JP2013186424A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that has excellent heat efficiency, consumes less power, and has excellent fixability to a wide variety of recording paper.SOLUTION: A fixing device fixes an unfixed toner image on paper by passing the paper through a fixing nip part N; the fixing nip part N is formed by laying a fixing belt 15a between a heating member 15c and a fixing member 15b, bringing the fixing member 15b into pressure contact with a pressure member 15d via the fixing belt 15a, and bringing the fixing belt 15a into contact with the pressure member 15d. The fixing belt 15a includes a base layer 15a1, and a belt elastic layer 15a2; and the thickness of the belt elastic layer 15a2 is equal to or more than 250 μm.

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus and an image forming apparatus having the same.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a heat roller fixing type fixing device is frequently used. The fixing device of the heat roller fixing system includes a roller pair (fixing roller and pressure roller) that are in pressure contact with each other, and the roller is heated by a heating unit including a halogen heater or the like disposed in both or one of the roller pairs. After the pair is heated to a predetermined temperature (fixing temperature), the recording paper on which the unfixed toner image is formed is fed to the pressure contact part (fixing nip part) of the roller pair, and the heat and pressure are passed through the pressure contact part. Thus, the toner image is fixed.

  By the way, in a fixing device provided in a color image forming apparatus, it is common to use an elastic roller provided with an elastic layer made of silicone rubber or the like on the surface of the fixing roller. By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed according to the unevenness of the unfixed toner image and comes into contact so as to cover the toner image surface. It is possible to perform heat fixing on an unfixed toner image satisfactorily.

  Further, due to the effect of releasing the distortion of the elastic layer at the fixing nip, it is possible to improve the releasability for color toners that are more likely to be offset than in monochrome. Further, since the nip shape of the fixing nip portion is convex upward (on the fixing roller side) (so-called reverse nip shape), it is possible to improve the paper peeling performance without using a peeling means such as a peeling claw. Paper can be peeled off (self-stripping), and image defects caused by the peeling means can be eliminated.

  By the way, in such a color fixing device, it is necessary to widen the nip width of the fixing nip portion in order to cope with a high speed. There are two methods for increasing the nip width: a method of increasing the elastic layer of the fixing roller and a method of increasing the diameter of the fixing roller.

  However, since the thermal conductivity of the elastic layer is very low, when there is a heating means inside the fixing roller as in the conventional case, the fixing roller temperature follows the fixing roller having a thick elastic layer when the process speed is increased. There is a problem that it will not. On the other hand, when the diameter of the fixing roller is increased, there are problems such as a longer warm-up time and increased power consumption.

  In order to solve such a problem, in recent years, in a color fixing device, a belt as disclosed in Patent Document 1 is used, and a fixing belt is stretched between a fixing roller and a heating roller. A belt fixing system in which a fixing roller and a pressure roller are brought into pressure contact with each other via a belt has been used.

  In this belt fixing device, since the fixing belt having a small heat capacity is heated, the warm-up time is short, and it is not necessary to incorporate a heat source such as a halogen lamp in the fixing roller, so that a low hardness elastic layer made of sponge rubber or the like is thickened. It is possible to provide a wide nip width.

JP 2011-39287 A

However, the conventional fixing device using the metal belt has the following problems.
That is, in the configuration of Patent Document 1, the elastic layer is not necessarily required, and the most preferable range is 50 μm to 100 μm. In this configuration, it is difficult to physically follow a wide variety of recording papers. For example, in the case where the surface unevenness of the paper such as embossed paper is large, it has the same unevenness as the elastic layer. There are some products, and it is very difficult to obtain good fixability to these recording papers.

  Accordingly, an object of the present invention is to provide a fixing device that has excellent thermal efficiency, low power consumption, and good fixability for a wide variety of recording papers.

  In order to solve the above problems, in the fixing device according to the present invention, a fixing belt is stretched between a heating member and a fixing member, and a pressure member is pressed against the fixing member via the fixing belt. A fixing device that fixes a non-fixed toner image on a transfer material by passing the transfer material through a fixing nip formed by contact between the fixing belt and the pressure member, the fixing belt comprising: a base layer; A belt elastic layer, wherein the belt elastic layer has a thickness of 250 μm or more.

  According to the above configuration, by making the belt elastic layer thick, it is possible to obtain good fixability not only on plain paper but also on special paper such as embossed paper as a transfer material. When the belt elastic layer is less than 250 μm, the unevenness of the embossed paper or the like cannot be followed, and the toner existing in the concave portion of the embossed paper may not be sufficiently melted.

  The base layer of the fixing belt is preferably made of a metal material. As a result, it is possible to increase the mechanical strength and at the same time to increase the thermal conductivity and to uniformly heat the fixing belt uniformly, so that it is possible to ensure better fixing properties (for example, the thermal conductivity of polyimide). Rate: 0.37 W / mK, while thermal conductivity of nickel steel: 59-90 W / mK). Further, the heat insulating property of the fixing belt is increased by increasing the thickness of the belt elastic layer. Accordingly, the effect of accumulating heat from the inner surface of the belt in the metal material can be exhibited, and the uniformity of the heat distribution in the fixing belt axial direction can be improved. Note that if the thickness of the belt elastic layer of the fixing belt becomes too thick, the heat transfer property is lowered. Therefore, the thickness of the belt elastic layer of the fixing belt is preferably 300 μm or less.

  The fixing belt has a multi-layer structure in which a surface layer is laminated on the surface of the belt elastic layer, and the surface layer is formed by covering the surface of the belt elastic layer with a fluororesin tube. And releasability can be ensured. As a result, the durability and scratch resistance of the fixing belt are improved, and the life of the fixing device can be extended. The thickness of the fluororesin tube constituting the surface layer is preferably 20 μm to 40 μm. By setting the thickness of the surface layer within this range, the surface layer can follow the unevenness of the embossed paper while exhibiting good fixability while securing the releasability, durability and scratch resistance of the fixing belt.

  The fixing member includes a rigid body and an elastic layer formed on a surface of the rigid body, and the pressure member is pressed against the fixing member when the pressure member is pressed against the fixing member via the fixing belt. It is preferable that the pressing amount is 20% to 30% of the thickness of the elastic layer of the fixing member. Here, the pressing amount of the pressure member to the fixing member means that the pressure member is fixed by urging the pressure member toward the fixing member from the state where the pressure member is in contact with the fixing member via the fixing belt. It means the distance moved by being pushed into the member side. The thickness of the elastic layer of the fixing member is preferably 7.5 mm to 15 mm.

  By setting the pressing amount of the pressure member to be 20% or more of the thickness of the elastic layer of the fixing member, the curvature of the fixing belt on the outlet side of the fixing nip is increased and the sheet peelability can be improved. In addition, the fixable range on the high temperature side is widened, and good fixability can be obtained. On the other hand, when the indentation amount exceeds 30%, an overpressure state occurs and the elastic layer is deteriorated over time, and accordingly, the hardness of the elastic layer is lowered and the durability may be impaired.

  An image forming apparatus equipped with the above fixing device can provide a fixing device and an image forming apparatus with low power consumption by using a fixing belt having a smaller heat capacity than a pair of rollers.

  As described above, according to the present invention, since the fixing belt has a multilayer structure including a base layer and a belt elastic layer, and the thickness of the belt elastic layer is 250 μm or more, it has excellent thermal efficiency, low power consumption, and a wide variety. It is possible to obtain a fixing device that does not cause fixing failure with respect to a recording sheet.

Schematic configuration diagram showing an image forming apparatus of the present invention 1 is a schematic configuration diagram showing a fixing device of the present invention. Schematic diagram showing the condition of the fixing belt and transfer material before fixing Schematic diagram showing the state of the fixing belt (belt elastic layer thickness less than 250 μm) and the transfer material during fixing Schematic diagram showing fixing belt (belt elastic layer thickness 250 μm or more) and transfer material during fixing Partial enlarged view of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an image forming apparatus of the present invention. The image forming apparatus 100 forms a multicolor or single color image on a predetermined sheet (sheet material) in accordance with image data transmitted from the outside. The image forming apparatus 100 includes four image forming units pa, pb, pc, pd, an intermediate transfer belt 11, a transfer roller 14, a fixing device 15, a paper feed tray 16, and a manual paper feed unit 17.

  The image data handled in the image forming apparatus 100 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, in each image forming unit, an image forming process is performed for any one of the color components of black (K), cyan (C), magenta (M), and yellow (Y). In the present embodiment, the photosensitive member 101a of the image forming unit pa is black, the photosensitive member 101b of the image forming unit pb is cyan, the photosensitive member 101c of the image forming unit pc is magenta, and the photosensitive member 101d of the image forming unit pd is yellow. An electrostatic latent image and a developer image relating to the components are formed.

  Of the four image forming units pa, pb, pc, and pd, the image forming unit pa will be described. The image forming unit pa includes a developing device 102a, a photoreceptor 101a, a charger 103a, and a cleaner unit 104a. The photoconductor 101 a is disposed on the upper part of the image forming apparatus 100. The charger 103a is a charging unit for uniformly charging the surface of the photoconductor 101a to a predetermined potential. Here, a roller-type charger 103a is used. However, a brush-type charger or a charger-type charger may be used as the charger 103a.

  The developing device 102a visualizes the electrostatic latent image formed on the photoconductor 101a with black (K) toner. The cleaner unit 104a removes and collects toner remaining on the surface of the photoreceptor 101a after development and image transfer. The other image forming units pb, pc, pd have the same configuration as the image forming unit pa, and the description thereof is omitted here. The developing units 102b, 102c, and 102d of the image forming units pb, pc, and pd contain cyan (C), magenta (M), and yellow (Y) toners, respectively.

  The optical system unit E includes a laser beam source (not shown), a deflector 4 such as a polygon mirror, a folding mirror 8 that guides the deflected beams to four sets of photoconductors 101a, 101b, 101c, and 101d. The deflected beam scans the surfaces of the photoconductors 101a, 101b, 101c, and 101d through the folding mirror 8 and the like. As described above, the optical system unit E has a function of forming an electrostatic latent image corresponding to the image data on the surface thereof by exposing the photosensitive members 101a to 101d charged according to the input image data. Have. Here, a laser scanning unit (LSU) is used as the optical system unit E. However, for example, an EL or LED writing head in which light emitting elements are arranged in an array may be used.

  The intermediate transfer belt 11 disposed above the photosensitive members 101a, 101b, 101c, and 101d is stretched between tension rollers 11a and 11b in a tensioned state. The intermediate transfer rollers 13a, 13b, 13c, and 13d are in pressure contact with the photoreceptors 101a, 101b, 101c, and 101d through the intermediate transfer belt 11, respectively. The transfer roller 14 is pressed against the tension roller 11 a via the intermediate transfer belt 11. The toner remaining on the intermediate transfer belt 11 is collected by a waste toner box 12.

  The intermediate transfer belt 11 is formed in an endless shape using a film having a thickness of about 100 μm to 150 μm, and is provided so as to be in contact with each of the photoreceptors 101 a to 101 d. Further, the toner images of the respective colors formed on the photoconductors 101a to 101d are sequentially transferred to the intermediate transfer belt 11 in a superimposed manner. The intermediate transfer belt 11 has a function of supporting a multicolor toner image on the surface thereof.

  Transfer of the toner image from the photoconductors 101 a to 101 d to the intermediate transfer belt 11 is performed by intermediate transfer rollers 13 a to 13 d that are in contact with the back side of the intermediate transfer belt 11. A high voltage transfer bias is applied to the intermediate transfer rollers 13a to 13d in order to transfer the toner image. In this embodiment, since the charging polarity of the toner is negative, a positive high voltage is used as the transfer bias.

  The intermediate transfer rollers 13a to 13d are rollers whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). This conductive elastic material is used to uniformly apply a high voltage to the intermediate transfer belt 11. In this embodiment, a roller shape is used as the transfer electrode, but a brush or the like may be used instead.

  A transfer roller 14 is disposed so as to contact the tension roller 11a via the intermediate transfer belt 11. The toner images (developer images) formed according to the hues on the photoconductors 101 a to 101 d are stacked on the intermediate transfer belt 11. Subsequently, the stacked toner images are guided to a contact position between the sheet and the intermediate transfer belt 11 by the rotation of the intermediate transfer belt 11 and transferred onto the sheet by a transfer bias applied to the transfer roller 14.

  The intermediate transfer belt 11 and the transfer roller 14 are pressed against each other so that a predetermined amount of nip is formed. In order to obtain the nip constantly, the transfer roller 11 uses either the transfer roller 14 or the intermediate tension roller 11a as a hard material (metal or the like), and the other includes a soft material such as an elastic roller (an elastic rubber roller, Or a foaming resin roller or the like) is used.

  The paper feed tray 16 disposed in the lower part of the image forming apparatus 100 is a tray for storing sheets used for image formation, and is provided below the image forming unit and the optical system unit E of the image forming apparatus 100. On the side. Further, the image forming apparatus 100 is provided with a paper transport path S for sending the paper in the paper feed tray 16 to the paper discharge tray 18 via the transfer roller 14 and the fixing device 15. Further, along this paper transport path S, a pickup roller 16a, a registration roller 19, a transfer roller 14, a fixing device 15, a transport roller r for transporting paper, and the like are disposed.

  The transport rollers r are small rollers for promoting and assisting the transport of paper, and a plurality of transport rollers r are provided along the paper transport path S. The pickup roller 16 a is a pull-in roller that is provided at the end of the paper feed tray 16 and supplies the paper from the paper feed tray 16 to the paper transport path S one by one. Further, the registration roller 19 temporarily holds the sheet being conveyed through the sheet conveyance path S, and transfers the sheet at the timing when the leading edge of the toner image on the photoreceptors 101a to 101d is aligned with the leading edge of the sheet, and the transfer roller 14 and the tension roller 11a. Carry between.

  Next, the paper conveyance path will be described in detail. The image forming apparatus 100 is provided with a paper feed cassette 16 for storing paper in advance, and a manual feed tray 17 used when a user prints a small number of sheets. Pickup rollers 17 a and 16 a are arranged in the vicinity of the paper feed cassette 160 and the manual feed tray 17. The pickup rollers 17a and 16a send out the sheets one by one to the sheet conveyance path S.

  The sheet conveyed from the sheet feeding cassette 10 is conveyed to the registration roller 14 by the conveying roller r in the conveying path. The sheet is conveyed between the transfer roller 14 and the tension roller 11a at the timing when the leading edge of the sheet and the leading edge of the image information on the intermediate transfer belt 11 are aligned, and the toner image carried on the intermediate transfer belt 11 is transferred to the sheet. Is transcribed. Subsequently, the sheet passes through the fixing device 15, whereby unfixed toner on the sheet is melted and fixed by heat. Thereafter, the paper is discharged from the paper discharge roller 18a onto the paper discharge tray 18 via the transport roller r.

  On the other hand, the paper stacked on the manual paper feed tray 17 is fed by the pickup roller 17a, reaches the registration roller 19 through a plurality of transport rollers r, and thereafter the paper fed from the paper feed cassette 16 The paper is discharged to the paper discharge tray 18 through a similar process. At this time, when the print request content is a double-sided print request, the rear end of the paper that has finished single-sided printing and passed through the fixing device 15 as described above is sandwiched by the paper discharge roller 18a, and the paper discharge roller 18a rotates in the reverse direction. Thus, after being guided to the conveyance roller r, the back side printing is performed through the registration roller 19 and then discharged to the discharge tray 18.

  The image forming apparatus 100 includes the fixing device 15 according to the present invention. As shown in FIG. 2, the fixing device 15 includes an endless fixing belt 15a, a fixing member 15b and a heating member 15c for suspending the fixing belt 15a, and pressure applied to the fixing member 15b via the fixing belt 15a. Member 15d.

  As a specific configuration of the fixing device 15 of the present embodiment, a fixing belt 15a having a diameter of 75 mm, a fixing roller having a diameter of 50 mm as the fixing member 15b, and a heating roller having a diameter of 35 mm as the heating member 15c are used as the pressing member 15d. A pressure roller having a diameter of 50 mm is used. The heating member 15c is not limited to the heating roller, and may be formed, for example, in an arc shape in cross section so that the fixing belt 15a can be smoothly slid on the arc surface.

  The fixing roller 15b has a substantially cylindrical shape, and is made of a hollow or solid metal core 15b1 made of SUS or the like as a rigid body, and an elastic made of a foam rubber material formed on the outer periphery of the core 15b1. The layer 15b2 has a two-layer structure. For the elastic layer 15b2, a rubber material having heat resistance such as silicone rubber and fluororubber is suitable. In this embodiment, a 15 mm thick silicone sponge rubber layer is formed as the elastic layer 15b2 on a solid core metal 15b1 having a diameter of 20 mm.

The pressure roller 15d has a substantially cylindrical shape, and includes a hollow metal core 15d1, an elastic layer 15d2 such as silicone rubber, and a release layer (not shown) such as fluororesin in order from the inside. . For the elastic layer 15d2, a rubber material having heat resistance such as silicone rubber and fluorine rubber is suitable. A fluororesin such as PFT (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) is suitable for the release layer. In this embodiment, a silicone rubber layer having a thickness of 1 mm is formed as an elastic layer 15d2 on the surface of a hollow metal core 15d1 having a diameter of 48 mm, and a PFA tube having a thickness of 30 μm is further coated thereon as a release layer. Yes. A heater lamp 21 is disposed inside the pressure roll 15d.

The heating roller 15c includes a substantially cylindrical cored bar made of a metal such as aluminum, an infrared absorption layer (not shown) is formed on the inner peripheral surface, and a release layer (such as PFA) is formed on the outer peripheral surface. (Not shown) is formed. The infrared absorption layer is formed as a black paint layer in which a carbon black-containing paint is applied to the inner surface of the core metal, thereby improving heating efficiency. In this embodiment, a release layer made of PFA is formed on the surface of a hollow metal core having a thickness of 0.7 mm. A heater lamp 21 is disposed inside the heating roll 15c.

  As shown in FIG. 3, the fixing belt 15a is formed on an outer surface of a (flexible) hollow cylindrical base layer 15a1 made of a metal material such as stainless steel or nickel. A belt elastic layer 15a2 made of (silicone rubber) is formed, and a surface layer 15a3 (release layer) made of a fluororesin having excellent heat resistance and releasability is formed on its outer surface. Examples of the fluororesin include PFA and PTFE.

  The surface layer 15a3 of the fixing belt is formed of a tube made of a fluororesin. By covering the surface of the belt elastic layer 15a2 with a fluororesin tube to form a surface layer, stable release properties can be secured, durability and scratch resistance are good, and a long life can be achieved. In this embodiment, a silicone rubber layer having a thickness of 250 μm is formed as a belt elastic layer 15a2 on a cylindrical nickel base material having a thickness of 50 μm as a base layer 15a1, and further coated with a PFA tube having a thickness of 30 μm to form a surface layer 15a3. It was.

  As described above, the present invention is characterized in that the thickness of the belt elastic layer 15a2 of the fixing belt is 250 μm or more, and this makes it possible to obtain good fixability even when embossed paper with unevenness is used as a transfer material. Can be obtained. Specifically, using the schematic diagrams of FIGS. 3 to 5, first, before thermocompression bonding between the fixing belt 15 a and the pressure roller 15 d, as shown in FIG. 3, the transfer material is used. An image of the unfixed toner T1 is formed on the surface of the paper P. FIG. 3 schematically shows a case where an unfixed toner T1 layer is formed on one surface of the paper.

  When the thickness of the belt elastic layer 15a2 of the fixing belt is less than 250 μm, the fixing belt 15 cannot follow the unevenness on the surface of the paper P as shown in FIG. Is melted to become the fixing toner T2, but the unfixed toner T1 adhering to the back of the concave portion on the surface of the paper P is not contacted with the fixing belt 15 and may remain as it is.

  On the other hand, in the present invention, since the thickness of the belt elastic layer 15a2 of the fixing belt is 250 μm or more, the fixing belt 15 can sufficiently follow the unevenness of the surface of the paper P as shown in FIG. All the toner adhering to the surface is melted to become the fixing toner T2. In particular, even when the surface layer 15a3 made of a fluororesin is formed on the surface of the belt elastic layer 15a2, the belt elastic layer 15a2 has a sufficient thickness, so that good fixability can be ensured. It becomes.

  As shown in FIG. 2, the fixing belt 15a is stretched in a state where a predetermined tension is applied between the fixing roller 15b and the heating roller 15c. As described above, the heating roller 15c and the pressure roller 15d each have a heater lamp 21 therein. Based on a signal from a temperature detector (not shown), the fixing belt 15a is controlled by the control unit so that the output to the heater lamp 21 is at a predetermined fixing temperature. The pressure roller 15d is disposed to face the fixing roller 15b with the fixing belt 15a interposed therebetween.

  A portion where the fixing roller 15b and the pressure roller 15d are in contact with each other via the fixing belt 15a between the fixing belt 15a and the pressure roller 15d is a fixing nip portion N. In the fixing nip portion N, the paper enters in the X direction, and the paper is thermocompression-bonded by the fixing roller 15b and the pressure roller 15d, so that the multicolor toner image transferred onto the paper is melted, mixed, and pressed. Heat fixing to paper.

  An elastic layer 15d2 made of silicone rubber having a thickness of 1 mm is formed on the pressure roller 15d, and an elastic layer 15b2 made of silicone rubber sponge rubber having a thickness of 15 mm thicker and softer than the elastic layer 15d2 is formed on the fixing roller 15b. Therefore, as shown in FIGS. 2 and 6, the pressure roller 15d is pushed toward the fixing roller 15b by the force urging toward the fixing roller 15b.

  In the fixing nip portion N, as the force for urging the pressure roller 15d toward the fixing roller 15b is increased, the contact width (nip width W) between the pressure roller 15d and the fixing roller 15b is increased and the fixing property is improved. improves. 2 and 6, the fixing belt 15a is schematically illustrated, but actually, in the vicinity of both ends in the circumferential direction of the fixing nip portion N (portions surrounded by circles in the drawing), the drawing is illustrated. A curved surface is formed that curves downward (curved convex toward the pressure roller).

  This curved surface is formed by pressing the pressure roller 15d toward the fixing roller 15b from the state where the pressure roller 15d is in contact with the fixing roller 15b via the fixing belt 15a, so that the pressure roller 15d moves toward the fixing roller 15b. As the distance moved by pressing, that is, the pressing amount D of the pressure roller 15d with respect to the fixing roller 15b (hereinafter referred to as “fixing roller pressing amount D”) increases, the curvature increases and the sheet peelability improves. On the other hand, if the fixing roller pressing amount D exceeds 30%, the elastic layer 15b2 of the fixing roller may be deteriorated. Therefore, in the present invention, the fixing roller push-in amount D is set to 20% to 30%, so that the durability of the fixing roller 15b is maintained and the sheet peeling property is improved and the good fixing property is obtained. It becomes possible.

  The elastic layer 15b2 of the fixing roller may be a single layer or a multilayer structure in which a plurality of layers are stacked. In the case of a multilayer structure, the pressing amount of the fixing roller may be 20% to 30% with respect to the total thickness of all layers. The sheet on which the multicolor toner image has been fixed is conveyed to the reverse sheet discharge path of the sheet conveyance path S by the conveyance roller r, and is discharged onto the sheet discharge tray 18 in a face-down state.

  Hereinafter, the present invention will be described in more detail with reference to examples. In this example, the fixability when an image was actually formed on plain paper and embossed paper was evaluated using the fixing device and the image forming apparatus described in the above embodiment. Further, the fixing possible temperature range when the fixing roller push-in amount was changed and the temporal change of the fixing roller were also evaluated.

Specifically, in addition to the fixing belt used in the above-described embodiment, two types of belts were prepared in which the thickness of the belt elastic layer of the fixing belt was changed to 200 μm and 300 μm, and each of these three types of fixing belts was used. The image fixability at the time was evaluated. Paper used for image formation, a plain paper having a basis weight of 64 g / m ^2, and the two kinds of embossed paper having a basis weight of 130 g / m ^2. The results are shown in Table 1.

  Regarding the evaluation of the fixing temperature range and the change over time of the fixing roller, a fixing belt having a belt elastic layer thickness of 250 μm is used, and fixing is performed by changing the urging force that urges the pressure roller toward the fixing roller. The roller pressing amount was changed between 18 and 35%. Then, the fixable temperature range at each push-in value was obtained. In order to obtain the fixable temperature range, first, an upper limit value (fixing upper limit temperature) and a lower limit value (fixing lower limit temperature) of the fixing temperature at which no offset or paper wrapping occurs are obtained. The fixable temperature range can be obtained from the temperature difference between these temperatures.

  Regarding the change over time of the fixing roller, the ASKER-C hardness (measured in accordance with SRIS 0101) H1 of the elastic layer 15d2 of the fixing roller before the start of the evaluation test is measured, and the pressing amount of the fixing roller is 18 to 35%. After fixing to a predetermined value, the ASKER-C hardness H2 of the elastic layer 15d2 of the fixing roller is measured again when the number of sheets passing through the image forming apparatus is 300,000. And when the hardness change rate (%) represented by (H1-H2) * 100 / H1 was within 20%, it was set as (circle), and when larger than 20%, it was set as x. Table 2 shows the evaluation results of the fixing temperature range and the change with time of the fixing roller.

  From Table 1, it can be seen that when the thickness of the belt elastic layer of the fixing belt is 250 μm or more, good fixability can be obtained even with paper having unevenness such as embossed paper. Furthermore, according to Table 2, by setting the pressing amount of the fixing roller to 20% to 30%, it is possible to maintain the durability of the fixing roller, improve the paper peelability, and maintain a wide fixing temperature range. It becomes. A wide fixing temperature range makes it difficult for fixing defects to occur even when the paper type, environment, or toner amount changes, that is, good fixing properties can be maintained.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 11 Intermediate transfer belt 14 Transfer roller 15 Fixing device 15a Fixing belt 15b Fixing roller (fixing member)
15c Heating roller (heating member)
15d Pressure roller (Pressure member)

Claims (4)

A fixing belt is stretched between the heating member and the fixing member, a pressure member is pressed against the fixing member via the fixing belt, and the fixing nip is formed by contacting the fixing belt and the pressure member. A fixing device that fixes a non-fixed toner image on the transfer material by passing the transfer material through the portion, wherein the fixing belt includes a base layer and a belt elastic layer, and the thickness of the belt elastic layer is 250 μm or more. There is a fixing device. 2. The fixing belt has a surface layer laminated on a surface of the belt elastic layer, and the surface layer is formed by covering a surface of the belt elastic layer with a fluororesin tube. The fixing device according to 1. The fixing member includes a rigid body and an elastic layer formed on a surface of the rigid body, and the pressure member for the fixing member when the pressure member is pressed against the fixing member via the fixing belt. The fixing device according to claim 1, wherein the pressing amount of the fixing member is 20% to 30% of the thickness of the elastic layer of the fixing member. An image forming apparatus comprising the fixing device according to claim 1.

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