JP2022192011A - Belt for electrophotography, electrophotographic image forming apparatus, and varnish for fixing device - Google Patents

Abstract

An electrophotographic belt having high thermal conductivity in the thickness direction and high tensile strength in the circumferential direction and in a direction orthogonal to the circumferential direction is provided. The endless belt for electrophotography has a base material, the base material contains a polyimide resin and carbon nanotubes, and the content of the carbon nanotubes in the base material is the total amount of the polyimide resin. product, the tensile strength in the circumferential direction and in the direction perpendicular to the circumferential direction of the substrate is 200 MPa or more, and the thermal conductivity in the thickness direction of the substrate is 0. .9 W/m·K or more. [Selection drawing] Fig. 4

Description

The present disclosure relates to an electrophotographic belt, an electrophotographic image forming apparatus, a fixing device and a varnish.

Polyimide resin has excellent mechanical strength, heat resistance, and insulating properties. It is suitably used as a fixing belt for heat-fixing a transferred toner image.

For example, as a belt (film) heating type fixing device, there is one having the following configuration. That is, there is a fixing device having an endless fixing belt and a pressing member arranged opposite to the fixing belt and forming a fixing nip portion together with the fixing belt. In such a fixing device, the fixing belt transfers heat supplied to the fixing belt from a heater arranged inside the fixing belt to the toner on the recording material at the fixing nip portion. is melted and fixed to the recording material.

As described above, the fixing belt is constantly heated during the process of forming an electrophotographic image, and is bent each time it passes through the fixing nip portion. Therefore, the base material of the fixing belt is required to have high mechanical strength (for example, high bending resistance such that cracks do not occur even when repeatedly bent) and sufficient heat resistance. A polyimide resin is a resin that provides a base material having both sufficient heat resistance and high mechanical strength. However, resin has several orders of magnitude lower thermal conductivity than metals and ceramics. Therefore, a fixing belt having a base material made of polyimide resin is disadvantageous compared to a fixing belt having a base material made of metal or ceramic in terms of efficiently transferring heat from a heater to toner. That is, in a fixing belt having a base material made of polyimide resin, the printing speed can be further increased, the power consumption required for supplying heat to the heater can be further reduced (energy saving), and the fixing device can be made more efficient. In order to meet the demand for further miniaturization, it is important to improve the thermal conductivity in the thickness direction.

Inorganic fillers with excellent thermal conductivity are used in order to reduce power consumption, increase fixing speed, and lower fixing temperature by increasing the thermal conductivity of the polyimide resin-based fixing belt. It is disclosed to contain (Patent Document 1).

However, in order to obtain a substrate with high thermal conductivity, it is necessary to increase the content of such fillers in the substrate. When the content of the filler in the base material is increased, the mechanical strength of the base material may decrease even if a polyimide resin having excellent strength is used as the binder resin. That is, as shown in each example of Patent Document 2, when the content of carbon nanotubes in the polyimide base material is increased, the mechanical strength of the polyimide base material may decrease.

JP-A-8-80580 JP 2004-123867 A

One aspect of the present disclosure is directed to providing an endless electrophotographic belt having high thermal conductivity in the thickness direction and high tensile strength in the circumferential direction and the direction perpendicular to the circumferential direction. be. Another aspect of the present disclosure is directed to providing a fixing device and an electrophotographic image forming apparatus capable of forming a high-quality electrophotographic image. Furthermore, one aspect of the present disclosure is to provide a varnish that can provide an endless-shaped polyimide film that has high thermal conductivity in the thickness direction and high tensile strength in the circumferential direction and in a direction perpendicular to the circumferential direction. It is aimed at

According to one aspect of the present disclosure, there is provided an endless electrophotographic belt comprising a substrate, the substrate comprising a polyimide resin and carbon nanotubes, wherein the substrate contains: The content of the carbon nanotubes is 15% by volume or less with respect to the total volume of the polyimide resin, the tensile strength in the circumferential direction of the substrate and in the direction perpendicular to the circumferential direction is 200 MPa or more, and An electrophotographic belt is provided in which the thermal conductivity in the thickness direction of the material is 0.9 W/m·K or more.

According to another aspect of the present disclosure, there is provided a fixing device comprising a fixing belt and a pressurizing rotating body arranged to face the fixing belt, wherein the fixing belt is the electrophotographic belt described above. provided. According to another aspect of the present disclosure, there is provided an electrophotographic image forming apparatus including the fixing device described above. According to still another aspect of the present disclosure, a varnish containing a polyamic acid, a solvent for the polyamic acid, carbon nanotubes, and a compound having a surface tension difference between the solvent and the solvent of 4 mN/m or more and 17 mN/m or less. provided.

According to one aspect of the present disclosure, it is possible to obtain an endless electrophotographic belt having high thermal conductivity in the thickness direction and high tensile strength in the circumferential direction and in a direction orthogonal to the circumferential direction. . Further, according to one aspect of the present disclosure, it is possible to obtain a fixing device and an electrophotographic image forming apparatus capable of forming a high-quality electrophotographic image. Furthermore, one aspect of the present disclosure is to obtain a varnish that provides an endless-shaped polyimide film that has high thermal conductivity in the thickness direction and exhibits high tensile strength in the circumferential direction and in a direction perpendicular to the circumferential direction. can.

2 is a schematic cross-sectional view of a fixing belt used in this embodiment; FIG. 1 is a schematic cross-sectional view of a fixing device used in this embodiment; FIG. 1 is a schematic cross-sectional view of an electrophotographic image forming apparatus used in this example; FIG. 4 is an X-ray diffraction pattern of a base material according to one example of the present embodiment.

This embodiment is an example for carrying out the present disclosure, and the present disclosure is not limited to this embodiment.
An electrophotographic belt according to one aspect of the present disclosure has a base material having an endless shape and containing a polyimide resin. The tensile strength of the substrate in the circumferential direction and in the direction perpendicular to the circumferential direction is 200 MPa or more, more preferably 230 MPa or more. By providing such tensile strength, durability against bending when used as an electrophotographic belt is sufficient.
Further, the base material contains carbon nanotubes (hereinafter sometimes referred to as "CNT"), and the ratio of CNTs to the total volume of the polyimide resin is 15% by volume or less. By suppressing the amount of CNTs in the base material to 15% by volume or less, the base material containing the polyimide resin can have the above tensile strength.

On the other hand, the substrate has a thermal conductivity in the thickness direction of 0.9 W/m·K or more, more preferably 1.0 W/m·K or more. Since the heat conductivity in the thickness direction of the base material is 0.9 W/m·K or more, the heat from the heater can be efficiently heated when the belt is used as an electrophotographic belt, especially as a fixing belt. It can be transmitted to the unfixed toner that is the target.

Here, the substrate according to one aspect of the present disclosure has a CNT content of 15% by volume or less with respect to the polyimide resin from the viewpoint of making the tensile strength in the circumferential direction and in the direction perpendicular to the circumferential direction 200 MPa or more. doing. Normally, with this level of CNT content, it is difficult to keep the thermal conductivity in the thickness direction of the substrate within the above range. However, as a result of examination by the present inventors, when the X-ray diffraction peak intensity ratio I(002)/I(100) detected by the reflection X-ray diffraction method of the CNT-blended polyimide base material is 35 or less, It has been found that a substrate having a thermal conductivity in the thickness direction of 0.9 W/m·K or more can be obtained while the content of CNTs in the polyimide resin is 15% by volume or less. Here, I(002) is the intensity of the diffraction peak derived from the (002) crystal face of CNT, and I(100) is the intensity of the diffraction peak derived from the (100) crystal face of CNT.

When the surface of the substrate is measured by a reflection X-ray diffraction method, the intensity of the diffraction peak derived from the (100) crystal plane of the carbon nanotube is defined as I (100), and the intensity of the diffraction peak derived from the (002) crystal plane of the carbon nanotube. When I (002) is the intensity of the diffraction peak, I (002) / I (100) is 35 or less, so that the thermal conductivity in the thickness direction of the base material is 0.9 W / m K or more. The inventors of the present invention presume the reason why this is possible.
In a polyimide base material containing CNTs, the CNTs tend to line up in the in-plane direction of the base material. CNTs have the property of easily conducting heat in their own longitudinal direction, and in a substrate in which the CNTs are arranged in the in-plane direction, the thermal conductivity is high in the in-plane direction and low in the thickness direction of the substrate. The X-ray diffraction peak intensity I(002) is proportional to the amount of CNTs aligned in the in-plane direction. Therefore, in a base material with a strong X-ray diffraction peak intensity I(002), most of the CNTs are arranged in the in-plane direction. Therefore, the thermal conductivity in the thickness direction of the substrate is low. On the contrary, the X-ray diffraction peak intensity I(002) becomes weaker as the CNTs are oriented in the thickness direction of the substrate. Therefore, the weaker the X-ray diffraction peak intensity I(002), the higher the thermal conductivity of the substrate in the thickness direction.

By the way, I(002) may be affected by the amount of CNT blended and the thickness of the substrate. On the other hand, I(100) is derived from the 6-membered carbon ring structure that constitutes the CNT, and therefore is not easily affected by the orientation direction of the CNT in the substrate. Therefore, by taking the X-ray diffraction peak intensity ratio I(002)/I(100) of I(002) based on I(100), the effects of the CNT compounding amount and the substrate thickness are eliminated. It can be used as an index of the state of alignment of CNTs in the substrate.

From the above, the polyimide base material having an X-ray diffraction peak intensity ratio I (002) / I (100) of 35 or less has a state in which the CNTs, which tend to line up in the in-plane direction of the base material, are oriented in the thickness direction. I can say. Therefore, a polyimide substrate having an X-ray diffraction peak intensity ratio I(002)/I(100) of 35 or less is a polyimide substrate having an X-ray diffraction peak intensity ratio I(002)/I(100) of greater than 35. In comparison, it has a high thermal conductivity in the thickness direction.

Here, the CNT in the present disclosure has a ratio (g/d) between the intensity g of the G band and the intensity d of the D band in its Raman spectroscopy spectrum of 10 or more, more preferably 15 or more. Although the details will be described later, CNTs with a small g/d ratio contain many defects in the graphite structure composed of ^sp2 carbon, which impedes lattice vibration and lowers the thermal conductivity of the CNTs themselves. Therefore, regardless of the orientation state of CNTs in the substrate, that is, the value of the X-ray diffraction peak intensity ratio I(002)/I(100), the thermal conductivity cannot be within the above range.

Next, a method for obtaining a state in which the CNTs are oriented in the thickness direction of the polyimide base material will be described. Specifically, a small amount of a specific organic compound is blended in advance with a varnish in which CNTs are dispersed (also referred to as a "polyimide precursor solution"). When the varnish film is heated to cyclodehydrate (imidize) to form a polyimide resin film, the CNTs, which tend to line up in the in-plane direction of the film, are effectively disturbed in the thickness direction by the organic compound. Since it is solidified, high thermal conductivity can be imparted in the thickness direction even with a small blending ratio of CNTs. More specifically, a small amount of an organic compound such as 2,4-dimethyl-3-pentanone, 2-methylsulfonylethanol, or o-chlorophenol is blended in advance with a varnish in which CNTs are dispersed. Although the mechanism is not clear, it is thought to be as follows. In the process of heating the varnish film to evaporate the solvent, evaporation of these organic compounds creates a microscopic surface tension difference at the gas-liquid interface of the solution, generating convection. It is considered that the CNTs aligned in the in-plane direction of the film are oriented in the thickness direction due to this convection.

That is, the substrate containing the polyimide resin in the present disclosure is a varnish containing a polyamic acid, a solvent for the polyamic acid, CNTs, and a compound having a surface tension difference of 4 mN/m or more and 17 mN/m or less with the solvent. It can be obtained by imidizing the membrane.

The thickness of the base material containing the polyimide resin in the present disclosure is preferably 40 μm or more and 150 μm or less, more preferably 70 μm or more and 100 μm or less. When the thickness is 40 μm or more, the in-plane orientation of the CNTs can be suppressed, and the thermal conductivity in the thickness direction can be easily increased. In addition, when the thickness is 150 μm or less, sufficient durability against bending can be obtained.

[Polyimide resin]
The polyimide resin used as the base material of the electrophotographic belt according to the present embodiment is obtained, for example, by reacting equimolar amounts of an aromatic tetracarboxylic dianhydride and an aromatic diamine in an aprotic polar organic solvent. A polyamic acid (hereinafter also referred to as "polyimide precursor") is produced as a precursor resin, processed into a desired shape at the stage of this soluble precursor solution, and then dehydrated and cyclized by heating. It can be produced by (imidation).

Aromatic tetracarboxylic dianhydrides include, but are not limited to, pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,3′,3,4 '-biphenyltetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride and the like. Any one of these exemplified aromatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination.

Aromatic diamines include, but are not limited to, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, and the like. Any one of these exemplified aromatic diamines may be used alone, or two or more thereof may be used in combination.

Among them, a polyimide resin obtained using a polyimide precursor of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine can have particularly high tensile strength and toughness. preferred from

Polar organic solvents include those whose functional groups have dipoles that react poorly with aromatic tetracarboxylic dianhydrides or aromatic diamines. For example, but not limited to, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), γ-butyrolactone (γ -BL) and the like. These organic solvents may be used alone or in combination of two or more. Among them, at least one selected from the group consisting of NMP and DMF is preferred.

[carbon nanotube]
Carbon nanotubes are most preferable as the thermally conductive particles (fillers) that improve the thermal conductivity of the polyimide resin. A carbon nanotube is a nano-sized cylindrical carbon having a structure in which a graphene sheet is rolled into a cylindrical shape. Graphene has a structure in which benzene rings ^are tightly packed with sp2 bonds, and carbon nanotubes have a characteristic endless cylindrical structure. is suppressed, exhibiting very high thermal conductivity. Therefore, it is possible to improve the thermal conductivity of the resin with the addition of a small amount compared to the high thermal conductivity inorganic filler.

Carbon nanotubes (hereinafter also referred to as "CNT") may be produced by any method without limitation. The chemical vapor deposition method can be most preferably used in terms of small amount.

CNTs that are more preferably used are multi-walled carbon nanotubes produced by chemical vapor deposition (CVD) because of their excellent thermal conductivity. The reason for this is that there are few defects on the surface of the CNT. The surface of CNT is a sheet structure (graphite structure) in which all benzene rings are bonded so that they are adjacent, and theoretically composed of ^sp2 carbons. However, some may have sp ³ carbons as well as sp ² carbons depending on the manufacturing method. Atoms such as hydrogen, oxygen, and nitrogen are bonded to the sp3 carbon ^, and these portions are called defects. Since heat is conducted through the graphite structure on the CNT, if there are many defects, the transfer of heat will be hindered.

As a method for distinguishing between CNTs with few defects and CNTs with many defects, there is a method of relatively comparing the g/d ratios of Raman spectra. The g in the g/d ratio is the peak intensity of the G band (near 1590 cm ⁻¹ ) in the Raman spectroscopy spectrum, and is the peak intensity derived from the graphite structure. Further, d is the peak intensity of the D band (near 1350 cm ⁻¹ ), which is the peak intensity derived from defects. If the g/d ratio is large (the intensity of the G band is large relative to the intensity of the D band), the CNT can be determined to have few defects. Preferred CNTs of the present invention have a g/d ratio of 10 or more, and more preferred CNTs have a g/d ratio of 15 or more.

The average fiber diameter of CNT is preferably 10 nm or more and 200 nm or less. When the average fiber diameter is 10 nm or more, an excessive increase in the specific surface area of CNTs can be suppressed, and aggregation of CNTs can be prevented. As a result, the CNTs can be better dispersed in the polyimide resin. As a result, it is possible to more reliably form a heat conduction path by the CNTs in the thickness direction of the base material. In addition, since it is possible to suppress contamination of the base material with aggregates of CNTs, breakage of the base material due to concentration of stress on the aggregates can be prevented. On the other hand, since the average fiber diameter is 200 nm or less, a sufficient number of CNTs can be present in the substrate even when the CNT content in the substrate is 15% by volume or less. As a result, it is possible to more reliably form a heat conduction path by the CNTs in the thickness direction of the base material.

Moreover, the fiber length of CNT is preferably 30 μm or less. By using CNTs with a fiber length of 30 μm or less, it is possible to prevent the surface properties of the substrate from being affected even when the thickness of the substrate is as thin as 100 μm.

[Organic compound]
In the present embodiment, in view of the fact that CNTs tend to be oriented in the plane direction of the film in the polyimide resin film (belt base material), polyimide A specific organic compound is added to the precursor solution. More specifically, it is an organic compound having a surface tension difference of 4 mN/m or more and 17 mN/m or less with the solvent. This compound is preferably blended at a ratio of 0.1% by mass or more and 6.0% by mass or less with respect to the total mass of the varnish. Compounds include, but are not limited to, ethylene glycol, 3-methoxy-3-methyl-butanol, diisobutylamine, 3′-nitroacetophenone, 5-(2-hydroxyethyl)-4-methylthiazole, furfuryl alcohol, o -chlorophenol, 2-hydroxyethylmethylsulfone, 2,4-dimethyl-3-pentanone and the like. These compounds may be used either singly or in combination of two or more.

The organic compound must remain in the film during baking of the polyimide precursor solution to generate convection, but it is preferable that the organic compound evaporates after baking and does not remain in the film and does not reduce the film strength. According to studies by the present inventors, the organic compound preferably has a boiling point of 120° C. or higher and 350° C. or lower, and particularly preferably has a boiling point of 140° C. or higher and 300° C. or lower. An organic compound whose boiling point is within the above temperature range can be prevented from evaporating from the film in the initial stage of baking the film of the polyimide precursor solution. As a result, it is possible to more reliably disturb the in-plane orientation of the CNTs in the film. Moreover, by using an organic compound having a boiling point of 350° C. or lower, it is possible to prevent the organic compound from excessively remaining in the polyimide film after baking.

[Fuser belt]
FIG. 1 is a schematic cross-sectional view of a fixing belt according to this embodiment. The fixing belt 1 has a base material 1a made of the polyimide resin described above and a release layer 1c made of a fluorine resin on at least the outer peripheral surface side of the base material 1a.

The release layer 1c is composed of a fluororesin, and plays a role of preventing adhesion of toner due to the low surface energy of the fluororesin. Examples of the fluororesin layer as the release layer include tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), polytetrafluoroethylene (PTFE), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). A tube-shaped resin is used. Among the materials exemplified above, PFA is preferable from the viewpoint of moldability and toner releasability. The thickness of the fluororesin layer is preferably 50 μm or less. This is because when laminated, the elasticity of the lower silicone rubber elastic layer can be maintained, and the surface hardness of the fixing belt can be prevented from becoming too high. Adhesiveness can be improved by subjecting the inner surface of the fluororesin tube to sodium treatment, excimer laser treatment, ammonia treatment, or the like in advance. In this example, a PFA tube having a thickness of 20 μm obtained by extrusion was used. The inner surface of the tube is treated with ammonia in order to improve wettability with an adhesive, which will be described later.

Furthermore, an elastic layer 1b made of silicone rubber may be additionally provided as an intermediate layer between the substrate 1a and the release layer 1c. The silicone rubber elastic layer 1b functions as an elastic layer supported by the fixing member in order to apply uniform pressure to the unevenness of the toner image and paper during fixing. In order to exhibit such a function, the material for the silicone rubber elastic layer 1b is easy to process, can be processed with high dimensional accuracy, and does not generate reaction by-products during heat curing. of liquid silicone rubber is preferably used. Moreover, it is because elasticity can be adjusted by adjusting the degree of cross-linking according to the kind and addition amount of the filler mentioned later.

In general, an addition reaction cross-linking liquid silicone rubber contains an unsaturated aliphatic group-containing organopolysiloxane, a silicon-bonded active hydrogen-containing organopolysiloxane, and a platinum compound as a cross-linking catalyst.
The organopolysiloxane having silicon-bonded active hydrogen reacts with the alkenyl group of the organopolysiloxane component having unsaturated aliphatic groups to form a crosslinked structure under the catalytic action of the platinum compound.

The silicone rubber elastic layer 1b may contain a filler in order to improve heat conductivity, reinforce the fixing belt, and improve heat resistance.

In particular, for the purpose of improving thermal conductivity, the filler preferably has high thermal conductivity. Specific examples include inorganic substances, particularly metals and metal compounds.
Specific examples of high thermal conductivity fillers are silicon carbide (SiC), silicon nitride _{( Si3N4} ), boron nitride (BN), aluminum nitride (AlN), alumina ( _Al2O3 ) _, zinc oxide (ZnO), Magnesium oxide (MgO), silica (SiO ₂ ), copper (Cu), aluminum (Al), silver (Ag), iron (Fe), nickel (Ni) and the like.
These can be used alone or in combination of two or more. The average particle size of the highly thermally conductive filler is preferably 1 μm or more and 50 μm or less from the viewpoint of handling and dispersibility.
As for the shape, spherical, pulverized, plate-like, whisker-like, etc. are used, and spherical ones are preferable from the viewpoint of dispersibility.

The thickness of the silicone rubber elastic layer 1b is preferably from 100 μm to 500 μm, more preferably from 200 μm to 400 μm, in view of its contribution to the surface hardness of the fixing belt and the efficiency of heat conduction to unfixed toner during fixing.

In this example, alumina was used as the high thermal conductive filler, and the elastic layer 1b had a thermal conductivity of 1.0 W/mK and a thickness of 300 μm.

[Electrophotographic fixing device]
An example of an electrophotographic fixing device using this fixing belt will be described below.
FIG. 2 is a schematic cross-sectional view of fixing device 100 according to one aspect of the present disclosure. The fixing device 100 has an endless fixing belt 1 and a pressure roller (pressurizing rotating body) 6 that is arranged opposite to the fixing belt and forms a fixing nip portion 14 together with the fixing belt. An electrophotographic belt according to one aspect of the present disclosure is attached as the fixing belt 1 .

2 is a fixing heater as a heating body, and 4 is a heat-resistant film guide and heater holder. The fixing heater 2 is fixed to the lower surface of the film guide/heater holder 4 along the length of the film guide/heater holder 4 so that the fixing belt 1 and its heating surface can slide. The fixing belt 1 is fitted around the film guide/heater holder 4 with a certain degree of freedom. The film guide/heater holder 4 is made of a highly heat-resistant liquid crystal polymer resin, and plays a role of holding the fixing heater 2 and forming a shape for separating the fixing belt 1 from the recording material P. The pressure roller 6 has a multi-layer structure in which a silicon rubber layer with a thickness of about 3 mm and a PFA resin tube with a thickness of about 40 μm are laminated in order on a stainless steel core. Both ends of the metal core of the pressure roller 6 are rotatably supported by bearings between side plates (not shown) of the device frame 13 on the far side and the front side. A fixing unit including a fixing heater 2 , a film guide/heater holder 4 , a fixing belt stay 5 and a fixing belt 1 is installed above the pressure roller 6 . This fixing unit is installed parallel to the pressure roller 6 with the fixing heater 2 facing downward. Both ends of the fixing belt stay 5 are urged to the pressure roller 6 by a pressure mechanism (not shown) with a force of 156.8 N (16 kgf) at one end and a total pressure of 313.6 N (32 kgf). As a result, the lower surface (heating surface) of the fixing heater 2 is pressed against the elastic layer of the pressure roller 6 via the fixing belt 1 with a predetermined pressing force, and the recording material guided and introduced by the guide member 7 is pressed. A fixing nip portion 14 having a predetermined width necessary for fixing the toner image t is formed on P. The recording material P exiting the fixing nip portion 14 is curvedly separated from the fixing belt 1 and sent out of the fixing device 100 by the pair of fixing discharge rollers 8 .
3 is a thermistor as a temperature detection means. The thermistor 3 (heater temperature sensor) is installed on the rear surface (surface opposite to the heating surface) of the fixing heater 2 as a heat source, and has a function of detecting the temperature of the fixing heater 2 . The pressure roller 6 is rotationally driven at a predetermined peripheral speed in the direction of the arrow. The fixing belt 1, which is in pressure contact therewith, is driven by the pressure roller 6 and rotates at a predetermined speed. At this time, the inner surface of the fixing belt 1 slides in close contact with the lower surface of the fixing heater 2 and rotates along the outer circumference of the film guide/heater holder 4 in the direction of the arrow.

The inner surface of the fixing belt 1 is coated with a semi-solid lubricant, which will be described later, to ensure slidability between the film guide/heater holder 4 and the inner surface of the fixing belt 1 . The thermistor 3 is arranged in contact with the rear surface of the fixing heater 2 and connected via an A/D converter 9 to a control circuit section (CPU) 10 as control means. This control circuit unit (CPU) 10 samples the output from each thermistor at a predetermined cycle, and is configured to reflect the temperature information obtained in this manner in temperature control. That is, the control circuit unit (CPU) 10 determines the content of temperature control of the fixing heater 2 based on the output of the thermistor 3, and the temperature of the fixing heater 2 is controlled by the heater drive circuit unit 11, which is a power supply unit. It plays a role of controlling power supply to the fixing heater 2 so as to achieve a target temperature (set temperature). The control circuit unit (CPU) 10 also plays a role of controlling a fixing belt life estimation sequence, which will be described later, and is connected to a drive motor 12 for the pressure roller 6 via an A/D converter 9 . The fixing heater has an alumina substrate and a resistive heating element on which a conductive paste containing a silver-palladium alloy is applied in a uniform film thickness of about 10 μm by screen printing. Further, the ceramic heater is coated with pressure-resistant glass.

[Electrophotographic image forming apparatus]
An example of an electrophotographic image forming apparatus equipped with a fixing device using the fixing belt will be described below.
FIG. 3 is a schematic cross-sectional view of an electrophotographic image forming apparatus according to this embodiment. Reference numeral 101 denotes a photosensitive drum as an image bearing member, which is rotationally driven in the counterclockwise direction of the arrow at a predetermined process speed (peripheral speed). The photosensitive drum 101 is charged to a predetermined polarity by a charging device 102 such as a charging roller during its rotation. Then, the charged surface is exposed to laser light 103 output from the laser optical system 110 based on the input image information. A laser optical system 110 outputs a laser beam 103 modulated (on/off) corresponding to time-series electric digital pixel signals of target image information from an image signal generator such as an image reading device (not shown). The surface is scanned and exposed. As a result, an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 101 by this scanning exposure. A mirror 109 deflects the output laser beam 103 from the laser optical system 110 to the exposure position of the photosensitive drum 101 . Then, the electrostatic latent image formed on the photosensitive drum 101 is visualized with yellow toner by the yellow developing device 104Y of the developing device 104 . This yellow toner image is transferred onto the surface of the intermediate transfer drum 105 at the primary transfer portion T1 where the photosensitive drum 101 and the intermediate transfer drum 105 contact each other. Toner remaining on the surface of the photosensitive drum 101 is cleaned by a cleaner 107 . The process cycle of charging, exposure, development, primary transfer, and cleaning as described above produces a magenta toner image (developer 104M operates), a cyan toner image (developer 104C operates), and a black toner image (developer 104K operates). ) are similarly repeated to form The toner images of respective colors sequentially superimposed on the intermediate transfer drum 105 in this way are secondary-transferred collectively onto the recording material P at the secondary transfer portion T2, which is the contact portion with the transfer roller 106. be. Toner remaining on the intermediate transfer drum 105 is cleaned by a toner cleaner 108 . The toner cleaner 108 can come into contact with and separate from the intermediate transfer drum 105 and is configured to come into contact with the intermediate transfer drum 105 only when cleaning the intermediate transfer drum 105 . Further, the transfer roller 106 is also capable of contacting and separating from the intermediate transfer drum 105, and is configured to be in contact with the intermediate transfer drum 105 only during secondary transfer. The recording material P that has passed through the secondary transfer portion T2 is introduced into a fixing device 100 as an image heating device, and undergoes fixing processing (image heating processing) of the unfixed toner image carried thereon. Then, the recording material P that has undergone the fixing process is discharged outside the machine, and a series of image forming operations are completed.

EXAMPLES Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples, but the present disclosure is not limited by these examples.
First, the physical property evaluation method will be described.

[Thermal conductivity]
To measure the thermal conductivity in the film thickness direction of the polyimide base material, a periodic heating method (temperature wave thermal analysis method) thermal diffusivity measurement device (trade name: FTC-1, manufactured by Advance Riko Co., Ltd.) was used at 25 ° C. Thermal diffusivity was measured. Here, the thermal conductivity was calculated by multiplying the obtained thermal diffusivity by the separately measured density and specific heat.

[Tensile strength]
The tensile strength in the circumferential direction and the direction perpendicular to the circumferential direction of the polyimide base material is measured using a precision universal testing machine (trade name: Autograph AG-X, Shimadzu Corporation) based on Japanese Industrial Standards (JIS K)-K-7161:2014. (manufactured by Co., Ltd.) at a tensile speed of 5 mm/min, a distance between grips of 40 mm, and 23°C.

[g/d ratio]
In the Raman spectroscopy spectrum of carbon nanotubes, the peak height (intensity) g of the 1590 cm ^-1 band (G band) due to the graphite structure and the 1350 cm ^-1 band (D band) due to defects in the graphite structure. A ratio g/d of the peak height (intensity) d was calculated. For Raman spectroscopic measurement, a 3D microscopic laser Raman spectrometer (trade name: Nanofinder 30, manufactured by Tokyo Instruments) was used under the conditions of an excitation laser light source of 532 nm, a wave number range of 900 to 2000, a diffraction grating of 1200 / mm, and an exposure time of 30 s. A Raman spectroscopy spectrum of the carbon nanotube was obtained.

[Reflection X-ray diffraction method]
The orientation of the carbon nanotubes in the polyimide substrate is evaluated using an X-ray diffraction device (trade name: MiniFlex600, manufactured by Rigaku) to measure the X-ray diffraction pattern and diffraction intensity from the sample by a reflection method. It was done by The measurement conditions for X-ray diffraction were as follows.
Tube voltage/current output: 40kV/15mA
X-ray source: CuKα (0.154184 nm)
Kβ filter: Ni filter Scanning axis: θ/2θ interlocking 2θ scanning range: 3° to 60°
θ/2θ axis step angle: 0.005° (2θ)
FIG. 4 is an example of an X-ray diffraction pattern obtained by the above measurement. The maximum intensity of the diffraction peak derived from the (002) crystal plane of the carbon nanotube appearing at 2θ = 25 to 30° is defined as I (002), and the (100) crystal plane of the carbon nanotube appearing at 2θ = 40 to 45°. Taking the maximum intensity of the diffraction peak as I(100), the ratio I(002)/I(100) was used as an index of the orientation of the carbon nanotubes in the polyimide substrate. For I(002) and I(100), values obtained by subtracting the X-ray diffraction intensity at 2θ=59 to 60° as a reference were used in order to eliminate the influence of the baseline.

Next, examples and comparative examples will be specifically described.
[Example 1]
3,3′,4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine in an equimolar amount of N-methyl-2-pyrrolidone (NMP, surface tension 33.8 mN/m) A reaction was performed to prepare an NMP solution of a polyimide precursor (polyamic acid) having a solid content concentration of 18% by mass and a viscosity of 6 Pa·s (hereinafter also referred to as "polyimide precursor solution"). Carbon nanotubes (trade name: VGCF-H; manufactured by Showa Denko Co., Ltd., average fiber diameter = 150 nm, average fiber length = 8 μm, g/d = 10 to 18) were added to the obtained polyimide precursor solution at a solid content volume ratio. It added so that it might become 15 volume%. Furthermore, as an organic compound, 2,4-dimethyl-3-pentanone (surface tension: 22.9 mN/m) was added to the polyimide precursor solution in an amount of 3% by mass. Then, it was dispersed for 60 minutes with a planetary mixer to obtain the varnish according to this example.

The obtained varnish was applied to the surface of an aluminum cylindrical core having an outer diameter of 70 mm and a length of 500 mm using a ring coating method. The surface of this cylindrical core was previously coated with ceramics so that it could be easily removed from the mold after the belt was formed.

As a drying step, the cylindrical core was rotated at a rotation speed of 60 rpm, and heated for 30 minutes while maintaining the temperature of the outer surface at 120° C. with a near-infrared heater. Furthermore, by heating at a temperature of 150° C. for 20 minutes and at a temperature of 200° C. for 30 minutes, the NMP was almost completely volatilized and the varnish coating was solidified.

Subsequently, as an imidization step of the polyimide precursor in the coating film, the imidization reaction proceeds by standing in a hot air circulating furnace for 30 minutes at a temperature of 250° C., followed by heating at a temperature of 350° C. for 30 minutes. , to form a polyimide film as a cured product. Then, after cooling to a temperature of 25° C., the polyimide film was demolded from the cylindrical core to obtain an endless substrate having a thickness of 80 μm.

The tensile strength, thermal conductivity in the thickness direction, and X-ray diffraction peak intensity ratio of the obtained substrate were measured according to the methods described above. As a result, as shown in Table 2, the tensile strength was 209 MPa, the thermal conductivity in the thickness direction was 1.64 W/m·K, and the X-ray diffraction peak intensity ratio was 22.3.

Furthermore, the overall rank was evaluated based on the following criteria.
(evaluation)
· Rank A: The base material satisfied both mechanical strength (tensile strength) of 200 MPa or more and thermal conductivity of 1.0 W/m·K or more.
· Rank B: The base material satisfied both mechanical strength (tensile strength) of 200 MPa or more and thermal conductivity of 0.9 W/m·K or more.
· Rank C: The base material did not satisfy any of the above items.

[Examples 2 to 11]
A varnish according to each example was prepared in the same manner as the varnish according to Example 1, except that at least one of the amount of CNT added, the type of organic compound, and the amount of the organic compound added was changed as shown in Table 1. did. Then, a base material was prepared in the same manner as in Example 1 except that the varnish according to each example was used and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. evaluated. Table 2 shows the evaluation results.

[Examples 12 to 14]
A varnish according to each example was prepared in the same manner as the varnish according to Example 1, except that the type and amount of the organic compound added were changed as shown in Table 1. Then, a base material was prepared in the same manner as in Example 1 except that the varnish according to each example was used and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. evaluated. Table 2 shows the evaluation results.

[Comparative Examples 1 and 2]
Varnishes according to Comparative Examples 1 and 2 were prepared in the same manner as the varnish according to Example 1, except that no organic compound was added and the amount of CNT added was changed as shown in Table 1. Then, the base material in the same manner as in Example 1 except that the varnish according to Comparative Example 1 or Comparative Example 2 was used, and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. was produced and evaluated. Table 2 shows the evaluation results.

In Comparative Example 1 in which 16% by volume of CNTs were added in solid content volume ratio, the thermal conductivity exceeded 0.9 W/m·K. However, the tensile strength was less than 200 MPa due to the high CNT content in the substrate. In Comparative Example 2, the tensile strength exceeded 200 MPa because the amount of CNT added was 13% by volume. However, since the CNTs were oriented in the in-plane direction of the substrate, the thermal conductivity in the thickness direction of the substrate was less than 0.9 W/m·K.

[Comparative Examples 3-5]
The compounds listed in Table 1 were used as the organic compounds in the varnish according to Example 1, and the amounts of the compounds added were changed as listed in Table 1. Varnishes according to Comparative Examples 3 to 5 were prepared in the same manner as the varnish according to Example 1 except for these. Then, the substrate was prepared in the same manner as in Example 1 except that the varnish according to Comparative Examples 3, 4 or 5 was used, and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. was produced and evaluated. Table 2 shows the evaluation results.

As shown in Table 2, all of the substrates according to Comparative Examples 3 to 5 had a thermal conductivity of less than 0.9 W/m·K. Regarding the substrates according to Comparative Examples 3 and 4, the difference in surface tension between the compound (glycerin or dicyclopropyl ketone) contained in the varnish and the solvent NMP exceeded 17 mN/m, so their compatibility was poor. In the process of evaporating the solvent when the varnish coating is heated and cured, convection due to the microscopic difference in surface tension is less likely to occur in the coating. As a result, it is presumed that it was difficult to obtain the effect of disturbing the orientation of the CNTs, which tend to line up in the in-plane direction of the coating film, in the thickness direction of the coating film. In addition, regarding the substrate according to Comparative Example 5, since the difference in surface tension between the compound (butyl cellosolve) and NMP was smaller than 4 mN/m, microscopic It is considered that convection due to the significant difference in surface tension was difficult to occur. As a result, it is presumed that it was difficult to obtain the effect of disturbing the orientation direction of the CNTs oriented in the in-plane direction of the coating film in the thickness direction of the coating film.

[Comparative Example 6]
In the varnish according to Example 1, without adding an organic compound, polyimide particles (trade name: P84NT; manufactured by Daicel-Evonik, particle diameter 1 to 10 μm) were added so that the solid content volume ratio was as shown in Table 1. was added to A varnish according to Comparative Example 6 was prepared in the same manner as the varnish according to Example 1 except for these. Then, a base material was produced in the same manner as in Example 1 except that the varnish according to this comparative example was used and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. evaluated. Table 2 shows the evaluation results. As shown in Table 2, the thermal conductivity in the thickness direction of the substrate according to this comparative example exceeded 0.9 W/(m·K). This is probably because the polyimide resin particles inhibited the in-plane orientation of the CNTs, and as a result, the CNTs were oriented in the thickness direction to some extent. On the other hand, the tensile strength was less than 200 MPa. Such a decrease in tensile strength is considered to be due to the fact that the total amount of thermally conductive fillers (CNT and polyimide resin particles) in the base material was as large as 25% by volume (15% by volume + 10% by volume).

[Comparative Example 7]
In the varnish according to Example 1, no organic compound was added, and boron nitride (trade name: MBN-010T; manufactured by Mitsui Chemicals, Inc., average particle size 0.9 μm) was added in the solid content volume ratio shown in Table 1. was added so as to be A varnish according to Comparative Example 7 was prepared in the same manner as the varnish according to Example 1 except for these. Then, a base material was produced in the same manner as in Example 1 except that the varnish according to this comparative example was used and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. evaluated. Table 2 shows the evaluation results. As shown in Table 2, the substrate according to this comparative example had a thermal conductivity in the thickness direction that greatly exceeded 0.9 W/m·K, but a tensile strength of less than 200 MPa. Such decrease in tensile strength is considered to be due to the total amount of thermally conductive fillers (CNT and boron nitride) in the base material being as high as 30% by volume (15% by volume + 15% by volume).

[Comparative Example 8]
In the varnish according to Example 1, no organic compound was added, and CNTs were changed from "VGCF-H" to "TNIM-8" (trade name, manufactured by Timesnano, average fiber = 30 to 80 nm, average fiber length = 10 µm Hereinafter, it was changed to g/d = 1.6 to 2.2). In addition, the solid content volume ratio was set to the amount shown in Table 1. A varnish according to Comparative Example 8 was prepared in the same manner as the varnish according to Example 1 except for these. Then, a base material was produced in the same manner as in Example 1 except that the varnish according to this comparative example was used and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. evaluated. Table 2 shows the evaluation results. As shown in Table 2, the tensile strength exceeded 200 MPa, but the thermal conductivity in the thickness direction was significantly below 0.9 W/(m·K).

[Comparative Example 9]
In the varnish according to Example 1, no organic compound was added, and CNTs were changed from "VGCF-H" to "Multi-wall L-MWNT-1020" (trade name, manufactured by NTP, average fiber diameter = 10 to 20 nm. , average fiber length = 5 μm or more, g / d = 1.4 to 2.4). In addition, the solid content volume ratio was set to the amount shown in Table 1. A varnish according to Comparative Example 9 was prepared in the same manner as the varnish according to Example 1 except for these. Then, a base material was produced in the same manner as in Example 1 except that the varnish according to this comparative example was used and the thickness of the polyimide film after baking was set to the thickness shown in Table 2. evaluated. Table 2 shows the evaluation results. As shown in Table 2, the tensile strength exceeded 200 MPa, but the thermal conductivity in the thickness direction was significantly below 0.9 W/(m·K).

[Evaluation as a fixing belt]
Fixing belts were produced by forming an elastic layer made of silicone rubber on the outer peripheral surface of each base material according to Examples 1 to 14 and a release layer made of fluororesin on the outer peripheral surface thereof. These fixing belts were attached to the fixing device shown in FIG. 2, and the fixing device was incorporated into the electrophotographic image forming apparatus shown in FIG. Using the electrophotographic image forming apparatus, 600,000 electrophotographic images were formed. As a result, high quality electrophotographic images could be stably formed. Further, no cracks occurred in the base material of the fixing belt during the process of forming 600,000 electrophotographic images.

Fixing belts were produced in the same manner as described above, except that the substrates according to Comparative Examples 1, 6, and 7 were used. These fixing belts were assembled into an electrophotographic image forming apparatus in the same manner as described above, except that these fixing belts were used. Then, 600,000 electrophotographic images were formed using the electrophotographic image forming apparatus. As a result, before the number of images formed reached 600,000, the substrate of the fixing belt cracked due to bending fatigue.
Further, fixing belts were produced in the same manner as described above except that the substrates according to Comparative Examples 2, 3, 4, 5, 8 and 9 were used. These fixing belts were assembled into an electrophotographic image forming apparatus in the same manner as described above, except that these fixing belts were used. Then, 600,000 electrophotographic images were formed using the electrophotographic image forming apparatus. As a result, no cracks occurred in the base material of any of the fixing belts during the process of forming images on 600,000 sheets. However, since the heat conductivity in the thickness direction was low, the fixability of the electrophotographic image was insufficient.

The disclosure of this embodiment includes the following configurations.
[Configuration 1]
An endless electrophotographic belt,
having a base material;
The base material contains polyimide resin and carbon nanotubes,
The content of the carbon nanotubes in the base material is 15% by volume or less with respect to the total volume of the polyimide resin,
The substrate has a tensile strength of 200 MPa or more in the circumferential direction and in a direction perpendicular to the circumferential direction, and
An electrophotographic belt, wherein the heat conductivity in the thickness direction of the substrate is 0.9 W/m·K or more.
[Configuration 2]
When the surface of the base material is measured by a reflection X-ray diffraction method,
When the intensity of the diffraction peak derived from the (100) crystal face of the carbon nanotube is I (100) and the intensity of the diffraction peak derived from the (002) crystal face of the carbon nanotube is I (002), I ( 002)/I(100) is 35 or less.
[Configuration 3]
3. The electrophotographic belt according to Structure 1 or 2, wherein the ratio (g/d) of the intensity g of the G band to the intensity d of the D band in the Raman spectrum of the carbon nanotube is 10 or more.
[Configuration 4]
A configuration in which the substrate comprises a cured product of a varnish containing polyamic acid, a solvent for the polyamic acid, the carbon nanotubes, and a compound having a surface tension difference between the solvent and the solvent of 4 mN/m or more and 17 mN/m or less. 4. The electrophotographic belt according to any one of 1 to 3.
[Configuration 5]
5. The electrophotographic belt according to Structure 4, wherein the compound is blended at a ratio of 0.1% by mass or more and 6.0% by mass or less with respect to the total mass of the varnish.
[Configuration 6]
6. The electrophotographic belt according to Structure 4 or 5, wherein the solvent for the polyamic acid is at least one organic solvent selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylformamide.
[Configuration 7]
The compounds include ethylene glycol, 3-methoxy-3-methyl-butanol, diisobutylamine, 3′-nitroacetophenone, 5-(2-hydroxyethyl)-4-methylthiazole, furfuryl alcohol, o-chlorophenol, 2 -Hydroxyethylmethylsulfone, 2,4-dimethyl-3-pentanone.
[Configuration 8]
8. The electrophotographic belt according to any one of Structures 1 to 7, wherein the substrate has a thickness of 40 μm or more and 150 μm or less.
[Configuration 9]
The electrophotographic belt according to any one of Structures 1 to 8, which has a fluororesin layer as a release layer on the outer peripheral surface of the substrate.
[Configuration 10]
10. The electrophotographic belt according to Arrangement 9, further comprising an elastic layer between the substrate and the release layer.
[Configuration 11]
11. The electrophotographic belt according to any one of Structures 1 to 10, wherein the electrophotographic belt is a fixing belt.
[Configuration 12]
A fixing device comprising: a fixing belt having an endless shape;
The fixing belt is an endless electrophotographic belt having an endless base material,
The base material contains polyimide resin and carbon nanotubes,
The content of the carbon nanotubes in the base material is 15% by volume or less with respect to the total volume of the polyimide resin,
The substrate has a tensile strength of 200 MPa or more in the circumferential direction and a direction perpendicular to the circumferential direction, and a thermal conductivity of 0.9 W/m·K or more in the thickness direction of the substrate. A fixing device characterized by:
[Configuration 13]
13. An electrophotographic image forming apparatus comprising the fixing device according to item 12.
[Configuration 14]
A varnish comprising a polyamic acid, a solvent for the polyamic acid, carbon nanotubes, and a compound having a surface tension difference between the solvent and the solvent of 4 mN/m or more and 17 mN/m or less.
[Configuration 15]
15. The varnish according to configuration 14, wherein the varnish contains the compound in a proportion of 0.1% by mass or more and 6.0% by mass or less with respect to the total mass of the varnish.
[Configuration 16]
16. The varnish according to configuration 14 or 15, wherein the solvent for the polyamic acid is at least one organic solvent selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylformamide.
[Configuration 17]
The compounds include ethylene glycol, 3-methoxy-3-methyl-butanol, diisobutylamine, 3′-nitroacetophenone, 5-(2-hydroxyethyl)-4-methylthiazole, furfuryl alcohol, o-chlorophenol, 2 17. The varnish according to any one of claims 14 to 16, which is at least one organic compound selected from the group consisting of -hydroxyethylmethylsulfone and 2,4-dimethyl-3-pentanone.

1a base material 1b elastic layer 1c release layer 1 fixing belt 2 heating element 3 temperature detecting means 4 film guide and heater holder 5 fixing belt stay 6 pressure roller P recording material t unfixed toner

Claims (17)

An endless electrophotographic belt,
having a base material;
The base material contains polyimide resin and carbon nanotubes,
The content of the carbon nanotubes in the base material is 15% by volume or less with respect to the total volume of the polyimide resin,
The substrate has a tensile strength of 200 MPa or more in the circumferential direction and in a direction perpendicular to the circumferential direction, and
An electrophotographic belt, wherein the heat conductivity in the thickness direction of the substrate is 0.9 W/m·K or more. When the surface of the base material is measured by a reflection X-ray diffraction method,
When the intensity of the diffraction peak derived from the (100) crystal face of the carbon nanotube is I (100) and the intensity of the diffraction peak derived from the (002) crystal face of the carbon nanotube is I (002), I ( 002)/I(100) is 35 or less. 2. The belt for electrophotography according to claim 1, wherein the ratio (g/d) of the intensity g of the G band to the intensity d of the D band in the Raman spectroscopy spectrum of the carbon nanotube is 10 or more. The substrate comprises a cured varnish containing a polyamic acid, a solvent for the polyamic acid, the carbon nanotubes, and a compound having a surface tension difference between the solvent and the solvent of 4 mN/m or more and 17 mN/m or less. Item 2. The electrophotographic belt according to item 1. 5. The electrophotographic belt according to claim 4, wherein the compound is blended at a ratio of 0.1% by mass or more and 6.0% by mass or less with respect to the total mass of the varnish. 5. The electrophotographic belt according to claim 4, wherein the solvent for said polyamic acid is at least one organic solvent selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylformamide. The compounds include ethylene glycol, 3-methoxy-3-methyl-butanol, diisobutylamine, 3′-nitroacetophenone, 5-(2-hydroxyethyl)-4-methylthiazole, furfuryl alcohol, o-chlorophenol, 2 5. The electrophotographic belt according to claim 4, wherein the organic compound is at least one organic compound selected from the group consisting of -hydroxyethylmethylsulfone and 2,4-dimethyl-3-pentanone. 2. The electrophotographic belt according to claim 1, wherein the base material has a thickness of 40 [mu]m or more and 150 [mu]m or less. 2. The electrophotographic belt according to claim 1, further comprising a fluororesin layer as a release layer on the outer peripheral surface of said substrate. 10. The electrophotographic belt according to claim 9, further comprising an elastic layer between said substrate and said release layer. 2. The electrophotographic belt according to claim 1, wherein said electrophotographic belt is a fixing belt. A fixing device comprising: a fixing belt having an endless shape;
The fixing belt is an endless electrophotographic belt having an endless base material,
The base material contains polyimide resin and carbon nanotubes,
The content of the carbon nanotubes in the base material is 15% by volume or less with respect to the total volume of the polyimide resin,
The substrate has a tensile strength of 200 MPa or more in the circumferential direction and a direction perpendicular to the circumferential direction, and a thermal conductivity of 0.9 W/m·K or more in the thickness direction of the substrate. A fixing device characterized by: An electrophotographic image forming apparatus comprising the fixing device according to claim 12 . A varnish comprising a polyamic acid, a solvent for the polyamic acid, carbon nanotubes, and a compound having a surface tension difference between the solvent and the solvent of 4 mN/m or more and 17 mN/m or less. 15. The varnish according to claim 14, wherein the varnish contains the compound in a proportion of 0.1% by mass or more and 6.0% by mass or less with respect to the total mass of the varnish. 15. The varnish according to claim 14, wherein the solvent for said polyamic acid is at least one organic solvent selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylformamide. The compounds include ethylene glycol, 3-methoxy-3-methyl-butanol, diisobutylamine, 3′-nitroacetophenone, 5-(2-hydroxyethyl)-4-methylthiazole, furfuryl alcohol, o-chlorophenol, 2 15. The varnish according to claim 14, which is at least one organic compound selected from the group consisting of -hydroxyethylmethylsulfone and 2,4-dimethyl-3-pentanone.

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