JP2000122440A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device equipped with an intermediate transfer body capable of obtaining a high-quality transferred image by preventing a phenomenon that toner is scattered to the periphery of a multicolor image and further preventing the occurrence of void at a background part around a line image. SOLUTION: This image forming device is equipped with an image carrier PR successively passing through an electrifying area Q0, a latent image writing position Q1, a developing area Q2, a primary transfer area Q3 and a cleaning area, the intermediate transfer body B successively passing through a secondary transfer area Q4 where a primarily transferred toner image Tn is secondarily transferred to a recording sheet S by a secondary transfer device T2, and a recording sheet carrying device SH successively carrying the recording sheet S to a fixing area Q5 where the secondarily transferred toner image Tn is fixed by a fixing device F; and the intermediate transfer body B is constituted of material where the dielectric constant εr of a transfer surface to which the toner image Tn is transferred is >=8.

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 such as an electrophotographic copying machine or a laser printer, and more particularly, to an intermediate transfer of an unfixed toner image formed on an image carrier such as an image carrier drum. The present invention relates to an image forming apparatus that transfers a recording sheet through a body.

[0002]

2. Description of the Related Art Conventionally, as this type of image forming apparatus,
For example, JP-A-62-206567 and JP-A-3-1
No. 92282, and the like. FIG. 5 is a diagram showing a schematic configuration of a general image forming apparatus provided with the intermediate transfer member. The surface of the image carrier (photoreceptor drum) PR rotating and moving in the direction of the arrow Ya is uniformly charged by the charger CR in the charging area Q0, and an electrostatic latent image is formed by the laser beam L at the latent image writing position Q1. It is formed. In the case of a full-color image, electrostatic latent images corresponding to four color images of K (black), Y (yellow), M (magenta), and C (cyan) are sequentially formed. 3.) Only an electrostatic latent image corresponding to the image is formed. In the case of a full-color image, the electrostatic latent images of each color sequentially formed on the surface of the image carrier PR are K (black) and Y (black) of a rotary developing device D that rotates around a rotation axis Da in a developing region Q2. The developing devices DK, DY, DM, and DC of four colors of yellow), M (magenta), and C (cyan) are developed into toner images Tn of the respective colors.

A slide frame F1 (indicated by a two-dot chain line) is supported by a pair of right and left slide rails SR, SR disposed below the image carrier PR so as to be able to enter and exit the image forming apparatus main body. A belt module BM is supported on the frame F1 so as to be vertically rotatable. The belt module BM includes a plurality of belt supporting rolls (Rd, Rf, Rt,
Rw), the intermediate transfer belt B rotatably supported by
, A primary transfer roll T1, and the backup roll T2.
It has a contact roll T2c that comes into contact with a, and a belt frame F2 that supports them.

The primary transfer unit T1 is supplied with a transfer voltage having a polarity opposite to the charge polarity of the toner by a power supply circuit E controlled by a controller C, and transfers the toner image Tn on the surface of the image carrier PR to a primary transfer area. 1 in the intermediate transfer belt B in Q3
Next transfer. In the case of a full-color image, the toner images of each color sequentially formed on the surface of the image carrier PR are sequentially primary-transferred onto the surface of the intermediate transfer belt B in the primary transfer area Q3. After the primary transfer, the surface of the image carrier PR is cleaned of residual toner by the image carrier cleaner CL1.
The charge is removed by the charge remover JR.

[0005] Below the backup roll T2a,
A secondary transfer slide frame Fs slidable back and forth (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR, SR is detachably supported on the image forming apparatus main body. A secondary transfer lifting frame Ft of the secondary transfer unit Ut is supported on the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta. The secondary transfer unit Ut includes a secondary transfer roll T2b, a secondary transfer roll cleaner CL3, a roll support lever Lr,
Sheet guide SG2 after transfer and sheet transport belt BH
And the secondary transfer elevating frame Ft supporting them.
And

The roll support lever Lr is a lever for supporting the secondary transfer roll T2b and the secondary transfer roll cleaner CL3. When the secondary transfer unit Ut is moved to the use position, the roll support lever Lr is driven by a motor (not shown). Rotated around the hinge axis La, the secondary transfer roll T2b is moved between a secondary transfer position in contact with the intermediate transfer belt B and a standby position separated from the intermediate transfer belt B. A secondary transfer area Q4 is formed by a contact area between the secondary transfer roll T2b and the intermediate transfer belt B,
The secondary transfer roll T2b, the backup roll T2a
The control unit T2c forms a secondary transfer unit T2. The contact roll T2 includes:
A secondary transfer voltage having the same polarity as the charging polarity of the toner in the developing device D is supplied from a power supply circuit E, and the power supply circuit E is controlled by a controller C.

The recording sheets stored in the paper feed tray are conveyed to the secondary transfer area Q4 at a predetermined timing. When the recording sheet passes through the secondary transfer area Q4, a secondary transfer voltage having the same polarity as the charge polarity of the toner is applied to the contact roll T2c at a predetermined timing. The transferred color toner images are collectively secondarily transferred to a recording sheet.

After the secondary transfer, residual toner is removed from the intermediate transfer belt B by the belt cleaner CL2. The toner adhered to the surface of the secondary transfer roll T2b is collected by a secondary transfer roll cleaner CL3. The secondary transfer roller T2b and the belt cleaner CL2 are disposed so as to be able to be separated from and separated from the intermediate transfer belt B (to be separated and contacted), and when a color image is formed, the unfixed toner of the final color is formed. The image is separated from the intermediate transfer belt B until the image is primarily transferred to the intermediate transfer belt B. The secondary transfer roll cleaner CL3 moves away from and moves together with the secondary transfer roll T2b. The recording sheet on which the toner image has been secondarily transferred is heated and fixed by the fixing device F when passing through the fixing area Q5. The recording sheet on which the toner image has been fixed is
The recording sheet is discharged to a discharge tray.

Conventionally, in a color image forming apparatus not using the intermediate transfer member, an unfixed toner image of each color formed on an image carrier drum or the like is formed on a recording sheet conveyed by conveying means such as a conveying belt. Since direct multiple transfer is performed, the image quality of a color image formed on a recording medium is affected by many factors such as the thickness and surface characteristics of the recording medium and the transport characteristics of the recording medium with respect to the image carrier.
However, in the color image forming apparatus using the intermediate transfer body as described above, since the composite image subjected to the multiple transfer on the intermediate transfer body has already been transferred to the recording medium, it is possible to eliminate the above unstable factor. Therefore, there is an advantage that the occurrence of image disturbance and color unevenness during multiple transfer can be effectively prevented.

[0010]

However, in the above-described image forming apparatus, immediately after the unfixed toner image on the image carrier is transferred onto the intermediate transfer member by the electric field formed by the primary transfer device, the following process is performed. Such a problem occurs. If the volume resistivity of the intermediate transfer member is low, the primary transfer from the image bearing member to the intermediate transfer member may be caused by a corona discharger or a bias roll.
The charge given by the next transfer unit is removed by the conductivity of the intermediate transfer body itself, and the static charge that holds the charge of the unfixed toner on the intermediate transfer body transferred from the image carrier to the intermediate transfer body is retained. Since the electric force does not work, the toner is scattered around the image due to the electrostatic repulsion between the toners and the force of the fringe electric field near the image edge, resulting in large image noise. In particular, this phenomenon appears remarkably around an image having a large amount of toner per unit area such as a multi-color image, which becomes a fatal image quality defect for a color image forming apparatus. As means for preventing such a phenomenon that toner scatters around an image, Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent Application Laid-Open No. 192282, it is known to increase the volume resistivity of a material constituting an intermediate transfer member. In other words, the charge of the toner primary-transferred from the image carrier to the intermediate transfer member is retained by the primary transfer device to maintain the electrostatic force of the charge accumulated on the intermediate transfer member, thereby preventing the toner from being scattered around the image. Is what you do.

However, it has been found that when the volume resistivity of the intermediate transfer member is increased to a region where the toner scattering phenomenon does not occur, the following problem newly occurs. If there is an image portion having a relatively small toner weight per unit area in the background portion of a line image having a large toner weight per unit area, the toner height of the line image and the background portion naturally differ. When such an image is secondarily transferred from the intermediate transfer member to the recording medium, when the recording medium comes into close contact with the image on the intermediate transfer member, the image of the background around the line is affected by the height of the line image. A gap occurs between the recording medium and the recording medium. Therefore, 2
Due to the interaction between the electric field generated at the time of the next transfer and the electric field formed by the charges accumulated in the intermediate transfer member, image quality defects such as whitening around the line image occur.

That is, the above-described image quality defect that the area around the line image is whitened (improper transfer of toner forming a background portion around the line image) is caused by electric field enhancement (fringe electric field) around the character due to toner charge distribution. Due to the high volume resistivity of the belt, the voltage drop in the gap portion around the character is small, and the character peripheral portion cannot be transferred due to the gap discharge, and the relative dielectric constant (εr) of 8 or more on the transfer surface It has been found that the use of the above material does not cause the image quality defect, and the present invention has been accomplished.

In JP-A-6-301297,
By setting the volume resistivity of the intermediate transfer belt material to 10 ¹¹ Ωcm or more and the capacity to 0.4 μF / m ² or less, it is possible to prevent the transfer voltage from fluctuating due to the environment and prevent transfer failure from occurring. PVD with relative permittivity εr of 8
JP-A-6-301 using F (polyvinylidene fluoride) with a thickness of 200 μm or more and a capacity of 0.4 μF / m ² or less.
In the range of the conditions described in Japanese Patent Application Publication No. 297, there is an image quality defect that the area around the line image is whitened. The capacitance needs to be 4 μF / m ² or more. The relationship between the relative dielectric constant (ε) and the capacitance (C) is expressed by the following equation (1). C = ε0 × εr × S / d (1) where: C: capacitance (F) ε0: relative permittivity of vacuum (8.85 × 10 ⁻¹² F / m) εr: relative permittivity S: area (m ² ) d: thickness (m)

The present invention has been completed in view of the above experimental results, and has the following description (O01) as a technical subject. (O01) An intermediate transfer member capable of obtaining a high-quality transfer image by preventing the phenomenon of toner scattering around the multicolor image and preventing the occurrence of whitening in the background around the line image To provide an image forming apparatus.

[0015]

In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that the relative permittivity of the transfer layer is set to 8 or more by focusing on the relative permittivity of the constituent material of the transfer surface. Thereby, the transfer failure of the toner forming the background portion around the line image is substantially prevented, and it has been found that the image defect does not occur, and the present invention has been accomplished.

Next, a description will be given of the present invention which has solved the above-mentioned problems. In the description of the present invention, reference numerals in parentheses added after constituent elements of the present invention denote later-described embodiments corresponding to the constituent elements of the present invention. Is the sign of the component. The reason why the present invention is described in association with the reference numerals of the components of the embodiments described later is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(Invention) In order to solve the above problems, the image forming apparatus of the first invention has the following requirements (A01) to (A04).
(A01) a charged area (Q0) whose rotating surface faces a charger (CR), a latent image writing position (Q1) where light corresponding to an image is irradiated, and development. The image carrier (PR) sequentially passing through the development area (Q2), the primary transfer area (Q3), and the cleaning area facing the roll (DR), and the rotating surface is the charged area (Q0). ), Is charged by the charger (CR), an electrostatic latent image is formed on the charged surface by the latent image forming device at the latent image writing position (Q1), and the developing device ( The electrostatic latent image is developed into a toner image (Tn) by D), and the toner image (Tn) is transferred to the intermediate transfer body (B) by the primary transfer unit (T1) in the primary transfer area (Q3). The image carrier cleaning in the cleaning area. The image carrier (PR), (A02) wherein the toner remaining on the surface of the image carrier (PR) after the primary transfer is cleaned by the toner carrier (CL1);
1 in the next transfer area (Q3) and the intermediate transfer body (B)
The secondary transfer area (Q) where the secondary-transferred toner image (Tn) is secondary-transferred onto the recording sheet (S) by the secondary transfer unit (T2).
4) The intermediate transfer member (B) sequentially passing through (4), (A03) 2
2 in the next transfer area (Q4) and the recording sheet (S)
A recording sheet transport device (SH) for sequentially transporting the recording sheet (S) to a fixing area (Q5) where the next transferred toner image (Tn) is fixed by the fixing device (F);
4) The intermediate transfer member (B) in which the transfer surface onto which the toner image (Tn) is transferred is made of a material having a relative dielectric constant (εr) of 8 or more.

In the present invention, the "intermediate transfer member"
For example, an "intermediate transfer belt" or an "intermediate transfer drum" can be used. The transfer surface of the intermediate transfer member (B) has a relative dielectric constant of 8 or more, and in the case of an intermediate transfer belt (B) having a layer structure of two or more layers, the lower layer has a problem in driving color registration. Without Young's modulus, as the resin material, polyimide resin,
Polyether ether ketone, polyamide, polyvinylidene fluoride and the like are used. When used for the intermediate transfer drum (B), the outer peripheral surface of a cylindrical substrate made of aluminum, stainless steel (SUS), copper or the like is coated with the same material as the intermediate transfer belt (B). Is done.

(Operation of the First Invention)
In the image forming apparatus of the present invention, the rotating surface of the image carrier (PR) has a charged area (Q) facing the charger (CR).
0), a latent image writing position (Q
1), a development area (Q2) facing the development roll (DR),
It sequentially passes through the primary transfer area (Q3) and the cleaning area. The rotating surface corresponds to the charged area (Q
In the latent image writing position (Q1), an electrostatic latent image is formed on the charged surface by the latent image forming device (Q1). The development area (Q
In 2), the electrostatic latent image is developed into a toner image (Tn) by the developing device (D), and the toner image (Tn) is intermediately transferred by the primary transfer device (T1) in the primary transfer area (Q3). Transferred to body (B). In the cleaning area, the residual toner on the surface of the image carrier (PR) after the primary transfer is cleaned by the image carrier cleaner (CL1). The intermediate transfer member (B) is provided in the primary transfer region (Q3)
And sequentially pass through the secondary transfer area (Q4). The toner image (Tn) primarily transferred to the intermediate transfer body (B) in the primary transfer area (Q3) is transferred onto the recording sheet (S) by the secondary transfer unit (T2) in the secondary transfer area (Q4). The secondary transfer is performed. The recording sheet conveying device (SH) includes a fixing region (Q5) where the secondary transfer region (Q4) and the toner image (Tn) secondary-transferred to the recording sheet (S) are fixed by a fixing device (F). , The recording sheet (S) is sequentially conveyed. The toner image (Tn) of the intermediate transfer member (B)
Is formed of a material having a relative dielectric constant (εr) of 8 or more. The intermediate transfer member (B) is made of a material having a relative dielectric constant (εr) of 8 or more, and has a high volume resistivity, thereby preventing the occurrence of white spots due to poor transfer around a line image generated in the secondary transfer. Further, it is possible to prevent the toner scattering phenomenon that occurs remarkably around an image having a large toner weight per unit area. Further, it is possible to prevent contamination inside the image forming apparatus due to the toner scattering phenomenon, so that maintenance can be facilitated. Further, since the amount of untransferred toner is reduced, the life of the cleaning member of the intermediate transfer body (B) is extended. Thus, a highly reliable image forming apparatus can be provided.

[0020]

(Embodiment 1) An embodiment 1 of an image forming apparatus of the present invention includes the following requirements (A) in the present invention.
(A05) The intermediate transfer member (B) having a configuration of two or more layers.

(Operation of First Embodiment) In the first embodiment of the image forming apparatus of the present invention having the above-described configuration, the intermediate transfer member (B) has a configuration of two or more layers. A material having a relative dielectric constant (εr) of 8 or more constituting the intermediate transfer member (B) is
When the strength of the material alone is insufficient, a two-layer structure with a material for providing strength can be used to manufacture an excellent intermediate transfer member.

[0022]

Next, specific examples (examples) of embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.

(Embodiment 1) FIG. 1 is an overall explanatory view of Embodiment 1 of the image forming apparatus of the present invention. In FIG. 1, an image forming apparatus U is an image forming apparatus main body (copier) having an automatic document feeder U1 and a platen glass PG supporting the same.
U2. The image forming apparatus main body U2 is operated by a user to input an operation command signal such as a copy start signal.
I (user interface) and an exposure optical system A.

Light reflected from the automatic document feeder U1 or a document (not shown) manually placed on the platen glass PG is passed through an exposure optical system A to a CCD (solid-state image pickup device) for R (red). ), G (green) and B (blue) electrical signals. IPS (Image Processing System)
Represents the RGB electrical signal input from the CCD as K
(Black), Y (yellow), M (magenta), and C (cyan) image data, temporarily store the image data, and convert the image data at a predetermined timing as image data for forming a latent image. Output to DL. Laser drive circuit DL
Changes the laser drive signal to R according to the input image data.
Output to OS (latent image writing device).

Image carrier P constituted by a photosensitive drum
R rotates in the direction of the arrow Ya, and the surface thereof is uniformly charged by the charger CR in the charging area Q0, and then the laser beam L of the ROS (latent image writing device) at the latent image writing position Q1. To form an electrostatic latent image. When forming a full-color image, K (black), Y
An electrostatic latent image corresponding to an image of four colors (yellow), M (magenta), and C (cyan) is sequentially formed. In the case of a monochrome image, only an electrostatic latent image corresponding to a K (black) image is formed. Is done. The latent image writing to the image carrier PR by the laser beam L is started after a lapse of a predetermined time from the detection of the reference mark Bm provided on the non-image portion of the intermediate transfer belt B by the belt position sensor SNb. . For full color images,
Since each color is superimposed, the belt position sensor SNb
Are the same for each color from the detection of the reference mark Bm to the start of latent image writing by the laser beam L.

The surface of the image carrier PR on which the electrostatic latent image is formed is rotated and sequentially passes through the development area Q2 and the primary transfer area Q3. The rotary type developing device D rotates K in the developing area Q2 sequentially with the rotation of the rotation axis Da.
It has four color developing units DK, DY, DM and DC of (black), Y (yellow), M (magenta) and C (cyan).
Each of the developing units DK, DY, DM, and DC has a developing roll DR for transporting a developer to the developing area Q2.
The electrostatic latent image on the image carrier PR passing through the development area Q2 is developed into a toner image (Tn).

Below the image carrier PR, a slide frame F1 (2) is provided by a pair of left and right slide rails SR, SR.
(Indicated by a dashed line) is slidably supported back and forth (in a direction perpendicular to the paper surface). A belt frame F2 of the belt module BM is supported on the slide frame F1 so as to be rotatable around a hinge axis F2a. The belt module BM includes the intermediate transfer belt B, a belt driving roll Rd, a tension roll Rt, and a walking roll R.
w, a plurality of belt supporting rolls (Rd, Rd, including an idler roll (free roll) Rf and a backup roll T2a).
Rt, Rw, Rf, T2a), a primary transfer roll T1, and the belt frame F2 that supports them.
The intermediate transfer belt B is rotatably supported by the belt support rolls (Rd, Rt, Rw, Rf, T2a).

When a full-color image is formed, a first-color electrostatic latent image is formed at the latent-image writing position Q1, and a first-color toner image Tn is formed at the developing region Q2. When the toner image Tn passes through the primary transfer area Q3,
The primary transfer is electrostatically transferred onto the intermediate transfer belt B by the next transfer roll T1. Thereafter, similarly, the second color toner image Tn is placed on the intermediate transfer belt B carrying the first color toner image Tn.
The third color toner image Tn and the fourth color toner image Tn are sequentially superimposed and primary-transferred, and a full-color multiple toner image is finally formed on the intermediate transfer belt B. When a monochromatic monocolor image is formed, only one developing unit is used, and the monochromatic toner image is primarily transferred onto the intermediate transfer belt B. After the primary transfer,
On the surface of the image carrier PR, the residual toner is
It is cleaned by L1 and is neutralized by the neutralizer JR.

Below the backup roll T2a,
A secondary transfer slide frame Fs slidable forward and backward (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR, SR is detachably supported on the image forming apparatus main body U2. A secondary transfer lifting frame Ft of the secondary transfer unit Ut is supported on the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta. The secondary transfer unit Ut includes a secondary transfer roll T2b,
Next transfer roll cleaner CL3 and roll support lever Lr
, Sheet guide SG2 after transfer, and sheet conveying belt B
H and the secondary transfer lifting frame Ft supporting them.
And

The roll support lever Lr is a rotatable lever that supports the secondary transfer roll T2b and the secondary transfer roll cleaner CL3. When the secondary transfer unit Ut is moved to the use position, The roll support lever Lr is rotated about a hinge axis La by a motor (not shown) to move the secondary transfer roll T2b to a secondary transfer position where the secondary transfer roll T2b contacts the intermediate transfer belt B and a standby position where the secondary transfer roll T2b is separated from the intermediate transfer belt B. To move between. The post-transfer sheet guide SG2 is connected to the secondary transfer roll T2b.
Further, the recording sheet (S) that has passed through the secondary transfer area Q4, which is the contact area of the intermediate transfer belt B, is guided to the downstream sheet transport belt BH. A contact roll T2c is in contact with the backup roll T2a, and the rolls T2a to T2c constitute a secondary transfer unit T2. The contact roll T2 has a developing device D
A secondary transfer voltage having the same polarity as that of the toner is supplied from a power supply circuit E, and the power supply circuit E is controlled by a controller C.

The recording sheets S stored in the paper feed tray TR1 are taken out by a pickup roll Rp at a predetermined timing, separated one by one by a separating roll Rs, and conveyed to a registration roll Rr. The recording sheet S conveyed to the registration roll Rr is transferred to the pre-transfer sheet guide SG in synchronization with the movement of the primary-transferred multi-toner image or single-color toner image to the secondary transfer area Q4.
It is transported from 1 to the secondary transfer area Q4. In the secondary transfer area Q4, the secondary transfer unit T2 electrostatically and collectively secondary-transfers the toner image Tn on the intermediate transfer belt B onto the recording sheet S. The residual toner is removed from the intermediate transfer belt B after the secondary transfer by the belt cleaner CL2. The toner adhered to the surface of the secondary transfer roll T2b is collected by the secondary transfer roll cleaner CL3.

The secondary transfer roller T2b and the belt cleaner CL2 are disposed so as to be able to freely contact (separate and contact) with the intermediate transfer belt B, and when a color image is formed, the final color is not determined. Until the toner image Tn is primarily transferred to the intermediate transfer belt B, the toner image Tn is separated from the intermediate transfer belt B. The secondary transfer roll cleaner CL3
Performs the separation / contact movement together with the secondary transfer roll T2b.
The recording sheet S on which the toner image Tn is secondarily transferred is conveyed to a fixing area Q5 by a post-transfer sheet guide SG2 and a sheet conveying belt BH, and is passed by a heating roll Fh and a pressure roll Fp when passing through the fixing area Q5. The sheet is heated and fixed by a fixing device F having a pair of fixing rolls. The recording sheet S on which the toner image Tn is fixed is discharged to a recording sheet discharge tray TR2. The codes Rp, R
The recording sheet conveying device SH is constituted by the elements indicated by s, Rr, SG1, SG2, and BH.

(Backup Roll T2a) On the other hand, the layer configuration of the backup roll T2a, which is a support roll of the intermediate transfer belt B and forms an opposite electrode of the secondary transfer roll T2b, may be a single layer or a multilayer. For example, in the case of a single layer, it is composed of a roll in which an appropriate amount of conductive fine powder such as carbon black is mixed with silicone rubber, urethane rubber, EPDM (ethylene propylene diene monomer) or the like. In the case of a two-layer structure, the backup roll T2a is made of silicone rubber, urethane rubber,
A core layer composed of foam such as EPDM (ethylene propylene diene monomer), and a conductive agent such as carbon black mixed with conductive silicone rubber, urethane rubber, EPDM (ethylene propylene diene monomer), etc. And a skin layer. The volume resistivity of the backup roll T2a is 10 ⁷ Ω · cm to 10 ⁹ Ω.
・ It is preferably in the range of cm.

(Secondary Transfer Roll T2b) The layer structure of the secondary transfer roll T2b is not particularly limited. For example, in the case of a two-layer structure, a core layer and a coating layer covering the surface thereof are provided. Consists of The core layer is made of silicone rubber, urethane rubber, EPDM (ethylene propylene diene monomer), or the like, or a foam thereof in which conductive powder is dispersed. The coating layer is preferably made of a fluororesin-based material in which conductive powder is dispersed. As the fluororesin, tetrafluoroethylene (T
FE), hexafluoropropylene copolymer (FE
P), perfluoroalkoxy resin (PFA) and the like. The volume resistivity of the secondary transfer roll T2b is 10 ⁶ to
It is preferably in the range of 10 ⁹ Ω · cm.

(Embodiment 1 of Intermediate Transfer Belt B) FIG. 2 is an explanatory view of the structure of an embodiment of the intermediate transfer belt B used in the image forming apparatus of the present invention, and FIG. FIG. In FIG. 2A, the intermediate transfer belt B has a two-layer structure of a polyimide layer and a cyanoresin layer (high dielectric constant layer). This intermediate transfer belt B is manufactured as follows. In the thermosetting seamless belt in which the base layer carbon black is dispersed, the carbon black is mixed with a polyimide varnish U for heat-resistant film of Ube Industries, Ltd. and mixed with a mixer or the like. This undiluted solution is poured into a cylindrical mold and centrifugally molded while heating. Remove the mold in a semi-cured state,
Thereafter, the removed belt is placed on an iron core, heated to 450 ° C., and fully cured (imidization reaction) to obtain a surface resistivity of 10 ¹²
A seamless belt having a thickness of 80 μm and a volume resistivity of 10 ¹⁰ Ωcm is obtained. Shin-Etsu Chemical Co., Ltd. high dielectric polymer cyanoresin CR
-V was mixed with a mixed solution of acetone and DMF with a predetermined amount of Daicel Huls Co., Ltd. blocked isocyanate,
This solution is coated on the polyimide film to a thickness of 20 μm and heated at 120 ° C. for 30 minutes to obtain a 20 μm thick high dielectric layer. The 20 μm-thick cyanoresin layer has a relative dielectric constant of 12 and a capacitance of 5.3 μF / m ² . The relative permittivity was measured by using an LCR meter 4642A manufactured by HP (Yokogawa Hewlett-Packard) Co., and performing aluminum deposition on the back surface of the sample, and applying an alternating current of 1 kHz frequency between this and the main electrode having a diameter of 10 mm. Voltage 5
V was applied and the measured value one minute later was taken as the relative dielectric constant of the sample.

(Embodiment 2 of Intermediate Transfer Belt B) FIG. 2B is an explanatory view of the structure of Embodiment 2 of the intermediate transfer belt B. FIG.
B, the intermediate transfer belt B has a polyimide layer and PV
It has a two-layer structure of a dF layer (high dielectric constant layer). This intermediate transfer belt B is manufactured as follows. In the thermosetting seamless belt in which the base layer carbon black is dispersed, the carbon black is mixed with a polyimide varnish U for heat-resistant film of Ube Industries, Ltd. and mixed with a mixer or the like. This undiluted solution is poured into a cylindrical mold and centrifugally molded while heating. The mold is released in a semi-cured state, and then the removed belt is put on an iron core, heated to 450 ° C., and fully cured (imidization reaction).
A seamless belt having a surface resistivity of 10 ¹² Ω / □ and a thickness of 80 μm is obtained. Further, a material containing PVDF (polyvinylidene fluoride) is spray-coated on the surface layer with Duflon K500 manufactured by Nippon Paint Co., Ltd., and heated at 230 ° C. for 10 minutes to have a thickness of 17 μm, a relative dielectric constant of 8, and a capacitance of 4.
A PVdF coat layer of 1 μF / m ² was formed.

(Comparative Example 1) The seamless belt formed in Example 1 was used as a base layer, and the surface thereof was coated with an FEP rubber paint (Daikin Latex GLS-2 manufactured by Daikin Industries, Ltd.).
31) is coated by a spray coating method,
Heating is performed for 0 minutes to obtain a 50 μm-thick surface layer made of fluororesin and fluororubber. The relative permittivity of the coat layer is 6.
4. The capacitance is 1.4 μF / m ² .

(Comparative Example 2) The seamless belt formed in Example 1 was used as a base layer, and the surface thereof was coated with a fluororesin paint (Lumiflon manufactured by Asahi Glass Industry Co., Ltd.) by a spray coating method. After heating for 20 minutes, a surface layer of fluorocarbon resin and fluororubber having a thickness of 20 μm is obtained.
The relative permittivity of the coat layer is 5.3 and the capacitance is 2.3 μF /
m ² .

(Results of Evaluation of Image Quality) FIG. 3 shows a high-density line image having an image density of 100% on a low-density background portion having an image density of 30% using the intermediate transfer belt B of Comparative Example 2 above. FIG. 6 is a diagram illustrating image densities when a toner image obtained by secondarily transferring the toner image is scanned in a direction from a background portion to a high-density portion to a background portion. As shown in FIG. 3, the image density in this case is as follows: background portion— (missing portion) —high density portion—
(Missing part)-The background part. Using the intermediate transfer belts B of Examples 1 and 2 and Comparative Examples 1 and 2, the image density 30
% Is formed on the intermediate transfer belt B on the intermediate transfer belt B, and the density of the toner image obtained by secondary transfer of the line image is determined from the background portion to the high density portion to the background. Scanning was performed in the direction of the part, and the concentration profile was plotted. Then, the image density after the secondary transfer was evaluated by measuring the distance (width) of the density reduction region of the background portion, that is, the missing portion. The image density was measured by the reflectance of light having a spot shape having a width of 35 μm. Table 1 shows the results. Table 1
In some, the width of the missing portion was less than 0.2 mm, and the image quality was judged as “good”, and the image quality defect of 0.2 mm or more was judged as “x”.

[0040]

[Table 1]

As can be seen from Table 1, in Examples 1 and 2 in which the relative dielectric constant of the transfer surface is high and the capacitance is large, a good image can be obtained with a small escape width.

(Modifications) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but falls within the scope of the present invention described in the appended claims. Thus, various changes can be made. Modified embodiments of the present invention will be exemplified below. (H01) The present invention relates to an intermediate transfer drum B as shown in FIG.
Also, the present invention can be applied to an image forming apparatus using the same. The intermediate transfer drum B in FIG. 4 is made of aluminum, stainless steel (SU
S), an outer peripheral surface of a cylindrical substrate formed of copper or the like is covered with a sheet-like intermediate transfer body similar to the intermediate transfer belt B of the first embodiment. The primary transfer units T1 and T1
The secondary transfer unit T2 is constituted by a corotron. In FIG. 4, components corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. (H02) The present invention is applicable to an image forming apparatus for forming a two-color image other than a full color image or a monocolor image. (H03) The present invention is applicable to a tandem-type color image forming apparatus in which a developing unit and an image carrier are combined for each of black, yellow, magenta, and cyan toners. (H04) The invention can be applied to an image forming apparatus using a belt image carrier.

[0043]

The above-described image forming apparatus of the present invention has the following effects. (E01) Equipped with an intermediate transfer member capable of preventing a phenomenon in which toner scatters around a multi-color image and preventing occurrence of whitening of a background portion around a line image and obtaining a high-quality transfer image. Image forming apparatus can be provided. (E02) The toner scattering phenomenon around an image having a large toner weight per unit area can be prevented. (E03) Since the toner scattering phenomenon is prevented and the amount of untransferred toner on the recording medium is reduced, the life of the cleaning member is extended, the contamination in the image forming apparatus is suppressed, and the maintenance of the image forming apparatus is easy. In this way, the reliability increases.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of Embodiment 1 of an image forming apparatus of the present invention.

FIG. 2 is a diagram illustrating the configuration of an embodiment of an intermediate transfer belt used in the image forming apparatus of the present invention. FIG. 2A is a diagram illustrating the configuration of a first embodiment of an intermediate transfer belt B, and FIG. FIG. 5 is an explanatory diagram of a configuration of a transfer belt B according to a second embodiment.

FIG. 3 shows an example in which a high-density line image with an image density of 100% is formed on an intermediate transfer belt on a low-density background portion with an image density of 30% using the intermediate transfer belt B of the comparative example. FIG. 9 is a diagram illustrating image densities when a toner image obtained by secondary transfer is scanned in a direction from a background portion to a high-density portion to a background portion.

FIG. 4 is a modified embodiment of the present invention applicable to an image forming apparatus using an intermediate transfer drum.

FIG. 5 is a diagram showing a schematic configuration of a general image forming apparatus provided with the intermediate transfer member.

[Explanation of symbols]

B: Intermediate transfer member (intermediate transfer belt, intermediate transfer drum)
CL1: image carrier cleaner, CR: charger, D: developing device, DR: developing roll, F: fixing device, PR: image carrier, Q0: charging area, Q1: latent image writing position, Q2: developing area , Q3: primary transfer area, Q4: secondary transfer area, Q5: fixing area, S: recording sheet, SH: recording sheet conveying device,
T1: primary transfer device, T2: secondary transfer device, Tn: toner image.

Claims (2)

[Claims] 1. An image forming apparatus having the following requirements (A01) to (A04): (A01) Irradiation with light corresponding to an image, a charged area whose rotating surface faces a charger. A latent image writing position, a development area facing a development roll, a primary transfer area, and an image carrier that sequentially passes through a cleaning area, wherein the rotating surface is charged by a charger in the charging area. An electrostatic latent image is formed on the charged surface by the latent image forming device at the latent image writing position; the electrostatic latent image is developed into a toner image by a developing device in the developing area; In the transfer area, the toner image is transferred to the intermediate transfer body by the primary transfer device, and in the cleaning area, the residual toner on the surface of the image carrier after the primary transfer is cleaned by the image carrier cleaner. (A02) the primary transfer area, and the secondary transfer area where the toner image primarily transferred to the intermediate transfer body is secondarily transferred to a recording sheet by a secondary transfer unit. An intermediate transfer member, (A03) a recording sheet transport device for sequentially transporting the recording sheet to the secondary transfer area, and a fixing area where the toner image secondary-transferred to the recording sheet is fixed by a fixing device;
4) The transfer surface on which the toner image is transferred has a relative dielectric constant (εr)
Is an intermediate transfer member composed of eight or more materials. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus satisfies the following requirement (A05), and (A05) the intermediate transfer body having a configuration of two or more layers.