JPH11143215A - Developing roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing roller at least having two-layer structure of a layer formed of high polymer material and a layer formed of material in which conductive filler is mainly blended on a conductive base substance, and capable of obtaining a high quality image at an initial stage and with time. SOLUTION: A 1st layer 4 on a core bar 3 is formed of conductive composite fiber 1 and a 2nd layer 5 being an outer periphery is formed of the conductive composite fiber 2. The fiber 1 is obtained by coating the periphery of the high polymer meterial (base polymer) (a) with a conductive composition (matrix polymer + conductive filler) (b). The fiber 2 is obtained by coating the periphery (surface) of the conductive composition (b) with the high polymer material (a). In the 1st layer 4, the conductive fillers in the surface layer of the fiber 1 come into contact with each other, so that resistance in a radial direction is controlled to be low. In the 2nd layer 5, the conductive fillers exist on an inner surface side, so that they do not come into contact with each other among the fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roller and a toner carrier used in an electrophotographic developing apparatus such as a copying machine, a facsimile, a laser printer, and the like. More specifically, a toner or a developer directly contacts the roller surface. The present invention relates to a dielectric developing roller having characteristics suitable for a direct contact type electrophotographic developing method without using a sleeve.

[0002]

2. Description of the Related Art Generally, a developing roller used in a copying machine, a facsimile or the like includes a conductive substrate, that is, a core metal and a dielectric layer coated around the core metal. Prepare. The dielectric layer contains at least one kind of polymer compound and a conductive filler. For such a polymer material, a thermoplastic resin is generally used,
Examples include polypropylene, polyester, polyurethane, and polyolefin. The characteristics required for the resin include charging characteristics with the toner, releasability of the toner (filming / fixing state of the toner to the toner carrier), mechanical strength, workability, and filling property when a filler is added. , Determined by the uniform dispersibility. Further, metal oxides such as carbon black, titanium oxide, and iron oxide are often used for the conductive filler. These materials are prepared into a compound by adding a resin (powder or compound), a filler and, if necessary, an additive, mixing and kneading the mixture, granulating the mixture, and granulating the mixture. The compound is formed into a roller shape by extrusion molding or injection molding. On the other hand, in the case of forming using a coating, a resin and a filler are dispersed in a solvent and a coating film is formed by a method such as spray coating or dipping.

[0003] Such a developing roller has a function of carrying the toner to the latent image carrier while carrying the toner by being rotationally driven. Most of the developing rollers used in the one-component developing device using a magnetic toner are formed by coating a resin material containing a magnetic material such as ferrite or a dielectric material such as a rubber material on the surface of the core metal as a coating layer. It has a structure having a plurality of magnetic poles by being magnetized. The developing roller used in a one-component developing device using a non-magnetic toner has almost the same structure. However, since the developing roller may be non-magnetic, a resin material or a rubber material can be used alone (including compounding of additives).
Alternatively, a dielectric material such as a resin material or a rubber material containing a nonmagnetic filler such as carbon as a resistance control agent is coated on the core metal surface as a coating layer. In some cases, a structure in which several layers are laminated by painting or the like is used.

[0004] Further, such a developing roller carries the toner due to frictional charging of the toner and magnetic characteristics (only in the case of magnetic toner), and conveys the toner to a position facing a photoreceptor (latent image carrier) to form a latent image. The toner is transferred to the electrostatic latent image portion formed on the carrier, and at this time, a bias may be applied to the developing roller. From such a function, the developing roller has predetermined electrical characteristics, specifically, volume resistivity and dielectric constant,
When a magnetic toner is used, magnetic properties are required. Also, the shape to carry the toner directly on the developing roller,
Specifically, the outer diameter, runout, surface roughness, undulation, and the like are required. Regardless of whether magnetic or non-magnetic toner is used, electrical characteristics are the most important of the above characteristics.

Conventionally, in the radial direction (thickness direction) of the developing roller
The electrical characteristics of the roller could be met by making them uniform, but in order to satisfy the current demand for high image quality, the electrical characteristics required for the surface layer and the inner layer are different, and specifically, developing rollers with different resistances in the radial direction are required. Has been requested. More specifically, in order to achieve high image quality, it is necessary to generate a minute electric field on the developing roller. To this end, the surface resistance of the developing roller must be higher in the radial direction than the resistance of the conductive substrate. Is desirable.

[0006] As a countermeasure, the surface layer is required to have a medium to high resistance, and the inner layer is required to have a low to medium resistance. Therefore, for the inner layer, conductive filler is mixed with resin or rubber to reduce
A roller having a two- or more-layer structure in which the surface layer is formed of only resin, rubber, a charge control agent, or the like, or a material slightly filled with a conductive filler to have a medium to high resistance. It has been demanded. For example, JP-A-2-226
In the antistatic developing roll disclosed in Japanese Patent No. 275, an elastic layer is provided on the outer periphery of a conductive metal core, and a thermoplastic resin layer in which a polyalkylene ether copolymer is dispersed thereon is further provided thereon. A developing roller in which an antistatic fiber layer is laminated has been proposed.

In order to form such a multilayer structure, painting is generally used in many cases, but there are many problems of durability (wear, peeling, etc. with time) of the coating film, many processing steps, and high cost. There are problems such as. On the other hand, at present, a single-layer (single-layer) structure can be reduced in cost because the number of processing steps is small, but it is difficult to change the resistance in the radial direction as in a multi-layer structure.

In general, the first layer (on the metal core) of a multi-layer structure as well as a single-layer structure is formed into a roller shape by injection molding, extrusion molding, or the like. In this case, a compound (pellet) is formed. Are often used. The compound is prepared by mixing and kneading a base resin (powder or compound) and a filler (powder). For this reason, how to uniformly disperse the filler in the base resin at the time of mixing and kneading is an important point that affects the control of electrical characteristics such as resistance. This applies not only to resin but also to rubber. If the dispersion state of the filler is non-uniform, a portion having a low resistance or a high resistance is partially generated, and the amount of toner adhered and the amount of charge become non-uniform, leading to uneven density on an image. In addition, due to the uneven dispersion of the filler, the stress of the resin is relaxed with the passage of time, whereby the adhesion between the fillers is different, and the resistance varies with time, and the variation is partially different. As a result, as described above, the toner characteristics, that is, the image characteristics, change over time.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a developing roller capable of obtaining a high-quality image at an early stage and over time.

[0010]

According to the first aspect of the present invention, there is provided a developing roller for achieving the above object.
In a developing roller having at least a two-layer structure of a layer of a polymer material on a conductive substrate and a layer formed of a material mainly containing a conductive filler, the first layer on the conductive substrate has a high level. A first composite conductive fiber formed by coating a conductive polymer material containing a conductive filler on a surface layer of a molecular material, and a second layer on the first layer is formed of a conductive polymer opposite to the first layer. Characterized by being formed of a second composite conductive fiber having a surface layer coated with a polymer material.

According to a second aspect of the present invention, both the first layer and the second layer are formed by mixing at least the first composite conductive fiber and the second composite conductive fiber,
The mixing ratio of the second composite conductive fiber in the second layer is larger than that in the first layer.

According to a third aspect of the present invention, the polymer material used for the first composite conductive fiber has a higher melting point than the polymer material used for the second composite conductive fiber. And

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the embodiment of the developing roller according to the present invention, conductive composite fibers are used in place of the above-mentioned conventional materials. In the conductive composite material, a conductive filler is first mixed with a matrix polymer to form a conductive composition. Further, the base polymer is kneaded and arranged so as to have a required structure, and wet spinning or melt spinning is performed to produce the base polymer. As the matrix polymer, polyethylene, nylon, or the like is used, and as the conductive filler, a metal oxide such as carbon black, titanium oxide, or iron oxide is used as in the case of the above-described conventional filler. A typical cross-sectional structure of the completed fiber is shown in FIGS.

The conductive composite fiber 1 shown in FIG. 1 has a conductive composition (matrix polymer + conductive filler) b coated around (surface) a polymer material (base polymer) a. On the other hand, the conductive conjugate fiber 2 shown in FIG. 2 has the polymer material a coated around the conductive composition b (surface). Therefore, the conductive composite fiber 1 shown in FIG. 1 has a lower surface resistance than the conductive composite fiber 2 shown in FIG.

In the embodiment of the developing roller according to the present invention shown in FIG. 3, the first layer 4 on the metal core 3 is formed of the conductive conjugate fiber 1, and the outer second layer 5 is formed of the conductive conjugate fiber 2. Is formed. In this structure, the first layer 4 is made of the conductive composite fiber 1
Since the conductive filler (conductive composition) in the surface layer of the above-mentioned layer contacts each other, the resistance in the radial direction can be controlled to be low. On the other hand, the second
The layer 5 has a structure in which, unlike the first layer 4, the conductive filler is on the inside and basically does not come into contact between the fibers.
Of course, when the second layer 5 is formed, the base polymer on the fiber surface is melted to form the roller surface, so that the conductive fillers may come into contact with each other.

Further, since the first layer 4 and the second layer 5 use fibers, the compound makes it possible to uniformly disperse the conductive filler and the polymer material. Compounds that are mixed and kneaded with powder should have conductive fillers finely dispersed in the polymer, but on the contrary, they tend to be uneven and the conductive fillers are sheared by the pressure during kneading. Because there are many. On the other hand, the conductive composite fibers 1 and 2
It is difficult to disperse the conductive filler finer than the compound, but since the conductive filler is already uniformly arranged in the polymer, when forming the layer of the developing roller, disperse it more uniformly than the compound. Is possible.

In the conductive composite fibers 1 and 2, since the conductive fillers are uniformly arranged, even if the resin shrinks due to stress relaxation or the like over time, the positional relationship between the fillers is hardly affected. If the resistance changes little. For this reason, toner characteristics, that is, image characteristics are less likely to fluctuate.

As an embodiment of the present invention, there is an embodiment in which conductive composite fibers 1 and 2 are mixed and used. By doing so, the resistance can be finely adjusted, and by increasing the mixing ratio of the conductive composite fiber 2 to the second layer 5 from the first layer 4, the surface resistance of the developing roller is higher than that of the core metal 3 side. Can,
Fine adjustment according to the toner characteristics is possible.

The method for forming the first layer 4 and the second layer 5 is as follows.
A method of winding the conductive composite fibers 1 and 2 around the cored bar 3 and then heating (using a heater, induction heating, or the like) the conductive composite fibers 1 and 2 in a mold or the like to fix the fibers together, A method of pulverizing and treating the same as a compound, melting the fibers by extrusion molding and injection molding, and forming a roller shape can be adopted. At this time, if the first layer 4 has a higher melting point than the polymer material of the second layer 5, the first layer 4 is melted when the conductive composite fiber 2 is melted to form the second layer 5. It can be formed without breaking, that is, without breaking.

[0020]

According to the first aspect of the present invention, as described above, the first layer on the conductive substrate is formed by covering the surface layer of the polymer material with the conductive polymer material containing the conductive filler. A second composite conductive fiber formed of the composite conductive fiber of the first aspect, wherein the second layer on the first layer is formed by coating the surface layer of the conductive polymer with a polymer material on the opposite side to the first layer. Therefore, conductive composite fibers having different structures are used for the first layer on the conductive substrate side and the second layer on the surface of the first layer, and the resistance of the first layer is higher than that of the second layer, and It is possible to control the uniform resistance even locally, and there is an effect that the uniformity and stability of the resistance at the initial stage and over time, that is, a high quality image can be obtained.

In the developing roller according to the present invention, both the first layer and the second layer are formed by mixing at least the first composite conductive fiber and the second composite conductive fiber, and
Since the mixture ratio of the second composite conductive fiber in the second layer is larger than that of the second layer, the mixture ratio of the two types of conductive composite fibers is changed and used for both the first and second layers. In addition to the above-mentioned common effect, there is an effect that the resistance of the layer can be finely adjusted by the mixing ratio, and a more stable image can be obtained.

In the developing roller according to the third aspect, the polymer material used for the first composite conductive fiber has a higher melting point than the polymer material used for the second composite conductive fiber. In addition to the common effect, when the conductive composite fiber is heated and melted to form the second layer on the first layer (extrusion molding, injection molding, etc.), the conductive composite fiber of the first layer does not melt, It is possible to form a multilayer structure without breaking the layer structure, to reduce the number of processing steps, and to produce at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first conductive conjugate fiber used in an embodiment of a developing roller according to the present invention.

FIG. 2 is a cross-sectional view of a second conductive conjugate fiber used in an embodiment of the developing roller according to the present invention.

3A and 3B are a cross-sectional view and an enlarged cross-sectional view illustrating an embodiment of a developing roller according to the present invention.

[Explanation of symbols]

1, 2 Conductive composite fiber a Polymer material (base polymer) b Conductive composition (matrix polymer + conductive filler) 3 Core 4 First layer 5 Second layer

Claims (3)

[Claims] 1. A developing roller having at least a two-layer structure of a layer of a polymer material on a conductive substrate and a layer formed of a material mainly mixed with a conductive filler, The first layer is formed of a first composite conductive fiber in which a surface of a polymer material is coated with a conductive polymer material containing a conductive filler, and the second layer on the first layer is the same as the first layer. Conversely, a developing roller formed of a second composite conductive fiber in which a polymer material is coated on a surface layer of a conductive polymer. 2. The first layer and the second layer are both formed by mixing and mixing at least the first composite conductive fiber and the second composite conductive fiber, and 2. The developing roller according to claim 1, wherein a mixing ratio of said second composite conductive fiber in said second layer is increased. 3. The polymer material used for the first composite conductive fiber has a higher melting point than the polymer material used for the second composite conductive fiber.
Or 2 developing roller.