JPH1063115A - Image forming device and production of its intermediate transfer belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of easily imparting a prescribed surface resistivity to an intermediate transfer belt material and suppressing the variation in the surface resistivity of this belt material to a lower level. SOLUTION: The secondary transfer member of this device has an intermediate transfer belt 6, a biasing roll 9 for secondarily transferring the unfixed toner image on this transfer belt to a recording medium P and a back up roll 8 facing this biasing roll 9 and supporting the transfer belt from its rear surface. At this time, the intermediate transfer belt 6 is composed of a thermosetting polyimide resin dispersed with conductive metal oxide having an average particle size of <1μm. This metal oxide is preferably prepd. by compounding 32 to 40 pts.wt. with 100 pts.wt. polyimide subjected to a surface treatment with a silane coupling agent. Such intermediate transfer belt is produced by casting and molding the stock soln of the polyamide dispersed with the metal oxide described above on a metallic sheet, then joining both ends of the resulted film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus using an electrophotographic method, such as a laser printer, a facsimile, and a composite OA device thereof.
More specifically, an image forming apparatus in which a toner image formed on an image carrier is once primarily transferred to an intermediate transfer belt and then transferred to a recording medium such as paper to obtain a reproduced image, The present invention relates to a method for manufacturing a transfer belt.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system is a laser in which a uniform charge is formed on an image carrier composed of a photoreceptor made of an inorganic or organic photoconductive material and an image signal is modulated. After forming an electrostatic latent image with light or the like, the electrostatic latent image is developed with charged toner to obtain a visualized toner image. Then, the toner image is transferred onto a recording medium such as paper directly or via an intermediate transfer member to obtain a required reproduced image. An image forming apparatus adopting a system in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer member and a toner image on the intermediate transfer member is secondarily transferred to a recording medium is disclosed in, for example, No. 206567 discloses this. Examples of a belt material used in an image forming apparatus employing an intermediate transfer member system include polyvinylidene fluoride (PVDF) (Japanese Patent Application Laid-Open Nos. 5-200904 and 6-228335) and polycarbonate (PC).
(JP-A-6-95521), polyalkylene terephthalate (PAT) (JP-A-6-149081), and a blend material of PAT and PC (JP-A-6-14)
No. 9083), a blend material of ethylene-tetrafluoroethylene copolymer (ETFE) and PC, ETF
Blend material of E and PAT, ETFE, PC and PAT
There has been proposed a conductive endless belt in which a conductive material such as carbon black is blended with a thermoplastic resin such as a blend material (Japanese Patent Application Laid-Open No. 6-149079). The above PVDF,
Conductive materials composed of thermoplastic resins such as PC have a Young's modulus of 24000 kg / cm ² or less, which is inferior in mechanical properties.
Belt deformation due to stress applied to the belt during driving is large, and when applied to an intermediate transfer belt, a high-quality transfer image cannot be obtained stably. Poor sex.

Japanese Patent Application Laid-Open No. 63-31263 proposes a seamless belt of a thermosetting polyimide resin material dispersed with carbon black as a material having excellent mechanical properties. This seamless belt was obtained by dispersing 5 to 20% by weight of carbon black as a conductive agent in a solution of polyamic acid as a polyimide precursor, casting the dispersion on a metal drum and drying, and then peeling off the drum. It is manufactured by stretching a film at a high temperature to obtain a polyimide film, and further cutting out the film into an appropriate size to form an aidless belt. Furnace black (Ketjen black) and acetylene black are used as carbon black, and as a solvent for dissolving polyamic acid,
Organic polar solvents such as dimethylacetamide and N-methylpyrrolidone are used. A general method of forming the film is to inject a polymer solution in which carbon black is dispersed into a cylindrical mold and heat the polymer solution to, for example, 110 to 150 ° C.
While rotating the cylindrical mold at a rotation speed of 1000 to 2000 rpm,
It is formed into a film by centrifugal molding. The obtained film is released in a semi-cured state and covered with an iron core.
At 50 ° C., the imidization reaction (ring-closing reaction of the polyamic acid) proceeds to perform the main curing.

However, only the carbon black having a high oil absorption of dibutyl phthalate (DBP) such as Ketjen black or acetylene black, which imparts conductivity, is blended with the polyimide resin to adjust the surface resistivity of the intermediate transfer belt material. Then, even if the amount is slightly increased or decreased, the surface resistivity greatly changes. Therefore, there is a problem that the intermediate transfer belt material cannot obtain a predetermined surface resistivity unless the compounding amount of the carbon black is strictly defined. Furthermore, carbon black having a high DBP oil absorption is liable to undergo secondary aggregation in a polymer solution, and thus has a disadvantage that resistance unevenness of a belt material is generally large. In the case of the rotary molding method such as the centrifugal molding method, when the evaporation of the solvent becomes uneven in the molding and main curing steps, minute irregularities are formed on the film surface. Therefore, when secondary transfer is performed using an intermediate transfer belt manufactured from such a film, minute transfer defects (white spots) occur in an image transferred to a recording medium due to minute unevenness. There are problems such as. On the other hand, if a smooth film is to be obtained, a molding / curing step for evaporating and drying the organic polar solvent and curing the polyamic acid usually requires about 8 hours, which increases the production cost of the belt.

[0005]

In the prior art, a seamless belt of carbon black-dispersed thermosetting polyimide resin having excellent mechanical properties strictly regulates the amount of carbon black for which the surface resistivity is to be adjusted. Otherwise, a predetermined surface resistivity cannot be given to the intermediate transfer belt material. Further, in order to prevent image defects due to unevenness of the belt surface, the present inventors, for the centrifugal molding step and the main curing step, reduce the rate of temperature rise to reduce the evaporation rate of the solvent or the circulation path of hot air. Evaluations have been made to make the evaporation rate of the solvent from the film surface uniform, such as changing the evaporation rate, and to improve the unevenness in evaporation at the time of desolvation. However, problems such as high belt manufacturing costs due to a long drying time remain unsolved.

As described above, in the conventional intermediate transfer belt of the image forming apparatus, it is not possible to stably and inexpensively manufacture a belt having excellent mechanical characteristics, less resistance unevenness, and having no irregularities on the surface. There was a problem. Then, an object of the present invention is to solve the above-mentioned problems, and it is possible to easily provide a predetermined surface resistivity to the intermediate transfer belt material and to reduce the variation in the surface resistivity of the belt material. An object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image by realizing a belt which can be suppressed to a small size and has no surface defects, and a method of manufacturing the intermediate transfer belt.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on an intermediate transfer belt of an image forming apparatus using a thermosetting polyimide resin having excellent mechanical properties as a constituent material so as to reduce the variation in the surface resistivity.・ As a result of repeated studies, it is easy to adjust the surface resistivity by using a conductive metal oxide having an average particle diameter equal to or less than a predetermined value in place of the conventional carbon black as the conductive agent, so that the surface resistivity can be easily adjusted. In the case where the metal oxide is not unevenly distributed, and when the casting molding method is employed as the film forming method, it has been found that the formation of irregularities on the film surface is particularly suppressed, and the present invention has been achieved. Was. That is, the image forming apparatus of the present invention includes an image carrier on which an electrostatic latent image corresponding to image information is formed, and a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner. An intermediate transfer belt on which a toner image carried on an image carrier is primarily transferred, a bias roll for secondary transfer of an unfixed toner image on the intermediate transfer belt to a recording medium, and an intermediate transfer facing the bias roll. A backup roll for supporting the belt from the back surface thereof, wherein the intermediate transfer belt material is made of a thermosetting polyimide resin in which a conductive metal oxide having an average particle diameter of less than 1 μm is dispersed. Further, the method for producing an intermediate transfer belt for an image forming apparatus according to the present invention is characterized in that the polyamic acid in which the conductive metal oxide having an average particle diameter of less than 1 μm or the metal oxide surface-treated with a silane coupling agent is dispersed. Or after casting a polyimide resin polymer liquid on a metal sheet,
It is characterized in that both ends of the sheet of the obtained film are joined.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
FIG. 1 is a simplified diagram showing an outline of an arrangement relationship of an intermediate transfer belt in an image forming apparatus having main components. FIG.
1, a charger 2, a developing device 3, a primary transfer device 4, a cleaning device 5, and the like are sequentially arranged on a peripheral surface of an image carrier 1 formed of a photosensitive drum along a rotation direction thereof. In addition, the intermediate transfer belt 6 is
a, 7b, 7c and the backup roll 8. The intermediate transfer belt 6 moves in the direction of the arrow while abutting on the surface of the image carrier 1, and performs primary transfer when passing between the image carrier 1 and the primary transfer device 4 arranged opposite thereto. The unfixed toner image primary-transferred by the device 4 is carried. The bias roll 9 and the belt cleaner 1 are located at positions facing the backup roll 8 and the belt transport roll 7a via the intermediate transfer belt 6, respectively.
0 is disposed, and the backup roll 8 supports the intermediate transfer belt 6 from the back surface. A transfer voltage is applied between the backup roll 8 and the bias roll 9, and the unfixed toner image carried on the intermediate transfer belt 6 is transferred to a recording medium such as paper P (hereinafter, represented by paper P). Next is transferred.

In the present invention, the intermediate transfer belt 6 is made of a thermosetting polyimide resin containing an appropriate amount of a conductive metal oxide having an average particle diameter of less than 1 μm. The intermediate transfer belt 6 will be described later in detail. . The backup roll 8 forms a counter electrode of the bias roll 9. The layer structure of the backup roll 8 may be either a single layer or a multilayer. For example, in the case of a single-layer structure, it is constituted by a roll in which an appropriate amount of conductive fine powder such as carbon black is mixed with silicone rubber, urethane rubber, EPDM or the like. 2
In the case of a layered structure, a roll in the case of a single layer whose volume resistivity is appropriately adjusted is used as a lower layer, and a conductive surface layer whose outer peripheral surface is coated with, for example, a fluorine-based resin. FEP (TFE-HFP copolymer), PFA
And the like. The hardness of the backup roll 8 is preferably in the range of 60 to 75 ° for Asker C.

A bias roll 9 for forming a transfer electrode includes:
While the toner image carried on the image carrier 1 is primarily transferred onto the intermediate transfer belt 6, the toner image is separated from the transfer belt 6;
When the toner image carried on the transfer belt 6 is secondarily transferred onto the sheet P, the toner image is pressed against the transfer belt 6 and pressed against the backup roll 8. The layer structure of the bias roll 9 is not particularly limited. For example, in the case of a two-layer structure, the bias roll 9 includes a core layer and a coating layer covering the surface thereof. The core layer is made of silicone rubber, urethane rubber, EPDM, or the like or a foam thereof in which conductive fine powder is dispersed. The coating layer is preferably made of the fluorine-based resin in which conductive fine powder is dispersed. The bias roll 9 generally has Asker C hardness.
In the range of 30 to 45 °.

As the primary transfer device 4, a corona transfer device such as a corotron, a transfer roll, a transfer blade or the like is used. A voltage of 1 to 4 kV is applied to the primary transfer device 4, and the toner image carried on the image carrier 1 is transferred to the intermediate transfer belt 6 by the action of an electric field generated between the image carrier 1 and the primary transfer device 4. Is primary-transferred. As described above, a transfer voltage for transferring the toner image carried on the intermediate transfer belt 6 to the paper P is applied between the backup roll 8 and the bias roll 9. Regarding the transfer voltage, a voltage may be applied to the core of the backup roll 8 or an electrically conductive electrode roll pressed against the roll 8, or a voltage may be applied to the bias roll 9. The belt cleaner 10 removes the toner remaining on the intermediate transfer belt 6 after the secondary transfer.

As described above, the intermediate transfer belt 6 is composed of a thermosetting polyimide resin and a conductive metal oxide. The thermosetting polyimide resin has characteristics that it has excellent mechanical properties as compared with a thermoplastic resin, and the deformation of the belt during driving is small. Polyimide resins are generally synthesized by polycondensation of tetracarboxylic dianhydride with diamine or diisocyanate. In the former diamine method, a solvent-soluble polyamic acid is usually synthesized by ring-opening polyaddition in an organic polar solvent, and a film is processed at this stage. Thereafter, the film-form polyamic acid is heated to a high temperature of 350 ° C. or more, and is imidized by dehydration condensation. In the latter diisocyanate method, a diisocyanate is usually added to a tetracarboxylic acid dianhydride solution in a polar solvent, and the solution is heated to decarbonate, thereby imidizing.

The tetracarboxylic acid component of the polyimide resin includes pyromellitic acid, naphthalene-1,4,5,8
-Tetracarboxylic acid, naphthalene-2,3,6,7-tetracarboxylic acid, 2,3,5,6-biphenyltetracarboxylic acid, 2,2 ', 3,3'-biphenyltetracarboxylic acid, 3,3 ', 4,4'-biphenyltetracarboxylic acid, 3,3', 4,4'-diphenylethertetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic acid, 3,3', 4,4 '-Diphenylsulfonetetracarboxylic acid, azobenzene-3,3', 4,
4'-tetracarboxylic acid, bis (2,3-dicarboxyphenyl) methane, bis (3,4-dicarboxyphenyl) methane, 2,2-bis (3,4-dicarboxyphenyl) propane, 2,2 -Bis (3,4-dicarboxyphenyl) hexafluoropropane and the like.

As the diamine component, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4-diaminochlorobenzene, m-xylylenediamine, p-xylylenediamine , 1,4-diaminonaphthalene, 1,5-
Diaminonaphthalene, 2,6-diaminonaphthalene,
2,4'-diaminobiphenyl, benzidine, 3,3 '
-Dimethylbenzidine, 3,3'-dimethoxybenzidine, 3,4'-diaminodiphenyl ether, 4,4 '
-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminoazobenzene, 4,4'-
Diaminodiphenylmethane and the like.

Examples of the diisocyanate component include compounds in which an amino group in the diamine component is substituted with an isocyanate group. Further, as the organic polar solvent, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-
Examples include methylcaprolactam, hexamethylphosphamide, dimethylsulfoxide, dimethylsulfone, tetramethylenesulfone and the like.

In order to impart conductivity to the polyimide resin, tin oxide, zinc oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide-tin oxide composite oxide (ATO), indium oxide-tin oxide composite oxide are used. A conductive metal oxide such as a material (ITO) is blended. These conductive metal oxides may be coated with insulating fine particles such as barium sulfate, magnesium silicate and calcium carbonate. The metal oxide having an average particle diameter of less than 1 μm is used. When the average particle size is 1 μm or more,
The weight per unit particle increases, and metal oxides are unevenly dispersed and dispersed in the belt material formed by the casting method, the centrifugal molding method, and the like, and the variation in the surface resistivity of the intermediate transfer belt tends to increase. . Average particle size is 1μ
The metal oxide is not particularly limited as long as it is less than m, but usually a metal oxide having a size of 0.01 μm or more is used due to restrictions on manufacturing cost. The metal oxides preferably used include a zinc-based oxide (Pastran Type-II) having an average particle size of 0.3 μm and a tin oxide-based composite oxide (product name: UF) having an average particle diameter of 0.3 μm manufactured by Mitsui Kinzoku Co., Ltd. ), 0.2 μm ATO, 0.2 μm
m, and barium sulfate having an average particle diameter of 0.4 μm coated with a tin-based oxide (Pastran Type)
-IV) and the like.

The amount of the metal oxide varies depending on the type, particle size, dispersion state, etc. of the oxide.
It is in the range of 30 to 38 parts by weight, preferably 33 to 36 parts by weight, per 100 parts by weight. The surface resistivity of the intermediate transfer belt can be reduced to 1 by selecting the metal oxide and adjusting the blending amount.
It is adjusted in the range of 0 ¹¹ to 10 ¹⁵ Ω / □. When transferring a toner image to an intermediate transfer belt by an electrostatic transfer method, it is important that the intermediate transfer belt has a predetermined surface resistivity. If the surface resistivity is too high, the intermediate transfer belt is significantly charged at the time of transfer of the toner image, so that peeling discharge occurs when the intermediate transfer belt separates from the image carrier, and the toner image transferred to the intermediate transfer belt Are scattered along with the peeling discharge. On the other hand, if the surface resistivity is too low, an excessive current flows between the intermediate transfer belt and the image carrier, so that the toner image once transferred to the intermediate transfer belt returns to the image carrier, so-called A phenomenon called retransfer occurs. In order to avoid these phenomena, the above range of the surface resistivity of the intermediate transfer belt is appropriate.

Conventional carbon black fine particles for adjusting the surface resistivity of the resin belt material are linked in a chain form (secondary aggregation) in the resin composition containing the same, thereby imparting conductivity to the belt material. Examples of carbon black include Ketjen Black (manufactured by Lion Aguso Co., Ltd.) having an oil absorption of 360 ml / 100 g, granular acetylene black (manufactured by Denki Kagaku) having an oil absorption of 288 ml / 100 g, and Vulcan XC-72 having an oil absorption of 265 ml / 100 g. (Manufactured by Cabot Corporation) and the like are used. Since carbon black having a higher DBP oil absorption forms a longer chain bond, the surface resistivity of the intermediate transfer belt varies depending on the length of the chain bond, and resistance unevenness increases. On the other hand, since the conductive metal oxide in the present invention can be uniformly dispersed in the polyimide resin, it does not essentially form a long chain bond unlike carbon black. Therefore, the adjustment of the surface resistivity is easy, and the variation can be suppressed. The oil absorption is A
It is a value measured in accordance with STM D2414-6TT and the amount of DBP absorbed by 100 g of carbon black expressed in ml.

The surface of the conductive metal oxide is preferably treated with a silane coupling agent. This treatment is performed by adding and mixing a metal oxide to a silane coupling agent solution dissolved in an appropriate solvent, and evaporating and drying the solvent. The surface-treated metal oxide (the surface-treated or non-treated conductive metal oxide is sometimes referred to as a conductive agent hereinafter) has improved compatibility with the polyimide resin, so that the dispersion is uniform, and the surface of the metal oxide is uniform. Variation in resistivity is further suppressed. The amount of the metal oxide surface-treated with the silane-based coupling agent varies depending on the type of the metal oxide for the same reason as that of the metal oxide not subjected to the surface treatment. In Although,
It is in the range of 32 to 40 parts by weight, preferably 35 to 38 parts by weight, based on 100 parts by weight of the polyimide resin. Examples of the silane coupling agent include vinyltrichlorosilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxy. Silane, γ
Methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N-
(Β-aminoethyl) -γ-aminopropylmethyldimethoxysilane and the like.

The relationship between the Young's modulus of the belt material and the amount of displacement of the belt due to load fluctuation during belt driving can be expressed by the following equation. Δl = α · P · l / (t · w · E) where Δl: belt displacement (μm) α: coefficient P: load (N) l: belt length between two tension rolls ( mm) t: belt thickness (mm) w: belt width (mm) E: Young's modulus of the belt material (N / mm ² ). That is, it is known that the elongation / shrinkage (displacement amount) of the belt due to disturbance (load fluctuation) at the time of driving the belt is inversely proportional to the Young's modulus of the belt material. Conventional thermoplastic resin materials such as polycarbonate and polyvinylidene fluoride have a Young's modulus of 2400 when carbon black is dispersed.
While it is about 0 kg / cm ² , the Young's modulus of the thermosetting polyimide resin in which the conductive metal oxide of the present invention is dispersed is 60,000 kg / cm ² or more. Therefore, a high-quality transfer image can be obtained with little expansion and contraction of the belt due to disturbance at the time of driving the belt.

The intermediate transfer belt of the present invention is manufactured as follows. In the case of the diamine method, the conductive agent is added to an organic polar solvent of a polyamic acid to be synthesized, and the mixture is sufficiently mixed with a mixer to prepare a film forming stock solution. In the case of the diisocyanate method, a solution of a polyimide to be synthesized or its powder is dissolved in an organic polar solvent, and a conductive agent is added to prepare a stock solution for film formation. In either method, the polymer concentration of the membrane-forming stock solution is in the range of 10 to 40% by weight,
A conductive agent may be added to the polymer raw material in advance. In addition, it is desirable that a film forming stock solution be passed through a filter before film formation to remove a conductive agent and foreign matters which are secondary aggregated and coarsened. The film forming method in the present invention may be either a rotary forming method using a rotating drum such as a centrifugal forming method, or a casting method of forming on a metal sheet, but the latter method in which the film surface is formed more smoothly. Is preferred. That is, since the seamless belt obtained by the rotary molding method uses a molding machine sealed at the time of molding, uneven evaporation of the solvent occurs due to non-uniform saturation vapor pressure of the solvent in the molding machine and the like, and the film surface is uneven. Fine irregularities are easily formed. In the casting method, a stock solution is cast from a slit die onto an endless metal sheet belt. The final molded film (belt material)
Has a thickness in the range of 40 to 100 μm, and is adjusted mainly by the polymer concentration of the film-forming stock solution, the compounding amount of the conductive agent, the extrusion amount, and the liquid film take-up speed.

In order to suppress the formation of minute irregularities on the surface of the film to be formed, it is desirable to gradually increase the drying temperature of the stock solution. For example, when the polymer of the stock solution is polyamic acid, the casting film on the belt is
Heat at 0 ° C. for about 2 hours. Then, 150-3
The polar solvent is almost completely evaporated by heating at a temperature of 50 ° C. for about two and a half hours. This step is performed at 150 ° C to 35 ° C.
Do not raise the temperature to 0 ° C all at once.
This is performed while the temperature is gradually increased in steps of up to five steps or continuously. Thereafter, the polyimide film is obtained by heating at 420 ° C. for 30 minutes to cause dehydration condensation of the polyamic acid. When the polymer of the film-forming stock solution is polyimide, the dehydration-condensation step may be omitted. At an arbitrary stage after the completion of the condensation step from the point at which the solvent evaporates in the drying step to form a self-supporting film,
It is preferable to perform a stretching process on the formed film.
The resulting polyimide film is cut into a suitable size, and the sheet edges are joined with an adhesive, whereby the intermediate transfer belt of the present invention is manufactured. As the adhesive, a one-component or two-component silicone-based elastic adhesive, a urethane-based elastic adhesive, a sheet-like hot-melt type silicone-based adhesive, a silane-modified polyimide-based adhesive, or the like is used. The silicone-based and urethane-based adhesives may be modified with various components or functional groups. These adhesives can be used alone or in combination with a high-strength adhesive such as an epoxy-based adhesive.

The operation of the present invention is as follows. The operation of the image forming apparatus according to the first aspect of the invention is as follows. The electrostatic latent image formed on the image carrier 1 according to the image information is developed by the toner in the developing device 3 and is visualized as an unfixed toner image. This toner image is transferred to the intermediate transfer belt 6 in the primary transfer section while being carried on the image carrier 1. When transferring a multicolor image, the primary transfer is repeated for each color of the toner stored in the developing device 3. When the primary transfer of the toner image from the image carrier 1 onto the intermediate transfer belt 6 is completed, and the intermediate transfer belt 6 carrying the toner image of a desired hue moves to the secondary transfer portion, it is synchronized with this. Then, the paper P is transported to the secondary transfer unit. Paper P
When passing through the secondary transfer portion while receiving the pressing force between the backup roll 8 and the bias roll 9,
By applying a transfer voltage between the transfer belts 9, the toner image carried on the transfer belt 6 is secondarily transferred onto the sheet P from the surface of the intermediate transfer belt 6. In the image forming apparatus of the present invention, the Young's modulus of the thermosetting polyimide resin in which the conductive metal oxide is dispersed is higher than that of the conventional thermoplastic resin material in which carbon black is dispersed. Belt displacement due to load fluctuation is small. In addition, since the average particle diameter of the metal oxide is less than 1 μm, the metal oxide is not unevenly distributed in the belt material during molding, and the variation in the surface resistivity of the intermediate transfer belt is reduced. Is possible. Furthermore, since the conductive metal oxide does not form a long chain bond unlike carbon black when secondary agglomerated, it is easy to adjust the surface resistivity of the intermediate transfer belt. Therefore, a high quality transfer image can be obtained.

According to a second aspect of the present invention, the conductive metal oxide is surface-treated with a silane-based coupling agent, and the surface-treated metal oxide has improved compatibility with a polyimide resin. Therefore, the variation in the surface resistivity is further reduced. The image forming apparatus according to the third aspect of the present invention is obtained by mixing 32 to 40 parts by weight of a metal oxide surface-treated with a silane coupling agent with 100 parts by weight of a polyimide resin constituting a belt material. It is easier to set the surface resistivity of the intermediate transfer belt to a predetermined value in the range of 10 ¹¹ to 10 ¹⁵ Ω / □ as compared with conventional carbon black. According to a fourth aspect of the present invention, an endless belt formed by seaming a film-like belt material is used as an intermediate transfer belt.

According to a fifth aspect of the present invention, there is provided a method of manufacturing an intermediate transfer belt for an image forming apparatus, comprising: forming a polymer solution of a polyamic acid or a polyimide resin in which a conductive agent having an average particle diameter of less than 1 μm is dispersed on a metal sheet by casting. Then, both ends of the obtained film are joined to produce an intermediate transfer belt. According to the fifth aspect of the invention, it is possible to suppress the formation of minute irregularities on the surface of the film to be formed by raising the drying temperature of the polymer liquid stepwise. Further, the same effect as that of the first aspect of the present invention is obtained, for example, the variation of the surface resistivity of the intermediate transfer belt can be reduced.

[0026]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples. (Image Forming Apparatus) FIG. 2 is an overall view of a digital color copying machine provided with an intermediate transfer belt as an image forming apparatus of the present invention. The components having the same functions as those of the components of the image forming apparatus shown in FIG. 1 are denoted by the same reference numerals in FIG. 2, light emitted from a document illumination lamp 12 moving along the lower surface of a document (not shown) placed on a platen 11 and reflected by the document is reflected by a movable mirror unit 13, a lens 14, and a fixed mirror. The light is converged on the CCD of the image reading unit via the line 15. The CCD converts the original image into an electric signal for each color by using a number of photoelectric conversion elements and filters of three colors of blue (B), green (G), and red (R). This electric signal is input to the image processing circuit 16,
The image processing circuit 16 has an image memory that converts a document image reading signal input for each color into a digital signal and stores it.

The optical writing control device 17 reads out the image data of the image processing circuit 16 at a predetermined timing and outputs it to the light beam writing device 18. Light beam writing device 18
Writes an electrostatic latent image corresponding to each color on the image carrier 1 composed of a photosensitive drum rotating in the direction of arrow A. Around the image carrier 1, a charger 2 for uniformly charging the surface thereof, a developing unit (developing device) 3 for developing an electrostatic latent image written on the image carrier 1 into a toner image of each color, and each color A transfer corotron (primary transfer device) 4 for transferring the toner image to the intermediate transfer belt 6, a cleaner unit (cleaning device) 5 having a static eliminator and a cleaning blade are arranged. The developing unit 3 has a developing device containing toner of each color of black (K), yellow (Y), magenta (M), and cyan (C), and develops the electrostatic latent image with the toner of each color. And visualize. The intermediate transfer belt 6 is
Backup Roll 8 and Belt Transport Roll 7
a, 7b, and 7c, and moves in the tangential direction while abutting on the surface of the image carrier 1. In this embodiment, of the rolls (7, 8) that stretch the transfer belt 6, the transfer belt 6
The belt transport roll 7a is configured as a drive roll, and the other rolls (7b, 7c, 8) are configured as driven rolls so that moves in the direction of arrow B. In order to prevent the transfer belt 6 from bending, the axis of the transport roll 7c is urged in the direction C by a spring (not shown).

On the back side of the intermediate transfer belt 6, the transfer corotron 4 is disposed at a primary transfer portion where the surface of the image carrier 1 and the transfer belt 6 come into contact. On the other hand, on the front side of the transfer belt 6 that carries the unfixed toner image, the bias roll 9 and the belt cleaner 10 are disposed to face the backup roll 8 and the belt transport roll 7a, respectively. An electrode roll 19 connected to a transfer voltage power supply is pressed against the backup roll 8, and a portion where the backup roll 8 and the bias roll 9 face each other forms a secondary transfer portion. Further, between the backup roll 8 and the belt transporting roll 7a, a peeling claw 20 for peeling the paper P carrying the secondary-transferred toner image from the transfer belt 6 is provided.
Is arranged. A cleaning blade 21 made of polyurethane is always in contact with the surface of the bias roll 9 to remove foreign matters such as toner particles and paper powder adhered during secondary transfer or the like.

An extractable paper feed tray 22 is provided below the main body of the image forming apparatus U, and a pickup roller 23 is disposed above the paper feed tray 22. This pickup roller 2
Downstream of 3, a pair of feed rolls 24 for preventing double feeding of the paper P, a paper transport roll 25, a guide member 26 for guiding the paper P, and a registration roll 27 are sequentially arranged. On the downstream side of the secondary transfer section, a transport belt 2 for transporting a sheet P carrying a secondary-transferred toner image sequentially
8, a fixing device 29 for fixing an unfixed toner image on the paper P, a pair of discharge rolls 30 for discharging the paper P on which the fixed image is formed outside the machine, and a paper discharge on which the discharged paper P is placed. A tray 31 is arranged.

(Operation of Image Forming Apparatus) The surface of the image carrier 1 rotating in the direction of arrow A is uniformly charged by the charger 2, and an electrostatic latent image is written by the light beam writing device 18. The electrostatic latent image on the image carrier 1 is developed by the developing unit 3 into an unfixed toner image. In the formation of the toner image, a toner image of a first color is formed first, and thereafter, every time the image carrier 1 rotates for a predetermined time, a toner image of a second color to a fourth color is formed. In this embodiment, K, Y, M, and C toner images are sequentially formed. The surface of the image carrier 1 is cleaned by the blade of the cleaner unit 5 after the toner image is transferred to the intermediate transfer belt 1. Here, in the optical writing control device 17,
First, the K-color digital signal of the first color is read and output to the light beam writing device 18. The writing device 18 writes an electrostatic latent image corresponding to K color on the surface of the image carrier 1. The electrostatic latent image corresponding to the color K is developed by the developing unit K in the developing unit 3 into a visualized toner image of the color K, and moves to the primary transfer unit. In the primary transfer section, an electric field having a polarity opposite to the charging polarity is applied to the toner image from the transfer corotron 4 disposed on the back side of the intermediate transfer belt 6 so that the K color toner image that has reached the primary transfer section is transferred. While being electrostatically attracted to the transfer belt 6, primary transfer is performed by moving the transfer belt 6 in the direction of arrow B.

The intermediate transfer belt 6 moves at the same cycle as the image carrier 1 while adsorbing and carrying the K toner image. When the transfer of the K toner image of the first color is completed, the blue (B) filter is used by the output from the optical writing controller 17 until the transfer start position of the K toner image on the transfer belt 6 reaches the primary transfer portion. Writing of the electrostatic latent image corresponding to the color-separated light image is started. When the transfer start position of the transfer belt 6 carrying the K toner image reaches the primary transfer portion, the transfer corotron 4 transfers the second color Y toner image. Subsequently, the electrostatic latent images corresponding to the light images color-separated by the green (G) and red (R) filters are developed.
The transfer of the M toner image and the C toner image is performed in the same manner as the transfer of the Y toner image. In this way, a multiple toner image superimposed on each color is formed on the intermediate transfer belt 6. Until the toner images of each color are primarily transferred onto the transfer belt 6, the bias roll 9, the peeling claw 20, and the belt cleaner 10 disposed on the surface side of the transfer belt 6 are in the retracted positions separated from the transfer belt 6. Is held.

On the other hand, the paper P stored in the paper feed tray 22
Are picked up one by one by a pickup roller 23 at a predetermined timing, and fed by a pair of feed rolls 24 and a sheet transport roll 25 to form a pair of registration rolls 2.
At 7, the operation is temporarily stopped. The sheet P is then transferred from the registration roll 27 to the secondary transfer section in synchronization with the transfer of the multiple toner images of each color (K, Y, M, C) transferred onto the intermediate transfer belt 6 to the secondary transfer section. Transported to the department. In the secondary transfer section, the bias roll 9 is in pressure contact with the backup roll 8 via the intermediate transfer belt 6. Then, the conveyed sheet P passes through the secondary transfer section by the press-contact conveyance between the rolls 8 and 9 and the movement of the transfer belt 6. At this time, the transfer belt 6 is electrostatically repelled by applying a transfer voltage having the same polarity as the charge polarity of the toner image from the electrode roll 19.
The toner image adsorbed and carried on the sheet P is secondarily transferred onto the sheet P from the surface of the transfer belt 6. When the bias roll 9 is pressed against the backup roll 8, foreign matter such as toner particles attached to the surface of the bias roll 9 is removed by the cleaning blade 21.

Although the transfer of a full-color image has been described above, when a single-color image is formed, the intermediate transfer belt 6 is used.
When, for example, a K-color toner image primary-transferred above moves to the secondary transfer section, the toner image is immediately transferred to the paper P. In the case of forming an image of a plurality of colors, the desired hue is selected, and when the multicolor toner image superimposed on those colors moves to the secondary transfer section, the toner image may be transferred to the paper P. . In the case of the transfer of the multicolor image, the rotation of the image carrier 1 and the movement of the intermediate transfer belt 6 are synchronized as described above so that the toner images of the respective colors accurately match without shifting at the primary transfer portion. I have. As described above, the paper P on which the toner image has been transferred to the desired hue is separated from the intermediate transfer belt 6 by the operation of the separation claw 20, placed on the transport belt 28, and transported to the fixing device 29. This fixing device 2
At 9, after fixing the unfixed toner image and fixing the permanent image, the sheet P is discharged to the sheet discharge tray 31 by the pair of sheet discharge rollers 30. When the secondary transfer is completed, the transfer belt 6 is cleaned by a belt cleaner 10 provided downstream of the secondary transfer unit to prepare for the next transfer.
The image forming apparatus of the present invention can also be used as a mono-color image forming apparatus in which a single-color toner is stored in the developing unit 3.

(Manufacture of Intermediate Transfer Belt) Example As a conductive metal oxide, barium sulfate coated with a tin oxide-based conductive layer and having an average particle diameter of 0.4 μm (Pastran Ty described above) was used.
pe-IV) whose surface was treated with γ-aminopropyltriethoxysilane was used. 36 parts by weight of this conductive metal oxide was added to 100 parts by weight of a resin component of a polyimide varnish (polyimide varnish for heat-resistant film using NMP as a solvent; U Varnish-S: manufactured by Ube Industries, Ltd.), and a mixer was added. And mixed well. The obtained film-forming stock solution was uniformly cast on a stainless steel sheet to a thickness of 200 μm,
Dry at 120 ° C for 120 minutes, and further at 150 ° C for 30 minutes.
30 minutes at 200 ° C., 60 minutes at 250 ° C., 30 minutes at 350 ° C., and 30 minutes at 420 ° C.
A polyimide film of 0 μm was obtained. The surface resistivity of the film was 10 ^13.0 Ω / □. The obtained polyimide film was cut into a length of 530 mm and a width of 320 mm.
Thereafter, a specially modified silicone (Silex 100; manufactured by Konishi Co., Ltd.) as a one-component elastic adhesive was applied to one end of the film at 20 mm, and both ends were overlapped. Then
A 1 kg weight was placed on the joint and cured at room temperature for 1 hour to produce an intermediate transfer belt.

(Relationship between the amount of the conductive metal oxide and the surface resistivity of the intermediate transfer belt material) Next, the metal oxide when the conductive metal oxide was mixed with 100 parts by weight of the thermosetting polyimide resin. FIG. 3 shows the relationship between the compounding amount and the surface resistivity of the resin sheet. As the polyimide resin sheet, a polyimide film obtained in the same manner as described above was used. As the conductive metal oxide, one subjected to a surface treatment with the silane coupling agent was used. Further, the measurement of the surface resistivity of the resin sheet in the present invention is performed by using a surface resistance meter (Hirester I).
P HR probe: 100 V using Mitsubishi Yuka Co., Ltd.)
The current value 30 seconds after the application of the voltage was read and determined. In FIG. 3, for example, when 35 parts by weight of a conductive metal oxide is blended, the surface resistivity is 15.5 (log Ω /
□), and the surface resistivity when 37 parts by weight of the metal oxide was blended was 11.0 (log Ω / □). It can be reduced to five digits. Also, the sheet resistance variation of the 300 mm long and 200 mm wide sheet containing 37 parts by weight of the metal oxide was within one digit.

Comparative Example FIG. 4 shows the relationship between the amount of carbon black and the surface resistivity of the resin sheet when carbon black (the above-mentioned granular acetylene black) was mixed with 100 parts by weight of the thermosetting polyimide resin. The polyimide resin sheet was manufactured according to the method disclosed in the above-mentioned JP-A-63-31263, according to the above-mentioned general method of film forming. According to this conventional resin sheet, for example, the surface resistivity when 11 parts by weight of carbon black is blended is 15.
5 (log Ω / □), the surface resistivity when 12 parts by weight of carbon black was blended was 12.9 (log Ω / □), and the surface resistivity when 12.5 parts by weight of carbon black was blended was 8. 5 (log Ω / □), and the decrease in surface resistivity with the increase of 1.5 parts by weight of carbon black was 7.0.
Digit and big. The sheet having a length of 300 mm and a width of 200 mm, in which 12 parts by weight of carbon black was blended, showed a large variation in surface resistance of two digits.

(Mechanical Property Test of Intermediate Transfer Belt Material) The tensile breaking strength and Young's modulus (tensile elastic modulus) of the intermediate transfer belt material are shown in Table 1 below. Examples of the belt material include: a thermosetting polyimide resin (PI) in which the conductive metal oxide is dispersed; a comparative example 1: a polycarbonate resin (PC);
Comparative Example 2: Polyvinylidene fluoride resin (PVDF), Comparative Example 3: ethylene-tetrafluoroethylene copolymer (E
Using TFE), the thermoplastic resins of Comparative Examples 1 to 3 were blended with 17 parts by weight of carbon black (the above-mentioned granular acetylene black) based on 100 parts by weight of each resin. The belt material of Comparative Examples 1 to 3 was a sheet having a thickness of 150 μm. The mechanical property test was based on JIS K7127. That is, the tensile strength at break was measured at a pulling speed of 200 mm / min using a strip test piece of 5 × 40 mm.
The Young's modulus was measured at a pulling speed of 20 mm / min using a strip specimen of 25 × 250 mm.

[0038]

[Table 1]

[0039]

According to the image forming apparatus of the present invention, it is easy to adjust the surface resistivity of the intermediate transfer belt material to a predetermined value, and the variation of the surface resistivity can be suppressed. In addition, the amount of displacement of the belt due to load fluctuation during belt driving is small. Further, according to the method of manufacturing the intermediate transfer belt, it is possible to suppress the formation of minute irregularities on the surface of the film to be formed. Therefore, the present invention can obtain a high-quality transfer image.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an outline of an arrangement relationship of an intermediate transfer belt in an image forming apparatus including main constituent members.

FIG. 2 is an overall view of an image forming apparatus shown as one embodiment of the present invention.

FIG. 3 is a graph showing an example of the relationship between the amount of metal oxide and the surface resistivity when a conductive metal oxide is mixed into a thermosetting polyimide resin sheet.

FIG. 4 is a graph showing the relationship between the compounding amount of carbon black and the surface resistivity when carbon black is compounded in a thermosetting polyimide resin sheet performed as a comparative example.

[Explanation of symbols]

U: image forming apparatus, P: paper (recording medium), 1: image carrier, 3: developing unit (developing device), 6: intermediate transfer belt, 8: backup roll, 9: bias roll.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29K 79:00 303: 06

Claims (5)

[Claims] An image carrier on which an electrostatic latent image corresponding to image information is formed; a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner; An intermediate transfer belt on which a toner image carried on the intermediate transfer belt is primarily transferred, a bias roll for secondary transfer of an unfixed toner image on the intermediate transfer belt to a recording medium, and an intermediate transfer belt facing the bias roll from the back surface. An image forming apparatus comprising: a backup roll for supporting; and the intermediate transfer belt material is made of a thermosetting polyimide resin in which a conductive metal oxide having an average particle diameter of less than 1 μm is dispersed. 2. The image forming apparatus according to claim 1, wherein said metal oxide is surface-treated with a silane coupling agent. 3. The image forming apparatus according to claim 2, wherein the amount of the metal oxide surface-treated with the silane coupling agent is 32 to 40 parts by weight based on 100 parts by weight of the polyimide resin. 4. An endless belt obtained by seaming a sheet of the belt material as the intermediate transfer belt.
The image forming apparatus according to any one of the above. 5. Casting a polymer liquid of a polyamic acid or a polyimide resin in which a conductive metal oxide having an average particle diameter of less than 1 μm or a metal oxide surface-treated with a silane coupling agent is dispersed, on a metal sheet. A method for manufacturing an intermediate transfer belt for an image forming apparatus, comprising joining both end portions of a sheet of an obtained film after molding.