JP2022191162A - Belt for electrophotography, image forming apparatus for electrophotography, method for manufacturing belt for electrophotography, and varnish - Google Patents

Abstract

To provide a belt for electrophotography that has predetermined thermal conductivity in a thickness direction and has high mechanical strength.SOLUTION: A belt for electrophotography in an endless shape has a base layer. The base layer includes a polyimide film including polyimide as a binder resin and a carbon nanotube. The polyimide has an imidization rate of 80% or more. At least one resin selected from the group consisting of polyphenyl sulfone, polysulfone, and polyether sulfone is present in at least part of a surface of the carbon nanotube. The tensile strength in a circumferential direction of the base layer and the tensile strength in a direction orthogonal to the circumferential direction are both 200 MPa or more.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an electrophotographic belt, an electrophotographic image forming apparatus, a method for manufacturing an electrophotographic belt, and a varnish.

Electrophotographic belts are subjected to loads such as heating, pressure, and bending during use in electrophotographic image forming apparatuses.
For example, in a belt (film) heating type fixing device, an electrophotographic belt as a fixing belt forms a fixing nip portion together with a pressing member arranged opposite to the fixing belt. At the fixing nip portion, the fixing belt transfers the heat accumulated in the fixing belt to the toner on the recording material. The heated toner is melted and fixed on the recording material. That is, the fixing belt plays a role of fixing the unfixed toner onto the recording material.

A more specific configuration example will be given. The endless fixing belt is internally provided with a ceramic heater as a heating element or a pressure pad as a pressing member. A rotatable pressure roller and a rotatable pressure belt are arranged at a position facing the fixing belt. The fixing belt is urged against the pressure roller and the pressure belt by an internal ceramic heater or pressure pad to form a fixing nip portion. A recording material bearing an unfixed toner image is introduced into the fixing nip portion and conveyed as the fixing belt rotates. During this process, heat from the fixing belt is applied to the unfixed toner and the recording material, and the unfixed toner is pressed against the recording material by the pressure applied to the unfixed toner at the fixing nip, causing the melted toner to adhere onto the recording material, forming a fixed toner image. It is formed. Thus, the fixing belt is repeatedly subjected to high pressure and high temperature at the fixing nip portion.

Therefore, the base layer of the electrophotographic belt used as the fixing belt is required to have sufficient heat resistance and high mechanical strength. Examples of high mechanical strength include strength such that cracks do not occur even with repeated bending. Therefore, polyimide is preferably used as a resin having excellent mechanical strength for the base layer of the electrophotographic belt.

On the other hand, polyimide has several orders of magnitude lower thermal conductivity than metals and ceramics. Therefore, in order to meet the demands for higher printing speed, lower power consumption required for supplying heat to the heater (energy saving), and smaller size of the fixing device, it is required to improve the thermal conductivity of the base layer of the fixing belt. It is

Recently, attention has been focused on films made of polyimide to which new functions such as electrical conductivity and thermal conductivity have been imparted.
In Patent Document 1, by increasing the thermal conductivity of a fixing belt having a polyimide film as a base layer, it is possible to reduce power consumption, increase the fixing speed, and lower the fixing temperature. A method for incorporating superior inorganic fillers is disclosed.
When high thermal conductivity is achieved by filling polyimide with highly thermally conductive particles (fillers), it is difficult to achieve high thermal conductivity by simply uniformly dispersing the fillers. In addition, the high filling of the filler causes a significant decrease in the excellent mechanical strength inherent in polyimide. Therefore, it is required to impart high thermal conductivity with a small amount of filler added.
Carbon nanotubes (hereinafter also referred to as CNTs), which have particularly excellent electrical or thermal properties, have been studied as fillers for imparting new functions to polyimide films. is being actively developed.

Patent Document 2 discloses a CNT-containing polyimide film with high thermal conductivity suitable for fuser belts.
However, CNTs are fibrous carbon and tend to agglomerate due to van der Waals forces and tend to localize as agglomerates in the polyimide film. Therefore, in a polyimide film containing agglomerated CNTs, the inherently high mechanical strength of polyimide may be significantly impaired. For example, as shown in Examples of Patent Document 3, when the CNT content is increased in order to increase the thermal conductivity, the mechanical strength of the polyimide film is significantly reduced.

Therefore, in order to suppress the formation of agglomerates of CNTs in a polyimide film, a method of preparing a solution in which CNTs are dispersed by mixing them with a surfactant or a specific polymer has been investigated.
Patent Document 3 discloses dispersing CNTs in an amide-based polar organic solvent containing a nonionic surfactant and/or polyvinylpyrrolidone (PVP). The resulting dispersion was mixed with a polyimide precursor and cured at a temperature of 350° C. for 60 minutes for dehydration imidization reaction, whereby a polyimide film in which CNTs were uniformly dispersed was obtained. Are listed.

JP-A-8-80580 JP 2004-123867 A JP 2006-124613 A

According to studies by the present inventors, the polyimide film described in Patent Document 3 still has room for improvement in terms of both mechanical strength and thermal conductivity in the thickness direction when used as a base layer for an electrophotographic belt. there were.

At least one aspect of the present disclosure is directed to providing an electrophotographic belt having a predetermined thermal conductivity in the thickness direction and high mechanical strength.
Also, at least one aspect of the present disclosure is directed to providing a method for manufacturing an electrophotographic belt having a predetermined thermal conductivity in the thickness direction and high mechanical strength.
Moreover, at least one aspect of the present disclosure is directed to providing a varnish capable of providing a polyimide film having a predetermined thermal conductivity in the thickness direction and excellent mechanical strength.

According to one aspect of the present disclosure, an endless electrophotographic belt has a base layer, the base layer includes a polyimide film containing polyimide as a binder resin and carbon nanotubes, and the polyimide The imidization rate of the carbon nanotube is 80% or more, and the carbon nanotube has at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone on at least part of its surface,
An electrophotographic belt is provided in which the tensile strength of the base layer in the circumferential direction and in the direction orthogonal to the circumferential direction is 200 MPa or more.
According to another aspect of the present disclosure, the above-described electrophotographic belt manufacturing method comprises: (i) at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone attaching to at least a portion of the surface of the carbon nanotube;
(ii) a step of dispersing the carbon nanotubes having the resin attached to at least a portion of the surface obtained in step (i) in a solution containing a polyimide precursor to obtain a dispersion;
(iii) forming a coating of the dispersion;
(iv) heating the coating film to imidize the polyimide precursor to form the base layer.
According to yet another aspect of the present disclosure, a varnish containing a polyimide precursor, carbon nanotubes, and a solvent, the carbon nanotubes having, on at least a portion of their surface, polyphenylsulfone, polysulfone, and polyphenylsulfone, polysulfone, and A varnish is provided in which at least one resin selected from the group consisting of polyethersulfones is present.

According to at least one aspect of the present disclosure, it is possible to obtain an electrophotographic belt having a predetermined thermal conductivity in the thickness direction and high mechanical strength. Further, according to at least one aspect of the present disclosure, it is possible to obtain a method for manufacturing an electrophotographic belt having a predetermined thermal conductivity in the thickness direction and high mechanical strength. Moreover, according to at least one aspect of the present disclosure, it is possible to obtain a varnish that has a predetermined thermal conductivity in the thickness direction and can provide a polyimide film having excellent mechanical strength.

1 is a schematic cross-sectional view showing an example of an electrophotographic belt; FIG. 1 is a schematic cross-sectional view showing an example of a fixing device; FIG. 1 is a schematic cross-sectional view showing an example of an electrophotographic image forming apparatus; FIG. FIG. 4 shows an energy decay curve obtained by a pulsed NMR method; FIG. 4 is a diagram showing Raman spectroscopy spectra for CNTs; FIG. 4 is a diagram showing an adsorption isotherm of a coating resin on the surface of CNTs. It is a figure which shows the relationship between a baking temperature and an imidization rate. FIG. 4 is a diagram showing the results of thermogravimetry;

In the present disclosure, the descriptions of “XX or more and YY or less” or “XX to YY” representing numerical ranges mean numerical ranges including the lower and upper limits, which are endpoints, unless otherwise specified. When numerical ranges are stated stepwise, the upper and lower limits of each numerical range can be combined arbitrarily.
A specific form for carrying out the present disclosure is shown below.
An electrophotographic belt according to one aspect of the present disclosure is an endless electrophotographic belt having a base layer. The base layer is composed of a polyimide film containing polyimide as a binder resin and carbon nanotubes. The imidization rate of the polyimide is 80% or more, and the carbon nanotube has at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone on at least part of its surface. there is Further, the tensile strength of the base layer in the circumferential direction and in the direction orthogonal to the circumferential direction is 200 MPa or more. Also, the thermal conductivity in the thickness direction of the base layer is preferably 0.4 W/m·K or more, more preferably 0.7 W/m·K or more.

Hereinafter, at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone is also referred to as coating resin. A carbon nanotube having a coating resin on at least a part of its surface is also referred to as a surface-coated CNT.

According to studies, when a polyimide film was produced according to the disclosure of Patent Document 3, there were cases where the mechanical strength of the polyimide film was remarkably lowered. Therefore, as a result of further investigation, it was found that the mechanical strength of the obtained base layer may be lowered when the baking temperature for the dehydration imidation reaction is set to 350° C. or higher.

In the production of polyimide film, there is a correlation between the imidization ratio of polyimide contained in the polyimide film and the mechanical strength of the polyimide film, and the higher the imidization ratio of the polyimide contained in the polyimide film, the higher the mechanical strength. It becomes a polyimide film having Generally, the baking temperature for producing a polyimide film is 300° C. or higher. That is, 350° C. or higher is required.

That is, by setting the baking temperature for the dehydration imidization reaction to 350° C. or higher, the imidization rate of the polyimide contained in the polyimide film can be increased to 80% or more. Originally, this should result in a polyimide film having high mechanical strength. However, when the technique described in Patent Document 3 is used and the firing temperature is set to 350° C. or higher, the resulting base layer may have low mechanical strength. The reason for this is considered as follows.

In the method described in Patent Document 3, in order to uniformly disperse the CNTs in the polyimide film, the CNTs are treated with an amide-based polar organic compound containing a nonionic surfactant and/or PVP before being mixed with the polyimide precursor. Disperse in solvent. As a result, the nonionic surfactant and/or PVP are present on at least part of the surface of the CNT. As a result, even in the subsequent process of mixing with the polyimide precursor and dehydration imidization reaction, aggregation of the CNTs can be suppressed, and a polyimide film in which the CNTs are uniformly dispersed can be obtained.

However, when the firing temperature is set to 350° C. or higher in order to increase the imidization rate, at least part of the nonionic surfactant and/or PVP present on the surface of the CNTs is considered to decompose and disappear due to high heat. . Therefore, it is considered that the effect of dispersing the CNTs was not obtained, the CNTs aggregated during the dehydration imidization reaction, and as a result the mechanical strength of the obtained polyimide film decreased.

It is considered that the same phenomenon as described above occurs in low-molecular-weight organic compounds (surfactants, etc.) or resins conventionally used to uniformly disperse CNTs in polyimide films. That is, for example, coconut oil, palm oil, linear alkylbenzene sulfonates, α-sulfo fatty acid methyl ester salts, α-olefin sulfonates, formaldehyde condensates of naphthalene sulfonates, polyoxyethylene alkyl sulfates, acyl - Low-molecular-weight compounds such as N-methyltaurate, glycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, and polyester , polyacrylic- or polyether-based resins, and vinyl-based resins such as PVP and PVA are all considered to decompose and disappear when subjected to high baking temperatures.

In the present disclosure, as a resin for surface treatment of CNTs (hereinafter also referred to as “coating resin”) for uniformly dispersing CNTs in a polyimide film, for example, phenyl represented by the following general formula (I) A resin containing a sulfonyl structure is mentioned.

Specifically, for example, at least one resin selected from the group consisting of polyphenylsulfone (hereinafter referred to as PPSU), polysulfone (hereinafter referred to as PSU), and polyethersulfone (hereinafter referred to as PESU) can be used. PPSU, PSU, and PESU are generally represented by the following general formula (II) (PPSU), the following general formula (III) (PSU), and the following general formula (IV) (PESU), respectively. Note that n in each formula represents an integer of 1 or more.

The coating resin has excellent adsorption power to CNTs. That is, after the surface-coated CNTs are obtained by attaching the coating resin to at least a part of the surface of the CNTs, the coating resin is separated from the surface of the CNTs when the surface-coated CNTs and the polyimide precursor are mixed. Hateful. As a result, the dispersibility of the surface-coated CNTs can be maintained even after mixing with the polyimide precursor.

Moreover, resins containing a phenylsulfonyl structure represented by general formula (I) belong to super engineering plastics. Super engineering plastics have higher heat resistance than engineering plastics such as polyacetal (POM) or polycarbonate (PC), which are said to have high heat resistance.
Specifically, the coating resin used in the present disclosure preferably has a temperature of 350° C. or more and 500° C. or less at 1% mass reduction in thermogravimetry (TG).

In the present disclosure, the coating resin and CNTs are mixed to adhere the coating resin to at least part of the surface of the CNTs. Then, the surface-coated CNTs thus obtained are dispersed in a solution containing a polyimide precursor, and then imidized.

Here, even when imidization is performed at a high baking temperature of, for example, 350° C. or higher in order to increase the imidization rate of the polyimide film, the coating resin does not decompose because it has high heat resistance. Therefore, CNTs can maintain a highly dispersed state. That is, it is possible to increase the imidization rate while suppressing CNT agglomeration and the resulting reduction in mechanical strength of the polyimide film, thereby effectively drawing out the inherent mechanical strength of the polyimide film. As a result, the present disclosure makes it possible to obtain an electrophotographic belt having both high mechanical strength and high thermal conductivity.

Specifically, in the electrophotographic belt according to one aspect of the present disclosure, the tensile strength of the base layer in the circumferential direction and in the direction orthogonal to the circumferential direction is 200 MPa or more. Also, the thermal conductivity in the thickness direction of the base layer is preferably 0.4 W/m·K or more, more preferably 0.7 W/m·K or more.

The base layer of the electrophotographic belt according to an aspect of the present disclosure preferably contains 5 to 20% by mass of the coating resin present on the surface of the carbon nanotubes with respect to the mass of the carbon nanotubes.

Commercially available products can be used as the coating resin, and examples of PPSU include "Ultrason P" (trade name; BASF) and "Raedel PPSU" (trade name: Solvay). . Examples of PSU include "Ultrason S" (trade name; BASF Corporation), "Udel PSU" (trade name; Solvay Corporation), and the like. PESU includes "Ultrazone E" (trade name; BASF), "Veradel PESU" (trade name; Solvay), "Sumika Excel PES" (trade name; Sumitomo Chemical Co.), "Mitsui PES" ( trade name; Mitsui Chemicals Fine Co., Ltd.) and the like.

(CNT)
From the viewpoint of maintaining the original mechanical strength of the polyimide film (preventing a decrease in mechanical strength), CNTs having a small fiber diameter, which can be expected to disperse stress, are preferable as the CNT. Further, from the viewpoint of improving the thermal conductivity of the base layer of the electrophotographic belt, CNTs having high thermal conductivity are preferred.
Examples of such CNTs include single-wall carbon nanotubes (SWCNT) (1 sheet), double-wall carbon nanotubes (DWCNT) (2 sheets), or multi-wall carbon nanotubes (MWCNT) (3 sheets or more).
The number of walls of MWCNT is said to be 10 or more (unconfirmed) in conventional multi-wall carbon nanotubes, which cannot be manufactured with desired walls. There is no particular limitation regarding the wall number of MWCNTs in this disclosure.

Furthermore, CNTs may contain elements other than carbon, such as nitrogen, boron, oxygen, and sulfur, although the elements are not limited, as long as they do not interfere with the object of the present disclosure.
CNTs can have a structure such as an armchair type, a zigzag type, a chiral type, etc., depending on the geometrical characteristics of the interatomic bonds. It can also be used with CNTs having

The method for producing CNTs is not particularly limited, but CNTs produced by the following production method may be used.

(1) Arc Discharge Method When arc discharge of about 20 V, 50 A is performed between carbon rods in an argon or hydrogen atmosphere at a pressure slightly lower than atmospheric pressure, MWCNTs are obtained in the cathode deposit. Also, when a carbon rod is mixed with a catalyst such as nickel/cobalt and arc discharge is performed, SWCNTs are generated in the substance adhering as soot to the inside of the container. The arc discharge method is said to produce CNTs of good quality with few defects.

(2) Laser evaporation method SWCNTs can be obtained by irradiating carbon mixed with a catalyst such as nickel/cobalt with strong pulsed light from a YAG laser. SWCNTs of relatively high purity can be obtained, and the tube diameter can be controlled by changing the conditions.

(3) Chemical Vapor Deposition (CVD method)
CNTs are obtained by contacting a carbon compound as a carbon source with catalyst metal fine particles at 500 to 1000°C. There are various variations in the type and arrangement of the catalyst metal, the type of carbon compound, etc., and both MWCNT and SWCNT can be synthesized by changing the conditions.
In addition, it is possible to obtain CNTs oriented perpendicular to the substrate surface by arranging the catalyst on the substrate. This method is considered to be the most suitable manufacturing method for large-scale synthesis because the raw materials can be supplied as gas.

CVD methods include the following fluidized catalyst method and a method using a catalyst supported on zeolite.
The fluidized catalyst method is a method developed from the vapor deposition method. The fluidized catalyst method is not a method in which fine catalyst particles are placed on a substrate in advance. In the fluidized catalyst method, fine catalyst particles or catalyst precursors that are converted to fine catalyst particles under CVD conditions are dispersed in raw material hydrocarbons (benzene, toluene, etc.). Then, the raw material hydrocarbon in which the catalyst fine particles or the catalyst precursor are dispersed is fed together with hydrogen to a reactor heated to about 1000° C. and reacted to obtain MWCNT.
Catalysts used in the fluidized catalyst method include iron, cobalt, nickel and the like.
As a post-treatment, the CNTs are heated to 1200° C. to remove the tar adhering to them, and the insufficiently graphitized portions are treated at a high temperature of 2000° C. to graphitize them.

In the method using a catalyst supported on zeolite, catalyst powder is placed on Y-type zeolite, which is a type of porous silicate containing iron/cobalt. Then, this catalyst powder is brought into contact with a mixed gas of acetylene and argon at 600 to 900.degree. As a result, CNT with less impurities can be obtained.
SWCNTs and MWCNTs can be produced separately by changing the contact conditions of the mixed gas with the catalyst powder. Also, by changing the type of zeolite, the shape of the produced CNTs changes.

In addition to the above, there is a manufacturing method using carbynes as a carbon source or a manufacturing method in which a carbon precursor polymer tube is carbonized.
The production method using carbynes as a carbon source is a production method in which polytetrafluoroethylene is reduced with magnesium to produce carbynes, which are then irradiated with electron beams or the like to synthesize CNTs from the carbynes.

In the production method of carbonizing a carbon precursor polymer tube, core/shell particles composed of a shell made of a carbon precursor polymer (polyacrylonitrile, etc.) and a core made of a thermally degradable polymer (polyethylene) are pyrolyzed. Disperse in an evanescent polymer. Then, the core/shell particles are melt-spun and stretched into a rod shape, followed by infusibilization/carbonization to obtain CNTs. Thus, the manufacturing method of carbonizing the carbon precursor polymer tube is a unique manufacturing method.

CNTs are preferably multi-walled carbon nanotubes produced by a vapor deposition method (CVD method) because of their excellent thermal conductivity. One of the reasons why the multi-walled carbon nanotubes produced by the CVD method have excellent thermal conductivity is that the surface of the CNTs has few defects.

The surface of CNT has a sheet structure (graphene structure) in which all benzene rings are bonded so as to be adjacent to each other, and is theoretically composed of SP2 carbons. However, depending on the manufacturing method, it may have not only SP2 carbon but also SP3 carbon in part. Atoms such as hydrogen, oxygen, and nitrogen are bound to the SP3 carbon. A portion having such SP3 carbon is called a defect.
Since heat is conducted through the graphene structure on CNTs, CNTs with many defects have poor heat conductivity.

Methods for evaluating the number of defects in CNT include a method for measuring the G/D ratio in Raman spectroscopy.
G in the G/D ratio is the peak intensity near 1590 cm ⁻¹ in the Raman spectroscopy spectrum, and is the peak intensity derived from the graphene structure (sheet structure composed of SP2 carbon). Also, D in the G/D ratio is the peak intensity near 1350 cm ⁻¹ , which is the peak intensity derived from defects. A higher G/D ratio (higher G intensity relative to D intensity) means fewer defects in the CNT.
The G/D ratio of the Raman spectrum of CNT is preferably 10 or more, more preferably 15 or more. The use of CNTs with a G/D ratio of 10 or more increases the thermal conductivity in the thickness direction of the polyimide film according to the present disclosure, specifically, for example, 0.7 W / m K or more. Especially effective.

(Surface-coated CNT)
The method for producing the surface-coated CNTs is not particularly limited, but a coating resin may be dissolved in a solvent in advance, and the CNTs may be added thereto. Alternatively, the CNTs may be put into the solvent and stirred, and then the coating resin may be added. In any case, it is necessary to prepare a solvent that dissolves the coating resin.
The solvent is not particularly limited as long as it dissolves the coating resin, but an amide solvent can be preferably used because it easily dissolves the coating resin. Amide solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAC), dimethylformamide (DMF), diethylformamide (DEF), N-methylpyrrolidone (MPD), tetramethylurea ( TMU) or hexamethylphosphoric amide (HMPA).

Surface-coated CNTs have very high heat resistance. Specifically, the temperature at 1% mass reduction in thermogravimetry (TG) of surface-coated CNTs is preferably 350° C. or higher.
The temperature at 1% mass reduction in thermogravimetry (TG) of the surface-coated CNTs is more preferably 400° C. or higher, more preferably 500° C. or higher.
Since the surface-coated CNTs have high heat resistance as described above, decomposition and gasification do not occur even when the firing temperature is set to, for example, 350 ° C. or higher in order to produce a polyimide film with a high imidization rate. .

(varnish)
Next, a varnish according to one aspect of the present disclosure will be described. The varnish according to the present disclosure can form a polyimide film having predetermined thermal conductivity in the thickness direction and high mechanical strength according to one aspect of the present disclosure. The varnish contains a polyimide precursor, the surface-coated CNTs, and a solvent.

(polyimide precursor)
As the polyimide precursor, polyamic acid or polyamic acid solution obtained by the following general production method can be used.
First, there is a production method in which a tetracarboxylic dianhydride and a diamine are reacted in a solvent at normal temperature and normal pressure under an inert gas atmosphere.
For example, by stirring pyromellitic dianhydride and 4,4'-diaminodiphenyl ether in a solvent, polyamic acid can be obtained immediately.
Depending on the type of diamine, an amide solvent such as those described above, or a solvent such as THF (tetrahydrofuran) or diglyme (diethylene glycol dimethyl ether) can be used as a reaction solvent, and a polyamic acid solution may be obtained.

Tetracarboxylic dianhydrides and diamines are described below.
Examples of tetracarboxylic dianhydrides include, for example, cyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, anhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, hexahydro-4,8-ethano-1H,3H-benzo[1,2 -c:4,5-c']difuran 1,3,5,7-tetrone and the like.
Further, as the aromatic tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic Acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride 3,4'-oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2 -bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride, 4,4-(p-phenylenedioxy)diphthalic dianhydride, 4,4-(m-phenylenedioxy)diphthalic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride and the like.
Although not particularly limited, the tetracarboxylic dianhydride is preferably an aromatic tetracarboxylic dianhydride in view of the properties of the resulting polyimide.
The tetracarboxylic dianhydride does not have to be one kind, and may be a mixture of two or more kinds.

Examples of diamines include p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, p-xylylenediamine, m-xylylenediamine, 4,4'-diamino Diphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis( 3-aminophenoxy)benzene, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 3,3'-dihydroxybenzidine, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis (trifluoromethyl)benzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(3-hydroxy- 4-aminophenyl)hexafluoropropane, 4,4′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenyl sulfone, bis[4-(4-aminophenoxy)phenyl] sulfone, aromatic diamines such as bis[4-(3-aminophenoxy)phenyl]sulfone and bis(3-amino-4-hydroxyphenyl)sulfone; diamines containing cyclic structures, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, diaminopropyltetramethylene, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2-bis-3-aminopropoxyethane, 2,2-dimethylpropylenediamine, 3-methoxyhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylene Aliphatic diamines such as diamine, 3-methylheptamethylenediamine, 5-methylnonamethylenediamine, 2,17-diaminoeicosadecane, 1,10-diamino-1,10-dimethyldecane, 1,12-diaminooctadecane etc. can be mentioned.
Although not particularly limited, the diamine is preferably an aromatic diamine in view of the properties of the resulting polyimide.
The diamine does not have to be of one type, and may be a mixture of multiple types.

Polyamic acid or polyamic acid solution can also be used by purchasing a commercially available product.
Specifically, the "U-Imido" series (product name; Unitika), the "Upia" series and the "U-Varnish" series (both product names; Ube Industries, Ltd.), the "HCI" series (product name; Hitachi Chemical Co., Ltd.) company), “Equrios” series (trade name; manufactured by Mitsui Chemicals, Inc.) and “Pyre-ML” series (trade name; I.S.T company), etc. can be used.

The method for producing the varnish according to the present disclosure is not particularly limited. For example, after producing surface-coated CNTs or a dispersion of surface-coated CNTs in advance, it is put into a solvent containing a polyimide precursor and mixed with a stirring device. , can get varnish.
The amount of surface-coated CNTs in the varnish is not particularly limited, but the amount of surface-coated CNTs is preferably 1% by volume or more and 50% by volume or less with respect to the amount of polyamic acid. A more preferable blending amount is 10% by volume or more and 30% by volume or less. If the amount of surface-coated CNTs to the amount of polyamic acid in the varnish is 10% by volume or more, the thermal conductivity of the base layer can be increased, and if it is 30% by volume or less, the mechanical strength of the base layer can be increased. can do.

(polyimide film)
The varnishes of the present disclosure can be used to prepare polyimide films for use as base layers of electrophotographic belts of the present disclosure. Although the manufacturing method is not limited, the varnish is heated and held at a temperature below the boiling point of the solvent to partially evaporate so that the varnish has an appropriate viscosity, and in order to cause an imidization reaction, it is heated and held at 300 ° C. or higher. A manufacturing method comprising the steps of: For example, a bank with a height of about 0.5 mm is made on the core using a metal plate, and varnish is poured into the bank. A varnish is applied using a bar coater, placed on a hot plate, and held at 200° C. for 1 hour to evaporate the solvent. Then, a polyimide film is obtained by holding at 350° C. for 1 hour in a muffle furnace.

(polyimide)
The polyimide contained in the polyimide film produced as the base layer of the electrophotographic belt according to the present disclosure has an imidization rate of 80% or more.
Polyimide can be obtained, for example, by dehydrating and cyclizing (imidizing) a precursor solution containing the above polyamic acid and solvent by heating.

In the present disclosure, polyimides with high tensile strength and toughness are preferred for blending CNTs with polyimides. If the strength of the polyimide itself is not sufficient, the addition of CNTs inevitably lowers the toughness and the tensile strength (breaking stress), so there is a possibility that the polyimide cannot be put to practical use. Further, when used as a base layer of a fixing belt, it is required to have higher heat resistance (glass transition temperature) in order to prevent deformation due to heat applied from a heater.
From the above, the most preferable polyimide is a polyamic acid obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride with p-phenylenediamine. .

(electrophotographic belt)
FIG. 1 is a schematic cross-sectional view showing an example of an electrophotographic belt according to the present disclosure. The electrophotographic belt 1 has a base layer 1a made of the above-described polyimide film, and a surface layer 1c as a release layer containing at least a fluororesin on the outer peripheral surface of the base layer 1a.
The thickness of the base layer 1a is preferably 40-150 μm.

The surface layer 1c contains a fluororesin and plays a role of preventing adhesion of toner due to the low surface energy of the fluororesin. As the surface layer 1c containing the fluororesin, a tube-shaped fluororesin is used. As the fluorine resin, for example, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. are used. be done. Among the materials exemplified above, PFA is preferable as the fluororesin from the viewpoint of moldability and toner releasability.

The thickness of the surface layer 1c is preferably 50 μm or less. This is because when the elastic layer 1b is provided under the surface layer 1c, the elasticity of the elastic layer 1b can be maintained and the surface hardness of the electrophotographic belt 1 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.

Furthermore, an elastic layer 1b made of silicone rubber may be additionally provided as an intermediate layer between the base layer 1a and the surface layer 1c. The elastic layer 1b functions, for example, as an elastic layer supported by the fixing member in order to apply a uniform pressure to the toner image and the unevenness of the recording material when the toner is fixed. In order to exhibit such a function, the material of the elastic layer 1b is an addition reaction cross-linking type liquid material because it is easy to process, can be processed with high dimensional accuracy, and does not generate reaction by-products during heat curing. It is preferred to use silicone rubber. In addition, elasticity can be adjusted by adjusting the degree of cross-linking according to the type and amount of filler to be added, which will be described 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 an unsaturated aliphatic group to form a crosslinked structure by the catalytic action of the platinum compound.

The elastic layer 1b may contain a filler in order to improve the thermal conductivity of the electrophotographic belt 1, reinforce it, and improve its heat resistance.
In particular, the filler preferably has high thermal conductivity for the purpose of improving the thermal conductivity of the electrophotographic belt. Specifically, inorganic substances, especially metals, metal compounds, etc. can be mentioned as the material of the high thermal conductive filler.

Specific examples of high thermal conductivity filler materials include 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. The shape of the high thermal conductivity filler may be spherical, pulverized, plate-like, whisker-like, etc. From the viewpoint of dispersibility, the spherical shape is preferred.

The thickness of the elastic layer 1b is preferably 100 μm or more and 500 μm or less, more preferably 200 μm or more and 400 μm, in terms of contribution to surface hardness of the electrophotographic belt and efficiency of heat conduction to unfixed toner during fixing when used as a fixing belt. The following are more preferred.

A method for manufacturing an electrophotographic belt according to the present disclosure includes a method for manufacturing an electrophotographic belt having the following steps (i) to (iv).
(i) attaching at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone to at least a portion of the surface of the carbon nanotube;
(ii) A step of dispersing the carbon nanotubes having a resin attached to at least a part of the surface obtained in the above step (i) in a solution containing a polyimide precursor to obtain a dispersion.
(iii) forming a coating film of the dispersion;
(iv) heating the coating film to imidize the polyimide precursor to form the base layer;

The baking temperature for imidization in the step (iv) is at least 250° C. or higher and 400° C. or lower, preferably 300° C. or higher and 400° C. or lower, more preferably 350° C. or higher and 400° C. or lower.

In the electrophotographic belt manufacturing method, after the step (iii) and before the step (iv), the coating film is heated to, for example, 50 to 250° C. to remove the solvent and cure the coating film. It may further have a step.

(fixing device)
An example of a fixing device using an electrophotographic belt according to one aspect of the present disclosure as a fixing belt will be described below.
FIG. 2 is a schematic cross-sectional view showing an example of a fixing device 100 using an electrophotographic belt according to the present disclosure as a fixing belt.
The fixing device 100 includes an electrophotographic belt 1 as a cylindrical fixing belt (endless belt) having an elastic layer, and a pressure roller 6 as a pressure member forming a fixing nip portion 14 with the fixing belt. It has The fixing device 100 also includes a fixing heater 2 as a heating element, and a heat-resistant film guide/heater holder 4 .

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 electrophotographic belt 1 and its heating surface can slide. The electrophotographic belt 1 is fitted around the film guide/heater holder 4 with some 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 electrophotographic belt 1 from the recording material P.

The pressure roller 6 has a multi-layer structure in which, for example, 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 an electrophotographic belt 1 is installed above the pressure roller 6 in FIG. 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 against the pressure roller 6 by a pressure mechanism (not shown) with a force of, for example, 156.8 N (16 kgf) and a total pressure of 313.6 N (32 kgf). As a result, the lower surface (heating surface) of the fixing heater 2 is brought into contact with the elastic layer of the pressure roller 6 via the electrophotographic belt 1 with a predetermined pressing force, thereby fixing the toner t on the recording material P. A fixing nip portion 14 having a predetermined width required for is formed.

A thermistor 3 (heater temperature sensor) as a temperature detection means is installed on the back 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 electrophotographic 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 electrophotographic belt 1 slides in close contact with the lower surface of the fixing heater 2 and is driven to rotate around the film guide/heater holder 4 in the direction of the arrow.

A semi-solid lubricant is applied to the inner surface of the electrophotographic belt 1 to ensure slidability between the film guide/heater holder 4 and the inner surface of the electrophotographic 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 3 at a predetermined cycle, and is configured to reflect the temperature information thus obtained in temperature control. That is, the control circuit unit (CPU) 10 determines the contents of temperature control of the fixing heater 2 based on the output of the thermistor 3 . Thus, the control circuit unit (CPU) 10 plays a role of controlling power supply to the fixing heater 2 by the heater driving circuit unit 11, which is a power supply unit, so that the temperature of the fixing heater 2 reaches the target temperature (set temperature). play. The control circuit unit (CPU) 10 also plays a role of controlling the fixing belt life estimation sequence, and is connected to the driving motor of the pressure roller 6 via the A/D converter 9 .

The fixing heater 2 has an alumina substrate and a resistive heating element on which a conductive paste containing a silver-palladium alloy is applied to form a uniform film with a 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 including the fixing device having the electrophotographic belt according to the present disclosure will be described below.
FIG. 3 is a schematic cross-sectional view showing an example of an electrophotographic image forming apparatus according to the present disclosure.

A photosensitive drum 101 as an image bearing member is rotationally driven in the counterclockwise direction of an 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 laser beam 103 output 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 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 that has undergone the fixing process is discharged from the machine, and a series of image forming operations is completed.

Examples according to the present disclosure will be described below, but the present disclosure is not limited to the description of the following examples.
As shown in the examples below, surface-coated CNTs were prepared in advance and then mixed with a polyimide precursor to prepare a varnish.

[Coating resin]
As the coating resin, the following commercially available products were used. In addition, as the resin used for adhering to the surface of the CNT in the comparative example (hereinafter referred to as comparative resin), the following commercially available products were used.
- Coating resin 1 (PPSU): Ultrason P3010 (trade name, manufactured by BASF)
- Coating resin 2 (PSU): Ultrason S3010 (trade name, manufactured by BASF)
- Coating resin 3 (PESU): Ultrason E1010 (trade name, manufactured by BASF)
・Comparison resin 1 (PVP): Rubiscol K30 (trade name, manufactured by BASF)
・ Comparative resin 2 (polyoxyethylene sorbitan monolaurate): Tween 20 (trade name, manufactured by Tokyo Chemical Industry Co., Ltd.)

[CNT]
CNTs used in Examples and Comparative Examples are shown below.
・ CNT1: VGCF-H (trade name, manufactured by Showa Denko)
・ CNT2: VGCF (trade name, manufactured by Showa Denko)
・ CNT3: L-60100 (trade name, manufactured by NTP)
・ CNT4: L-1020 (trade name, manufactured by NTP)

[Polyamic acid]
Polyamic acid (hereinafter also referred to as PAA) solutions used in Examples and Comparative Examples are shown below.
・PAA1: U-Varnish S301
(Product name, manufactured by Ube Industries, polyamic acid content: 18% by mass)
・ PAA2: U imide AH
(Product name, manufactured by Unitika Ltd., polyamic acid content: 18% by mass)
・PAA3: JIV-1002
(Product name, JFE Chemical Co., Ltd., polyamic acid content: 18% by mass)

Evaluation of each physical property of each of the above materials will be described below.
(Heat resistance of coating resin and comparative resin)
In order to compare the heat resistance of Coating Resins 1 to 3 with the heat resistance of Comparative Resin 1 or Comparative Resin 2, Table 1 shows the temperature at 1% mass reduction in thermogravimetry (TG).

(Adsorption force of coating resin and comparison resin to CNT)
The adsorptive power of the coating resin or the comparative resin to CNTs and the adsorptive power of polyamic acid (hereinafter referred to as PAA) to CNTs were compared by the following two methods.
1) Method using Hansen solubility parameter 2) Method using pulsed NMR

1) Method Using Hansen Solubility Parameter The Hansen solubility parameter (hereinafter referred to as HSP) is a value used to predict interactions between substances, and is a known index in the field of dispersions. The theory of HSP is described, for example, in “Coal Science Conference Proceedings, 55, P86-P89 (2018)”.
HSP consists of the following three parameters (unit: MPa0.5).
・δd: energy due to intermolecular dispersion force ・δp: energy due to intermolecular dipole interaction ・δh: energy due to intermolecular hydrogen bonding These three parameters can be regarded as coordinates in a three-dimensional space (Hansen space). can. When the HSPs of two substances are placed in the Hansen space, the closer the distance between the two points (hereinafter referred to as Ra), the easier it is for them to interact with each other.
That is, the distance between two points when the CNT and the HSP of the coating resin are placed in the Hansen space is Ra _{(CNT-coating resin)} , and the distance between the two points when the HSP of the CNT and the PAA are placed in the Hansen space is 2 Let Ra _(CNT-PAA) be the distance between the points. At this time, when Ra _{(CNT-coating resin)} is smaller than Ra _(CNT-PAA) , the coating resin has a stronger interaction with CNTs than PAA. Therefore, when the surface-coated CNT and PAA are mixed, it is possible to suppress the separation of the coating resin from the surface of the CNT by replacing the coating resin existing on the surface of the CNT with the PAA.

Table 1 shows Ra _{(CNT-coating resin)} of coating resins 1 to 3, comparative resin 1, or comparative resin 2 with respect to CNT1. The Ra of PAA1 to CNT1 _(CNT-PAA) is 16.1.

According to Table 1, in Coating Resins 1 to 3, Ra _{(CNT-coating resin)} is smaller than Ra _(CNT-PAA) (16.1). Therefore, even when the surface-coated CNTs obtained using the coating resins 1 to 3 are mixed with the PAA1, it is thought that the adsorption of the coating resins 1 to 3 on the surface of the CNTs 1 is maintained. be done. Although Comparative Resin 1 has low heat resistance, Ra _{(CNT-coating resin)} of Comparative Resin 1 is smaller than Ra _(CNT-PAA) (16.1). Therefore, even when CNT1 having the surface of Comparative Resin 1 adsorbed thereon is mixed with PAA1, adsorption of Comparative Resin 1 on the surface of CNT1 is considered to be maintained. On the other hand, although Comparative Resin 2 has high heat resistance, Ra _{(CNT-coating resin)} of Comparative Resin 2 is greater than Ra _(CNT-PAA) (16.1). Therefore, when the CNT1 having the surface of the comparative resin 2 adsorbed thereon is mixed with the PAA1, it is highly likely that the comparative resin 2 is desorbed from the surface of the CNT1.

2) Technique using pulse NMR As a technique for comparing the adsorption force in a solution, there is a technique using pulse NMR, which can obtain relaxation information of solvent motion (observed atomic nucleus is 1H). For an outline of the technique or an operation method, the method described in "Journal of Imaging Society of Japan, 55(2), P160-P165 (2016)" can be referred to.

Relaxation refers to the process by which energy once absorbed is attenuated. For example, consider the case of using N-methyl-2-pyrrolidone (hereinafter referred to as NMP) as a solvent. At this time, when NMP in a free state not in contact with the CNT surface contacts the CNT surface, the excited nuclear spin of NMP relaxes due to energy exchange with the nuclear spin of CNT. When the coating resin does not exist on the surface of the CNT, NMP molecules, which are the solvent, frequently come into contact with the surface of the CNT, so that the relaxation time of NMP is remarkably short. On the other hand, when the measurement is performed under the same conditions, when the coating resin is present on the surface of the CNT, the more the coating resin on the surface of the CNT, the less frequently the solvent NMP comes into contact with the surface of the CNT. , the relaxation time of NMP increases.
FIG. 4 shows energy decay curves of NMP in pulse NMR for a mixture of CNT1/coating resin 1/solvent:NMP and a mixture of CNT1/PAA1/solvent:NMP. The steeper the slope of the curve, ie, the greater the decrease in pulse signal intensity over time, the less adsorption.

From FIG. 4, it is considered that PAA1 is not stably adsorbed on the surface of CNT1 and the decay time of NMP is short because the surface of CNT1 is exposed. On the other hand, the coating resin 1 is strongly adsorbed on the surface of the CNT 1 and covers the surface of the CNT 1, so it is considered that the decay time of NMP is long.

(Thermal conductivity of CNT)
In order to evaluate the thermal conductivity of CNTs, the G/D ratio of Raman spectra was obtained. As already mentioned, the larger the G/D ratio, the smaller the number of defects and the higher the thermal conductivity of the CNT.
The G / D ratio is the peak height of the 1590 cm ^-1 band (G band) due to the graphene structure and the peak height of the 1350 cm ^-1 band (D band) due to defects in the graphene structure in the Raman spectroscopy spectrum. calculated as the ratio of A 3D microscopic laser Raman spectrometer (trade name: Nanofinder 30; manufactured by Tokyo Instruments Co., Ltd.) was used for the Raman spectroscopic measurement. The measurement conditions were 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.

As an example, Raman spectra of CNT1 and CNT4 are shown in FIG. Table 2 shows the fiber diameters, fiber lengths and G/D ratios of CNT1 to CNT4.

As shown in FIG. 5 and Table 2, CNT1 or CNT2 has a large G/D ratio, and CNT1 in particular has a G/D ratio of 15 or more and is a CNT with very few defects. is suitable.

[Imidation rate for baking temperature of polyamic acid]
The imidization rate was calculated by measuring the infrared absorption spectrum of the sample using a Fourier transform infrared spectrophotometer Spectrum 3 FT-IR (manufactured by PerkinElmer). Measurements were made by the single reflection ATR method with a germanium crystal.
Specifically, when the absorbance "B" derived from the benzene ring absorption band near 1515 cm ^-1 is used as a reference, the ratio of the absorbance "A" of the C=O stretching vibration derived from the imide group at 1710 cm ^-1 "A/B" was measured. Assuming that the absorbance ratio "A/B" when completely imidized is 1.7, it was calculated by "imidization ratio = (A/B) x 100/1.7".

FIG. 7 shows the imidization ratios of PAAs 1 to 3 with respect to the sintering temperature.
As shown in FIG. 7, imidization progresses rapidly when the firing temperature is around 200°C to 300°C, and the imidization rate begins to saturate around 350°C, reaching 80% or more, and saturating around 400°C. It is speculated that

(Adsorption evaluation of coating resin on CNT surface)
In order to confirm that the coating resin was adsorbed on the surface of the CNTs, an adsorption isotherm was prepared for a combination of CNT1 and coating resin 1 as an example. If the adsorption isotherm is a curve conforming to the Langmuir adsorption isotherm, it is the basis for adsorption (monomolecular adsorption) of the coating resin in the first layer. In addition, by identifying the point where the adsorption isotherm changes from the Langmuir adsorption isotherm to the polymolecular adsorption isotherm, the state where the surface of the CNT is covered with the coating resin and the adsorption is completed (adsorption saturation) can be confirmed. can be done.

First, 1 g of CNT 1 and an arbitrary amount of 5% by mass NMP solution of coating resin 1 are added to a container, and an additional solvent (NMP/methyl alcohol = 3/1.2) is added to make the total amount 66.66 g. made into a solution. 30 g of glass beads (φ1 mm) were added to the mixed solution, and after shaking with a paint shaker (Toyo Seiki Seisakusho) for 2 hours, the glass beads were removed to obtain a dispersion.
The dispersion was subjected to solid-liquid separation by centrifugation (12,000 rpm, 2.5 hours), and the supernatant was collected. The amount of coating resin 1 in the supernatant was calculated from HPLC analysis, the amount of coating resin 1 on the solid side was calculated, and the amount of coating resin 1 per unit weight (1 g) of CNT 1 was obtained. , and the adsorption isotherms of CNT1 and coating resin 1 (see FIG. 6).

The created adsorption isotherm is a curved curve. For example, two equations, Langmuir's adsorption isotherm and polymolecular adsorption isotherm, are described in "Journal of Agricultural Engineering Society, Vol. 68, No. 4, P351-P361". I was able to get a fitting.

From the above adsorption isotherm, it was confirmed that the coating resin 1 was strongly adsorbed to the CNT 1 in the NMP/methyl alcohol mixed solvent. Furthermore, it was confirmed that one layer of the CNT 1 was covered with the coating resin 1, and adsorption was almost completed. As a result of estimating the amount of coating resin 1 per unit weight (1 g) of CNT 1 at the time when the adsorption was almost completed, it was 0.082 g/g-CNT.

[Example 1]
(Production of surface-coated CNT1)
1 g of CNT 1 and 1.8 g of a 5% by mass NMP solution of coating resin 1 were added to a container, and an additional solvent (NMP/methyl alcohol = 3/1.2) was added to make the total amount of the mixed solution 66.66 g. and 30 g of glass beads (φ1 mm) were added to the mixed solution, and after shaking with a paint shaker (Toyo Seiki Seisakusho) for 2 hours, the glass beads were removed to obtain a dispersion. The dispersion was subjected to solid-liquid separation by centrifugation (12,000 rpm, 2.5 hours), and the supernatant was removed to obtain a sediment containing surface-coated CNT1.
Then, the amount of coating resin 1 in the supernatant was calculated by high performance liquid chromatography analysis (hereinafter referred to as HPLC analysis) of the supernatant. When the coating amount of the surface-coated CNTs 1 (amount (g) of the coating resin 1 per unit weight (1 g) of the CNTs) was obtained by subtracting the value from the amount of the coating resin 1 charged at the beginning, the result was 0. 082 g/g-CNT.
The sediment was then heated on a hot plate at 200° C. for 1 hour to completely remove NMP to obtain surface-coated CNT1. Thermogravimetry (TG) of the surface-coated CNT1 was performed to obtain a mass loss curve (see FIG. 8). The temperature at 1% mass reduction was obtained from FIG. 8 and found to be 542° C. (see Table 3).

[Examples 2 to 8]
According to the method described in Example 1, surface-coated CNT2 to surface-coated CNT8 were produced using combinations of CNTs and coating resins shown in Table 3. Also, according to the method described in Example 1, the amount of coating resin per unit mass (1 g) of CNT and the temperature at 1% mass reduction were determined. Table 3 shows the results obtained.

[Comparative Examples 1 and 2]
According to the method described in Example 1, a combination of the CNTs described in Table 3 and the comparative resin 1 or comparative resin 2 was used to produce comparative surface-coated CNT1 and comparative surface-coated CNT2.
Further, according to the method described in Example 1, the amount of the coating resin per unit mass (1 g) of the CNTs was determined for the comparative surface-coated CNT1 and the comparative surface-coated CNT2. Further, thermogravimetry (TG) was performed on the comparative surface-coated CNT1 and the comparative surface-coated CNT2 to obtain mass loss curves (see FIG. 8). The temperature at 1% mass reduction was obtained from FIG. Table 3 shows the results obtained.

The coating amount of 0.082 g/g-CNT in surface-coated CNT 1 in Table 3 is the amount of coating resin 1 at the time when adsorption of the first layer is completed. Moreover, compared with the surface-coated CNT1, the case where the amount of the coating resin 1 adsorbed on the surface of the CNT is small is the surface-coated CNT2, and the case where it is large (in the case of multi-layer adsorption) is the surface-coated CNT3. In all cases, the temperature at 1% weight loss was higher than 350°C. On the other hand, in the comparative surface-coated CNT1 and the comparative surface-coated CNT2, the temperature at the time of 1% mass reduction was below 350°C.
Varnishes were prepared in the combinations shown in Table 4 using the CNTs having resin attached to their surfaces obtained in the above Examples and Comparative Examples. The preparation method is shown below.

[Example 9]
(Manufacture of varnish 1)
A method for obtaining varnish 1 using the sediment containing surface-coated CNTs 1 obtained in Example 1 is shown below.
7.5 g of PAA1 (solid content concentration: 18% by mass) and 1.24 g of sediment containing surface-coated CNT1 (solid content concentration: 25%) were put into a container. Next, the container was kneaded for 15 minutes with a rotation-revolution kneader (product name: Rentaro, manufactured by Thinky Corporation) and degassed for 15 minutes to obtain Varnish 1.

[Examples 10 to 17]
Varnishes 2-9 were prepared in the same manner as described in Example 9, except that the combinations of PAA and surface-coated CNTs were as described in Table 4.

[Comparative Example 3 and Comparative Example 4]
Comparative varnish 1 and comparative varnish 2 were prepared in the same manner as described in Example 9, except that the combination of PAA and comparative surface-coated CNTs was as shown in Table 4.

[Comparative Example 5]
Comparative varnish 3 was prepared in the same manner as in Example 9, except that CNT 1 not coated with resin was used.

Using the varnish obtained in the above example, a polyimide film was produced by the method described below.
[Example 18]
A method for obtaining a polyimide film 1 using the surface-coated CNT-blended varnish 1 obtained in Example 1 is shown below. When the amount of Varnish 1 was increased, the number of batches was increased or scaled up without changing the formulation.
1 kg of PAA1 (U-varnish S301, solid content concentration 18% by mass) and 180 g of varnish 1 (solid content concentration 25% by mass) were put into a stirring vessel and dispersed for 60 minutes with a planetary mixer to obtain a film-forming varnish. got 1. This blending ratio was calculated so that the blending amount of the surface-coated CNTs was 13.2% by volume with respect to the solid content of PAA1, that is, the polyamic acid.
The resulting film-forming varnish 1 was applied to the surface of a cylindrical aluminum core having an outer diameter of 30 mm and a length of 500 mm using a ring coating method. The surface of the cylindrical core body was preliminarily coated with ceramics to facilitate removal from the mold after the belt was formed.
As a drying process, the core was rotated at 60 rpm, and the surface was heated with a near-infrared heater for 30 minutes while maintaining the temperature at 120°C. Furthermore, by heating at 150° C. for 20 minutes and at 200° C. for 30 minutes, NMP was almost completely volatilized and the coating film was solidified.
Subsequently, as an imidization step, the film was allowed to stand still in a hot air circulating furnace and heated at 250° C. for 30 minutes and 350° C. for 30 minutes to promote imidization and form a polyimide film. After cooling to about room temperature, the film was removed from the core to obtain an endless polyimide film 1 having a thickness of 85 μm.

[Examples 19 to 27, Comparative Examples 6 to 10]
Polyimide films 2 to 10 and comparative polyimide films 1 to 5 were obtained according to the method described in Example 18, except that the baking conditions and the type of varnish used were changed as shown in Table 5. rice field. Table 5 shows the film thicknesses of the obtained polyimide films 2 to 10 and comparative polyimide films 1 to 5.

<Evaluation of polyimide film>
(Confirmation of presence of imidization and coating resin)
Infrared absorption spectra were measured for sample pieces cut from each of the polyimide films produced above.
As a result, in any polyimide film, the absorption generated by the imidization reaction appeared near 1715 cm ⁻¹ , confirming that polyamic acid was converted to polyimide.
Moreover, in the polyimide films 1 to 8 and the comparative polyimide films 5 and 6, the absorption caused by the SC bond appeared near 1480 cm ⁻¹ , confirming that the coating resin was contained. On the other hand, in the comparative polyimide films 1 to 4 and 7, no absorption due to the SC bond appeared near 1480 cm ⁻¹ .

(Imidation rate)
The imidization rate of each polyimide film prepared above was determined by the method described above.
Table 6 shows the results obtained.

(tensile strength)
The tensile strength in the circumferential direction and the direction orthogonal to the circumferential direction of each polyimide film produced above was measured.
Tensile strength was measured based on Japanese Industrial Standards (JIS) K 7161:2014 using a precision universal testing machine (trade name: Autograph AG-X, manufactured by Shimadzu Corporation) at a tensile speed of 5 mm/min and a distance between grips. Measured at 40 mm and 23°C. Table 6 shows the results obtained.
In any polyimide film, the same value was obtained for the tensile strength in the circumferential direction and the tensile strength in the direction perpendicular to the circumferential direction. .

(Thermal conductivity)
For each of the polyimide films prepared above, the thermal diffusivity at 25° C. was measured using a periodic heating method (temperature wave thermal analysis method) thermal diffusivity measuring device (trade name: FTC-1, manufactured by Advance Riko Co., Ltd.). The thermal conductivity (thickness direction) was calculated by multiplying the obtained thermal diffusivity by the separately measured density and specific heat.
Table 6 shows the results obtained.

(Comprehensive evaluation)
Based on the evaluation results of imidization rate, tensile strength, and thermal conductivity, each polyimide film prepared above was comprehensively evaluated according to the following criteria.
Specifically, a polyimide film having a high thermal conductivity of 0.4 W/m·K or more and a tensile strength of 200 MPa or more in both the circumferential direction and the direction perpendicular to the circumferential direction. It was set as rank "A". Among them, polyimide films having a thermal conductivity of 0.7 W/m·K or more were ranked as “A+”.
On the other hand, a polyimide film having a thermal conductivity of 0.4 W/m·K or more but having a tensile strength of less than 200 MPa both in the circumferential direction and in a direction orthogonal to the circumferential direction was ranked "B".
Table 6 shows the results.

As shown in Tables 5 and 6, the imidization ratios of the polyimide films produced at a baking temperature of 350° C. or higher all exceeded 80%.
However, the comparative polyimide film 5 containing CNT1 with no resin adhered to the surface had a tensile strength of 198 MPa and a thermal conductivity of 0.69 W/m·K. The reason why the tensile strength is low even though the imidization ratio of the polyimide in the comparative polyimide film 5 is as high as 80% is considered to be that the CNTs formed aggregates in the polyimide film.
On the other hand, the polyimide films 1 to 10 containing the surface-coated CNTs had improved tensile strength compared to the comparative polyimide film 5, and the effect of the surface coating was recognized. That is, in the polyimide films 1 to 10, it is considered that the repulsive force between the CNTs was generated due to the coating of the surface of the CNTs in the film with the resin, and the effect of suppressing aggregation was exhibited. In other words, it is considered that the CNT surface adsorption of the coating resin is strong enough to be maintained during varnishing and baking.

On the other hand, in the comparative polyimide films 1 to 3, which were prepared at a baking temperature of 350 ° C. or higher using a varnish containing CNT whose surface was treated with PVP or polyoxyethylene sorbitan monolaurate, both the tensile strength and the thermal conductivity of the comparative polyimide It was inferior to membrane 5. It is considered that this is because the surface covering state of the CNTs was not maintained during the process of preparing the polyimide film, and the CNTs aggregated for one of the following two reasons.
Reason 1: The resin or surfactant replaced the polyamic acid in the varnish and desorbed from the CNT surface.
Reason 2: The resin or surfactant was decomposed or gasified and desorbed due to the high baking temperature.

A fixing belt was produced by forming an elastic layer made of silicone rubber on the outer peripheral surface of the polyimide film according to Examples 18 to 27, and further forming a surface layer made of fluororesin on the outer peripheral surface. When this fixing belt was used in a fixing device having the configuration shown in FIG. 2 and tested, good energy-saving properties and fixed images were obtained, and it functioned without any problems even after 600,000 sheets were fed.
On the other hand, in the case of using fixing belts similarly manufactured using the polyimide films according to Comparative Examples 6 to 10, the polyimide film cracked due to bending fatigue before the number of sheets passed reached 600,000.

Disclosure according to embodiments of the present invention includes the following configurations and methods.
(Configuration 1)
An endless electrophotographic belt,
having a base layer,
The base layer comprises a polyimide film containing polyimide as a binding resin and carbon nanotubes,
The imidization rate of the polyimide is 80% or more,
The carbon nanotube has at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone on at least part of its surface,
An electrophotographic belt, wherein the base layer has a tensile strength of 200 MPa or more in the circumferential direction and in a direction orthogonal to the circumferential direction.
(Configuration 2)
The electrophotographic belt according to Structure 1, wherein the heat conductivity in the thickness direction of the base layer is 0.7 W/m·K or more.
(Composition 3)
3. The electrophotographic belt according to Structure 1 or 2, wherein the G/D ratio of the Raman spectrum of the carbon nanotubes is 10 or more.
(Composition 4)
The electrophotographic belt according to any one of Structures 1 to 3, wherein the base layer contains 5 to 20% by weight of the resin present on the surface of the carbon nanotubes relative to the weight of the carbon nanotubes.
(Composition 5)
5. The electrophotographic belt according to any one of structures 1 to 4, wherein the base layer has a thickness of 40 to 150 μm.
(Composition 6)
The electrophotographic belt according to any one of Structures 1 to 5, further comprising a surface layer containing a fluororesin on the outer peripheral surface of the base layer.
(Composition 7)
7. The electrophotographic belt of configuration 6, further comprising an elastic layer between the base layer and the surface layer.
(Composition 8)
The electrophotographic belt according to any one of structures 1 to 7, wherein the electrophotographic belt is a fixing belt.
(Method 1)
A method for manufacturing an electrophotographic belt according to any one of structures 1 to 8,
(i) attaching at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone to at least a portion of the surface of the carbon nanotube;
(ii) a step of dispersing the carbon nanotubes having the resin attached to at least a portion of the surface obtained in step (i) in a solution containing a polyimide precursor to obtain a dispersion;
(iii) forming a coating of the dispersion;
(iv) heating the coating to imidize the polyimide precursor to form the base layer;
A method for manufacturing an electrophotographic belt, comprising:
(Composition 9)
An electrophotographic image forming apparatus comprising the electrophotographic belt according to any one of Structures 1 to 8.
(Configuration 10)
A varnish containing a polyimide precursor, carbon nanotubes, and a solvent,
A varnish characterized in that the carbon nanotube has at least one resin selected from the group consisting of polyphenylsulfone, polysulfone and polyethersulfone present on at least part of its surface.
(Composition 11)
11. The varnish according to configuration 10, wherein the G/D ratio of the Raman spectroscopy spectrum of the carbon nanotubes is 10 or more.

1 Electrophotographic Belt 1a Base Layer 1b Elastic Layer 1c Surface Layer 100 Fixing Device 101 Photosensitive Drum 102 Charging Device 104 Developing Device 105 Intermediate Transfer Drum 106 Transfer Roller 107 Cleaner 108 Toner Cleaner

Claims (12)

An endless electrophotographic belt,
having a base layer,
The base layer comprises a polyimide film containing polyimide as a binding resin and carbon nanotubes,
The imidization rate of the polyimide is 80% or more,
The carbon nanotube has at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone on at least part of its surface,
An electrophotographic belt, wherein the tensile strength of the base layer in the circumferential direction and in the direction orthogonal to the circumferential direction is 200 MPa or more. 2. The electrophotographic belt according to claim 1, wherein the heat conductivity in the thickness direction of the base layer is 0.7 W/m.K or more. 2. The belt for electrophotography according to claim 1, wherein the G/D ratio of the Raman spectroscopic spectrum of said carbon nanotubes is 10 or more. 2. The electrophotographic belt according to claim 1, wherein said base layer contains 5 to 20% by mass of said resin present on the surface of said carbon nanotubes relative to the mass of said carbon nanotubes. 2. The electrophotographic belt of claim 1, wherein the base layer has a thickness of 40-150 μm. 2. The electrophotographic belt according to claim 1, further comprising a surface layer containing a fluororesin on the outer peripheral surface of said base layer. 7. The electrophotographic belt of claim 6, further comprising an elastic layer between said base layer and said surface layer. 2. The electrophotographic belt of claim 1, wherein said electrophotographic belt is a fuser belt. A method for producing the electrophotographic belt according to any one of claims 1 to 8,
(i) attaching at least one resin selected from the group consisting of polyphenylsulfone, polysulfone, and polyethersulfone to at least a portion of the surface of the carbon nanotube;
(ii) a step of dispersing the carbon nanotubes having the resin attached to at least a portion of the surface obtained in step (i) in a solution containing a polyimide precursor to obtain a dispersion;
(iii) forming a coating of the dispersion;
(iv) heating the coating to imidize the polyimide precursor to form the base layer;
A method for manufacturing an electrophotographic belt, comprising: An electrophotographic image forming apparatus comprising the electrophotographic belt according to any one of claims 1 to 8. A varnish containing a polyimide precursor, carbon nanotubes, and a solvent,
A varnish characterized in that the carbon nanotube has at least one resin selected from the group consisting of polyphenylsulfone, polysulfone and polyethersulfone present on at least part of its surface. 12. The varnish according to claim 11, wherein the G/D ratio of the Raman spectroscopy spectrum of said carbon nanotubes is 10 or more.

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