JP2024074770A - Resin film, endless belt and image forming apparatus - Google Patents

Abstract

[Problem] To provide a resin film that suppresses the occurrence of cracks at bent portions even when repeatedly bent. [Solution] A resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, the content of the solvent being more than 2200 ppm and not more than 10000 ppm relative to the entire resin layer. [Selected Figures] None

Description

The present invention relates to a resin film, an endless belt, and an image forming device.

Patent Document 1 proposes "an endless belt having a polyimide resin layer in which the content of at least one solvent selected from solvent group A consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents is 50 ppm or more and 2000 ppm or less."
Patent Document 2 proposes "an endless belt including a polyimide resin layer containing two or more kinds of at least one of a component derived from a tetracarboxylic dianhydride and a component derived from a diamine compound, and containing at least one solvent selected from solvent group A consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents in an amount of 50 ppm or more and 2000 ppm or less."
Patent Document 3 proposes "an intermediate transfer belt to be installed in an image forming apparatus including an image carrier, a developing means for developing a latent image formed on the image carrier with toner, an intermediate transfer belt onto which the toner image developed by the developing means is primarily transferred, and a transfer means for secondarily transferring the toner image carried on the intermediate transfer belt to a recording medium, the intermediate transfer belt being made of a polyimide resin or a polyamideimide resin, the polyimide resin or the polyamideimide resin containing only γ-butyrolactone in an amount of 5 ppm or more and 5000 ppm or less as a residual solvent."

JP 2017-223837 A JP 2019-045677 A JP 2014-170048 A

The problem to be solved by the first embodiment of the present invention is to provide a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, in which the occurrence of cracks in bent portions is suppressed even when the resin film is repeatedly bent, compared to a case in which the solvent content is 2200 ppm or less or exceeds 10000 ppm with respect to the entire resin layer.
The problem to be solved by the second embodiment of the present invention is to provide a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, in which the occurrence of cracks at bent portions is suppressed even when the resin film is repeatedly bent, as compared with a resin film having a tensile breaking strength of less than 270 N/ ^mm2 .

Means for solving the above problems include the following means.
<1> A resin layer including at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents,
A resin film having a solvent content of more than 2200 ppm and not more than 10000 ppm relative to the entire resin layer.
<2> The resin film according to <1>, wherein the solvent is at least one selected from the group consisting of alkoxy group-containing amide solvents and ester group-containing amide solvents.
<3> The alkoxy group-containing amide solvent is at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide and 3-n-butoxy-N,N-dimethylpropanamide,
The resin film according to <2>, wherein the ester group-containing amide solvent is methyl 5-dimethylamino-2-methyl-5-oxo-pentanoate.
<4> The resin film according to any one of <1> to <3>, wherein the solvent is 3-methoxy-N,N-dimethylpropanamide.
<5> The resin layer contains a polyimide resin having a structural unit derived from phenylenediamine and a structural unit derived from diaminodiphenyl ether,
<4> The resin film according to any one of <1> to <4>, wherein a content ratio of the structural units derived from the phenylenediamine and the structural units derived from the diaminodiphenyl ether in the polyimide resin (structural units derived from phenylenediamine/structural units derived from diaminodiphenyl ether) is 80/20 or more and 99.7/0.3 or less in terms of a molar ratio.
<6> The resin film according to any one of <1> to <5>, wherein the content of the solvent is 2500 ppm or more and 9000 ppm or less with respect to the entire resin layer.
<7> The resin film according to <6>, wherein the content of the solvent is 6,000 ppm or more and 7,000 ppm or less with respect to the entire resin layer.
<8> The resin film according to any one of <1> to <7>, wherein the boiling point of the solvent is 200° C. or higher and 280° C. or lower.
<9> The resin film according to any one of <1> to <8>, which has a folding resistance of 300,000 or more times in an MIT test using a clamp with a curvature radius R of 2 mm.
<10> A resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents,
A resin film having a tensile breaking strength of 270 N/ ^mm2 or more.
<11> An endless belt made of the resin film according to any one of <1> to <10>.
<12> An image forming apparatus comprising the endless belt according to <11>.
<13> An image carrier;
a charging device for charging the surface of the image carrier;
an electrostatic image forming device for forming an electrostatic image on a surface of a charged image carrier;
a developing device that develops the electrostatic image formed on the surface of the image carrier into a toner image by using a developer containing a toner;
A transfer device that transfers the toner image onto a recording medium;
A fixing device that fixes the toner image onto the recording medium,
12. An image forming apparatus, wherein at least one selected from the group consisting of a transfer device and a fixing device has the endless belt according to <11>.

According to the invention related to <1>, there is provided a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, in which the occurrence of cracks in bent portions is suppressed even when the resin film is repeatedly bent, compared to a case in which the solvent content is 2,200 ppm or less or exceeds 10,000 ppm with respect to the entire resin layer.
According to the invention related to <2>, <3> or <4>, there is provided a resin film in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, as compared with the case where the solvent is a urea-based solvent.
According to the invention related to <5>, there is provided a resin film in which the occurrence of cracks at bent portions is suppressed even when the resin film is repeatedly bent, compared with a case in which the content ratio of the structural units derived from phenylenediamine and the structural units derived from diaminodiphenyl ether in the polyimide resin (structural units derived from phenylenediamine/structural units derived from diaminodiphenyl ether) is less than 80/20 or more than 99.7/0.3 in molar ratio.
According to the invention related to <6>, a resin film is provided in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared with cases in which the solvent content is less than 2,500 ppm or more than 9,000 ppm.
According to the invention related to <7>, a resin film is provided in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared to cases in which the solvent content is less than 6,000 ppm or more than 7,000 ppm.
According to the invention related to <8>, a resin film is provided in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared to cases in which the boiling point of the solvent is lower than 200°C or higher than 280°C.
According to the invention related to <9>, there is provided a resin film in which the occurrence of cracks at bent portions is suppressed even when the resin film is repeatedly bent, as compared with a case in which the number of folding cycles in an MIT test using a clamp with a curvature radius R of 2 mm is less than 300,000.
According to the invention related to <10>, there is provided a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, in which the occurrence of cracks at bent portions is suppressed even when the resin film is repeatedly bent, compared with a resin film having a tensile breaking strength of less than 270 N/ ^mm2 .
According to the invention related to <11>, there is provided an endless belt in which, in a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, the occurrence of cracks in a bent portion is suppressed even when the resin film is repeatedly bent, compared with an endless belt made of a resin film having a solvent content of 2200 ppm or less or exceeding 10000 ^ppm relative to the entire resin layer, or compared with an endless belt made of a resin film having a tensile breaking strength of less than 270 N/mm2.
According to the invention related to <12> or <13>, there is provided an image forming apparatus equipped with an endless belt in which, in a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, the occurrence of cracks at bending portions is suppressed even when the resin film is repeatedly bent, compared with an endless belt made of a resin film having a solvent content of 2200 ppm or less or exceeding ¹⁰⁰⁰⁰ ppm relative to the entire resin layer, or an endless belt made of a resin film having a tensile breaking strength of less than 270 N/mm2.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram illustrating another example of an image forming apparatus according to the present embodiment. FIG. 2 is a schematic configuration diagram illustrating an example of a fixing device according to the first embodiment. FIG. 11 is a schematic configuration diagram illustrating an example of a fixing device according to a second embodiment. FIG. 2 is a schematic perspective view illustrating an example of an endless belt unit according to the embodiment.

Hereinafter, an embodiment of the present invention will be described as an example. These descriptions and examples are merely illustrative of the embodiment, and are not intended to limit the scope of the present invention.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.

Each component may contain multiple types of the corresponding substance.
When referring to the amount of each component in a composition, if the composition contains multiple substances corresponding to each component, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

<Resin film>
The resin film according to the first embodiment has a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, and the solvent content is more than 2,200 ppm and not more than 10,000 ppm with respect to the entire resin layer.

The resin film according to the first embodiment, due to the above-mentioned configuration, suppresses the occurrence of cracks at the bent portion even when it is repeatedly bent. The reason for this is presumed to be as follows.

Resin films having a resin layer may be used in a bent state. When the bent portion is repeatedly subjected to bending deformation, cracks due to fatigue may occur at the bent portion.

The resin film according to the first embodiment has a solvent content of more than 2200 ppm and not more than 10000 ppm relative to the entire resin layer. By making the solvent content more than 2200 ppm relative to the entire resin layer, the flexibility of the resin film is increased, and cracks at the bent portion are suppressed even when the bent portion is repeatedly subjected to bending deformation.
Furthermore, by setting the content of the solvent to 10,000 ppm or less based on the entire resin layer, the flexibility of the resin film does not become too high, and permanent deformation is suppressed.
Furthermore, the resin layer contains at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents. These solvents have highly polar functional groups, so that their boiling points are high and they are less likely to volatilize. Therefore, the content of the solvent in the resin layer is less likely to change over time. Therefore, the flexibility of the resin film is easily maintained, and cracks at the bent portion are suppressed even when the bent portion is repeatedly subjected to bending deformation.

As a result, the resin film according to the first embodiment is less susceptible to cracking at bent portions even when repeatedly bent.

The resin film according to the second embodiment has a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, and has a tensile breaking strength of 270 N/ ^mm2 or more.

The resin film according to the second embodiment, due to the above-mentioned configuration, suppresses the occurrence of cracks at the bent portion even when it is repeatedly bent. The reason for this is presumed to be as follows.

The resin film according to the second embodiment has a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents. The inclusion of the solvent improves the flexibility of the resin film, and for the same reason as above, the content of the solvent in the resin layer is less likely to change over time, making it easier to maintain the flexibility of the resin film.
Furthermore, by setting the tensile breaking strength of the resin film to 270 N/mm ² or more, the stress generated during actual use becomes sufficiently smaller than the elastic limit.

Therefore, the resin film according to the second embodiment is less likely to crack at the bent portion even when it is repeatedly bent.

Hereinafter, the resin film corresponding to both the first and second embodiments will be described in detail. However, an example of the resin film of the present invention may be a resin film corresponding to either the first or second embodiment.

(Resin Layer)
-solvent-
The resin layer contains at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents.
The content of the solvent is more than 2200 ppm and not more than 10000 ppm with respect to the entire resin layer.

From the viewpoint of further suppressing the occurrence of cracks in the bent portion, the content of the solvent is preferably 2500 ppm or more and 9000 ppm or less, more preferably 4000 ppm or more and 8000 ppm or less, and even more preferably 6000 ppm or more and 7000 ppm or less, relative to the entire resin layer.

The solvent (residual solvent) contained in the resin layer constituting the resin film can be measured by collecting a measurement sample from the resin layer of the resin film to be measured and measuring the solvent using a gas chromatograph mass spectrometer (GC-MS) etc. Specifically, the solvent can be analyzed using a gas chromatograph mass spectrometer (Shimadzu GCMS QP-2010) equipped with a drop-type pyrolysis device (Frontier Labs PY-2020D).
The solvent contained in the resin layer constituting the resin film is measured at a thermal decomposition temperature of 400° C. by precisely weighing 0.40 mg of a measurement sample from the resin layer.
Pyrolysis equipment: Frontier Labs: PY-2020D
Gas chromatograph mass spectrometer: Shimadzu GCMS QP-2010
Thermal decomposition temperature: 400°C
Gas chromatograph inlet temperature: 280°C
Injection method: split ratio 1:50
Column: Frontier Labs: Ultra ALLOY-5, 0.25 μm, 0.25 μm ID, 30 m
Gas chromatographic temperature program: 40°C ⇒ 20°C/min ⇒ 280°C-10 min Retention mass range: EI, m/z = 29-600

Urea-based solvents Urea-based solvents are solvents having a urea group (N-C(=O)-N). Specifically, the urea-based solvent may be a solvent having a structure of "*-N(Ra ¹ )-C(=O)-N(Ra ² )-*". Here, Ra ¹ and Ra ² each independently represent a hydrogen atom, an alkyl group, a phenyl group, or a phenylalkyl group. The * at both ends of the two N atoms represent bonding sites with other atomic groups in the structure. The urea-based solvent may be a solvent having a ring structure in which the * at both ends of the two N atoms are linked together via a linking group consisting of, for example, alkylene, -O-, -C(=O)-, or a combination thereof.

The alkyl group represented by Ra ¹ and Ra ² may be any of linear, branched, and cyclic, and may have a substituent. Specific examples of the alkyl group include alkyl groups having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms) (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, etc.).
Examples of the substituent on the alkyl group include an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a ketone group, an ester group, and an alkylcarbonyloxy group.
Specific examples of the ketone group include a methylcarbonyl group (acetyl group), an ethylcarbonyl group, an n-propylcarbonyl group, etc. Specific examples of the ester group include a methoxycarbonyl group, an ethoxycarbonyl group, an n-propoxycarbonyl group, an acetoxy group, etc. Specific examples of the alkylcarbonyloxy group include a methylcarbonyloxy group (acetyloxy group), an ethylcarbonyloxy group, an n-propylcarbonyloxy group, etc.

The phenyl skeleton of the phenyl group and the phenylalkyl group represented by Ra ¹ and Ra ² may have a substituent. Examples of the substituent of the phenyl skeleton include the same as the substituent of the alkyl group described above.

In addition, when the urea-based solvent has a ring structure in which both ends* of the two N atoms are linked, the number of ring members is preferably 5 or 6.

Examples of urea-based solvents include 1,3-dimethylurea, 1,3-diethylurea, 1,3-diphenylurea, 1,3-dicyclohexylurea, tetramethylurea, tetraethylurea, 2-imidazolidinone, propyleneurea, 1,3-dimethyl-2-imidazolidinone, and N,N-dimethylpropyleneurea.
Among these, from the viewpoint of further suppressing the occurrence of cracks in the bent portion, 1,3-dimethylurea, 1,3-diethylurea, tetramethylurea, tetraethylurea, 1,3-dimethyl-2-imidazolidinone, and N,N-dimethylpropyleneurea are preferred as the urea-based solvent, and tetramethylurea, tetraethylurea, 1,3-dimethyl-2-imidazolidinone, and N,N-dimethylpropyleneurea are most preferred.

Alkoxy group-containing amide solvent, ester group-containing amide solvent Alkoxy group-containing amide solvent is a solvent having an alkoxy group and an amide group. On the other hand, ester group-containing amide solvent is a solvent having an ester group and an amide group. Examples of the alkoxy group and the ester group include the same groups as the alkoxy group and the ester group exemplified as the "substituents of the alkyl group showing Ra ¹ and Ra ² " in the explanation of the urea solvent. The alkoxy group-containing amide solvent may have an ester group, and the ester group-containing amide solvent may have an alkoxy group.

Hereinafter, both alkoxy group-containing amide solvents and ester group-containing amide solvents will be referred to as "alkoxy group- or ester group-containing amide solvents."

The alkoxy group- or ester group-containing amide solvent is not particularly limited, but specific examples include amide solvents represented by the following general formula (Am1) and amide solvents represented by the following general formula (Am2).

In formula (Am1), Rb ¹ , Rb ² , Rb ³ , Rb ⁴ , Rb ⁵ , and Rb ⁶ each independently represent a hydrogen atom or an alkyl group. Rb ⁷ represents an alkoxy group or an ester group.
The alkyl group represented by Rb ¹ to Rb ⁶ has the same meaning as the "alkyl group represented by Ra ¹ and Ra ² " described in the explanation of the urea-based solvent.
The alkoxy group and ester group represented by ^Rb7 have the same meaning as the alkoxy group and ester group exemplified as "substituents of the alkyl group represented by ^Ra1 and ^Ra2 " in the description of the urea-based solvent.

Specific examples of amide solvents represented by general formula (Am1) are shown below, but are not limited to these.

In the specific examples of amide solvents represented by general formula (Am1), Me = methyl group, Et = ethyl group, nPr = n-propyl group, and nBu = n-butyl group.

In formula (Am2), Rc ¹ , Rc ² , Rc ³ , Rc ⁴ , Rc ⁵ , Rc ⁶ , Rc ⁷ , and Rc ⁸ each independently represent a hydrogen atom or an alkyl group. Rc ⁹ represents an alkoxy group or an ester group.
The alkyl group represented by Rc ¹ to Rc ⁸ has the same meaning as the "alkyl group represented by Ra ¹ and Ra ² " described in the explanation of the urea-based solvent.
The alkoxy group and ester group represented by Rc ⁹ have the same meaning as the alkoxy group and ester group exemplified as "the substituent of the alkyl group represented by Ra ¹ and Ra ² " in the description of the urea-based solvent.

Specific examples of amide solvents represented by general formula (Am2) are shown below, but are not limited to these.

In the specific examples of amide solvents represented by general formula (Am2), Me = methyl group, Et = ethyl group, and nPr = n-propyl group.

Among these, from the viewpoint of further suppressing the occurrence of cracks at bent portions, 3-methoxy-N,N-dimethylpropanamide (exemplary compound B-4), 3-n-butoxy-N,N-dimethylpropanamide (exemplary compound B-7), and 5-dimethylamino-2-methyl-5-oxo-methyl pentanoate (exemplary compound C-3) are preferred as alkoxy group or ester group-containing amide solvents, with 3-methoxy-N,N-dimethylpropanamide (exemplary compound B-4) being more preferred.

The solvent is preferably at least one selected from the group consisting of alkoxy group-containing amide solvents and ester group-containing amide solvents.
Alkoxy group-containing amide solvents and ester group-containing amide solvents are easy to dissolve the materials (e.g., resins) constituting the resin layer in the production of the resin film. In addition, the solvent has a high boiling point and is therefore difficult to volatilize. Therefore, the content of the solvent in the resin layer is unlikely to change over time. Therefore, the flexibility of the resin film is easily maintained, and cracks at the bent portion are suppressed even when the bent portion is repeatedly subjected to bending deformation.

The alkoxy group-containing amide solvent is preferably at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide and 3-n-butoxy-N,N-dimethylpropanamide, and the ester group-containing amide solvent is preferably methyl 5-dimethylamino-2-methyl-5-oxo-pentanoate.
The solvent is particularly preferably 3-methoxy-N,N-dimethylpropanamide.

By using the solvent as an alkoxy group-containing amide solvent and an ester group-containing amide solvent, the material (e.g., resin) constituting the resin layer in the production of the resin film is more easily dissolved. In addition, the solvent has a high boiling point and is less likely to volatilize. Therefore, the content of the solvent in the resin layer is less likely to change over time. Therefore, the flexibility of the resin film is easily maintained, and cracks at the bent parts are suppressed even when the bent parts are repeatedly subjected to bending deformation.

The boiling point of the solvent is preferably from 200° C. to 280° C., more preferably from 205° C. to 275° C., and even more preferably from 210° C. to 275° C.
Here, the boiling point of the solvent is the boiling point under atmospheric pressure (101 kPa).

By setting the boiling point of the solvent to 200° C. or higher, the solvent is less likely to volatilize from the resin layer. Therefore, the content of the solvent in the resin layer is less likely to change over time. Therefore, the flexibility of the resin film is easily maintained, and cracks at the bent portion are suppressed even if the bent portion is repeatedly subjected to bending deformation.
Furthermore, by setting the boiling point of the solvent to 280° C. or lower, the amount of residual solvent after heat treatment at about 300° C. in the baking step in the resin film manufacturing method described below is not excessive.

-resin-
The resin layer contains a resin. The resin is not particularly limited, but is preferably a polyimide resin from the viewpoint of suppressing the occurrence of cracks at the bent portion.
The polyimide resin may be a polyimide obtained by imidizing a polyimide precursor described below.

The polyimide resin preferably has a structural unit derived from a tetracarboxylic acid dihydrate and a structural unit derived from a diamine compound.
In particular, the polyimide resin preferably has, as the structural units derived from the diamine compound, a structural unit derived from phenylenediamine and a structural unit derived from diaminodiphenyl ether.
From the viewpoint of suppressing cracking at bent portions, the content ratio of the structural units derived from phenylenediamine and the structural units derived from diaminodiphenyl ether in the polyimide resin (structural units derived from phenylenediamine/structural units derived from diaminodiphenyl ether) in terms of molar ratio is preferably 80/20 or more and 99.7/0.3 or less, and more preferably 85/15 or more and 95/5 or less.

The content of the above structural units is measured as follows.
First, from several mixed samples of phenylenediamine and diaminodiphenyl ether at known mixing ratios, the peak intensity ratio between the peak at 1515 cm ⁻¹ (peak due to phenylenediamine) and the peak at 1500 cm ⁻¹ (peak due to diaminodiphenyl ether) is obtained by measuring with an infrared spectrophotometer (IR), and a calibration curve is drawn between the peak intensity ratio and the mixing ratio.
Next, the peak intensity ratio is obtained from a sample of the resin layer of the resin film to be measured by an infrared spectrophotometer (IR), and the mixing ratio is calculated from a calibration curve. The obtained mixing ratio is defined as the content ratio of the structural unit derived from phenylenediamine and the structural unit derived from diaminodiphenyl ether in the polyimide resin.

Here, the structural units derived from the monomers forming the resin of the resin layer can be measured, for example, by analyzing and quantifying the components detected by pyrolysis gas chromatography mass spectrometry (GC-MS). Specifically, first, a measurement sample of the resin layer is prepared from the resin film to be measured. Next, the measurement sample is measured using a gas chromatograph mass spectrometer (Shimadzu Corporation: GCMS QP-2010) equipped with a drop-type pyrolysis device (Frontier Labs: PY-2020D). The pyrolysis gas chromatograph mass spectrometer then decomposes the polyimide resin down to its monomer units, and the structure and ratio of the monomers are determined by mass analysis of the decomposition products obtained by decomposition.

-Conductive particles-
The resin layer constituting the resin film according to the present embodiment may contain conductive particles added to impart conductivity as necessary. The conductive particles may be conductive (e.g., volume resistivity less than ¹⁰ Ω·cm, the same applies below) or semiconductive (e.g., volume resistivity 10 ^Ω ·cm or more and ¹⁰ Ω·cm or less, the same applies below), and may be selected depending on the purpose of use.
Examples of conductive particles include carbon black, metals (such as aluminum and nickel), metal oxides (such as yttrium oxide and tin oxide), and ion-conductive substances (such as potassium titanate and LiCl).
These conductive particles may be used alone or in combination of two or more kinds. The conductive particles should have a primary particle size of less than 10 μm (preferably 1 μm or less).

Among these, carbon black is preferable as the conductive particles, and acidic carbon black having a pH of 5.0 or less is particularly preferable.
Examples of acidic carbon black include carbon black whose surface has been subjected to an oxidation treatment, such as carbon black obtained by providing a carboxyl group, a quinone group, a lactone group, a hydroxyl group, or the like to the surface.
When the acidic carbon black is applied to a transfer belt having a resin layer containing a polyimide resin, from the viewpoints of stability of electrical resistance over time and electric field dependence for suppressing electric field concentration due to the transfer voltage, it is preferable that the carbon black has a pH of 4.5 or less, and more preferably has a pH of 4.0 or less.
The pH of the acidic carbon black is a value measured by the pH measurement method specified in JIS Z8802 (2011).

Specific examples of carbon black include Orion Engineered Carbons' "Special Black 350," "Special Black 100," "Special Black 250," "Special Black 5," "Special Black 4," "Special Black 4A," "Special Black 550," "Special Black 6," "Color Black FW200," "Color Black FW2," and "Color Black FW2V," as well as Cabot's "MONARCH 1000," "MONARCH 1300," "MONARCH 1400," "MOGUL-L," and "REGAL 400R."

The amount of conductive particles is not particularly limited, but from the standpoint of the appearance, mechanical, and electrical quality of the resin film, it is preferable that the amount is 1 part by mass or more and 40 parts by mass or less (preferably 10 parts by mass or more and 30 parts by mass or less) per 100 parts by mass of resin in the resin layer.

(Other additives)
The resin layer constituting the resin film according to the present embodiment may contain various fillers for the purpose of imparting various functions such as mechanical strength. In addition, when the resin layer contains polyimide as a resin, it may contain a catalyst for promoting an imidization reaction, a leveling material for improving the quality of the film formation, and the like.

Fillers added to improve mechanical strength include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica, and talc. In addition, fluororesin powders such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) may be added to improve the water repellency and release properties of the surface of the resin layer.

Catalysts for promoting the imidization reaction may include dehydrating agents such as acid anhydrides, and acid catalysts such as phenol derivatives, sulfonic acid derivatives, and benzoic acid derivatives.

A surfactant may be added to improve the film-forming quality of the resin layer. The surfactant used may be cationic, anionic, or nonionic.

The content of other additives may be selected according to the desired properties of the resin layer.

(Layer structure)
The resin film according to the present embodiment may be a resin film made of a laminate having a functional layer such as a release layer on at least one of the inner and outer peripheral surfaces of the resin layer.

(Physical properties of resin film)
The resin film according to the present embodiment has a folding resistance of preferably 300,000 or more, more preferably 400,000 or more, and even more preferably 500,000 or more, in an MIT test using a clamp with a curvature radius R of 2 mm.

The number of times that the resin film can be repeatedly bent in the MIT test indicates the number of times that the resin film can be bent until it breaks.
By setting the bending resistance to 0,000 times or more, the resin film can be made more suppressible in the occurrence of cracks at the bent portion even when the film is repeatedly bent.

The number of times the sample endures folding in the MIT test is measured as follows.
The MIT test is in accordance with JIS P 8115:2001 (MIT test machine method).
Specifically, a rectangular test piece having a width of 15 mm and a length of 200 mm is cut out from the resin film in the circumferential direction. Both ends of the rectangular test piece are fixed, and a tensile force of 1 kgf is applied to the rectangular test piece, which is repeatedly bent (folded) in the left and right directions at 90° with a clamp having a curvature radius R of 2 mm as a fulcrum. The number of times until the rectangular test piece breaks is defined as the number of folding times.
The MIT test is carried out in an environment of a temperature of 22° C. and a humidity of 55% RH.

The resin film according to this embodiment has a tensile breaking strength of 270 N/mm ² or more.
From the viewpoint of further suppressing the occurrence of cracks at the bent portion, the tensile breaking strength is preferably 320 N/mm2 or ^more and 500 N/ ^mm2 or less, more preferably 375 N/ ^mm2 or more and 475 N/ ^mm2 or less, and even more preferably 400 N/ ^mm2 or more and 450 N/ ^mm2 or less.

The tensile strength at break is measured as follows.
A 5 mm wide strip is cut out from the resin film, and this is placed in a tensile tester Model 1605N (manufactured by Aiko Engineering Co., Ltd.) and pulled at a constant speed of 10 mm/sec to measure the tensile breaking strength.

(Method of manufacturing resin film)
The resin film according to this embodiment is preferably obtained by applying a coating liquid for forming a resin film to an article to be coated, followed by drying and baking.
Specific examples of the method for producing the resin film include the following methods.
The method for producing a resin film includes, for example, a step of applying a polyimide precursor composition onto a cylindrical substrate (mold) to form a coating film (coating film forming step), a step of drying the coating film formed on the substrate to form a dry film (drying step), a step of imidizing the dry film (heating treatment) to imidize the polyimide precursor to form a polyimide resin molded body (baking step), and a step of removing the polyimide resin molded body from the substrate to form a resin film (removing step). This polyimide resin molded body becomes a resin layer. Specifically, for example, it is as follows.
The polyimide precursor composition is as described later in "-Polyimide precursor composition-".

First, the polyimide precursor composition is applied to the inner or outer surface of a cylindrical substrate to form a coating film. For example, a cylindrical metal substrate is preferably used as the cylindrical substrate. Substrates made of other materials such as resin, glass, and ceramic may be used instead of metal. In addition, a glass coat, a ceramic coat, or the like may be provided on the surface of the substrate, and a release agent such as a silicone-based or fluorine-based release agent may be applied.
The shape of the substrate is not limited to a cylindrical shape, and may be a plate shape or other shape, depending on the application of the resin film.

In order to coat the polyimide precursor composition with good accuracy, it is preferable to carry out a step of degassing the polyimide precursor composition before coating. By degassing the polyimide precursor composition, foaming during coating and the occurrence of defects in the coating film can be suppressed.
Methods for degassing the polyimide precursor composition include a method under reduced pressure and a method using centrifugation, and degassing under reduced pressure is preferred because it is simple and has a high degassing ability.

Next, the cylindrical substrate on which the coating film of the polyimide precursor composition has been formed is heated or placed in a vacuum environment to dry the coating film and form a dry film. At least 30% by mass, preferably at least 50% by mass, of the contained solvent is volatilized.

Next, the dried film is subjected to an imidization treatment (heat treatment), thereby forming a polyimide resin molded body.
The heating conditions for the imidization treatment are, for example, 150°C to 400°C (preferably 200°C to 300°C) for 20 minutes to 60 minutes, whereby the imidization reaction occurs and a polyimide resin molded body is formed. During the heating reaction, it is preferable to gradually increase the temperature stepwise or at a constant rate before reaching the final heating temperature. The imidization temperature varies depending on, for example, the types of tetracarboxylic dianhydride and diamine used as raw materials, and is set to a temperature at which the imidization is completed, since insufficient imidization results in poor mechanical and electrical properties.
Thereafter, the polyimide resin molded body is removed from the cylindrical substrate to obtain a resin film.
When obtaining a resin film having a functional layer such as a release layer in addition to a resin layer, the resin film is obtained by forming an appropriate functional layer on a molded product of a polyimide resin.

-Polyimide precursor composition-
The polyimide precursor composition contains a resin having a repeating unit represented by general formula (I) (hereinafter referred to as a "polyimide precursor") and at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents.
The polyimide precursor composition contains a polyimide precursor having at least two or more kinds of structural units derived from a tetracarboxylic dianhydride and a diamine compound. The polyimide precursor may be a copolymer having a repeating unit represented by general formula (I), or may be a mixture of different kinds of homopolymers having a repeating unit represented by general formula (I).
The polyimide precursor composition may contain conductive particles and other additives, if necessary.

(Polyimide precursor)
The polyimide precursor may be a resin (polyamic acid) having a repeating unit represented by the general formula (I).

In general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.

In the general formula (I), the tetravalent organic group represented by A is a residue obtained by removing four carboxyl groups from the starting tetracarboxylic dianhydride.
On the other hand, the divalent organic group represented by B is a residue obtained by removing two amino groups from a diamine compound serving as a raw material.

In other words, the polyimide precursor having the repeating unit represented by the general formula (I) is a polymer of a tetracarboxylic dianhydride and a diamine compound. That is, the polyimide precursor contains a component derived from the tetracarboxylic dianhydride and a component derived from the diamine compound.

The tetracarboxylic acid dianhydride may be either an aromatic or aliphatic compound, but is preferably an aromatic compound. In other words, in general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenylsulfone tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-dimethyldiphenylsilane tetracarboxylic dianhydride, 3,3',4,4'-tetraphenylsilane tetracarboxylic dianhydride, 1,2,3,4-furan tetracarboxylic dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4, Examples of such an anhydride include 4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, 3,3',4,4'-perfluoroisopropylidenediphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, bis(phthalic acid)phenylphosphine oxide dianhydride, p-phenylene-bis(triphenylphthalic acid) dianhydride, m-phenylene-bis(triphenylphthalic acid) dianhydride, bis(triphenylphthalic acid)-4,4'-diphenylether dianhydride, bis(triphenylphthalic acid)-4,4'-diphenylmethane dianhydride, and 4,4'-oxydiphthalic dianhydride (ODPA).

Examples of aliphatic tetracarboxylic dianhydrides include butane tetracarboxylic dianhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentyl acetic dianhydride, 3,5,6-tricarboxynorbonane-2-acetic dianhydride, 2,3,4,5-tetrahydrofuran tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo[2,2,2]-octo-7-ene aliphatic or alicyclic tetracarboxylic dianhydrides such as 1,3,3a,4,5,9b-hexahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, and 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione.

Among these, the tetracarboxylic dianhydride is preferably an aromatic tetracarboxylic dianhydride, specifically, for example, pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, and further, pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, and particularly, 3,3',4,4'-biphenyl tetracarboxylic dianhydride.

The tetracarboxylic dianhydrides may be used alone or in combination of two or more.
When two or more kinds are used in combination, aromatic tetracarboxylic dianhydrides or aliphatic tetracarboxylic acids may be used in combination, or an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic dianhydride may be used in combination.

When the polyimide precursor contains two or more structural units derived from tetracarboxylic dianhydrides, the form of the structural units derived from the tetracarboxylic dianhydrides is not particularly limited. For example, the structural units derived from the tetracarboxylic dianhydrides may be contained as a copolymer or a mixture of copolymers using two or more types of tetracarboxylic dianhydrides. In addition, the structural units may be contained as a mixture of a homopolymer using one type of tetracarboxylic dianhydride and a homopolymer or a copolymer using a different tetracarboxylic dianhydride.
When the polyimide precursor contains two or more types of structural units derived from tetracarboxylic dianhydride, the components derived from the tetracarboxylic dianhydride preferably contain a structural unit derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride in order to suppress the generation of cracks when the polyimide precursor is wound.

In particular, when the polyimide precursor contains structural units derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride, it is preferable that the content of structural units derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride relative to the total structural units derived from tetracarboxylic dianhydride is 70% by mass or more and 99% by mass or less (preferably 80% by mass or more and 95% by mass or less).

On the other hand, a diamine compound is a diamine compound that has two amino groups in its molecular structure. Diamine compounds can be either aromatic or aliphatic compounds, but aromatic compounds are preferred. In other words, the divalent organic group represented by B in general formula (I) is preferably an aromatic organic group.

Examples of the diamine compound include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenylether, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindan, 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindan, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethane, and the like. chloromethylbenzanilide, 3,5-diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-methylene-bis(2-chloroaniline), 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl] Propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)-biphenyl, 1,3'-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4'-(m-phenyleneisopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 4,4'-bis[4-(4-amino-2-trifluoromethyl)pheno aromatic diamines having two amino groups bonded to an aromatic ring and a heteroatom other than the nitrogen atom of the amino groups, such as diaminotetraphenylthiophene; aliphatic diamines and alicyclic diamines, such as 1,1-meta-xylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanedimethyldiamine, tricyclo[6,2,1,0 ^2.7 ]-undecylenedimethyldiamine, and 4,4'-methylenebis(cyclohexylamine).

Among these, the diamine compound is preferably an aromatic diamine compound, specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, and particularly, p-phenylenediamine and 4,4'-diaminodiphenyl ether are preferred.

The diamine compound may be used alone or in combination of two or more. In order to prevent breakage during meandering, it is preferable to use two or more diamine compounds. When two or more diamine compounds are used in combination, aromatic diamine compounds or aliphatic diamine compounds may be used in combination, or an aromatic diamine compound and an aliphatic diamine compound may be used in combination.

When the polyimide precursor contains two or more structural units derived from a diamine compound, the form of the structural unit derived from the diamine compound is not particularly limited.For example, the structural unit derived from the diamine compound may be contained as a copolymer or a mixture of copolymers using two or more diamine compounds.In addition, it may be contained as a mixture of a homopolymer using one diamine compound and a homopolymer or a copolymer using a different diamine compound.
When the polyimide precursor contains two or more structural units derived from a diamine compound, it is preferable that the polyimide precursor contains at least a structural unit derived from p-phenylenediamine or a structural unit derived from diaminodiphenyl ether (4,4'-diaminodiphenyl ether, etc.) in terms of suppressing the occurrence of cracks at bent portions. For the same reason, the polyimide precursor may contain both a structural unit derived from p-phenylenediamine and a structural unit derived from diaminodiphenyl ether. Among these, it is preferable that the polyimide precursor contains at least a structural unit derived from p-phenylenediamine.

In particular, when the polyimide precursor contains a structural unit derived from p-phenylenediamine, the content of the structural unit derived from p-phenylenediamine relative to the total structural units derived from the diamine compound is preferably 70 mass % or more and 90 mass % or less (preferably 75 mass % or more and 85 mass % or less).
When two or more types of structural units derived from diamine compounds are contained, a preferred combination is, as described above, a combination of a structural unit derived from p-phenylenediamine and a structural unit derived from diaminodiphenyl ether (4,4'-diaminodiphenyl ether, etc.).
In order to suppress the occurrence of cracks at bent portions, the content ratio of the structural units derived from p-phenylenediamine and the structural units derived from diaminodiphenyl ether is preferably 70/30 or more and 90/10 or less in mass ratio.
From the same viewpoint, the content ratio of the structural units derived from phenylenediamine and the structural units derived from diaminodiphenyl ether (structural units derived from phenylenediamine/structural units derived from diaminodiphenyl ether) is preferably 80/20 or more and 99.7/0.3 or less, more preferably 85/15 or more and 95/5 or less, in terms of molar ratio.

The polyimide precursor may be a partially imidized resin.
Specifically, examples of the polyimide precursor include resins having repeating units represented by general formulae (I-1), (I-2) and (I-3).

In general formulae (I-1), (I-2) and (I-3), A represents a tetravalent organic group, and B represents a divalent organic group. A and B have the same meanings as A and B in general formula (I).
l represents an integer of 1 or more, and m and n each independently represent 0 or an integer of 1 or more.

Here, in the bond portion of the polyimide precursor (the reaction portion between the tetracarboxylic dianhydride and the diamine compound), the ratio of the number of bonds (2n+m) that are closed by imide ring to the total number of bonds (2l+2m+2n), i.e., the imidization rate of the polyimide precursor, is represented by "(2n+m)/(2l+2m+2n)". This value is preferably 0.2 or less, more preferably 0.15 or less, and most preferably 0.1 or less.
By setting the imidization rate within this range, gelation and precipitation separation of the polyimide precursor can be suppressed.

The imidization rate of the polyimide precursor (the value of "(2n+m)/(2l+2m+2n)") is measured by the following method.

-Measurement of imidization rate of polyimide precursor-
Preparation of Polyimide Precursor Sample (i) A polyimide precursor composition to be measured is applied onto a silicon wafer to a film thickness of 1 μm or more and 10 μm or less to prepare a coating sample.
(ii) The coating sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating sample with tetrahydrofuran (THF). The solvent for immersion is not limited to THF, and can be selected from solvents that do not dissolve the polyimide precursor and are miscible with the solvent components contained in the polyimide precursor composition. Specifically, alcohol solvents such as methanol and ethanol, and ether compounds such as dioxane can be used.
(iii) The coating sample is taken out of the THF, and the THF adhering to the surface of the coating sample is removed by blowing _N2 gas. The coating sample is dried under reduced pressure of 10 mmHg or less at a temperature range of 5°C to 25°C for 12 hours or more to prepare a polyimide precursor sample.

Preparation of 100% imidized standard sample (iv) In the same manner as in (i) above, the polyimide precursor composition to be measured is applied onto a silicon wafer to prepare a coating sample.
(v) The coating sample is heated at 380° C. for 60 minutes to carry out an imidization reaction, and a 100% imidized control sample is prepared.

(vi) Measurement and Analysis: Using a Fourier transform infrared spectrophotometer (FT-730 manufactured by Horiba, Ltd.), the infrared absorption spectra of the 100% imidized standard sample and the polyimide precursor sample are measured. The ratio I'(100) of the absorption peak (Ab'(1780 cm ^-1 )) derived from the imide bond near 1780 cm ^{- 1} to the absorption peak (Ab'(1500 cm ^-1 )) derived from the aromatic ring near 1500 cm-1 of the 100% imidized standard sample is calculated.
(vii) Similarly, a polyimide precursor sample is measured, and the ratio I(x) of the absorption peak due to the imide bond at about 1780 cm ^-1 (Ab(1780 cm ^-1 )) to the absorption peak due to the aromatic ring at about 1500 cm ^-1 (Ab(1500 cm ^-1 )) is calculated.

The measured absorption peaks I'(100) and I(x) are used to calculate the imidization rate of the polyimide precursor based on the following formula.
Formula: Imidization rate of polyimide precursor=I(x)/I′(100)
Formula: I'(100) = (Ab'(1780 cm ^-1 ))/(Ab'(1500 cm ^-1 ))
Formula: I(x)=(Ab(1780 cm ⁻¹ ))/(Ab(1500 cm ⁻¹ ))

This measurement of the imidization rate of a polyimide precursor is also applied to the measurement of the imidization rate of an aromatic polyimide precursor. When measuring the imidization rate of an aliphatic polyimide precursor, a peak derived from a structure that does not change before and after the imidization reaction is used as the internal standard peak instead of the absorption peak of the aromatic ring.

-Terminal amino group of polyimide precursor-
The polyimide precursor may include a polyimide precursor (resin) having an amino group at its terminal, and preferably a polyimide precursor having an amino group at all of its terminals.

In order to provide an amino group at the molecular end of the polyimide precursor, for example, the molar equivalent of the diamine compound used in the polymerization reaction is added in excess of the molar equivalent of the tetracarboxylic dianhydride. The molar equivalent ratio of the tetracarboxylic dianhydride to the diamine compound is preferably in the range of 0.92 to 0.9999, more preferably in the range of 0.93 to 0.999, relative to 1 molar equivalent of the diamine compound.
When the molar equivalent ratio of the diamine compound to the tetracarboxylic dianhydride is 0.9 or more, the effect of the amino group at the molecular terminal is large, and good dispersibility is easily obtained. Also, when the molar equivalent ratio is 0.9999 or less, the molecular weight of the obtained polyimide precursor is large, and for example, when it is made into a molded product of a polyimide resin, sufficient strength (tear strength, tensile strength) is easily obtained.

The terminal amino groups of the polyimide precursor are detected by reacting trifluoroacetic anhydride (which reacts quantitatively with amino groups) with the polyimide precursor composition. That is, the terminal amino groups of the polyimide precursor are trifluoroacetylated with trifluoroacetic anhydride. After the treatment, the polyimide precursor is purified by reprecipitation or the like to remove excess trifluoroacetic anhydride and trifluoroacetic acid residues. For the polyimide precursor after the treatment, the amount of fluorine atoms introduced in the polyimide precursor is quantified by nuclear magnetic resonance ( ¹⁹ F-NMR), and the amount of terminal amino groups of the polyimide precursor is measured.

The number average molecular weight of the polyimide precursor is preferably 5,000 or more and 100,000 or less, more preferably 7,000 or more and 50,000 or less, and further preferably 10,000 or more and 30,000 or less.
When the number average molecular weight of the polyimide precursor is within the above range, the solubility of the polyimide precursor in the composition and the mechanical properties of the film formed are good.
By adjusting the molar equivalent ratio between the tetracarboxylic dianhydride and the diamine compound, a polyimide precursor having a desired number average molecular weight can be obtained.

The number average molecular weight of the polyimide precursor is measured by gel permeation chromatography (GPC) under the following measurement conditions.
Column: Tosoh TSKgel α-M (7.8 mm I.D. x 30 cm)
Eluent: DMF (dimethylformamide) / 30 mM LiBr / 60 mM phosphoric acid Flow rate: 0.6 mL / min
Injection volume: 60 μL
Detector: RI (Differential Refractive Index Detector)

The content (concentration) of the polyimide precursor may be from 0.1% by mass to 40% by mass, preferably from 0.5% by mass to 25% by mass, and more preferably from 1% by mass to 20% by mass, based on the total polyimide precursor composition.

-Method for producing polyimide precursor composition-
The method for producing the polyimide precursor composition is not particularly limited. For example, a method for obtaining a polyimide precursor by polymerizing the above-mentioned tetracarboxylic dianhydride and a diamine compound in a solvent containing at least one solvent selected from the group consisting of a urea-based solvent, an alkoxy group-containing amide-based solvent, and an ester group-containing amide-based solvent can be mentioned.

The reaction temperature during the polymerization reaction of the polyimide precursor may be, for example, 0° C. or higher and 70° C. or lower, preferably 10° C. or higher and 60° C. or lower, and more preferably 20° C. or higher and 55° C. or lower. By setting the reaction temperature at 0° C. or higher, the progress of the polymerization reaction is promoted, the time required for the reaction is shortened, and the productivity is easily improved. On the other hand, if the reaction temperature is set to 70° C. or lower, the progress of the imidization reaction occurring within the molecules of the generated polyimide precursor is suppressed, and precipitation or gelation due to a decrease in the solubility of the polyimide precursor is easily suppressed.
The time for the polymerization reaction of the polyimide precursor is preferably in the range of 1 hour to 24 hours, depending on the reaction temperature.

[Examples of using resin film]
The resin film according to this embodiment can be used as an endless belt.
The resin film according to the present embodiment can be used as a functional layer of a part called Dynamic Flex in a flexible printed circuit (FPC), which is repeatedly bent during the product's life cycle. Examples of Dynamic Flex include hard disk drives, optical pickups, and hinges of mobile phones.
In addition, the resin film according to the embodiment can be used as an electrical insulating material, a pipe covering material, an electromagnetic wave insulating material, a heat source insulator, and an electromagnetic wave absorbing film.

<Endless belt>
The endless belt according to the present embodiment is made of the resin film according to the present embodiment, that is, the endless belt according to the present embodiment has a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents, and the content of the solvent is more than 2200 ppm and not more than 10000 ppm based on the entire resin layer.
The endless belt according to the present embodiment can be used, for example, as an endless belt for an electrophotographic image forming apparatus. Examples of the endless belt for an electrophotographic image forming apparatus include an intermediate transfer belt, a transfer belt (recording medium conveying belt), a fixing belt (heating belt, pressure belt), a conveying belt (recording medium conveying belt), etc. The endless belt according to the present embodiment can be used, in addition to the endless belt for an image forming apparatus, as a belt-shaped member such as a conveying belt, a driving belt, a laminate belt, an electric insulating material, a pipe covering material, an electromagnetic wave insulating material, a heat source insulator, and an electromagnetic wave absorbing film.

<Image forming apparatus>
The image forming apparatus according to the present embodiment includes the endless belt described above. When the endless belt is used as a belt such as an intermediate transfer belt, a transfer belt, or a conveyor belt (a recording medium conveyor belt), the image forming apparatus according to the present embodiment may be, for example, the image forming apparatus shown below.
Examples of the image carrier include an image carrier, a charging device that charges the surface of the image carrier, an electrostatic image forming device that forms an electrostatic image on the surface of the charged image carrier, a developing device that develops the electrostatic image formed on the surface of the image carrier into a toner image using a developer containing toner, and a transfer device that transfers the toner image to the surface of a recording medium via the endless belt according to this embodiment.
The transfer device may include an endless belt unit, which will be described later.

In the image forming apparatus according to this embodiment, it is preferable that at least one selected from the group consisting of the transfer device and the fixing device has the endless belt according to this embodiment.

When the fixing device has the endless belt according to this embodiment, the image forming apparatus according to this embodiment has, for example, a transfer device that includes an intermediate transfer body, a primary transfer device that performs primary transfer of a toner image formed on an image carrier to the intermediate transfer body, and a secondary transfer device that performs secondary transfer of the toner image transferred to the intermediate transfer body to a recording medium, and the intermediate transfer body includes the endless belt according to this embodiment.

When the fixing device has the endless belt according to the present embodiment, the image forming apparatus according to the present embodiment is preferably applied to a belt such as a fixing belt (heating belt, pressure belt) etc. Specific examples of the image forming apparatus include the following.
The configuration may include an image carrier, a charging device that charges the surface of the image carrier, an electrostatic image forming device that forms an electrostatic image on the surface of the charged image carrier, a developing device that develops the electrostatic image formed on the surface of the image carrier as a toner image with a developer containing toner, a transfer device that transfers the toner image to a recording medium, and a fixing device that fixes the toner image to the recording medium. The fixing device may include a first rotating body and a second rotating body that is disposed in contact with the outer surface of the first rotating body, and at least one of the first rotating body and the second rotating body is the endless belt of this embodiment.

The image forming apparatus according to this embodiment may also be configured to include, for example, a recording medium transport body (recording medium transport belt) for the transfer device to transport the recording medium, and a transfer device for transferring the toner image formed on the image carrier to the recording medium transported by the recording medium transport body, and the endless belt according to this embodiment may be included as the recording medium transport body.

Examples of the image forming apparatus according to this embodiment include a normal monochromatic image forming apparatus that contains only a single color toner in the developing device, a color image forming apparatus that performs repeated primary transfer of a toner image held on an image holder onto an intermediate transfer body, and a tandem-type color image forming apparatus in which multiple image holders equipped with developing devices for each color are arranged in series on an intermediate transfer body.

The image forming device according to this embodiment will be described below with reference to the drawings.

Fig. 1 is a schematic diagram showing an example of an image forming apparatus according to the present embodiment. The image forming apparatus shown in Fig. 1 is an image forming apparatus in which the endless belt according to the present embodiment is used as an intermediate transfer body (intermediate transfer belt).
1, the image forming apparatus 100 according to the present embodiment is of a so-called tandem type, and includes charging devices 102a to 102d, exposure devices 114a to 114d, developing devices 103a to 103d, primary transfer devices (primary transfer rolls) 105a to 105d, and image carrier cleaning devices 104a to 104d, which are arranged around the four image carriers 101a to 101d, which are electrophotographic photosensitive members, in the order of their rotation direction. Note that a static eliminator may be provided to remove residual potential remaining on the surfaces of the image carriers 101a to 101d after transfer.

The intermediate transfer belt 107 is supported by the support rolls 106a to 106d, the drive roll 111, and the opposing roll 108 while being tensioned, forming an endless belt unit 107b. The intermediate transfer belt 107 can move the image carriers 101a to 101d and the primary transfer rolls 105a to 105d in the direction of arrow A while contacting the surfaces of the image carriers 101a to 101d, by the support rolls 106a to 106d, the drive roll 111, and the opposing roll 108. The area where the primary transfer rolls 105a to 105d contact the image carriers 101a to 101d via the intermediate transfer belt 107 becomes the primary transfer area, and a primary transfer voltage is applied to the contact area between the image carriers 101a to 101d and the primary transfer rolls 105a to 105d.

As a secondary transfer device, the counter roll 108 and the secondary transfer roll 109 are arranged facing each other through the intermediate transfer belt 107 and the secondary transfer belt 116. The secondary transfer belt 116 is supported by the secondary transfer roll 109 and the support roll 106e. A recording medium 115 such as paper moves in the direction of arrow B in the area sandwiched between the intermediate transfer belt 107 and the secondary transfer roll 109 while contacting the surface of the intermediate transfer belt 107, and then passes through the fixing device 110. The area where the secondary transfer roll 109 contacts the counter roll 108 through the intermediate transfer belt 107 and the secondary transfer belt 116 becomes the secondary transfer section, and a secondary transfer voltage is applied to the contact area between the secondary transfer roll 109 and the counter roll 108. In addition, intermediate transfer belt cleaning devices 112 and 113 are arranged so as to contact the intermediate transfer belt 107 after transfer.

In a multi-color image forming apparatus 100 with this configuration, the image carrier 101a rotates in the direction of arrow C, and its surface is charged by the charging device 102a, after which an electrostatic charge image of a first color is formed by an exposure device 114a such as a laser beam. The formed electrostatic charge image is developed (visualized) with a developer containing toner by the developing device 103a, which contains the toner corresponding to that color, to form a toner image. The developing devices 103a to 103d each contain a toner (e.g., yellow, magenta, cyan, black) that corresponds to the electrostatic charge image of each color.

When the toner image formed on the image carrier 101a passes through the primary transfer section, it is electrostatically transferred (primary transfer) onto the intermediate transfer belt 107 by the primary transfer roll 105a. Thereafter, the toner images of the second, third, and fourth colors are sequentially transferred by the primary transfer rolls 105b to 105d so as to be superimposed on the intermediate transfer belt 107 holding the toner image of the first color, and finally a multi-colored multi-toner image is obtained.

The multiple toner images formed on the intermediate transfer belt 107 are electrostatically transferred to the recording medium 115 as they pass through the secondary transfer section. The recording medium 115 with the transferred toner images is transported to the fixing device 110, where it is fixed by heating and/or pressure, and then discharged outside the machine.

After the primary transfer, residual toner is removed from the image carriers 101a to 101d by the image carrier cleaning devices 104a to 104d. Meanwhile, residual toner is removed from the intermediate transfer belt 107 after the secondary transfer by the intermediate transfer belt cleaning devices 112 and 113, in preparation for the next image formation process.

--Image carrier--
As the image carriers 101a to 101d, known electrophotographic photoreceptors are widely used. As the electrophotographic photoreceptor, an inorganic photoreceptor having a photosensitive layer made of an inorganic material, an organic photoreceptor having a photosensitive layer made of an organic material, etc. are used. As the organic photoreceptor, a function-separated organic photoreceptor in which a charge generating layer that generates charges by exposure and a charge transport layer that transports charges are laminated, or a single-layer organic photoreceptor that performs the functions of generating charges and transporting charges is preferably used. Furthermore, as the inorganic photoreceptor, one in which a photosensitive layer is made of amorphous silicon is preferably used.

The shape of the image carrier is not particularly limited, and any known shape, such as a cylindrical drum, sheet, or plate, can be used.

-Charging device-
The charging devices 102a to 102d are not particularly limited, and a wide variety of known chargers are applicable, such as contact chargers using conductive (here, "conductive" in the charging device means, for example, a volume resistivity of less than ¹⁰ Ωcm) or semiconductive (here, "semiconductive" in the charging device means, for example, a volume resistivity of ¹⁰ Ωcm or more and ¹⁰ Ωcm or less) rollers, brushes, films, or rubber blades, and scorotron chargers and corotron chargers that utilize corona discharge. Of these, contact chargers are preferable.

The charging devices 102a to 102d normally apply a direct current to the image carriers 101a to 101d, but may also apply an alternating current superimposed thereon.

--Exposure equipment--
The exposure devices 114a to 114d are not particularly limited, and for example, a known exposure device such as a light source such as a semiconductor laser light, an LED (Light Emitting Diode) light, or a liquid crystal shutter light, or an optical device capable of exposing the surface of the image carriers 101a to 101d in a predetermined image pattern via a polygon mirror from these light sources, is widely used.

-Developing device-
The developing devices 103a to 103d are selected according to the purpose, and examples thereof include known developing devices that use a one-component developer or a two-component developer with a brush or roller or the like for contact or non-contact development.

- Primary transfer roll -
For example, in the case of a single-layer structure, the primary transfer rolls 105a to 105d are made of foamed or non-foamed silicone rubber, urethane rubber, or EPDM, etc., with an appropriate amount of conductive particles such as carbon black blended therein.

--Image carrier cleaning device--
The image carrier cleaning devices 104a to 104d are for removing residual toner adhering to the surfaces of the image carriers 101a to 101d after the primary transfer process, and in addition to a cleaning blade, brush cleaning, roll cleaning, or the like is used. Of these, it is preferable to use a cleaning blade. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.

- Secondary transfer roll -
The layer structure of the secondary transfer roll 109 is not particularly limited, but for example, in the case of a three-layer structure, it is composed of a core layer, an intermediate layer, and a coating layer covering the surface of the core layer. The core layer is a foam such as silicone rubber, urethane rubber, or EPDM with conductive particles dispersed therein, and the intermediate layer is composed of these non-foamed materials. Examples of materials for the coating layer include tetrafluoroethylene-hexafluoropropylene copolymers and perfluoroalkoxy resins. It is desirable for the volume resistivity of the secondary transfer roll 109 to be 10 ⁷ Ωcm or less. It may also be a two-layer structure excluding the intermediate layer.

- Opposing roll -
The opposing roll 108 forms an opposing electrode for the secondary transfer roll 109. The layer structure of the opposing roll 108 may be either a single layer or a multilayer. For example, in the case of a single layer structure, the opposing roll 108 is constituted by a roll in which an appropriate amount of conductive particles such as carbon black is mixed into silicone rubber, urethane rubber, or EPDM. In the case of a two-layer structure, the opposing roll is constituted by a roll in which the outer peripheral surface of an elastic layer made of the above-mentioned rubber material is covered with a high resistance layer.

A voltage of 1 kV or more and 6 kV or less is usually applied to the opposing roll 108 and the core of the secondary transfer roll 109. Instead of applying a voltage to the core of the opposing roll 108, a voltage may be applied to an electrically conductive electrode member in contact with the opposing roll 108 and the secondary transfer roll 109. Examples of the electrode member include a metal roll, a conductive rubber roll, a conductive brush, a metal plate, and a conductive resin plate.

- Fixing device -
As the fixing device 110, for example, a known fixing device such as a heat roller fixing device, a pressure roller fixing device, or a flash fixing device is widely used.

- Intermediate transfer belt cleaning device -
In addition to a cleaning blade, a brush cleaner, a roll cleaner, or the like may be used as the intermediate transfer belt cleaning devices 112 and 113. Among these, it is preferable to use a cleaning blade. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.

Next, an image forming apparatus using the endless belt of this embodiment as a recording medium transport body (paper transport belt) will be described.
2 is a schematic diagram showing another example of an image forming apparatus according to the present embodiment, in which the endless belt according to the present embodiment is used as a recording medium transport body (paper transport belt).

In the image forming apparatus shown in FIG. 2, units Y, M, C, and BK are provided with photoconductor drums (image carriers) 201Y, 201M, 201C, and 201BK, respectively, which rotate in the clockwise direction of the arrow. Around the photoconductor drums 201Y, 201M, 201C, and 201BK, chargers 202Y, 202M, 202C, and 202BK, exposure devices 203Y, 203M, 203C, and 203BK, color developing devices (yellow developing device 204Y, magenta developing device 204M, cyan developing device 204C, and black developing device 204BK), and photoconductor drum cleaning members 205Y, 205M, 205C, and 205BK are arranged.

The units Y, M, C, and BK are arranged in parallel on the paper transport belt 206 in the order of units BK, C, M, and Y, but an appropriate order can be set according to the image formation method, such as the order of units BK, Y, C, and M.

The paper transport belt 206 is supported by belt support rolls 210, 211, 212, and 213 while applying tension from the inner side, forming an endless belt unit 220. The paper transport belt 206 rotates in the counterclockwise direction of the arrow at the same peripheral speed as the photoconductor drums 201Y, 201M, 201C, and 201BK, and is arranged so that a part of the paper transport belt 206 located between the belt support rolls 212 and 213 contacts each of the photoconductor drums 201Y, 201M, 201C, and 201BK. The paper transport belt 206 is equipped with a belt cleaning member 214.

Transfer rolls 207Y, 207M, 207C, and 207BK are disposed inside paper transport belt 206, facing the contact between paper transport belt 206 and photoconductor drums 201Y, 201M, 201C, and 201BK, and form a transfer area in which the toner image is transferred to paper (transferee) 216 via photoconductor drums 201Y, 201M, 201C, and 201BK and paper transport belt 206. Transfer rolls 207Y, 207M, 207C, and 207BK may be disposed directly below photoconductor drums 201Y, 201M, 201C, and 201BK, as shown in FIG. 2, or may be disposed at a position shifted from directly below.

The fixing device 209 is positioned so that the paper is transported after passing through the transfer areas of the paper transport belt 206 and the photoconductor drums 201Y, 201M, 201C, and 201BK.

The paper 216 is transported to the paper transport belt 206 by the paper transport roll 208.

In the image forming apparatus shown in FIG. 2, in unit BK, photoconductor drum 201BK is rotated. In conjunction with this, charger 202BK is driven to charge the surface of photoconductor drum 201BK to the desired polarity and potential. Photoconductor drum 201BK, whose surface has been charged, is then imagewise exposed by exposure unit 203BK, and an electrostatic charge image is formed on the surface.

The electrostatic image is then developed by the black developing device 204BK. As a result, a toner image is formed on the surface of the photoconductor drum 201BK. The developer used here may be either one-component or two-component.

This toner image passes through the transfer area between the photoconductor drum 201BK and the paper transport belt 206, and the paper 216 is electrostatically attracted to the paper transport belt 206 and transported to the transfer area, where it is sequentially transferred onto the surface of the paper 216 by the electric field formed by the transfer bias applied from the transfer roll 207BK.

Then, any toner remaining on the photoconductor drum 201BK is cleaned and removed by the photoconductor drum cleaning member 205BK. The photoconductor drum 201BK is then prepared for the next image transfer.

The above image transfer is also performed in units C, M and Y using the same method.

The paper 216 onto which the toner image has been transferred by the transfer rolls 207BK, 207C, 207M and 207Y is further transported to a fixing device 209 where the toner image is fixed.
In this way, the desired image is formed on the paper.

Next, we will explain an image forming apparatus that uses the endless belt of this embodiment as a fixing belt (heating belt, pressure belt).

An example of an image forming apparatus in which the endless belt according to the present embodiment is used as a fixing belt (heating belt, pressure belt) is an image forming apparatus similar to the image forming apparatus shown in Figures 1 and 2. In the image forming apparatus shown in Figures 1 and 2, a fixing device in which the endless belt according to the present embodiment described later is used is applied as the fixing device 110 or the fixing device 209.
Hereinafter, a fixing device in which the endless belt according to this embodiment is applied as a fixing belt (heating belt, pressure belt) will be described.

- Fixing device -
The fixing device has various configurations, and includes, for example, a first rotating body and a second rotating body disposed in contact with the outer surface of the first rotating body.

As first and second embodiments of the fixing device, a fixing device including a heating belt and a pressure roll will be described below.
The fixing device is not limited to the first and second embodiments, and may be a fixing device including a heating roll or a heating belt and a pressure belt. The endless belt according to the present embodiment may be applied to either the heating belt or the pressure belt.
Furthermore, the fixing device is not limited to the first and second embodiments, and may be an electromagnetic induction heating type fixing device.

First Aspect of Fixing Device A fixing device according to a first aspect will be described below. Fig. 3 is a schematic diagram showing an example of the fixing device according to the first aspect.

As shown in FIG. 3, the fixing device 60 according to the first embodiment is configured to include, for example, a rotating heating roll 61 (an example of a first rotating body), a pressure belt 62 (an example of a second rotating body), and a pressure pad 64 (an example of a pressing member) that presses the heating roll 61 via the pressure belt 62.
The pressing pad 64 may be configured to press the pressure belt 62 and the heating roll 61 relatively. Therefore, the pressure belt 62 side may be pressed against the heating roll 61, or the heating roll 61 side may be pressed against the pressure belt 62.

A halogen lamp 66 (an example of a heating means) is disposed inside the heating roll 61. The heating means is not limited to a halogen lamp, and other heat generating members may be used.

On the other hand, for example, a temperature sensor 69 is placed in contact with the surface of the heating roll 61. Based on the temperature measurement value by this temperature sensor 69, the lighting of the halogen lamp 66 is controlled, and the surface temperature of the heating roll 61 is maintained at the desired set temperature (for example, 150°C).

The pressure belt 62 is supported for free rotation by, for example, a pressure pad 64 and a belt running guide 63 arranged inside. The pressure belt 62 is arranged so as to be pressed against the heating roll 61 by the pressure pad 64 in the pinch region N (nip portion).

The pressure pad 64 is disposed, for example, inside the pressure belt 62 in a state in which it is pressed against the heating roll 61 via the pressure belt 62 , and forms a sandwiching region N between the pressure pad 64 and the heating roll 61 .
The pressure pad 64, for example, has a front clamping member 64a arranged on the entrance side of the clamping area N to ensure a wide clamping area N, and a peeling clamping member 64b arranged on the exit side of the clamping area N to impart distortion to the heating roll 61.

In order to reduce the sliding resistance between the inner circumferential surface of the pressure belt 62 and the pressure pad 64, for example, a sheet-like sliding member 68 is provided on the surfaces of the front clamping member 64a and the peeling clamping member 64b that come into contact with the pressure belt 62. The pressure pad 64 and the sliding member 68 are held by a holding member 65 made of metal.
The sliding member 68 is provided, for example, such that its sliding surface contacts the inner peripheral surface of the pressure belt 62 , and is involved in retaining and supplying the oil present between the sliding member 68 and the pressure belt 62 .

For example, a belt running guide 63 is attached to the holding member 65, and the pressure belt 62 rotates.

The heating roll 61 is rotated in the direction of the arrow S by, for example, a drive motor (not shown), and the pressure belt 62 is driven by this rotation to rotate in the direction of the arrow R, which is opposite to the rotation direction of the heating roll 61. That is, for example, while the heating roll 61 rotates in the clockwise direction in FIG. 3, the pressure belt 62 rotates in the counterclockwise direction.

Then, the paper K (an example of a recording medium) having an unfixed toner image thereon is guided, for example, by the fixing entrance guide 56 and transported to the clamping area N. Then, as the paper K passes through the clamping area N, the toner image on the paper K is fixed by the pressure and heat acting on the clamping area N.

In the fixing device 60 according to the first aspect, for example, a front clamping member 64a having a concave shape conforming to the outer peripheral surface of the heating roll 61 ensures a wider clamping area N than in a configuration without the front clamping member 64a.

In addition, in the fixing device 60 according to the first aspect, for example, the peeling and pinching member 64b is arranged to protrude from the outer peripheral surface of the heating roll 61, so that the distortion of the heating roll 61 is locally increased in the exit area of the pinching region N.

By arranging the peeling and pinching member 64b in this manner, for example, when the paper K after fixing passes through the peeling and pinching area, it passes through a locally formed large distortion, so that the paper K is easily peeled off from the heating roll 61.

As an auxiliary means for peeling, for example, a peeling member 70 is disposed downstream of the pinching region N of the heating roll 61. The peeling member 70 is held by a holding member 72 with the peeling claws 71 in close proximity to the heating roll 61 in a direction opposite to the rotation direction of the heating roll 61 (counter direction).

Second Aspect of Fixing Device A fixing device according to a second aspect will be described below. Fig. 4 is a schematic diagram showing an example of the fixing device according to the second aspect.

As shown in FIG. 4, the fixing device 80 according to the second aspect includes, for example, a fixing belt module 86 having a heating belt 84 (an example of a first rotating body), and a pressure roll 88 (an example of a second rotating body) arranged to press against the heating belt 84 (fixing belt module 86). A pinch region N (nip portion) is formed where the heating belt 84 (fixing belt module 86) and the pressure roll 88 come into contact with each other. In the pinch region N, paper K (an example of a recording medium) is pressurized and heated, and the toner image is fixed.

The fixing belt module 86 includes, for example, an endless heating belt 84, a heating pressure roll 89 around which the heating belt 84 is wound around the pressure roll 88 and which is rotated by the rotational force of a motor (not shown) and presses the heating belt 84 from its inner surface against the pressure roll 88, and a support roll 90 which supports the heating belt 84 from the inside at a position different from the heating pressure roll 89.
The fixing belt module 86 includes, for example, a support roll 92 arranged on the outside of the heating belt 84 and defining its circular path, an attitude correction roll 94 that corrects the attitude of the heating belt 84 from the heating pressure roll 89 to the support roll 90, and a support roll 98 that applies tension to the heating belt 84 from its inner surface downstream of the clamping region N, which is the region where the heating belt 84 (fixing belt module 86) and the pressure roll 88 come into contact with each other.

The fixing belt module 86 is provided, for example, such that a sheet-like sliding member 82 is interposed between the heating belt 84 and the heating pressure roll 89 .
The sliding member 82 is provided, for example, so that its sliding surface is in contact with the inner circumferential surface of the heating belt 84 , and is involved in the retention and supply of oil present between the sliding member 82 and the heating belt 84 .
Here, the sliding member 82 is provided in a state in which both ends thereof are supported by support members 96, for example.

Inside the heating pressure roll 89, for example, a halogen heater 89A (an example of a heating means) is provided.

The support roll 90 is, for example, a cylindrical roll made of aluminum, and has a halogen heater 90A (an example of a heating means) disposed therein so as to heat the heating belt 84 from the inner peripheral surface side.
At both ends of the support roll 90, for example, spring members (not shown) are provided to press the heating belt 84 outward.

The support roll 92 is a cylindrical roll made of, for example, aluminum, and a release layer made of fluororesin and having a thickness of 20 μm is formed on the surface of the support roll 92 .
The release layer of the support roll 92 is formed, for example, to prevent toner and paper powder from the outer circumferential surface of the heating belt 84 from accumulating on the support roll 92 .
Inside the support roll 92, for example, a halogen heater 92A (an example of a heat source) is disposed, and the heating belt 84 is heated from the outer circumferential surface side.

In other words, for example, the heating belt 84 is heated by the heating pressure roll 89 and the support rolls 90 and 92.

The posture correction roll 94 is, for example, a cylindrical roll made of aluminum, and an end position measuring mechanism (not shown) that measures the end position of the heating belt 84 is disposed near the posture correction roll 94.
The posture correction roll 94 is provided with an axial displacement mechanism (not shown) that displaces the contact position in the axial direction of the heating belt 84 in accordance with the measurement results of the end position measurement mechanism, and is configured to control the meandering of the heating belt 84.

On the other hand, the pressure roll 88 is supported so as to be rotatable, and is pressed against the portion of the heating belt 84 wound around the heating pressure roll 89 by a biasing means such as a spring (not shown). As a result, as the heating belt 84 (heating pressure roll 89) of the fixing belt module 86 rotates in the direction of arrow S, the pressure roll 88 rotates in the direction of arrow R, following the heating belt 84 (heating pressure roll 89).

Then, the paper K having the unfixed toner image (not shown) is transported in the direction of the arrow P and guided to the clamping area N of the fixing device 80, where the toner image is fixed by the pressure and heat acting on the clamping area N.

In the fixing device 80 according to the second embodiment, a halogen heater (halogen lamp) is used as an example of a heat source. However, the present invention is not limited to this. Radiant lamp heating elements (heating elements that emit radiation (infrared rays, etc.)) other than halogen heaters, and resistive heating elements (heating elements that generate Joule heat by passing a current through a resistor: for example, a ceramic substrate on which a resistive film is formed and then fired) may also be used.

<Endless belt unit>
An example of an endless belt unit according to the present embodiment includes an endless belt according to the present embodiment and a plurality of rolls around which the endless belt is stretched under tension.

In addition, the endless belt unit of this embodiment includes, for example, endless belt unit 107b shown in FIG. 1 and endless belt unit 220 shown in FIG. 2, a cylindrical member and a number of rolls around which the cylindrical member is stretched under tension.

For example, an endless belt unit according to the present embodiment may be an endless belt unit shown in FIG.
FIG. 5 is a schematic perspective view showing the endless belt unit according to the present embodiment.
As shown in FIG. 5, the endless belt unit 130 according to this embodiment includes the endless belt 30 according to the above-described embodiment. For example, the endless belt 30 is stretched under tension between a driving roll 131 and a driven roll 132 arranged opposite each other.
Here, in the endless belt unit 130 according to this embodiment, when the endless belt 30 is used as an intermediate transfer body, the endless belt unit 130 may be provided with rolls supporting the endless belt 30, such as a roll for performing the primary transfer of a toner image on the surface of a photoconductor (image carrier) onto the endless belt 30, and a roll for performing the secondary transfer of the toner image transferred onto the endless belt 30 onto a recording medium.
The number of rolls supporting the endless belt 30 is not limited, and may be arranged according to the mode of use. The endless belt unit 130 having the above configuration is incorporated into an apparatus and used, and rotates in a state supporting the endless belt 30 as the driving roll 131 and the driven roll 132 rotate.

The following examples are provided, but the present invention is not limited to these examples.

Example 1
(Preparation of polyimide precursor composition)
200 g of tetramethylurea, a urea-based solvent, was added as a solvent to a flask equipped with a stirrer, a thermometer, and a dropping funnel. 20.20 g of p-phenylenediamine was added as a diamine compound, and the mixture was stirred at 20° C. for 10 minutes. 21.38 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added as an aromatic tetracarboxylic dianhydride to the solution, and the mixture was dissolved and reacted by stirring for 24 hours while maintaining the reaction temperature at 40° C., to obtain a polyimide precursor composition containing a polyimide precursor.

(Coating film forming process and drying process)
The prepared polyimide precursor composition was applied to the outer surface of a cylindrical aluminum mold (substrate) and rotary dried at 150° C. for 30 minutes.
(Firing process)
Next, this mold was heated in an oven at 300° C. for 1 hour while rotating at 20 rpm, and then removed from the oven.
(Removal process)
The polyimide resin molded body formed on the outer peripheral surface of the mold was removed from the mold to obtain an endless belt having a resin layer with a thickness of 0.08 mm.

<Examples 2 to 21 and Comparative Examples 1 to 5>
An endless belt was obtained in the same manner as in Example 1, except that the type of solvent in (Preparation of polyimide precursor composition) and the oven temperature and heating time in (Baking step) were changed as shown in Table 1.

<Examples 22 to 27>
An endless belt was obtained in the same manner as in Example 4, except that the type of diamine compound in (Preparation of polyimide precursor composition) was changed as shown in Table 2.

<Evaluation>
The tensile breaking strength and number of times of folding resistance by the MIT test of the endless belt obtained in each example were measured according to the procedure described above, and the results are shown in Table 1. In addition, A to D in the column of the number of times of folding resistance by the MIT test were described according to the following standards.
-standard-
The percentage (%) of the actual measured value [(actual measured value of number of times that the specimen can withstand folding in the MIT test ÷ target value of number of times that the specimen can withstand folding in the MIT test) × 100] was calculated when the target value of the number of times that the specimen can withstand folding in the MIT test (300,000 times) was taken as 100, and based on this value, one of A to D was recorded in Table 1 according to the following criteria.
AA: 230%≦actual value ratio A: 200%≦actual value ratio<230%
B: 120%≦actual value ratio<200%
C: 100%≦actual value ratio<120%
D: Percentage of actual measurement value < 100%

The number of times that the MIT test can endure folding is the number of times that a strip-shaped test piece obtained from an endless belt can be repeatedly bent, as described above, until it breaks. Since breakage is caused by the occurrence of cracks at the bends, the greater the number of times that the MIT test can endure folding, the more unlikely it is that the endless belt will crack at the bends when it is repeatedly bent.

The abbreviations in Tables 1 and 2 are as follows.
Solvent type Urea: Urea-based solvent Alkoxyamide: Amide-based solvent containing an alkoxy group Esteramide: Amide-based solvent containing an ester group

The above results show that the endless belt of this embodiment is an endless belt that suppresses the occurrence of cracks at the bent portion even when repeatedly bent.

In addition, when a resin film was produced according to the production conditions of the endless belt of each example, and the tensile breaking strength and the number of times it could be broken by the MIT test were measured, the same results were obtained as for the endless belt of each example. This shows that the resin film also suppresses the occurrence of cracks at the bent parts even when repeatedly bent.

<Resin film>
(Coating film forming process and drying process)
The prepared polyimide precursor composition was applied onto a glass plate (substrate) with a bar coater and dried at 150° C. for 30 minutes.
(Firing process)
The glass plate was then heated in an oven and then removed from the oven.
(Removal process)
The polyimide resin film formed on the glass plate was peeled off from the glass plate to obtain a resin film having a thickness of 0.08 mm.

(((1))) A resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents,
A resin film having a solvent content of more than 2200 ppm and not more than 10000 ppm relative to the entire resin layer.
(((2))) The resin film according to (((1))), wherein the solvent is at least one selected from the group consisting of alkoxy group-containing amide solvents and ester group-containing amide solvents.
(((3))) the alkoxy group-containing amide solvent is at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide and 3-n-butoxy-N,N-dimethylpropanamide,
The resin film according to (((2))), wherein the ester group-containing amide solvent is methyl 5-dimethylamino-2-methyl-5-oxo-pentanoate.
(((4))) The resin film according to any one of (((1))) to (((3))), wherein the solvent is 3-methoxy-N,N-dimethylpropanamide.
((((5)))) the resin layer comprises a polyimide resin having a structural unit derived from phenylenediamine and a structural unit derived from diaminodiphenyl ether,
The resin film according to any one of (((1))) to (((4))), wherein a content ratio of the structural units derived from the phenylenediamine and the structural units derived from the diaminodiphenyl ether in the polyimide resin (structural units derived from phenylenediamine/structural units derived from diaminodiphenyl ether) is, in terms of a molar ratio, 80/20 or more and 99.7/0.3 or less.
(((6))) The resin film according to any one of (((1))) to (((5))), wherein the content of the solvent is 2500 ppm or more and 9000 ppm or less with respect to the entire resin layer.
(((7))) The resin film according to (((6))), wherein the content of the solvent is 6000 ppm or more and 7000 ppm or less with respect to the entire resin layer.
(((8))) The resin film according to any one of (((1))) to (((7))), wherein the boiling point of the solvent is 200° C. or higher and 260° C. or lower.
(((9))) The resin film according to any one of (((1))) to (((8))), which has a folding resistance of 300,000 or more times in an MIT test using a clamp having a radius of curvature R of 2 mm.
(((10))) A resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents,
A resin film having a tensile breaking strength of 350 N/ ^mm2 or more.
(((11))) An endless belt made of the resin film according to any one of (((1))) to (((10))).
((11))) An image forming apparatus comprising the endless belt described in ((11)).
(((12))) an image carrier; and
a charging device for charging the surface of the image carrier;
an electrostatic image forming device for forming an electrostatic image on a surface of a charged image carrier;
a developing device that develops the electrostatic image formed on the surface of the image carrier into a toner image by using a developer containing a toner;
A transfer device that transfers the toner image onto a recording medium;
A fixing device that fixes the toner image onto the recording medium,
At least one selected from the group consisting of the transfer device and the fixing device has the endless belt according to ((11))).

According to the invention (((1))), there is provided a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, in which the occurrence of cracks in bent portions is suppressed even when the resin film is repeatedly bent, compared to a case in which the solvent content is 2200 ppm or less or exceeds 10000 ppm with respect to the entire resin layer.
According to the invention pertaining to ((2)), ((3))) or ((4)), there is provided a resin film in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, as compared to the case in which the solvent is a urea-based solvent.
According to the invention (((5))), there is provided a resin film in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared with a case in which the content ratio of phenylenediamine-derived structural units and diaminodiphenyl ether-derived structural units in the polyimide resin (phenylenediamine-derived structural units/diaminodiphenyl ether-derived structural units) is less than 80/20 or more than 99.7/0.3 in molar ratio.
According to the invention (((6))), a resin film is provided in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared to cases in which the solvent content is less than 2500 ppm or more than 9000 ppm.
According to the invention (((7))), a resin film is provided in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared to cases in which the solvent content is less than 6000 ppm or more than 7000 ppm.
According to the invention (((8))), there is provided a resin film in which the occurrence of cracks at bent portions is suppressed even when the film is repeatedly bent, compared to cases in which the boiling point of the solvent is less than 200°C or more than 280°C.
According to the invention (((9))), there is provided a resin film which is less susceptible to cracking at bent portions even when bent repeatedly, as compared to a case in which the number of folds tolerable is less than 300,000 in an MIT test using a clamp with a radius of curvature R of 2 mm.
According to the invention (((10))), there is provided a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, in which the occurrence of cracks at bent portions is suppressed even when the resin film is repeatedly bent, compared to a resin film having a tensile breaking strength of less than 270 N/ ^mm2 .
According to the invention (((11))), there is provided an endless belt in which, in a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, the occurrence of cracks in bending portions is suppressed even when the resin film is repeatedly bent, compared to an endless belt made of a resin film having a solvent content of 2200 ppm or less or exceeding ¹⁰⁰⁰⁰ ppm, relative to the entire resin layer, or compared to an endless belt made of a resin film having a tensile breaking strength of less than 270 N/mm2.
According to the invention related to (((12))) or (((13))), there is provided an image forming apparatus equipped with an endless belt in which, in a resin film having a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy group-containing amide-based solvents, and ester group-containing amide-based solvents, the occurrence of cracks at bent portions is suppressed even when the resin film is repeatedly bent, compared to an endless belt made of a resin film having a solvent content of ²²⁰⁰ ppm or less or exceeding 10000 ppm relative to the entire resin layer, or an endless belt made of a resin film having a tensile breaking strength of less than 270 N/mm2.

60 Fixing device, 61 Heating roll, 62 Pressure belt, 63 Belt running guide, 64 Pressing pad, 64a Front pinching member, 64b Peeling pinching member, 65 Holding member, 66 Halogen lamp, 68 Sliding member, 69 Temperature-sensitive element, 70 Peeling member, 71 Peeling claw, 72 Holding member, 80 Fixing device, 82 Sliding member, 84 Heating belt, 86 Fixing belt module, 88 Pressure roll, 89A Halogen heater, 89 Heating pressure roll, 90A Halogen heater, 90 Support roll, 92A Halogen heater, 92 Support roll, 94 Posture correction roll, 96 Support member, 98 Support roll, 100 Image forming device, 101a to 101d Image carrier, 102a to 102d Charging device (charging means), 103a to 103d, 204Y, 204M, 204C, 204BK Developing device (developing means), 104a to 104d Image carrier cleaning device, 105a to 105d Primary transfer roll, 106a to 106e Support roll, 107 Intermediate transfer belt, 107b, 130, 220 Endless belt unit, 108 Opposed roll, 109 Secondary transfer roll, 110, 209 Fixing device (fixing means), 111 Drive roll, 112, 113 Intermediate transfer belt cleaning device, 114a to 114d Exposure device (latent image forming means) 115 Recording medium, 116 Secondary transfer belt, 201Y, 201M, 201C, 201BK Photoconductor drum (image carrier), 202Y, 202M, 202C, 202BK Charger (charging means), 203Y, 203M, 203C, 203BK Exposure device (latent image forming means), 205Y, 205M, 205C, 205BK Photoconductor drum cleaning member, 206 Paper conveying belt, 207Y, 207M, 207C, 207BK Transfer roll (transfer means), 214 Belt cleaning member, 216 Paper (recording medium)

Claims (13)

a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents;
A resin film having a solvent content of more than 2200 ppm and not more than 10000 ppm relative to the entire resin layer. The resin film according to claim 1, wherein the solvent is at least one selected from the group consisting of alkoxy group-containing amide solvents and ester group-containing amide solvents. the alkoxy group-containing amide solvent is at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide and 3-n-butoxy-N,N-dimethylpropanamide,
3. The resin film according to claim 2, wherein the ester group-containing amide solvent is methyl 5-dimethylamino-2-methyl-5-oxo-pentanoate. The resin film according to claim 1, wherein the solvent is 3-methoxy-N,N-dimethylpropanamide. the resin layer contains a polyimide resin having a structural unit derived from phenylenediamine and a structural unit derived from diaminodiphenyl ether,
2. The resin film according to claim 1, wherein a content ratio of the structural units derived from the phenylenediamine and the structural units derived from the diaminodiphenyl ether in the polyimide resin (structural units derived from phenylenediamine/structural units derived from diaminodiphenyl ether) is, in terms of a molar ratio, 80/20 or more and 99.7/0.3 or less. The resin film according to claim 1, wherein the content of the solvent is 2500 ppm or more and 9000 ppm or less with respect to the entire resin layer. The resin film according to claim 6, wherein the content of the solvent is 6000 ppm or more and 7000 ppm or less with respect to the entire resin layer. The resin film according to claim 1, wherein the boiling point of the solvent is 200°C or higher and 280°C or lower. The resin film according to claim 1, which has a folding resistance of 300,000 or more times in an MIT test using a clamp with a curvature radius R of 2 mm. a resin layer containing at least one solvent selected from the group consisting of urea-based solvents, alkoxy-group-containing amide-based solvents, and ester-group-containing amide-based solvents;
A resin film having a tensile breaking strength of 270 N/ ^mm2 or more. An endless belt made of the resin film according to any one of claims 1 to 10. An image forming device equipped with the endless belt according to claim 11. An image carrier;
a charging device for charging the surface of the image carrier;
an electrostatic image forming device for forming an electrostatic image on a surface of a charged image carrier;
a developing device that develops the electrostatic image formed on the surface of the image carrier into a toner image by using a developer containing a toner;
A transfer device that transfers the toner image onto a recording medium;
A fixing device that fixes the toner image onto the recording medium,
12. An image forming apparatus, wherein at least one selected from the group consisting of the transfer device and the fixing device comprises the endless belt according to claim 11.