JP3444141B2 - Image forming device - Google Patents

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 that forms a toner image using an electrostatic latent image or the like. More specifically, the present invention relates to an image forming apparatus such as electrophotographic recording, electrostatic recording, ionography, and magnetic recording.

[0002]

2. Description of the Related Art Conventionally, there are several types of color image forming apparatuses for forming a color image on a recording medium.
As one of them, there is a so-called tandem type image forming apparatus in which four image forming units corresponding to each of four colors are arranged and a toner image of each color is sequentially primary-transferred onto a recording medium to obtain a color image.

FIG. 4 is a schematic configuration diagram of a conventional tandem type color image forming apparatus. In FIG. 4, for example, K
A drum-type image carrier 41 carrying toner images of (black), Y (yellow), M (magenta), and C (Cyan).
K, 41Y, 41M, 41C, optical scanning devices 40K, 40Y, 40M, 40C for forming electrostatic latent images corresponding to the above four colors on these image carriers, and formed on each image carrier The developing device 42K for developing the formed electrostatic latent image with the toners of the four colors K, Y, M, and C to form toner images of the respective colors,
42Y, 42M, 42C, transfer bias rollers 43K, 43Y, 43M, 43C for transferring the toner images formed on the respective image carriers to the recording medium 19, and cleaners 46K,
46Y, 46M, 46C and image carriers 41K, 41Y,
There is shown a tandem type image forming apparatus provided with charging rollers 45K, 45Y, 45M and 45C for precharging that uniformly charge the surfaces of 41M and 41C.

In this image forming apparatus, image carriers 41K, 41Y, 41M and 41C which rotate in the directions of arrows A, respectively.
The electrostatic latent images corresponding to the respective colors are formed on the upper surface, the electrostatic latent images are developed with the toners of the respective colors, and the toner images of the respective colors are formed. A color image is formed by being sequentially transferred so as to be superposed on the recording medium 19 which moves to. This image forming apparatus is advantageous in terms of image forming speed because it can form one color image in one cycle, but there is a positional deviation between the toner images of the respective colors when the images are transferred onto the recording medium 19. However, there is a weak point that the image quality is easily deteriorated. Therefore, in order to suppress the positional deviation between the toner images to be small, it is necessary to precisely control the conveying speed of the recording medium, which is disadvantageous in terms of manufacturing cost.

On the other hand, the toner images of the respective colors are sequentially primary-transferred onto the intermediate transfer member to form a multicolor toner image in which the toner images of the respective colors are superposed on the intermediate transfer member, and the multicolor toner image is collectively formed on the recording medium. There is an image forming apparatus of a so-called intermediate transfer system in which secondary transfer is performed. As one of the intermediate transfer systems, a color image forming apparatus using the following intermediate transfer belt is known.

FIG. 5 is a schematic configuration diagram of a conventional intermediate transfer type color image forming apparatus. The color image forming apparatus shown in FIG. 5 includes an optical scanning device 50 and a drum type image carrier 5.
1, rotary developing device 52, transfer bias roller 5
3, an erase lamp 54, a charging roller 55 for precharging, and an intermediate transfer belt 56. In the developing device 52, developing units 52K, 52Y, 52M and 52C for K, Y, M and C colors are incorporated,
By rotating the developing device 52 in the arrow B direction by the rotary mechanism, the developing units 52K, 52Y, 52M, 5
A predetermined developing unit of 2C is set at the developing position P.

First, the optical scanning device 50 irradiates the image carrier 51 with the exposure light of the first color to form an electrostatic latent image of the first color on the image carrier 51. The electrostatic latent image of the first color is developed at the developing position P as the image carrier 51 rotates in the direction of arrow A.
The toner image of the first color is formed on the image carrier 51 by being developed by the developing unit 52K for the first color which is conveyed to the developing position P. The toner image of the first color formed on the image carrier 51 is conveyed to the primary transfer position T1, and the image carrier 51 and the first transfer bias roll 53a are transferred.
And are primary-transferred onto the intermediate transfer belt 56.

After the primary transfer, the surface of the image carrier 51 is scraped of residual toner by a cleaner 58, discharged by an erase lamp 54, uniformly charged by a charging roller 55 for precharging, and then an optical scanning device. The electrostatic latent image formation of the second color by 50 is performed. The electrostatic latent image of the second color is developed by the developing unit 52Y for the second color set at the developing position P, and the toner image of the second color is formed on the image carrier 51. At the timing when the second color toner image is conveyed to the primary transfer position T1, the first color toner image already formed on the intermediate transfer belt 56 circulates in the direction of arrow C of the intermediate transfer belt 56. With this, the toner image of the second color is conveyed again to the primary transfer position T1 and the toner image of the second color is superposed on the toner image of the first color on the intermediate transfer belt 56 at the primary transfer position T1. First-transcribed. Similarly, electrostatic latent image formation of the third color and the fourth color, development, and primary transfer are sequentially repeated to form toner images of four colors on the intermediate transfer belt 56. The four-color toner image formed on the intermediate transfer belt 56 is conveyed to the secondary transfer position T2, secondarily transferred onto the recording medium 19 by the second transfer bias roll 53b and the backup roll 53c, and then fixed. The color image is completed by being fixed on the recording medium 19 by the device 57.

In this system, since the toner images of the respective colors are superposed and transferred onto the intermediate transfer belt 56 whose properties are controlled, the toner images of the respective colors are recorded on the recording medium made of various materials whose properties are easily changed depending on the environmental conditions. It is easier to control the positional deviation between the toner images than in the image forming apparatus in FIG. However, in this image forming apparatus, in order to form one color image, it is necessary to repeat the image forming process including electrostatic latent image formation, development, and primary transfer for 4 cycles, which is a weak point that the image forming speed is slow. is there. However, the problem of the image forming speed is that, for example, four image forming units and one or a plurality of intermediate transfer members are combined to form a color image by superimposing toner images on the intermediate transfer member in one cycle. This can be solved by configuring the above.

[0010]

By the way, the intermediate transfer member used in the image forming apparatus is required to have physical properties satisfying the following four conditions. 1. Blur, that is, the toner scattering phenomenon is less likely to occur when the toner image on the image carrier is transferred to the intermediate transfer member.

2. It has self-removing property, that is, the charge on the surface of the intermediate transfer body is naturally removed without using a charge remover. 3. The transfer efficiency, that is, the ratio at which the toner image on the image carrier is transferred onto the intermediate transfer member is as high as possible. 4. Retransfer, that is, a phenomenon in which a toner image once transferred onto the intermediate transfer member is not transferred to the image carrier side when the toner image of the next color is transferred onto the intermediate transfer member is unlikely to occur.

As the physical properties of the intermediate transfer member, electrical resistance can be mentioned first. In general, it is known that the surface resistance of the transferred material should be increased to suppress the occurrence of the blur phenomenon, and that the surface resistance of the transferred material should be decreased to improve the self-eliminating property. , Both of them are contradictory conditions, and it is extremely difficult to make them compatible.

Regarding transfer efficiency and retransfer, it is desirable to have physical properties such that an effective transfer electric field is efficiently applied between the image carrier and the intermediate transfer member, and discharge and charge injection are less likely to occur. . In order to obtain an intermediate transfer member satisfying these conditions, for example, JP-A-8-3
As disclosed in JP-A-0109 or JP-A-8-50419, a method is disclosed in which the intermediate transfer member has a two-layer structure and the volume resistivity of the outer layer is higher than the volume resistivity of the inner layer. Has been done. In order to obtain an intermediate transfer member having a high transfer efficiency by this method, the outer layer is formed as thin as possible, for example, 30 μm or less, and its volume resistivity is high, for example, 10 ¹⁴ Ω · cm or more. There is a need. By doing so, a charge having a polarity opposite to that of the toner supplied from the power source and moving from the lower layer of the intermediate transfer member toward the surface layer is blocked near the surface layer of the intermediate transfer member, so that the transfer electric field can be efficiently obtained. However, in the intermediate transfer member having such a structure, since the surface resistance is increased in order to increase the transfer efficiency, the self-eliminating property tends to decrease. Therefore, an additional device such as a static eliminator is required to neutralize the surface of the intermediate transfer member, which is not preferable in terms of cost.

Therefore, it is conceivable to reduce only the surface resistance while keeping the volume resistivity of the outer layer high.
Such control of the resistance of the intermediate transfer member is not only difficult in manufacturing, but even if such a material is obtained, blurring may occur due to the low surface resistance. The hardness of the intermediate transfer body is one of the important physical properties as well as the electric resistance. Generally, if the surface hardness of the intermediate transfer member is low and the elasticity is high, blurring is unlikely to occur. This is because when the hardness of the surface of the intermediate transfer body is low and the elasticity is high, the frictional force increases due to the minute deformation of the surface of the intermediate transfer body and the movement of the toner on the surface of the intermediate transfer body is suppressed, so that blurring is less likely to occur. it is conceivable that. On the other hand, in order to secure the transfer nip and equalize the transfer pressure, the hardness inside the intermediate transfer body needs to be low, but the intermediate transfer body as a whole needs to have a certain hardness.

As described above, the physical properties required for the intermediate transfer member are often contradictory to each other, and it is not easy to obtain an intermediate transfer member having these required physical properties. The present invention is
In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus provided with an intermediate transfer member that is less likely to cause blurring and retransfer, and has high transfer efficiency and high self-removing property.

[0016]

In a first image forming apparatus of the present invention for achieving the above object, an image carrier on which a toner image is formed, and a toner image formed on the image carrier is transferred. An intermediate transfer member, a primary transfer unit for transferring the toner image formed on the image carrier to the intermediate transfer member, and a toner image transferred on the intermediate transfer member to a predetermined recording medium. In an image forming apparatus equipped with a secondary transfer means, the intermediate transfer member comprises a conductive support base and three layers formed on the support base and having different hardness and volume resistivity. Of the three layers, the hardness of the first layer formed on the supporting substrate is H1, the hardness of the second layer formed on the first layer is H2, and the hardness of the second layer is H2. The hardness of the third layer formed on the second layer is H
3, the hardness of each of these layers satisfies the relationship of H1 <H2 and H3 <H2, and the volume resistivity of the first layer is ρ1, and the volume resistivity of the second layer is Is defined as ρ2 and the volume resistivity of the third layer is defined as ρ3, the volume resistivity of each of these layers satisfies the relationship of ρ1 ≦ ρ3 ≦ ρ2.

The second aspect of the present invention which achieves the above object.
The image forming apparatus described above carries a plurality of image carriers on which toner images are formed, and a plurality of primary transfer toner images formed by transferring the plurality of toner images formed on the plurality of image carriers. The toner images formed on the image carrier and the first intermediate intermediate transfer bodies, which are in charge of
Primary transfer means for transferring onto the intermediate transfer member of the second stage, the first transfer means
A second stage intermediate transfer member carrying a secondary transfer toner image formed by transferring a plurality of primary transfer toner images formed on a plurality of stage intermediate transfer members, the first stage The toner images formed on the plurality of intermediate transfer members of
In an image forming apparatus provided with a secondary transfer means for transferring onto the intermediate transfer body of the second stage and a tertiary transfer means for transferring the toner image transferred onto the intermediate transfer body of the second stage onto a predetermined recording medium. Each of the first-stage and second-stage intermediate transfer bodies is formed by laminating a conductive support base and three layers formed on the support base and having mutually different hardness and volume resistivity. Of the three layers, the hardness of the first layer formed on the surface of the supporting substrate is H1,
The hardness of the second layer formed on the surface of the first layer is H2,
When the hardness of the third layer formed on the surface of the second layer is H3, the hardness of each of these layers satisfies the relationship of H1 <H2 and H3 <H2. When the volume resistivity of the layer is ρ1, the volume resistivity of the second layer is ρ2, and the volume resistivity of the third layer is ρ3, the volume resistivity of each layer is ρ1 ≦ ρ3 ≦ ρ2. It is characterized by satisfying.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram of a first embodiment of an image forming apparatus of the present invention. This embodiment is an embodiment of the first image forming apparatus of the present invention. Figure 1
1 shows a color image forming apparatus. The color image forming apparatus includes an optical scanning device 10, a drum type image carrier 11, K (black), Y (yellow), M (magenta) and C.
(Cyan) four-color developing unit 12K, 12Y, 1
A rotary developing device 12 having 2M and 12C mounted therein, an erase lamp 14, a charging roller 15 for precharging, an intermediate transfer drum 16, a transfer bias roller 18, and a fixing device 17 are provided. In addition to these, a power source (not shown) for applying a predetermined bias potential to the intermediate transfer drum 16 and the transfer bias roller 18 is provided. Of these, the power supply for applying a predetermined bias potential to the intermediate transfer drum 16 corresponds to the primary transfer means in the present invention, and the transfer bias roller 18 and the power supply for applying a predetermined bias potential to the transfer bias roller 18 Corresponds to the secondary transfer means in the present invention.

The intermediate transfer drum 16 in this embodiment
Corresponds to the intermediate transfer member referred to in the present invention. The intermediate transfer member of the present invention is not limited to such a drum type, and may have another shape, for example, a belt type. The optical scanning device 10 emits a laser beam according to an image signal and scans the laser beam in the main scanning direction of the image carrier 11 with a polygon mirror.

The image carrier 11 carries the electrostatic latent image formed on the surface by the optical scanning device 10 and rotates in the direction of arrow A. Fine particles are attached to the surface of the image carrier 11. The application of fine particles will be described later. Rotary developing device 12
By rotating in the direction of arrow B, K, Y, M, C
4 developing units 12K, 12Y, 12M, 12C
A predetermined developing unit among them can be set at the developing position P facing the image carrier 11. Each of the developing units contains spherical toners and carriers of K, Y, M, and C colors adjusted to have a constant mixing ratio and mixed and stirred, and the toners and carriers are stored on the developing sleeve 12s. And a magnetic brush provided inside the developing sleeve 12s forms a magnetic brush on the developing sleeve 12s. The toner is mixed and stirred with the carrier, and is negatively charged by friction. The intermediate transfer drum 16 to which a developing bias in which a DC component of −500V is superimposed on an AC component is applied from a power source (not shown) to the developing sleeve 12s of each developing unit is pressed against the image carrier 11 with a predetermined load. ing. Further, the transfer bias roller 18 is press-contacted with the intermediate transfer drum 16 so as to be retractable at a portion different from the contact with the image carrier 11. The shaft of the intermediate transfer drum 16 and the transfer bias roller 18 are connected to a power source (not shown) so that a desired electric potential can be applied. Fine particles are provided on the surface of the intermediate transfer drum 16 as in the image carrier 11.

The charging roller 15 is connected to a power source (not shown) and is configured to uniformly apply a desired potential to the surface of the image carrier 11 by a bias in which a predetermined direct current component and an alternating current component are superposed. Next, the operation of the image forming apparatus of this embodiment will be described. After the surface of the image carrier 11 is uniformly charged to −650 V by the charging roller 15, the laser beam corresponding to the image signal of the first color is irradiated on the surface of the image carrier 11 by the optical scanning device 10 to generate the first color. An electrostatic latent image corresponding to (K) is formed. With the rotation of the image carrier 11 in the direction of arrow A, the electrostatic latent image of the first color is conveyed to the developing position P and is visualized by the developing unit 12K for the first color set at the developing position P. On the image carrier 11
The toner image 13a of the color is formed.

Toner image 13 formed on the image carrier 11
a is conveyed to the primary transfer position T1. Intermediate transfer drum 1
A positive charge is applied to 6, and the toner image 13a on the image carrier 11 is transferred onto the intermediate transfer drum 16 by the electric field created by the positive charge applied to the intermediate transfer drum 16 to obtain a toner image 13b. The process up to this point is the first color image forming cycle, the surface of the image carrier 11 after transfer is neutralized by the erase lamp 14, and the charging roller 1 for precharging is charged.
After being uniformly charged at 5, the process proceeds to the second color image forming cycle.

The image forming process for the second and subsequent colors is almost the same as that for the first color. That is, after the surface of the image carrier 11 is uniformly charged by the charging roller 15, the optical scanning device 1
When 0, a laser beam corresponding to the image signal of the second color is applied to the surface of the image carrier 11 to form an electrostatic latent image corresponding to the second color (Y). With the rotation of the image carrier 11 in the direction of arrow A, the electrostatic latent image of the first color is conveyed to the developing position P and is visualized by the developing unit 12Y for the second color set at the developing position P. As a result, the second color toner image 13c is formed on the image carrier 11.

Here, the first-color toner image already transferred onto the intermediate transfer drum 16 is synchronized with the timing when the second-color toner image 13c on the image carrier 11 is conveyed to the primary transfer position T1. 13b rotates once in the direction of arrow C together with the intermediate transfer drum 16 and is conveyed again to the primary transfer position T1, and the second color toner image 13c is superimposed on the first color toner image 13b. Second color toner image 1
3c is superposed and transferred onto the toner image 13b of the first color on the intermediate transfer drum 16 by the electric field generated by the positive charge applied to the intermediate transfer drum 16 and transferred.
Toner images 13b and 13d are obtained on the top. The transfer bias roller 18 is retracted from the intermediate transfer drum 16 while the toner image is transferred onto the intermediate transfer drum 16.

Similarly, the toner images 13e and 13g of the third color (M) and the fourth color (C) are sequentially formed on the image carrier 11, and they are sequentially transferred to the intermediate transfer drum 16 to form an intermediate image. On the transfer drum 16, the toner images 13b, 13
Full-color toner image 1 in which d, 13f, and 13h are superimposed
3i is obtained. The full-color toner image 13i on the intermediate transfer drum 16 is conveyed to the secondary transfer position T2. On the other hand, in synchronization with this, the recording medium 19 is supplied to the secondary transfer position T2 from a tray (not shown). At the secondary transfer position T2, an electric field generated by the positive charges applied to the recording medium 19 by the transfer bias roller 18 causes
The full-color toner image 13i on the intermediate transfer drum 16 is collectively transferred onto the recording medium 19 to form a full-color toner image 13j on the recording medium 19. The recording medium 19 on which the toner image 13j is formed passes through the fixing device 17 and passes through the fixing device 1.
The toner image 13j is melted on the recording medium 19 by the heat applied by 7 to obtain a fixed image, and the full-color image formation is completed.

Next, the image carrier 11, the rotary developing device 12, the charging roller 15, the intermediate transfer drum 16, and the transfer bias roller 18 used in this embodiment will be described. The image carrier 11 is a cylindrical body having an organic photoreceptor surface layer and having an outer diameter of 20 mm and an axial length of 320 mm. Each developing unit of the rotary developing device 12 has a rotating developing sleeve 12s, and a 7-pole magnet roll is fixedly arranged in the developing sleeve 12s coaxially with the developing sleeve 12s. The developer is mixed and charged by the rotating paddle 12p disposed adjacent to the developing sleeve 12s and then charged, and then supplied onto the peripheral surface of the developing sleeve 12s, and the developer supplied onto the developing sleeve 12s is developed. The surface is smoothed by the developer layer thickness regulating member, and a developer layer having a predetermined thickness is formed on the developing sleeve 12s. The developing sleeve 12s has an outer diameter of 10 mm and an axial length of 320 mm. The distance between the developing sleeve 12s and the image carrier 11 at the developing position P is set to 0.5 mm. Since the magnet roll in the developing sleeve 12s is set so that the portion facing the image carrier 11 corresponds to the gap between the magnets, the toner layer thickness is less than 0.5 mm at the developing position P. The toner flies toward the image carrier 11 due to the electric field, and visualizes the electrostatic latent image on the image carrier 11.

The transfer bias roller 18 is a SUS (stainless steel) shaft covered with an elastic layer of urethane or the like in which carbon is dispersed to make it conductive, and has a size of 10 mm in outer diameter and 320 mm in axial length. Is. The charging roller 15 forms an elastic layer such as EPDM (ethylene / propylene / diene terpolymer) in which carbon is dispersed around the SUS shaft, and further, an acrylic resin in which carbon is dispersed on the surface of the elastic layer. An overcoat layer is formed, and the size is 10m in outer diameter.
m, and the axial length is 320 mm.

FIG. 2 is a sectional view of the intermediate transfer drum used in each embodiment of the present invention. As shown in FIG. 2, the intermediate transfer drum 16 includes a first support layer 21, a second support layer 22, and a second support layer 22 on a conductive support substrate (in this embodiment, on the outer peripheral surface of a cylindrical shaft 20 having an outer diameter of 30 mm). And the third layer 23 are sequentially laminated in a concentric pattern. The first layer 21 is formed by dispersing carbon in EPDM to adjust the volume resistivity to 10 ⁶ Ω · cm and forming it as a layer having a layer thickness of 5 mm.

The second layer 22 is made of polyimide and a small amount of car
The volume resistivity is 10 by dispersing the bon. ¹⁵Adjusted to Ω · cm
It is formed as a layer having a layer thickness of 20 μm. First
Layer 23 of 3 has carbon dispersed in fluororubber latex
And the volume resistivity is 10¹¹Adjust to Ω · cm and adjust it to the layer thickness
It is formed as a 20 μm layer. In the present invention,
The hardness of the first layer of the intermediate transfer member is H1, and the hardness of the second layer is
Is H2 and the hardness of the third layer is H3, each of these layers
The hardness of H1 <H2 and H3 <H2 Which satisfies the relationship of
The volume resistivity of the first layer is ρ1, and the volume resistivity of the second layer is ρ
2. When the volume resistivity of the third layer is ρ3,
The volume resistivity of the layer is ρ1 ≦ ρ3 ≦ ρ2 Must satisfy the following relationship.

Here, the hardness of the first layer 21 is Asker C.
It has a hardness of 70 or less measured by a hardness meter,
In addition, it is preferable that the hardness of the third layer 23 has a hardness of 6 or less as measured by a micro hardness meter. The hardness measured by the Asker C hardness tester refers to a value measured by a spring hardness tester Asker C (JIS / S6050), specifically, a diameter of 5.08 mm and a protrusion height of 2.5.
When the 4 mm hemispherical indenter is pushed into the object to be measured, the amount of the object to be pressed is expressed by a load, and the hardness when the load is 800 gf is Asker C hardness 100. The hardness measured by a micro hardness tester refers to a value measured by a dynamic ultra-micro hardness tester DUH201 manufactured by Shimadzu Corporation. Specifically, a triangular pyramid indenter having a ridge line angle of 115 degrees is used and a test load of 0.25 gf and a load are applied. Speed 0.014
It is a value measured under a measurement condition of 5 gf / sec.

Regarding the volume resistivity, the first layer 21 is 1
The second layer 22 has a volume resistivity of 0 ⁴ Ω · cm or more and 10 ¹⁰ Ω · cm or less, and the second layer 22 has a volume resistivity of 10 ¹² Ω · cm or more and 10 ¹⁶ Ω · cm or more.
It has the following volume resistivity and the third layer 23 has a resistance of 10 ⁷ Ω.
It preferably has a volume resistivity of not less than 10 cm and not more than 10 ¹² Ω.cm. Next, the reasons for defining the hardness and volume resistivity of each layer as described above will be described.

Regarding the hardness, the hardness of the first layer 21 is set to the second
Hardness less than that of the layer 22 of A, preferably Asker C
The hardness measured by the hardness meter is 70 or less in order to secure the width of the transfer nip and ensure the uniformity of the pressure. The hardness of the first layer 21 is Asker C
If the hardness measured by the hardness meter exceeds 70, the width of the transfer nip may not be sufficiently secured, and the transfer efficiency may decrease, and toner may easily aggregate at the transfer nip. Transfer dropouts easily occur in line images. Therefore, the hardness of the first layer 21 is preferably 70 or less as measured by an Asker C hardness meter.

The hardness of the third layer 23 is set to the second layer 22.
The hardness of the intermediate transfer member is set to be lower than the above hardness, preferably 6 or less by a micro hardness tester, in order to suppress the occurrence of blur by lowering the surface hardness of the intermediate transfer member. That is, by lowering the hardness of the intermediate transfer body surface, the frictional force increases due to the micron-level deformation of the intermediate transfer body surface, and the toner on the intermediate transfer body surface becomes difficult to move. The toner is wrapped due to the deformation of the level, and blurring is less likely to occur.

The hardness H2 of the second layer 22 is set to the first layer 21.
Hardness H1 of the third layer 23 and hardness H3 of the third layer 23
The larger values are the effect of ensuring the transfer nip width by the macro-level deformation of the intermediate transfer drum 16 by the first layer 21, and the micron-level deformation of the surface of the intermediate transfer drum 16 by the third layer 23. This is because the blur-preventing effect due to is effective. If the hardness H2 of the second layer 22 is less than the hardness H1 of the first layer 21 or less than the hardness H3 of the third layer 23, the above effect is lost.

Next, the volume resistivity of the first layer 21, the second layer 22 and the third layer 23 will be described. When the resistance of the first layer 21 is high, the voltage drop in the first layer 21 is large, the transfer electric field is weakened, and high transfer efficiency cannot be obtained. In particular, when the resistance is higher than 10 ¹⁰ Ω · cm, a sufficient transfer electric field cannot be obtained. Further, when the volume resistivity of the first layer 21 is a low resistance of less than 10 ⁴ Ω · cm, current leakage easily occurs. Therefore, the volume resistivity of the first layer 21 is preferably 10 ⁴ Ω · cm or more and 10 ¹⁰ Ω · cm or less. By setting the volume resistivity within this range, electric charges provided from the conductive shaft 20 below the first layer 21 can reach the second layer 22 without leaking.

The volume resistivity of the second layer 22 is equal to that of the first layer 21.
When the resistance is lower than that of the third layer 23, for example,
In the case of 10 ¹² Ω · cm or less, the charge is not sufficiently blocked in the second layer 22, and the current flows away through the second layer 22 to obtain a sufficient transfer electric field. The transfer efficiency is reduced. In addition, the first layer 21, the second
The electric charges that have passed through the second layer 22 and the third layer 23 may be injected into the toner on the surface of the intermediate transfer drum 16 and cause retransfer. Therefore, the volume resistivity of the second layer 22 is preferably 10 ¹² Ω · cm or more and 10 ¹⁶ Ω · cm or less.

Regarding the volume resistivity of the third layer 23, as described above, by setting the hardness of the third layer 23 to be lower than the hardness of the second layer 22, the micron on the surface of the intermediate transfer drum 16 can be obtained. Blur prevention due to the deformation of the level is exerted, so that even if the surface resistance of the third layer 23 is low to some extent, for example, about 10 ⁷ Ω · cm in volume resistivity, the occurrence of blur can be effectively prevented. it can. However, it is known that the surface resistance of the intermediate transfer drum 16 is preferably low, and the volume resistivity of 10 ¹² Ω · cm or less causes no problem in terms of self-static elimination. Therefore, the third layer 23 has a hardness lower than that of the second layer 22, and the volume resistivity is 1
By setting the resistance to be not less than 0 ⁷ Ω · cm and not more than 10 ¹² Ω · cm, both self-removing property and prevention of blur can be achieved.

Regarding transfer efficiency and retransfer,
By setting the volume resistivity of the second layer 22 to be higher than that of any other layer, it is possible to block charges in the second layer 22 and efficiently apply a high electric field. It is possible to eliminate the cause of retransfer by reversing the charge of the toner, such as the injection phenomenon and the discharge phenomenon.

It is preferable that both the second layer 22 and the third layer 23 have a thickness of 30 μm or less. As described above, in order to obtain high transfer efficiency, it is necessary to block the charges in the second layer 22, but the second layer 22 and the third layer
If the layer 23 is thick, a sufficient electric field cannot be obtained. Next, the application of fine particles will be described.

In the present invention, the giving of fine particles means an average particle size of 1
The toner image on the surface of the image carrier 11 or the surface of the intermediate transfer drum 16 has a high transfer efficiency by adhering particles having a good releasability such as SiO _{2 having a} size of not less than 500 nm and not more than 500 nm to the surface of the image carrier 11 or the surface of the intermediate transfer drum 16. It means to be able to transfer with. The fine particles having a volume resistivity adjusted to about 10 ¹⁴ Ω · cm are used. In addition, it is desirable to use fine particles whose surface has been subjected to a hydrophobic treatment.

In the present embodiment, hydrophobized SiO ₂ fine particles having an average particle diameter of 20 nm are used to adjust the particle size through a mesh of 10 μm, and then dispersed and adhered to the surface of the image carrier 11 and the surface of the intermediate transfer drum 16 in advance. I will let you. Although a part of the previously given fine particles is transferred to the recording medium 19 and lost due to image formation, most of the fine particles circulate between the image carrier 11 and the intermediate transfer drum 16, and , Fine particles of the same kind externally added to the toner are supplied to the image carrier 11 through the developing device and also to the intermediate transfer drum 16, so that the particles having a substantially constant quantity are transferred to the image carrier 1 and the intermediate transfer drum 16. It is held on the surface of the drum 16.

Next, the transfer operation of each layer on the surface of the intermediate transfer drum 16 of this embodiment will be described. In the primary transfer, in order to transfer the toner having a negative charge from the surface of the image carrier 11 to the intermediate transfer drum 16, a voltage of + 900V having a polarity opposite to that of the toner is applied to the shaft 20 of the intermediate transfer drum 16. . The positive charges applied to the intermediate transfer drum 16 reach the second layer 22 with almost no voltage drop here because the resistance of the first layer 21 is low. Since the second layer 22 has a high resistance, a current passing through the second layer 22 and flowing into the image carrier 11 is a slight current of 10 μA or less. As a result, a sufficient electric field efficiently acts on the toner layer, and high transfer efficiency is obtained. Further, since the phenomenon of charge injection into the toner layer and the phenomenon of discharge in a minute gap are unlikely to occur, reversal of toner charge does not occur, and therefore retransfer does not easily occur.

In the present embodiment, the spherical toner is used as described above, and since the image carrier 11 and the intermediate transfer drum 16 are provided with fine particles, 99.8%.
A high transfer efficiency exceeding the range can be obtained. This makes it possible to obtain a high-quality full-color image free from defects such as density reduction and blur. Further, since the surface of the intermediate transfer drum 16 has high self-removing property, it is not necessary to provide an additional means such as a destaticizing device in this image forming apparatus. Also, the transfer efficiency is 1
Since it is close to 00% and retransfer does not occur, ghost and color mixing in the developing device do not occur. Further, since this image forming apparatus can be made cleaner-less, the image carrier 11 and the intermediate transfer drum 16 are not worn by the cleaner blade, the life is extended, and waste toner is not generated. Can be realized.

Next, a second embodiment of the present invention will be described. FIG. 3 is a schematic configuration diagram of the image forming apparatus according to the second embodiment of the present invention. This embodiment is an embodiment of the second image forming apparatus of the present invention. FIG. 3 shows a color image forming apparatus. The color image forming apparatus includes an image carrier that rotates in the direction of arrow A corresponding to four color images of the optical scanning device 30, K (black), Y (yellow), M (magenta), and C (Cyan). 31
a, 31b, 31c, 31d, developing units 32a, 32b,
32c, 32d, erase lamps 34a, 34b, 34
c, 34d, charging rollers 35a, 35 for precharging
b, 35c, 35d, first stage intermediate transfer drums 36a, 36b rotating in the direction of arrow B, respectively, second stage intermediate transfer drum 36c rotating in the direction of arrow C, transfer bias roller 38, and fixing device 37. Is provided. In addition to these, the intermediate transfer drums 36a, 36b,
A power supply (not shown) is provided for applying a predetermined bias potential to 36c and the transfer bias roller 38. Of these, the power supply for applying a predetermined bias potential to the intermediate transfer drums 36a and 36b corresponds to the primary transfer means in the present invention, and the power supply for applying a predetermined bias potential to the intermediate transfer drum 36c is the present invention. The secondary transfer means referred to above, and the transfer bias roller 38 and the power supply for applying a predetermined bias potential to the transfer bias roller 38 correspond to the tertiary transfer means referred to in the present invention.

The intermediate transfer drum 16 in this embodiment
Corresponds to the intermediate transfer member referred to in the present invention. The intermediate transfer member of the present invention is not limited to such a drum type, and may have another shape, for example, a belt type. Next, the optical scanning device 30 and the image carriers 31a, 31b, 31c, 31 used in the present embodiment.
d, the developing devices 32a, 32b, 32c, 32d, the charging rollers 35a, 35b, 35c, 35d, the intermediate transfer drums 36a, 36b, 36c, and the transfer bias roller 38 will be described. The optical scanning device 30 is K
(Black), Y (yellow), M (magenta), and C (cyan) The light source 30a that emits four light beams based on the image signals of four colors, and the four light beams emitted from the light source 30a A common optical system 30b that includes a deflection optical element that commonly deflects and guides these four light beams in parallel to each other, and a separation optical system that separates the four light beams guided to the common optical system 30b into mutually different directions. 30c and separation optical system 30c
It is equipped with cylindrical mirrors 30d, 30e, 30f, 30g for guiding the four light beams separated by the above to respective corresponding image carriers 31a, 31b, 31c, 31d. Body 31a,
Optical scanning is performed on 31b, 31c and 31d in a predetermined main scanning direction.

Image carriers 31a, 31b, 31c, 31d
Is the same as the image carrier 11 of the first embodiment and has the surface layer of the organic photoconductor, the outer diameter is 20 mm, and the axial length is 320 m.
It is a cylindrical body of m. Image carriers 31a, 31b, 31c,
On the surface of 31d, like the image carrier 11 of the first embodiment,
Fine particles are added. Developing devices 32a, 32b, 32
In c and 32d, spherical toners of K, Y, M and C colors and carriers are adjusted so as to have a constant mixing ratio and accommodated while being mixed and stirred. Each developing device 32
Similar to the developing unit of the first embodiment, a, 32b, 32c, and 32d have a developing sleeve (see FIG. 1: 12s), and a 7-pole magnet roll is fixed in the developing sleeve coaxially with the developing sleeve. It is arranged. The developer is supplied to the outer peripheral surface of the developing sleeve after being mixed by a paddle disposed adjacent to the developing sleeve and negatively charged by friction. The surface of the developer is leveled by a developer layer thickness regulating member, and a developer layer having a predetermined layer thickness is formed on the developing sleeve. The developer layer has a magnetic brush shape on the developing sleeve by a magnet roll provided inside the developing sleeve. The developing sleeve has an outer diameter of 10 mm and an axial length of 320 mm. The distance between the developing sleeve and the image bearing members 31a, 31b, 31c, 31d is set to 0.5 mm. The magnet roll in the developing sleeve is composed of the image carriers 31a, 31b, 31c, 31.
The portion facing d is set so as to hit the pole, and the toner layer thickness of that portion is formed to be thinner than 0.5 mm, so that the toner easily fly. Since a developing bias in which a DC component of −500 V is superimposed on an AC component is applied to the developing sleeve by a power source (not shown), the toner moves to the image carrier by the electric field and develops the electrostatic latent image.

Charging rollers 35a, 35b, 35c, 35
Similarly to the charging roller 15 of the first embodiment, d also has an elastic layer such as EPDM in which carbon is dispersed around the shaft of SUS, and an overcoat layer of acrylic resin in which carbon is dispersed on the surface of the elastic layer. The outer diameter is 10 mm and the axial length is 320 mm.
Is. Charging rollers 35a, 35b, 35c, 35d
Is applied with a voltage obtained by superimposing an AC component on a predetermined DC bias component from a power source (not shown), so that a desired bias potential is uniformly applied to the surfaces of the image carriers 31a, 31b, 31c, 31d.

The intermediate transfer member of this embodiment has a two-stage structure of a first stage and a second stage. The first stage intermediate transfer drum 36a includes image carrier members 31a and 31b and a second stage. Is arranged in pressure contact with the intermediate transfer drum 36c of
The first stage intermediate transfer drum 36b includes the image carrier 31c,
31d and the second stage intermediate transfer drum 36c are arranged in pressure contact with each other. Therefore, in the present embodiment, the toner image on the image carrier is transferred from the image carrier to the first stage intermediate transfer drum, and from the first stage intermediate transfer drum to the second stage intermediate transfer drum. And the transfer from the second stage intermediate transfer drum to the recording medium.

In the intermediate transfer system of the first embodiment described above, the image carrier 11 at the primary transfer position T1.
From the start of the primary transfer of the toner image to the intermediate transfer belt 16 from the start of the toner image to the intermediate transfer belt 16 and then to the primary transfer position T1 again by the rotation of the intermediate transfer belt 16 causing the toner image to return to the primary transfer position T1. Then, the primary transfer of the toner image of the next color is started. Therefore, the intermediate transfer belt 16 is
It must have the surface area required to carry one screen of the image to be formed.

On the other hand, in this embodiment, both the first-stage intermediate transfer drums 35a and 35b and the second-stage intermediate transfer drum 36 are simultaneously transferred to the next process while receiving the transfer of the toner image from the previous process. Transfer is possible,
Since it is not necessary to have the surface area for one screen of the image, the whole intermediate transfer means can be made compact. Therefore, the intermediate transfer system of this embodiment is more advantageous than the intermediate transfer belt system of the second embodiment in terms of downsizing the image recording apparatus.

Intermediate transfer drums 36a, 36 of this embodiment
An intermediate transfer drum similar to the intermediate transfer drum 16 of the first embodiment shown in FIG. 2 is used for b and 36c. Further, fine particles are applied to the surfaces of the intermediate transfer drums 36a, 36b, 36c, as in the intermediate transfer drum 16 of the first embodiment. The transfer bias roller 38 is the same as the transfer bias roller 18 of the first embodiment, and is arranged to be retractable with respect to the intermediate transfer drum 36c.

Image carriers 31a, 31b, 31c, 31d
As the fine particles applied to the surfaces of the intermediate transfer drums 36a, 36b, and 36c, like the fine particles used in the image forming apparatus according to the first embodiment, the surface is subjected to a hydrophobic treatment, the average particle diameter is 20 nm, and the volume resistance is Si with a rate of about ¹⁴ Ω · cm
O ₂ is used. After the particles are sized through a 10 μm mesh, the image carrier 31a, 31b, 31c, 31
d and the intermediate transfer drums 36a, 36b and 36c are dispersed and attached in advance. The particles thus provided circulate between the image carriers and the intermediate transfer drum, and part of them are transferred to the recording medium 19 at the time of the third transfer, but the same kind of particles are externally added to the toner. Fine particles are constantly supplied to the image carriers 31a, 31b, 31c and 31d through the developing process, and are also supplied to the intermediate transfer drums 36a, 36b and 36c. It is maintained on the surfaces of the carriers 31a, 31b, 31c, 31d and the intermediate transfer drums 36a, 36b, 36c.

Next, the operation of the image forming apparatus of this embodiment will be described. First, the surface of the image carrier 31b is uniformly charged to −650 V by the charging roller 35b for precharge for the second color (Y), and then the light corresponding to the image signal of the second color is emitted from the optical scanning device 30. Beam the image carrier 31
The surface b is irradiated and an electrostatic latent image corresponding to the second color (Y) is formed. The electrostatic latent image of the second color formed on the surface of the image carrier 31b is arranged so as to face the image carrier 31b, and a developing bias in which an AC component is superimposed on a DC component of -500V is applied by a power source (not shown). The image bearing member 3 is developed by the Y toner developing device 32b and is visualized.
A second color toner image 33a is formed on 1b.

Next, at the transfer position T1 where the image carrier 31b and the intermediate transfer drum 36a face each other, the toner image 33a of the second color is transferred to the intermediate transfer drum 36a by the electric field generated by the positive charges applied to the intermediate transfer drum 36a. The toner image 33b of the second color is formed by being transferred onto the surface 36a. In this first-stage transfer, the toner image 33a having a negative charge is transferred from the surface of the image carrier 31a to the intermediate transfer drum 36.
In order to transfer the toner to a, a voltage of + 900V having a polarity opposite to that of the toner is applied to the shaft of the intermediate transfer drum 36a. The applied positive charges reach the high-resistance second layer 22 with almost no voltage drop in the third layer 23 because the resistance of the third layer 23 (see FIG. 2) is low. Second layer 2
The current flowing through 2 to the image carrier 31b is 10
It is a small current of μA or less. As a result, the image carrier 31
A sufficient electric field efficiently acts on the toner layer on b, and high transfer efficiency can be obtained. Further, since the phenomenon of charge injection into the toner layer and the phenomenon of discharge in a minute gap are unlikely to occur, reversal of toner charge does not occur, and thus retransfer is also unlikely to occur. Further, in the present embodiment,
Since spherical toner is used and fine particles are applied to each image carrier and each intermediate transfer drum, 99.8.
A high transfer efficiency exceeding 100% can be obtained.

The process up to this point is the first image forming cycle for the second color, after which the electrostatic latent image on the image carrier 31b is erased by the erase lamp 34b. Second
After the image forming cycle for the color is started, the image forming cycle for the first color is started at a predetermined timing. First
The latent image forming process and the developing process for the image carrier 31a of the color (K) are performed in the same manner as for the second color.
A toner image 33c of the first color is formed on the top. The second color toner image 33b already formed on the intermediate transfer drum 36a is directed toward the transfer position T2 at which the image carrier 31a and the intermediate transfer drum 36a face each other as the intermediate transfer drum 36a rotates in the direction of the arrow B. Of the first color toner image 3 on the image carrier 31a at the timing when the front end of the second color toner image 33b is conveyed and reaches the transfer position T2.
3c is transferred so as to be superimposed on the toner image 33b of the second color, and the toner image 33 in which the first color and the second color are combined is formed.
d is formed on the intermediate transfer drum 36a. The synthetic toner image 33d is formed on the intermediate transfer drum 36a and the intermediate transfer drum 36a as the intermediate transfer drum 36a rotates in the arrow B direction.
is conveyed toward the transfer position T3 where c and c face each other,
When the front end of the synthetic toner image 33d reaches the transfer position T3, the second transfer to the intermediate transfer drum 36c is started, and the toner image 33e is formed on the intermediate transfer drum 36c.

This second transfer is performed by the intermediate transfer drum 3
Transfer is performed from the intermediate transfer drums 6a and 36b to the intermediate transfer drum 36c between the intermediate transfer drums of the same material. Generally, it is difficult to obtain a high transfer efficiency by transferring between the intermediate transfer drums of the same material, but according to the experiments of the present inventors, even the same material, for example, a polyimide intermediate transfer drum in which carbon is dispersed is used. It has been confirmed that a spherical toner is used as a developer and fine particles are applied in the transfer between the two, and a transfer efficiency close to 100% can be obtained. In this embodiment, the intermediate transfer drums 36a, 36b, 36c
Since the third layer 23 (see FIG. 2) on the surface has a hardness lower than that of the second layer 22, for example, a hardness of 6 or less by a micro hardness tester, it is possible to transfer between hard materials such as polyimide. The conditions are different, and the transfer efficiency tends to be slightly lowered.
Therefore, in order to compensate for the decrease in transfer efficiency, the intermediate transfer drum 3
It is effective to deflect the surface properties of 6a, 36b, 36c, such as volume resistivity and elasticity. Generally, when the charged toner is moved from one member surface to another member surface by the action of an electric field, it is better to transfer the member surface from the lower volume resistivity to the higher volume resistivity. It is known that the toner migration is more likely to occur than the one-sided transfer. Therefore, in the present embodiment, the volume resistivity of the third layer on the surfaces of the intermediate transfer drums 36a and 36b is set to 10 ¹¹ Ω · cm, whereas the volume resistivity of the third layer 23 on the surface of the intermediate transfer drums 36c is set. The resistivity is set to 10 ¹² Ω · cm.

Further, regarding the hardness of the third layer 23,
Experiments by the present inventors have revealed that transfer from a hard material side to a soft material side is easier than transfer from a soft material side to a hard material side. Therefore, the hardness of the third layer 23 on the surfaces of the intermediate transfer drums 36a and 36b is set to the third hardness on the surface of the intermediate transfer drum 36c.
The hardness is set lower than the hardness of the layer 23. In particular,
By changing the molecular weights and crosslink densities of the intermediate transfer drums 36a, 36b, 36c, a difference of about 1.0 is provided in the measurement value by the micro hardness meter.

The toner image 33e formed on the intermediate transfer drum 36c is rotated by the intermediate transfer drum 36c in the direction of arrow C, and the intermediate transfer drum 36c and the intermediate transfer drum 36b are rotated.
And are conveyed toward the transfer position T6 facing each other.
On the other hand, the image forming process for the third and fourth colors is
The toner image 33f, 33g of the third and fourth colors is started on the image carriers 31c, 31d at a timing delayed by a predetermined time from the start time of the image forming process of the first and second colors. Are formed at a predetermined timing, and the image carrier 31d and the intermediate transfer drum 36b are formed.
The toner image 33g of the fourth color on the image carrier 31d is transferred onto the intermediate transfer drum 36b at the transfer position T4 where and are opposite to each other. The fourth formed on the intermediate transfer drum 36b
The toner image 33h of the color is the arrow B on the intermediate transfer drum 36b.
The image carrier 31c and the intermediate transfer drum 3 are rotated in the direction of the arrow.
6b is conveyed toward the transfer position T5 opposite to each other, and the third color toner image 33f on the image carrier 31c is transferred at the timing when the front end of the fourth color toner image 33h reaches the transfer position T5. Transfer is started so as to be superimposed on the toner image 33h of the fourth color. The combined toner images 33i of the fourth and third colors formed on the intermediate transfer drum 36b are indicated by the arrow B on the intermediate transfer drum 36b.
With the rotation in the direction, the intermediate transfer drum 36b and the intermediate transfer drum 36c are conveyed to the transfer position T6 facing each other.

When the toner image 33i formed on the intermediate transfer drum 36b is conveyed to the transfer position T6,
The toner image 33e formed on the intermediate transfer drum 36c is synchronized with the timing of being conveyed to the transfer position T6, and the toner image 33i on the intermediate transfer drum 36b is formed on the toner image 33e on the intermediate transfer drum 36c. The transfer is started so as to be superposed. In this way, the formation of the four-color toner image 33j in which the toner images of the first color to the fourth color are combined is started on the intermediate transfer drum 36c. The four-color toner image 33j formed on the intermediate transfer drum 36c is conveyed to the transfer position T7 where the intermediate transfer drum 36c and the transfer bias roll 38 face each other as the intermediate transfer drum 36c rotates in the direction of arrow C. At the transfer position T7, the recording medium 19 is transferred from a tray (not shown) at a predetermined timing.
Is conveyed, and is transferred onto the recording medium 19 at the transfer position T7.
The color toner images 33j are collectively transferred (third stage transfer). The transfer bias roller 38 is retracted from the intermediate transfer drum 36c while the toner image is transferred onto the intermediate transfer drum 36c.

The four-color toner image 33j is transferred by the third transfer.
The recording medium 19 on which is transferred is conveyed to the fixing device 37. The toner image 33j is heated by the fixing device 37 and melted and fixed on the recording medium 19. In this way, full-color image formation is completed. In this embodiment, in order to further improve the transfer efficiency, the intermediate transfer drum 36
A peripheral speed difference of about 1% is provided between the peripheral speeds of a and 36b and the intermediate transfer drum 36c.

This peripheral speed difference is also due to the difference in the image bearing members 31a, 3a.
1b, 31c, 31d and intermediate transfer drums 36a, 36b
Between the intermediate transfer drums 36a, 36b and the intermediate transfer drum 36c, and between the intermediate transfer drum 36c and the transfer roller 3. By providing the peripheral speed difference in this way, not only the transfer efficiency can be improved, but also the character and line omission can be prevented.

[0062]

As described above, according to the image forming apparatus of the present invention, the surface layer of the intermediate transfer member has a three-layer structure, and the three layers have appropriate hardness relationships and volume resistivity relationships. By setting to (1), it is possible to obtain an image forming apparatus provided with an intermediate transfer member which is less likely to cause blurring and retransfer, and has high transfer efficiency and high self-removing property.

Further, since the surface of the intermediate transfer drum is self-erased, it is not necessary to provide additional means such as a static eliminator in the image forming apparatus. Further, since the cleaner-less image forming apparatus can be used, waste toner is not generated and the drum is not worn, so that it is possible to realize an image forming apparatus that has a long life and is environmentally friendly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of an intermediate transfer drum used in each embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a second embodiment of an image forming apparatus of the present invention.

FIG. 4 is a schematic configuration diagram of a conventional tandem type color image forming apparatus.

FIG. 5 is a schematic configuration diagram of a conventional intermediate transfer type color image forming apparatus.

[Explanation of symbols]

10 Optical Scanning Device 11 Image Carrier 12 Rotary Developing Device 12K, 12Y, 12M, 12C Developing Unit 12p Paddle 12s Developing Sleeve 13a, 13b, 13c, 13d, 13e, 13f, 1
3g, 13h, 13i, 13j Toner image 14 Erase lamp 15 Charging roller 16 Intermediate transfer drum 17 Fixing device 18 Transfer bias roller 19 Transfer medium 20 Shaft 21 First layer 22 Second layer 23 Third layer 30 Optical scanning device 30a Light source 30b Common optical system 30c Separation optical systems 30d, 30e, 30f, 30g Cylindrical mirrors 31a, 31b, 31c, 31d Image carriers 32a, 32b, 32c, 32d Developing devices 33a, 33b, 33c, 33d, 33e, 33f, Three
3g, 33h, 33i, 33j Toner images 34a, 34b, 34c, 34d Erase lamps 35a, 35b, 35c, 35d Charging rollers 36a, 36b, 36c Intermediate transfer drum 37 Fixer 38 Transfer bias rollers 40K, 40Y, 40M, 40C Light Scanning device 41K, 41Y, 41M, 41C Image carrier 42K, 42Y, 42M, 42C Developing device 43K, 43Y, 43M, 43C Transfer bias roller 45K, 45Y, 45M, 45C Charging roller 46K, 46Y, 46M, 46C Cleaner 50 light Scanning device 51 Image carrier 52K, 52Y, 52M, 52C Developing unit 53 Transfer bias roller 53a Transfer roll 54 Erase lamp 55 Charging roller 56 Intermediate transfer belt 57 Fixing device 58 Cleaner

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114

Claims (9)

(57) [Claims] 1. An image carrier on which a toner image is formed, an intermediate transfer member on which the toner image formed on the image carrier is transferred,
A primary transfer unit that transfers the toner image formed on the image carrier onto the intermediate transfer member, and a secondary transfer unit that transfers the toner image transferred onto the intermediate transfer member onto a predetermined recording medium are provided. In the image forming apparatus, the intermediate transfer member is formed by laminating a conductive support base and three layers formed on the support base and having mutually different hardness and volume resistivity. Of the three layers, the hardness of the first layer formed on the supporting base is H1, the hardness of the second layer formed on the first layer is H2, and the hardness of the second layer is on the second layer. When the hardness of the formed third layer is H3, the hardness of each of these layers satisfies the relationship of H1 <H2 and H3 <H2, and the volume resistivity of the first layer is ρ1. , Ρ2 is the volume resistivity of the second layer, and ρ3 is the volume resistivity of the third layer. In this case, the image forming apparatus is characterized in that the volume resistivity of each of these layers satisfies the relationship of ρ1 ≦ ρ3 ≦ ρ2. 2. The first layer is 10 ⁴ Ω · cm or more 10
^It has a volume resistivity of ¹⁰ Ω · cm or less, and the second layer is 1
It has a volume resistivity of 0 ¹² Ω · cm or more and 10 ¹⁶ Ω · cm or less, and the third layer has a volume resistivity of 10 ⁷ Ω · cm or more and 10 ¹² Ω · cm or more.
The image forming apparatus according to claim 1, wherein the image forming apparatus has a volume resistivity of not more than cm. 3. The image forming apparatus according to claim 1, wherein each of the second layer and the third layer has a thickness of 30 μm or less. 4. The first layer has a hardness of 70 or less according to an Asker C hardness tester, and the third layer.
2. The image forming apparatus according to claim 1, wherein said layer has a hardness of 6 or less as measured by a micro hardness meter. 5. The supporting base is cylindrical or cylindrical, and the first layer, the second layer, and the third layer are concentrically formed on the outer peripheral surface of the supporting base. The image forming apparatus according to claim 1, wherein the image forming apparatuses are sequentially laminated. 6. A plurality of image bearing members on which a toner image is formed,
A plurality of first-stage intermediate transfer bodies that share and carry a plurality of primary transfer toner images formed by transferring a plurality of toner images formed on the plurality of image carriers,
Primary transfer means for transferring the toner image formed on the image bearing member onto the intermediate transfer member of the first stage, a plurality of primary transfer toners formed on the plurality of intermediate transfer members of the first stage The second stage intermediate transfer member carrying a secondary transfer toner image formed by transferring the image, and the toner images formed on the plurality of first stage intermediate transfer members are transferred to the second stage. Secondary transfer means for transferring onto the intermediate transfer member of the eye, and the second
In an image forming apparatus provided with a tertiary transfer means for transferring the toner image transferred onto the intermediate transfer body of the first stage to a predetermined recording medium, each of the intermediate transfer bodies of the first stage and the second stage is
A conductive support base and three layers formed on the support base and having different hardness and volume resistivity from each other are laminated, and the support base surface among the three layers is formed on the surface of the support base. First formed
Where H1 is the hardness of the layer, H2 is the hardness of the second layer formed on the surface of the first layer, and H3 is the hardness of the third layer formed on the surface of the second layer. Has a hardness of H1 <H2 and H3 <H2. Further, the volume resistivity of the first layer is ρ1, the volume resistivity of the second layer is ρ2, and the volume resistivity of the third layer is ρ2. An image forming apparatus, wherein the volume resistivity of each layer satisfies the relationship of ρ1 ≦ ρ3 ≦ ρ2, where the volume resistivity of the layer is ρ3. 7. The third layer of the intermediate transfer member of the first stage has a volume resistivity smaller than that of the third layer of the intermediate transfer member of the second stage. The image forming apparatus according to claim 6, wherein 8. The third layer of the first-stage intermediate transfer member has a hardness lower than that of the third layer of the second-stage intermediate transfer member. The image forming apparatus according to claim 6. 9. The image forming apparatus according to claim 1, wherein the intermediate transfer member has fine particles having an average particle diameter of 1 nm or more and 500 nm or less adhered to the surface of the intermediate transfer member.