JPH1184901A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of color slippage or a break of an end section derived from permanent elongation of an intermediate transfer belt. SOLUTION: In this image forming device capable of forming a toner image on a photosensitive drum 1, temporarily transferring the toner image on the intermediate transfer belt 20, and thereafter, transferring the same on the intermediate transfer belt 20 to a transfer material P, the elongation ratio of the intermediate transfer belt 20 at an extension load of 0.05 kg/cm<3> , is made beyond 0.03% and the elongation ratio at the extension load of 0.1 kg/cm<3> is made below 1.5%. In such a manner, the occurrence of the color slippage is prevented and the break on the end part is restrained as a result of the permanent elongation of the intermediate transfer body regardless of the repeated use.

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 intermediate transfer member, such as an electrophotographic copying machine and a laser beam printer.

[0002]

2. Description of the Related Art An image forming apparatus using an intermediate transfer member includes:
This is very effective for sequentially stacking and transferring a plurality of component color images to create a color image. For example, JP-A-63-30
The color shift can be reduced when the toners of the respective colors are superimposed on the image, as compared with the transfer method described in the 1960 publication. Further, the image is transferred from the intermediate transfer member to the transfer material without the need for holding means (for example, gripping, adsorbing, giving a curvature to the gripper) as shown in FIG. 1 of JP-A-63-301960. Therefore, a wide variety of transfer materials can be selected. For example, from thin paper (40 g / m ² ) to thick paper (200 g / m ² )
In addition, transfer is possible regardless of the width and the length. Therefore, transfer to envelopes, postcards, label paper, and the like is possible.

The above-mentioned intermediate transfer member may be in the form of a drum or a belt. However, it is difficult to reduce the cost of the apparatus as a whole, and the degree of freedom in designing the arrangement of the intermediate transfer member is high. Thus, a belt-shaped intermediate transfer member, a so-called intermediate transfer belt, is effective.

[0004]

However, when a conventional intermediate transfer belt made of resin or rubber is repeatedly used while being stretched over rollers, there are the following disadvantages. (1) The permanent transfer of the intermediate transfer belt gradually increases over a long period of use, and the intermediate transfer belt slides on the rollers, so that the toner images sequentially formed on the photoreceptor are sequentially transferred onto the intermediate transfer belt in order. When the images are superimposed on each other, a color shift occurs between the toner images of the respective colors, and a clear image cannot be obtained. (2) When the intermediate transfer belt is biased on the roller in the width direction (left and right in the moving direction), the end of the intermediate transfer belt may be rubbed against a flange or the like and may be damaged.

To solve such a problem, see, for example,
Japanese Patent Publication No. 293385 proposes that an intermediate transfer belt made of rubber is reinforced with a woven polyamide fabric.

However, in this case, the difference in electrical resistance between the rubber and the woven fabric becomes too large, and the electrical resistance in the thickness direction of the intermediate transfer belt becomes extremely high depending on the material and thickness of the woven fabric. Electrostatic transfer cannot be performed.
Further, traces of the woven fabric appear in the image, and a high-quality image cannot be obtained. In particular, polyamide fibers have a disadvantage in that stress relaxation occurs in the belt in long-term use due to high flexibility.

On the other hand, Japanese Patent Application Laid-Open No. 6-149079 discloses an intermediate transfer belt using PVDF or polycarbonate as a material. However, these belts do not have elasticity, and therefore, transfer failure and image defects occur. In other words, a so-called hollow image is not transferred except for the outline of, and when repeatedly used, tearing and cracking due to resin fatigue are likely to occur, and there is a problem in durability. Further, since the material has almost no elongation property, a considerable tension load is required to stretch the intermediate transfer belt with a constant tension, which leads to an increase in size and cost of the entire apparatus. .

Accordingly, an object of the present invention is to provide an image forming apparatus which does not cause color shift due to permanent elongation of the intermediate transfer belt even when used repeatedly.

Another object of the present invention is to provide an image forming apparatus in which the end of the intermediate transfer belt is not damaged.

Another object of the present invention is to provide an image forming apparatus capable of obtaining a uniform image without being affected by the core layer.

Another object of the present invention is to provide a transfer efficiency from the first image bearing member to the intermediate transfer member and a transfer efficiency from the intermediate transfer member to the second transfer member.
An object of the present invention is to provide an image forming apparatus having extremely high transfer efficiency to an image carrier.

It is another object of the present invention to provide a second image carrier such as paper or O.sub.2 which does not cause transfer failure of a minute portion of an image, and has a uniform and uniform image quality without a 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 of the HP sheet.

It is another object of the present invention to provide an image forming apparatus in which the characteristics of the intermediate transfer member are not changed even when the intermediate transfer member is subjected to severe and durable use by repeated use, and the same characteristics as those in the initial stage can be maintained. Is to do.

Another object of the present invention is to provide an image forming apparatus in which filming does not occur due to adhesion of toner to the surface of an intermediate transfer member.

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

[0016]

According to the first aspect of the present invention, a toner image is formed on a first image carrier, and the toner image is temporarily formed on an intermediate transfer member. In the image forming apparatus for transferring the image onto the second image carrier from the intermediate transfer member, and then transferring the intermediate transfer member from the intermediate transfer member to the second image bearing member.
And the elongation at tension load of 05kg / cm ³ is 0.03% or more, and elongation is 1.5% or less in the tension load of 0.1 kg / cm ^3, characterized in that.

According to a second aspect of the present invention, there is provided the image processing apparatus, further comprising a plurality of developing units for sequentially forming toner images of a plurality of different colors on the surface of the first image carrier.

The present invention according to claim 3 is characterized in that the intermediate transfer member is a seamless intermediate transfer belt.

According to a fourth aspect of the present invention, the intermediate transfer belt has two or more layers including an elastic layer and a coating layer.

According to a fifth aspect of the present invention, the elastic layer includes:
It has a core layer made of fibers inside, and the interval between adjacent fibers is 50 to 3000 μm.

The present invention according to claim 6 is characterized in that the core layer is spiral.

The present invention according to claim 7 is characterized in that the core layer is a woven fabric.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> As described above, a conventional intermediate transfer belt using a resin or rubber has a low mechanical strength and, when used repeatedly, causes color shift due to permanent elongation of the belt. There has been a problem in that the end of the belt is easily damaged by rubbing with a flange or the like.

In order to solve such a problem, the present applicant has provided a core layer on an intermediate transfer belt made of resin or rubber, thereby improving the mechanical strength of the intermediate transfer belt and reducing the permanent elongation by the reinforcing effect. We devised means to do it.

On the basis of the above idea, an intermediate transfer belt having a core layer of various thicknesses inside the elastic layer and a coating layer of various thicknesses on the core layer was prototyped and examined. By considering the shape of the layer, the strength and thickness of the core thread, the thickness and hardness of the elastic layer, the thickness of the coating layer, and the material as appropriate,
It has been found that the intermediate transfer belt intended by the present invention can be obtained.

In the present invention, if the elongation rate of the intermediate transfer belt under a tension load of 0.05 kg / cm ³ is less than 0.03%, the intermediate transfer belt has almost no elongation. Therefore, if the intermediate transfer belt 20 is stretched over the rollers 64, 65, and 66 in FIG. 9 as it is, it is difficult to maintain appropriate tension while maintaining the tension. At this time, when the roller 66 having the role of a tension roller in FIG. 9 is moved in the direction of the arrow outside the intermediate transfer belt 20, the intermediate transfer belt 20 can be kept in tension. However, with the above-described elongation rate, the load applied to the roller 66 becomes large, and the elongation of the intermediate transfer belt 20 is extended by 1 mm. The above tension is required. This state requires the belt tensioning unit to be made rigid and rigid, that is, causes the belt tensioning unit to become large and costly. On the other hand, 0.1 kg / cm ²
When the elongation ratio under a tension load exceeds 1.5%, when the intermediate transfer belt is stretched and rotated for a long time under a constant tension, the stress of the belt gradually relaxes. For example, FIG.
As shown in Comparative Example 1, when the stretched rotation is performed for 500 to 1000 hours or more, the tension may be reduced to 80% or less of the initial tension, and the intermediate transfer belt 20 obviously undergoes permanent elongation at this point. I have. For this reason, for example, even when this belt having a core layer is used as the intermediate transfer belt 20, color misregistration occurs in the entire image little by little during repeated use, or color misregistration occurs in a part of the image. Will occur. Further, if the stretching rotation is continued, the intermediate transfer belt 20 will eventually come off from the belt stretching unit, causing breakage or cracking and making it unusable.

Hereinafter, the intermediate transfer member of the present invention will be described using a belt-like intermediate transfer member as an example, but the present invention is not limited thereto.

As shown in FIG. 1, the intermediate transfer member of the present invention has an elastic layer 1 and a core 2 embedded in a layer inside the elastic layer 1. The elastic layer 1 is formed of an elastic body made of rubber, elastomer, resin or the like. The core 2 is formed of a spiral, ring-shaped or woven fabric fiber as shown in FIG. It is preferable to embed the fiber in the elastic layer 1 in the form of a spiral or a woven fabric from the viewpoint of ease of production and cost.

By embedding the core 2 in the elastic layer 1 as described above, permanent elongation of the intermediate transfer member can be prevented, and an intermediate transfer member having excellent durability can be obtained.

When the fibers are embedded in the elastic layer 1 in a spiral shape, adjacent fibers are almost parallel in the elastic layer 1 as shown in FIG.

In the intermediate transfer member of the present invention, the distance between adjacent fibers is 50 to 3000 μm. Furthermore, 1
It is preferably from 2000 to 2000 μm, particularly preferably from 200 to 1800 μm. If the fiber gap is smaller than 50 μm, the electric resistance of the fiber is greatly different from the electric resistance of the elastic layer 1, so that the electric characteristics of the intermediate transfer body are greatly changed and good electrostatic transfer becomes difficult. There is an adverse effect of becoming. Conversely, if the fiber spacing is larger than 3000 μm, undulation becomes noticeable on the surface of the intermediate transfer member, and image density unevenness (core mark image) due to unevenness on the surface of the intermediate transfer member is likely to occur.

As shown in FIG. 5, even when the core 2 is made of a woven fabric, the fiber spacing is 50 to 3000 in both the vertical and horizontal directions of the woven fabric.
μm, preferably 100 to 2000 μm, and even 20
0 to 1800 μm.

When the core 2 is formed by arranging ring-shaped fibers, the fiber spacing is also 50 to 3000 μm, preferably 100 to 2000 μm, and more preferably 200 to 1800 μm.
m.

In the present invention, as shown in FIG. 4, the distance between adjacent fibers means the distances I ₁ , I ₂ , I ₃ , I ₄ , I ₄ between arbitrarily selected adjacent six fibers. An arithmetic mean of ₅ (that is, 5 intervals). In the present invention, the six adjacent fibers are located at the position where the toner image is most likely to be held, that is, within 5 cm from the center line C in the width direction of the intermediate transfer member as shown in FIG. If it does so, it is arbitrarily selected within the range of 10 cm in width centered on the line C in FIG.

In some cases, a plurality of woven fabrics may be stacked to form the core 2. In this case, it is necessary that the fiber interval of the woven fabric closest to the outer surface of the intermediate transfer member is in the range of 50 to 3000 μm. It is. This is because the woven fabric closest to the outermost surface has the greatest effect on the surface properties of the intermediate transfer member. In addition,
The outer surface of the intermediate transfer member refers to a surface on which a toner image is carried.

The elastic material used for the elastic layer 1 includes natural rubber, isoprene rubber, styrene-butadiene rubber, 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, fluorine rubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile rubber, thermoplastic elastomers (eg, polyethylene, polyolefin, polyvinyl chloride) System, polyurethane system, polyamide system, polyester system, fluororesin system), polystyrene, chloropolyethylene, 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, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, etc.), styrene-methacrylic ester copolymer (styrene) -Methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, etc.), styrene-α-methyl methacrylate copolymer, styrene-acrylonitrile-ethyl acrylate copolymer Such as styrene-based resins (styrene or styrene-substituted Methacrylate resin, butyl methacrylate resin, ethyl acrylate resin, butyl acrylate resin, modified acrylic resin (silicone modified acrylic resin, vinyl chloride resin modified acrylic resin, acrylic urethane) Resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, rosin-modified maleic acid resin,
Phenol 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 and polyvinyl Butyral resin,
One or two or more selected from the group consisting of polyamide resins, modified polyphenylene oxide resins, and the like can be used. However, the material is not limited to the above.

The elastic layer 1 has a hardness of 10 to 95 °, more preferably 20 to 80 °, so as to prevent poor transfer, in particular, a portion other than the outline of the image from being sufficiently transferred, that is, a so-called hollow image. It is preferably in the range of 25 to 70 °. In the present invention, the method for measuring hardness is JIS-A
Shall be followed.

Therefore, as the material used for the elastic layer 1, it is preferable to use rubber, elastomer or soft resin among the above-mentioned materials.

A conductive agent may be added to the elastic layer 1 in order to adjust the resistance value. The conductive agent is not particularly limited. For example, carbon, metal powder such as aluminum and nickel, metal oxide such as titanium oxide, quaternary ammonium salt-containing polymethyl methacrylate, polyvinyl aniline, polyvinyl pyrrole, and polydiamine acetylene,
One or more kinds selected from the group consisting of conductive polymer compounds such as polyethyleneimine, boron-containing polymer compounds, and polypyrrole can be used. However, the conductive agent is not limited to the above. When a conductive agent is added, the content thereof is 5 to 40 based on 100 parts by weight of the material (rubber, elastomer, resin, etc.) of the elastic layer 1.
Parts by weight are preferred.

The thickness of the elastic layer 1 is preferably 0.3 to 2 mm. If the thickness of the elastic layer 1 is too thick, smooth driving becomes difficult. On the other hand, if the elastic layer 1 is too thin, mechanical strength cannot be obtained, and stress is likely to be reduced by repeated use.

The fibers used for the core 2 include, for example, natural fibers such as cotton, silk, hemp, wool, etc., chitin fibers, alginate fibers, regenerated fibers such as regenerated cellulose fibers, semi-synthetic fibers such as acetate fibers, and polyester fibers. , Nylon fiber, acrylic fiber, polyolefin fiber, polyvinyl alcohol fiber, polyvinyl chloride fiber, polyvinylidene chloride fiber, polyurethane fiber, polyalkyl paraoxybenzoate fiber, polyacetal fiber, aramid fiber,
One or more selected from the group consisting of synthetic fibers such as polyfluoroethylene fibers and phenol fibers, inorganic fibers such as carbon fibers, glass fibers, and boron fibers, and metals such as iron fibers and copper fibers can be used. .

The thickness of the fiber is preferably 2 to 500 μm, more preferably 20 to 200 μm, particularly preferably 50 to 180 μm. If the fibers are too thin, the mechanical strength of the intermediate transfer member will be low, permanent elongation is likely to occur, and durability will be poor. On the other hand, if the fiber is too thick, an excessive tension is required for elongation. Furthermore, traces of the core due to the thickness of the fibers tend to be conspicuous.

The thickness of the fiber in the present invention is defined as follows. <Method of measuring fiber thickness> The intermediate transfer belt is cut in the thickness direction, and the cut surface is appropriately enlarged by an arbitrary means such as a microscope (FIG. 4). 2. If an arbitrary fiber is selected and the cross-sectional shape of the fiber is a circle, the diameter of the fiber is defined as the thickness of the fiber. If the cross-sectional shape of the fiber is not a circle, the cross-sectional area of the fiber is determined, and the diameter of a circle having the same area as the area is defined as the thickness of the fiber.

The fiber used in the present invention may be a single fiber (filament) or a plurality of filaments, and may be right-handed, left-handed, single-twisted, plied, or twisted. Any twisting method such as twin yarn may be used. Also,
Multiple types of fibers may be blended. Further, in some cases, the yarn may be used after being subjected to an appropriate conductive treatment.

The surface releasability of the surface of the intermediate transfer member can be improved by performing a surface treatment with bleaching powder or the like and by providing a coating layer 101 as shown in FIG.

As the coating layer 101, the elastic layer 1 described above is used.
The same material can be used, but the contact angle of water is preferably 80 degrees or more. Therefore, it is preferable that the coating layer 101 contains an additive such as silicone resin fine powder. The thickness of the coating layer is preferably as thin as not to impair the flexibility of the elastic layer, and specifically 1 to 500 μm, more preferably 5 to 500 μm.
~ 200 µm is preferred. The elastic layer 1 is also provided on the coating layer 101.
A conductive agent may be added as in the case of (1). The content of the conductive agent is 5 parts by weight of the conductive agent with respect to 100 parts by weight of the material of the coating layer 101.
~ 40 parts by weight are preferred.

The intermediate transfer member of the present invention is preferably in the form of an endless belt or a tube, and has no seam (seamless).

The electric resistance of the intermediate transfer member of the present invention is 1 ×
It is preferably from 10 ⁴ Ω to 1 × 10 ¹¹ Ω. If the resistance value of the intermediate transfer body is too high, the transfer bias drops in the intermediate transfer body, and when the developer of the second color or later is primarily transferred, the developer that has completed the primary transfer before that is the first one. The image returns to the image carrier, and an image having a desired hue cannot be obtained. Also, if the resistance value of the intermediate transfer member is too low, a large difference is generated in the resistance value of the intermediate transfer member between the portion that has undergone the primary transfer and the portion that has not undergone the primary transfer,
As a result, it becomes impossible to efficiently transfer the developer of the second color and thereafter, and it is impossible to obtain an image having a desired color tone.

The electric resistance of the intermediate transfer member in the present invention is a value measured by the following method.

<Method of Measuring Resistance Value of Intermediate Transfer Member> (1) The intermediate transfer member 20 is stretched as shown in FIG. 7, and the intermediate transfer member 20 is sandwiched between two metal rollers 202 and 203. DC power supply 204, resistor 20 having appropriate resistance value
5. Connect the potentiometer 206. (2) The intermediate transfer member 20 is moved by the drive roller 200 and the metal roller 201 in the direction of the arrow so that the movement speed of the surface of the intermediate transfer member 20 becomes 120 mm / sec. (3) Apply +1 kV from the DC current to the circuit,
5 is read by a potentiometer 206. The atmosphere at the time of measurement was as follows: temperature 23 ± 5 ° C., humidity 50 ± 1.
0% RH. (4) From the obtained potential difference Vr, a current I flowing through the circuit is obtained. (5) Resistance value of the intermediate transfer member 20 = applied voltage (1 kV) / current value I.

The method of producing the intermediate transfer member 20 of the present invention is not particularly limited, but it can be produced, for example, as follows.

First, an elastic material is wound around a mold. Next, the core body 2 is wound on the elastic material layer, and further covered with the elastic material formed in a cylindrical shape. The core 2 is preferably coated with an adhesive. Finally, it is vulcanized and its surface is polished. Thus, the intermediate transfer body 20 having the core 2 inside is obtained. The coating layer 101 provided as needed can be formed by, for example, spray coating, dip coating, electrostatic coating, or the like.

Next, a method of measuring the elongation rate in the present invention will be described with reference to FIG. 23 to 25 as measurement effects
The intermediate transfer belt 20 that has been left for at least one day at 50 ° C. and 50% to 60% is used.

First, two roller-like supports 5 of the same dimensions
00 and 501 are arranged at appropriate intervals above and below so as to be parallel to the ground. One is fixed so that it does not move, and it is set as the fixed belt support 500. The other is made to be able to move in the up-down direction, and is set as a movable belt support 501.

The intermediate transfer belt 20 for measuring the elongation is stretched between the two supports 500 and 501. After the stretch
A load 502 of the same weight is applied to each of the left and right ends of the movable tilt support 501 so as to provide an even load.

When a load is applied, the intermediate transfer belt 20 extends downward by ΔL as shown by the arrow in FIG. The elongation rate is calculated by measuring the elongation of the intermediate transfer belt 20 one minute after the start of the load application.

The width Wcm of the intermediate transfer belt 20 under no load,
The circumference is Rcm and the thickness is tcm. The weight of the movable belt support 501 is represented by W ₁ , and the weight suspended by the load 502 is represented by W ₂ .

The tension load (kg / cm ³ ) at this time is as follows.

Tension load (kg / cm ³ ) = (W ₁ + 2 × W)
₂ ) / (R × W × t) Further, as shown in FIG. 8, the downward moving distance of the movable belt support 501 at the time of the above-mentioned tension load, that is, the extension of the intermediate transfer belt 20 is calculated. Assuming ΔLcm, the elongation ratio is as follows.

Elongation (%) = (2 × ΔL × 100) / R Next, an image forming apparatus according to the present invention will be described with reference to FIG.

Reference numeral 100 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a "photosensitive drum") repeatedly used as a first image carrier, having a predetermined peripheral speed (process speed) in a counterclockwise direction indicated by an arrow. It is driven to rotate. As the photosensitive drum 100, it is preferable to use a photosensitive drum containing fine powder of ethylene tetrafluoride resin (PTFE) in at least the outermost layer because higher transfer efficiency can be obtained. This is considered because the surface energy of the outermost layer of the photosensitive drum is reduced by containing the fine powder of PTFE, and the releasability of the toner is improved.

In the course of rotation, the photosensitive drum 100 is uniformly charged to a predetermined polarity and potential by the primary charger 102, and then the image exposure means 3 (color separation / imaging exposure optical system for a color original image, image information A first color component image (for example, a yellow color component image) of a target color image is subjected to image exposure by a scanning exposure system using a laser scanner that outputs a laser beam modulated according to a time-series electric digital pixel signal. Is formed.

Next, the electrostatic latent image is developed by the first developing device (yellow developing device 41) with yellow toner Y as the first color. At this time, since the developing units of the second to fourth developing units (the magenta developing unit 42, the cyan developing unit 43, and the black developing unit 44) are turned off and do not act on the photosensitive drum 100, The above-described first color yellow toner image is not affected by the second to fourth developing units.

The intermediate transfer member 20 has rollers 64, 65, 66
, And is rotationally driven clockwise at the same peripheral speed as the photosensitive drum 100.

The first formed and supported on the photosensitive drum 100
In the process in which the yellow toner image of the color passes through the nip portion between the photosensitive drum 100 and the intermediate transfer body 20, the intermediate transfer is performed by the electric field formed by the primary transfer bias applied from the primary transfer roller 62 to the intermediate transfer belt 20. Belt 20
Are sequentially transferred (primary transfer) to the outer peripheral surface of the substrate.

After the transfer of the first color yellow toner image corresponding to the intermediate transfer member 20, the surface of the photosensitive drum 100 is
The cleaning is performed by the cleaning device 13.

Hereinafter, similarly, the magenta toner image of the second color,
The cyan toner image of the third color and the black toner image of the fourth color are sequentially superimposed on the intermediate transfer member 20 and transferred to form a composite color image corresponding to the target color image.

Reference numeral 63 denotes a secondary transfer roller, which is supported in parallel with the secondary transfer opposing roller 64 and is disposed on the surface of the intermediate transfer member 20 so as to be separated from below.

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

In the primary transfer step of the toner images of the first to third colors from the photosensitive drum 100 to the intermediate transfer member 20, the secondary transfer roller 63 can be separated from the intermediate transfer member 20.

In the secondary transfer of the composite color toner image transferred onto the intermediate transfer member 20 to the transfer material P as the second image carrier, the secondary transfer roller 63 is brought into contact with the intermediate transfer member 20. At the same time, the transfer material P is fed from the paper feed roller 11 through the transfer material guide 10 to the contact nip between the intermediate transfer body 20 and the secondary transfer roller 63 at a predetermined timing, and the secondary transfer bias is applied to the power supply 28. Is applied to the secondary transfer roller 63. With this secondary transfer bias, the composite color toner image is transferred (secondary transfer) from the intermediate transfer member 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 heated and fixed.

After the image transfer to the transfer material P is completed, the cleaning charging member 7 is brought into contact with the intermediate transfer body 20 and is transferred to the transfer material P by applying a bias having a polarity opposite to that of the photosensitive drum 100. Instead, a charge having a polarity opposite to that of the photosensitive drum 100 is applied to the toner (transfer residual toner) remaining on the intermediate transfer body 20. 26 is a bias power supply.

The transfer residual toner described above is transferred to the photosensitive drum 100
The intermediate transfer body 20 is cleaned by being electrostatically transferred to the photosensitive drum 100 in the nip portion and the vicinity thereof.

For cleaning the intermediate transfer member, any cleaning device such as blade cleaning, fur brush cleaning, electrostatic cleaning, or a combination thereof can be used, but from the viewpoint of miniaturization and cost reduction of the device. FIG. 9 shows an example of a preferable cleaning method.
There is a method for cleaning the intermediate transfer member by electrostatically transferring the transfer residual toner to the photosensitive drum 100 as shown in FIG.

In FIG. 9, the cleaning charging member 7
Can take various forms, such as a metal roll, a conductive elastic roll, a conductive fur brush, and a conductive blade.

In the image forming apparatus shown in FIG. 9, while the developer is primarily transferred from the photosensitive drum 100 to the intermediate transfer member 20, the transfer residual toner on the intermediate transfer member 20 generated in the previous image forming step is exposed. It may be returned to the drum 100 (hereinafter referred to as “simultaneous primary transfer cleaning method”). The primary transfer simultaneous cleaning method has an advantage that a throughput is not reduced because a cleaning step is not particularly required.

Further, as shown in FIG. 10, a transfer residual toner collecting member 8 may be provided.

The transfer residual toner collecting member 8 is also made of a metal roll,
Various forms, such as a conductive elastic roll, a conductive fur brush, and a conductive blade, can be used. 27 is a bias power supply.

A voltage having a polarity opposite to that of the voltage applied to the cleaning charging member 7 is applied to the transfer residual toner collecting member 8, so that the transfer residual toner can be electrostatically cleaned.

In the image forming apparatus shown in FIG. 10, a bias having a polarity opposite to that of the photosensitive drum 100 is applied to the transfer residual toner collecting member 8 when the power is turned on, for example, so that the transfer residual toner in the transfer residual toner collecting container 9 is removed. To charge the photosensitive drum 1
It is also conceivable to collect it in the cleaning device 13 of 00. This method has an advantage that the transfer residual toner collecting container 9 can be downsized.

<Example 1> A rubber compound having the following composition was uniformly wound to a thickness of 0.3 mm around a cylindrical mold having a diameter of about 140 mm. Next, the adhesive was coated on the surface of nylon / thread (100 μm in diameter) and spirally wound at a pitch of 0.2 mm on the compound.

This yarn has relatively elasticity and gives the intermediate transfer member 20 of the present invention an elastic restoring force against deformation applied from the outside.

Further, a polyester yarn (170 μm in diameter) was spirally wound around the upper layer of the yarn at a pitch of 0.07 mm. The purpose of the core yarn is to provide a deformation preventing force that overcomes the external force applied to the belt. With these two types of core yarns, it is possible to maintain an elongation ratio at an appropriate tension load.

Next, a rubber compound having the following composition, extruded in a tube shape, was put on the upper layer of the core yarn, and then vulcanized and polished to give a 0.4 mm thick elastic layer on the core layer. A rubber belt with a core layer having a thickness of about 0.8 to 0.9 mm having an elastic layer having a thickness of 0.3 mm below the core layer was obtained.

Rubber-containing hydrin rubber 25 parts (parts by weight, hereinafter the same) EPDM rubber 75 parts Vulcanizing agent 2 parts Vulcanization aid 1 part Vulcanization accelerator 3 parts Conductive carbon black 9 parts Ozone deterioration inhibitor 1 part Plasticizer (Naphthene process oil) 30 parts Next, a coating material for obtaining a coating layer on the belt was prepared according to the following formulation.

Paint-containing polyurethane resin 100 parts Fluororesin fine powder (average particle size 0.05 μm) 40 parts Xylene 300 parts The above-mentioned paint is spray-coated on a belt, touch-dried at room temperature, and then heated at 120 ° C. for 2 hours. Thus, the residual solvent was removed and the coating was crosslinked to obtain an intermediate transfer belt 20 having a tough coating layer having a thickness of 20 μm as shown in FIGS. 1 and 6. The resistance value of the obtained intermediate transfer belt is 4.
It was 7 × 10 ⁹ Ω.

The intermediate transfer belt 20 was mounted on an electrophotographic four-color full-color image forming apparatus shown in FIG.
A full-color image was printed on 0 g / m ² paper, the transfer efficiency was defined as follows, and the transfer efficiency was measured.

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 transfer material) = image density on transfer material / (image density on transfer material + transfer residual image density on intermediate transfer belt).

In the present embodiment, the photosensitive drum 100 is an OPC photosensitive drum containing PTFE fine powder in the outermost layer. Therefore, high primary transfer efficiency was obtained.

The cleaning method of the intermediate transfer belt 20 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 is capable of continuously printing 40,000 full-color images. went. At this time, the current value applied from the bias power supply 26 to the cleaning charging member 7 is +40 μA.

From the beginning, there was no unevenness in image density due to the core, and a good image free from color shift and defective cleaning due to permanent elongation of the belt was obtained even after 40,000 sheets of durability.

Next, only the transfer belt stretching unit shown in FIG. 9 was taken out, and the belt was driven to rotate for 1000 hours by external driving, and a relaxation durability test was performed. The result is shown in FIG. The horizontal axis shows time, and the vertical axis shows the maintenance ratio with respect to the initial tension. As shown in Example 1, the retention rate was 90% or more even after 1000 hours, and almost no belt relaxation was observed.

The dimensions of the intermediate transfer belt 20 of the present invention are 238 mm in width, 440.1 mm in circumference, and 0.9 mm in thickness, and are 0.05 kg / cm ³ and 0.1 kg / cm ³ in the measuring device shown in FIG. The elongation percentage under a tension load of cm ³ was 0.05% and 0.8%, respectively.

The image forming conditions of this embodiment will be described below.

Non-image part surface potential: -550 V Image part surface potential: -150 V Color developer (for all four colors): non-magnetic one-component toner Primary transfer voltage: +500 V Secondary transfer voltage: +1500 V Process speed: 120 mm / sec Development Bias: Vdc = −400 V Vac = 1600 Vpp Frequency = 1800 Hz <Example 2> A rubber compound similar to that of Example 1 was uniformly wound with a thickness of 0.5 mm around a cylindrical mold having a diameter of about 140 mm. Next, the vertical and horizontal pitch as shown in FIG.
A seamless woven cloth made of cotton yarn (diameter 140 μm) having a diameter of 0.1 mm is put on the rubber upper layer.

A rubber compound having the same composition as that used in Example 1 previously extruded into a tube was put thereon, and then vulcanized and polished to form a 0.3 mm thick layer on the core layer. With an elastic layer, thickness about 0.80-0.
A rubber belt with a core layer of 95 mm was obtained.

Next, a paint having the same composition as that used in Example 1 was spray-coated on a rubber belt, dried by touch at room temperature, and then heated at 120 ° C. for 2 hours to remove the residual solvent, and The coating was crosslinked to obtain an intermediate transfer belt 20 having a tough coating layer having a thickness of 25 μm as shown in FIG. The resistance value of the obtained intermediate transfer belt is 8.2 × 10 ⁹
Ω.

The obtained intermediate transfer belt was incorporated in the image forming apparatus shown in FIG. 9, and the transfer efficiency was measured and 30,000 full-color continuous printings were performed in the same manner as in Example 1.

The cleaning charging member 7 is the same as that of the first embodiment, and the transfer residual toner collecting member 8 is 1 × 1.
An electrically conductive fur brush having a resistance of 0 ² Ω, and the photosensitive drum 100 is an OP in which the outermost layer does not contain PTFE fine powder.
C photosensitive drum was used.

From the beginning, there was no image density unevenness due to the core, and a good image free from color misregistration due to the permanent elongation of the belt was obtained even after 30,000 sheets of durability. The other image formation is the same as in the first embodiment.

The dimensions of the intermediate transfer belt 20 of the present invention are 240 mm in width, 440 mm in circumference, and 0.9 mm in thickness.
The elongation percentages under the tension loads of 0.05 kg / cm ³ and 0.1 kg / cm ³ were 0.4% and 1.3%, respectively.
FIG. 11 shows the result of the relaxation durability test as Example 2.

<Comparative Example 1> The rubber compound used in Example 1 was wound around a cylindrical mold, and a nylon (diameter: 60 μm) coated with an adhesive was spirally formed on the compound at a pitch of 8 mm. Wrapped around.

Next, a paint having the same composition as that used in Example 1 was spray-coated on the rubber belt, and dried by touch at room temperature, followed by heating at 120 ° C. for 2 hours to remove the residual solvent. An intermediate transfer belt having a coating layer having a thickness of 25 μm was obtained. The resistance value of the obtained intermediate transfer belt was 8.7 × 1.
0 ⁸ Ω.

The obtained intermediate transfer belt was incorporated in the image forming apparatus shown in FIG. 9, and the transfer efficiency was measured and full-color continuous printing of 40,000 sheets was performed in the same manner as in Example 1.

A good image was obtained without any unevenness in image density at the initial stage, but after 20,000 sheets were run, a high-definition image could not be obtained due to a color shift caused by permanent elongation of the belt. .

This is presumed to be a cause of color misregistration due to fluctuations in the peripheral speed of the intermediate transfer belt, which are thought to be due to belt relaxation, and deviation or meandering of the belt. The dimensions of this belt are the same as those in Example 2, and are 0.05 kg / cm ³ and 0.1 mm.
The elongation ratio under a tension load of 1 kg / cm ³ was 2.
1% and 5.6%. FIG. 11 shows the result of the relaxation durability test as Comparative Example 1.

[0109]

As described above, according to the present invention,
In an image forming apparatus that forms a toner image on a first image carrier, temporarily transfers the toner image onto an intermediate transfer member, and then transfers the toner image from the intermediate transfer member onto a second image carrier, Since the elongation rate of the transfer body under a tension load of 0.05 kg / cm ³ was 0.03% or more, and the elongation rate under a tension load of 0.1 kg / cm ³ was 1.5% or less, the repetition was performed. Even when used, there is no occurrence of color shift due to permanent elongation of the intermediate transfer member, and no end portion is damaged.

[Brief description of the drawings]

FIG. 1 is a perspective view of an intermediate transfer belt provided with a ring-shaped core inside an elastic layer.

FIG. 2 is a perspective view of an intermediate transfer belt provided with a woven cloth core inside an elastic layer.

FIG. 3 is a perspective view showing a state in which adjacent fibers are parallel to each other when fibers are helically embedded in an elastic layer.

FIG. 4 is a diagram for explaining an interval between adjacent fibers.

FIG. 5 is a diagram for explaining a fiber interval that can be placed on an intermediate transfer belt whose core is a woven cloth.

FIG. 6 is a perspective view showing an intermediate transfer belt in which a coating layer is provided on the surface of an elastic layer.

FIG. 7 is a view for explaining a method of measuring the resistance value of the intermediate transfer member.

FIG. 8 is a view for explaining a method of measuring the elongation rate of the intermediate transfer member.

FIG. 9 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 10 is a longitudinal sectional view showing a schematic configuration of another image forming apparatus according to the present invention.

FIG. 11 is a diagram illustrating a result of a relaxation durability test of the intermediate transfer belt.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 elastic layer 2 core body 20 intermediate transfer body (intermediate transfer belt) 41, 42, 43, 44 developing unit 100 first image carrier (photosensitive drum) 101 covering layer P second image carrier (transfer material)

Claims (7)

[Claims] 1. A toner image is formed on a first image carrier,
An image forming apparatus for temporarily transferring the toner image onto an intermediate transfer member, and then transferring the toner image from the intermediate transfer member onto a second image carrier, wherein the intermediate transfer member has a weight of 0.05 kg / cm ³ . An image forming apparatus, wherein an elongation ratio under a tension load is 0.03% or more, and an elongation ratio under a tension load of 0.1 kg / cm ³ is 1.5% or less. 2. The image forming apparatus according to claim 1, further comprising a plurality of developing units for sequentially forming a plurality of toner images of different colors on the surface of the first image carrier. 3. The image forming apparatus according to claim 1, wherein the intermediate transfer member is a seamless intermediate transfer belt. 4. The image forming apparatus according to claim 3, wherein the intermediate transfer belt has two or more layers including an elastic layer and a coating layer. 5. The elastic layer has a core layer made of fibers inside, and a distance between adjacent fibers is 50 to 300.
The image forming apparatus according to claim 4, wherein the thickness is 0 μm. 6. The image forming apparatus according to claim 5, wherein the core layer has a spiral shape. 7. The image forming apparatus according to claim 5, wherein the core layer is a woven fabric.