JPH04256978A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a high-quality color image which is color-balanced by eliminating transfer memory caused by impressing transfer bias in the case of attraction, which is generated much on a transfer body in which a fixed drum is used, and restraining the unevenness of transfer efficiency, which occurs when the transfer memory is eliminated. CONSTITUTION:The voltage of transfer or attraction bias is controlled so that the surface potential of a transfer material 1 at the time when the transfer material 1 is carried to an image transfer part may be always at a constant value while the rotation for a 1st color is performed at a part attracted only by the attraction bias of the transfer material 1 carried to an image transfer part, that is, the part A of the transfer material 1 which is from the leading edge of the transfer material 1 to l, obtained by setting the peripheral length on a transfer body 3 from an attracting roller 15 to the image transfer part as l, along the carrying direction, and a part attracted by the attraction bias and the transfer bias, that is, a part B which is from the peripheral length lto the trailing edge of the transfer material.

Description

[Detailed description of the invention]

The present invention transfers a visible image formed on an image carrier by an electrophotographic process or an electrostatic recording process multiple times to a transfer material supported on a movable transfer material carrier, thereby producing a color image. The present invention relates to a color image forming apparatus.

0001

2. Description of the Related Art Conventionally, as such a color image forming apparatus, an electrophotographic color image forming apparatus as shown in FIG. 6, for example, has been widely used. A brief explanation will be given below.

In the electrophotographic color image forming apparatus of this example,
The photosensitive drum 4 as an image carrier is uniformly charged by a primary charger 14 such as a roller or a corona charger. Next, exposure 1 is performed based on an image signal of the first color from an exposure device comprising a light emitting element 13 such as a laser or an LED.
The first color electrostatic latent image formed on the image carrier by step 6 is
For example, the image is visualized using a developing device 2a containing a yellow (Y) developer.

On the other hand, as can be understood by referring to FIG. 7(A), the outer periphery of the drum frame (housing) 3a is composed of cylindrical members arranged at both ends and a connecting member that connects the two cylindrical members. A transfer material carrier made of a flexible sheet of dielectric material such as polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), fluorinated ethylene propylene copolymer (FEP), etc. is placed in the surface notch. For example, the drum-shaped transfer body 3 configured by stretching the transfer material 1 holds the tip of the supplied transfer material 1 with a gripper 3c or the like as a transfer material holding means, and then rotates to remove the transferred material. Wrap material 1 around the surface of the transfer body. At this time, the transfer material 1 is sandwiched between an adsorption member 15 such as a grounded adsorption roller and a flexible sheet 3b forming the surface of the transfer member, and at the same time, the adsorption charger 7 charges the flexible sheet 3b. It is held on the surface of the transfer body 3 by electrostatic adsorption force due to charges applied to the back surface. Subsequently, the transfer material 1 is conveyed to an image transfer area located at a position facing the photosensitive drum 4 by the rotation of the transfer body 3, and the visible image formed on the photosensitive drum 4 is transferred by a transfer charger 8. .

Thereafter, the residual developer remaining on the photosensitive drum 4 is removed by the cleaner 5, and the photosensitive drum 4 is uniformly charged again by the primary charger 14. An electrostatic latent image is formed based on a color image signal. This electrostatic latent image is generated by a developing device 2b containing, for example, magenta (M) developer corresponding to the second color image signal.
The image is developed into a visible image.

This second color visible image is transferred again by the transfer charger 8 to the transfer material 1 on the transfer body 3 onto which the first color visible image was previously transferred. The above process is carried out using a developer such as cyan (C) as the third color and black (BK) as the fourth color to form visible images of the third and fourth colors on the photosensitive drum 4, and The image is superimposed and transferred onto the transfer material 1 on the transfer body 3 in the same manner as the visible image.

The transfer material 1 onto which the visible images of each color have been transferred as described above is conveyed by the rotation of the transfer body 3 to the separation charger 9 disposed opposite to the inside and outside of the transfer body 3.
The electrostatic attraction force between the transfer material 1 and the flexible sheet 3b is removed by the separation charger 9, and the transfer material 3 is separated by the separation claw 11 while being neutralized by the separation charger 10. The separated transfer material 1 is guided to a fixing device 6 by a transfer material conveyance path, and is fixed by the fixing device 6.

After the transfer material 1 has been separated, the transfer material 3 is cleaned by a transfer material cleaner (not shown) to remove the developer adhering to the flexible sheet 3b that forms its surface, and then is placed facing the flexible sheet 3b with the sheet 3 in between. A set of sheet static eliminator chargers 12 provided at the same time removes static electricity and initializes the sheet electrically.

[0008] Above, we have described an embodiment in which a drum-shaped transfer body with a cutout structure is used as a transfer body used when forming a color image by a multiple transfer method.
), the method of applying a bias to the transfer body 3, which has a structure in which a conductive drum housing 3a without notches is covered with a flexible sheet 3b as described above, can also produce the same effect as the above-mentioned notch structure transfer drum. Multiple transfers can be performed. This type of transfer body 3 has a simpler interior than the above-mentioned notch structure transfer body 3, which reduces costs, and since the flexible sheet 3b is supported from the inside by the entire drum, the notch structure This has the advantage that deformation and damage to the sheet, which are problems with structural transfer bodies, can be reduced. Therefore, color image forming apparatuses using conductive drums (hereinafter referred to as "solid drums") that do not have the above-mentioned notches are currently attracting attention.

The image forming method of the color image forming apparatus using the solid drum as the transfer member 3 is very similar to the color image forming apparatus using the above-mentioned notched drum. Image formation by the color image forming apparatus will be described below with reference to FIG. Detailed explanations will be omitted by using the same names and symbols for the items.

First, the transfer material 1 supplied from the transfer material conveyance path is sandwiched between the transfer member 3 and the adsorption roller 15 by the adsorption roller 15 that approaches and separates from the transfer member 3 . At the same time, a DC voltage is applied to the drum casing 3a as an attraction and first color transfer bias, and the electric charge induced from the attraction roller 15 thereby holds the transfer material 1 on the transfer body 3 by electrostatic attraction. The amount of charge injected into the transfer material 1 at this time is smaller than the amount of charge when the capacitances of the transfer material 1 and the flexible sheet 3b are sufficiently charged with the same bias. This is because when the charge is injected into the transfer material 1 by the suction roller 15, the transfer body 3 carrying the transfer material 1 is rotating, so the contact time with the suction roller 15 that injects the charge is short, and the charge is injected. This is because it is insufficient. Therefore, due to incomplete charge injection, the transfer material 1 that has passed through the suction roller 15
Since the surface potential of indicates the polarity of the bias applied to the transfer body 3, the polarity of the bias applied to the transfer body 3 is determined by the polarity of the bias applied to the image carrier 4.
If the polarity of the visible image above is set to be easy to transfer, good transfer can be achieved by appropriately setting the size.

In this way, the transfer material 1 held on the transfer body 3 is conveyed to the image transfer section by the rotation of the transfer body 3, and the visible image of the first color formed on the image carrier 4 is transferred thereto. Ru. Next, when transferring the second color visible image, the above-mentioned bias value is changed to correct the surface potential that has dropped due to the transfer material 1 on the transfer body 3 transferring the first color visible image. Such correction is similarly performed when transferring the third and fourth colors, and the visible image formed on the image carrier 4 is superimposed and transferred onto the transfer material 1 on the transfer body 3.

After the transfer process has been completed, the transfer material 1 is neutralized by the separation charger 9, thereby removing the electrostatic adhesion force between it and the transfer body 3, and the transfer material 1 is separated and neutralized by the transfer body 3 carrying it. The charger 10 separates the parts while suppressing peeling discharge. The visible image formed on the transfer material 1 is then fixed by a fixing device 6 to become a permanent image.

The transfer process in a color image forming apparatus using a solid drum has been described above, but the developing process in this color image forming apparatus is similar to that in the color image forming apparatus using a notched drum shown in FIG. It is the same as the process.

[0014]

In the color image forming apparatus as described above, the image carrier 4 is in contact with the transfer body 3 that holds and conveys the transfer material 1, or the image carrier 4 is in contact with the transfer material 3 that holds and conveys the transfer material 1.
They are arranged with a minute gap of about 50 to 300 μm in thickness between them. This is to ensure that the developer forming the visible image on the image carrier 4 is efficiently transferred to the transfer material 1, but when there is no developer on the image carrier 4, the image carrier When a potential difference of several hundred to several KV occurs between the surface of the image carrier 4 and the surface of the transfer body 3, electric discharge occurs because the distance between the surface of the image carrier 4 and the surface of the transfer body 3 is minute, and the image carrier 4
A phenomenon occurs in which charges of opposite polarity move onto the transfer body 3. This movement of charges often occurs particularly when a transfer bias is applied in a state where the transfer material 1 is not held on the transfer body 3. For example, in the reversal development method using negative toner, if the above situation occurs, the polarity of the transfer bias is positive, so a large amount of positive charge will move onto the image carrier 4. If the positive charge that has moved onto the image carrier 4 is a small amount, it is removed by the primary charger 14 located downstream of the transfer section of the image carrier 4 in the rotational direction. If it exceeds the limit, there is a limit to the mobility of the photosensitive layer forming the surface of the image carrier 4 with respect to positive charges, so that it becomes impossible to remove them even if the bias applied to the primary charger 14 is increased. The positive charge that cannot be removed by the primary charger 14 is
This disturbs the surface potential on the image carrier 4 after the primary charging, and appears in the image formed as a so-called transfer memory during the next image formation.

In particular, in the solid drum transfer body 3 described above, since the transfer material 1 is also electrostatically attracted by the transfer bias of the first color, the timing at which the transfer bias is applied is
In the case of a notched drum, this is when the leading edge of the transfer material 1 has been conveyed to the image transfer section, whereas in the case of a solid drum, the transfer body 3 and the suction roller 15 are located upstream of the image transfer section in the rotational direction of the transfer body 3. This is when the leading edge of the transfer material 1 is conveyed to the opposing transfer material 1 adsorption section. Therefore, unlike the transfer body 3 using a notched drum, the transfer body 3 which is a solid drum in which a transfer bias is applied to the entire surface of the transfer body 3 corresponds to the portion of the transfer body 3 indicated by Ltr in FIG. At the Lpho portion on the image carrier 4, a potential difference of several KV occurs between the surfaces of the image carrier 4 and the transfer member 3, which has the disadvantage that transfer memory as described above is likely to occur.

In order to solve the above problem, as shown in FIG. 9, instead of grounding the suction roller 15, a suction bias power supply 18 for suctioning the transfer material 1 is provided separately from the transfer bias power supply 17. A method is used in which the transfer bias is applied to the suction roller 15 immediately before the leading edge of the transfer material 1 enters the image transfer section, similarly to the notched drum transfer body 3. However, although this solves the above-mentioned transfer memory problem, the surface potential of the transfer material 1 conveyed to the image transfer section differs greatly between the leading edge and the trailing edge of the transfer material 1, as shown in FIG. A new problem arises. This is because when suctioning the transfer material 1, the suction roller 1
This is due to the fact that the potential of the transfer member 3, which is the opposite pole of the transfer member 5, changes due to the application of a transfer bias during the adsorption process of the transfer material 1.

In the above method, the length LP of the transfer material 1 is the distance (l) between the transfer material adsorption section and the image transfer section on the circumferential surface of the transfer body.
Since the transfer material 1 is larger, at the time when the leading end of the transfer material 1 is conveyed to the image transfer section, the rear end of the transfer material 1 is still electrostatically attracted by the transfer material adsorption section. That is, at the time when the transfer bias is applied, the potential difference Vtr-abh between the output Vtr of the adsorption bias power supply 18 and the output Vabh of the transfer bias power supply 17 includes a potential fluctuation of the difference δVtr-abh before and after the application of the transfer bias. As a result, the amount of charge Q injected into the transfer material 1 changes between the leading edge and the trailing edge of the transferring material.

In general, the polarity of the adsorption bias is set so that the adsorption charge injected during the adsorption process is not canceled out by the charge (that is, the developer) injected each time an image is transferred. polarity. Therefore, when using a transfer and adsorption bias power supply circuit like the conventional example, the transfer material 1 after applying the transfer bias
The amount of charge Q2 injected to
-abh, the charge amount Q1 increases compared to the amount of charge Q1 injected during adsorption when no transfer bias is applied. That is, VA is the surface potential of a region A from the tip of the transfer material 1 to a length (1) along the transport direction, and similarly, VA is the surface potential of a region B downstream from the length (1) of the transfer material 1 in the transport direction. When the surface potential is VB, the difference in the amount of injected charge above is δ
A difference δVA-B occurs in the surface potential between the two by Q1-2. As a result, the surface potential of the transfer member 3 during the first color transfer is approximately several hundred to
A difference of several kilovolts is generated, and this difference in surface potential causes a large change in transfer efficiency between the leading and trailing ends of the transfer material 1. In particular, in color images, uniformity such as contrast is more likely to be a problem than in monochrome images, and the above-mentioned partial change in transfer efficiency becomes a major cause of disrupting color balance.

Therefore, an object of the present invention is to solve the transfer memory caused by the application of a transfer bias during adsorption, which often occurs in transfer bodies using solid drums, and to eliminate unevenness in transfer efficiency that occurs when solving this transfer memory. It is an object of the present invention to provide a color image forming apparatus which can obtain high quality color images with uniform color balance.

[0020]

Means for Solving the Problems The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention:
In a color image forming apparatus that forms a color image by transferring a visible image on an image carrier multiple times to a transfer material carried by a movable transfer member, a transfer bias power supply that supplies a transfer bias to the transfer member; The apparatus includes an adsorption member as a means for adsorbing a transfer material to a transfer body, and an adsorption bias power supply that supplies an adsorption bias to the adsorption member, and a reference potential of the adsorption bias power supply is set as an output potential of the transfer bias power supply. This is a color image forming apparatus characterized by:

According to another aspect of the present invention, in a color image forming apparatus that forms a color image by transferring a visible image on an image carrier multiple times to a transfer material carried by a movable transfer member, the transfer a transfer bias power source for supplying a transfer bias to the transfer body; an adsorption member as a means for adsorbing a transfer material to the transfer body; and an adsorption bias power supply for supplying an adsorption bias to the adsorption member, the transfer bias power supply and A color image forming apparatus is provided in which at least one of the attraction bias power supplies switches the output value of the transfer bias and/or the attraction bias during at least the first image formation.

[0022] In both of the above inventions, the transfer body has a structure in which a conductive support is covered with a flexible sheet, or a conductive substance is coated on the support side as an electrode. It can be constructed by covering a flexible sheet.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A color image forming apparatus according to the present invention will be explained in detail below with reference to the drawings. FIG. 1 shows an embodiment of the present invention in the electrophotographic color image forming apparatus previously explained with reference to FIGS. The same numbers will be given and detailed explanation will be omitted. In this embodiment, the transfer body 3 is a solid drum having the same structure as that described with reference to FIG. 7(B). In other words, the transfer body 3 has a drum structure in which the outer circumferential surface of a cylindrical conductive drum housing 3a without a notch portion is covered with a dielectric flexible sheet 3b. In some cases,
The transfer body 3 may also have a structure in which a drum casing 3a without a notch is covered with a flexible sheet 3b coated with a conductive material as an electrode on the drum casing 3a side.

In this embodiment, the attraction bias power supply 18 that applies an attraction bias to the attraction member 15 such as an attraction roller is different from the above-mentioned conventional example in that the reference electrode of the attraction bias power supply 18 is not grounded. , are connected to the output terminal of the transfer bias power supply 17. The color image forming process in this embodiment will be explained below.

First, the transfer material 1 supplied from the transfer material conveyance path is transferred to the transfer body 3 and the suction roller 15 that approaches and separates from the transfer body 3.
At the transfer material adsorption section where the transfer material comes into contact, the transfer material is sandwiched between the adsorption roller 15 and the transfer body 3 and is electrostatically attracted to the surface of the transfer body by the suction roller 15 to which a suction bias is applied from the leading end of the transfer material. At this time, no transfer bias is applied to the transfer body 3, and the transfer body 3 is grounded via the transfer bias power supply 17 circuit.

Next, the transfer material 1 electrostatically attracted to the transfer body 3
is conveyed to the image transfer section by the rotation of the transfer body 3, and its surface potential is increased to a voltage (approximately 1 KV) that allows good transfer of the first color by the first color transfer bias applied just before the image transfer section. let By applying this transfer bias, the visible image on the image carrier 4 is electrostatically transferred onto the transfer material 1. At this time, the suction bias power supply 18 applying the suction bias to the suction roller 15 is
Since the output potential of the transfer bias power supply 17 is used as a reference potential, the output value of the attraction bias is necessarily varied with respect to ground.

As a result, the potential difference Vtr-abh between the output terminals of the transfer bias power supply 17 and the adsorption bias power supply 18 does not fluctuate before and after the application of the transfer bias for the first color, and the injection from the adsorption roller to the transfer material, which causes uneven transfer, is eliminated. The amount of charge Q can always be kept constant. Therefore,
The surface potential of the transfer material 1 entering the image transfer section is always kept constant, and transfer defects due to variations in the surface potential of the transfer material 1 can be prevented.

Thereafter, as explained in the conventional example, the second and third color visible images are superimposed and transferred onto the transfer material 1 from the image carrier 4, separated from the transfer material 3 by the separation charger 9, and transferred to the fixing device. 6 and becomes a permanent image. This second color,
When transferring the third color, a transfer bias higher than or equal to the transfer bias value of the first color is applied so that the second and third colors can be transferred well.

FIG. 2 shows changes in the output voltages of the transfer and attraction bias power supplies 17 and 18 and changes in the surface potential of the transfer material 1 immediately before the image transfer section in the image forming process of the present invention.

FIG. 3 is a schematic sectional view of a color image forming apparatus to which a second embodiment of the present invention is applied. In this embodiment, unlike the embodiments described above, a bias power supply circuit is used which can ground the attraction bias power supply 18 and vary the value of the output voltage of the attraction bias power supply 18 at a predetermined timing during image formation for the first color. ing. In this embodiment, when the transfer bias is applied, the potential difference Vt between the output terminals of the transfer and attraction bias power supplies 17 and 18 before and after the transfer bias is applied.
The adsorption bias is changed by an amount corresponding to the difference δVtr-abh between r-abh. That is, similarly to the above embodiment, even when a transfer bias is applied, the transfer bias power supply 17
and the potential difference between the output terminals of the adsorption bias power supply 18 Vtr-a
The adsorption bias power supply 18 is used to keep bh at a constant value.
The output value of is changed. Therefore, the transfer material 1 is always injected with a constant amount of adsorption charge Q1 from the adsorption roller 15, and the transfer material 1 is conveyed to the image transfer section regardless of whether or not a transfer bias is applied during adsorption. The surface potential at that time is constant.

[0031]This embodiment differs from the above-mentioned embodiments in that
Although it is necessary to change the suction bias at a predetermined timing t when transferring the first color image, since the suction bias power supply 18 is grounded, a more stable suction bias can be supplied at a lower cost than the suction bias power supply of the previous embodiment. There are advantages.

In the image forming process in this embodiment,
The changes in the output voltages of the transfer and suction biases are the same as in FIG. 2 of the above-mentioned embodiment, but in the same figure, the time t indicating the timing at which the suction bias is varied is the transfer from the suction roller contact position to the image transfer section. When the distance on the body circumferential surface is l, the radius of the transfer body 3 is r, and the rotational angular velocity of the transfer body 3 is ω,
It can be expressed by the following equation (l).

t=distance (l)/rω
(l
) FIG. 4 shows a color image forming apparatus to which a third embodiment of the present invention is applied. In this embodiment, unlike the previously described embodiments, the transfer bias power supply 17, not the attraction bias power supply 18, can vary its output value stepwise in accordance with an external signal.

In this embodiment, a portion A of the transfer material 1 (where the circumferential length on the transfer member 3 from the suction roller 15 to the image transfer portion is 1) surface potential VA of the area B of the transfer material 1 (the area from the circumference 1 to the rear end of the transfer material)
The output voltage is changed by the difference δVA-B between the surface potential VB and the surface potential VB so that it is superimposed on the transfer bias when the portion B of the transfer material 1 enters the image transfer portion described above due to the rotation of the transfer body 3. .

As a result, the transfer material 1 enters the image transfer section.
The surface potential of the transfer material 1 is always kept constant, and transfer defects due to variations in the surface potential of the transfer material 1 can be prevented. FIG. 5 shows a transfer and adsorption bias power supply 17 in the image forming process of the present invention.
, 18 and the surface potential of the transfer material 1 immediately before the image transfer section are shown.

Incidentally, the image forming process in the color image forming apparatus using this embodiment has been described in the case where the transfer bias of the first color changes by only one step during the transfer process of the first color, but the length of the transfer material 1 When LP is in the relationship shown in equation (2) with the distance l on the transfer body 3 described above, the transfer bias is controlled so as to change in n steps during image transfer of the first color.

LP ≦n×distance (l) (n is 1, 2, 3, 4...
...) (2) Also, in this example, 2
The values of the transfer biases for colors and subsequent colors also change by n steps when the transfer bias for the first color changes by n steps, similar to the transfer bias for the first color, unlike the above-described embodiment.

This embodiment differs from the previous embodiments in that it is necessary to change the transfer bias in multiple stages, but this only increases the variable range and timing of the transfer bias power supply, which originally varied the output value for each color. Therefore, when using a transfer bias power supply as shown in FIG. 11, for example, it is not necessary to separately provide output value control of the adsorption bias power supply in the image formation control sequence, so the firmware should be simple. Can be done.

[0039]

As explained above, the color image forming apparatus according to the present invention uses a power supply circuit that controls the transfer and attraction bias so that the surface potential of the transfer material on the transfer body is constant, so that the color image forming apparatus according to the present invention The surface potential of the transfer material when it is conveyed to the image transfer section is determined by the part of the transfer material that is attracted only by the attraction bias and the part that is attracted by the attraction bias and the transfer bias. It is possible to always maintain a constant value during the rotation of the first color, and therefore it is possible to suppress unevenness in transfer efficiency that occurs when solving transfer memory problems with transfer bodies that use solid drums, and to improve color balance. It is possible to obtain high quality color images.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing output values of a transfer bias power source and an adsorption bias power source, and a surface potential of a transfer material conveyed to an image transfer section.

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

FIG. 4 is a schematic configuration diagram of still another embodiment of the color image forming apparatus according to the present invention.

FIG. 5 is a diagram showing output values of a transfer bias power source and an adsorption bias power source, and a surface potential of a transfer material conveyed to an image transfer section.

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

FIG. 7 is a perspective view of the transfer body.

FIG. 8 is a schematic configuration diagram of a conventional color image forming apparatus.

FIG. 9 is a schematic configuration diagram of a conventional color image forming apparatus.

FIG. 10 is a diagram showing output values of a transfer bias power source and an adsorption bias power source and a surface potential of a transfer material conveyed to an image transfer section in a conventional apparatus.

FIG. 11 is a block diagram of a conventional transfer bias power supply.

[Explanation of symbols]

Claims (2)

[Claims] 1. A color image forming apparatus that forms a color image by transferring a visible image on an image carrier multiple times to a transfer material carried by a movable transfer member, in which a transfer bias is applied to the transfer member. It has a bias power source, a suction member as a means for suctioning the transfer material to the transfer body, and an adsorption bias power supply that supplies a suction bias to the suction member, and the reference potential of the suction bias power source is set to the reference potential of the transfer bias power source. A color image forming apparatus characterized in that an output potential is set as an output potential. 2. In a color image forming apparatus that forms a color image by transferring a visible image on an image carrier multiple times to a transfer material carried by a movable transfer member, a transfer unit that applies a transfer bias to the transfer member A bias power source, an adsorption member as a means for adsorbing a transfer material to the transfer body, and an adsorption bias power supply supplying an adsorption bias to the adsorption member, and at least one of the transfer bias power supply and the adsorption bias power supply: A color image forming apparatus characterized in that output values of a transfer bias and/or an adsorption bias are switched during at least the first image formation.