JP2023178219A - Fixing film and method for manufacturing the same, fixing device, and electrophotographic image forming apparatus - Google Patents

Abstract

To provide a fixing film that can prevent, at high level, peeling of a slide layer from a substrate and generation of an abnormal noise during formation of an electrophotographic image.SOLUTION: A fixing film has a cylindrical substrate, a slide layer formed on an inner peripheral surface of the substrate and including polyimide resin, and a release layer formed on an outer peripheral surface of the substrate. The slide layer has a first coating and a second coating laminated in order from a side closer to the substrate. The first coating includes a first constitutional unit represented by a specific formula, or the first constitutional unit and a second constitutional unit represented by a specific formula, and the mass ratio between the content of the first constitutional unit and the content of the second constitutional unit (A):(B) is 100:0 to 60:40. The second coating includes only the second constitutional unit.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fixing film, a method for manufacturing the same, a fixing device, and an electrophotographic image forming apparatus.

An on-demand fixing type fixing device installed in an electrophotographic image forming apparatus includes a fixing film, a ceramic heater fixed inside the fixing film, and a pressure roller. Then, the ceramic heater is pressed toward the pressure roller via the fixing film to form a fixing nip. As the pressure roller is rotated, the fixing film is driven to rotate while its inner peripheral surface slides on the ceramic heater. In the fixing film, the inner peripheral surface of the cylindrical metal base (hereinafter sometimes referred to as "metal base") is coated with a heat-resistant resin such as polyimide to improve sliding properties with the ceramic heater. A sliding layer consisting of may be provided.

The invention disclosed in Patent Document 1 relates to a fixing belt used in an image heating device that heats and fixes an unfixed image. Patent Document 1 discloses a polyimide resin layer having an imidization rate of 70 to 93% and containing a combination of specific structural units, thereby having both excellent flexibility and high abrasion resistance. It is disclosed that it can be made into a resin layer.

Patent No. 4429384

When the present inventor examined the fixing belt according to Patent Document 1, it was found that abnormal noise may occur due to the stick-slip phenomenon in the sliding friction between the ceramic heater and the sliding layer, especially when driving at low speed where the process speed is low. there were. Abnormal noise is likely to occur when the static frictional force between the ceramic heater and the sliding layer is greater than the dynamic frictional force. The reason for this is thought to be that as the process speed becomes lower, the fixation time between the ceramic heater and the inner circumferential surface of the fixing belt becomes longer, and the static frictional force becomes larger.

At least one aspect of the present disclosure is directed to providing a fixing film that can prevent, at a high level, peeling of a sliding layer from a substrate and generation of abnormal noise during formation of an electrophotographic image. Further, at least one aspect of the present disclosure provides a fixing device that contributes to the stable formation of high-quality electrophotographic images over a long period of time, and an electrophotographic image forming system that can stably form high-quality electrophotographic images. It is aimed at providing equipment.

According to at least one aspect of the present disclosure, the fixing film includes a cylindrical base, a sliding layer containing a polyimide resin formed on the inner peripheral surface of the base, and an outer peripheral surface of the base. a release layer formed on the substrate, the sliding layer is formed by laminating a first coating and a second coating in order from the side closer to the base, and the first coating has the following formula (A): A first structural unit represented by the formula (B), or the first structural unit and the second structural unit represented by the following formula (B), and the first structural unit and the second structural unit A fixing film is provided in which the mass ratio (A):(B) of the content of is 100:0 to 60:40, and the second coating contains only the second structural unit:

Further, according to at least one aspect of the present disclosure, the method for manufacturing the fixing film described above includes polyamic acid A having a structural unit A represented by the following formula (a) on the inner circumferential surface of the base; A polyamic acid B having a constituent unit B represented by the following formula (b) is prepared such that the mass ratio of the constituent unit A and the constituent unit B (constituent unit A: constituent unit B) is 100:0 to 60:40. a first step of forming a coating film a of a first polyimide precursor solution mixed as described above; and a second polyimide precursor containing the polyamic acid B as the only polyamic acid on the inner peripheral surface of the coating film a. a second step of forming a coating film b of a solution, imidizing the polyamic acid A in the coating film a, or the polyamic acid A and the polyamic acid B to form the first coating film; A third step of imidizing the polyamic acid B in b to form the second coating is provided.

Further, according to at least one aspect of the present disclosure, a fixing device including the above-described fixing film is provided.

Further, according to at least one aspect of the present disclosure, an electrophotographic image forming apparatus including the above fixing device is provided.

According to at least one aspect of the present disclosure, it is possible to obtain a fixing film that can highly prevent peeling of a sliding layer from a substrate and generation of abnormal noise during formation of an electrophotographic image. Further, according to at least one aspect of the present disclosure, there is provided a fixing device that contributes to the stable formation of high-quality electrophotographic images over a long period of time, and an electrophotography that can stably form high-quality electrophotographic images. An image forming apparatus can be obtained.

1 is a schematic cross-sectional view of a fixing device according to an embodiment of the present disclosure. FIG. 1 is a schematic cross-sectional view of a fixing film according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view of a sliding layer according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram of a coating device used in forming a sliding layer in Examples.

The present inventor has made repeated studies to solve the above problems. As a result, it has been found that a fixing film having the following structure can prevent the sliding layer from peeling off from the substrate and the generation of abnormal noise during the formation of an electrophotographic image at a high level.
<Configuration>
A cylindrical base body, a sliding layer containing a polyimide resin formed on the inner circumferential side of the base body, and a release layer formed on the outer circumferential side of the base body, the sliding layer is formed by laminating a first film and a second film in order from the side closest to the substrate, and the first film is a first structural unit represented by the following formula (A), or a first structural unit. a second structural unit represented by the following formula (B), and the mass ratio (A):(B) of the content of the first structural unit and the second structural unit is 100:0. ~60:40, and the second coating contains only the second structural unit:

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the scope of the present disclosure is not limited to only this embodiment, and various changes can be made without departing from the gist of the present invention.

<Fixing device>
A fixing device according to an embodiment of the present disclosure will be described using FIG. 1.
The fixing device 40 of this embodiment is an on-demand fixing method using a ceramic heater 43 as a planar heating element. The fixing device 40 includes a fixing nip portion 46 between a cylindrical fixing film 41, a ceramic heater 43 that serves as a heating element and a sliding member, a film guide and heater holder 42 that serves as a sliding member, and the fixing film 41. A pressure roller 45 is provided. The fixing film 41 is backed up by a ceramic heater 43 and a film guide/heater holder 42 at a fixing nip portion 46 . That is, the ceramic heater 43 and the film guide/heater holder 42 can also be said to be backup members for the fixing film 41.

The ceramic heater 43 forms a resistance heating element by applying a conductive paste containing a silver-palladium alloy to a film of uniform thickness on an aluminum nitride substrate by screen printing. The ceramic heater 43 is fixedly supported by being fitted into a groove provided along the longitudinal direction of the film guide/heater holder 42 (the width direction perpendicular to the recording material conveyance direction, the front and back directions in FIG. 1). The inner peripheral surface of the fixing film 41 and the back surface of the substrate (the surface opposite to the surface on which the resistance heating element is formed) are configured to be slidable. Further, the ceramic heater 43 is energized by means not shown to generate heat, and is controlled to a predetermined set temperature.

As will be described later, the fixing film 41 has a structure in which a sliding layer made of polyimide resin is formed on the inner peripheral surface of a cylindrical base. The fixing film 41 is an endless film that is rotated in accordance with the rotation of the pressure roller 45 while its inner peripheral surface side is rubbed by the film guide/heater holder 42 and the ceramic heater 43 in use. Both ends of the fixing film 41 in the rotational axis direction are rotatably supported by a fixed portion (not shown) such as a frame of the fixing device 40.
Further, inside the fixing film 41, a film guide/heater holder 42, a ceramic heater 43, and a stay 44 which is a support member are arranged. The stay 44 is arranged in the direction of the rotation axis of the fixing film 41, and both ends thereof are supported by a fixed portion (not shown) such as a frame of the fixing device 40. A film guide/heater holder 42 is supported by the stay 44.

The film guide/heater holder 42 is molded from a heat-resistant and heat-insulating liquid crystal polymer or the like, and is disposed along the stay 44 in the direction of the rotation axis of the fixing film 41 . The fixing film 41 is loosely fitted onto the film guide/heater holder 42. The rotation of the fixing film 41 is regulated and guided while the inner circumferential surface of the fixing film 41 is rubbed against the outer circumferential surface of the film guide/heater holder 42 formed in a partially cylindrical shape.

An unillustrated semi-solid lubricant (grease) containing a solid component (thickener) and a base oil component (oil) is applied to the inner circumferential surface of the fixing film 41 . This ensures slidability between the ceramic heater 43 and the sliding layer of the fixing film 41. Examples of thickeners include solid lubricants such as graphite and molybdenum disulfide, metal oxides such as zinc oxide and silica, polytetrafluoroethylene (PTFE) and tetrafluoroethylene-perfluoroether copolymer (PFA), Examples include fine particles of fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP). These thickeners are added to lubricants in the form of powder with a particle size of about 3 μm. Further, examples of the base oil component include heat-resistant polymer resin oils such as silicone oil, fluorosilicone oil, and perfluoropolyether (PFPE).

The pressure roller 45 is composed of a stainless steel core 45a, a silicone rubber elastic layer 45b, and a surface layer 45c made of a fluororesin (PFA) tube for imparting mold release properties. Both end shaft portions of the core bar 45a are rotatably supported by bearings on a fixed portion (not shown). The pressure roller 45 is connected to a rotation drive device (not shown) such as a motor, and is driven to rotate during use.
Further, both ends of the stay 44 are urged against the pressure roller 45 by a spring pressure mechanism (not shown) with a force of 16 kgf (156.8 N) on one end side and a total pressure of 32 kgf (313.6 N). As a result, the lower surface of the ceramic heater 43 is pressed against the elastic layer of the pressure roller 45 with a predetermined pressing force through the fixing film 41, thereby forming a fixing nip portion 46 of a predetermined width necessary for fixing the toner. Form.
The pressure roller 45 is connected to a rotation drive device (not shown), and as the fixing film 41 rotates following the pressure roller 45, the recording material is nipped and conveyed in the fixing nip portion 46. Further, the surface of the fixing film 41 is heated by the ceramic heater 43 to a predetermined temperature necessary for melting the toner. This predetermined temperature is detected by a thermistor as a temperature detection means (not shown) provided so as to be in contact with the inner circumferential surface of the fixing film 41, and is adjusted by controlling the energization to the ceramic heater 43 by a controller (not shown). be done.
In this manner, while the surface of the fixing film 41 is kept at a predetermined temperature, the recording material P on which an image has been formed using unfixed toner is nipped and conveyed in the fixing nip section 46 . As a result, by heating the recording material P that is in contact with the outer peripheral surface of the fixing film 41, the toner image T on the recording material P is heated and pressurized, melted and mixed, and then cooled and placed on the recording material P. The toner image T is heated and fixed.

<Fixing film>
The fixing film according to this embodiment rotates while sliding on the backup member with the inner circumferential surface in the presence of a lubricant, and is used to heat and fix the toner image on the recording material on the outer circumferential surface. The fixing film 41 of this embodiment will be explained using FIGS. 2 and 3.
As shown in FIG. 2, the fixing film 41 includes at least a cylindrical base 12, a sliding layer 11 formed on the inner peripheral surface of the base 12, and a surface layer formed on the outer peripheral surface of the base 12. It has a mold release layer 15. The fixing film 41 may have an elastic layer 13 between the base 12 and the release layer 15, and the elastic layer 13 may be provided with a primer interposed therebetween. Furthermore, the release layer 15 may be placed between the elastic layer 13 and the adhesive layer 14.
Each configuration will be specifically explained below.

[Base]
In view of the need for heat resistance and bending resistance, metals such as stainless steel (SUS), nickel, and nickel alloys are preferably used as the material for the base body 12. The base body 12 needs to have high mechanical strength while having a low heat capacity. Therefore, the thickness of the base body 12 is preferably 20 μm to 50 μm, more preferably 25 μm to 45 μm.

[Elastic layer]
The elastic layer 13 functions as a layer carried by the fixing member in order to apply uniform pressure to the toner image and the unevenness of the paper during fixing. In order to achieve this function, addition reaction cross-linked liquid silicone is used as the elastic layer 13 because it is easy to process, can be processed with high dimensional accuracy, and does not generate by-products during heat curing. It is preferable to use a cured rubber product. Further, addition reaction crosslinking type liquid silicone rubber is preferable because the degree of crosslinking can be adjusted and the elasticity can be adjusted depending on the type and amount of filler added, which will be described later.
Generally, addition reaction crosslinking type liquid silicone rubber contains an organopolysiloxane having an unsaturated aliphatic group, an organopolysiloxane having active hydrogen bonded to silicon, and a platinum compound as a crosslinking catalyst. Organopolysiloxanes having silicon-bonded active hydrogen react with alkenyl groups in organopolysiloxanes having unsaturated aliphatic groups to form a crosslinked structure under the catalytic action of a platinum compound.

The elastic layer 13 may contain a filler to improve thermal conductivity and reinforcement of the fixing film, and to improve heat resistance. As the filler, from the viewpoint of improving thermal conductivity, highly thermally conductive fillers such as inorganic substances, particularly metals and metal compounds are preferable.
Specific examples of highly thermally conductive fillers include silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), boron nitride (BN), aluminum nitride (AlN), alumina (Al ₂ O ₃ ), and zinc oxide (ZnO). ), magnesium oxide (MgO), silica (SiO ₂ ), copper (Cu), aluminum (Al), silver (Ag), iron (Fe), nickel (Ni), and the like. These can be used alone or in combination of two or more. The average particle diameter of the highly thermally conductive filler is preferably 1 μm or more and 50 μm or less from the viewpoint of ease of handling and dispersibility. Further, the highly thermally conductive filler may have a spherical, pulverized, plate-like, whisker-like, or other shape, but a spherical filler is preferable from the viewpoint of dispersibility.

For example, the elastic layer 13 is formed as follows. First, an addition reaction crosslinking type silicone rubber composition containing an addition reaction crosslinking type liquid silicone rubber and optionally a filler is coated on the outer circumferential surface of the substrate 12 on which the sliding layer 11 is formed by a known method. , forming a coating film of the composition. Thereafter, the elastic layer 13 can be formed by heating the coating film for a certain period of time using a heating means such as an electric furnace to advance a crosslinking reaction.
In terms of contribution to the surface hardness of the fixing film 41 and efficiency of heat conduction to unfixed toner during fixing, the thickness of the elastic layer 13 is preferably 100 μm or more and 500 μm or less, more preferably 200 μm or more and 400 μm or less.

[Adhesive layer]
The adhesive layer 14 is formed from a cured product of an addition-curing silicone rubber adhesive coated on the surface of the elastic layer 13 . Addition-curing silicone rubber adhesives are addition-curing silicone rubbers that are blended with self-adhesive components such as silanes having functional groups such as acryloxy groups, hydrosilyl groups (SiH groups), epoxy groups, and alkoxysilyl groups. include. The thickness of the adhesive layer 14 can be, for example, 1 μm to 10 μm.

[Release layer]
The release layer 15 is made of, for example, a resin such as tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), polytetrafluoroethylene (PTFE), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). A fluororesin tube formed into a tube shape is used. Among these, PFA tubes are preferred from the viewpoint of moldability and toner releasability. Adhesion can be improved by previously subjecting the inner surface of the fluororesin tube to sodium treatment, excimer laser treatment, ammonia treatment, or the like.
The thickness of the release layer 15 is preferably 50 μm or less. If the thickness is 50 μm or less, the elasticity of the lower elastic layer 13 can be maintained when laminated, and the surface hardness of the fixing member can be prevented from becoming excessively high. The thickness of the release layer 15 is preferably 5 μm or more from the viewpoint of suppressing unevenness during coating of the fluororesin tube and from the viewpoint of durability.

The release layer 15 is formed, for example, by covering the outer peripheral surface of the elastic layer 13 coated with an addition-curing silicone rubber adhesive with a PFA tube using a known technique. The method of coating the PFA tube is not particularly limited, but for example, a method of coating the PFA tube by vacuum expanding it from the outside (vacuum expansion coating method) can be used. Between the coated PFA tube and the elastic layer 13, there is excess addition-curing silicone rubber adhesive that does not contribute to adhesion, and air that has been drawn in during tube coating. A method for handling this excess adhesive and air is to move it in the longitudinal direction of the fixing film while jetting air from a ring-shaped nozzle with an inner diameter slightly larger than the outer diameter of the fixing film. can be mentioned. Further, excess adhesive and air can also be removed by using a method such as using an O-ring having an inner diameter smaller than the outer diameter of the fixing film.
Next, the addition-curing silicone rubber adhesive is cured and bonded by heating for a predetermined time using a heating means such as an electric furnace. Then, by cutting both ends to a desired length, a fixing film as a fixing member according to the present embodiment can be manufactured.

[Sliding layer]
As the sliding layer 11, a resin having both high durability and high heat resistance, such as polyimide resin, is suitably used. The sliding layer 11 made of polyimide resin is formed by applying a solution or gel containing a polyimide precursor (polyamic acid) to the inner peripheral surface of the base 12, drying it, and then heating it to dehydrate the precursor. Obtained by ring-closing reaction (imidization reaction). The polyimide precursor is obtained by polymerizing approximately equimolar amounts of an aromatic tetracarboxylic dianhydride or its derivative and an aromatic diamine in an aprotic polar organic solvent.

Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4 '-benzophenonetetracarboxylic dianhydride (BTDA), 2,3,6,7-naphthalenetetracarboxylic dianhydride, and the like. These aromatic tetracarboxylic dianhydrides can be used alone or in combination of two or more.
Examples of aromatic diamines include 4,4'-oxydianiline (4,4'-ODA), p-phenylenediamine (PPDA), m-phenylenediamine (MPDA), and the like. These aromatic diamines can be used alone or in combination of two or more.
Examples of the aprotic polar organic solvent include N,N-dimethylacetamide (DMAC), dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP).

As shown in FIG. 3, the sliding layer 11 according to the present disclosure is formed by laminating a first coating 11-a and a second coating 11-b in order from the side closer to the base 12. The first coating 11-a includes a first structural unit represented by the following formula (A), or the first structural unit and a second structural unit represented by the following formula (B), and The mass ratio (A):(B) of the content of the first structural unit and the second structural unit is 100:0 to 60:40. Further, the second coating 11-b includes only the second structural unit. By forming the sliding layer 11 into a laminated structure consisting of the first coating and the second coating as described above, peeling of the sliding layer 11 from the base and generation of abnormal noise during electrophotographic image formation can be prevented. can be prevented at a high level. That is, the second film 11-b containing the polyimide resin containing only the second structural unit exhibits high Martens hardness. Therefore, even when the process speed is low, stick-slip is less likely to occur, and abnormal noise can be prevented from occurring. On the other hand, since the second coating 11-b has a small coefficient of linear expansion, when it is in direct contact with the metal substrate, it may not be able to sufficiently follow the expansion and contraction of the metal substrate due to temperature changes, and may peel off. Therefore, in the present disclosure, a first coating 11-a having a larger coefficient of linear expansion than the second coating 11-b is interposed between the second coating 11-b and the metal base 12. Since the first film 11-a can follow the expansion and contraction of the metal base 12 well, it can more reliably prevent the sliding layer 11 from peeling off from the metal base.

(First polyimide precursor solution)
The first polyimide precursor solution used to form the first coating 11-a will be explained.
The polyimide resin having the first structural unit contains approximately equimolar amounts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline in an aprotic polar A solution of a polyimide precursor (polyamic acid A) having a structural unit A represented by the following formula (a) obtained by reacting in an organic solvent (hereinafter also referred to as "polyimide precursor solution (a)") It can be obtained by heating to remove the solvent in the solution (the aprotic polar organic solvent) and further imidizing the polyamic acid A.
On the other hand, the polyimide resin having the second structural unit contains approximately equimolar amounts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine in an aprotic polar organic solvent. A solution of a polyimide precursor (polyamic acid B) having a structural unit B represented by the following formula (b) (hereinafter also referred to as "polyimide precursor solution (b)") obtained by reacting in The polyamic acid B can be obtained by removing the solvent (the aprotic polar organic solvent) in the solution and further imidizing the polyamic acid B.
Mix polyimide precursor solutions (a) and (b) so that the mass ratio of the structural unit A and the structural unit B (structural unit A: structural unit B) is 100:0 to 60:40, Obtain a first polyimide precursor solution. Note that when the mass ratio is 100:0, the polyimide precursor solution (a) becomes the first polyimide precursor solution.

(Second polyimide precursor solution)
The second polyimide precursor solution used to form the second coating 11-b will be explained.
The polyimide resin having only the second structural unit is obtained by heating the polyimide precursor solution (b) to remove the solvent (the aprotic polar organic solvent) in the solution, and then adding the polyamic acid B to the polyimide resin. It can be obtained by imidization. Therefore, the polyimide precursor solution (b) becomes a second polyimide precursor solution containing the polyamic acid B as the only polyamic acid.

(Method for forming sliding layer 11)
Next, a method for forming the sliding layer 11 using polyimide resin will be explained using FIG. 4.
Generally, a polyimide resin film can be formed by coating a polyimide precursor solution as described above. In this embodiment as well, the polyimide precursor solution is applied to the inner circumferential surface of the base 12 and then heated and dried to form a polyimide sliding layer through a dehydration ring-closing reaction. As the coating method, known methods such as a dip method, a ring coat method, and a spray method can be applied. Among these, the ring coating method is preferred.

A ring coating method coating apparatus 20 shown in FIG. 4 has pillars 201 and 202 arranged parallel to each other on a substrate 21. A coating head 22a is fixed on the support column 201, and a coating liquid supply device (not shown) is connected thereto. The coating head 22a is formed in a cylindrical shape, has a supply path from the coating liquid supply device arranged in the center, and has a slit (not shown) perpendicular to the support column 201 on the outer peripheral surface. Then, the coating liquid (polyimide precursor solution) supplied from the coating liquid supply device is discharged from the slit so as to cover the outer peripheral surface of the coating head 22a.
A workpiece moving device 26 is supported by the support column 202 so as to be movable along the support column 202 . The workpiece moving device 26 is rotated by a motor 27 provided on the support 202, and moves along the support 202 up and down in the plane of FIG. A work hand 25 that holds the base body 12 is arranged at the tip of the work moving device 26 . Therefore, the base body 12 held by the work hand 25 is moved up and down in the plane of FIG. 4 together with the work hand 25 by the work moving device 26.
When applying the coating liquid to the inner peripheral surface of the substrate 12, the substrate 12 is coated while supplying the polyimide precursor solution, which is the coating liquid, to the outer peripheral surface of the coating head 22a from the coating liquid supply device. It is moved along the outer periphery of the head 22a. Thereby, the coating liquid can be applied almost evenly over the entire inner circumferential surface of the base 12. In the coating device 20, the coating thickness of the coating liquid can be arbitrarily changed by adjusting the supply speed of the coating liquid and the moving speed of the workpiece moving device 26.

The polyimide precursor solution applied to the inner circumferential surface of the base body 12 is fired by a heating means such as an electric furnace, and the polyimide sliding layer 11 is obtained. The applied polyimide precursor solution is preferably heated in multiple stages. That is, first, in the first stage of firing (first stage firing), at least a portion of the solvent contained in the polyimide precursor solution is removed by heating to form a coating film of the polyimide precursor. Then, it is preferable to proceed with the imidization reaction of the polyimide precursor after the second stage of firing (second stage firing). In particular, in the first stage baking, it is preferable to dry the solvent in the coating film of the polyimide precursor solution by heating at a temperature T1 lower than the boiling point of the solvent. Next, a second stage firing is performed in which polyamic acid A and polyamic acid B in the coating film of the polyimide precursor obtained after the first stage firing are imidized at a temperature T2 higher than that of the first stage firing; It is preferable to carry out the firing in multiple stages including a third stage firing at a temperature T3 higher than the temperature T2 in eye firing.

Specifically, first, a first polyimide precursor solution is applied to the inner peripheral surface of the substrate 12 to form a coating film a of the first polyimide precursor solution (first step). At this time, if necessary, the coating film a is heated at a temperature T1-1 lower than the boiling point of the solvent contained in the first polyimide precursor solution to evaporate the solvent in the coating film a. Dry the coating film a (drying step 1, first stage baking of the coating film a).
Next, a second polyimide precursor solution is applied to the inner peripheral surface of the coating film a to form a coating film b of the second polyimide precursor solution (second step). At this time, if necessary, the coating film b is heated at a temperature T1-2 lower than the boiling point of the solvent contained in the second polyimide precursor solution to evaporate the solvent in the coating film b. Dry the coating film b (drying step 2, first stage baking of the coating film b).
Next, in a state in which the coating film a that has undergone the drying step 1 and the coating film b that has undergone the drying step 2 are laminated, the coating film a and the coating film b are heated to a temperature lower than the temperature T1-1 and the temperature T1-2. Heating is performed at a high temperature T2 (second stage firing), and subsequently, heating is performed at a temperature T3 higher than temperature T2 (third stage firing). In this way, polyamic acid A or polyamic acid A and polyamic acid B in coating film a are imidized to form a first coating 11-a, and polyamic acid B in coating film b is imidized to form a second coating. 11-b is formed (third step). As a result, a sliding layer 11 consisting of a laminated film of the first coating 11-a and the second coating 11-b is obtained.

Before the second step of baking (imidization reaction) of coating film a, a second polyimide precursor solution is applied to the inner peripheral surface of coating film a to form coating film b, and then coating film a and coating film By imidizing the polyamic acid in b, the imidization reaction can also proceed at the interface between the first coating and the second coating. Therefore, delamination at the interface between the first coating and the second coating can be prevented. Note that the second stage baking is preferably carried out gradually at a temperature of 260° C. or lower in order to proceed with imidization without blocking the molecular mobility of the polyamic acid. Further, the third stage firing is preferably performed at a high temperature of 350° C. or higher in order to sufficiently advance the imidization reaction for obtaining the properties of polyimide. Similarly to the second stage firing, the third stage firing may be performed by gradually raising the temperature, and in that case, the highest temperature is preferably 350° C. or higher.

As for the thickness of the sliding layer 11, the total thickness of the first coating 11-a and the second coating 11-b is preferably 5 μm to 25 μm. Particularly, when the total thickness is 7 μm to 20 μm, both abrasion resistance at the fixing nip portion and heat conductivity for transmitting heat from the heater to the base 12 are easily achieved.
In order to set the thickness of the sliding layer 11 such that the first coating 11-a and the second coating 11-b each have a thickness of 7 μm, for example, the following method can be used. That is, depending on the polyimide precursor solid content concentration (approximately 18% by mass) of the first polyimide precursor solution and the second polyimide precursor solution, the inner surface of the base 12 is adjusted so that the coating thickness of each precursor solution is 40 μm. The precursor solution may be applied to the peripheral surface by a ring coating method or the like.

(Imidization rate)
In this embodiment, the imidization rate of the second coating 11-b is preferably 75% or more. Here, the imidization rate is the reaction rate in the imidization reaction when polyimide is produced by heating and baking the precursor (polyamic acid) in the polyimide precursor solution to dehydrate and cyclize (imidize). It is about. The imidization rate can be determined by the total reflection measurement (ATR) method using a Fourier transform infrared spectrophotometer (FT-IR). A specific measuring method will be explained in Examples.
If the imidization rate of the second coating is 75% or more, the abrasion resistance will not decrease due to the flexibility of the sliding layer itself, and the abrasion powder at the fixing nip area will be suppressed from causing an increase in torque. can. Note that the imidization rate of the second coating is generally 100% or less.

(Martens hardness)
In this embodiment, it is preferable that the Martens hardness of the second coating measured by the nanoindenter method is larger than the Martens hardness of the first coating measured by the nanoindenter method. Specifically, it is preferable that the Martens hardness of the second coating is 350 N/mm ² or more and 450 N/mm ² or less, and the Martens hardness of the first coating is 200 N/mm ² or more and 300 N/mm ² or less. . Since the Martens hardness of the first coating and the second coating are within the above ranges, the stick-slip phenomenon during sliding friction with the ceramic heater is less likely to occur, and the sliding layer has excellent suppressive power against the generation of abnormal noise. Obtainable.
Note that the details of the measurement method will be explained in Examples.

(linear expansion coefficient)
In this embodiment, it is preferable that the linear expansion coefficient of the second coating is smaller than that of the first coating. Specifically, the linear expansion coefficient of the second coating is 1.5×10 ^-6 /℃ or more and 5.0×10 ^-6 /℃ or less, and the linear expansion coefficient of the first coating is 2.0×10 It is preferably ^-5 /°C or more and 5.0×10 ^-5 /°C or less. By setting the linear expansion coefficients of the first coating and the second coating within the above ranges, it is possible to prevent the sliding layer from peeling off from the metal substrate and to prevent the generation of abnormal noise during electrophotographic image formation. achievable at an even higher level. Note that the details of the measurement method will be explained in Examples.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples.
First, the physical property evaluation method will be explained.

[Martens hardness]
The Martens hardness in the normal direction (indentation direction) of the sliding layer 11 is measured by the nanoindenter method using a microhardness tester (trade name: Picodenter HM-500, manufactured by Fisher Instruments). went. A diamond Vickers indenter was used as a probe (indenter). The sample was isolated by peeling off the sliding layer 11 from the base layer 12 with a razor or the like, and the back side was attached to a 300 μm thick SUS plate using an adhesive or the like, with the surface to be measured facing the front side. It was measured using The measurement conditions were a temperature of 23° C., a test load of 2 mN, and a load application time of 7 seconds. Martens hardness was calculated from the load displacement curve (graph of load and indentation displacement) obtained by measurement. More specifically, if As(h) is the surface area calculated from the maximum indentation depth h of the indenter when the maximum load F is applied, the Martens hardness (HM) can be obtained from the following equation.
HM [N/mm ² ]=F/As(h)=F/(26.43×h ² )

[Linear expansion coefficient]
The linear expansion coefficient in the circumferential direction of the sliding layer 11 was determined using a thermomechanical analyzer (TMA) in accordance with Japanese Industrial Standards (JIS) K 7197:2012 (Test method for linear expansion coefficient by thermomechanical analysis of plastics). It was calculated from the obtained curve of deformation versus temperature. However, in a state in which the first coating and the second coating are laminated, it is not possible to obtain the linear expansion coefficient of each coating. Therefore, by separately fabricating a sliding layer consisting only of the first coating 11-a and a sliding layer consisting only of the second coating 11-b on the inner peripheral surface of the base layer 12, samples isolated from each The coefficient of linear expansion was measured using The measurement dimensions are circumferential length 10 mm x width 5 mm, the measurement conditions are a load of 0.02 N, a temperature increase rate of 5 ° C / min, and the amount of deformation per 1 ° C is calculated as an average value of 50 to 200 ° C. This was defined as the coefficient of linear expansion [/°C].

[Imidization rate]
The imidization rate of the second coating 11-b was calculated by the total reflection measurement (ATR) method using a Fourier transform infrared spectrophotometer (FT-IR). Using germanium as an ATR prism, an infrared absorption spectrum was obtained from the surface of the second coating 11-b of the sliding layer 11 under conditions of a resolution of 4 cm ⁻¹ and an integration count of 8 times. Among them, the absorbance of the peak near 1712 cm ⁻¹ based on the C=O vibration of the imide ring was defined as α. In addition, when the second coating contains the second structural unit, the absorbance of the peak around 1515 cm ⁻¹ based on the skeletal vibration of the imide ring was defined as β. When the second coating contains the first structural unit, a peak based on the skeletal vibration of the imide ring appears near 1500 cm ⁻¹ , so its absorbance was determined as β. The ratio α/β serves as an indicator of the degree of progress of imide ring formation, that is, imidization. Furthermore, assuming that the second coating 11-b obtained by firing for 4 hours at a final imidization temperature of 450° C. is in the state when the imidization reaction is completely completed (imidization rate 100%), When α/β at that time is expressed as (α/β) ₁₀₀ , the imidization rate is defined by the following formula.
Imidization rate [%] = (α/β)/(α/β) ₁₀₀ ×100

Evaluation of the fixing film 41 formed by a series of steps described below will be described below.

[Durability evaluation]
The durability evaluation of the fixing film 41 was performed using an on-demand type fixing device 40 shown in FIG. 1 which incorporates the fixing film of the example or comparative example. With the pressing force being 156.8 N (16 kgf) on one end and the total pressing force being 313.6 N (32 kgf), the moving speed (peripheral speed) of the surface of the pressing roller 45 was set to 320 mm/sec. It was driven to rotate. 500,000 sheets of paper of the same size (A4 landscape, product name: GF-C081, manufactured by Canon Inc.) were printed at a rate of 70 sheets/min while the surface temperature of the paper passing section of the fixing film 41 was controlled to 170°C. I passed the paper continuously. Note that 0.8 g of grease (trade name: Molycoat HP-300, manufactured by DuPont-Toray Specialty Materials) as a lubricant was applied to the inner peripheral surface of the fixing film 41. The grease contains fine PTFE powder particles (particle size: 3 μm) as a thickener and perfluoropolyether as a base oil component. Then, evaluation was performed based on the following criteria.
Rank AA: 500,000 sheets could be passed while the load torque was 600 mN·m or less.
Rank A: 500,000 sheets could be passed with the load torque exceeding 600 mN·m and below 800 mN·m.
Rank B: The load torque exceeded 800 mN·m when the number of sheets passed reached 300,000.
Rank C: When the number of sheets passed reached 100,000, a part of the sliding layer peeled off and the base was exposed.

[Slidability evaluation]
The sliding properties of the fixing film 41 were evaluated in the initial state and in the state after 500,000 sheets had been passed, and the evaluation was based on the following criteria.
Rank AA: When the process speed of the fixing device is 60 mm/sec, abnormal noise caused by self-excited vibration of the fixing film due to stick-slip occurs in both the initial state and after passing 500,000 sheets. No occurrence was observed. Note that stick-slip is more likely to occur as the process speed is slower. Therefore, for this evaluation, the slower the process speed, the more severe the conditions.
Rank A: When the process speed of the fixing device is 120 mm/sec, abnormal noise is caused by self-excited vibration of the fixing film due to stick-slip in both the initial state and after 500,000 sheets have been passed. No occurrence of this was observed.
Rank B: When the process speed of the fixing device is 120 mm/sec, abnormal noise is caused by self-excited vibration of the fixing film due to stick-slip in either the initial state or after 500,000 sheets have been passed. The occurrence of was observed.
Next, Examples and Comparative Examples will be specifically described.

[Example 1]
Approximately equimolar amounts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline were reacted in N-methyl-2-pyrrolidone (NMP). As a result, a polyimide precursor solution (a) containing polyamic acid A having the structural unit A represented by the formula (a) and having a solid content concentration of 18% by mass and a viscosity of 6 Pa·s was obtained. The polyimide precursor solution (a) was then used as a first polyimide precursor solution. The first polyimide precursor solution was applied to the inner circumferential surface of the substrate 12 by a ring coating method to a coating thickness of 40 μm to form a coating film a of the first polyimide precursor solution. The cylindrical base 12 was made of stainless steel (SUS) with an inner diameter of 24 mm and a thickness of 30 μm. Next, the cylindrical substrate was heated in a heating furnace at a temperature of 150° C. for 5 minutes to evaporate NMP from the coating film a (first stage baking of the coating film a). The cylindrical substrate was taken out of the heating furnace, and then the second polyimide precursor solution was applied onto the inner circumferential surface of coating film a in the following manner.
First, as the second polyimide precursor solution, a solid obtained by reacting approximately equimolar amounts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine in NMP was used. A polyimide precursor solution (b) containing polyamic acid B having a constituent unit B represented by the above formula (b) and having a concentration of 18% by mass and a viscosity of 6 Pa·s was used. This second polyimide precursor solution was applied onto the inner circumferential surface of coating film a by a ring coating method to a coating thickness of 40 μm to form coating film b of the second polyimide precursor solution. Next, the cylindrical substrate was heated again in a heating furnace at a temperature of 150° C. for 5 minutes to evaporate NMP from coating film b (first stage baking of coating film b). Then, the cylindrical substrate having the laminated film of coating film a and coating film b was placed in a heating furnace. Then, coating film a and coating film b were heated stepwise for 1 hour at a temperature of 200°C to 260°C (second stage baking), and then heated stepwise for 1 hour to a temperature of 260°C to 350°C (3 Stage firing). In this way, the polyamic acid A in the coating film a and the polyamic acid B in the coating film b are imidized, and the first coating 11-a and the second coating 11-b are laminated in the sliding layer 11 with a thickness of 7 μm each. I got it.

Subsequently, a hydrosilyl silicone primer (trade name: DY39-051 A/B, manufactured by Dow Toray Industries, Inc.) was coated on the outer peripheral surface of the cylindrical substrate 12 on which the sliding layer 11 was formed, and heated to 200°C. The film was cured by heating for 5 minutes. Then, an addition reaction crosslinking liquid silicone rubber composition containing an addition reaction crosslinking liquid silicone rubber and alumina as a highly thermally conductive filler is coated on the outer peripheral surface to a thickness of 250 μm, and heat cured at 200°C for 30 minutes. In this way, a silicone rubber elastic layer 13 was formed. Note that the thermal conductivity of the elastic layer 13 was 1.0 W/mK. Further, on the outer peripheral surface of the elastic layer 13, a 3 μm thick adhesive layer 14 made of an addition-curing silicone rubber adhesive (trade name: SE1819 CV A/B, manufactured by Dow Toray Industries, Inc.) was formed. Then, a 20 μm thick PFA tube obtained by extrusion molding is coated on the outer peripheral surface of the adhesive layer 14 as a fluororesin release layer 15 by a method of vacuum expanding and covering from the outside (vacuum expansion coating method), It was heated and cured at 200°C for 2 minutes. The PFA tube used had its inner surface treated with ammonia in advance.
The fixing film 41 produced as described above was incorporated into the fixing device, and the durability and sliding properties of the sliding layer 11 were evaluated under the above conditions. The results are shown in Table 1.

[Example 2]
A solution obtained by mixing the polyimide precursor solution (a) and the polyimide precursor solution (b) prepared in Example 1 so that the mass ratio (constituent unit A:constituent unit B) was 80:20 was added to the first polyimide. It was used as a precursor solution. Other than that, the same procedure as in Example 1 was followed to obtain a fixing film having a sliding layer 11 in which a first coating and a second coating were laminated to a thickness of 7 μm.

[Example 3]
A solution obtained by mixing the polyimide precursor solution (a) and the polyimide precursor solution (b) prepared in Example 1 at a mass ratio (constituent unit A:constituent unit B) of 60:40 was added to the first polyimide. It was used as a precursor solution. Other than that, the same procedure as in Example 1 was followed to obtain a fixing film having a sliding layer 11 in which a first coating and a second coating were laminated to a thickness of 7 μm.

[Example 4]
Regarding the first polyimide precursor solution and the second polyimide precursor solution, the same ones as in Example 1 were used. In the film forming process of the first coating 11-a and the second coating 11-b, the same procedure as in Example 1 was performed up to the second stage baking. Then, in the third firing step, each film was laminated to a thickness of 7 μm using the same procedure as in Example 1, except that it was heated stepwise from 260°C to 300°C for 1 hour to advance imidization. A fixing film having a sliding layer 11 was obtained.

[Example 5]
Regarding the first polyimide precursor solution and the second polyimide precursor solution, the same ones as in Example 1 were used. In the film forming process of the first coating 11-a and the second coating 11-b, the same procedure as in Example 1 was performed up to the second stage baking. Then, in the third stage firing, each film was laminated to a thickness of 7 μm using the same procedure as in Example 1, except that it was heated stepwise from 260°C to 400°C for 1 hour to advance imidization. A fixing film having a sliding layer 11 was obtained.

[Example 6]
Regarding the first polyimide precursor solution and the second polyimide precursor solution, the same ones as in Example 2 were used. The process of forming the first coating 11-a and the second coating 11-b and subsequent steps were performed in the same manner as in Example 5, and a fixing film having a sliding layer 11 in which each coating was laminated with a thickness of 7 μm was prepared. Obtained.

[Example 7]
Regarding the first polyimide precursor solution and the second polyimide precursor solution, the same ones as in Example 3 were used. The process of forming the first coating 11-a and the second coating 11-b and subsequent steps were performed in the same manner as in Example 5, and a fixing film having a sliding layer 11 in which each coating was laminated with a thickness of 7 μm was prepared. Obtained.

[Comparative example 1]
The polyimide precursor solution (a) prepared in Example 1 was used as the first polyimide precursor solution and the second polyimide precursor solution. This polyimide precursor solution (a) was coated on the inner peripheral surface of the substrate 12 by a ring coating method so that the coating thickness was 80 μm. This was heated for 5 minutes inside a heating furnace at 150°C to evaporate the NMP solvent and solidify the coating film, and then heated stepwise at 200°C to 260°C for 1 hour. The mixture was further heated stepwise from 260°C to 350°C for 1 hour. Through these steps, a fixing film having a sliding layer 11 having a thickness of 14 μm and having the same composition and no distinction between the first coating and the second coating was obtained.

[Comparative example 2]
The polyimide precursor solution (b) prepared in Example 1 was used as the first polyimide precursor solution and the second polyimide precursor solution. Other than that, the same procedure as in Example 5 was followed to obtain a fixing film having a sliding layer 11 with a thickness of 14 μm and having the same composition and no distinction between the first coating and the second coating.

[Comparative example 3]
The polyimide precursor solution (b) prepared in Example 1 was used as the first polyimide precursor solution. On the other hand, the polyimide precursor solution (a) prepared in Example 1 was used as the second polyimide precursor solution. Other than that, the same procedure as in Example 4 was followed to obtain a fixing film having a sliding layer 11 in which each film was laminated to a thickness of 7 μm.

[Comparative example 4]
Similarly to Comparative Example 1, the polyimide precursor solution (a) prepared in Example 1 was used as the first polyimide precursor solution and the second polyimide precursor solution. Other than that, the same procedure as in Example 5 was followed to obtain a fixing film having a sliding layer 11 with a thickness of 14 μm and having the same composition and no distinction between the first coating and the second coating.

The fixing films 41 according to Examples 2 to 7 and Comparative Examples 1 to 4 produced as described above were incorporated into the fixing device 40, and the durability and sliding properties of the sliding layer 11 were confirmed as in Example 1. was evaluated. The results are shown in Table 1.

From the results of Examples 1 to 7, it was found that as the sliding layer 11, on the base 12 side, a first layer made of a polyimide resin containing 60% by mass or more of the highly flexible first structural unit represented by formula (A) was used. A coating 11-a is provided, and on the other hand, a second coating 11-b made of a polyimide resin having a hard and rigid second structural unit represented by formula (B) is provided on the sliding surface side with the ceramic heater. It has been found that by doing so, a sliding layer can be obtained that has good adhesion to the base 12 and has a high ability to suppress noise generation and wear.
In Comparative Examples 1 and 4, the substrate was not exposed, and there was no problem in the adhesion between the sliding layer and the substrate. However, since the second coating was formed of a polyimide resin having the first structural unit, abnormal noise was generated from the beginning of the durability, and as wear progressed due to the durability, an increase in torque was observed. On the other hand, in Comparative Examples 2 and 3, the adhesion between the sliding layer and the base was insufficient, and the base was exposed during durability, resulting in an increase in torque.

The present disclosure includes the following configurations.

[Configuration 1]
A fixing film,
a cylindrical base;
a sliding layer containing polyimide resin formed on the inner peripheral surface side of the base;
a release layer formed on the outer peripheral surface side of the base;
has
The sliding layer is formed by laminating a first coating and a second coating in order from the side closer to the base,
The first coating includes a first structural unit represented by the following formula (A), or the first structural unit and a second structural unit represented by the following formula (B), and The mass ratio (A):(B) of the content of the first structural unit and the second structural unit is 100:0 to 60:40,
The second coating is a fixing film containing only the second structural unit:

[Configuration 2]
The fixing film according to configuration 1, wherein the second coating has an imidization rate of 75% or more.
[Configuration 3]
The Martens hardness of the second coating measured by the nanoindenter method is larger than the Martens hardness of the first coating measured by the nanoindenter method, and the linear expansion coefficient of the second coating is greater than the Martens hardness measured by the nanoindenter method of the second coating. The fixing film according to configuration 1 or 2, which has a coefficient of linear expansion smaller than that of the coating.
[Configuration 4]
Structures 1 to 3, wherein the Martens hardness of the second coating is 350 N/mm ² or more and 450 N/mm ² or less, and the Martens hardness of the first coating is 200 N/mm ² or more and 300 N/mm ² or less. The fixing film according to any one of the above.
[Configuration 5]
The linear expansion coefficient of the second coating is 1.5×10 ⁻⁶ /°C or more and 5.0×10 ⁻⁶ /°C or less, and the linear expansion coefficient of the first coating is 2.0×10 ⁻⁵ /°C. The fixing film according to any one of configurations 1 to 4, which has a temperature of at least 5.0×10 ⁻⁵ /° C.

[Configuration 6]
A method for producing a fixing film according to any one of configurations 1 to 5, comprising:
A polyamic acid A having a structural unit A represented by the following formula (a) and a polyamic acid B having a structural unit B represented by the following formula (b) are placed on the inner circumferential surface of the base, and the structural units A and A first step of forming a coating film a of a first polyimide precursor solution obtained by mixing the structural unit B so that the mass ratio (constituent unit A: structural unit B) is 100:0 to 60:40;
a second step of forming a coating film b of a second polyimide precursor solution containing the polyamic acid B as the only polyamic acid on the inner peripheral surface of the coating film a;
The polyamic acid A in the coating film a, or the polyamic acid A and the polyamic acid B, are imidized to form the first coating, and the polyamic acid B in the coating film b is imidized to form the first coating. a third step of forming a second coating;
A method for producing a fixing film characterized by having:

[Configuration 7]
The first step includes a drying step 1 of heating the coating film a at a temperature T1-1 lower than the boiling point of the solvent contained in the first polyimide precursor solution to dry the coating film a,
The second step includes a drying step 2 of heating the coating film b at a temperature T1-2 lower than the boiling point of the solvent contained in the second polyimide precursor solution to dry the coating film b,
The third step heats the coating film a that has undergone the drying process 1 and the coating film b that has undergone the drying process 2 at a temperature T2 higher than the temperature T1-1 and the temperature T1-2, Next, heating at a temperature T3 higher than the temperature T2 to imidize the polyamic acid A and the polyamic acid B to form the first coating and the second coating.
The method for producing a fixing film according to configuration 6.
[Configuration 8]
A fixing device comprising the fixing film according to any one of configurations 1 to 5.
[Configuration 9]
An electrophotographic image forming apparatus comprising the fixing device according to configuration 8.

11...Sliding layer 11-a...First coating 11-b...Second coating 12...Base 15...Release layer 41...Fixing film 42...Film guide/heater holder 43...Ceramic heater

Claims (9)

A fixing film,
a cylindrical base;
a sliding layer containing polyimide resin formed on the inner peripheral surface side of the base;
a release layer formed on the outer peripheral surface side of the base;
has
The sliding layer is formed by laminating a first coating and a second coating in order from the side closer to the base,
The first coating includes a first structural unit represented by the following formula (A), or the first structural unit and a second structural unit represented by the following formula (B), and The mass ratio (A):(B) of the content of the first structural unit and the second structural unit is 100:0 to 60:40,
A fixing film characterized in that the second coating contains only the second structural unit:

The fixing film according to claim 1, wherein the second coating has an imidization rate of 75% or more. The Martens hardness of the second coating measured by the nanoindenter method is larger than the Martens hardness of the first coating measured by the nanoindenter method, and the linear expansion coefficient of the second coating is greater than the Martens hardness measured by the nanoindenter method of the second coating. The fixing film according to claim 1, having a linear expansion coefficient smaller than that of the coating. 4. The second coating has a Martens hardness of 350 N/ ^mm2 or more and 450 N/ ^mm2 or less, and the first coating has a Martens hardness of 200 N/ ^mm2 or more and 300 N/ ^mm2 or less. fixing film. The linear expansion coefficient of the second coating is 1.5×10 ⁻⁶ /°C or more and 5.0×10 ⁻⁶ /°C or less, and the linear expansion coefficient of the first coating is 2.0×10 ⁻⁵ /°C. 4. The fixing film according to claim 3, having a temperature of 5.0×10 ⁻⁵ /° C. or higher. A method for producing a fixing film according to any one of claims 1 to 5, comprising:
A polyamic acid A having a structural unit A represented by the following formula (a) and a polyamic acid B having a structural unit B represented by the following formula (b) are placed on the inner circumferential surface of the base, and the structural units A and A first step of forming a coating film a of a first polyimide precursor solution obtained by mixing the structural unit B so that the mass ratio (constituent unit A: structural unit B) is 100:0 to 60:40;
a second step of forming a coating film b of a second polyimide precursor solution containing the polyamic acid B as the only polyamic acid on the inner peripheral surface of the coating film a;
The polyamic acid A in the coating film a, or the polyamic acid A and the polyamic acid B, are imidized to form the first coating, and the polyamic acid B in the coating film b is imidized to form the first coating. a third step of forming a second coating;
A method for producing a fixing film characterized by having:

The first step includes a drying step 1 of heating the coating film a at a temperature T1-1 lower than the boiling point of the solvent contained in the first polyimide precursor solution to dry the coating film a,
The second step includes a drying step 2 of heating the coating film b at a temperature T1-2 lower than the boiling point of the solvent contained in the second polyimide precursor solution to dry the coating film b,
The third step heats the coating film a that has undergone the drying process 1 and the coating film b that has undergone the drying process 2 at a temperature T2 higher than the temperature T1-1 and the temperature T1-2, Next, heating at a temperature T3 higher than the temperature T2 to imidize the polyamic acid A and the polyamic acid B to form the first coating and the second coating.
The method for manufacturing a fixing film according to claim 6. A fixing device comprising the fixing film according to claim 1. An electrophotographic image forming apparatus comprising the fixing device according to claim 8.

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