JPH11352807A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an image unevenness derived from the variations in resistance of a transfer roller, and to improve various failure caused by environmental dependency of the transfer roller resistance value, in the image forming device of electrophotographic system. SOLUTION: In this image forming device of the electrophotographic system capable of transferring the development image of monochrome or multicolor formed on the image carrier to transfer material adopting the transfer roller, the transfer roller 1 adopted for the above transfer is composed of the structure providing a layer 1-1, 1-2, and 1-3 of rubber and/or resin of at least, beyond 3 layers on a core bar 1-0, and making the specific resistance of the layer 1-3 located in the middle position is made below the specific resistance of the layer 1-1 located on the part below the layer located in the middle. In such a manner, the image unevenness as the result of variation in the resistance value of the transfer roller is made possible to be improved, and the various failure caused by the environmental dependency of the resistance value of the transfer roller is made possible to be improved.

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 using an electrophotographic system, such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus for transferring a monochromatic or multicolor developed image formed on an image carrier to a transfer material is known, and is applied to a copying machine, a printer, a facsimile, and the like. Have been. FIG. 3 is a diagram illustrating an example of an electrophotographic image forming apparatus having a single-color configuration.
In this image forming apparatus, when an image forming process is started, first, a drum-shaped photosensitive member 11 serving as an image carrier is charged by a charging device 12.
Is charged uniformly, and an electrostatic latent image is formed by image writing (or exposure of a document image) by the laser light 13 modulated according to the image signal, and the electrostatic latent image is formed by the developing device 14. The developed image (toner image) is developed by toner, and the developed image (toner image) is transferred to a transfer material 19 such as transfer paper by a transfer device (for example, a transfer roller) 15. Then, the transfer material 19 after the transfer is conveyed to the fixing device 16, and the toner image is fixed on the transfer material 19 by the fixing device 16. On the other hand, the photoreceptor 11 after the transfer is transferred to the cleaning device 17.
, And the charge is removed by the charge removing device 18 to reach the next image forming step.

FIG. 4 is a view showing an example of an electrophotographic image forming apparatus having a multicolor structure. In this image forming apparatus, a developing device 24 includes black (BK), cyan (C),
A developing device for four colors of magenta (M) and yellow (Y) is provided, and a belt-shaped intermediate transfer body (hereinafter, intermediate transfer belt) 25 is provided. Here, the image forming process will be described by taking as an example a case where four full-color images are formed in the order of BK, C, M, and Y. First, a drum-shaped photosensitive member 21 as an image carrier is uniformly charged by a charging device 22. After being charged, an electrostatic latent image of BK is formed by writing an image with a laser beam 23 modulated according to an image signal corresponding to black (BK), and this electrostatic latent image is formed by a BK developing device of a developing device 24. Is developed and visualized by the BK toner, and the BK developed image is primarily transferred to the intermediate transfer belt 25. Then, the photoconductor 21 after the transfer is cleaned by the cleaning device 29, and is discharged by the discharging device 30. Next, after the photosensitive member 21 is uniformly charged by the charging device 22, an electrostatic latent image of C is formed by writing an image with a laser beam 23 modulated according to an image signal corresponding to cyan (C), or the like. This electrostatic latent image is developed and visualized by the C toner of the C developing device of the developing device 24, and the C developed image is primarily transferred by being superimposed on the BK developed image on the intermediate transfer belt 25. Then, the photoconductor 21 after the transfer is cleaned by the cleaning device 29, and is discharged by the discharging device 30. Thereafter, latent image formation, development, and primary transfer to the intermediate transfer belt 25 are similarly sequentially performed for magenta (M) and yellow (Y).
After the toner images of the four colors BK, C, M, and Y are superimposed on the intermediate transfer belt 25, they are secondarily transferred collectively to a transfer material 31 such as transfer paper by a transfer device (for example, a transfer roller) 27. . Then, the transfer material 31 after the transfer is transferred to the fixing device 28.
And the fixing device 28 fixes the four color toner images on the transfer material 31 to obtain a full color image. On the other hand, the cleaning device 26 that has been separated at the time of the primary transfer process comes into contact with the intermediate transfer belt 25 after the transfer, and the intermediate transfer belt 25 is cleaned by the cleaning device 26, and the next image forming process is performed.

[0004] In the above-described electrophotographic image forming apparatus of single color or multicolor, from the viewpoint of environmental problems, there is a growing tendency to remove the corona even in the electrophotographic method, and the photosensitive member as an image carrier is increased. A transfer device for transferring a developed image from a body or an intermediate transfer belt to a transfer material is also shifting from a conventional corona transfer method to a belt transfer method, a roller transfer method, or the like. The present invention relates to the transfer roller system among them, and the image forming apparatus shown in FIG. 3 or FIG. 4 is described by using an example in which transfer rollers are used for the transfer devices 15 and 27. There are various inconveniences such as the occurrence of image unevenness due to variations in the resistance value of the transfer roller and environmental dependence. Therefore, as a conventional technology for the transfer roller, a sponge roller is used for the transfer roller to suppress an abnormal image called an insect-eating print, and the rubber hardness of the transfer roller is specified (to reduce a nip pressure). Various proposals have been made, for example, to increase the specific resistance of the surface of the transfer roller (JP-A-2-212873) in order to make it less susceptible to the resistance fluctuation (to the environment).

[0005]

At present, in an electrophotographic image forming apparatus, a system using a transfer roller as a transfer device is employed in a low-speed machine or the like. Roller cleaning system, in which the input toner to the transfer roller is reverse-transferred to the photoreceptor or intermediate transfer member, and the input toner to the transfer roller using a solid roller and directly using a cleaning blade etc. It is divided into two methods of removing.

The present invention relates mainly to the latter system having a cleaning blade. This type of transfer roller forms a lower layer and an uppermost layer on a cored bar, and each of the layers has the following functions. Roller having a two-layer structure separated into the following functions: cleaning function, lower layer function: elastic function for securing the nip. Here, for simplicity of explanation, an adhesive layer generally used to secure an adhesive force between the core metal / lower layer and the lower layer / uppermost layer of the transfer roller is omitted. In general, rubber is used as the main material of the uppermost layer, and rubber is used as the main material of the lower layer.

However, when the existing transfer roller having the two-layer structure as described above is used, there are the following problems. When a rubber material in which carbon (C) is dispersed for controlling the resistance is used for the lower layer of the transfer roller, the resistance of the lower layer is relatively small depending on the environment, but the uneven resistance of the roller due to the non-uniform dispersion of carbon. Is large, density unevenness occurs in the image. Similarly, when an ionic conductive material is used as the resistance control material of the lower layer, the resistance variation of the roller is reduced, but the environmental dependence of the resistance value is increased, or the temperature dependence of the resistance value is increased, and Since the specific resistance of the rubber layer at room temperature and normal humidity cannot be reduced to 10 ⁶ Ω · cm or less, the bias applied to the roller at low temperature and low humidity needs to be extremely higher than that at high temperature and high humidity at room temperature and normal humidity. Therefore, complicated control is required. At low temperature and low humidity, the image at the edge of the transfer paper is in an insufficient transfer state, even though the center of the transfer paper is in the optimum transfer state.
For example, in the case of a configuration in which the secondary transfer is performed from the intermediate transfer body 25 to the transfer material 31 using the transfer roller 27 as in the image forming apparatus of FIG. 4, insufficient transfer at the edge of the transfer paper even if the secondary transfer bias is increased. Is not improved, or even if it is improved, there is a quality problem that the transfer bias at the center of the transfer paper is in an excessive transfer state (transfer failure at the end of the transfer paper). When a transfer material having a high whiteness and a large content of CaCO ₃ -containing components is used, there is a problem that paper powder adheres to the transfer roller over time, causing poor cleaning, and causing back transfer stains.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and aims at improving image unevenness due to variation in the resistance value of a transfer roller and various disadvantages due to environmental dependence of the transfer roller resistance value. The aim is to improve Further, the present invention occurs at low temperature and low humidity,
It is an object of the present invention to improve the transfer failure at the end of the transfer paper, and to further improve the problem due to the adhesion of paper powder to the transfer roller.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, a monochromatic or multicolor developed image formed on an image carrier is transferred to a transfer material using a transfer roller. In an electrophotographic image forming apparatus,
The transfer roller used for the transfer has a structure in which at least three or more rubber and / or resin layers are provided on a cored bar, and a specific resistance of an intermediate layer is a layer located at the intermediate position. It is characterized in that the specific resistance is equal to or less than that of a layer located below.

According to a second aspect of the present invention, there is provided an electrophotographic image forming apparatus for transferring a monochromatic or multicolor developed image formed on an image carrier to a transfer material by using a transfer roller. The transfer roller has a configuration in which at least three or more rubber and / or resin layers are provided on a cored bar, and the specific resistance of the intermediate layer is 1
It is characterized by being from × 10 ³ Ω · cm to 1 × 10 ⁶ Ω · cm.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the surface layer of the transfer roller includes:
Temperature: 10 ° C.-Humidity: 15% RH The surface layer resistivity in an environment is 1.0 × 10 ⁸ Ω / □ or more (□: unit area).

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the surface of the transfer roller contains at least a mixed composition of a fluorine resin and an acrylic polymer. is there.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the surface of the transfer roller contains at least a mixed composition of a fluorine resin and a urethane polymer. is there.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described. First, for comparison with the present invention, problems of the existing transfer roller will be described in more detail. FIG. 2 shows an example of the configuration of a transfer roller used in a method of cleaning the transfer roller with a blade. FIG. 2A shows a cross-sectional structure of a conventional transfer roller having a two-layer structure, and FIG. 2B shows a layer structure of the transfer roller. In FIG. 2, a rubber material is generally used for a lower layer 2-1 formed on a cored bar 2-0, and the lower layer 2-1 is a rubber layer. This is because the transfer roller 2 is required to have an elastic function for securing the nip, and if an excessive force is applied to the nip, as described in the section of the problem to be solved, the characters and the line portion This is due to the occurrence of a transfer defect called a hollow. The layer 2-2 formed on the lower layer 2-1 is a surface layer, and a resin material having a small coefficient of friction is generally used for the surface layer. This is because when a roller is formed only with the rubber layer 2-1, most of the rubber material has high chemical affinity for the toner and the friction coefficient is large, so that the toner cleaning performance by the cleaning blade cannot be sufficiently secured. It is due to.

Here, if the transfer roller is an insulator, it cannot perform its function by itself. Therefore, it is necessary to control the resistance value of the rubber layer 2-1 and the surface layer 2-2 by any method. Therefore, EPDM or Si rubber in which carbon is dispersed is used as a rubber having a conductive function, and epichlorohydrin rubber, urethane rubber, or the like is generally used as a rubber having an ionic conductive mechanism. However, each rubber has the following problems.

Carbon-dispersed rubber: Due to insufficient dispersibility of carbon in the rubber material, there is a large variation in the resistance of the roller, and density unevenness occurs in the image. In particular, in the case of a full-color image forming apparatus as shown in FIG. 4, not only a density difference but also a color tone difference appears, so that a system that easily appears as an abnormal image and requires a high image quality cannot withstand actual use.

Ion-based conductive mechanism rubber: The resistance value has temperature dependency (low temperature: large resistance), and the specific resistance of the rubber layer at room temperature and normal humidity is 10 ⁷ Ω · cm or more. Rubber resistance at the time of 10 ⁸ Ω · c
m or more. Also, since the surface layer resistance needs to be a certain level or more (when the resistance of the surface layer is low, when the image is transferred to a transfer material having a width shorter than the width of the transfer roller in a low-temperature and low-humidity environment, the image of the transfer material end portion is Transfer may be insufficient). As a result, the volume resistance of the transfer roller at low temperature and low humidity cannot be set to 10 ⁷ Ω · cm or less. For this reason, it is necessary to make the bias applied to the roller at low temperature and low humidity extremely high at high temperature and high humidity compared to normal temperature and normal humidity. For this reason, there is a problem that complicated control such as controlling the bias applied to the transfer roller by detecting the temperature with a temperature sensor or the like or heating the roller with a heater so that the temperature does not fall below a certain temperature is required as a system. .

The present invention solves the above-mentioned problems of the conventional transfer roller, and the embodiments of the present invention will be sequentially described below according to the claims.

(Claim 1) FIG. 1 shows a configuration example of a transfer roller used in the image forming apparatus of the present invention. FIG. 1A shows a cross-sectional structure of the transfer roller of the present invention,
(B) is a diagram showing a layer configuration of the transfer roller. The transfer roller 1 has a core metal 1-0 on which a rubber layer 1-1, an intermediate layer 1-3, and a surface layer 1-2 are formed. It is a layered roller. Of course, the present invention is not limited to this, and includes those having an adhesive layer such as a primer between each layer and those having a layer for imparting other functions.

In FIG. 1, a rubber layer 1-1 and a surface layer 1-2 are provided.
Is a rubber layer 2-1 of the conventional transfer roller shown in FIG.
Although this is a part which does not differ from the constitutional function of the surface layer 2-2, the transfer roller 1 of the present invention solves the problem of the conventional transfer roller by adding the function of the intermediate layer denoted by reference numeral 1-3. That is, by setting the specific resistance of the intermediate layer 1-3 to be equal to or less than the specific resistance of the rubber layer 1-1 positioned below the intermediate layer, the roller resistance variation, which is a problem of the carbon dispersion system described above, is suppressed. In addition, it is possible to suppress the transfer bias fluctuation at the time of low temperature and low humidity, which is a problem with the rubber roller of the ionic conductive mechanism.

The reason for this is that in the conventional transfer roller 2, the roller surface layer 2 in the shaded portion of FIG.
-2, while the resistance of the rubber layer 2-1 contributed to the transfer current required to transfer the toner to the transfer material, the transfer roller 1 of the present invention has the resistance of the intermediate layer 1-3. 1 (a), the rubber layer region involved in the transfer current is greatly increased, and the variation in the resistance value, which is a problem in the carbon dispersion system, is further averaged and reduced. The transfer bias fluctuation (increase) at low temperature and low humidity, which was a problem with the ion-conductive rubber roller, was greatly reduced, and the rubber layer area involved in the transfer current was greatly increased. Even if it is the same as before, the rubber layer resistance contributing to the transfer is substantially reduced, so that the roller resistance contributing to the transfer is reduced, and the fluctuation (increase) of the transfer bias at low temperature and low humidity can be suppressed. I think That.

(Claim 2) In order to suppress the variation in the resistance of the transfer roller and the fluctuation of the transfer bias at low temperature and low humidity, which are the effects of the first aspect, the lower the resistance of the intermediate layer 1-3, the lower the resistance. It is valid. However, the intermediate layer 1-
If the resistance of the surface layer 1-2 is too low, the applied bias will destroy the coating defect of the surface layer 1-2. The surface resistivity of the surface layer 1-2 required for suppressing the edge transfer failure at low temperature and low humidity Has to be made higher resistance, and the optimum range of the surface resistivity of the surface layer 1-2 is extremely narrowed, which is not practical. Also, of course,
If the resistance of the intermediate layer 1-3 is high, the intended effect cannot be exhibited.

From the above, as a result of the examination, it is found that the specific resistance of the intermediate layer 1-3 of the transfer roller 1 satisfies 1 × 10 ³ Ω · cm ≦ intermediate layer specific resistance ≦ 1 × 10 ⁶ Ω · cm. It has been concluded that the desired effect can be obtained without causing the above-mentioned problems. It should be noted that the specific resistance is a resistance value obtained when 100 V of Hiresta is applied.

(Claim 3) As described above, when a developed image is transferred to a transfer material (for example, A4 lengthwise paper) having a width shorter than the width of the intermediate transfer belt or the transfer roller in a low-temperature and low-humidity environment, An abnormal image may occur in which the image at the edge of the transfer material is insufficiently transferred. It has been found that this phenomenon occurs when the surface resistance of the surface layer of the transfer roller is low. Therefore, in the transfer roller 1 of the present invention, in order to clarify how much surface resistance is required for the surface layer 1-2,
The following experiment was performed.

Experiment: First, epichlorohydrin rubber having a specific resistance of 10 ⁸ Ω · cm was provided as a base rubber on a cored bar.
On top of that, an aminosilane layer having a thickness of 3 μm and a resistance adjusted to a specific resistance of 2 × 10 ³ Ω · cm was provided for the purpose of the intermediate layer of the present invention. Thereafter, a surface layer in which titanium oxide is dispersed in a commercially available fluororesin is formed.In this case, the dispersion amount of titanium oxide is changed, and a surface layer having a different surface resistance is provided on the intermediate layer. No. 1 to 6 transfer rollers were formed. These six rollers are mounted on a commercially available Ricoh color copier: Pretail 600 having a configuration as shown in FIG.
At 5% RH), the presence or absence of the above-mentioned edge transfer failure was confirmed. The results are shown in Table 1 below. The surface resistance (Ω / □) of the surface layer is a surface resistance value obtained when 100 V of Hiresta was applied in an environment of 10 ° C. and 15% RH.

[0026]

[Table 1]

According to Table 1, the surface resistance of the secondary transfer roller is 1
It was found that if it was × 10 ⁸ Ω / □ or more, the problem of poor edge transfer at low temperature and low humidity, which was a problem, did not occur. On the other hand, when the surface layer is directly provided on the epichlorohydrin base rubber without providing the intermediate layer on the transfer roller, the surface layer surface resistance required for suppressing the end transfer failure is 3.0 × 10 ⁷ Ω / □ or more. It was found that it was necessary to increase the surface resistance of the surface layer by about one digit. This is presumably because the intermediate layer has a low resistance, so that the transfer charge at the edge of the transfer material becomes more intense.

(Claims 4 and 5) The surface layer of the transfer roller is used by adjusting the resistance by adding a resistance control material to a fluororesin from the viewpoints of blade cleaning properties (low friction coefficient), durability and flame retardancy. Generally, it is done. However, PVd
Conventional with a surface layer in which a resistance control material is added to a single fluorine-based resin such as F (polyvinylidene fluoride), ETFE (ethylene-tetrafluoroethylene resin), or PFA (tetrafluoro-perfluoroalkylvinyl ether resin) When a transfer material having high whiteness, that is, a CaCO ₃ -containing component is used in the transfer roller of the above, paper dust adheres to the transfer roller over time, and cleaning failure occurs, thereby causing back transfer of the transfer material. was there. For this reason, process measures have been taken, such as applying a lubricant such as zinc stearate to the surface of the transfer roller to prevent paper powder from adhering to the roller surface over time. However, even in this case, if the lubricant is out of supply, the above-mentioned back dirt will occur, so the supply of the lubricant will cause the durability of the transfer roller unit, and the intended durability cannot be achieved. It was expensive.

The present inventors have conducted various studies on the materials constituting the surface layer of the transfer roller, and as a result, have found that the surface layer 1-2 of the transfer roller 1 contains "a mixture of at least a fluorine resin and an acrylic polymer. Including the composition (Claim 4) "or" Containing at least a mixed composition of a fluororesin and a urethane-based polymer (Claim 5) "solves the above-mentioned problems caused by the adhesion of paper powder. I found what I could do.

[0030]

As described above, according to the first aspect of the invention, an electrophotographic image is formed by transferring a monochromatic or multicolor developed image formed on an image carrier to a transfer material using a transfer roller. In the forming apparatus, the transfer roller used for the transfer has a configuration in which at least three or more rubber and / or resin layers are provided on a cored bar, and the specific resistance of an intermediate layer is the intermediate resistance. By adjusting the specific resistance of the layer located below the layer positioned below the specific resistance to below, it is possible to improve the image unevenness due to the variation in the resistance value of the transfer roller, and to determine the environmental dependence of the resistance value of the transfer roller. Various inconveniences caused by the above can be improved.

According to a second aspect of the present invention, there is provided an electrophotographic image forming apparatus for transferring a monochromatic or multicolor developed image formed on an image carrier to a transfer material using a transfer roller. The transfer roller has a configuration in which at least three or more rubber and / or resin layers are provided on a cored bar, and the specific resistance of the intermediate layer is 1
By setting the resistance to × 10 ³ Ω · cm to 1 × 10 ⁶ Ω · cm, it is possible to improve the image unevenness due to the variation in the resistance value of the transfer roller, and to make the resistance value of the transfer roller dependent on the environment. Various inconveniences caused by the above can be improved. Further, it is possible to improve the transfer failure at the end of the transfer paper, which occurs at the time of low temperature and low humidity.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the surface layer of the transfer roller includes:
Temperature: 10 ° C.-Humidity: 15% RH In the environment, the surface resistivity is 1.0 × 10 ⁸ Ω / □ or more (□: unit area). It is possible to improve the transfer failure that occurs at the end of the transfer paper.

According to a fourth aspect of the invention, in the image forming apparatus of the first aspect, the surface of the transfer roller is configured to contain at least a mixed composition of a fluorine resin and an acrylic polymer. In addition to the effects of the above item 1, it is possible to improve the problem caused by the adhesion of the paper powder to the transfer roller.

According to a fifth aspect of the present invention, in the image forming apparatus of the first aspect, the surface of the transfer roller is configured to contain at least a mixed composition of a fluorine resin and a urethane polymer. In addition to the effects of the above item 1, it is possible to improve the problem caused by the adhesion of the paper powder to the transfer roller.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention, in which (a)
FIG. 2 is a diagram illustrating a cross-sectional structure of a transfer roller, and FIG. 2B is a diagram illustrating a layer configuration of the transfer roller.

FIGS. 2A and 2B are diagrams illustrating an example of a conventional technique, in which FIG. 2A is a diagram illustrating a cross-sectional structure of a transfer roller, and FIG. 2B is a diagram illustrating a layer configuration of the transfer roller.

FIG. 3 is a schematic configuration diagram illustrating an example of an electrophotographic image forming apparatus having a single color configuration.

FIG. 4 is a schematic configuration diagram illustrating an example of an electrophotographic image forming apparatus having a multicolor configuration.

[Explanation of symbols]

 1: transfer roller 1-0: core metal 1-1: rubber layer 1-2: surface layer 1-3: intermediate layer 11, 21: photosensitive member (image carrier) 14: developing device 15, 27: transfer roller 24 : Developing device with 4 color developing devices 25: Intermediate transfer member (image carrier)

Claims (5)

[Claims] An electrophotographic image forming apparatus for transferring a monochromatic or multicolor developed image formed on an image carrier to a transfer material using a transfer roller, wherein the transfer roller used for the transfer is: It has a configuration in which at least three or more rubber and / or resin layers are provided on a cored bar, and the specific resistance of an intermediate layer is equal to or less than the specific resistance of a layer located below the intermediate layer. An image forming apparatus, characterized in that: 2. An electrophotographic image forming apparatus for transferring a monochromatic or multicolor developed image formed on an image carrier to a transfer material using a transfer roller, wherein the transfer roller used for the transfer is: It has a structure in which at least three or more rubber and / or resin layers are provided on a cored bar, and the specific resistance of the intermediate layer is 1 × 10 ³ Ω · cm to 1 × 10 ⁶ Ω · cm. An image forming apparatus, comprising: 3. The temperature of the surface layer of the transfer roller: 10
2. The image forming apparatus according to claim 1, wherein the surface resistivity in a 15 ° C.-humidity environment is 1.0 × 10 ⁸ Ω / □ or more (□: unit area). 4. The image forming apparatus according to claim 1, wherein the surface of said transfer roller contains at least a mixed composition of a fluorine resin and an acrylic polymer. 5. The image forming apparatus according to claim 1, wherein the surface of the transfer roller contains at least a mixed composition of a fluorine resin and a urethane polymer.