阅读说明：本技术 中间转印带和图像形成装置 (Intermediate transfer belt and image forming apparatus ) 是由 吉田英一 滨口进一 小贺伊都 津川刊 大平晃 于 2019-06-03 设计创作，主要内容包括：本发明的目的是提供一种使用了聚酰胺酰亚胺的耐久性优异的中间转印带。此外,本发明的另一个目的是提供一种具备上述中间转印带的图像形成装置。本发明的中间转印带用于电子照相方式的图像形成装置,其中,所述中间转印带含有聚酰胺酰亚胺、导电剂以及分散剂,并且所述分散剂具有嵌段聚合物结构。(The purpose of the present invention is to provide an intermediate transfer belt using polyamide imide and having excellent durability. Another object of the present invention is to provide an image forming apparatus including the intermediate transfer belt. The intermediate transfer belt of the present invention is used in an electrophotographic image forming apparatus, and includes a polyamide imide, a conductive agent, and a dispersant, and the dispersant has a block polymer structure.)

1. An intermediate transfer belt for use in an electrophotographic image forming apparatus,

The intermediate transfer belt contains polyamide imide, a conductive agent and a dispersant, and the dispersant has a block polymer structure.

2. The intermediate transfer belt according to claim 1,

the dielectric loss tangent is in the range of 0.2 to 1.5 under the environment of 23 ℃ and 10 kHz.

3. The intermediate transfer belt according to claim 1 or 2,

The dispersant has a block polymer structure comprising a segment derived from a basic (meth) acrylate and a segment derived from a neutral (meth) acrylate.

4. The intermediate transfer belt according to any one of claims 1 to 3,

The conductive agent exhibits acidity.

5. The intermediate transfer belt according to any one of claims 1 to 4,

The content of the dispersant is in the range of 1 to 20 parts by mass relative to 100 parts by mass of the conductive agent.

6. The intermediate transfer belt according to any one of claims 1 to 5,

The average particle size of the conductive agent is within the range of 0.05-0.20 mu m.

7. An image forming apparatus comprising the intermediate transfer belt according to any one of claims 1 to 6.

Technical Field

The present invention relates to an intermediate transfer belt and an image forming apparatus, and more particularly, to an intermediate transfer belt having excellent durability and an image forming apparatus including the intermediate transfer belt.

Background

Conventionally, as an electrophotographic image forming apparatus using an intermediate transfer belt, there has been known an electrophotographic image forming apparatus in which a toner image formed on a photoreceptor is primarily transferred to the intermediate transfer belt, and the toner image on the intermediate transfer belt is secondarily transferred to a transfer material such as a transfer paper (recording paper). That is, a toner image formed on a photoreceptor and charged with a predetermined polarity is transferred to an intermediate transfer belt by electrostatic force, and then the toner image of the intermediate transfer belt is transferred to a transfer material by electrostatic force.

An image forming apparatus using the intermediate transfer belt is widely used as a color image forming apparatus because toner images formed on respective photoreceptors can be sequentially superimposed on the intermediate transfer belt by electrostatic force, and the superimposed toner images can be transferred to a transfer material at one time.

Generally, an intermediate transfer belt is formed by adding carbon black dispersed as a conductive filler to polyimide or polyamideimide having excellent mechanical properties, electrical insulation properties, and heat resistance to adjust the electrical resistance.

Compared with polyimide, polyamideimide has high solvent solubility and can be fired at low temperature, thus having great advantages in production. However, since polyamideimide has lower mechanical strength and voltage resistance than polyimide, there are the following problems: resistance changes and strength decreases due to repeated use, and there is a risk of breakage.

In order to improve the strength of an intermediate transfer belt using polyamideimide, an intermediate transfer belt having improved abrasion resistance by containing a polyamideimide with a phosphate ester and a polybenzimidazole, respectively, has been disclosed (see patent documents 1 and 2).

However, even when these intermediate transfer belts are used, the improvement of durability is insufficient, and an intermediate transfer belt using polyamideimide which is less in resistance change and strength reduction even after repeated use is desired.

Disclosure of Invention

Technical problem to be solved by the invention

the present invention has been made in view of the above problems and circumstances, and an object of the present invention is to provide an intermediate transfer belt using polyamideimide and having excellent durability. Another object of the present invention is to provide an image forming apparatus including the intermediate transfer belt.

Means for solving the problems

The inventors of the present invention have studied the cause of the above-described problems and the like in order to solve the above-described problems, and as a result, have found and completed the present invention as follows: in the intermediate transfer belt using polyamideimide, by dispersing the conductive agent using a dispersant having a block polymer structure, strength reduction can be reduced even if it is repeatedly used.

That is, the above-described technical problem of the present invention is solved by the following means.

1. An intermediate transfer belt used in an electrophotographic image forming apparatus, wherein the intermediate transfer belt contains a polyamide imide, a conductive agent, and a dispersant, and the dispersant has a block polymer structure.

2. The intermediate transfer belt according to claim 1, wherein the dielectric tangent is in a range of 0.2 to 1.5 at 10kHz in an environment of 23 ℃.

3. The intermediate transfer belt according to item 1 or 2, wherein the dispersant has a block polymer structure containing a segment derived from a basic (meth) acrylate and a segment derived from a neutral (meth) acrylate.

4. The intermediate transfer belt according to any one of claims 1 to 3, wherein the conductive agent exhibits acidity.

5. The intermediate transfer belt according to any one of claims 1 to 4, wherein a content of the dispersant is in a range of 1 to 20 parts by mass with respect to 100 parts by mass of the conductive agent.

6. The intermediate transfer belt according to any one of claims 1 to 5, wherein an average particle diameter of the conductive agent is in a range of 0.05 to 0.20 μm.

7. An image forming apparatus comprising the intermediate transfer belt according to any one of items 1 to 6.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above means of the present invention, an intermediate transfer belt using polyamideimide and having excellent durability can be provided. Further, an image forming apparatus having the above-described intermediate transfer belt may be provided.

The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.

By using a dispersant having a block polymer structure, even when polyamideimide is used, the same durability as polyimide can be obtained. The expression mechanism is believed to be due to the separation of the functions between the electrophile segment and the solvophilic/oleophilic segment in the block polymer. When the dispersant is a conventional random copolymer type polymer, since the segments of the electroconducting agent and the segments of the solvophilic/resin-philic agent are not distinguished, the dispersant is in a state of insufficient adsorption with the electroconducting agent, dissolution in the solvent and in the resin.

By performing functional separation using a dispersant having a block polymer structure, adsorption to the conductive agent is sufficient, and aggregation of the conductive agents with each other can be suppressed, whereby dispersion stability can be maintained. Further, since the lipophilic segment exists in the same molecule, the conductive agent and the resin are homogenized, the voltage applied to the transfer belt becomes uniform, and the conversion into the transfer electric field does not change the thermal energy or the like. These are represented by a reduction in the dielectric loss tangent. Specifically, the dielectric loss tangent at 10kHz in an environment of 23 ℃ is estimated to be 1.5 or less. When the dielectric loss tangent is 1.5 or less, the conversion efficiency into a transfer electric field becomes high, and secondary transfer can be performed at a low voltage. As a result, it is considered that the load on the transfer belt is reduced, and the resistance change and the reduction in mechanical strength can be suppressed.

Drawings

Fig. 1 is a cross-sectional configuration view showing an example of an image forming apparatus that can use the intermediate transfer belt of the present invention.

Detailed Description

The intermediate transfer belt of the present invention is an intermediate transfer belt used in an image forming apparatus of an electrophotographic system, wherein the intermediate transfer belt contains a polyamideimide, a conductive agent, and a dispersant, and the dispersant has a block polymer structure. The above features are technical features common to the following embodiments.

In the embodiment of the present invention, from the viewpoint of the effect of the present invention, the dielectric loss tangent is preferably in the range of 0.2 to 1.5 at 10kHz in an environment of 23 ℃.

Further, when the dispersant has a block polymer structure containing a segment derived from a basic (meth) acrylate and a segment derived from a neutral (meth) acrylate, the dispersion stability of the conductive agent is enhanced, and therefore, it is preferable.

Further, when the electric agent exhibits acidity, the affinity with the segment derived from the basic (meth) acrylate in the dispersant is enhanced, so that the conductive agent is stably dispersed, which is preferable.

In the present invention, the content of the dispersant is preferably in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the conductive agent. This makes it possible to set the resistance value (volume resistivity) of the intermediate transfer belt within a preferable range, which is preferable.

In addition, from the viewpoint of stably dispersing the conductive agent, the average particle diameter of the conductive agent is preferably in the range of 0.05 to 0.20 μm.

The intermediate transfer belt of the present invention may be preferably provided in an image forming apparatus.

Hereinafter, the present invention, its technical features, and forms and modes for carrying out the present invention will be described in detail. In the present application, "to" means that numerical values described before and after the reference numeral are included as the lower limit value and the upper limit value.

In the present invention, "(meth) acrylate" means "at least one of acrylate and methacrylate", and "(meth) acryl" means "at least one of acryl and methacryl". For example, "(meth) acrylic acid" means "at least one of acrylic acid and methacrylic acid".

< overview of intermediate transfer Belt >)

The intermediate transfer belt of the present invention is an intermediate transfer belt used in an image forming apparatus of an electrophotographic system, wherein the intermediate transfer belt contains a polyamideimide, a conductive agent, and a dispersant, and the dispersant has a block polymer structure.

By using a dispersant having a block polymer structure in the intermediate transfer belt of the present invention, functional separation is performed, thereby maintaining dispersion stability. Further, since the resin-philic segment exists in the same molecule, the conductive agent and the resin are uniformized, the voltage applied to the transfer belt becomes uniform, and the voltage is efficiently converted into the transfer electric field. These are shown by the decrease in the dielectric loss tangent, and the dielectric loss tangent at 10kHz in an environment of 23 ℃ is estimated to be 1.5 or less. Since the secondary transfer can be performed at a low voltage, it is considered that the load on the transfer belt is reduced, and the resistance change and the reduction in mechanical strength can be suppressed. The lower the dielectric loss tangent, the more uniform the dispersion state, with a lower limit of 0.2.

The dielectric loss tangent can be measured as follows.

After sputtering silver on both sides of the test sample, the sample was cut into piecesIs used as a measurement sample. The value of the dielectric loss tangent can be calculated using, for example, a system 1296/1260 manufactured by SOLARRON corporation and having a capacitance value of 10kHz in an environment of 23 ℃.

The intermediate transfer belt preferably has a resistance (volume resistivity) of 10⁵～10¹¹Omega cm.

The thickness of the intermediate transfer belt may be suitably determined depending on the purpose of use, etc., but is usually preferably in the range of 50 to 500 μm, more preferably 200 to 400 μm, which satisfies mechanical properties such as strength and flexibility.

Further, the shape of the intermediate transfer belt preferably has the following advantages: the intermediate transfer belt of the annular structure does not generate thickness variation caused by superposition; any portion may be set as a start position of the belt rotation; the control mechanism of the rotation start position and the like may be omitted.

The intermediate transfer belt of the present invention may be composed of only a base material, or may be provided with other layers such as an elastic layer and a surface layer on the base material as needed.

< substrate >

The base material of the present invention contains polyamideimide, a conductive agent, a dispersant, and the dispersant has a block polymer structure.

Further, the resistance value (volume resistivity) of the base material is preferably 10⁵～10¹¹Omega cm. The base material contains a conductive agent in order to adjust the resistance value of the base material within a predetermined range. Preferably, the conductive agent exhibits acidity. The thickness of the base material is preferably in the range of 50 to 500. mu.m, more preferably in the range of 200 to 400. mu.m. In addition, various well-known additives may be added to the base material.

[ polyamideimide ]

The polyamideimide is a resin having an imide group having rigidity and an amide group imparting flexibility in a molecular skeleton, and a resin having a generally known structure can be used as the polyamideimide used in the present invention.

As a general method for synthesizing a polyamideimide resin, there are known: acid chloride process (a): a known method for producing a halogenated compound of a trivalent carboxylic acid derivative having an acid anhydride group, most typically a chloride of the derivative, by reacting the halogenated compound with a diamine in a solvent (see, for example, Japanese patent publication No. 42-15637). Alternatively, as another method, there are known: isocyanate method (b): any of the above-mentioned methods can be used, for example, a known method of producing the compound by reacting a trivalent derivative containing an anhydride group and a carboxylic acid with an aromatic isocyanate in a solvent (for example, Japanese patent publication No. 44-19274). Hereinafter, each manufacturing method will be explained.

(a) Acid chloride process

as the halide of the trivalent carboxylic acid derivative having an acid anhydride group, for example, compounds having structures represented by the following general formula (1) and general formula (2) can be used.

[ chemical formula 1]

(in the formula, X represents a halogen element).

[ chemical formula 2]

(wherein X represents a halogen element and Y represents-CH₂-、-CO-、-SO₂-or-O-).

in the above formulae, the halogen element is preferably chlorine, and specific examples of the derivative include: acid chlorides of polycarboxylic acids such as terephthalic acid, isophthalic acid, 4,4 '-biphenyldicarboxylic acid, 4, 4' -diphenyl ether dicarboxylic acid, 4,4 '-biphenylsulfone dicarboxylic acid, 4, 4' -benzophenonedicarboxylic acid, pyromellitic acid, trimellitic acid, 3', 4, 4' -benzophenonetetracarboxylic acid, 3', 4, 4' -biphenylsulfone tetracarboxylic acid, and 3, 3', 4, 4' -biphenyltetracarboxylic acid.

These compounds may be used alone or in combination. As a part of them, as required, there can be used: acid chlorides of polycarboxylic acids such as adipic acid, sebacic acid, maleic acid, fumaric acid, dimer acid, stilbenedicarboxylic acid, 1, 4-cyclohexanedicarboxylic acid, and 1, 2-cyclohexanedicarboxylic acid.

On the other hand, as the diamine, there is no particular limitation, and there can be used: any of aromatic diamine, aliphatic diamine, and alicyclic diamine, and aromatic diamine is preferably used.

Examples of the aromatic diamine include: m-phenylenediamine, p-phenylenediamine, diaminodiphenyl ether, methylenediamine, hexafluoroisopropylidenediamine, diaminom-xylene, diaminop-xylene, 1, 4-naphthalenediamine, 1, 5-naphthalenediamine, 2, 6-naphthalenediamine, 2, 7-naphthalenediamine, 2' -bis- (4-aminophenyl) propane, 2' -bis- (4-aminophenyl) hexafluoropropane, 4 ' -diaminodiphenyl sulfone, 4 ' -diaminodiphenyl ether, 3' -diaminodiphenyl sulfone, 3' -diaminodiphenyl ether, 3, 4-diaminobiphenyl, 4 ' -diaminobenzophenone, 3, 4-diaminodiphenyl ether, isopropylidenedianiline, 3' -diaminobenzophenone, 3,4 ' -diaminodiphenyl ether, and the like, O-tolidine, 2, 4-toluenediamine, 1, 3-bis- (3-aminophenoxy) benzene, 1, 4-bis- (4-aminophenoxy) benzene, 1, 3-bis- (4-aminophenoxy) benzene, 2-bis- [4- (4-aminophenoxy) phenyl ] propane, bis- [4- (4-aminophenoxy) phenyl ] sulfone, bis- [4- (3-aminophenoxy) phenyl ] sulfone, 4 '-bis- (4-aminophenoxy) biphenyl, 2' -bis- [4- (4-aminophenoxy) phenyl ] hexafluoropropane, 4 '-diaminodiphenyl sulfide, 3' -diaminodiphenyl sulfide, and the like.

Further, as the diamine, if a siloxane compound having amino groups at both ends is used, for example, 1, 3-bis (3-aminopropyl) -1,1,3, 3-tetramethyldisiloxane, α, ω -bis (3-aminopropyl) polydimethylsiloxane, 1, 3-bis (3-aminophenoxymethyl) -1,1,3, 3-tetramethyldisiloxane, α, ω -bis (3-aminophenoxymethyl) polydimethylsiloxane, 1, 3-bis (2- (3-aminophenoxy) ethyl) -1,1,3, 3-tetramethyldisiloxane, α, ω -bis (2- (3-aminophenoxy) ethyl) polydimethylsiloxane, 1, 3-bis (3- (3-aminophenoxy) propyl) -1,1,3, 3-tetramethyldisiloxane, α, ω -bis (3- (3-aminophenoxy) propyl) polydimethylsiloxane, etc., to obtain siloxane-modified polyamideimide.

In order to obtain the polyamideimide (polyamideimide resin) of the present invention by the acid chloride method, a derivative halide of the trivalent carboxylic acid having an acid anhydride group and a diamine are dissolved in an organic polar solvent, and then reacted at a low temperature (0 to 30 ℃) to prepare a precursor of polyamideimide (polyamide-polyamic acid).

Examples of the organic polar solvent that can be used include: formamide solvents (e.g., sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, N-dimethylformamide and N, N-diethylformamide), acetamide solvents (e.g., N-dimethylacetamide and N, N-diethylacetamide), pyrrolidone solvents (e.g., N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone), phenol solvents (e.g., phenol, o-cresol, m-cresol, p-cresol, xylenol, halogenated phenol and catechol), and ether solvents (e.g., phenol, o-cresol, m-cresol, p-cresol, xylenol, halogenated phenol and catechol)E.g. tetrahydrofuran, bisAlkane, dioxolane, etc.), alcohol solvents (e.g., methanol, ethanol, butanol, etc.), cellosolve solvents (e.g., butyl cellosolve, etc.), hexamethylphosphoramide, N-methyl-2-pyrrolidone, etc. These solvents are preferably used alone or as a mixed solvent, and particularly preferably used solvents are N, N-dimethylacetamide and N-methyl-2-pyrrolidone.

The dispersion liquid in which the conductive agent of the present invention is dispersed or various known additives may be mixed into the polyamide-polyamic acid solution obtained above to prepare a coating liquid. After the coating liquid is applied to a support (mold for molding), conversion from polyamide-polyamic acid to polyamideimide is performed by treatment such as heating.

Examples of the imidization method include: a method of dehydration ring-closing by heat treatment; and a method of chemical ring closure using a dehydration ring closure catalyst. In the case of the dehydration ring-closing by the heat treatment, for example, the reaction temperature is in the range of 300 to 400 ℃, preferably 180 to 350 ℃, and the heat treatment time is in the range of 30 seconds to 10 hours, preferably 5 minutes to 5 hours. In addition, when the dehydration ring-closure catalyst is used, the reaction temperature is in the range of 0 to 180 ℃, preferably 10 to 80 ℃, and the reaction time is in the range of several tens of minutes to several days, preferably 2 hours to 12 hours. As examples of the dehydration ring-closing catalyst, there may be mentioned: acid anhydrides such as acetic acid, propionic acid, butyric acid and benzoic acid.

(b) Isocyanate process

As the derivative of the trivalent carboxylic acid having an acid anhydride group used in the isocyanate method, for example, a compound having a structure represented by the following general formula (3) or the following general formula (4) can be used.

[ chemical formula 3]

(wherein R represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a phenyl group).

[ chemical formula 4]

(wherein R represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a phenyl group, and Y represents-CH₂-、-CO-、-SO₂-or-O-).

Any derivative having the above general formula can be used, and trimellitic anhydride is preferably used. Further, derivatives of trivalent carboxylic acids having these acid anhydride groups may be used alone or in combination according to the purpose.

Next, as one of the aromatic polyisocyanates used for synthesizing the polyamideimide of the present invention, there may be mentioned, for example: 4,4 ' -diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, 4 ' -diphenylether diisocyanate, 4 ' - [2, 2-bis (4-phenoxyphenyl) propane ] diisocyanate, biphenyl-4, 4 ' -diisocyanate, biphenyl-3, 3' -diisocyanate, biphenyl-3, 4 ' -diisocyanate, 3' -dimethylbiphenyl-4, 4 ' -diisocyanate, 2' -dimethylbiphenyl-4, 4 ' -diisocyanate, 3' -diethylbiphenyl-4, 4 ' -diisocyanate, 2' -diethylbiphenyl-4, 4 ' -diisocyanate, 3' -dimethoxybiphenyl-4, 4 ' -diisocyanate, 2' -dimethoxybiphenyl-4, 4 ' -diisocyanate, naphthalene-1, 5-diisocyanate, naphthalene-2, 6-diisocyanate, and the like.

These aromatic polyisocyanates may be used alone or in combination. As a part of these, as necessary, there can be used: aliphatic and alicyclic isocyanates such as hexamethylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, isophorone diisocyanate, 4' -dicyclohexylmethane diisocyanate, trans-cyclohexane-1, 4-diisocyanate, hydrogenated m-xylylene diisocyanate, and lysine diisocyanate, and polyisocyanates having 3 or more functions.

The conductive agent dispersion liquid of the present invention and various known additives are mixed into a solution containing a polyamideimide precursor obtained by dissolving a derivative of a trivalent carboxylic acid having each acid anhydride group described above and an aromatic polyisocyanate in an organic polar solvent to prepare a coating liquid. After the coating liquid is applied to the support, a precursor of polyamideimide is converted to polyamideimide by performing a heat treatment. When converted into polyamideimide by this method, polyamideimide is not substantially produced (carbon dioxide gas is generated) via the polyamic acid. An example of polyamide imidization using trimellitic anhydride and an aromatic isocyanate is shown in the following reaction formula (I).

[ chemical formula 5]

Reaction formula (I)

(wherein Ar represents an aromatic group).

Further, when polyamideimide is used as a substrate, the polyamideimide has high solubility in an organic polar solvent unlike polyimide, and thus the conductive agent dispersion liquid of the present invention and various known additives may be mixed into a polyamideimide solution to prepare a coating liquid. As the solvent, the above-mentioned organic polar solvent can be used.

In addition, as the base material, in addition to polyamideimide, polyimide, polycarbonate, polyphenylene sulfide, polyvinylidene fluoride, polyalkylene terephthalate (polyethylene terephthalate, polybutylene terephthalate, or the like), polyether ketone, polyether ether ketone, ethylene tetrafluoroethylene copolymer can be used. In this case, the content of the polyamideimide in the base material is preferably 51% by mass or more, more preferably 90% by mass, and still more preferably all of the polyamideimide, relative to the entire resin.

[ dispersing agent ]

The dispersant of the present invention has a block polymer structure. Specifically, the dispersant preferably has a block polymer structure containing a segment derived from a basic (meth) acrylate and a segment derived from a neutral (meth) acrylate. By having such a block structure, the function of the dispersant can be separated by different segments, unlike a polymer of a random copolymer type.

(fragment derived from basic (meth) acrylate)

The dispersant having a block polymer structure of the present invention preferably contains a segment derived from a basic (meth) acrylate (hereinafter also referred to as segment a). Specifically, the dispersant is preferably a block polymer derived from a (meth) acrylate having a basic group. The basic group is preferably an amino group or an amino group substituted with an alkyl group, and the segment a is preferably a segment (monomer unit) represented by the following general formula (5).

[ chemical formula 6]

General formula (5)

(in the formula, R⁴Represents a hydrogen atom or a methyl group, R⁵Represents an alkylene group having 1 to 10 carbon atoms, R⁶And R⁷Each independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms)

As a group consisting of R⁵Specific examples of the alkylene group having 1 to 10 carbon atoms,

Examples thereof include: alkylene groups such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene and heptamethylene. R⁵Preferably an alkylene group having 1 to 5 carbon atoms.

As a group consisting of R⁶And R⁷Specific examples of the alkyl group having 1 to 10 carbon atoms include: and a straight-chain or branched alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. R⁶And R⁷Preferably, each of the alkyl groups is independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

As examples of (meth) acrylates which can form such a segment, mention may be made, for example, of: n, N-dimethylaminoethyl (meth) acrylate, and tert-butylaminoethyl (meth) acrylate.

Further, a plurality of such (meth) acrylates may be used.

In the dispersant of the present invention, the content of the constituent unit derived from the basic (meth) acrylate is preferably in the range of 10 to 90% by mass based on all the constituent units in the polymer. More preferably 20 to 80 mass%.

(fragment derived from neutral (meth) acrylate)

The dispersant having a block polymer structure of the present invention preferably contains a segment derived from a neutral (meth) acrylate (hereinafter also referred to as segment B). Specifically, the dispersant is preferably a block polymer derived from a (meth) acrylate having a neutral group. As neutral groups, mention may be made of: alkyl groups, ether groups, oxycarbonyl groups, hydroxyl groups, and the like. The fragment B is preferably a fragment (monomer unit) represented by the following general formula (6).

[ chemical formula 7]

General formula (6)

(wherein n represents an integer of 1 to 10. R¹Represents a hydrogen atom or a methyl group. R²Represents an alkylene group having 1 to 10 carbon atoms. R³An alkylene group having 1 to 10 carbon atoms).

In the general formula (6), n is preferably an integer of 1 to 7, more preferably an integer of 1 to 5.

As a group consisting of R²Specific examples of the alkylene group having 1 to 10 carbon atoms include: methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, and the like. R²Preferably an alkylene group having 1 to 5 carbon atoms.

As a group consisting of R³Specific examples of the alkylene group having 1 to 10 carbon atoms include: methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, and the like. R³Preferably 1 to 8 carbon atomsThe alkylene group is more preferably an alkylene group having 3 to 8 carbon atoms.

The partial structure represented by the general formula (6) contained in the segment B may be composed of one monomer unit or may be composed of a plurality of monomer units.

The partial structure (monomer unit) included in the segment B may be only the partial structure represented by the general formula (6), or may be composed of other partial structures. When the segment B contains other partial structures, the other partial structures may be contained in any manner such as random copolymerization, block copolymerization, and the like.

The segment B preferably contains 10 to 90% by mass, more preferably 20 to 80% by mass of the partial structure represented by the general formula (6). Fragment B preferably does not have the following partial structure: which contains a basic group such as a general formula (5) constituting the fragment A. When the segment B has a partial structure containing a basic group, the proportion of the partial structure containing a basic group in the segment B is preferably 1% by mass or less.

The further partial structures which may be contained in fragment B are preferably composed of the following monomers: a monomer copolymerizable with the monomer constituting the partial structure represented by the general formula (6) and the monomer constituting the segment A. Specific examples of monomers that can form the other partial structure of segment B include: aromatic unsaturated monomers (styrene monomers), (meth) acrylates, and the like. As the aromatic unsaturated monomer, there may be mentioned: styrene, alpha-methylstyrene, and the like. Examples of the (meth) acrylate include: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, glycidyl (meth) acrylate, benzyl (meth) acrylate, hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, and the like.

The other partial structure that may be contained in the fragment B is preferably a partial structure (monomer unit) represented by the following general formula (7).

[ chemical formula 8]

General formula (7)

(in the formula, R⁸Represents a hydrogen atom or a methyl group. R⁹Represents an alkyl group having 1 to 10 carbon atoms which may have a substituent).

R of the formula (7)⁹Specific examples of the alkyl group having 1 to 10 carbon atoms in (A) include: and linear or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl. R⁹Preferably an alkyl group having 1 to 5 carbon atoms which may have a substituent. When represented by R⁹When the alkyl group having 1 to 10 carbon atoms has a substituent, examples of the substituent include: and (4) an aryl group. The number of carbon atoms of the aryl group is usually 6 to 12, preferably 6 to 9. Specific examples of the aryl group include: phenyl, tolyl, xylyl, mesityl, naphthyl, and the like. The position of the substituent is not particularly limited. The number of the substituent is usually 1 to 4, preferably 1 to 3, and more preferably 1.

The polymerization reaction is carried out by a known method.

(Block Polymer)

The dispersant of the present invention has a block polymer structure. Specifically, the dispersant preferably has a block polymer structure containing at least a segment derived from a basic (meth) acrylate and a segment derived from a neutral (meth) acrylate. Furthermore, it is preferably a block copolymer having a segment a and a segment B.

The method for preparing the block copolymer is not particularly limited. The block copolymer is obtained by, for example, block polymerization using living radical polymerization or the like, and sequentially polymerizing monomers. The polymerization reaction of the monomers may be carried out by preparing the block A composed of the segment A and then polymerizing the monomers of the block B composed of the segment B onto the block A, or by preparing the block B and then polymerizing the monomers of the block A onto the block B. Further, in the preparation of the block copolymer, the block A and the block B may be prepared separately by polymerization of monomers, and then, the block A and the block B may be coupled.

The block copolymer is preferably a diblock copolymer comprising a block A and a block B, and usually comprises a linkage of (block A) - (block B), (block B) - (block A), or the like. It should be noted that the living radical polymerization method is a polymerization method capable of precisely controlling the molecular structure while maintaining the simplicity and versatility of radical polymerization. In the living radical polymerization method, there is a method (ATRP) using a transition metal catalyst due to a difference in the method of stabilizing the polymerization growth end; a method using a sulfur-based reversible chain transfer agent (RAFT); a method using an organotellurium compound (TERP), and the like. Among these methods, the method using an organic tellurium compound (TERP) described in WO2004/14848 and WO2004/14962 is preferably used from the viewpoint of the diversity of monomers that can be used and the control of the molecular weight in the high molecular region.

The weight average molecular weight Mw of the dispersant of the present invention is preferably in the range of 7000 to 20000. When the amount is 7000 or more, thermal decomposition of the dispersant is suppressed in the firing step (300 to 400 ℃) of dehydrating ring closure by heat treatment to imidize polyamide, thereby suppressing aggregation of carbon black and maintaining uniformity of electric resistance. From the viewpoint of solubility as a conductive agent dispersion, the weight average molecular weight Mw is preferably 20000 or less.

The weight average molecular weight Mw can be determined by gel permeation chromatography. One example of the measurement conditions is as follows.

Calibration curves were prepared using GPC (trade name: HPLC 11Series, manufactured by Agilent Technology Co.), a column (trade name: Shodex GPC LF-804, manufactured by Showa Denko K.K.), a mobile phase (10mM LiBr/N-methylpyrrolidone solution), polystyrene (molecular weights 1090000, 775000, 427000, 190000, 96400, 37900, 10200, 2630, 440, 92) as a standard substance, and the weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured.

[ conductive agent ]

As the conductive agent dispersed in the base layer of the present invention, a known electron conductive material or ion conductive material can be used.

Examples of the electron conductive material include: carbon for rubbers such as carbon black, SAF (super abrasion resistance), ISAF (quasi super abrasion resistance), HAF (high abrasion resistance), FEF (good extrudability), GPF (general purpose), SRF (medium reinforcement), FT (fine particle thermal decomposition), MT (medium particle thermal decomposition), carbon for color (ink) subjected to oxidation treatment, thermal decomposition carbon, natural graphite, synthetic graphite, carbon nanotube, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, germanium and other metals, metal oxides, polyaniline, polypyrrole, polyacetylene and other conductive polymers.

Further, as the ion conductive substance, for example: inorganic ion conductive materials such as sodium perchlorate, lithium perchlorate, calcium perchlorate, lithium chloride and the like; tridecylmethyldihydroxyethylammonium perchlorate, lauryltrimethylammonium perchlorate, modified aliphatic-dimethylethylammonium ethyl sulfate, N-bis (2-hydroxyethyl) -N- (3 '-dodecyloxy-2' -hydroxypropyl) methylammonium ethyl sulfate, 3-lauramidopropyl-trimethylammonium methyl sulfate, stearamidopropyl dimethyl- β -hydroxyethyl-ammonium-dihydrogenphosphate, quaternary ammonium perchlorates such as tetrabutylammonium fluoroborate, stearylammonium acetate, and laurylammonium acetate, sulfates, ethyl sulfate salts, methyl sulfate salts, phosphates, fluoroborates, acetates, and other organic ion conductive materials and charge transfer complexes.

In the present invention, the conductive agent preferably exhibits acidity. By using a conductive agent exhibiting acidity, high affinity with the dispersant of the present invention can be exhibited and dispersion stability can be improved.

The display of acidity means: 2g of the conductive agent was added to 20mL of distilled water, and after stirring for 5 minutes, the pH of the aqueous dispersion at 23 ℃ was less than 7.0.

The conductive agent may be added so that the volume resistance value and the surface resistance value of the intermediate transfer body fall within desired ranges. In general, the amount of the additive is preferably in the range of 10 to 20 parts by mass per 100 parts by mass of the resin, and more preferably in the range of 10 to 16 parts by mass per 100 parts by mass of the resin.

Examples of such a conductive agent include: acid carbon black, acid carbon nanotubes.

The kind of the carbon nanotube is not particularly limited, and a single-walled carbon nanotube or a multi-walled carbon nanotube can be used. Among them, the multilayered carbon nanotube is preferable from the viewpoint of electrical properties, mechanical properties, and affinity with a thermoplastic resin. The number of layers of the multilayered carbon nanotube is preferably 20 to 50. When the number of layers of the multilayered carbon nanotube layer is within the above range, the electrical conductivity and mechanical properties of the intermediate transfer belt can be further improved.

The diameter of the carbon nanotube is preferably 3 to 500nm, more preferably 10 to 200 nm. The length of the carbon nanotube is preferably 0.1 to 50 μm, and more preferably 0.5 to 20 μm.

the cylindrical graphite structure, which is a characteristic of the carbon nanotube, can be confirmed by a high-resolution transmission electron microscope. The graphite layer is preferably clearly visible and linear in a transmission electron microscope, but the graphite layer may be disordered. The disordered graphite layer is sometimes defined as a carbon nanofiber, but such a disordered graphite layer is also included in the concept of the carbon nanotube of the present invention.

As the conductive agent in the present invention, it is preferable to use acidic carbon black having a pH of 5.0 or less from the viewpoint that good dispersibility and dispersion stability in a resin composition (resin component) can be obtained, and a difference in resistance of a semiconductive belt is reduced, and electric field dependency is reduced, and further stability with time of resistance is improved without occurrence of electric field concentration due to transfer voltage.

The carbon black is subjected to oxidation treatment to impart carboxyl groups, quinone groups, lactone groups, hydroxyl groups, and the like to the surface thereof, thereby producing the above-mentioned acidic carbon black having a pH of 5.0 or less. The oxidation treatment is carried out by the following method: an air oxidation method of contacting and reacting with air under a high temperature atmosphere; a method of reacting with nitrogen oxide and ozone at normal temperature; and a method in which air oxidation is performed at a high temperature and then ozone oxidation is performed at a low temperature. Specifically, acidic carbon black having a pH of 5.0 or less can be produced by a contact method. Examples of the contact method include a channel method and a gas black method.

Further, the acid carbon black can be produced by a furnace black method using gas or oil as a raw material. Further, after these treatments, liquid-phase oxidation treatment with nitric acid or the like may be performed, as necessary. The acid carbon black can be produced by the contact method as described above, but is usually produced by a closed furnace method. In this furnace method, only carbon black having a high pH and low volatility is generally produced, but the above-mentioned liquid-phase oxidation treatment may be carried out to adjust the pH value.

The pH of the acidic carbon black of the present invention is preferably pH5.0 or less, more preferably pH4.5 or less, and still more preferably pH4.0 or less. The acid carbon having a ph of 5.0 or less has an oxygen-containing functional group such as a carboxyl group, a hydroxyl group, a quinone group, a lactone group, etc. on the surface, and therefore has good dispersibility in a resin, and can obtain good dispersion stability, reduce a difference in resistance of a semiconductive tape, and reduce electric field dependency, and hardly cause electric field concentration by a transfer voltage. The lower limit of the pH of the acidic carbon black is about 2.0.

The content of volatile components in the acidic carbon black having a pH of 5.0 or less is preferably in the range of 1 to 25% by mass, more preferably in the range of 3 to 20% by mass, and still more preferably in the range of 3.5 to 15% by mass. When the content of the above volatile component is less than 1% by mass, the effect of the oxygen-containing functional group attached to the surface may be lost, and the dispersibility in the resin component may sometimes be reduced. On the other hand, if the content of the above-mentioned volatile component is more than 25% by mass, decomposition may occur when it is dispersed in the resin composition, or water adsorbed onto the oxygen-containing functional group of the surface thereof may increase, whereby the appearance of the belt surface in the present invention is sometimes deteriorated.

On the other hand, when the content of the volatile component is set in the range of 1 to 25% by mass, the dispersion in the resin composition can be made more favorable. The content of the volatile component can be determined from the proportion of organic volatile components (carboxyl group, hydroxyl group, quinonyl group, lactone group, etc.) which appear when the carbon black is heated at 950 ℃ for 7 minutes.

As the acidic carbon black having a ph of 5.0 or less, specifically, there can be used: "Printex 150T" manufactured by Degussa corporation (ph4.5, volatile component 10.0 mass%), "Special black 350" manufactured by Degussa corporation (ph3.5, volatile component 2.2 mass%), "Special black 100" manufactured by Degussa corporation (ph3.3, volatile component 2.2 mass%), "Special black 250" manufactured by Degussa corporation (ph3.1, volatile component 2.0 mass%), "Special black 5" manufactured by Degussa corporation (ph3.0, volatile component 15.0 mass%), "Special black 4" manufactured by Degussa corporation (ph3.0, volatile component 14.0 mass%), "Special black 4A" manufactured by Degussa corporation (ph3.0, volatile component 14.0 mass%), and "Special black 4A" manufactured by Degussa corporation (ph3.0, volatile component 2.0 mass%), and "Special black 2.5 FW 2.2 mass%," volatile component 2.5% manufactured by Degussa corporation (ph3.0, volatile component 2.0 mass%), and a 5.0 mass%), volatile component 20.0 mass%), Color black FW2(pH2.5, volatile component 16.5 mass%) manufactured by Degussa, Color black FW2V (pH2.5, volatile component 16.5 mass%) manufactured by Degussa, MONARCH 1000 (pH2.5, volatile component 9.5 mass%) manufactured by Cabot, "MONARCH 1300 (pH2.5, volatile component 9.5 mass%) manufactured by Cabot, MONARCH 1400 (pH2.5, volatile component 9.0 mass%) manufactured by Cabot, MOGUL-L (pH2.5, volatile component 5.0 mass%) manufactured by Cabot, REGAL 400R (pH4.0, volatile component 3.5 mass%) manufactured by Cabot, and the like.

Since the acidic carbon black having a pH of 5.0 or less has excellent dispersibility in the resin composition due to the effect of the oxygen-containing functional group present on the surface, it is preferable to increase the amount of the conductive powder to be added, as compared with general carbon black. This increases the amount of conductive particles in the semiconductive belt, and thus, the effect of using the acidic carbon black can be exhibited to the maximum extent by suppressing the above-described fluctuation in the resistance value in the plane.

From the viewpoint of dispersion stability of the conductive agent, the average particle diameter of the conductive agent is preferably in the range of 0.05 to 0.20 μm. The average particle diameter of the conductive agent can be determined by taking a cross section of the intermediate transfer belt with an electron microscope and binarizing the cross section with an image processing device.

< elastic layer >

The elastic layer is a layer having desired conductivity and elasticity, which can be formed on the outer peripheral surface of the base material, as necessary. The elastic layer is preferably made of a rubber material. The thickness of the elastic layer may be, for example, 50 to 400 μm. Examples of the rubber material include rubber having, for example: and rubber elastic resins such as urethane rubber, Chloroprene Rubber (CR), and nitrile rubber (NBR). The rubber material preferably contains chloroprene rubber or nitrile rubber from the viewpoint of controlling the electrical resistance of the intermediate transfer belt.

The elastic layer may contain known additives. For example, a conductive agent may be contained to exhibit desired conductivity. As the conductive agent, a material for imparting conductivity to the resin material of the intermediate transfer belt can be used.

< surface layer >)

The surface layer may be formed on the outer peripheral surface of the substrate or on the outer peripheral surface of the elastic layer as needed, and the surface layer is preferably cured by irradiating a coating film of a surface layer forming coating liquid containing the metal oxide fine particles (a), the (meth) acrylate monomer (B) containing the refractive index nD in the range of 1.6 to 1.8, and the active energy ray-curable composition containing the polyfunctional (meth) acrylate (C) other than the (meth) acrylate monomer (B). The durability of the intermediate transfer belt can be improved.

In the intermediate transfer belt of the present invention, the (meth) acrylate monomer (B) having a refractive index nD in the range of 1.6 to 1.8 is preferably at least one or more selected from the group consisting of compounds represented by the following formulae (a) to (g).

[ chemical formula 9]

In the total content of the metal oxide fine particles (A), the structural units derived from the (meth) acrylate monomer (B) having a refractive index nD in the range of 1.6 to 1.8, and the structural units derived from the polyfunctional (meth) acrylate (C) other than the (meth) acrylate monomer (B), the content of the metal oxide fine particles (A) is preferably 5 to 30% by mass, the content of the structural units derived from the (meth) acrylate monomer (B) is preferably 20 to 50% by mass, and the content of the structural units derived from the polyfunctional (meth) acrylate (C) is preferably 40 to 75% by mass.

The metal oxide fine particles (a) are preferably surface-treated metal oxide fine particles.

Method for manufacturing intermediate transfer belt "

Next, a method for producing a seamless belt using a base material as an intermediate transfer belt by using a coating liquid containing a carbon black dispersion containing the above polyamideimide or its precursor and acidic carbon black will be described.

That is, in the present invention, when the seamless belt is produced using a composition containing the carbon black dispersion, the polyamideimide or the precursor thereof, and, for example, N-methylpyrrolidone as a solvent, and various additives added as necessary, it can be roughly realized by the following steps. That is, the production can be carried out by the following steps: a step of preparing a coating liquid; a step of applying the coating liquid to a support (a molding die) and casting the coating liquid; a step of removing the solvent in the coating film applied and cast on the support by heating; a step (also referred to as a firing step) of heating at an elevated temperature to promote imidization of precursors contained in the coating film; and a step of releasing the formed film from the support to produce a seamless belt.

First, a case where centrifugal molding is used as a support (molding die) will be described as an example. The following description is merely exemplary, and the conditions and the like are not limited thereto.

The step of preparing the coating liquid is preferably the following step: the carbon black dispersion in which the acidic carbon black is dispersed is prepared in advance by a dispersant having a block polymer structure containing a segment (a) derived from a basic (meth) acrylate and a segment (B) derived from a neutral (meth) acrylate, and then the carbon black dispersion is mixed with a polyamideimide or a precursor thereof.

The centrifugal molding preferably used in the step of applying/casting the coating liquid onto a support (molding die) is composed of a cylindrical rotating body, and the coating liquid is uniformly applied/cast (formed into a coating film) onto the entire inner surface of the cylinder while slowly rotating the cylindrical rotating body. Thereafter, the rotation speed is raised to a specified speed, and when the specified speed is reached, the rotation speed is maintained at a constant speed and is continued for a desired time.

Then, the coating film is rotated and the temperature is gradually increased to evaporate the solvent in the coating film at a temperature of about 80 to 150 ℃. In the step of removing the solvent in the coating film coated/cast on the support by heating, it is preferable to efficiently circulate and remove the vapor in the atmosphere (volatilized solvent, etc.). When a film having self-supporting properties is obtained, the temperature is returned to normal temperature, and the film is transferred to a heating furnace (firing furnace) capable of high-temperature treatment.

Thereafter, the step of heating at an elevated temperature to promote imidization of the precursor contained in the coating film is performed, and then high-temperature heat treatment (firing) at about 300 to 400 ℃ is performed to sufficiently imidize the precursor.

After the imidization was completed, the film was gradually cooled and peeled from the mold. Thereby, a seamless belt is formed. It is preferable to form a release agent or a release layer in the mold in advance so as to facilitate peeling.

< image Forming apparatus >)

Next, an image forming method and an image forming apparatus according to the present invention will be described.

The image forming apparatus preferably has the following mechanism on an electrostatic latent image carrier (hereinafter, also referred to as a photoreceptor): a charging mechanism, an exposure mechanism, a developing mechanism based on a developer containing a small-particle-diameter toner, and a transfer mechanism for transferring a toner image formed by the developing mechanism onto a transfer material via an intermediate transfer belt.

Specifically, there may be mentioned: a copying machine, a laser printer, and the like, and particularly, an image forming apparatus capable of continuously printing 5000 sheets or more is preferable. In such an apparatus, since a large number of printed matters are generated in a short time, an electric field is easily generated between the intermediate transfer belt and the transfer material, but the generation of the electric field is suppressed by the intermediate transfer belt of the present invention, and the secondary transfer can be stably performed.

An image forming apparatus capable of using the intermediate transfer belt of the present invention includes: a photoreceptor for forming an electrostatic latent image according to image information; a developing device for developing an electrostatic latent image formed on the photoreceptor; a primary transfer mechanism for transferring the toner image on the photoreceptor to an intermediate transfer belt; a secondary transfer mechanism for transferring the toner image on the intermediate transfer belt to a transfer material such as paper or an OHP sheet. Further, by having the intermediate transfer belt of the present invention as an intermediate transfer belt, stable toner image formation can be performed without generating peeling discharge at the time of secondary transfer.

As an image forming apparatus that can use the intermediate transfer belt of the present invention, there are: a monochrome image forming apparatus for forming an image using a monochrome toner; a color image forming device for sequentially transferring the toner images on the photoreceptor to the intermediate transfer belt; and a tandem type color image forming apparatus in which a plurality of photoreceptors of respective colors are arranged in tandem on an intermediate transfer belt.

The intermediate transfer belt of the present invention is effective when used for tandem-type color image formation.

Fig. 1 is a cross-sectional view showing an example of an image forming apparatus that can use the intermediate transfer belt of the present invention.

In fig. 1, reference numerals 1Y, 1M, 1C, and 1K denote photoreceptors, 4Y, 4M, 4C, and 4K denote developing mechanisms, 5Y, 5M, 5C, and 5K denote primary transfer rollers as primary transfer mechanisms, 5A denotes a secondary transfer roller as a secondary transfer mechanism, 6Y, 6M, 6C, and 6K denote cleaning mechanisms, 7 denotes an endless belt type intermediate transfer belt unit, 24 denotes a thermal roller type fixing device, and 70 denotes an intermediate transfer belt.

This image forming apparatus is called a tandem-type color image forming apparatus and is provided with a plurality of sets of image forming sections 10Y, 10M, 10C, and 10K, an endless belt-shaped intermediate transfer belt unit 7 as a transfer section, an endless belt-shaped paper conveying mechanism 21 that conveys a recording member P, and a hot roller-type fixing device 24 as a fixing mechanism. The original image reading apparatus SC is disposed on the upper portion of the main body a of the image forming apparatus.

The image forming section 10Y for forming a yellow image, which is one of the toner images formed on the photoreceptors of different colors, includes a drum-shaped photoreceptor 1Y as a first photoreceptor, a charging mechanism 2Y provided around the photoreceptor 1Y, an exposure mechanism 3Y, a developing mechanism 4Y, a primary transfer roller 5Y as a primary transfer device, and a cleaning mechanism 6Y. The image forming section 10M for forming a magenta image, which is one of the toner images of different colors, includes a drum-shaped photoreceptor 1M as a first photoreceptor, a charging mechanism 2M, an exposure mechanism 3M, a developing mechanism 4M, a primary transfer roller 5M as a primary transfer device, and a cleaning mechanism 6M, which are provided around the photoreceptor 1M. The image forming section 10C for forming a cyan image, which is one of the toner images having different colors, includes a drum-shaped photoreceptor 1C as a first photoreceptor, a charging mechanism 2C, an exposure mechanism 3C, a developing mechanism 4C, a primary transfer roller 5C as a primary transfer device, and a cleaning mechanism 6C, which are provided around the photoreceptor 1C. The image forming unit 10K for forming a black image includes, as one of the toner images having different colors, a drum-shaped photoreceptor 1K as a first photoreceptor, a charging mechanism 2K, an exposure mechanism 3K, a developing mechanism 4K, a primary transfer roller 5K as a primary transfer device, and a cleaning mechanism 6K provided around the photoreceptor 1K.

The endless belt-like intermediate transfer belt unit 7 has, as an intermediate transfer endless belt-like second image carrier, an endless belt-like intermediate transfer belt 70 wound around by a plurality of rollers and rotatably supported.

The images of the respective colors formed by the image forming portions 10Y, 10M, 10C, and 10K are successively transferred onto the rotating endless belt-like intermediate transfer belt 70 by the primary transfer rollers 5Y, 5M, 5C, and 5K, and are sequentially transferred, forming a composite color image. A recording member P such as paper is fed as a transfer material contained in a paper feed cassette 20 by a paper feed transport mechanism 21, and is conveyed to a secondary transfer roller 5A as a secondary transfer device via a plurality of intermediate rollers 22A, 22B, 22C, and 22D and a resist roller 23, so that a color image is transferred onto the recording member P at once. The recording member P to which the color image has been transferred is subjected to a fixing process by a heat roller type fixing device 24, and is then sandwiched by paper discharge rollers 25 and placed on a paper discharge tray 26 outside the machine.

On the other hand, the color image is transferred onto the recording member P by the secondary transfer roller 5A, and then the residual toner is removed by the cleaning mechanism 6A from the endless belt-shaped intermediate transfer belt 70 on which the curvature separation is performed on the recording member P.

In the image forming process, the primary transfer roller 5K is always in contact with the photoreceptor K. The other primary transfer rollers 5Y, 5M, and 5C are respectively brought into abutment with the corresponding photoreceptors 1Y, 1M, and 1C only at the time of color image formation.

When only the recording member P is secondary-transferred by the secondary transfer roller 5A, the secondary transfer roller 5A abuts against the endless belt-like intermediate transfer belt 70.

Further, the frame body 8 can be pulled out from the apparatus main body a through the support rails 82L, 82R.

The frame 8 includes image forming portions 10Y, 10M, 10C, and 10K and an endless belt-shaped intermediate transfer unit 7.

The image forming portions 10Y, 10M, 10C, and 10K are arranged in vertical columns. An endless belt-shaped intermediate transfer belt unit 7 is disposed on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the drawing. The endless belt-like intermediate transfer belt unit 7 includes: an endless belt-like intermediate transfer belt 70 wound around rollers 71, 72, 73, 74, and 76 and rotatable; primary transfer rollers 5Y, 5M, 5C, 5K; and a cleaning mechanism 6A.

By the drawing operation of the frame 8, the image forming portions 10Y, 10M, 10C, and 10K and the endless belt-like intermediate transfer belt unit 7 are integrated and drawn out from the main body a.

As described above, the photoreceptors 1Y, 1M, 1C, and 1K are charged, exposed, and developed to form toner images, the toner images of the respective colors are superimposed on the endless belt-shaped intermediate transfer belt 70 and transferred to the recording member P at one time, and the fixing device 24 of the heat roller type is fixed and fixed by applying pressure and heat. The photoreceptors 1Y, 1M, 1C, and 1K after the toner images are transferred to the recording member P are cleaned of the toner remaining on the photoreceptors at the time of transfer by the cleaning mechanism 6A, and then the above-described charging, exposure, and development cycles are repeated to form the next image.