come into contact with the first cleaning web again in a state where the toner adhering to the first cleaning web is not fixed. The second cleaning means is
A pressure roller that is rotatably supported and causes the second cleaning web to abut on the surface of the fixing unit via the first cleaning web;
A relay roller that is rotatably supported and applies tension to the second cleaning web;
The fixing device according to claim 1, further comprising: an endless belt-shaped second cleaning web that is stretched by a pressure roller and a relay roller to form a loop-shaped movement path. apparatus. The first cleaning means
A delivery roller for delivering the first cleaning web;
A winding roller for winding the first cleaning web after coming into contact with the fixing unit;
The fixing device according to claim 1, further comprising: a first cleaning web that is sandwiched between the fixing unit and the pressure roller via the second cleaning web and contacts the fixing unit. apparatus. The second cleaning web
The fixing device according to claim 1, wherein the fixing device has a thickness larger than that of the first cleaning web.   The fixing device according to claim 1, wherein the first cleaning web and the second cleaning web are impregnated with different oils. An electrostatic latent image is formed by irradiating a photosensitive drum having a photosensitive layer on the surface thereof, charging means for charging the surface of the photosensitive drum, and signal light corresponding to image information on the charged photosensitive drum surface. Exposure means; developing means for supplying toner to the electrostatic latent image on the surface of the photosensitive drum to form a toner image; transfer means for transferring the toner image to a recording medium with or without an intermediate transfer medium; An image forming apparatus comprising: a fixing unit that fixes an unfixed toner image on a recording medium; and a cleaning unit that removes toner remaining on the surface of the photosensitive drum after the transfer of the toner image.
The fixing means is
An image forming apparatus comprising the fixing device according to claim 1.

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