JPH10186875A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain uniform images in spite of repetitive use by forming an intermediate transfer medium having at least a first layer and a second layer in this order, using a binder consisting of thermoplastic elastomer for the first layer and using a specific binder for the second layer. SOLUTION: The intermediate transfer medium has at least the first layer 101 and the second layer 102 in this order. The binder used for the first layer 101 consists of the thermoplastic elastomer. The intermediate transfer medium is so formed that the tensile breaking rupture elongation of the binder used for the second layer 102 attains >=150%, the tensile rupture strength attains >=300kgf/cm<2> and the 100% tensile stress attains <=250kgf/cm<2> . The transfer efficiency from the first image carrying member to the intermediate transfer belt and the transfer efficiency from the intermediate transfer belt to the second image carrying member are extremely high according to this constitution. The color drift by the permanent elongation of the intermediate transfer belt does not arise and the uniform images are obtainable even if the intermediate transfer belt is repetitively used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method, and more particularly, to a method in which a toner image formed on a first image carrier is once transferred to an intermediate transfer member and then further transferred. The present invention relates to an electrophotographic image forming apparatus for obtaining an image formed product, and more particularly to an image forming apparatus using an intermediate transfer belt.

[0002]

2. Description of the Related Art An image forming apparatus using an intermediate transfer member includes:
A color image forming apparatus or a multi-color image forming apparatus or a multi-color image forming apparatus that sequentially outputs a plurality of component color images of the color image information or the multi-color image information and outputs an image formed by combining and reproducing the color image or the multi-color image. It is effective as an image forming apparatus having a forming function and a multicolor image forming function.

FIG. 1 is a schematic view showing an example of an image forming apparatus using an intermediate transfer belt as an intermediate transfer member.

FIG. 1 shows a color image forming apparatus (copier or laser beam printer) using an electrophotographic process. The intermediate transfer belt 20 uses a medium-resistance elastic body.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) which is repeatedly used as a first image carrier, and rotates at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow. Driven.

[0006] The photosensitive drum 1 rotates in the primary charging device 2 during the rotation process.
Is charged uniformly to a predetermined polarity and potential, and then image exposure means 3 (not shown) (modulation in accordance with a color original image separation / imaging exposure optical system, a time-series electric digital pixel signal of image information) (E.g., a scanning exposure system using a laser scanner that outputs a converted laser beam) to form an electrostatic latent image corresponding to a first color component image (for example, a yellow color component image) of a target color image. You.

Next, the electrostatic latent image is developed by a first developing device (yellow developing device 41) with yellow toner Y as a first color. At this time, the developing devices of the second to fourth developing devices (the magenta developing device 42, the cyan developing device 43, and the black developing device 44) are turned off and do not act on the photosensitive drum 1, The first color yellow toner image is not affected by the second to fourth developing units.

The intermediate transfer belt 20 is driven to rotate clockwise at the same peripheral speed as the photosensitive drum 1.

[0009] The first type formed and supported on the photosensitive drum 1
In the process in which the yellow toner image of the color passes through the nip portion between the photosensitive drum 1 and the intermediate transfer belt 20, an electric field formed by the primary transfer bias applied from the primary transfer roller 62 to the intermediate transfer belt 20 causes Intermediate transfer belt 2
0 is sequentially transferred to the outer peripheral surface (primary transfer).

The surface of the photosensitive drum 1 on which the transfer of the first color yellow toner image corresponding to the intermediate transfer belt 20 has been completed is cleaned by the cleaning device 13.

[0011] Similarly, a magenta toner image of the second color, a cyan toner image of the third color, and a black toner image of the fourth color are successively superimposed on the intermediate transfer belt 20 and transferred to correspond to the target color image. Thus, a combined color toner image is formed.

Numeral 63 designates a secondary transfer roller which corresponds to the secondary transfer opposing roller 64 and is supported in parallel with the intermediate transfer belt 20.
Are disposed on the lower surface of the device so as to be separated therefrom.

A primary transfer bias for sequentially superimposing transfer of toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer belt 20 is applied from a bias power supply 29 with a polarity (+) opposite to that of the toner. You. The applied voltage is, for example, +100
V to 2 kV.

In the primary transfer process of the first to third color toner images from the photosensitive drum 1 to the intermediate transfer belt 20,
The next transfer roller 63 can be separated from the intermediate transfer belt 20.

The transfer of the composite color toner image transferred onto the intermediate transfer belt 20 onto a transfer material P, which is a second image carrier, is performed while the secondary transfer roller 63 is in contact with the intermediate transfer belt 20. From the paper feed roller 11 to the transfer material guide 10
The transfer material P is fed to the contact nip between the intermediate transfer belt 20 and the secondary transfer roller 63 at a predetermined timing, and the secondary transfer bias is supplied from the power supply 28 to the secondary transfer roller 6.
3 is applied. With this secondary transfer bias, the composite color toner image is transferred (secondary transfer) from the intermediate transfer belt 20 to the transfer material P as the second image carrier. The transfer material P to which the toner image has been transferred is introduced into the fixing device 15 and is fixed by heating.

After the image transfer to the transfer material P is completed, a charging member (cleaner) 7 for cleaning is provided on the intermediate transfer belt 20.
Is applied, and a bias having a polarity opposite to that of the photosensitive drum 1 is applied, so that toner remaining on the intermediate transfer belt 20 without being transferred to the transfer material P (transfer residual toner) is opposite to the photosensitive drum 1. A polar charge is provided. 26 is a bias power supply.

The transfer residual toner is electrostatically transferred to the photosensitive drum 1 in a nip portion with the photosensitive drum 1 and in the vicinity thereof, thereby cleaning the intermediate transfer member.

In a color electrophotographic apparatus having an image forming apparatus using the above-mentioned intermediate transfer belt, a second image carrier is attached or adsorbed on a transfer drum, which is a conventional technique, and the first image carrier is Compared with a color electrophotographic apparatus having an image forming apparatus for transferring an image from the body, for example, a transfer apparatus as described in JP-A-63-301960, a transfer material as a second image carrier The image can be transferred from the intermediate transfer belt without requiring any processing or control (for example, gripping by a gripper, adsorbing and giving a curvature), so that thin paper (40 g, such as envelopes, postcards and label paper) can be transferred. / M ² paper) to thick paper (200 g / m ² paper), regardless of the width, width, length, or thickness of the second image carrier. It has the advantage of being able to.

Due to such advantages, color copiers and color printers using an intermediate transfer belt have already begun to operate in the market.

[0020]

However, these color electrophotographic apparatuses do not sufficiently function as apparatuses which fully utilize the above-mentioned advantages and which are truly expected and satisfied by users. It is the current situation. That is, when the image forming apparatus using the intermediate transfer body is repeatedly used in various environments, the following problems still remain.

(1) The transfer efficiency from the first image carrier, for example, the photosensitive drum to the intermediate transfer member, and the transfer efficiency from the intermediate transfer member to the second transfer member
Transfer efficiency to an image carrier such as paper or an OHP sheet is not sufficiently high. Therefore, a cleaning device to be provided on the photosensitive drum and the intermediate transfer member is indispensable, and a load on the member is increased in order to clean a large amount of the residual toner. It becomes quite complicated,
It has become expensive.

(2) An image transferred to the intermediate transfer member and a part of the image transferred to the second image carrier are not transferred as shown in FIG. (Referred to as an image). This is caused by the fact that the transfer efficiency does not reach 100% as described in (1). As the cause, the material used for the intermediate transfer body, surface properties, resistance, or the magnitude of the applied bias at the time of transfer, its timing or the mechanical configuration of the image forming apparatus, etc. are considered to act in combination, The main cause is unknown. However, it is known that the deterioration becomes worse as the durability of the intermediate transfer member progresses or as the environment becomes lower in temperature and humidity.

(3) As shown in FIG. 1, the intermediate transfer belt 20 is provided with an intermediate transfer member cleaner 7.
This is an apparatus for removing untransferred toner from the intermediate transfer member before the next series of transfer steps starts. There are various cleaning methods including blade cleaning, fur brush cleaning, or a combination thereof.
When the cycle of adhesion and release is repeated thousands or tens of thousands of times, the toner that cannot be completely removed by the cleaner 7 is gradually deposited on the surface of the intermediate transfer belt 20, so that so-called filming is formed. become. In this case, the transferability of the toner from the first image carrier is deteriorated, resulting in an image having a spot-like white spot due to poor transfer of the filmed portion, and lowering the image quality or lowering the overall transfer efficiency. Invite.

(4) By repeatedly using the intermediate transfer belt,
As the durability increases, the surface property of the intermediate transfer belt may change. In extreme cases, the surface of the intermediate transfer member is scraped or cracked, so that good transfer efficiency and a uniform image obtained at the initial stage cannot be expected.

Furthermore, when a conventional intermediate transfer belt made of resin or rubber is repeatedly used while being stretched with an arbitrary tension, there are the following additional problems.

(5) The permanent elongation of the intermediate transfer belt gradually increases, the tension cannot be sufficiently taken, the belt and the shaft slide, and a shift (color shift) occurs between the toner images of each color during the primary transfer, so that the image is sharp. No image is obtained.

(6) If the belt is biased in one direction, the belt end may be rubbed against a flange or the like, and the belt end may be damaged.

To solve such a problem, see, for example,
Japanese Patent Application Laid-Open No. 293385 proposes that in a transfer fixing device that melt-transfers toner onto a transfer material (simultaneous transfer fixing) in a secondary transfer section, a rubber intermediate transfer belt is reinforced with a polyamide woven fabric. Then, the difference in electrical resistance between rubber and woven fabric becomes too large,
Depending on the thickness, the electrical resistance value in the thickness direction of the intermediate transfer belt becomes extremely high, and good electrostatic transfer cannot be performed. Further, since the thickness of the woven fabric, the thickness of the fiber, and the density of the woven fabric are not taken into consideration, traces of the woven fabric appear on the image, and a high-quality image cannot be obtained. In addition, since the belt has a multilayer structure, the cost is considerably high.

On the other hand, in US Pat. No. 5,409,557, an intermediate transfer belt is disclosed as an intermediate transfer member having a coating layer made of a conductive agent and a resin on an upper layer of a reinforcing material, but this intermediate transfer belt has almost no elasticity. In a primary transfer portion between a first image carrier such as a photosensitive drum and an intermediate transfer belt and a secondary transfer portion for transferring an image to a second image carrier due to a rigid member having no high hardness, A sufficient transfer area, a so-called transfer nip, cannot be secured. Particularly, in the case of a full-color image in which a large amount of toner is applied on the entire image portion, a so-called solid image, partial transfer failure is likely to occur, and the color tone changes. An image that looks white or missing, that is, a so-called hollow image. Further, since the intermediate transfer belt has a rigid resin characteristic, the belt is easily cracked or damaged due to friction between the belt end portion and the belt driving member due to repeated use, and cannot be used for a long time.

JP-A-6-228335 and JP-A-6-149079 disclose intermediate transfer belts using PVDF or polycarbonate as a material, but these belts have elasticity. As described above, defects on the image as described above, for example, a transfer failure or a hollow image occurs, and when repeatedly used, a crack or a crack due to resin fatigue easily occurs, and the conventional durability, for example, several thousand times or more Can not expect a lifetime.

In the intermediate transfer belt, the first and second layers and the surface layer of the present invention, which have a significant effect on transfer efficiency, surface abrasion resistance, toner contamination and filming, etc. Stronger properties are required for flexibility and flexibility than for the binder used for the surface layer of the drum.

However, the present invention proposes an image forming apparatus using a novel intermediate transfer belt which has solved the above-mentioned problems.

An object of the present invention is to provide an extremely high transfer efficiency from the first image bearing member to the intermediate transfer belt and an extremely high transfer efficiency from the intermediate transfer belt to the second image bearing member. An object of the present invention is to provide an image forming apparatus which does not cause color shift due to permanent elongation of a belt.

Another object of the present invention is to provide a uniform image quality of a second image carrier, such as paper or an OHP sheet, which does not cause transfer failure of a minute portion of an image and which has no so-called hollow image. An object of the present invention is to provide an image forming apparatus that can be achieved without depending on the type.

Still another object of the present invention is to maintain the same characteristics as those of the initial state without changing the characteristics of the intermediate transfer belt even when the intermediate transfer belt is subjected to severe and durable use by repeated use. An object of the present invention is to provide an image forming apparatus in which an end is not damaged.

It is a further object of the present invention to provide an image forming apparatus which does not cause filming due to toner adhesion to the surface of the intermediate transfer belt.

A still further object of the present invention is to provide an image forming apparatus which does not adversely affect an organic photosensitive member and has a long photosensitive member life.

Still another object is that the layer structure of the intermediate transfer belt is higher than the second layer of the intermediate transfer belt having at least the first layer and the second layer, or the outermost layer of the intermediate transfer belt. Even when an image is repeatedly output for a long period of time when using a mixture of a large amount of lubricating powder, the second layer or the outermost layer does not peel off or crack from the lower layer, and has uniform conductivity and transferability. To realize, or to prevent image defects from being caused by contamination of the photoreceptor even when a bleeding object from the lower layer occurs, or to transfer from the first image carrier to the intermediate transfer belt and from the intermediate transfer belt to the It is another object of the present invention to provide an image forming apparatus in which no leak occurs even when a transfer bias is set high in order to increase transfer efficiency when transferring to an image carrier.

[0039]

According to the present invention, there is provided an image forming apparatus for transferring an image formed on a first image carrier onto an intermediate transfer member and further transferring the image onto a second image carrier. In the apparatus, the intermediate transfer body has at least a first layer and a second layer in this order, and the binder used for the first layer is made of a thermoplastic elastomer, and the binder used for the second layer is Tensile elongation at break of 150% or more, tensile strength at break of 300 kgf / cm ² or more, and 1
An image forming apparatus characterized in that a 00% tensile stress is 250 kgf / cm ² or less.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic elastomer used in the present invention has intermediate properties between a crosslinked rubber and a resin, and has appropriate elasticity and flexibility higher than those of a general resin. Since it does not have a vulcanizing step such as rubber, it is a material excellent in moldability.

Therefore, the present inventors have found that they are suitable as a material for the intermediate transfer belt of the present invention.

The thermoplastic elastomer (referred to as TPE) of the present invention has not a simple polymer blend but a block copolymer having a clear hard segment and a soft segment in a polymer chain. The category of the block copolymer also includes a diblock copolymer, a triblock copolymer, a star polymer, a multiblock copolymer, and a graft copolymer.

The type and composition ratio of the soft segment in the block copolymer are determined by the hardness,
It provides softness of elasticity, and gives flexibility that can follow various changes with respect to expansion and contraction and bending of the belt.

On the other hand, the type and composition ratio of the hard segment gives strength against tearing and pulling, and can cope with a desired belt tension load.

A force is applied to secure the belt strength. Therefore, in the present invention, it is particularly important to preferably select the types and ratios of the soft segment and the hard segment.

The soft segments used in the present invention include, for example, polyisoprene, polybutadiene, hydrogenated polybutadiene, amorphous polyethylene, polyvinyl chloride, polyether, polyester, ethylene-propylene rubber, isobutene-isoprene rubber, fluorine rubber, silicone rubber Is mentioned. As the hard segment, for example, polystyrene, polyethylene, polypropylene, polyurethane, polyester, polyvinyl chloride,
Examples thereof include polyamide, polybutylene-terephthalate, a fluororesin, and polyisoprene, and a TPE having desired characteristics can be obtained in combination with the above soft segment.

As the TPE used in the present invention, in the case of polystyrene, for example, styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer, styrene-ethylene-butylene-styrene copolymer, styrene-ethylene-propylene-styrene copolymer, etc. In the case of polyvinyl chloride, there are crosslinked (three-dimensional) vinyl chloride-linear vinyl chloride polymer, and in the case of olefin, polyethylene-EPDM copolymer, polypropylene-EPDM copolymer, polyethylene-EPM copolymer, polypropylene-EPM copolymer , And the like.
T (1.4-butadienediol-terephthalic acid condensate) -PTMEGT (polytetramethylene glycol-
Terephthalic acid condensate) copolymers. Examples of polyamides include copolymers having a basic skeleton of a nylon oligomer-dicarboxylic acid-polyether oligomer. Examples of the nylon oligomer include nylon 6, nylon 66, and the like. Nylon 61
0, nylon 612, nylon 11, nylon 12, and the like. As the polyether oligomer, for example, polyether glycol, polypropylene glycol, and polytetramethylene glycol can be used. Examples of the urethane type include a polyurethane-polycarbonate polyol copolymer, a polyurethane-polyether polyol copolymer, a polyurethane-polycaprolactone polyester copolymer, and a polyurethane-adipate polyester copolymer.

On the other hand, with respect to the binder used for the second layer, the transfer efficiency from the first image carrier, for example, the photosensitive drum to the intermediate transfer belt, and the transfer efficiency from the intermediate transfer member to the second image carrier, for example, paper or When the second layer of the intermediate transfer belt using a combination of two or more layers in order to increase the transfer efficiency to the OHP sheet, a material obtained by mixing a large amount of highly lubricating powder with the binder of the outermost layer is used. Even if a binder having a high surface roughness is used, the adhesion between the outermost layer and the lower layer may not be good because the base layer is originally a belt and the outermost surface has high lubricity. For this reason, although the durability of about 1 to 20,000 sheets is maintained even in this state, if the durability is further extended (for example, about 30,000 sheets), the outermost layer may be peeled off or cracked from the lower layer, When the transfer is completed, the conduction of the peeled portion is not sufficient, and the image is not sufficiently transferred, causing unevenness of the image, or the cracked portion is not sufficiently transferred, and the surface state cracked in the image is transferred as it is. There was something. As a result, the intermediate transfer belt must be replaced every 20,000 to 30,000 sheets, which may increase the running cost.

When a high-lubricity powder mixed in a large amount in the outermost layer binder of the second layer is used, the adhesiveness between the binder and the high-lubricity powder may be insufficient. In some cases, the barrier property against bleed from the lower layer of the outermost layer may be reduced. In some cases, a bleed material from the lower layer passes through the interface with the conductive powder, contaminating the photoreceptor and causing image defects.

In the present invention, since the binder used for the second layer has preferable physical properties in the present invention, it is possible to contain a large amount of a highly lubricating filler, and It has strong resistance to load factors such as deformation, pressing force, friction and scraping on the surface of the intermediate transfer member. The intermediate transfer belt having such a configuration can maintain high transfer efficiency and acquire durability that can withstand repeated use for a long time. Having the above characteristics,
The binder used for the second layer has a 100% tensile stress of 250 kgf / cm ² or less, preferably 200 kgf / cm ² or less.
kgf / cm ² or less and tensile elongation at break of 150%
And preferably 180% or more, and a tensile strength at break of 3%.
00 kgf / cm ² or more, preferably 350 kgf / c
Those having a range of m ² or more can be used. 100% tensile stress of 250 kgf / cm ² or more, tensile elongation at break of 1
If it is 50% or less, it is impossible to add a large amount of a highly lubricating filler, and it becomes a coating layer that is difficult to deform and bend, and cannot follow repeated bending and deformation, and cracks and peeling from the film surface occur. Will happen.

On the other hand, the 100% tensile stress is 10 kgf / c.
m ^2, tensile when elongation at break is 900% or more, high lubricity filler addition of a large amount is susceptible becomes weak film strength, resulting flame to wear abrasion. Also, many binders give tack. The tensile breaking strength is
The larger the value, the more preferable. However, this is also effective only in relation to the tensile elongation at break, and a single value of each physical property value in the range beyond the present invention cannot be meaningful. In the present invention, the sum of the three physical properties is significant.

The binder used for the second layer of the intermediate transfer member used in the present invention includes rubber, elastomer and resin. Examples of the rubber and elastomer include natural rubber, isoprene rubber, styrene-butadiene rubber and butadiene rubber. , Butyl rubber, ethylene-propylene rubber,
Ethylene-propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, acrylonitrile butadiene rubber, urethane rubber,
Syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, acrylic rubber, silicone rubber, fluoro rubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile rubber, and thermoplastic elastomers (for example, polystyrene, polyolefin, polyvinyl chloride) , Polyurethane, polyamide, polyester, fluororesin, etc.), or one or more selected from the group consisting of: However, it is not limited to the above materials.

Further, as the resin, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-
Butadiene copolymer, styrene-vinyl chloride copolymer,
Styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylate copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer Copolymer, styrene-octyl acrylate copolymer and styrene-phenyl acrylate copolymer), styrene-methacrylate copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer and styrene) -Phenyl methacrylate copolymer),
Styrene resins such as styrene-α-chloromethyl acrylate copolymer and styrene-acrylonitrile-acrylate copolymer (a homopolymer or copolymer containing styrene or a styrene substituent), methyl methacrylate resin, methacrylic Butyl resin, ethyl acrylate resin,
Butyl acrylate resin, modified acrylic resin (silicone modified acrylic resin, vinyl chloride resin modified acrylic resin, acryl / urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, rosin Modified maleic resin, phenolic resin,
Epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, ionomer resin, polyurethane resin, silicone resin, fluorine resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral resin, One or more kinds selected from the group consisting of a polyamide resin and a modified polyphenylene oxide resin can be used. However, it is not limited to the above materials.

In the present invention, more preferably, the binder used for the second layer is a polyurethane, for example, a polyester polyurethane or a polyol polyurethane. In the case of the polyurethane, the types of the OH component and the NCO component such as polyester or polyol are used. By appropriately changing the amount and the amount, 100% tensile stress and elongation as binder physical properties can be changed.

In the present invention, the configuration which can be manufactured in the shortest process and can achieve low cost has a TPE layer having the first layer as the lowermost layer, and a second layer as a surface layer on the first layer. Is a two-layered intermediate transfer belt having the following layers.

At this time, the adhesion between the TPE layer and the surface resin layer using the binder of the present invention is higher than when the conventional lower layer is simply a rubber layer because TPE has both properties of rubber and resin. Adheres strongly to the surface resin. In particular, when the lower layer and / or the upper layer contains a crosslinking agent, exists in a free state in the layer, and has a crosslinking point in the upper layer and the lower layer, some heat treatment is performed in the process after the two-layer superposition. , A reaction occurs between the upper and lower layers, and not only a mere physical bond but also a chemical bond is formed between the two, so that the bond strength between the two layers can be obtained more than normally imagined.

Conversely, if a resin is used for both the upper layer and the lower layer, the adhesive strength becomes much stronger than that of the above-described configuration. However, at the same time, as a reaction, the belt is inferior in deformation, bending, and bending, and is easily broken due to a slight force and cracks from edges, resulting in almost no durability. Due to the high hardness of the resin, it is not possible to obtain more appropriate belt surface elasticity. For this reason, in this configuration, the possibility of the intermediate transfer member aimed at by the present invention is very low.

In the present invention, the content of the highly lubricating powder in the binder of the second layer is preferably in the range of 40 to 80% by weight based on the total solid content of the binder of the second layer. When the content of the highly lubricating powder is less than 40% by weight, the effect is insufficient. With the endurance, the transfer efficiency gradually decreases and filming tends to occur. The lubricity tends to fall off due to insufficient lubricity, and the surface becomes rough with the endurance.

The high lubricating powder used in the present invention is not particularly limited as long as it can impart lubricity to the surface of the intermediate transfer member, and various materials can be used.

The following method can be used to determine the lubricity of the powder used in the present invention.

20 parts by weight of the powder to be tested and 100 parts by weight of the urethane prepolymer are mixed and stirred, 5 parts by weight of a curing agent are added and mixed, and then spray-coated on a PET plate to prepare a test sample. At this time, care should be taken to adjust the viscosity of the coating with a mixed solvent of toluene and MEK to obtain a uniform coating surface. On the other hand, a comparative painted sample is prepared in the same manner except that the powder to be tested is not added. Next, a surface property measuring device HEIDON 14-DR (manufactured by Shinto Kagaku)
Is used to measure the slip resistance of both. As a measuring method, an unpainted PET plate was fixed to an ASTM plane indenter as a measurement object, and 100 mm / 100 mmf was applied under a vertical load of 200 gf.
min. The coating sample is moved horizontally at the speed of. If the slip resistance of the test sample is 80% or less of the comparative sample, it can be determined that the test powder is a highly lubricating powder.

Accordingly, examples of the highly lubricating powder include the following, but are not necessarily limited thereto. Granular carbon such as graphite, carbon fluoride, spherical graphite, ethylene tetrafluoride resin, ethylene trifluoride chloride resin, ethylene tetrafluoride hexafluoride propylene resin, vinyl fluoride resin, vinylidene fluoride resin, difluoride Ethylene chloride resins and their copolymers, silicone resins, silicone rubbers, silicone-based compounds such as silicone elastomers, PE, PP, PS, acrylic resins, nylon resins, phenolic resins, epoxy resins, and these compounds, mixtures, One or more of inorganic substances such as silica, alumina, titanium oxide, magnesium oxide, tin oxide, and iron oxide are appropriately selected, and ethylene tetrafluoride resin is particularly preferable.

The shape and particle size of the highly lubricating powder are not particularly limited, and any shape can be used.
The particle size is not limited, but is preferably 0.02 to 50 μm in consideration of dispersibility and surface properties. Further, if necessary, the surface treatment may be performed within a range that does not impair the lubricating property, and a dispersant may be used within a range that does not cause a problem in various properties.

In the present invention, the tensile elongation at break, tensile strength at break, and 100% tensile stress are measured by a measuring method according to JIS K6301. At this time, the preferred pulling speed is 500 mm / min. The measurement is performed at 25 ° C. under normal pressure.

The preparation of the measurement sample is as follows.

A binder having a plate shape such as a film or a plate thin film is about 200 to 400 μm.
And molded into a No. 3 dumbbell shape.

The binder dissolved in the solution is
After the solvent is removed, a molding die is prepared in advance so as to have a No. 3 dumbbell shape, the solution is poured into the mold, the solvent is removed, and a molded sample is obtained.

At this time, it is particularly preferable to use the following method for drying the solvent since the solvent can be completely removed. First, drying at room temperature for 24 hours, then drying at 50-80 ° C., preferably 70 ° C. for 4 hours, and finally drying under reduced pressure for about 60 hours.
C. for 2 hours.

In the present invention, between the first and second layers,
You may have the layer which consists of a binder which has a tensile stress and / or elongation of the range which does not correspond to this invention.

For example, a surface treatment agent such as a primer may be applied to further improve the adhesiveness between the first and second layers.

Examples of the surface treating agent include those using a silane compound, those using a titanate compound, those using an isocyanate resin, those using an epoxy resin, and those using a thermoplastic resin. Not something.

Further, in order to further improve the effect of preventing bleeding from the elastic layer, a bleed preventing layer may be provided between the first layer and the elastic layer, between the core layer and between the first and second layers. Good.

Examples of the bleed prevention layer include resins having a high barrier property, such as nylon, vinylidene chloride, polyethylene terephthalate, polyvinyl alcohol, and ethylene vinyl alcohol, but are not limited thereto.

In order to further improve the effect of preventing leakage, a leakage prevention layer may be provided between the first layer and the elastic layer, between the core layer and between the first and second layers.

As the leak preventing layer, a resin having high leak resistance, for example, nylon, polystyrene, polyethylene,
Examples include, but are not limited to, vinylidene chloride, polyethylene terephthalate, polyvinyl alcohol, ethylene vinyl alcohol, and the like.

In order to protect the second layer from abrasion, cracks and the like, a surface protective layer may be provided on the second layer.

Examples of the surface protective layer include, but are not limited to, resins having high abrasion resistance, such as polyurethane, nylon, polycarbonate, acryl, polystyrene, polyethylene, vinylidene chloride, and polyethylene terephthalate.

The binder, the surface treating agent, the bleed preventing layer, the leak preventing layer, and the surface protective layer may be applied by a spray coating method, a dipping method, a roll coating method, a brush coating method, Examples include powder coating.

The binder, the surface treatment agent, the bleed prevention layer, the leak prevention layer and the surface protection layer used for the first layer or the second layer may impart conductivity, and may cause leakage. In the case of using a second layer having no conductive layer or an intermediate transfer member to which a low voltage is applied, a binder, a surface treatment agent, a bleed prevention layer, a leak prevention layer, and a surface protection layer used for the first layer are electrically conductive. There is no problem giving the property.

The first layer used in the present invention needs to have a hardness that does not cause poor transfer or a hollow image, and the preferred range is 35 to 98 °, more preferably 35 to 95 °.
°, more preferably 40 to 95 °, and the measurement method is in accordance with the method of JIS-A.

The hardness of the intermediate transfer member is 40 to 40.
98 ° is a preferred range. If the angle is less than 40 °, if the photosensitive drum or the transfer roller is kept in contact with the transfer roller under a constant pressure for a long period of time, that portion is permanently deformed and becomes concave, resulting in poor transfer. If the angle is 98 ° or more, a dropout image may be caused.

A conductive agent may be added to adjust the resistance of the intermediate transfer member used in the present invention. The conductive agent is not particularly limited. For example, carbon, metal powders such as aluminum and nickel, metal oxides such as titanium oxide, quaternary ammonium salt-containing polymethyl methacrylate, polyvinyl aniline, polyvinyl pyrrole, and polydiamine One or more kinds selected from the group consisting of acetylene, polyethyleneimine, boron-containing polymer compounds, and conductive polymer compounds such as polypyrrole can be used. However, it is not limited to the above conductive agent.

The intermediate transfer member used in the present invention has, for example, a roller shape comprising at least a first layer 101 and a second layer 102 on a cylindrical conductive support 100 as shown in FIG. The belt shape and various aspects as shown in FIGS. 3 to 6 can be selected as desired and as required. In FIG. 4, the first layer 101 and the second
And a bleed prevention layer 103 between the first and second layers. In FIG. 5, an elastic layer 104 is provided below the first layer 101. Further, a single-layer or multiple-layer coating layer may be provided above the second layer.

The thickness of the intermediate transfer belt is preferably as large as possible so that the belt can be smoothly driven, and thin as long as the mechanical strength and flexibility of the belt are not impaired. Specifically, 0.05 to 2 mm is preferable. More preferably, it is 0.1 to 2 mm. The thickness of each layer such as the first layer and the second layer of the intermediate transfer belt is preferably as thin as not to impair the flexibility, and specifically, 10 to 1500 μm, and more preferably 50 to 1000 μm. .

According to the results of the study by the present inventors, it has been found that there is an appropriate range in the electric resistance value of the intermediate transfer belt in order to obtain a better image.

That is, if the resistance value of the intermediate transfer belt is too high, when the developer of the second color or later is primarily transferred, the developer whose primary transfer has been completed before returning to the first image carrier. As a result, an image having a desired color tone cannot be obtained. On the other hand, if the resistance value of the intermediate transfer belt is too low, the resistance value of the intermediate transfer belt is greatly different between the portion that has undergone the primary transfer and the portion that has not.
As a result, it becomes impossible to efficiently transfer the developer after the color tone, and it is impossible to obtain an image having a desired tint. The range of the resistance value of the intermediate transfer belt from which a higher quality image can be obtained without such an adverse effect is from 1 × 10 ⁴ to 1 × 1 by the following measurement method.
The present inventors have found that it is 0 ¹¹ Ω.

<Method of Measuring Resistance Value of Intermediate Transfer Belt> (1) The intermediate transfer belt is stretched as shown in FIG. 8, and the intermediate transfer belt is sandwiched between two metal rollers 202 and 203. Connect a resistor with a suitable resistance value and a potentiometer.

(2) The intermediate transfer belt is driven by the driving roller 200 such that the moving speed of the surface of the intermediate transfer belt becomes 100 to 300 mm / sec.

[0089] (3) is applied from the DC current + 1 kV circuit, read the electric potential difference V _r across the resistor at a potentiometer. The atmosphere at the time of measurement was as follows: temperature 23 ± 5 ° C., humidity 50 ± 1.
0% RH.

[0090] (4) from the potential difference V _r obtained, obtains the current value I flowing through the circuit.

(5) Resistance value of intermediate transfer belt = applied voltage (1 kV) / current value I

In FIG. 7, reference numeral 200 denotes a driving roller, 201 denotes a metal roller, 204 denotes a power source, 205 denotes a resistor, and 206 denotes a potentiometer.

[0093]

Embodiments will be described below. In the following description, “parts” is parts by weight.

(Example 1) Polyester TP in which hard segments are mainly composed of polybutylene terephthalate having crystallinity and soft segments are mainly composed of polybutylene adipate diol forming linear molecular chains.
E (1) was used as a binder for the first layer.

Polyester TPE (1) 100 parts Conductive carbon black 2 parts Antioxidant 0.5 part

The above compound was kneaded with a biaxial extrusion kneader, and additives such as carbon were sufficiently and uniformly dispersed in the binder so as to obtain a desired electric resistance. Next, the diameter 14
The above-mentioned kneaded polyester TPE was extruded into a cylindrical shape at a set temperature of 100 to 150 ° using a single-screw extruder having a die having a thickness of 0 mm and a thickness of 0.1 mm.
A belt (1) having a diameter of 0 mm, a diameter of 141 mm, and a thickness of 0.15 mm was obtained. The belt hardness at this time is 93 °,
The electric resistance was 2.3 × 10 ¹⁰ Ω.

The binder for the second layer has a tensile elongation at break of 473% and a tensile elongation at break of 691 kgf / c.
m ² , 100% tensile stress is 85 kgf / cm ² . Polycarbonate urethane (1) was used.

Next, a paint was prepared by the following paint formulation,
The surface layer of the belt (1) is spray-coated to have a film thickness of 3
A second layer having a thickness of 2 μm was formed, and an intermediate transfer belt (1) of the present invention as shown in FIGS. 3 and 4 was obtained.

100 parts of polycarbonate urethane (1) (solid content: 30%) Polytetrafluoroethylene fine powder 60 parts Dispersing aid 2 parts MEK / DMF (1/1) mixed solvent 500 parts

The electric resistance of the intermediate transfer belt is 5.6.
× 10 ¹¹ Ω.

The intermediate transfer belt was mounted on the full-color electrophotographic apparatus shown in FIG. 1, a full-color image was printed on 80 g / m ² paper, and the transfer efficiency was defined as follows to measure the transfer efficiency. Was.

Primary transfer efficiency (transfer efficiency from photosensitive drum to intermediate transfer belt) = image density on intermediate transfer belt /
(Transfer residual image density on photosensitive drum + image density on intermediate transfer belt).

Secondary transfer efficiency (transfer efficiency from intermediate transfer belt to paper) = image density on paper / (image density on paper + transfer residual image density on intermediate transfer belt).

In this embodiment, as the photosensitive drum 1, an organic photosensitive drum (OP) containing a fine powder of PTFE in the outermost layer is used.
C photosensitive drum). Therefore, high primary transfer efficiency was obtained.

The cleaning method of the intermediate transfer belt is a primary transfer simultaneous cleaning method using an elastic roller having a resistance of 1 × 10 ⁸ (Ω) for the cleaning charging member 7, and a continuous transfer of 50,000 full-color images. Printed. At this time, the value of the current applied from the bias power supply 26 to the cleaning charging member 7 is +40 (μA).

From the beginning, there was no image density unevenness caused by uneven resistance of the belt, and a good image free from color shift and defective cleaning caused by permanent elongation of the belt was obtained even after 50,000 sheets of durability. Further, the first layer and the second layer did not have toner filming on the surface, did not have cracks, abrasion and abrasion, and had the same surface properties as the initial stage.

Table 1 shows the results.

Example 2 Styrene TPE which is a styrene coblock polymer having a styrene-polybutadiene-polyisoprene-styrene skeleton in which the hard segment is mainly composed of polystyrene and the soft segment is mainly composed of polybutadiene-polyisoprene
(2) was used as a binder for the first layer.

As the binder for the second layer, a tensile breaking elongation of 500% and a tensile breaking strength of 450 kgf / cm
^2. Polyester urethane (2) having a 100% tensile stress of 100 kgf / cm ² was used.

A belt was obtained in the same manner as in Example 1 by adding conductive titanium oxide to styrene TPE (2) and adjusting the electric resistance. This hardness is 92 °.

The upper layer of the belt was treated with a silane coupling agent to obtain a 1.0 μm layer as an adhesion reinforcing layer. Next, as the second layer, polytetrafluoroethylene fine powder
A coating material was prepared in the same formulation as in Example 1 except that the above-mentioned parts were used as parts, and a layer having a thickness of 18 μm was obtained on the upper layer of the adhesion reinforcing layer by spray coating to obtain an intermediate transfer belt (2). The electrical resistance of this intermediate transfer member was 1.7 × 10 ¹² Ω, and the belt thickness was 0.13 mm.

Next, a full-color image repetition copy test of 30,000 sheets was performed in the same manner as in Example 1. No color shift due to belt elongation was observed, and a high image density obtained from good transfer efficiency was maintained. No hollow image occurred. No filming of toner was observed on the belt surface after 30,000 sheets.
Further, no cracks, bending or scratches occurred. Table 1 shows the results.

(Example 3) Diameter 182 mm, length 320
The polyester TPE kneaded product of Example 1 was cross-head extruded with respect to an aluminum cylindrical roller having a thickness of 5 mm and a thickness of 5 mm to obtain a TPE drum having a layer thickness of 0.2 mm. Next, except that the polytetrafluoroethylene fine powder was changed to 73 parts, the coating material used for the second layer of Example 1 was coated to a film thickness of 12 μm by spray coating to obtain a film of the present invention as shown in FIG. An intermediate transfer drum (3) was obtained. This drum was mounted on a full-color electrophotographic apparatus shown in FIG. 9 and evaluated. Reference numeral 20 in FIG. 9 indicates an intermediate transfer drum.

Using an OPC photosensitive drum as a photosensitive member,
Repeated full color image print tests were performed. The full-color print image had a uniform image quality in the solid image. Even after the endurance test of 50,000 sheets, despite the fact that a large amount of highly lubricating powder was mixed in the second layer, no cracks or floating were observed on the surface of the intermediate transfer member, and the image quality was the same as the initial one. Obtained.

(Comparative Example 1) Rubber compounded SBR rubber 25 parts (parts by weight, the same applies hereinafter) EPDM rubber 75 parts Vulcanizing agent 1.5 parts Vulcanizing aid 2 parts Vulcanization accelerator (MBT) 3 parts Conductive carbon Black 9 parts Dispersing aid (stearic acid) 1 part Plasticizer (naphthenic process oil) 30 parts

The rubber compound obtained by the above formulation was wound around a cylindrical mold, vulcanized and polished to obtain a 0.8 mm thick rubber belt having only an elastic layer.

Next, a paint having the same composition as that used in the second layer used in Example 1 was spray-coated on the rubber belt, dried by touch at room temperature, and then heated to remove the residual solvent. .

The resistance value of the obtained intermediate transfer belt is 5 × 1.
0 ⁸ Ω.

The obtained intermediate transfer belt was incorporated in the image forming apparatus shown in FIG. 1, and the transfer efficiency was measured and 10,000 full-color continuous printings were performed in the same manner as in Example 1.

In the initial stage, a good image was obtained without image density unevenness, but after 10,000 sheets of durability, a high-definition image could not be obtained due to a color shift caused by permanent elongation of the belt. Was. No cracks occurred on the belt surface layer. Table 1 shows the results. Note that the image forming conditions are the same as in the first embodiment.

(Comparative Example 2) A durability test was carried out in the same manner as in Example 1 except that the coating material of the second layer in Example 1 was formulated as follows.

Coating composition Polyurethane prepolymer 100 parts (solid content 40%) Curing agent (including solvent) 70 parts (solid content 30%) Polytetrafluoroethylene resin powder (particle size 0.3 μm) 100 parts Conductive titanium oxide Particles (particle size: 0.5 μm) 15 parts Dispersing aid 5 parts Toluene 80 parts

The above coating material was spray-coated on the outer peripheral surface of the belt (1), and then heated at 100 ° C. for 1 hour to remove the residual solvent and to cause the coating to crosslink.
An intermediate transfer belt having a tough second layer having a thickness of 30 μm was obtained. The proportion of the tetrafluoroethylene resin powder in the total solid content of the surface layer was 56.8% by weight. As a binder for a second layer which is a surface layer of the intermediate transfer member, 70 parts of a curing agent (including a solvent) is added to 100 parts of a polyurethane prepolymer (including a solvent), and the resultant is dried and cured. Breaking elongation 130%, tensile breaking strength 400kg
f / cm ² and 100% M were 300 kgf / cm ² .

After the endurance of 18,000 sheets, fine cracks were generated on the surface of the intermediate transfer belt. At this stage, the transfer efficiency and the image quality were not affected, but after about 21,000 sheets, a small transfer failure occurred from a cracked portion, and development occurred in which the portion became white.

[0125]

[Table 1]

[0126]

According to the present invention, it is possible to provide an image forming apparatus capable of obtaining a uniform image without color shift due to permanent elongation of the intermediate transfer belt even when used repeatedly.

Further, an image forming apparatus having extremely high transfer efficiency from the first image bearing member to the intermediate transfer member and extremely high transfer efficiency from the intermediate transfer member to the second image bearing member can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic view of a full-color image forming apparatus having a belt-shaped intermediate transfer member.

FIG. 2 is a perspective view of a drum-shaped intermediate transfer member.

FIG. 3 is a perspective view of a belt-shaped intermediate transfer member.

FIG. 4 is a partial perspective view showing an example of a belt-shaped intermediate transfer member.

FIG. 5 is a partial perspective view showing another example of a belt-shaped intermediate transfer member.

FIG. 6 is a diagram illustrating an example of an image having a hollow portion.

FIG. 7 is a schematic diagram of a resistance measuring device used in the present invention.

FIG. 8 is a schematic view of a full-color image forming apparatus having a drum-shaped intermediate transfer member.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 primary charger 3 image exposure means 7 cleaning charging member 10 transfer material guide 11 paper feed roller 13 photosensitive drum cleaning device 15 fixing device 20 intermediate transfer belt 41 yellow developing device 42 magenta developing device 43 cyan Color developing device 44 Black developing device 63 Secondary transfer roller 64 Secondary transfer opposing roller 101 First layer 102 Second layer 103 Bleed prevention layer 104 Elastic layer

Claims (7)

[Claims] 1. An image forming apparatus for transferring an image formed on a first image carrier onto an intermediate transfer member, and further transferring the image onto a second image carrier, wherein the intermediate transfer member includes at least A first layer and a second layer in this order;
The binder used for the second layer is made of a thermoplastic elastomer, and the binder used for the second layer has a tensile elongation at break of 15%.
0% or more, tensile strength at break 300 kgf / cm ² or more,
An image forming apparatus having a 100% tensile stress of 250 kgf / cm ² or less. 2. The image forming apparatus according to claim 1, wherein said thermoplastic elastomer is a block copolymer. 3. The image forming apparatus according to claim 2, wherein the block copolymer comprises a hard segment and a soft segment. 4. The image forming apparatus according to claim 1, wherein the binder used for the second layer is urethane. 5. The thermoplastic elastomer has a hardness of 35.
The image forming apparatus according to claim 1, wherein the intermediate transfer member has a hardness of 40 to 98 ° (JIS-A). 6. The image forming apparatus according to claim 1, wherein said intermediate transfer member is a seamless belt. 7. The image forming apparatus according to claim 1, wherein the first layer forms the lowermost layer of the belt, and the second layer forms the uppermost layer.