JPH0862996A - Color image forming device - Google Patents

Abstract

PURPOSE: To provide a color image forming device capable of obtaining high image quality by efficiently removing toner remaining on an intermediate transfer medium at a low cost. CONSTITUTION: In the color image forming device successively transferring color toner images formed on an image forming carrier 2 onto the intermediate transfer medium 1 in each color, to form color images thereon and then, transferring the color images to a recording substrate 9 collectively, to form the color images, as the intermediate transfer medium 1, one having a surface coated with a fluorocarbon coating agent is used, a urethane rubber blade 12 is used for cleaning the medium 1 and simultaneously the surface roughness of the medium 1 is set <=0.45Ra [μm] in center line average height.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention sequentially transfers toners of respective colors formed on a photosensitive drum (image forming carrier) onto an intermediate transfer medium, forms a color image on the intermediate transfer medium, and then forms the image. The present invention relates to a color image forming apparatus that collectively transfers the formed color image onto recording paper.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed as a color image forming apparatus. Among them, a method of forming a color image on an intermediate transfer medium and then collectively transferring the color image onto recording paper is disclosed in JP-A-5-142955. Is disclosed in. Many intermediate transfer media have been proposed, such as endless belt-shaped media and cylindrical drum-shaped media.

In the method using the intermediate transfer medium, as described above, a color image is once formed on the intermediate transfer medium, and then collectively transferred onto a recording paper. Therefore, the higher the transfer efficiency during this batch transfer, the better, and ideally 100%. However, it is very difficult to achieve a transfer rate of 100%, so even after the batch transfer to recording paper is completed,
On the intermediate transfer medium, residual toner that has not been transferred to the recording paper is attached. When the next printing process is continuously performed in this state, the residual toner affects the next image and the fineness of the image is lost. Therefore, every time you print one sheet,
A cleaning operation is required to remove the toner remaining on the intermediate transfer medium.

As a cleaning method, a peeling method in which a rubber blade or a brush is used to mechanically remove it, and Japanese Patent Laid-Open No. Hei.
As disclosed in -296785, there is a reverse bias method in which an appropriate voltage is applied between the intermediate transfer medium and the photoconductor drum, and the residual toner is collected in the developing device by the electric field thereof.

[0005]

However, depending on the intermediate transfer medium used, it may be difficult to remove the residual toner by any cleaning method. That is, since the residual toner adheres to the intermediate transfer medium by the electrostatic force and the mechanical adhesive force, in order to remove the residual toner from the intermediate transfer medium, it is necessary to apply a force exceeding these forces. Here, the electrostatic force is a force that the charged toner receives from the action of the electric field formed by the charged electric charge of itself, and in this case, it acts in the direction of pressing the toner against the intermediate transfer medium. The mechanical adhesive force is a force due to the adhesiveness or frictional load between the intermediate transfer medium and the toner. For effective cleaning, it is necessary to reduce these forces.

Since the electrostatic charge is affected by the charging charge of the toner as described above, it can be weakened by reducing the toner charge amount. However, the decrease in the toner charge amount is not preferable because there is a problem that the toner adheres to areas other than the image area such as fogging of the photoconductor and that the toner is scattered around the image. Further, in order to weaken the mechanical adhesion, a method of adding an additive to the toner to reduce the adhesiveness and the friction coefficient can be considered, but it is not only difficult to improve only certain specific characteristics of the toner. However, since such a method also adversely affects other characteristics, there is a problem that a great development cost is required to achieve the intended effect.
That is, it is difficult to improve the image quality of a low-cost color image by such means.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a color toner image formed on an image forming carrier by sequentially transferring each color toner image onto an intermediate transfer medium. In a color image forming apparatus in which a color image is formed on a transfer medium and then the color image is collectively transferred to a recording support to form a color image, a fluorine-based coating agent is applied to the surface as the intermediate transfer medium. Used for cleaning the intermediate transfer medium, a urethane rubber blade is used to clean the intermediate transfer medium, and the surface roughness of the intermediate transfer medium is 0.45 Ra as a center line average roughness.
It is characterized in that it is set to [μm] or less.

[0008]

In the color image forming apparatus of the present invention, an intermediate transfer medium having a surface coated with a fluorine-based coating agent is used, and a urethane rubber blade is used for cleaning the intermediate transfer medium. The surface roughness of the intermediate transfer medium is 0.45 as a centerline average roughness.
By setting Ra [μm] or less, the residual toner on the intermediate transfer medium can be efficiently removed at a low cost by a simple method. Therefore, the above problem can be solved.

[0009]

【Example】

[Description of Configuration] FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. Reference numeral 1 denotes an intermediate transfer medium, which is one in which carbon is dispersed in order to prevent the intermediate transfer medium itself from being charged. If the resistance value of this intermediate transfer medium is larger than 10 ¹¹ Ω · cm, the discharge after transfer is large and the toner is scattered,
When the image disturbance becomes large and when it is 10 ⁴ Ω · cm or less, the charged electric charge easily escapes to the contact member, the transfer potential is lowered, and the transfer rate is lowered. Therefore, 10 ⁵ to 10
The range of ¹⁰ Ω · cm is good, preferably 10 ⁷ to 10 ⁹ Ω ·
cm is good. In this example, a cylindrical drum made of aluminum was molded with silicon rubber in which carbon was dispersed, and the surface of the silicon rubber was coated with a fluororesin such as PFA or FEP having excellent releasability.

A photosensitive drum 2 as an image forming carrier is installed in contact with the intermediate transfer medium 1, and a charging device 3 and an exposure device 4 are provided around the photosensitive drum 2.
And yellow (Y), magenta (M), cyan (C),
Developing unit 5 containing toner of black (K) color
Y, 5M, 5C, and 5K are provided, each developing unit is composed of developing devices 51Y, 51M, 51C, and 51K, and toners 52Y, 52M, and 52C are provided in the toner storage tank of the developing means, respectively. 52K is stored.

The photoconductor drum 2 has a photoconductive layer provided on a conductive support, and any of a selenium photoconductor, an organic photoconductor, a zinc oxide photoconductor, an amorphous silicon photoconductor, etc. can be used.

The charging device 3 as a charging means is provided so as to face the surface of the photoconductor. In this embodiment, a contact type charging roller as shown in the figure is provided. The charging roller is composed of, for example, a metal shaft laminated with a conductive rubber. In addition, a conductive charging blade and a non-contact type corona discharger can be used.

The exposure device 4 as an exposure means serves to convert an image signal into light and irradiate the photoconductor. As the exposure device 4, a combination of a light source such as a laser or an LED array and an image forming optical system can be used. In this embodiment, an LED array is used as the light source and a SELFOC lens is used as the image forming optical system.

Each developing unit as a developing means adsorbs toner (52Y, 52M, 52C, 52K) on a toner carrier (53Y, 53M, 53C, 53K) and conveys it in the direction of the arrow in the figure. The electrostatic latent image formed on the photoconductor is developed. As the developing device, any known technique such as a two-component magnetic brush developing device, a one-component magnetic brush developing device and a one-component non-magnetic developing device can be used.

A secondary transfer means 6 is provided in contact with the intermediate transfer medium 1 and downstream of the developing unit. Any transfer means may be used as long as it can electrostatically transfer the toner, and a corona discharger or a contact-type conductive material is used. In this embodiment, a conductive roller is used as shown in the figure. This roller is constructed by laminating a resistance material having elasticity such as rubber or sponge on a metal support. If necessary, the surface of the resistor material may be covered with a protective material or the like. At the time of transfer, a voltage having a polarity opposite to the toner charge is applied to the metal support of the transfer roller.

Heating and pressurizing means (7, 8) are provided on the downstream side of the secondary transfer means 6 in the conveying direction of the recording support.
The heating and pressing means are provided so as to face each other in a pair with the recording paper sandwiched therebetween. Among them, the heating means 7 is provided on the front side of the recording paper on which the toner image is transferred,
Pressed with a constant pressure. This heating means is a metallic hollow member having a halogen lamp built therein. Further, a heating resistance layer made of Ni-P or the like is formed on the surface of a substrate such as glass or ceramic, and Ta2O5,
Those formed of a protective layer such as a fluororesin can also be used. In opposition to this, on the back side of the recording paper on which the toner image is not transferred, there is provided a pressing means 8 composed of an elastic roll. This roller is made by laminating rubber on a metal pipe, and the rubber is preferably silicone or the like. In this embodiment, the roller 7 is provided with a heating means, and the roller 8 has a surface laminated with silicone rubber.

The secondary transfer means 6 is opposed to the intermediate transfer medium 1.
A cleaner 11 is provided on the downstream side. Cleaner 1
A cleaning blade 12 made of urethane rubber is attached to 1 to remove residual toner. Further, here, there is provided a recording paper (recording support) insertion means (not shown),
The recording support 9 is fed to the intermediate transfer medium by the feed roller 10.

[Description of Operation] The intermediate transfer medium 1 and the photoconductor drum 2 are rotated at the same speed at a constant peripheral speed in the direction of the arrow in the figure by a driving unit (not shown). Based on the recording start signal, the photosensitive drum 2 is uniformly charged by the charging device 3. Next, the exposure device 4 irradiates the photoconductor with light corresponding to the image signal to form an electrostatic latent image. Here, light is applied to a portion corresponding to the image.
As a result, the image signal is formed so that the charged electric charge is erased in the image portion and the charged electric charge is left as it is in the non-image portion. The electrostatic latent image is visualized by the developing device units (5Y, 5M, 5C, 5K) provided in contact with or close to the photosensitive drum 2. Since reversal development is used in this embodiment, a bias potential is applied between the conductive support of the photosensitive drum 2 and each toner carrier (53Y, 53M, 53C, 53K). Therefore, the charged toner (52Y, 52M, 52C, 52K) on each toner carrier adheres to the photosensitive drum 2 by electrostatic force and is developed. The toner developed on the photosensitive drum is electrostatically transferred onto the intermediate transfer medium by the primary transfer voltage applied to the intermediate transfer medium 1 facing the photosensitive drum 2.

A voltage having a polarity opposite to the charging polarity of the toner is applied to the intermediate transfer medium 1 by a voltage applying means (not shown). When the leading position of recording on the intermediate transfer medium reaches the photosensitive drum 2 developed with the yellow toner 52Y, the yellow toner 52Y on the photosensitive drum is transferred one after another according to the movement of the intermediate transfer medium.

When the last part of the yellow image is developed on the photosensitive drum 2, magenta toner 52M is developed on the photosensitive drum 2 so as to coincide with the leading position of the yellow image on the intermediate transfer medium 1. start. When the recording head position on the intermediate transfer medium 1 reaches the photosensitive drum developed with the magenta toner 52M, the magenta toner 52M is transferred onto the intermediate transfer medium 1 onto which the yellow toner image has been transferred. Similarly, cyan toner 52C and black toner 52
K is transferred onto the intermediate transfer medium. In this way, the transfer of each color toner is completed in the order of Y, M, C, K,
A multicolor image is formed on the intermediate transfer medium.

When all the color toners have been transferred onto the intermediate transfer medium 1 and the leading portion of the image approaches the transfer roll 6, the transfer roll 6 is moved by an unillustrated movable means to form the intermediate transfer medium 1.
First, the recording support 9 is fed by the paper feed roll 10 and sent to the transfer roll 6. Transfer roll 6
Is applied with a secondary transfer voltage having a polarity opposite to the charging polarity of the color toner image formed on the intermediate transfer medium 1 by a method not shown, and the color image formed on the intermediate transfer medium is recorded. It is superposed on the support and is secondarily transferred to the recording support at once. At this time, when the leading portion of the color image approaches the transfer roll 6 which is the secondary transfer means, the cleaner 11 which has been separated from the intermediate transfer medium 1 until then contacts the intermediate transfer medium to remove the residual toner. When the cleaning up to the end of the image is completed, the cleaner 11 is separated from the intermediate transfer medium again.

The color toner image transferred onto the recording support 9 is moved to the heating / pressurizing means (7, 8), and the recording support 9 onto which the color toner image is transferred is heated by the heating / pressurizing means. Pressurized with heating. When the recording support 9 is inserted between the heating roll 7 and the pressure roll 8, the heat of the heating roller 7 is transferred to the color toner image on the recording support,
The toner is heated and melted. The toner that has passed through the heating and pressing means (7, 8) is naturally cooled, returns to the solid state again, and is fixed on the recording support 9.

After the toner is fixed on the recording support 9,
The recording support is discharged to a stacker (not shown) outside the apparatus.

As described above, the method of reducing the toner charge amount and weakening the mechanical adhesion of the toner leads to deterioration of image quality and increase of development cost, which is not preferable. Therefore, the present invention is intended to solve the above-mentioned problems by improving the processing accuracy of the surface of the intermediate transfer medium. The surface of the intermediate transfer medium 1 is usually coated with a fluorine-based coating agent to improve the releasability of the toner. Sometimes there was a difference. Since the surface processing accuracy can be measured as the surface roughness, the relationship between the surface roughness of the intermediate transfer medium and the cleaning characteristics was measured.

In the measurement, first, the steps of transferring the toner image formed on the photosensitive drum 2 onto the intermediate transfer medium by applying a transfer voltage are performed in yellow, magenta, cyan, and
The four black colors are sequentially performed to form a color image on the intermediate transfer medium 1. After transferring this image to recording paper at once,
Residual toner on the intermediate transfer medium was removed by the cleaner 11, and the toner removal state at that time was evaluated. The results are shown in Table 1.

[0026]

[Table 1]

The mark X in the table indicates that the cleaning was not successful in one rotation of the intermediate transfer medium, and the toner that could not be removed by the cleaning at the time of the next image formation had an effect, and the toner transfer from the photoconductor drum to the intermediate transfer medium. It indicates that the rate is lowered and the recorded image is deteriorated. The △ symbol
Although the transfer efficiency is not lowered and the image is not deteriorated, the cleaning is insufficient, and the mark “◯” indicates that the toner on the intermediate transfer medium can be completely removed. The surface roughness of the intermediate transfer medium is measured based on the center line average roughness defined in JIS B0601.

By the way, the cleaner 11 collectively transfers the color image on the intermediate transfer medium 1 onto a recording sheet, and then presses a cleaning blade 12 onto the intermediate transfer medium,
A method is used to remove the residual toner that could not be transferred. Therefore, it is desirable that the blade does not damage the intermediate transfer medium, and the material may be silicone rubber or urethane rubber. In this embodiment, urethane rubber is used.

From the above-mentioned cleaning characteristics, when the urethane rubber blade is used as the cleaning blade, the surface roughness of the intermediate transfer medium is 0.45 Ra [μm] or less as the center line average roughness. The residual toner could be removed most efficiently.

In this embodiment, each of the photoconductor and the exposure device is one.
Although the example applied to the one-drum type device mounted one by one has been described, as shown in FIG. 2, the photosensitive drums (2Y, 2M, 2C, 2K) and the exposure device (4) are provided on the surface of the intermediate transfer medium 1.
Y, 4M, 4C, 4K) can also be applied to a device having a plurality of installed. A belt-shaped intermediate transfer medium is also applicable.

[0031]

As described above in detail, according to the present invention, the color toner images formed on the image forming carrier are sequentially transferred onto the intermediate transfer medium for each color to thereby form the intermediate transfer medium. A color image forming apparatus for forming a color image by forming a color image on the recording support after the color image is formed on the recording support, and a fluorine coating agent is applied to the surface of the intermediate transfer medium. By using a urethane rubber blade for cleaning the intermediate transfer medium and setting the surface roughness of the intermediate transfer medium at the center line average roughness to 0.45 Ra [μm] or less, the intermediate transfer is performed. The surface of the medium can be sufficiently cleaned, and a high-definition color image having no residual image can be formed during the next printing.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of another embodiment of the present invention.

[Explanation of symbols]

 1 Intermediate Transfer Medium 2 Photosensitive Drum 3 Charging Device 4 Exposure Device 5Y, 5M, 5C, 5K Developing Unit 6 Secondary Transfer Means 7 and 8 Heating and Pressurizing Means 9 Recording Support 10 Paper Feed Roller 11 Cleaner 12 Blade

Claims (1)

[Claims] 1. A color toner image formed on an image forming carrier is sequentially transferred onto an intermediate transfer medium for each color to form a color image on the intermediate transfer medium, and then the color image is recorded and supported. In a color image forming apparatus for transferring a batch to a body to form a color image, a urethane coating is used to clean the intermediate transfer medium, the surface of which is coated with a fluorine-based coating agent. And the surface roughness of the intermediate transfer medium as a centerline average roughness of 0.
A color image forming apparatus characterized by being set to 45 Ra [μm] or less.