JP2001265135A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a contact pressure in a primary transfer nip part, and also to form a satisfactory transfer electric field over a wide area in the primary transfer nip part, while suppressing the deterioration of the primary transfer efficiency, a retransfer phenomenon and a missing of middle phenomenon, and to obtain a uniform image free of unevenness. SOLUTION: For the rear side of an intermediate transfer belt 20, the surface resistivity is controlled such that ρs<109 [Ω/(square)] by conduction processing. By moving a frame with assembled rollers 20a to 20c for stretching the belt 20 in the photoreceptor drum 1 direction, the belt 20 comes into contact with the photoreceptor drum 1 due to own tension, and then the primary transfer part is formed by the belt 20 without, having to use a primary transfer roller. When a primary transfer bias is applied on the tension roller 20c by a high- voltage power source 12, the rear side of the belt 20 has the same potential over the entire length, the primary transfer bias works on the primary transfer part, and the toner image on the photoreceptor drum 1 is transferred primarily to the belt 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying method in which a toner image formed on an image carrier by, for example, an electrophotographic method is transferred to an intermediate transfer member and then transferred to a recording material to obtain an image on the recording material. The present invention relates to an image forming apparatus such as a printer or a printer.

[0002]

2. Description of the Related Art Conventionally, there is an image forming apparatus which transfers a toner image formed on an image carrier using an electrophotographic method to a recording material and fixes the toner image to obtain a permanent image on the recording material.
Also, with the development of the information society in recent years, the demand for color image forming apparatuses is expanding.

There are various types of color electrophotographic systems. For example, multiple development is performed in which a color image is superimposed and formed on the surface of a photoreceptor (image carrier) by repetition of development, and then collectively transferred to a recording material. Method, a multiple transfer method that repeats the formation of a toner image on the photoreceptor surface by development and its transfer to a recording material, and the formation of a toner image on the photoreceptor surface and its transfer to an intermediate transfer body are repeated. There is an intermediate transfer system for performing batch transfer to a recording material.

Among these, the intermediate transfer system has excellent advantages, such as being free from color mixing and being applicable to various recording media. FIG. 5 is a schematic diagram illustrating an example of a conventional image forming apparatus provided with an intermediate transfer member that forms a color image using an electrophotographic method.

This image forming apparatus has a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier, rotates the photosensitive drum 1 in a direction of an arrow R1, and uses a charger 2 in the rotating process. The surface is uniformly charged, and image exposure L by a laser beam is performed from the exposure device 3 via the reflection mirror 4 to sequentially form an electrostatic latent image of a color component corresponding to a target color image on the surface of the photosensitive drum 1. Form.

The latent image developing device 5 (yellow developing device 5Y, magenta developing device 5M, cyan developing device 5
C, black developing device 5K), and yellow, magenta, cyan, and black toner images are sequentially formed on photosensitive drum 1, and each time the toner images are formed one by one, they are formed on intermediate transfer belt 6. And a primary transfer nip portion (primary transfer portion) where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact with each other
Is transferred by the primary transfer roller 7 (primary transfer), and while the intermediate transfer belt 6 rotates four times, a color image in which four color toner images are superimposed and transferred on the intermediate transfer belt 6 is obtained.

The photosensitive drum 1 is, for example, a negatively chargeable O
In the case of the PC photoreceptor, the exposed portion by the image exposure L is
With a negative polarity toner. Therefore 1
A high transfer power supply 12 applies a positive transfer bias having a polarity opposite to the charge polarity of the toner to the next transfer roller, and electrostatically attracts the toner to the intermediate transfer belt 6 to transfer the toner. As the primary transfer roller 7, a low-resistance roller of 10 ⁵ Ωcm or less is generally used.

The primary transfer residual toner remaining on the surface of the photosensitive drum 1 due to the primary transfer is removed and collected by the drum cleaner 10 every time the primary transfer is completed one by one.
Thereafter, the photosensitive drum 1 is subjected to image formation of a toner image of the next color, and the above-described charging and subsequent steps are performed.

The intermediate transfer belt 6 includes driving rollers 6a, 2
It is stretched and supported by the next transfer opposing roller 6b and the tension roller 6c, and is rotationally driven in the direction of arrow R2 by the rotational drive of the drive roller 6a. Examples of the intermediate transfer belt 6 include PVDF, polyamide, polyimide, PET,
A resin film made of a resin film having a thickness of about 50 to 200 μm, such as polycarbonate, or a resin layer having a good releasability provided on a rubber base layer having a thickness of about 0.5 to 2 mm is used.

Next, the recording material supplied to the secondary transfer nip portion (secondary transfer portion) where the four color toner images on the intermediate transfer belt 6 are brought into contact with the intermediate transfer belt 6 and the secondary transfer roller 8. The toner image is collectively transferred onto the recording material P by the secondary transfer roller 8 (secondary transfer), and a color image using a toner corresponding to the target color image is obtained on the recording material P.

In the secondary transfer, the secondary transfer roller 8 is brought into contact with the intermediate transfer belt 6 with the recording material P supplied to the secondary transfer portion interposed therebetween. A four-color toner image on the intermediate transfer belt 6 is applied by applying a positive transfer bias having a polarity opposite to that of the secondary transfer opposite roller 6b to the ground of the back surface of the intermediate transfer belt 6 or the secondary transfer opposite roller 6b to which an appropriate bias is applied. Is electrostatically attracted to the recording material P.

The recording material P on which the color image has been formed is sent to a fixing device (not shown), and the toner is fixed on the recording material P to form a color permanent image, and then discharged outside the image forming apparatus. The intermediate transfer belt 6 has the remaining 2
After the toner remaining after the next transfer is removed by the belt cleaner 9, the apparatus is prepared for the next image formation.

[0013]

In the image forming apparatus using the intermediate transfer member as described above, in order to obtain a uniform image without unevenness, the primary transfer to the intermediate transfer belt 6 is performed by the photosensitive drum 1. It is important to form a sufficient transfer electric field in a wide range in the primary transfer nip where the belt and the intermediate transfer belt 6 are in contact with each other. This can be realized by providing a sufficient contact area between the intermediate transfer belt 1 and the primary transfer roller 7 by strongly pressing the primary transfer roller 7 against the back surface of the intermediate transfer belt 6.

However, when the primary transfer roller 7 is pressed strongly, the contact pressure in the primary transfer nip increases, and a force is generated to separate the toner image into the photosensitive drum 1 and the intermediate transfer belt 6. I do. Originally, all the toner constituting the toner image by the primary transfer should be transferred to the intermediate transfer belt 6. However, since a part of the toner image is strongly pressed to the photosensitive drum 1 side, the force to return to the photosensitive drum 1 is increased. It happens.

The force for returning the toner to the photosensitive drum may deteriorate the primary transfer efficiency or cause the toner image once primary-transferred onto the intermediate transfer belt to be transferred to the photosensitive drum again at the time of the primary transfer of the toner image of the next color or later. This causes a reverse transfer, a so-called retransfer phenomenon. In addition, since the pressure tends to concentrate at the central portion of the line image where the density is high, a so-called centering phenomenon occurs in which the line image after the transfer is lost in white.

As described above, in the conventional image forming apparatus,
If a sufficient transfer electric field is to be formed in a wide range in the primary transfer nip, the contact pressure in the primary transfer nip will inevitably increase. There was a problem that a drop-out phenomenon was inevitable.

An object of the present invention is to reduce the contact pressure in the primary transfer nip, and to form a sufficient transfer electric field over a wide range in the primary transfer nip.
An object of the present invention is to provide an image forming apparatus capable of obtaining a uniform image without unevenness, which suppresses the deterioration of the next transfer efficiency, the retransfer phenomenon, the hollow phenomenon, and the like.

[0018]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier on which a toner image is formed, an intermediate transfer body supported by a plurality of supports including a drive support, and a primary charging unit that is in primary contact with the image carrier and the intermediate transfer body A high-voltage power supply for applying a voltage to transfer the toner image on the image carrier to an intermediate transfer member, wherein the toner image on the intermediate transfer member is transferred to a transfer material. The body has at least the surface resistivity ρs of the back
Has the following characteristic: ρs <10 ⁹ [Ω / □], wherein the image carrier is in contact with the intermediate transfer member without a pressing member facing the intermediate transfer member across the surface thereof. An image forming apparatus.

According to the present invention, the primary transfer voltage is applied to any one of the supports of the intermediate transfer member by the high-voltage power supply, or by directly applying the primary transfer voltage to the back surface of the intermediate transfer member. A primary transfer voltage is applied to the next transfer section. A plurality of color toner images are sequentially formed on the image carrier, and a plurality of color toner images on the image carrier are superimposed on the intermediate transfer member and primary-transferred. The intermediate transfer member is of a self-decay type.

A plurality of the image carriers are provided along a moving direction of the intermediate transfer member, and a plurality of color toner images are formed on the plurality of image carriers, and the plurality of image carriers are formed on the plurality of image carriers. The primary transfer is performed by superposing a plurality of color toner images on the intermediate transfer member. The intermediate transfer member is a self-decay type, the charge relaxation time of the intermediate transfer member is τ (second), and the time required for a part of the surface of the intermediate transfer member to move between two adjacent image carriers is T. (Seconds), the intermediate transfer member satisfies the relationship of τ ≦ T.

Four image carriers are provided along the direction of movement of the intermediate transfer member, and a support member for adjusting the tension of the surface of the intermediate transfer member is provided between the second and third image carriers. Can be provided. The surface of the intermediate transfer member is formed in a single-layer structure of resin or rubber or a multi-layer structure obtained by combining them. A conductive treatment is performed on the back surface of the intermediate transfer member. The intermediate transfer member is an intermediate transfer belt formed as an endless belt.

[0022]

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

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention. This image forming apparatus is configured as a full-color laser beam printer.

The present invention makes it possible to perform primary transfer without using a dedicated contact type primary transfer means such as a primary transfer roller.
A major feature is that the contact pressure in the next transfer nip is reduced, and a sufficient transfer electric field can be formed in a wide range in the primary transfer nip.

In this embodiment, for this purpose, the primary transfer is performed by applying the primary transfer bias from the primary high voltage power supply 12 to the tension roller 20c using the intermediate transfer belt 20 whose back surface is made conductive. did. Intermediate transfer belt 20
Are supported by being stretched over a driving roller 20a, a secondary transfer facing roller 20b, and a tension roller 20c.
Other configurations of the image forming apparatus of the present embodiment are basically the same as those of the conventional image forming apparatus shown in FIG. 5, and in FIG. 1, the same members as those in FIG. Unless otherwise described, the description is omitted.

In this embodiment, the process speed of the image forming apparatus is 17 mm / sec, and the image is formed in the same manner as in the conventional image forming apparatus. Developing device 5 (5Y-5)
The toner used in K) is a negative toner having a triboelectric charge (triboelectric charge) of about −25 μC / g in a normal environment. The photosensitive drum 1 is negatively chargeable and has a diameter of 47 m.
m, and used at a charging potential of −550 V and an exposure potential of −150 V.

The intermediate transfer belt 20 is a single-layer seamless belt made of a polyimide resin whose resistance is adjusted by carbon dispersion, and has a thickness of 75 μm, a circumference of 400 mm, and a width direction (length in the same direction as the longitudinal direction of the photosensitive drum). Sa) 250
mm.

According to the present embodiment, the intermediate transfer belt 2
The back surface of 0 is electrically conductive. The conductive treatment is performed by applying an isopropyl alcohol spray (Aerodag G, manufactured by Acheson Japan Co., Ltd.) in which ultrafine graphite is dispersed to the intermediate transfer belt 20.
By applying a coating having a thickness of about 10 μm on the back surface of the substrate.

The intermediate transfer belt 20 is JIS
According to K6911, a conductive rubber is used as an electrode to obtain good contact between the electrode and the surface of the intermediate transfer belt, and then the volume of the belt is measured using an ultra-high resistance meter (Advantest R8340 manufactured by Advantest). The resistivity ρv and the surface resistivity ρs were measured. The applied voltage was 100 V, and the application time was 30 seconds. As a result, values as shown in Table 1 were obtained.

[0030]

[Table 1] As described above, the intermediate transfer belt 20 has a very low surface resistivity on the back surface and the belt back surface is maintained at the same potential over the entire circumference, so that the entire belt back surface functions as an electrode. Therefore, the application of the primary transfer bias to the primary transfer unit can be realized by applying a positive bias from the high voltage power supply 12 to the tension roller 20c, and the primary transfer can be performed without the primary transfer roller.

In this embodiment, the primary transfer nip moves a belt frame (not shown) incorporating rollers 20a, 20b and 20c in the direction of the photosensitive drum 1 by applying a load so that a predetermined total load is applied at the nip portion. By doing so, the intermediate transfer belt 2 stretched over the rollers 20a to 20c
0 is pushed into the photosensitive drum 1 side, and is formed by making contact with the photosensitive drum 1 using the tension of the belt 20. The optimal primary transfer bias in this embodiment is 300
V.

On the other hand, the secondary transfer from the intermediate transfer belt 20 to the recording material P is performed by using the secondary transfer opposing roller 20b, which has the same potential as the back surface of the intermediate transfer belt 20, as the opposing pole and the high voltage power supply 13 This is performed by applying a bias to the secondary transfer roller 8.

In this embodiment, the above-mentioned intermediate transfer belt 20 is mounted on the image forming apparatus shown in FIG. 1, and the load (total load at the nip) applied to the belt frame is changed variously.
The next transfer was performed, and conditions such as the total load when an optimal primary transfer nip that forms uniform primary transfer without unevenness was formed were examined. Table 2 shows the total load, the nip width (the nip length in the direction perpendicular to the longitudinal direction of the photosensitive drum), and the average contact pressure calculated from these.

For comparison, an intermediate transfer belt 20 similar to the above was mounted on a conventional image forming apparatus having a primary transfer roller 7 shown in FIG. The total load at the time of forming was evaluated. Table 2 also shows the results.

[0035]

[Table 2] As shown in Table 2, according to the present embodiment, it can be seen that the contact pressure at the primary transfer nip can be greatly reduced as compared with the conventional example. Further, in the configuration of the present embodiment, since the entire back surface of the intermediate transfer belt 20 functions as an electrode, a sufficient transfer electric field can be formed in a wide range in the transfer nip portion. As a result, a sufficient transfer electric field is formed in a wide range within the transfer nip portion while suppressing the contact pressure in the transfer nip portion as compared with the related art, thereby suppressing the deterioration of the primary transfer efficiency, retransfer, and the dropout phenomenon. The obtained uniform image can be obtained.

In the above, if the surface resistivity of the back surface of the intermediate transfer belt 20 is high, even if a positive bias is applied to the tension roller 20c from the high voltage power supply 12, the voltage drop on the back surface of the belt cannot be ignored. An improper bias cannot be applied to the next transfer portion, resulting in transfer failure due to insufficient transfer current.

The present inventors have confirmed that the intermediate transfer belt 20 has at least a surface resistivity ρs
Is within the range of ρs <10 ⁹ [Ω / □], it is possible to achieve the same effect as the primary transfer electrode as described above.

In the above description, the intermediate transfer belt 20 is a single-layer resin belt whose back surface is made conductive. However, as long as at least the back surface is made conductive, a single-layer rubber belt can be used as a multi-layer structure combining resin or rubber. Belt. Although the primary transfer bias is applied to the tension roller 20c, it may be applied to the drive roller 20a or the secondary transfer opposing roller 20b.
0 can be directly applied to the back surface.

Although an image forming apparatus for forming a color image using one photosensitive drum and an intermediate transfer belt has been described, a monochrome image such as a monochrome image is formed using one photosensitive drum and an intermediate transfer belt. The present invention can be applied to an image forming apparatus that forms the above image, and a similar effect can be obtained.

As described above, according to this embodiment,
Using an intermediate transfer belt having a low back resistance, a primary transfer nip is formed by contacting the photosensitive drum using only the tension of the belt, and a primary transfer bias is applied to a roller on which the intermediate transfer belt is stretched by applying a primary transfer bias. Since the secondary transfer is performed, it is possible to obtain a uniform image without deterioration of the primary transfer efficiency, re-transfer, and hollow phenomenon. In addition, omitting the primary transfer roller makes it possible to omit not only the roller itself, but also a roller support member, a contact pressure adjusting spring, and the like, thereby achieving simplification of the apparatus configuration and cost reduction.

Embodiment 2 FIG. 2 is a schematic diagram showing another embodiment of the image forming apparatus of the present invention.

This image forming apparatus is an in-line type apparatus provided with an intermediate transfer member. Image forming units PY, four colors of yellow, magenta, cyan, and black are arranged along the upper orbit of the intermediate transfer belt 22. PM, PC, and PK are arranged, and each image forming unit has a photosensitive drum 1Y,
1M, 1C, 1K, charging rollers 2Y, 2M, 2C, 2
K, laser exposure devices 3Y, 3M, 3C, 3K, developing units 5Y, 5M, 5C, 5K, drum cleaners 10Y, 10
M, 10C and 10K are provided respectively.

The intermediate transfer belt 22 is basically stretched and supported by a driving roller 22a, a secondary transfer opposing roller 22b, and a tension roller 22c.
It is also supported by 2d, and is rotationally driven in the direction of arrow R3 by the drive roller 22a. The intermediate transfer belt 22 is
In the same manner as in the first embodiment, a load is applied to the belt frame so that a predetermined total load is obtained at the nip portion.
By moving in the .about.1K direction, all of the photosensitive drums 1Y to 1K are brought into contact with each other using the tension of the belt, thereby forming each primary transfer unit.

The auxiliary support roller 22d abuts on the intermediate transfer belt 22 to finely adjust the belt tension so that the contact pressure between the intermediate transfer belt 22 and the photosensitive drum 1 is set to an optimum value in all the primary transfer sections. For, preferably,
Two inner image forming units P which are not image forming units at both ends
It is installed on the back side of the belt between M and PC.

Each of the image forming units PY to PK has a predetermined timing, and the photosensitive drum 1 (1Y to 1
K), a toner image of each color is formed by image exposure and development, and the toner image of each color is transferred by being superimposed on each primary transfer portion where the photosensitive drum 1 and the intermediate transfer belt 22 are in contact with each other. The secondary transfer roller 8 collectively and secondarily transfers the superimposed and transferred four-color toner images onto the recording material P supplied to the secondary transfer portion to form a target color image on the recording material P. Obtain a color image with the corresponding toner.

Also in this embodiment, the toner used in the developing unit 5 (5Y to 5K) is a negative toner having a triboelectric charge of about -25 μC / g in a normal environment.
(1Y to 1K) are negatively chargeable, and the diameter of the photosensitive drum 1 is 30 mm. Similarly, the photosensitive drum 1 is used at a charging potential of -550 V and an exposure potential of -150 V.

The intermediate transfer belt 22 has the same configuration as that used in the first embodiment. That is, the intermediate transfer belt 22 is a single-layer seamless belt made of polyimide resin whose resistance has been adjusted by carbon dispersion.
An isopropyl alcohol spray in which ultrafine graphite is dispersed is applied to the back surface to make the back surface conductive. However,
In the present embodiment, the intermediate transfer belt 22 has a short charging relaxation time and has a self-decaying electrical characteristic.

The thickness of the intermediate transfer belt 22 is 75 μm as in the first embodiment, but the circumference is 1115 mm and the width in the width direction (the length in the same direction as the lengthwise direction of the photosensitive drum) is 310 m.
m.

As in the first embodiment, the back surface of the intermediate transfer belt 22 has a very low surface resistivity, the belt back surface is kept at the same potential over the entire circumference, and the entire back surface of the belt acts as an electrode. By simply applying a positive bias to the tension roller 22c, each image forming unit P
The primary transfer bias can be simultaneously applied to the primary transfer portions of Y to PK, and the primary transfer can be performed without the primary transfer roller in the primary transfer portion of each image forming portion.

2 to the recording material P from the intermediate transfer belt 22
In the next transfer, as in the first embodiment, a positive bias is applied to the secondary transfer roller 8 from the high-voltage power supply 13 using the secondary transfer opposite roller 22b having the same potential as the back surface of the intermediate transfer belt 22 as the opposite pole. It is implemented by doing.

In this embodiment, the intermediate transfer belt 22 is mounted on the image forming apparatus shown in FIG. 2, and the primary transfer is performed by changing the load applied to the belt frame (total load at the nip). The conditions such as the total load when forming an optimal primary transfer nip which results in a non-uniform primary transfer were examined. Table 3 shows the total load at that time, the nip width (the nip length in the direction perpendicular to the longitudinal direction of the photosensitive drum), and the average contact pressure calculated from these.

[0052]

[Table 3] As shown in Table 3, according to the present embodiment, similar to the first embodiment, it can be seen that the contact pressure at the primary transfer nip can be greatly reduced. Further, since the entire back surface of the intermediate transfer belt 22 functions as an electrode, a sufficient transfer electric field can be formed in a wide range in the transfer nip portion. As a result, a sufficient transfer electric field is formed in a wide range within the transfer nip portion while suppressing the contact pressure in the transfer nip portion as compared with the related art, thereby suppressing the deterioration of the primary transfer efficiency, retransfer, and the dropout phenomenon. A uniform image was obtained for all colors.

As described above, according to the present embodiment,
Even in an in-line type image forming apparatus capable of high-speed full-color printing, an intermediate transfer belt with a low back resistance is used. Each primary transfer nip is formed in contact with the photosensitive drum, and a primary transfer bias is applied to one of the rollers on which the intermediate transfer belt is stretched, so that primary transfer is performed. It is possible to obtain a uniform color image without deterioration in efficiency, re-transfer, and hollow phenomenon. Also, omission of the primary transfer roller,
By omitting the roller support member, the spring for adjusting the contact pressure, and the like, simplification of the device configuration and reduction in cost can be realized.

Embodiment 3 In this embodiment, according to the self-attenuating type intermediate transfer belt 22 used in Embodiment 2, the same primary transfer bias is applied to obtain good primary images of toner images of four colors. Explain that transfer is possible.

Here, the self-decay type means that the charge relaxation time of the intermediate transfer member is τ (second), and a portion between two adjacent image carriers (between two adjacent primary transfer portions) is a part of the intermediate transfer member. When the time required for the movement of the object is T (seconds), it means that the characteristic that the relationship of τ ≦ T is satisfied is provided. on the other hand,
Those that do not satisfy this condition are called charge-up types.

As shown in FIG. 3, the charge relaxation time τ of the intermediate transfer member is such that the surface potential V applied at the charging position of the intermediate transfer member attenuates exponentially with time and V / e
(E is a natural logarithm base, e = 2.718...) And is defined as a time until it falls.

Here, whether or not a certain intermediate transfer belt 22 is a self-decay type, that is, whether or not the charge relaxation time τ of the intermediate transfer belt satisfies τ ≦ T is determined by measurement using the apparatus shown in FIG. it can.

The intermediate transfer belt 22 is stretched around a driving roller 207 as a measuring jig and a metal tension roller 206, and rotates in a direction indicated by an arrow at a speed of 117 mm / sec. The intermediate transfer belt 22 is moved to the charging roller 20 at the charging position.
1. An AC power supply 202 sandwiched between metal opposing rollers 208 and having a peak-to-peak voltage Vpp of about 3 kV, for example, +500 V
Is charged by the DC power source 203.

The charging roller 201 is of a well-known contact charging type. For example, a medium resistance layer of about 100 to 200 μm and a volume resistivity of about 10 ⁶ Ωcm is provided on an elastic conductive rubber having a thickness of about 3 mm. It has a fixed layer of 10 μm (eg, a nylon resin) and is formed into a cylindrical shape having a diameter of about 12 mm.

The surface potential W of the intermediate transfer belt 22 charged by the charging roller 201 is measured by a surface voltmeter probe 204 and a voltmeter main body 205 provided at a position rotated for T seconds downstream from the charging position. Note that T is 0. 0 of the time required for a part of the intermediate transfer belt to move between two adjacent image carriers of the image forming apparatus of the present embodiment.
It is the same time as 8 seconds.

At this time, if the surface potential W of the intermediate transfer belt 22 is measured as W ≦ 500 / e [V], it is a belt having τ of 0.8 seconds or less, that is, a self-damping belt. If it is determined that W> 500 / e [V], it can be determined that the belt has a τ of more than 0.8 seconds, that is, a belt of a charge-up type.

In this embodiment, the intermediate transfer belt 22 of the self-attenuation type used in the embodiment 2 is used as the intermediate transfer belt A, and a charge-up type intermediate transfer belt B is prepared separately, and these are used for an image forming experiment. Then, characteristics in image formation were examined.

The intermediate transfer belt B, like the intermediate transfer belt A, is a single-layer seamless polyimide resin belt having a thickness of 75 μm and a circumference of 1115 mm, but the resistance adjustment by carbon dispersion is set to a higher resistance. The back surface of the intermediate transfer belt B is also made conductive by applying an isopropyl alcohol spray (Aerodag G manufactured by Acheson Japan) with a thickness of about 10 μm to disperse ultrafine graphite.

As in the case of the first embodiment, JIS-K691
By using a conductive rubber as an electrode in accordance with No. 1 and obtaining good contact between the electrode and the surface of the intermediate transfer belt, an ultra-high resistance meter (Advantest R834 manufactured by Advantest)
0), the volume resistivity ρv of the belt and the surface resistivity ρs
Was measured. The applied voltage was 100 V, and the application time was 30 seconds. As a result, values as shown in Table 4 were obtained.

[0065]

[Table 4] The intermediate transfer belts A and B are mounted on the image forming apparatus shown in FIG. 2, and the primary transfer of each color is performed by applying the same primary transfer bias to form a full-color image. (1) The transfer efficiency was examined and summarized in three stages: good, medium, and poor. Regardless of which belt was used, the primary transfer bias was set to 300 V in order to optimize the transfer efficiency of the yellow image. Table 5 shows the results
Shown in In Table 5, the symbol 1 indicates that the transfer efficiency is ○: good, Δ: medium, ×: poor.

[0066]

[Table 5] As shown in Table 5, the self-decay type intermediate transfer belt A
, Good primary transferability was obtained for each color, but when the charge-up type intermediate transfer belt B was used, the primary transferability was not so high.

This is because, in the case of the intermediate transfer belt B, charges gradually accumulate inside the belt as it sequentially passes through the image forming portions PY to PK in FIG. 2, and the belt is electrostatically charged up. The effective impedance in the thickness direction of the intermediate transfer belt that passes through the transfer nip becomes higher as it passes through the downstream image forming unit, and the transfer current in the downstream image forming unit becomes insufficient, and the transfer efficiency deteriorates. To do that.

Therefore, in the color image forming apparatus, the back surface of the intermediate transfer belt is made conductive, and a primary transfer bias is applied to a driving roller or the like supporting the intermediate transfer belt to apply a primary transfer bias to the primary transfer portions of all image forming portions. When the primary transfer of each color is performed by applying the primary transfer bias,
If the intermediate transfer belt is further self-damping, the same
By applying the secondary transfer bias, good primary transferability can be achieved in all image forming portions.

The same thing as in the present embodiment can be applied to the first embodiment. In the first embodiment, since the intermediate transfer belt 20 is not of a self-decay type, the primary transfer bias applied from the high voltage power supply 12 is transferred later. The higher the color toner image, the higher the level. However, if the intermediate transfer belt 20 is of a self-attenuating type, the primary transfer of all color toner images can be performed by applying the same primary transfer bias.

In each of the above embodiments, the intermediate transfer belt is used as the intermediate transfer body. However, the present invention is also applicable to an image forming apparatus using a hollow intermediate transfer drum whose surface is supported by a plurality of supports. Can be applied, and a similar effect can be obtained.

[0071]

As described above, according to the present invention,
An intermediate transfer body such as an intermediate transfer belt having a low back surface resistance was brought into contact with the photosensitive drum using only the tension of the belt without using the primary transfer roller to form a primary transfer nip. Can be reduced, and a sufficient transfer electric field can be formed in a wide range in the primary transfer nip. Therefore, it is possible to obtain a uniform color or monochromatic image without unevenness in which the primary transfer efficiency is reduced, the retransfer phenomenon and the hollow phenomenon are suppressed. Further, by omitting the primary transfer roller, the roller support member, the spring for adjusting the contact pressure, and the like, the simplification of the device configuration and the reduction in cost can be realized.

Further, by arranging a plurality of photosensitive drums in parallel along the moving direction of the intermediate transfer member, even in an image forming apparatus such as an in-line type which realizes high-speed color printing, primary transfer efficiency deteriorates for all colors. It is possible to obtain a uniform color image without unevenness, in which retransfer and a hollow phenomenon are suppressed, and similarly, a primary transfer roller, its supporting member,
By omitting the spring for adjusting the contact pressure and the like, it is possible to simplify the apparatus configuration and reduce the cost. Further, by using the self-decay type intermediate transfer member, the primary transfer of each color can be favorably performed with the same primary transfer bias.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 3 is a graph showing the transition of the surface potential of the self-attenuation type intermediate transfer belt used in the present invention.

FIG. 4 is a diagram showing a measurement system for measuring a charge relaxation time of an intermediate transfer member.

FIG. 5 is a schematic configuration diagram illustrating a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5Y-5K Developing device 8 Secondary transfer roller 12 Primary transfer high voltage power supply 13 Secondary transfer high voltage power supply 20, 22 Intermediate transfer belt 20a, 22a Driving roller 22d Auxiliary support roller

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsunori Ishiyama 3- 30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Yasuo Yoda 3- 30-2 Shimomaruko, Ota-ku, Tokyo F term in Canon Inc. (reference) 2H030 AB02 BB23 BB24 BB42 2H032 AA05 AA15 BA07 BA09 BA13

Claims (12)

[Claims] An image carrier on which a toner image is formed; an intermediate transfer member supported by a plurality of supports including a driving support;
1 is attached to the primary transfer section where the image carrier and the intermediate transfer body are in contact.
A high-voltage power supply for applying a next charging voltage to transfer the toner image on the image carrier to an intermediate transfer member, wherein the toner image on the intermediate transfer member is transferred to a transfer material. The intermediate transfer member has at least a surface resistivity ρs of the back surface.
Has the following characteristic: ρs <10 ⁹ [Ω / □], wherein the image carrier is in contact with the intermediate transfer member without a pressing member facing the intermediate transfer member across the surface thereof. Image forming device. 2. The method according to claim 1, wherein a primary transfer voltage is applied to one of the supports of the intermediate transfer body by the high-voltage power supply.
The image forming apparatus according to claim 1, wherein a primary transfer voltage is applied to the primary transfer unit. 3. The image forming apparatus according to claim 1, wherein the primary transfer voltage is applied to the primary transfer portion by directly applying a primary transfer voltage to the back surface of the intermediate transfer member by the high-voltage power supply. 4. The image transfer device according to claim 1, wherein a plurality of toner images are sequentially formed on the image carrier, and the plurality of color toner images on the image carrier are superimposed on the intermediate transfer member and primary-transferred. The image forming apparatus according to any one of the above items. 5. The image forming apparatus according to claim 4, wherein said intermediate transfer member is of a self-decay type. 6. A plurality of image carriers are provided along a direction of movement of the intermediate transfer member, and form toner images of a plurality of colors on the plurality of image carriers. The image forming apparatus according to claim 1, wherein primary transfer is performed by superimposing a plurality of color toner images on the intermediate transfer member. 7. The image forming apparatus according to claim 6, wherein said intermediate transfer member is of a self-decay type. 8. The method according to claim 1, wherein the charging relaxation time of the intermediate transfer member is τ.
(Second), where T (second) is the time required for a part of the surface of the intermediate transfer member to move between two adjacent image carriers, the intermediate transfer member satisfies the relationship: τ ≦ T. 7 is an image forming apparatus. 9. The image carrier according to claim 1, wherein four image carriers are provided along a moving direction of the intermediate transfer member, and a tension adjusting member for adjusting a tension of a surface of the intermediate transfer member is provided between the second and third image carriers. The image forming apparatus according to claim 6, further comprising a support member. 10. The image forming apparatus according to claim 1, wherein the surface of the intermediate transfer member has a single-layer structure of resin or rubber or a multi-layer structure obtained by combining them. 11. The image forming apparatus according to claim 1, wherein a conductive treatment is performed on a back surface of the intermediate transfer member. 12. The image forming apparatus according to claim 1, wherein the intermediate transfer member is an intermediate transfer belt formed on an endless belt.