JPH11352809A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image defect caused by the resistance value fluctuation owing to the environmental change of a transfer belt. SOLUTION: This device is allowed to obtain a correlation of the current measurement value between a transfer roller 10a and the drive roller 10b, and the volume resistivity of the transfer belt base layer 8a in advance, and to subsequently examine the correlation between the volume resisvitity of the transfer belt base layer 8a and secondary transfer bias, by referring to the secondary bias causing 'tunneling' under the LL environment and the secondary bias making the secondary transfer efficiency beyond 85%. Then, the correlation between the volume resistivity of the transfer belt base layer 8a and the secondary bias is, shown as the correlation of the current measurement value between the transfer roller 10a and the driving roller 10b, and the secondary transfer bias. Now, the device is allowed to measure the current between the transfer roller 10a and the drive roller 10b, and to set the secondary transfer bias based on this current measurement value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer or a copying machine, and more particularly to an image forming apparatus for transferring a toner image formed on an image carrier to a transfer material by a transfer belt. It concerns the device.

[0002]

2. Description of the Related Art Conventionally, in a color image forming apparatus using an intermediate transfer body or a color image forming apparatus using a multi-developing method, a color image or a multicolor image composed of a plurality of developers is transferred to an intermediate transfer body or a photosensitive drum. After being formed on the image carrier, the image is transferred collectively to the transfer material,
The image forming product obtained by combining the color image information is output.

When an intermediate transfer member or a multiple developing system is used,
There is an advantage that superposition of each component image and displacement (color displacement) do not occur.

In an image forming apparatus using an intermediate transfer member or a multi-developing system, the peripheral length of an image carrier for carrying a color image composed of a plurality of developers must be at least as large as the maximum paper passing size. For example, when passing A3 size paper, the circumference of this image carrier is at least 420 m.
m or more, and 134 mm or more in diameter when the image carrier is a drum.

However, when an image carrier having a small radius of curvature on the surface is used, when the toner image is electrostatically transferred to the transfer material, the transfer material cannot be separated in curvature, and the electrostatic charge is applied to the image carrier. There was a problem that it would be adsorbed in a random manner.

In order to prevent the transfer material from being attracted to the image carrier, the transfer material after the transfer has been removed by a corona separation charger so that the transfer material is separated from the image carrier. However, a corona separation charger requires a high-voltage power supply to supply a bias to the charger,
There is a problem that a large amount of ozone is generated due to corona discharge.

[0007] In the present specification, "transfer material"
Is transfer paper, recording paper, printing paper, card, envelope, postcard, O
The material is not limited to paper, such as an HP sheet.

[0008]

The above-mentioned problem has been solved by using a belt as a transfer means. That is, the transfer material is attracted to the belt, and the transfer of the toner image from the image carrier and the separation of the transfer material are performed at the same time, thereby solving the attraction of the transfer material to the image carrier.

However, when a belt is used as the transfer means, the resistance of the transfer belt fluctuates due to environmental changes or paper passing durability, that is, long-term use. Image failure occurs.

Note that the resistance value fluctuation of the transfer belt is a reversible fluctuation in the case of an environmental change or the like, while the resistance value fluctuation due to paper passing durability is an irreversible fluctuation.

Accordingly, a main object of the present invention is to provide an image forming apparatus capable of preventing an image defect due to a change in the resistance value of a transfer belt due to an environmental change.

Another object of the present invention is to provide an image forming apparatus capable of preventing an image defect caused by a change in the resistance value of a transfer belt due to long-term use.

[0013]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image forming apparatus comprising: an image carrier that carries a toner image; a transfer unit that transfers the toner image to a transfer material; and a bias power supply that applies a bias to the transfer unit.
The transfer unit has a transfer belt and a plurality of rollers around which the transfer belt is wound. The transfer belt is disposed so as to be able to contact and separate from the image carrier, and is applied to the rollers from the bias power supply. An image forming apparatus comprising a detecting unit for detecting a bias current or voltage to be applied.

The transfer belt is formed in a multilayer structure, and has a base layer containing at least a thermosetting urethane elastomer;
It is preferable to provide a surface layer containing a fluorine-modified resin on the surface of the base layer. The volume resistivity of the base layer is 1 × 10 ⁹ [Ω]
· Cm] or less. When the volume resistivity of the base layer becomes 1 × 10 ⁹ [Ω · cm] or more due to long-term use, it is preferable to recommend the user to replace the transfer belt.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows an image forming apparatus according to the present embodiment. The image forming apparatus includes a photosensitive drum 1, a charging roller 2 serving as a charging unit, an exposure device 3, a developing device 4, a transfer device 5, and A fixing device 6 and the like are provided.

The photosensitive drum 1 rotates at a predetermined peripheral speed (process speed = 117 mm / s) in the direction of arrow a, and is uniformly charged to a predetermined polarity and potential by the charging roller 2 during the rotation process. Image exposure by an image exposure device (such as a color original image color separation / imaging optical system, a scanning exposure system using a laser scanner that outputs a laser beam modulated according to a time-series electric digital pixel signal of image information, etc.) 3 By receiving L, an electrostatic latent image corresponding to the first color component (for example, a yellow component image) of the target color image is formed.

The developing device 4 includes a first developing device (yellow developing device) 4a, a second developing device (magenta developing device) 4b, a third developing device (cyan developing device) 4c, and a fourth developing device (black developing device). 4d, and is rotated in the direction of arrow b by a rotation driving device (not shown), and the first to fourth developing devices 4a to 4d are
It is arranged so as to face the photosensitive drum 1 during the development process.

The above-described electrostatic latent image is developed by the first developing device 4a with the first color yellow toner.

The transfer device 5 includes intermediate transfer members (in this embodiment, intermediate transfer drums) 7 and 2 which are image carriers for performing primary transfer.
The intermediate transfer drum 7 is driven to rotate at the same peripheral speed as the photosensitive drum 1 in the direction of arrow c.

The first type formed and supported on the photosensitive drum 1
The yellow toner image of (1) passes through the nip portion between the photosensitive drum 1 and the intermediate transfer drum 7, and the electric field and pressure generated by the primary transfer bias applied to the intermediate transfer drum 7 from the primary transfer bias power supply 9 As a result, intermediate transfer is performed on the outer peripheral surface of the intermediate transfer drum 7. This step is called primary transfer.

Hereinafter, similarly, the second color magenta toner image and the third color cyan toner formed and carried on the photosensitive drum 1 by the second developing unit 4b, the third developing unit 4c, and the fourth developing unit 4d. The image and the black toner image of the fourth color are sequentially superimposed and transferred on the intermediate transfer drum 7 to form a composite color toner image corresponding to the target color image.

First from the photosensitive drum 1 to the intermediate transfer drum 7
The primary transfer bias applied from the primary transfer bias power supply 9 for sequentially superimposing and transferring the toner images of the first to fourth colors is
It has the opposite polarity (plus) to the toner. The photosensitive drum 1
The transfer belt 8 and the intermediate transfer cleaning roller 12 are separated from the intermediate transfer drum 7 in the process of sequentially transferring the first to fourth color toner images from the intermediate transfer drum 7 to the intermediate transfer drum 7.

The transfer belt 8 is supported in parallel with the intermediate transfer drum 7 and is mounted on the lower surface of the transfer belt 8 so as to be able to contact and separate therefrom by appropriate means. The transfer belt 8 is wound around a transfer roller 8a and a drive roller 8b, and rotates in the direction of arrow d. The desired secondary transfer bias is supplied from the secondary transfer bias power supply 11 to the transfer roller 10a and the drive roller 1a.
0b.

Then, the transfer material P passes from a paper feed cassette (not shown) through registration rollers 13a and 13b and a pre-transfer guide 14, and is transferred to a transfer nip formed by the transfer belt 8 contacting the intermediate transfer drum 7. Paper is fed at a predetermined timing. At this time, as described above, the secondary transfer bias is applied from the secondary transfer bias power supply 11 to the transfer roller 10a and the drive roller 10b, and the transfer material P is transferred from the intermediate transfer drum 7 to the transfer material P.
The composite color toner image is transferred thereon. This step 2
Next transfer.

The transfer material P to which the composite color toner image has been transferred is conveyed to the fixing device 6, where the composite color toner image is heated and welded and discharged outside the apparatus.

The transfer residual toner remaining on the intermediate transfer drum 7 without being secondary-transferred is originally cleaned by the intermediate transfer member cleaning roller 12 to which a bias in which a DC voltage is superimposed on an AC voltage is applied from a power supply 15. When the polarity is changed to the opposite polarity (plus), the photosensitive drum 1 is electrostatically attracted, and the intermediate transfer drum 7 is cleaned. Photosensitive drum 1
The toner adsorbed on the photosensitive drum cleaner 1
7 to be collected.

Next, the structure of the intermediate transfer drum 7 will be described in detail with reference to FIG.

The intermediate transfer drum 7 is provided, for example, as a cylindrical conductive support 7a, an elastic layer 7b made of rubber, elastomer, resin or the like provided thereon, and further as an upper layer of the elastic layer 7b. It has at least one surface layer 7c and has a roller shape.

In this embodiment, a cylindrical aluminum having a thickness of 3 mm is used as the conductive support 7a. The thickness of the elastic layer 7b depends on the shape of the transfer nip, color shift due to rotation,
Considering the material cost and the like, it is desirable to be about 0.5 to 7.0 mm. In addition, the thickness of the surface layer 7c is equal to the thickness of the lower elastic layer 7b.
It is preferable to use a thin layer in order to further convey the flexibility to the upper layer or the surface of the photosensitive drum.
About 30 μm is desirable.

The intermediate transfer drum 7 used in this embodiment has a thickness of the elastic layer 7b of 5 mm, a thickness of the surface layer 7c of 20 μm, and a total outer diameter of 186 mm.

The elastic layer 7b emphasizes only the volume resistivity, and mixes acrylonitrile-butadiene (NBR) with epichlorohuman phosphorus rubber to control the elastic layer 7b to 10 ⁵ to 10 ⁶ Ω · cm.

The resistance value of the intermediate transfer drum 7 is shown in FIG.
Was measured by the measuring device 20 shown in FIG. This measuring device 20
Aluminum cylinder 2 abutting on the surface of intermediate transfer drum 7
1. High voltage power supply 22 and standard resistor 23 are provided.

When the resistance value of the intermediate transfer drum 7 is measured, the aluminum cylinder 21 is rotated by a rotary driving body (not shown), and the contacting intermediate transfer drum 7 is driven to rotate. The contact pressure at this time was set to a total pressure of 1 kgf as in the actual use state during image formation. By applying a constant DC voltage (1 kV) from the high-voltage power supply 22 to the conductive support 7 a of the intermediate transfer drum 7, the current flowing through the elastic layer 7 b of the intermediate transfer drum 7 flows into the aluminum cylinder 21, Grounded via a standard resistor (1 kΩ).

Assuming that the voltage between both ends of the standard resistor 23 is Vr [V], the resistance value Rc of the intermediate transfer drum 7 is obtained by the following equation.

Rc [Ω] = 10 ⁶ / Vr [V] For the surface layer 7c, a material in which PTFE powder is dispersed with a urethane resin as a binder for the purpose of improving releasability was used. When the surface resistivity of this surface layer was measured, it was 10 ¹⁰ Ω
Met.

The measurement of the surface resistivity of the surface layer 7c is performed by using the elastic layer 7
b coated with a surface layer 7c is 100 × 100 mm,
Cut out the thickness into an appropriate sheet, and advance
Applied voltage: 1 kV, discharge: 5 sec, char using R8340A and R12704 manufactured by
The measurement was carried out under the following conditions: ge: 30 sec, measure: 30 sec. The volume resistivity including the elastic layer 7b and the surface layer 7c was 2 × 10 ⁷ Ω · cm (when 300 V was applied).

Next, the structure of the transfer belt 8 will be described in detail with reference to FIG.

The transfer belt 8 is formed in a two-layer structure of a base layer 8a and a thin surface layer 8b thereon, and the surface layer 8b is formed with a high resistivity in order to suppress the occurrence of separation failure in a high temperature and high humidity environment. On the other hand, the base layer 8a has a low resistivity in order to reduce the volume resistance of the transfer belt 8 so that the secondary transfer voltage can be reduced as much as possible.

Further, in order to satisfy mechanical characteristics such as bending characteristics and tensile strength characteristics, the base layer 8a is made of an elastomer in which carbon black is dispersed. Base layer 8
The thermosetting urethane elastomer used for the material (a) is an ether type and is generally harder to hydrolyze than an ester type urethane rubber, but has a tackiness due to a lower surface roughness due to centrifugal molding. In the use state, the surface having tackiness is on the inner side, and the sliding surface with the roller is brought. Further, since a fluorine-modified resin is provided on the surface layer 8b side, there is no problem of tackiness in use.

As a result, in a state where the transfer roller 10a and the drive roller 10b are stretched and wound by 8%, problems such as meandering, offset, and the like do not occur, and it is possible to sufficiently cope with long-term use.

Next, the material and electrical characteristics of the transfer belt used in this embodiment will be described.

First, using a centrifugal mold having an inner diameter of 65 mm, a fluorine-modified resin is cast-molded on the surface layer 8b side to a thickness of 20 μm, and then a thermosetting urethane elastomer of the base layer 8a (for example, ENDURE (inoac C)
o. ,)) Is molded inside. The volume resistivity of the urethane elastomer layer was controlled to less than 1 × 10 ⁹ Ω · cm by carbon dispersion, the total belt thickness was adjusted to 300 μm, and the volume resistivity of the entire belt was adjusted to 1 × 10 ¹⁰ Ω.

The resistance value of the transfer belt 8 is determined by cutting the transfer belt 8 into a sheet of 100 × 100 mm,
Using R8340A and R12704 manufactured by test Co., Ltd., applied voltage: 10 V, discharge: 5 seconds
c, charge: 30 sec, measure: 30
It was measured under the condition of sec.

Next, the structure of the transfer roller 10a will be described with reference to FIG.

The transfer roller 10a has an outer diameter of 20 mm, and has a two-layer structure of a SUS core bar 10a2 (14 mm in diameter) and an elastic layer 10a1 (thickness 3 mm) on it. The elastic layer 10a1 has a volume resistivity of 1 × 10 ⁵ Ω · cm.
Acrylonitrile butadiene rubber (hereinafter referred to as “NBR”). The configuration of the driving roller 10b will be described with reference to FIG.

The outer diameter of the driving roller 10b is 20 mm.
It has a two-layer structure of a SUS core bar 10b2 (diameter 14 mm) and an elastic layer 10b1 (thickness 3 mm) thereon. The elastic layer 10b1 has a volume resistivity of 1 × 10 ⁵ Ω · cm.
NBR is used.

Next, a method for measuring the resistance value of the transfer belt will be described. FIG. 7 shows a configuration around the transfer belt 8, the transfer roller 10a, the drive roller 10b, and the intermediate transfer drum 7 in this embodiment.

When the transfer belt 8 is separated from the intermediate transfer drum 7, the transfer roller 10a and the drive roller 10b
Supported only by. Therefore, the transfer roller 10
If a bias is applied between the roller a and the drive roller 10b and the voltage between the rollers and the current flowing between the rollers can be known, the resistance value of the transfer belt 8 can be measured. FIG. 8 shows a conceptual diagram of the transfer belt measurement. In this measurement, the transfer belt 8 and the transfer roller 10a are moved by the driving roller 10b at the process speed (1
17 mm / s).

When +100 V is applied to the transfer roller 10 a by the secondary transfer belt power supply 11, the current flowing through the “transfer roller → transfer belt → drive roller” circuit is measured by the current measuring device 18.

Then, a correlation between the current measurement value I _measure [A] by the above-described transfer belt measurement method and the volume resistivity ρ _sub [Ω · cm] of the base layer of the transfer belt 8 could be obtained as shown in FIG. The base volume resistivity of the transfer belt can be known from the correlation between the measured current value I _measure and the base volume resistivity ρ _sub of the transfer belt.

Next, as shown in the graph of FIG. 10, the volume resistivity of the transfer belt base layer and the secondary transfer bias [k
V], the “penetration” in a low-temperature and low-humidity environment (hereinafter referred to as “LL environment”, which is 15 ° C. and 10% RH).
When the secondary transfer bias [kV] at which an image defect starts to occur and the amount of applied toner on the intermediate transfer drum is 1.3 mg / cm ² , the secondary transfer efficiency is 85%.
Focusing on the secondary transfer bias described above, it was obtained.

Here, an image defect called "penetration" is caused by
Discharge generated between the surface of the transfer material and the toner on the image carrier (the intermediate transfer drum in the present embodiment) on the upstream side of the transfer nip reverses the charge inherent in the toner (minus in the present embodiment). This is an image defect that is caused by the fact that the toner to be originally transferred is not transferred onto the transfer material by being charged to the polarity (positive in this embodiment).

The above-mentioned secondary transfer efficiency η is obtained from the weight of the toner W _paper on the intermediate transfer drum before the secondary transfer and the weight of the toner W _ITM on the transfer material after the secondary transfer, as follows: η [%] = W _ITM [Mg / cm ² ] / W _paper [mg / cm ²
cm ² ] × 100.

The evaluation of the “penetration” and the transfer efficiency was made according to Can.
On-CLC paper (weighing 80 g / cm ² ) was used as LL environment-leaved paper.

In other words, the secondary transfer bias is set to a bias at which the secondary transfer efficiency is as high as possible (85% or more in this case) without "penetration".

Accordingly, FIG. 9 is a graph showing the volume resistivity of the transfer belt base layer of FIG. 10, the secondary transfer bias at which “penetration” starts to occur, and the secondary transfer bias at which the secondary transfer efficiency becomes 85% or more. The correlation between the measured current value [A] and the optimum secondary transfer bias [kV] with respect to the volume resistivity of the transfer belt base layer shown in FIG. 11 can be obtained as shown in the graph of FIG.

However, from FIG. 10, when the volume resistivity of the base layer of the transfer belt is 1 × 10 ⁹ [Ω · cm] or more, the transfer belt having no “penetration” and the transfer belt providing the maximum transfer efficiency coincide with each other. It can be seen that there is no area.

By performing the secondary transfer bias control according to FIG. 11, the base layer volume resistivity of the transfer belt becomes 1 × 10
When it is less than ⁹ [Ω · cm], image defects due to “penetration” can be prevented.

That is, in this embodiment, first, the correlation between the measured current value between the transfer roller and the drive roller and the volume resistivity of the transfer belt base layer is obtained, and then the volume resistance of the transfer belt base layer is obtained. The correlation between the rate and the secondary transfer bias is
The examination was performed in relation to the secondary transfer bias at which “penetration” occurs in the LL environment and the secondary transfer bias at which the secondary transfer efficiency becomes 85% or more. Next, the correlation between the volume resistivity of the transfer belt base layer and the secondary transfer bias was expressed as the correlation between the measured current value between the transfer roller and the drive roller and the secondary transfer bias.

Therefore, by measuring the current between the transfer roller and the drive roller and setting the secondary transfer bias based on the measured current value, the volume resistivity of the base layer of the transfer belt is 1 × 10 ⁹ [Ω · cm]. ], The secondary transfer bias control could be performed with a high secondary transfer efficiency of 85% or more while preventing the occurrence of “penetration” in the LL environment.

Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIG.

In the first embodiment, the secondary transfer bias is controlled by measuring the current value between the transfer roller and the drive roller and knowing the volume resistivity of the transfer belt base layer, thereby obtaining high transfer efficiency. In addition, image defects due to "penetration" were prevented. However, when the volume resistivity of the transfer belt base layer is 1 × 10 ⁹ Ω · cm or more, there is no transfer bias that simultaneously satisfies high transfer efficiency and prevention of “penetration”. Further, the transfer belt used in the first embodiment has a property that the volume resistivity of the base layer is increased by performing the paper passing durability.

FIG. 12 shows the relationship between the number of sheets passed and the volume resistivity of the base layer of the transfer belt.

According to the graph of FIG. 12, since the volume resistivity of the transfer belt base layer increases by about one digit per 100,000 pages of the paper passage durability, the volume resistivity of the transfer belt base layer increases due to the paper passage durability. If it is 1 × 10 ⁹ [Ω · cm] or more, it is impossible to suppress image defects even if the transfer bias control as in the first embodiment is performed.

Therefore, in this embodiment, the point in time when the base layer volume resistivity of the transfer belt is detected to be 1 × 10 ⁹ [Ω · cm] or more is determined as the life of the transfer belt, and the user is asked to exchange the transfer belt. The notification prevents the occurrence of an image defect.

In the above embodiment, the case where the present invention is applied to an image forming apparatus having an intermediate transfer member has been described. However, as described above, the present invention can also be applied to a multi-developing type color image forming apparatus. In this case, the image carrier is a photosensitive drum.

Further, in the above-described embodiment, the intermediate transfer member as the image carrier is described as the intermediate transfer drum. However, an intermediate transfer belt may be used.

[0070]

As is apparent from the above description, according to the image forming apparatus of the present invention, the transfer means includes a transfer belt and a plurality of rollers wound around the transfer belt. By having a detecting means for detecting a bias current or a voltage applied to the roller from a bias power supply, which is disposed so as to be able to abut and separate from the carrier,
An image defect due to a change in resistance value due to a change in the environment of the transfer belt can be prevented, and a good image can be obtained.

Further, when the volume resistivity of the base layer of the transfer belt becomes 1 × 10 ⁹ [Ω · cm] or more due to long-term use, it is recommended that a user replace the transfer belt with a defective image. Can be prevented from occurring.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic configuration diagram illustrating an intermediate transfer drum of the first embodiment.

FIG. 3 is a schematic sectional view showing a resistance measuring device of the intermediate transfer drum.

FIG. 4 is a schematic sectional view showing a transfer belt of the first embodiment.

FIG. 5 is a schematic sectional view showing a transfer roller of the first embodiment.

FIG. 6 is a schematic sectional view showing a drive roller of the first embodiment.

FIG. 7 is a schematic configuration diagram illustrating a periphery of a transfer belt, a transfer roller, a drive roller, and an intermediate transfer drum.

FIG. 8 is an explanatory diagram showing a method for measuring the resistance of the transfer belt.

FIG. 9 is a graph showing a correlation between a current measured value by transfer belt resistivity measurement and a transfer belt base layer volume resistivity in the first embodiment.

FIG. 10 is a graph showing the dependence of image defects and transfer efficiency on the volume resistivity of a transfer belt base layer in an LL environment.

FIG. 11 is a graph showing a correlation between a current measured value by transfer belt resistivity measurement and an optimal secondary transfer belt in the first embodiment.

FIG. 12 is a graph showing the dependency of the volume resistivity of the transfer belt base layer on the number of sheets passed through in the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 5 transfer device 7 intermediate transfer drum (image carrier) 8 transfer belt 10a transfer roller 10b drive roller 11 secondary transfer bias power supply

Claims (4)

[Claims] 1. An image forming apparatus comprising: an image carrier that carries a toner image; a transfer unit that transfers the toner image to a transfer material; and a bias power supply that applies a bias to the transfer unit. Has a transfer belt and a plurality of rollers around which the transfer belt is wound, the transfer belt is disposed so as to be able to contact and separate from the image carrier, and a bias applied to the roller from the bias power supply. An image forming apparatus comprising a detecting unit for detecting a current or a voltage of the image forming apparatus. 2. The transfer belt is formed in a multilayer structure.
The image forming apparatus according to claim 1, further comprising: a base layer containing at least a thermosetting urethane elastomer; and a surface layer containing a fluorine-modified resin on the surface of the base layer. 3. The volume resistivity of the base layer is 1 × 10 ⁹ [Ω].
.Cm]. 4. When the volume resistivity of the base layer becomes 1 × 10 ⁹ Ω · cm or more due to long-term use, the user is recommended to replace the transfer belt. Or the image forming apparatus of 3.