JPH07175316A - Developer carrying body - Google Patents

Abstract

PURPOSE:To obtain an inexpensive developer carrying body which does not cause fixing of a developer due to bleeding of a softening agent by controlling the polymer and the softening agent for the body in such a manner that the difference of SP values between the polymer and the softening agent is smaller than the difference of SP values between the softening agent and the resin which constitutes a developer. CONSTITUTION:A surface layer 1b comprising a rubber elastic material is formed on a core material 1a such as iron and aluminum, and then the surface is polished to obtain a developer roller l as a cylindrical developer carrying body. The surface layer 1b of the developer roller 1a consists of butadiene as the base polymer and a paraffin-base processed oil as a softening agent. These materials are controlled in such a manner that the difference of SP values between these is smaller than the difference of SP values of polystyrene of the toner resin and the paraffin-base processed oil. Thereby, since the compatibility between the processed oil and the butadiene is higher than the compatibility between the processed oil and the polystyrene, the process oil as a softening agent does not bleed out from the rubber of the surface layer J9 even in a toner atmosphere and the roller maintains a stable state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer carrying member of a developing device used for an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., and more specifically, a surface layer of an elastic body containing a polymer and a softening agent. The present invention relates to a developer carrying body on which a developer is formed and which is carried and supplied to an image carrying body.

[0002]

2. Description of the Related Art In a developing device employing a contact type developing system using a non-magnetic one-component developer, the developer on the developer carrying member is directly contacted with the developer on the image carrying member. However, if at least one of the developer carrier and the image carrier is not soft, the developer (visible image) transferred to the latent image is destroyed. For example, an image defect may appear as a jitter image or the surface of the developer bearing member or the image bearing member may be damaged. Also,
The torque increases between the developer bearing member and the image bearing member, and the drive system is also added.

As a soft image bearing member, a resin belt or a metal belt on which an OPC layer is formed is known, but from the viewpoint of driving cost and increasing the size,
It is said that the drum or the hard type image carrier is more advantageous. Therefore, the present inventors have studied a soft developer carrier for contact development on a hard type image carrier.

Japanese Unexamined Patent Publication (Kokai) No. 62-257185 proposes to use a foam as a developer carrying member.
By using a foam, an image forming apparatus is proposed which gives the developer carrier sufficient softness and is extremely advantageous against image destruction. However, since the foam has poor creep properties, indentations remain on the contact portion with the image carrier, and black or white streaks are likely to occur on the image. Further, when a foam is used, the thickness of the developer thin layer on the developer carrying member becomes uneven due to the unevenness of the surface, and uneven image density may occur.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 2-1881, a highly releasable resin layer is provided on solid rubber, and direct contact between the rubber and the developer is avoided, so that the developer is fixed to the surface. Proposed is a highly durable and durable developer carrier. In the case of this developer carrying member, since the substrate is solid rubber, it exhibits relatively good creep properties, but since the surface layer is a resin with poor creep properties, minute indentations are not improved. Further, the cost is high due to the process of forming the surface layer by spray painting or dipping. Further, since it is harder than the foam, it is necessary to reduce the hardness of the rubber by adding a softening agent or the like.

[0006]

Therefore, the inventors of the present invention form a developer carrying member only with a core material and solid rubber without providing a surface layer of a highly releasable resin or the like on solid rubber. Was desirable in terms of image quality and cost. As a technical issue in that case, high releasability (high durability =
There is no sticking of the developer to the developer carrier), low hardness, and non-staining property (no adverse effect on the image carrier). However, rubber itself is relatively sticky, and the addition of a softening agent further increases the stickiness, or the most worrying thing is that bleeding of the softening agent causes the developer to stick to the surface. Is to do.
Such sticking of the developer causes a change in the charge amount of the developer, which causes background stain and a change in image density.

Japanese Patent Laid-Open No. 5-59222 proposes to add liquid rubber to solid synthetic rubber or natural rubber as a formulation of the bleed-free softening agent. As a result, as the developer carrier alone,
Although a stable product without bleeding can be obtained, it is common to provide a highly releasable resin layer on the surface without considering the stability in a developer atmosphere. Further, liquid rubber is expensive as a softening agent, and there is a problem in terms of stable supply. Further, the liquid rubber may cause a curing reaction depending on the vulcanizing agent and may not act as a softening agent. For example, liquid nitrile rubber is cured with a peroxide vulcanizing agent.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an inexpensive developer carrying member in which the developer is not fixed by the bleeding of the softening agent.

[0009]

In order to achieve the above object, the present invention provides an image bearing member in which a surface layer is formed of an elastic body containing a polymer and a softening agent, and the surface of which carries a developer. In the developer carrier to be conveyed and supplied, the difference between the SP value (solubility parameter value) of the polymer and the SP value of the softening agent is the SP value of the softening agent and the SP of the resin constituting the developer.
It is characterized by being smaller than the difference from the value.

[0010]

In the present invention, the elastic body forming the surface layer of the developer carrying member contains the polymer and the softening agent. The softening agent reduces the hardness of the surface layer of the developer carrying member. The difference between the SP value of the polymer and the SP value of the softening agent is the SP value of the softening agent and the SP of the resin forming the developer.
Since the difference is smaller than the difference, the compatibility between the polymer and the softening agent is higher than the compatibility between the softening agent and the resin of the developer, and the softening agent does not bleed even in the developer atmosphere.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a developer carrying member of a developing device used in an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. Table 1
Shows a compounding example of rubber which is an elastic body used for the surface layer of the developer carrying member. Although various polymers can be used as the base of this rubber, butadiene (BR01, manufactured by JSR, SP value = 8.4) is used in this example. Here, as the unit of SP value,

The unit shown in Equation 1 was used.

[Equation 1]

[Table 1]

Butadiene was used as the base polymer of the above rubber because it has a relatively good releasability among various synthetic rubbers. In addition to this butadiene, carbon black, zinc oxide, stearic acid as a conductivity-imparting agent, accelerator TT and accelerator CZ as a vulcanization accelerator, sulfur as a vulcanization agent, etc. are added. In the formulation example A containing the above additives, hardness 40 (JIS, measurement value by A type hardness meter) is shown, but in order to further reduce hardness, paraffin-based process oil (P400, manufactured by Fuji Kosan, SP
The value = 6.5) was selected as the softening agent, and 12 parts by weight was added as in Formulation Example B. As a result of the addition of the softening agent, the hardness is 3
A molded product of 0 (measured by JIS, type A hardness meter) could be obtained.

Then, as shown in FIG. 1, a surface layer 1b made of a rubber elastic body of the above compounding example B is molded on a core material 1a of φ10 mm of iron, aluminum or the like (150 ° C., 20 minutes, press vulcanization). After that, the surface was polished to obtain a developing roller 1 having a diameter of 20 mm as a cylindrical developer carrying member. The volume resistivity of the developing roller 1 is equal to the applied voltage 10
The measurement of V showed 1 × 10 ⁷ Ωcm. Also, the surface roughness R
z was 6 μm. As described above, since the developing roller 1 according to this embodiment has the single-layer structure of the surface layer 1b, it can be manufactured at low cost.

An image was formed by combining the developing roller 1 and a toner as a developer containing polystyrene resin (SP value = 9.6) as a main component, and the image was evaluated. FIG. 2 is a front view showing a schematic configuration of a developing device 10 of a copying machine used for image formation and a photoconductor 20 as an image carrier. The toner 3 in the hopper 2 is conveyed to a pressure contact portion with the developing roller 1 by a toner replenishing roller 4 as a developer replenishing member composed of a cylindrical sponge or the like, and the developing roller 1 and the toner which rotate in the arrow directions, respectively. It is charged by the contact friction with the replenishing roller 2 and adheres onto the developing roller 1. Then, the toner 4 on the developing roller 1
Is uniformly thinned on the surface of the developing roller 1 by the blade 5 as a layer thickness regulating member such as a rubber plate or a metal plate. The uniformly thinned toner is conveyed by the developing roller 1 to a contact portion with the photoconductor 20 rotating in the arrow direction,
The latent image on the photoconductor 20 is developed.

An image was formed using the above copying machine, and the image was evaluated. As a result, abnormalities due to slip between the photoconductor and the developing roller, which occurred when the developing roller according to the conventional formulation example A was used, were found. The image is gone. This is because the torque between the photoconductor 20 and the developing roller 1 can be reduced by achieving the low hardness of the surface layer of the developing roller 1.

Further, the toner was not fixed to the surface of the developing roller 1 and the image quality was not deteriorated. This is because the difference between the SP value of butadiene as the base polymer, which is the material of the surface layer 1b of the developing roller 1, and the SP value of the paraffinic process oil as the softening agent is different from that of polystyrene of the toner resin and that of the paraffinic process oil. Since the difference from the SP value is smaller, the compatibility between the process oil and butadiene becomes higher than the compatibility between the process oil and polystyrene, and the process oil, which is a softening agent, remains in the surface layer 1b even in the toner atmosphere. This is because the stable state was maintained without bleeding (melting out) from the rubber.

[0017]

According to the present invention, the difference between the SP value of the polymer of the elastic body forming the surface layer of the developer carrying member and the SP value of the softening agent constitutes the SP value of the softening agent and the developer. Resin S
By making the difference smaller than the P value, the compatibility between the polymer and the softening agent becomes higher than the compatibility between the softening agent and the resin of the developer, so that the softening agent does not bleed even in the developer atmosphere. Become. Therefore, there is an effect that the developer does not adhere to the developer carrier, and a stable image can be obtained with no background stain or density change.

Further, since the surface layer of the developer carrier is made low in hardness by the softening agent, there is an effect that problems such as image destruction and torque are eliminated. Further, since the surface layer of the developer carrying member has a single layer structure, there is an effect that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a developing roller according to an embodiment.

FIG. 2 is a front view showing a schematic configuration of a developing device and a photoconductor of a copying machine used in an image evaluation experiment.

[Explanation of symbols]

 1 Development Roller 1a Core Material 1b Surface Layer

Claims (1)

[Claims] 1. A developer carrying member having a surface layer formed of an elastic body containing a polymer and a softening agent, carrying the developer on the surface and feeding the developer to the image carrying member, wherein the SP value and the softening of the polymer are achieved. A developer carrier, wherein the difference between the SP value of the developer and the SP value of the softener and the resin constituting the developer is smaller.