JP2009042303A - Pressure roller and image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent images by improving durability and preventing offset caused by charge-up over the whole region of a pressure roller in a longitudinal direction. <P>SOLUTION: The pressure roller 20 includes a releasing layer 24 provided on the outermost layer, an adhesive layer 23 provided under the releasing layer 24, and an insulating elastic layer 22 provided under the adhesive layer 23. A resistance value of the releasing layer 24 is 10<SP>6</SP>-10<SP>9</SP>Ω/sq. A resistance value of the adhesive layer 23 is 10<SP>5</SP>Ω/sq. or lower. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image heating apparatus and a pressure roller used in an image forming apparatus such as an electrophotographic printer, a copying machine, and an electrostatic recording apparatus.

  An image forming apparatus using an electrophotographic system such as a conventional laser beam printer will be described.

  FIG. 8 is a schematic configuration diagram of an electrophotographic engine portion of the image forming apparatus.

  The electrophotographic engine portion includes a primary charger 202, an exposure unit 203, a developing device 204, a transfer roller (transfer device) 205, and a cleaning device 207 around a photosensitive drum (photoconductor) 201. Here, the primary charger 202 charges the photosensitive drum 1 along the rotation direction of the photosensitive drum 201. The exposure unit 203 exposes the photosensitive drum 201 to form an electrostatic latent image. The developing device 204 forms a toner image by attaching toner (developer) to the electrostatic latent image. The transfer roller (transfer device) 205 transfers the toner image on the photosensitive drum 201 to the recording material P. The cleaning device 207 removes residual toner.

  The recording material P as a transfer destination of the toner image is fed from a feeding cassette (not shown) and fed to the photosensitive drum 201. The recording material P fed to the photosensitive drum 201 is transferred with a toner image by a transfer roller (transfer device) 205 and then conveyed to a heat fixing device 206, where the recording material P on which the toner image is fixed is the device. Discharged outside.

  As the heat fixing device 206, a heat roller type or film heating type device is widely used. In particular, a method of suppressing power consumption as much as possible without supplying power to the heat fixing device during standby, and more specifically, a film heating method for fixing a toner image on the recording material P via a film between a heater portion and a pressure roller A heat fixing method based on the above has been proposed (Patent Documents 1 and 2).

  FIG. 9 shows a schematic configuration diagram of a main part of a heat fixing apparatus to which such a method is applied.

  The apparatus shown in FIG. 9 includes a heating member (heating body, hereinafter referred to as a heater) 211 and a pressure rotating body (hereinafter referred to as a pressure roller) 220. Here, the heater 211 is fixedly supported by a stay holder (support body) 212. The pressure roller 220 is pressed against the heater 211 so that a nip portion (fixing nip portion) N having a predetermined nip width is formed with a heat-resistant thin film (hereinafter referred to as a fixing film) 213 interposed therebetween. Is provided.

  The heater 211 is heated and adjusted to a predetermined temperature by energization. The fixing film 213 is conveyed and moved in the direction of arrow a shown in FIG. 9 while being in close contact with and sliding on the surface of the heater 211 at the fixing nip portion N by a driving means (not shown) or the rotational force of the pressure roller 220. It is. The fixing film 213 is provided in a cylindrical shape, an endless belt shape, or a roll-ended end web shape.

In the state where the heater 211 is heated and adjusted to a predetermined temperature and the fixing film 213 is conveyed and moved in the direction of the arrow, the material as a material to be heated is fixed between the fixing film 213 and the pressure roller 220 in the fixing nip N. A recording material P on which an unfixed toner image t is formed and supported is introduced. Then, the recording material P is brought into close contact with the surface of the fixing film 213 and is nipped and conveyed together with the fixing film 213 at the fixing nip portion N.

  In the fixing nip portion N, the recording material P / toner image t is heated by the heater 211 via the fixing film 213, and the toner image t on the recording material P is heated and fixed. The recording material portion that has passed through the fixing nip N is peeled off from the surface of the fixing film 213 and conveyed.

A ceramic heater is generally used as the heater 211 as a heating member. This is because the energization heating resistor layer 2112 is formed on the surface of the ceramic substrate 2111 (the surface facing the fixing film 213) along the longitudinal direction of the substrate by screen printing or the like. The protective layer 2113 is covered. Here, the longitudinal direction of the substrate is the axial direction of the pressure roller 220 and is perpendicular to the drawing (cross section) of FIG. The ceramic substrate 2111 is a substrate of electrical insulation, good thermal conductivity, and low heat capacity such as alumina. The energization heating resistance layer 2112 is made of silver palladium (Ag / Pb) .Ta ₂ N or the like.

  In the heater 211, when the energization heat generating resistance layer 2112 is energized, the energization heat generation resistance layer 2112 generates heat, and the entire heater rapidly rises in temperature. The temperature rise of the heater 211 is detected by the temperature detecting means 214 disposed on the back surface of the heater, and fed back to an energization control unit (not shown). The energization control unit controls energization to the energization heating resistor layer 2112 so that the heater temperature detected by the temperature detection unit 214 is maintained at a predetermined substantially constant temperature (fixing temperature). That is, the heater 211 is heated and adjusted to a predetermined fixing temperature.

  The fixing film 213 has a thickness as thin as 20 to 70 μm in order to efficiently apply the heat of the heater 211 to the recording material P as the material to be heated in the fixing nip portion N. The fixing film 213 has a three-layer structure of a film base layer, a primer layer, and a releasable layer. The film base layer side is a heater side, and the releasable layer side is a pressure roller side. The film base layer is made of polyimide, polyamideimide, PEEK, or the like, which has higher insulation than the glass protective layer 2113 of the heater 211, and has heat resistance and high elasticity. Further, the film base layer maintains the mechanical strength such as the tear strength of the entire fixing film 213. The primer layer is formed as a thin layer having a thickness of about 2 to 6 μm. The releasable layer is a toner offset prevention layer for the fixing film 213, and is formed by coating a fluororesin such as PFA, PTFE, FEP or the like having good releasability to a thickness of about 10 μm.

  The pressure roller 220 foams heat-resistant rubber or heat-resistant rubber on the cored bar 221 to form an elastic layer 222, and is coated or coated with a fluororesin having a good releasability on the adhesive layer 223. It is formed and configured as a coated release layer 224. Here, the cored bar 221 is made of Al, Fe, or the like. The heat-resistant rubber that forms the elastic layer 222 is made of insulating silicone rubber, fluorine rubber, or the like. The fluororesin that forms the release layer 224 is made of PFA, PTFE, FEP, or the like.

  The stay holder 212 is formed of a heat-resistant plastic member, for example, and holds the heater 211 and also serves as a conveyance guide for the fixing film 213.

  In the film heating type heating apparatus using such a thin fixing film 213, the pressure roller 220 having the elastic layer 222 is in pressure contact with the heater 211, so that the heater 211 has high rigidity. It becomes flat according to the flat lower surface of 211. As a result, a fixing nip portion N having a predetermined width is formed. With this configuration, heat fixing that can be quick started by heating only the fixing nip portion N is realized.

In the heat fixing apparatus as described above, when the unfixed toner image t on the recording material P is heat-fixed, a part of the toner is not fixed but adheres to the fixing film 213 side, and the next rotation of the fixing film 213 is performed. It is known that an offset phenomenon sometimes occurs to the recording material P side.

  There are various factors that cause the offset phenomenon, and one of the factors is excessive charging of the surfaces of the fixing film 213 and the pressure roller 220, that is, so-called charge-up.

  For example, when the dried recording material P is peeled from the fixing nip portion and conveyed, the rear surface of the recording material P is discharged from the nip portion, and the surface of the fixing film 213 corresponds to the rear end of the recording material. The part to do is charged up linearly. When the toner image t of the succeeding recording material P is fixed while this potential is maintained, an offset that peels off the image of the succeeding recording material P corresponding to the charged-up position may occur.

  Further, when the recording material P is passed through the heat fixing device 206, the fluororesin on the surface of the pressure roller 220 is gradually charged negatively due to the friction between the recording material P and the fixing film 213. As a result, the negatively charged toner on the recording material P receives a force in a direction away from the recording material P from the pressure roller 220, and an offset is generated.

In order to prevent such an offset caused by the charging of the surfaces of the fixing film 213 and the pressure roller 220, the following method has been proposed. This is because the elastic layer 222 and the release layer 224 of the pressure roller 220 are made conductive and the cored bar 221 is grounded (Patent Document 3), or the release layer 224 on the surface of the pressure roller 220 is made conductive and the roller surface is made conductive. This is a method in which a conductive brush or the like is brought into contact and grounded (Patent Document 4).
JP-A-63-313182 JP-A-4-44075 JP-A-9-114293 Japanese Patent Laid-Open No. 9-134085

  However, the offset prevention method shown in the above conventional example has been concerned about the following.

  First, in the method disclosed in Patent Document 3, in order to make the elastic layer 222 of the pressure roller 220 conductive, a conductive agent such as carbon is dispersed. The That is, if a conductive agent such as carbon is dispersed in the silicone rubber or the like constituting the elastic layer 222, the rubber strength is reduced. Therefore, when a large amount of the recording material P is passed through the image forming apparatus, the hardness of the pressure roller 220 may be greatly reduced, or the elastic layer 222 may be defective. This tendency becomes more prominent when rubber having low hardness is used. Accordingly, when the pressure roller 220 having a small outer diameter is used to reduce the size of the apparatus and the pressure roller 220 having a low hardness is used to obtain a desired fixing nip N, a more serious problem occurs. There is concern.

  Also, if a conductive agent such as carbon is dispersed in silicone rubber or the like that constitutes the elastic layer 222 of the pressure roller 220, the rubber hardness increases, so it is difficult to reduce the hardness of the roller, and the desired roller hardness can be obtained. There are concerns about problems such as disappearance. Furthermore, there is a concern that problems in the production of the pressure roller, such as the roller molding itself becoming difficult, may occur.

  Further, as disclosed in Patent Document 4, there is a concern about the following in the method of making the surface layer conductive while the pressure roller elastic layer 222 remains insulated.

An electrical contact such as a conductive brush for grounding the surface of the pressure roller 220 is provided in a non-sheet passing portion at the end in the longitudinal direction of the pressure roller 220 in order to prevent contact failure due to contamination with paper powder or toner. There is a need. Therefore, the resistance value of the surface layer of the pressure roller 220 needs to be a somewhat low resistance value (10 ⁵ Ω / □ or less) in order to perform static elimination uniformly in the vicinity of the electrical contact such as a conductive brush and in the distance.

On the other hand, if the resistance of the pressure roller 220 surface layer is low, the transfer charge leaks, so the toner holding force of the recording material P becomes weak, and another offset is likely to occur. In order to prevent the transfer charge from leaking and to prevent the surface of the pressure roller 220 from being charged up, the surface resistance of the pressure roller 220 is preferably about 10 ⁶ to 10 ⁹ Ω. As described above, there is a problem that it is impossible to achieve both maintenance of the transfer charge of the recording material P and prevention of charge-up in the entire longitudinal direction of the pressure roller 220.

  The present invention has been made in view of the above circumstances, and has an object of obtaining excellent images with excellent durability, preventing offset caused by charge-up over the entire longitudinal direction of the pressure roller.

In order to achieve the above object, the present invention provides:
A pressure roller provided so as to be in pressure contact with the heating means and sandwiching and conveying the recording material on which the developer image is formed at a nip portion formed between the heating means;
A first conductive layer provided in the outermost layer;
A second conductive layer provided below the first conductive layer;
An insulating elastic layer provided under the second conductive layer;
With
The resistance value of the first conductive layer is 10 ⁶ to 10 ⁹ Ω / □, and the resistance value of the second conductive layer is 10 ⁵ Ω / □ or less.

  According to the present invention, it is excellent in durability, and it is possible to prevent an offset due to charge-up over the entire longitudinal direction of the pressure roller and obtain a good image.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

(1) Image Forming Apparatus FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier, and a photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel.

The photosensitive drum 1 is rotationally driven in the direction of arrow R shown in FIG. 1, and first, the surface thereof is uniformly charged by a charging roller 2 as a charging device. Next, scanning exposure is performed with a laser beam E that is ON / OFF controlled according to image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a developing method, a jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal development are often used in combination.

  The visualized toner image (developer image) is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. At this time, the recording material P is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure. The recording material P onto which the toner image has been transferred is conveyed to a heat fixing device 6 as an image heating device and fixed as a permanent image. On the other hand, the residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

  By repeating the above operation, image formation can be performed one after another. The image forming apparatus according to the present exemplary embodiment can perform printing at a printing speed of 600 dpi, 22 sheets / minute (LTR vertical feed: process speed of about 150 mm / sec).

(2) Heat Fixing Device FIG. 2 is a diagram showing a schematic configuration of the heat fixing device 6 of the present embodiment, where (a) is a sectional view and (b) is a front view. FIG. 3 is a schematic view showing the main part of the heat fixing device 6 of this embodiment, (a) is a cross-sectional view showing the layer structure of the fixing film 13, and (b) is a method for grounding the fixing film 13. FIG.

  As shown in FIG. 2, the heat fixing device 6 includes a fixing member 10 as a heating unit and a pressure roller (a pressure rotating body, a pressure member) 20. The fixing member 10 includes a fixing film 13 as a flexible sleeve, a heat insulating stay holder 12, and a heater 11 as a heater (heating body, heating element).

  The fixing film 13 is a film having a small heat capacity. As shown in FIG. 3A, a release layer 133 such as PFA, PTFE, FEP or the like is provided directly on the surface of a thin metal tube 131 such as SUS or via a primer layer. A composite or film coated composite layer film. Here, the metal element tube 131 constitutes a third conductive layer provided in the lower layer of the release layer 133 having an exposed portion that is partially exposed on the surface of the fixing film 13. Further, the release layer 133 constitutes a fluororesin layer provided on the outermost layer that contacts the pressure roller 20. SUS is stainless steel, PFA is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, PTFE is polytetrafluoroethylene, and FEP is a tetrafluoroethylene hexafluoropropylene copolymer.

  When the release layer 133 is directly formed on the surface of the metal element tube 131, the surface may be subjected to a surface treatment such as a blast treatment. The fixing film 13 preferably has a thickness of 100 μm or less in order to enable a quick start, and has a sufficient strength to constitute a long-life heat fixing device 6 and has a durability of 20 μm or more. Is required.

  Therefore, the thickness of the fixing film 13 is optimally 20 μm or more and 100 μm or less. In this embodiment, a fixing film 13 is used in which a SUS blank having an outer diameter of 18 mm and a thickness of 27 μm is coated with a 15 μm thick PFA tube by heat welding. The fixing film 13 is provided so as to be slidable against the heater 11.

The fixing film 13 is grounded via a diode 101 as a rectifying element (self-bias element) in order to prevent image defects such as offset. In this embodiment, the following method is applied as the grounding method. As shown in FIGS. 2B and 3B, a metal rubber tube 131 is exposed on the surface of the end portion of the fixing film 13, and a conductive rubber ring provided on the end portion of the pressure roller 20 or the like. It is made to contact with the conduction means 31. The conduction means 31 is grounded via the diode 101 and the safety resistor 102. Here, the fixing film 13 may be grounded without passing through the diode 101.

  4 is a schematic view showing another form of the structure shown in FIG. 3, (a) is a sectional view showing the layer structure of the fixing film 13, and (b) is a fixing film 13 and a pressure roller. It is a figure which shows 20 grounding methods.

  The configuration of the fixing film 13 is not limited to the above configuration, and may be a configuration as shown in FIG. In FIG. 4A, a release layer 133 is formed on a heat-resistant resin film layer 131a having a low heat capacity such as polyimide, polyamideimide, PEEK, PES, PPS, PFA, PTFE, and FEP with a conductive primer layer 132 interposed therebetween. Shown in the formed configuration. In this case, since the fixing film 13 is grounded, the conductive primer layer 132 is partially exposed on the surface of the fixing film 13 as shown in FIG. Here, the heat resistant resin film layer 131a constitutes a third conductive layer. PEEK is polyetheretherketone, PES is polyethersulfone, and PPS is polyphenylene sulfide.

The heater 11 is a heater provided inside the fixing film 13, and an energization heating resistance layer 112 made of silver palladium or the like is formed on an Al ₂ O ₃ or AlN substrate 111 having high thermal conductivity, and further from above. The thin glass protective layer 113 is covered. The surface or back surface of the heater 11 on which the energization heating resistor layer 112 is formed is brought into contact with the fixing film 13 to heat the nip portion where the toner image on the recording material P is melted and fixed.

  The heat insulating stay holder 12 is a holder for holding the heater 11 and preventing heat radiation in the direction opposite to the nip portion, and is formed of liquid crystal polymer, phenol resin, PPS, PEEK, or the like. A fixing film 13 is loosely fitted on the heat insulating stay holder 12 with a margin, and the fixing film 13 is rotatably arranged in the direction of the arrow shown in FIG.

  Further, since the fixing film 13 rotates while rubbing against the internal heater 11 and the heat insulating stay holder 12, the frictional resistance between the heater 11 and the heat insulating stay holder 12 and the fixing film 13 needs to be kept small. . For this reason, a small amount of lubricant such as heat resistant grease is interposed on the surfaces of the heater 11 and the heat insulating stay holder 12. Thereby, the fixing film 13 can be smoothly rotated.

(3) Pressure member FIG. 5 is a sectional view showing a schematic configuration of the pressure roller 20 of the present embodiment. In the following description, the longitudinal direction refers to the axial direction of the pressure roller 20.

  The pressure roller 20 foams heat-resistant rubber or heat-resistant rubber on a core metal 21 to form an elastic layer 22, and is coated with RTV silicone rubber that is primed as an adhesive layer 23 and has adhesiveness. Further, a release layer 24 is formed. Here, the core metal 21 is made of Al, Fe, or the like. The heat-resistant rubber that forms the elastic layer 22 is made of insulating silicone rubber, fluorine rubber, or the like. The release layer 24 constitutes the first conductive layer provided as the outermost layer in the pressure roller 20, and is a tube in which a conductive agent such as carbon is dispersed in a fluorine resin such as PFA, PTFE, FEP. Is formed by coating or coating.

The release layer 24 preferably has a resistance value of 10 ⁹ Ω / □ or less in order to prevent charge-up due to rubbing against the fixing film 13 or the recording material P. On the other hand, the release layer 24 preferably has a resistance value of 10 ⁶ Ω / □ or more in order to prevent offset due to a decrease in toner retention of the recording material due to leakage of transfer charge.

The adhesive layer 23 is a layer for adhering the release layer 24 to the elastic layer 22, and constitutes a second conductive layer provided below the release layer 24. The adhesive layer 23 is in contact with the exposed portion of the metal element tube 131 of the fixing film 13 as shown in FIGS. 3B and 4B, and transports the charge of the release layer 24 in the longitudinal direction. It is a charge transfer layer for making the potential of the pressure roller 20 uniform. For this reason, the resistance value of the adhesive layer 23 needs to be low to some extent, and is preferably 10 ⁵ Ω / □ or less. Accordingly, the conductive layer is adjusted to 10 ⁵ Ω / □ or less by dispersing a conductive agent such as carbon in the adhesive layer 23.

  In this way, by grounding the adhesive layer 23 of the pressure roller 20 through the metal tube 131, the pressure roller 20 can be brought into contact with the surface layer of the pressure roller 20 without contacting an electric contact member such as a conductive brush. Since the surface layer can be grounded, offset can be prevented at low cost.

  In this embodiment, the cost can be reduced by providing the adhesive layer 23 for adhering the release layer 24 to the elastic layer 22 as the second conductive layer. Further, the adhesive layer 23 includes silicone rubber, fluororubber, silicone rubber foam, or fluororubber foam so that the pressure roller 20, the heat fixing device 6, and the image forming apparatus have a long service life. Can be realized.

  In this embodiment, the release layer 24 is made of a conductive fluororesin to form a conductive PFA tube having a thickness of 30 μm, and the adhesive layer 23 has a thickness of 10 μm. Further, a pressure roller having a roller outer diameter of 18 mm and a roller hardness of 40 ° (Asker-C 600 g load) is used. By using the conductive fluororesin as the release layer 24, it is possible to extend the life of the pressure roller 20, the heat fixing device 6, and the image forming apparatus.

  The pressure roller 20 is sufficiently pressed (pressed) in the direction of the fixing member 10 by pressure means (not shown) so as to form nip portions necessary for heat fixing from both ends in the longitudinal direction. Then, the pressure roller 20 is rotationally driven in the direction of the arrow shown in FIG. 2A by rotational driving (not shown) from the end in the longitudinal direction through the cored bar 21. Thereby, the fixing film 13 is driven to rotate in the direction of the arrow shown in FIG. Note that a driving roller (not shown) may be provided inside the fixing film 13 and the driving roller may be rotationally driven to rotate the fixing film 13 and the pressure roller 20 to be driven.

  In this way, the recording material P on which the toner image is formed (carryed) is heated by being nipped and conveyed by the nip portion formed between the fixing member 10 (fixing film 13) and the pressure roller 20. The As a result, the toner image on the recording material P is fixed to the recording material P as a permanent image.

  Next, a specific experimental example will be described.

  Table 1 shows the configuration of the pressure roller for which a comparative experiment was performed.

  Here, in Comparative Example 1, the elastic layer 22, the adhesive layer 23, and the release layer 24 are all insulated, and in Comparative Examples 2 to 4, only the release layer 24 is electrically conductive. In Comparative Example 5, all of the elastic layer 22, the adhesive layer 23, and the release layer 24 are conductive.

  Table 2 shows the results of comparative experiments on offset and durability for Comparative Examples 1 to 5 and this example.

  The offset level was confirmed as follows. That is, after passing 100 sheets of paper (Xx (made by Xerox Co., Ltd.) 4200) having high resistance in a low temperature and low humidity environment where the surfaces of the fixing film 13 and the pressure roller 20 are likely to be charged, 600 dpi is likely to occur. This was done by passing a halftone image consisting of one isolated dot. In addition, the evaluation of the durability of the pressure roller confirmed whether there were any problems with the pressure roller after the endurance of 75,000 sheets, 1.5 times the life of the main body of the device (50,000 sheets). I went there.

From Table 2, it can be seen that in Comparative Example 1, the pressure roller 20 is insulated, and the fixing film 13 and the pressure roller 20 are charged up, so the offset level is poor. Further, in Comparative Example 2, it was found that the offset due to the transfer charge leakage occurred because the resistance of the release layer 24 was as low as 10 ⁵ Ω / □. Further, in Comparative Example 4, since the resistance of the release layer 24 is as high as 10 ¹⁰ Ω / □ or more, the charge-up of the fixing film 13 and the pressure roller 20 cannot be sufficiently suppressed, and an offset occurs. all right.

On the other hand, in Comparative Example 3 where the resistance of the pressure roller 20 is 10 ⁶ to 10 ⁹ Ω / □, the following was found. That is, the offset due to the charge-up of the fixing film 13 and the pressure roller 20 is improved in the vicinity where the release layer 24 is in contact with the base layer of the fixing film 13, but the charge-up is performed in the vicinity of the center portion away from the contact portion. An offset occurs.

  Furthermore, in Comparative Example 5 in which the release layer 24 and the elastic layer 22 are made conductive, although there is no problem with electrostatic offset, a problem has occurred in the pressure roller by passing 50,000 sheets.

  In contrast to these comparative examples, in the configuration of this example, since the charge-up of the fixing film 13 and the pressure roller 20 is suppressed over the entire longitudinal direction, no offset occurred. In addition, since a conductive agent such as carbon was not dispersed in the elastic layer 22, problems such as a failure of the pressure roller 20 did not occur even when 75,000 sheets were passed.

  In this example, PFA tubes are used for the release layers of Comparative Examples 1 to 5, but it has been confirmed that similar results can be obtained even when a fluororesin is coated.

  FIG. 6 is a diagram showing another form of the grounding method of the fixing film 13.

  In the present embodiment, the example in which the conductive adhesive layer 23 is directly brought into contact with the exposed portion of the metal base tube 131 has been described. However, the present invention is not limited to this. That is, as shown in FIG. 6, the release layer 24 may be interposed between the adhesive layer 23 and the exposed portion of the metal element tube 131. In this case, it was found that although the effect of preventing the charge-up of the fixing film 13 and the pressure roller 20 is slightly reduced, a sufficient offset prevention effect can be obtained at the process speed of this embodiment.

As described above, in this embodiment, the elastic layer 22 of the pressure roller 20 is insulated, the resistance of the release layer 24 is 10 ⁶ to 10 ⁹ Ω / □, and the elastic layer 22 and the release layer 24 are bonded. The adhesive layer 23 is set to 10 ⁵ Ω / □ or less. Accordingly, it is possible to prevent the occurrence of offset due to the charge-up of the surface of the fixing film 13 and the pressure roller 20 over the entire longitudinal direction without causing deterioration of the durability of the pressure roller 20, and a good image can be obtained. Can be obtained. That is, in the heat fixing device 6 and the image forming apparatus of the present embodiment, the offset can be prevented with a simple and low-cost configuration without deteriorating the durability of the pressure roller 20, and a good image can be obtained. Can be obtained.

  FIG. 7 is a cross-sectional view illustrating a schematic configuration of the pressure roller according to the second embodiment of the present invention.

In this example, instead of the conductive adhesive layer 23 of Example 1 described above, a conductive agent such as carbon is dispersed in a heat-resistant rubber such as silicone rubber as shown in FIG. The charge transfer layer 23a is formed. The charge transfer layer 23a had a thickness of 1 mm and a resistance value of 10 ⁵ Ω / □. The process speed of the image forming apparatus of this embodiment was 180 mm / s, 30 sheets / minute (LTR longitudinal feed), and the main body life was 150,000 sheets. In the present embodiment, constituent parts different from those in the first embodiment will be described, and description of constituent parts similar to those in the first embodiment will be omitted.

  In the configuration of Example 1, if the life of the image forming apparatus is about 70,000 sheets, a sufficient offset prevention effect can be obtained over the apparatus life. However, if the apparatus life exceeds 100,000 sheets, the adhesive layer 23 is worn, It has been found that the offset prevention effect is reduced. Further, as shown in the first embodiment, when the adhesive layer 23 of the pressure roller 20 is brought into contact with the exposed portion of the metal element tube 131 through the release layer 24, the fixing film 13 and the pressure roller 20 are in contact with each other. It turns out that it is difficult to handle high-speed machines because the effect of preventing charge-up is slightly diminished.

  Therefore, as in this embodiment, a method of ensuring the durability of the contact portion with the exposed portion of the metal element tube 131 by forming the charge transfer layer 23a with a conductive silicone rubber layer is effective.

  In this configuration, a conductive agent such as carbon is dispersed in a heat-resistant rubber such as silicone rubber as the charge transfer layer 23a. However, since the thickness is reduced, a high-hardness rubber that can ensure durability can be used. Does not affect the roller hardness. Therefore, although the manufacturing cost of the pressure roller 20 is slightly increased, it can be said that this is an effective configuration for a high-speed and long-life image forming apparatus.

  Table 3 shows the result of comparing the transition of the offset level due to durability in the configuration of the present embodiment and the configuration of the first embodiment. The offset was confirmed using a low-temperature, low-humidity environment and high-resistance paper (Xx4200 untreated paper) as in Example 1.

  From Table 3, in the configuration of Example 1, no offset image was generated up to 75,000 sheets, but the adhesive layer 23 was worn from the vicinity of 100,000 sheets passed, and the exposed portion of the metal base tube 131 and the adhesive layer It turns out that contact with 23 becomes unstable and offset begins to occur.

  On the other hand, in the configuration of this example, even when 150,000 sheets were passed, the contact between the exposed portion of the metal tube 131 and the charge transfer layer 23a was maintained, and no occurrence of offset was observed.

  In the present embodiment, conductive silicone rubber is used as the charge transfer layer 23a. However, the same applies to the case where the conductive layer is formed by dispersing a conductive agent such as carbon in a heat-resistant rubber such as fluorine rubber or a foam thereof. The effect of was obtained. In addition, if the thickness of the charge transfer layer 23a is in the range of 0.2 to 1.5 mm, it is confirmed that the same effect can be obtained without being affected by an increase in hardness or a decrease in durability of the pressure roller 20. It was done.

As described above, in this embodiment, the elastic layer 22 of the pressure roller 20 is insulated, the resistance of the release layer 24 is set to 10 ⁶ to 10 ⁹ Ω / □, and the charge transfer layer 23a underneath is formed of silicone rubber. , Made of fluororubber or its foam. Accordingly, it is possible to prevent the occurrence of offset due to the charge-up of the surfaces of the fixing film 13 and the pressure roller 20 over the entire longitudinal direction throughout the life of the apparatus without causing a decrease in the durability of the pressure roller 20.

  In Example 3 of the present invention, a configuration in which two types of PFA tubes having different resistance values are coated on the elastic layer 22 of the pressure roller 20 (the first conductive layer and the second conductive layer contain a conductive fluororesin). Composition). As a result, the life of the pressure roller 20, the heat fixing device 6, and the image forming apparatus is extended.

Specifically, a conductive PFA tube having a thickness of 10 μm and a resistance value of 10 ⁵ Ω / □ or less is coated on the elastic layer 22 as a charge transfer layer 23 a, and further a thickness of 30 μm and a resistance value of 10 ⁶ to 10 ^9. A conductive PFA tube of Ω / □ is coated as the release layer 24. The process speed of the image forming apparatus of this embodiment was 200 mm / s, 35 sheets / minute (LTR longitudinal feed), and the main body life was 2 million sheets. In the present embodiment, constituent parts different from those in the first and second embodiments will be described, and the description of the same constituent parts as those in the above embodiment will be omitted.

  By forming the charge transfer layer 23a with a fluororesin such as a PFA tube as in the present embodiment, the surface of the fixing film 13 and the pressure roller 20 is prevented from being charged for a longer period than in the second embodiment, thereby preventing an offset. be able to. This is because the manufacturing process of the pressure roller 20 is complicated and the manufacturing cost is higher than that of the second embodiment. However, paper powder, toner, and the like are difficult to adhere, and electrical contact between the fixing film 13 base layer and the charge transfer layer 23a is difficult. Because it is kept.

  Table 4 shows the transition of the offset level due to durability in the configuration of the present embodiment and the configuration of the second embodiment. The offset was confirmed using a low-temperature, low-humidity environment and high-resistance paper (Xx4200 untreated paper) as in the above-described example.

  From Table 4, when the charge transfer layer 23a is a conductive silicone rubber layer as in Example 2, the following can be seen. The offset image is not generated up to 150,000 sheets, but dirt such as paper dust starts to adhere to the conductive silicone rubber part from the vicinity of 200,000 sheets, and the contact with the exposed part of the metal base tube 131 is unstable. The offset starts to occur.

  On the other hand, in the configuration of the present embodiment, even when 250,000 sheets are passed, no adhesion of dirt such as paper dust is observed, and the contact with the exposed portion of the metal element tube 131 is maintained, and the occurrence of offset is not caused. I couldn't see it. In this embodiment, an example in which conductive PFA tubes having different resistance values are coated has been described. However, similar results can be obtained even when fluororesins having different resistance values are coated.

As described above, in this embodiment, the elastic layer 22 of the pressure roller 20 is insulated, the surface layer of the pressure roller 20 is a conductive fluorine tube of 10 ⁶ to 10 ⁹ Ω / □, and the resistance value is 10 ^{5 in the} lower layer. Conductive fluorine tube of Ω / □ or less is covered. As a result, the durability of the pressure roller 20 is not lowered, and the electrical contact at the end of the pressure roller 20 can be secured for a long period of time, and the surface of the fixing film 13 and the pressure roller 20 is charged up over the entire longitudinal direction. It is possible to prevent the occurrence of an offset due to.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to the present invention. 1 is a diagram illustrating a schematic configuration of a heat fixing apparatus according to a first exemplary embodiment, in which (a) is a cross-sectional view and (b) is a front view. (A) It is a figure which shows the layer structure of the fixing film (metal base tube) of Example 1, (b) is a figure which shows the grounding method of the fixing film of Example 1. FIG. It is the schematic which shows another form with respect to the structure shown in FIG. 3, (a) is a figure which shows the layer structure of a fixing film (heat-resistant resin film), (b) is a figure which shows the grounding method of a fixing film It is. 2 is a cross-sectional view illustrating a schematic configuration of a pressure roller according to Embodiment 1. FIG. It is a figure which shows the other form (when a release layer is passed) about the grounding method of the fixing film of Example 1. FIG. It is sectional drawing which shows schematic structure of the pressure roller of the present Example 2. It is a schematic block diagram of the conventional image forming apparatus. It is a schematic block diagram of the conventional heat fixing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fixing member 11 Heater 13 Fixing film 20 Pressure roller 21 Core metal 22 Elastic layer 23 Adhesive layer 23a Charge transfer layer 24 Release layer

Claims (7)

A pressure roller provided so as to be in pressure contact with the heating means and sandwiching and conveying the recording material on which the developer image is formed at a nip portion formed between the heating means;
A first conductive layer provided in the outermost layer;
A second conductive layer provided below the first conductive layer;
An insulating elastic layer provided under the second conductive layer;
With
The pressure roller, wherein the resistance value of the first conductive layer is 10 ⁶ to 10 ⁹ Ω / □, and the resistance value of the second conductive layer is 10 ⁵ Ω / □ or less.   2. The pressure roller according to claim 1, wherein the second conductive layer is an adhesive layer for bonding the first conductive layer to the elastic layer.   3. The pressure roller according to claim 1, wherein the second conductive layer includes silicone rubber, fluororubber, silicone rubber foam, or fluororubber foam. 4.   The pressure roller according to claim 1 or 2, wherein the first conductive layer and the second conductive layer contain a conductive fluororesin. Heating means;
The pressure roller according to any one of claims 1 to 4, provided so as to be in pressure contact with the heating means;
With
An image heating apparatus that heats the recording material by nipping and conveying the recording material on which a developer image is formed at a nip portion formed between the heating unit and the pressure roller. The heating means includes a flexible sleeve that contacts the pressure roller, and a heater that is pressed by the pressure roller via the flexible sleeve,
The flexible sleeve has a fluororesin layer provided on the outermost layer that contacts the pressure roller, and an exposed portion that is partially exposed on the surface of the flexible sleeve. A third conductive layer provided, provided to be slidable against the heater,
The third conductive layer is grounded, and the pressure roller and the heating means are the first conductive layer or the second conductive layer of the pressure roller, and the third conductive layer. The image heating apparatus according to claim 5, wherein the image heating apparatus is provided so as to be in contact with the exposed portion.   The image heating apparatus according to claim 6, wherein the third conductive layer is grounded through a rectifying element.

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