JP2003241478A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if a test pattern for density control is formed in a non-image area on an intermediate transfer body during image formation, secondary transfer can be performed without causing back contamination of the transfer material. To provide an image forming apparatus capable of performing the above. An image carrier, an electrostatic latent image device, a developing device for a plurality of colors, an intermediate transfer member, a primary transfer device, a current detection device, a cleaning member, a density detection device, and a secondary transfer device. Means for primary transferring electrostatically the toner image on the image bearing member onto the intermediate transfer member, and performing the primary transfer on the intermediate transfer member by at least two colors or more. In the image forming apparatus for forming a color toner image on the intermediate transfer member by repeating the process for the toner image, and secondary-transferring the color toner image collectively to the transfer material, the density detecting means A bias applied to the primary transfer unit when the test pattern whose density has been detected passes through the primary transfer portion is controlled based on a detection result of the current detection unit.

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 utilizing electrophotography. Specifically, a plurality of developing devices are arranged around the photosensitive drum, and after the toner images formed on the photosensitive drum are overlaid on the intermediate transfer member in respective colors,
The present invention relates to an image forming apparatus that transfers images to a transfer material all at once and forms a test pattern for image stability control on a non-image portion on an intermediate transfer member.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic color image forming apparatus, in addition to a first image carrier such as a photosensitive drum,
A device having a second image carrier such as an intermediate transfer member is known. These perform so-called primary transfer in which the toner image formed on the first image carrier is transferred onto the second image carrier, and the process of the primary transfer is repeated a plurality of times to obtain the second image carrier. After superimposing the toner images of plural colors on the upper surface, the toner images of the plural colors are collectively secondarily transferred onto a transfer material such as paper being conveyed, and the toner images are melted and added to the transfer material by a fixing device. It is fixed by pressure.

FIG. 6 shows an example of an image forming apparatus having the above-mentioned structure using an intermediate transfer belt (intermediate transfer member) as a second image carrier.

The photosensitive drum 3 rotating in the direction of arrow A is uniformly charged by the charger 5, and the laser beam 6 forms an electrostatic latent image.

Around the photosensitive drum 3, Y, M, C
The three developing devices 1-1, 1-2, 1-3 containing the three color toners and the developing device 1-4 containing the Bk toner are arranged. These developing units 1-
One of 1, 1-2 and 1-3 is selected to be close to the photosensitive drum 3 by the exchanging means 4, and the developing unit 1-4 is always close to each other. Is used for developing an electrostatic latent image on the photosensitive drum 3 to form a toner image on the photosensitive drum 3.

Next, when a bias is applied to the primary transfer roller 8, a charge having a polarity opposite to that of the toner is applied to the back surface of the intermediate transfer belt 7, and the toner image developed on the photosensitive drum 3 is primary. Primary transfer is performed on the intermediate transfer belt 7 via the transfer nip portion 9. The primary transfer residual toner remaining on the surface of the photosensitive drum 3 after the primary transfer is removed and collected by the cleaning member 13, and the residual charge is removed by the exposure 14, and the process of forming an image of the next color is started.

By repeating this primary transfer process for the toner images of four colors, a full-color toner image of four colors is formed on the intermediate transfer belt 7. Then
The secondary transfer outer roller 10a, the intermediate transfer belt 5, and the secondary transfer outer roller 10b formed between the secondary transfer portion 11 sandwiched and conveyed on the back surface of the transfer material 12 are biased to the secondary transfer outer surface. A charge having a polarity opposite to that of the toner is applied from the roller 10b to collectively transfer the full-color toner images.
Secondary transfer to 2. The full-color toner image is fixed by a fixing device (not shown) to obtain an image on the transfer material 12. The secondary transfer residual toner remaining on the intermediate transfer belt 7 after the above-mentioned secondary transfer is removed by a cleaning member (not shown).

As the primary transfer roller and the secondary transfer roller, it is common to use rollers having a resistance of 10 + 10 Ω · cm or less.

The intermediate transfer belt 7 may be, for example, an endless resin belt having a thickness of about 50 to 300 μm, the resistance of which is adjusted to a volume resistivity of about 1011 to 10 + 16 Ω · cm. For example, as the material of the resin belt, a resin film such as PVdF (polyvinylidene fluoride), nylon, PET (polyethylene terephthalate), or polycarbonate can be used.
To adjust the resistance, use carbon, ZnO, Sn on the resin belt.
The volume resistivity can be adjusted to about 10 + 8 to 10 + 12 Ω · cm by using O 2, TiO 2, and other conductive fillers. By achieving low to medium resistance in this way,
Image defects due to the accumulation of charges on the intermediate transfer belt 7 can be prevented, and the neutralization mechanism can be omitted.

Further, as another example, as the material of the intermediate transfer belt 7, a rubber material (chloroprene rubber, EPDM, NBR, urethane rubber, etc.) having a lower hardness than the resin and a thickness of about 0.5 to 2 mm is used. Resistivity 10 + 11 to 10 + 16
It can also be adjusted to about Ω · cm before use.

Generally, in an image forming apparatus, if the density of a formed image changes due to changes in various conditions such as the use environment and the number of prints, the original correct color tone cannot be obtained.

Therefore, in the conventional image forming apparatus,
In order to detect the current image formation status, it is considered that the color tone of the toner image on the intermediate transfer body is close to that of the actual toner image on the transfer material, and the image of the non-image area on the intermediate transfer body is being formed. A test pattern for density detection is formed between the two, etc., and the density is automatically detected by the density detecting means, and the density of the test patterns Y, M, C is detected by the density detecting means 15 of FIG. By feeding back the result to the image forming conditions such as exposure amount and developing bias, the density is controlled to form a color image with the original density.
I was getting a stable image. Incidentally, there are many intermediate transfer bodies in which the resistance of a resin such as polyimide or polycarbonate is adjusted with carbon, and therefore the intermediate transfer body 7 is black,
Bk density detection is often performed on the photosensitive drum.

The space between the images of the non-image portion on the intermediate transfer member during the above-mentioned image formation will be described below.

For example, in the case of forming two toner images (α) and (β) on the intermediate transfer belt 7, first, a monochromatic Y toner image is developed by the developing device 1-1 which is selectively close to the photoconductor 3. (ΑY) and (βY) are developed, and then primary-transferred onto the intermediate transfer belt 7 as shown in FIG. 7A, and the developing device selectively adjacent to the photoconductor 3 is replaced with the developing device 1-1. A monochromatic M toner image (αM) (βM) is developed on the photoconductor 3 by the developing device 1-2, and then primary-transferred in sequence onto the toner image (αY) (βY) on the intermediate transfer belt 7. Then, as shown in FIG. 7B, the toner image (αYM) is formed on the intermediate transfer member.
(.Beta.YM) is formed, and then the developing device 1-3 in which the developing device selectively adjacent to the photoconductor 3 is replaced with the developing device 1-2. 3 is developed, and then primary-transferred on the toner images (αYM) and (βYM) on the intermediate transfer belt 7 in sequence.
As shown in FIG. 7C, the toner image (αYM
C) (βYMC) is formed, and the toner image (αk) (β) of the single color k is formed by the developing device 1-4 that is always close to the photosensitive drum.
k) is developed in this order on the photoconductor 3 and then primary-transferred sequentially on the toner images (αYMC) (βYMC) on the intermediate transfer belt 7 to form a toner image (αYMC) on the intermediate transfer body.
MCk) (βYMCk) is formed, and the toner image (αYMCk) (βYMCk) on the intermediate transfer belt 7 formed by the repeated primary transfer process is secondarily transferred to the transfer material 12.

Between the images of the non-image portion on the intermediate transfer member during the image formation described above is (αY) (βY) in FIG. 7A.
7 (b), (βYM) (αYM), and FIG. 7 (c) (αYMC) (βYMC).

However, when the test pattern is present between the images of the non-image portion on the intermediate transfer member, as shown in FIG.
There is a problem that a toner image patch is electrostatically attached to the secondary transfer outer roller 10b to which a bias having a polarity opposite to that of the toner is applied, and the back of the transfer material 12-β is stained with a test pattern.

In the above conventional example, when the toner image patch reaches the secondary transfer portion as shown in FIG. 9, the secondary transfer outer roller 1 is used.
0b avoids the test pattern and restarts the secondary transfer of the toner image (βYMCk) when the transfer material 12-β reaches the secondary transfer site. 10b is detached.

[0018]

However, the toner image (αYMCk) (βYMC
The distance between the images of k) is narrow, and the moving speed of the intermediate transfer member 7 is high, which causes the following problems.

When the above-mentioned test pattern is avoided by failing to secure a sufficient timing for attaching and detaching the secondary transfer outer roller, the outer transfer roller 10b quickly "dismounts" from the intermediate transfer belt 7 or slowly. On the intermediate transfer belt 7 "
Toner image on the transfer material 12-α (αYM
Toner image (βYMC) on the trailing edge of Ck or on the transfer material 12-β
k) causes the secondary transfer failure at the tip of the toner image (αYM
If Ck) (βYMCk) is prevented from causing a secondary transfer failure, the test pattern may be delayed due to the "delay" timing being delayed or the "wearing" timing being early.
However, there is a problem that the back surface of the transfer material 12-β is soiled with a test pattern.

The present invention has been made in view of the above problems, and an object thereof is to achieve a transfer material even if a test pattern for density control is formed in a non-image area on an intermediate transfer member during image formation. An object of the present invention is to provide an image forming apparatus that can perform secondary transfer without causing back stains.

[0021]

To achieve the above object, the present invention provides an image carrier, an electrostatic latent image means for forming an electrostatic latent image on the image carrier, and an electrostatic latent image. Developing means for developing a plurality of colors to form a toner image, an intermediate transfer body, a primary transfer means arranged to face the image carrier through the intermediate transfer body, and a primary transfer means. Current detecting means for detecting a flowing current, a cleaning member for cleaning the image carrier, density detecting means for detecting the density of a test pattern formed in a non-image area on the intermediate transfer body, and the intermediate transfer body And a secondary transfer unit that sandwiches and conveys the transfer material, and the primary transfer unit applies a bias to the toner to transfer electric charges having a polarity opposite to that of the toner to the intermediate portion of the primary transfer portion. The toner image on the image carrier is applied to the back surface of the transfer member to transfer the intermediate image. The color toner image is formed on the intermediate transfer member by repeating the step of performing the primary transfer electrostatically on the body and the primary transfer to the intermediate transfer member for at least two or more color toner images. In the image forming apparatus, the secondary transfer means applies a charge having a polarity opposite to that of the toner to the back surface of the transfer material to electrostatically collectively secondary transfer the color toner images onto the transfer material. The bias applied to the primary transfer means when the test pattern whose density has been detected in step 4 passes through the primary transfer portion is controlled based on the detection result of the current detection means.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 3 is a sectional view of an image forming apparatus according to the present invention.

The photosensitive drum 3 which rotates in the direction of arrow A is an amorphous silicon type photosensitive member having a positive charging characteristic, which is uniformly charged to +300 to +700 V by the charger 5 and an electrostatic latent image is formed by the laser beam 6. To be done.

Around the photosensitive drum 3, Y, M, C
3 developing devices 1-1, 1-2, 1-3 containing the negatively charged toners of each of the three colors and a developing device 1 containing the negatively charged Bk toners 1- 4 are arranged.

One of the developing devices 1-1, 1-2, and 1-3 is selected to be close to the photosensitive drum 3 by the exchange means 4, and the developing devices 1-4 are always close to each other. One of the two developing devices that are close to each other is used for developing the electrostatic latent image on the photosensitive drum 3, and forms a toner image on the photosensitive drum 3.

Next, by applying a bias to the primary transfer roller 8, a charge having a polarity opposite to that of the toner is applied to the back surface of the intermediate transfer belt 7, and the toner image developed on the photosensitive drum 3 is a primary image. Primary transfer is performed on the intermediate transfer belt 7 via the transfer nip portion 9. The primary transfer residual toner remaining on the surface of the photosensitive drum 3 after the primary transfer is removed and collected by the cleaning member 13, and the residual charge is removed by the exposure 14, and the process of forming an image of the next color is started. The primary transfer bias is controlled by detecting the current during the pre-rotation before image formation so that the primary transfer current value during the primary transfer is always the same.

By repeating this primary transfer process for the toner images of four colors, a full-color toner image of four colors is formed on the intermediate transfer belt 7. Then
The secondary transfer outer roller 10a, the intermediate transfer belt 5, and the secondary transfer outer roller 10b formed between the secondary transfer portion 11 sandwiched and conveyed on the back surface of the transfer material 12 are biased to the secondary transfer outer surface. A charge having a polarity opposite to that of the toner is applied from the roller 10b to collectively transfer the full-color toner images.
Secondary transfer to 2. The full-color toner image is fixed by a fixing device (not shown) to obtain an image on the transfer material 12. The secondary transfer residual toner remaining on the intermediate transfer belt 7 after the above-mentioned secondary transfer is removed by a cleaning member (not shown).

As the primary transfer roller and the secondary transfer roller, rollers having a resistance of 10 + 10 Ω · cm or less were used.

The intermediate transfer belt 7 is, for example, an endless PI (polyimide) resin belt having a thickness of about 75 μm, which is made of carbon and has a volume resistivity of 10 + 8 to 10 + 9 Ω · c.
The resistance adjusted to about m was used.

In the present embodiment, in order to detect the current image forming state, it is considered that the color tone of the toner image on the intermediate transfer member is close to the actual color tone of the toner image on the transfer material, and the intermediate color image during image formation is formed. A test pattern for density detection is formed between the images of the non-image areas on the transfer body, and the density is automatically detected by the density detection means, and the density detection means 15 of FIG.
By detecting the densities of the test patterns Y, M, and C and feeding back the detection results to the image forming conditions such as the exposure amount and the developing bias (hereinafter referred to as patch detection), a color image with the original density is formed. The concentration was controlled accordingly. Since the intermediate transfer belt 7 whose resistance has been adjusted with carbon is black, the Bk density was detected on the photosensitive drum.

In the present embodiment, patch detection is performed based on the image information of each color. That is, the image ratio of each color is obtained from the image information, the consumption amount of each color toner is calculated from the image ratio, and the test pattern is formed in order from the toner whose consumption reaches a certain threshold, and patch detection is performed. However, in the present embodiment, when one of the Y, M, and C test patterns is formed, the test patterns of other colors are not formed.

When a Y test pattern (hereinafter referred to as a Y patch) is formed as shown in FIG. 7A, the Y patch passes through the primary transfer site three times until the primary transfer of Bk. During the passage, the primary transfer bias determined by calculation from the current at the time of transferring the normal toner image is applied. When an M test pattern (hereinafter referred to as an M patch) is formed as shown in FIG. 7B, the M patch again passes through the primary transfer site twice, and as shown in FIG. After that, when a C patch) is formed, the C patch once again passes through the primary transcription site once. The primary transfer bias while these primary transfer sites of the test pattern are passing again is controlled and applied as in the case of the Y patch.

The method of setting the bias when the primary transfer portion of the patch passes again will be described below.

First, the photosensitive drum 3 is uniformly charged to +700 V by the uniform charger 5, a patch is formed on the drum by the laser beam 6, and then primary transfer is performed to form a unit area on the intermediate transfer belt 7. Weight per unit is 0.3 mg /
A test pattern of 30 mm × 30 mm in cm 2 is formed. In that state, the light is passed through the primary transfer site to which a bias is applied, and the patch density on the intermediate transfer body after the passage is measured. Then, as shown in FIG. 1, a bias Vtr1 (primary transfer current I
When tr1) is decreased, the patch density after passing through the primary transcription site decreases, and the density becomes almost zero at the V1 primary transcription bias. This state indicates that the patch toner has been retransferred onto the photosensitive drum at the primary transfer portion.

Next, the surface potential of the photosensitive drum 3 is 0 and +7.
FIG. 2 shows the relationship between the primary transfer bias and the primary transfer current when the voltage is 00V. From FIG. 2, the above-mentioned current value when V1 is T1, V0 when the surface potential of the photosensitive drum 3 is 0 and the transfer current I1 and V2 when Vtr1 are obtained.

In the present embodiment, the primary transfer current is detected by the current detecting means and the primary transfer bias is controlled so as to reach Itr1 in FIG. Vtr11 is obtained as the primary transfer bias at that time.

Then, the bias applied to the primary transfer means when the patch of the non-image portion on the intermediate transfer belt 7 passes through the primary transfer portion again, Vtr11− (Vtr11−V0) × (Vtr−Vtr11 ) / (Vtr
1-V2) to calculate and control.

<Second Embodiment> FIG. 5 is a sectional view of an image forming apparatus according to a second embodiment of the present invention. Embodiment 1
The difference from the configuration of is that the developing device 1-
That is, the surface potential detecting means for detecting the surface potential of the non-image portion of the photosensitive drum is added upstream of the primary transfer roller 8 on the downstream side of 1 to 1-3.

The method of setting the bias when the patch again passes through the primary transfer site will be described below.

First, a 30 mm × 30 mm toner patch image having a weight per unit area of 0.3 mg / cm 2 is formed on the intermediate transfer member, and in that state, a toner image is passed through a primary transfer portion to which a bias is applied. The patch density of the toner image on the intermediate transfer body after the passage is measured. Then, as shown in FIG. 4, when the toner image on the normal photosensitive drum is lowered from the bias Vtr1 for primary transfer, the patch density after passing through the primary transfer portion decreases, and the surface potential V0 of the photosensitive drum or less is reduced. The density becomes almost zero at the primary transfer bias of V1 to V2. This state indicates that the toner patch image has been retransferred to the photosensitive drum at the primary transfer portion.

Next, Va = V0-V1, Vb = V0-V
Calculate 2 to obtain.

Therefore, when the patch of the non-image portion on the intermediate transfer belt 7 passes through the primary transfer portion again, the bias applied to the primary transfer means is changed from Vtr1 to Vret (V
Control is performed so that a <Vret <Vb).

[0044]

As is apparent from the above description, according to the present invention, cleaning is performed by attaching the toner patch image in the non-image area to the image carrier at the primary transfer portion and cleaning the image carrier. Since the material is collected by the member, it is possible to obtain an effect that the secondary transfer outer roller and the back of the transfer material are not contaminated, and a color image having an original density can be stably formed, and the secondary transfer can be favorably performed.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the first embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining the second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 7 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 8 is a diagram for explaining a situation of a conventional example.

FIG. 9 is a diagram for explaining a situation of a conventional example.

[Explanation of symbols]

1-1 to 1-4 developing device 3 photosensitive drum 4 exchange means 7 Intermediate transfer belt 8 Primary transfer roller 10a Secondary transfer inner roller 10b Secondary transfer outer roller 11 Secondary transcription site 12 Transfer material 13 Cleaning member

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Claims (5)

[Claims] 1. An image carrier, an electrostatic latent image means for forming an electrostatic latent image on the image carrier, and a plurality of color developing means for developing the electrostatic latent image to form a toner image. An intermediate transfer member, a primary transfer unit arranged to face the image carrier via the intermediate transfer member, a current detection unit for detecting a current flowing through the primary transfer unit, and the image carrier. A cleaning member for cleaning, a density detection unit for detecting the density of a test pattern formed in a non-image area on the intermediate transfer member, and a transfer member, which is arranged so as to face the intermediate transfer member and holds the transfer material therebetween. A secondary transfer unit is provided, and by applying a bias to the primary transfer unit, a charge having a polarity opposite to that of the toner is applied to the back surface of the intermediate transfer member at the primary transfer portion to apply the toner on the image carrier. The image is electrostatically primary-transferred onto the intermediate transfer member, and then primary-transferred onto the intermediate transfer member. By repeating this step for at least two or more color toner images, a color toner image is formed on the intermediate transfer member, and the secondary transfer means applies a charge having a polarity opposite to that of the toner to the back surface of the transfer material. In the image forming apparatus that secondarily transfers the color toner images to the transfer material electrostatically all at once by the method, when the test pattern whose density is detected by the density detecting means passes through the primary transfer portion, An image forming apparatus, wherein the bias applied to the primary transfer means is controlled based on the detection result of the current detection means. 2. The image forming apparatus according to claim 1, wherein a bias for primary transfer of the toner image is controlled based on a detection result of the current detecting unit. 3. A bias applied to the primary transfer means when the test pattern whose density has been detected by the density detection means passes through the primary transfer portion, based on the detection result of the current detection means. The image forming apparatus according to claim 1 or 2, further comprising an arithmetic unit that determines by the above. 4. An image carrier, an electrostatic latent image means for forming an electrostatic latent image on the image carrier, and a plurality of color developing means for developing the electrostatic latent image to form a toner image. An intermediate transfer member, a primary transfer unit arranged to face the image carrier via the intermediate transfer member, and a downstream unit of the developing device and an upstream unit of the primary transfer unit in a rotation direction of the image carrier. A potential detecting means for detecting the surface potential of the image carrier, a cleaning member for cleaning the image carrier, and a density detector for detecting the density of the test pattern formed in the non-image area on the intermediate transfer member. And a secondary transfer unit that is disposed so as to face the intermediate transfer member and that nips and conveys a transfer material. The primary transfer unit applies a bias to generate an electric charge having a polarity opposite to that of the toner. By applying to the back surface of the intermediate transfer body at the primary transfer site, The toner image is electrostatically primary-transferred onto the intermediate transfer member, and the step of primary-transferring onto the intermediate transfer member is repeated for toner images of at least two colors to obtain a color toner on the intermediate transfer member. Forming an image,
In the image forming apparatus, in which the color toner images are secondarily transferred to the transfer material electrostatically collectively by applying a charge having a polarity opposite to that of the toner to the back surface of the transfer material by the next transfer means, An image forming apparatus, wherein a bias applied to the primary transfer means when the density-detected test pattern passes through the primary transfer portion is controlled based on a detection result of the potential detection means. 5. The bias applied to the primary transfer means when the test pattern whose density is detected by the density detection means passes through the primary transfer portion is calculated based on the detection result of the potential detection means. The image forming apparatus according to claim 4, further comprising an arithmetic unit that determines the image.