JPH0754836A - Conductive roll - Google Patents

Abstract

PURPOSE:To provide a toner charging property stably for a long period while restraining the bleed and bloom of low molecular weight component from a basic layer to prevent a photosensitive drum from being contaminated by preventing a conductive roll from the adhesion of toner thereto. CONSTITUTION:While a basic layer 12 made of a conductive elastic body is provided on the outer peripheral surface of a shaft body 10, a coating layer 14 made of polyurethane thermoplastic elastomer cross-linked by amino resin is provided on the outer peripheral surface of the basic layer 12.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive roll, and more particularly to a conductive roll which is required to have low hardness or flexibility and conductivity such as a developing roll and a charging roll used in an electrophotographic copying machine or a facsimile. It is a thing.

[0002]

BACKGROUND ART A conductive roll such as a developing roll or a charging roll used in an electrophotographic copying machine or a facsimile is required to have low hardness or flexibility and conductivity. In order to satisfy these requirements, conventionally, a rubber layer made of a conductive rubber material having a low hardness is provided on the outer peripheral surface of a predetermined shaft body (core bar) with a predetermined thickness to provide a conductive structure. Rolls are used. Specifically, as the conductive rubber material, a rubber material such as EPDM, SBR, NR, etc. is blended with an electronic conductive agent such as carbon black or metal powder to adjust the volume resistivity to 10 ⁶ Ωcm or less. At the same time, a large amount of a softening agent such as process oil and liquid polymer is added to have a hardness of about 30 ° to 50 ° (Hs: J
The one adjusted to as low as ISA) is used.

However, in the case of a conductive roll provided with only such a rubber layer, for example, when it is used as a developing roll, a low molecular weight component (softening agent, etc.) in the rubber is brought into contact with the photosensitive drum when the photosensitive roll surface is contacted. In many cases, the function of the photosensitive drum is hindered because the photosensitive drum is contaminated and the rubber adheres to the photosensitive drum.

On the other hand, it has been considered to provide a thin resin coating layer on the roll surface in order to prevent adhesion and contamination due to the rubber layer, but when the resin hardness is high, the roll hardness also increases. There is a problem. Therefore, conventionally, as a material for forming the coating layer, in addition to being excellent in flexibility, the adhesiveness with rubber is good, the tackiness is low, and the storage stability is excellent. A thermoplastic elastomer is used.

However, since the thermoplastic elastomer has a relatively large coefficient of friction, it has a problem that the toner is liable to thermally and physically adhere. Therefore, a phenomenon in which the toner adheres to the surface of the roll and spreads (toner filming) occurs due to long-term or continuous use, and as a result, the toner is not sufficiently charged or the toner is hard to be placed on the roll. was there. Further, since the thermoplastic elastomer has a relatively large network of molecular chains, there is a problem that a low molecular weight component (softening agent, etc.) in the rubber permeates the coating layer due to long-term use, causing bleeding and blooming. There are problems that the toner is difficult to be charged, cracks are generated on the roll surface, and the surface of the photosensitive drum is contaminated.

[0006]

The present invention has been made in view of such circumstances, and a problem to be solved by the present invention is to prevent toner from adhering to a conductive roll and to stabilize toner for a long period of time. It is to obtain the charging property and suppress the bleeding and blooming to prevent the photosensitive drum from being contaminated.

[0007]

In order to solve the above problems, the gist of the present invention is that a base layer made of a conductive elastic body is provided on the outer peripheral surface of a shaft, and the outer peripheral surface of the base layer is provided. And a coating layer made of a thermoplastic polyurethane elastomer cross-linked with an amino resin is provided on the conductive roll.

In the present invention, preferably, the coating layer is made conductive by blending an electronic conductive agent or an ionic conductive agent, and more preferably, the coating layer is made of an inorganic powder or an organic powder. It will be matte depending on the composition. And, preferably, the coating layer has a thickness of 1 to 100 μm.
Will be formed.

[0009]

FUNCTIONS AND EFFECTS In summary, in the conductive roll according to the present invention, the coating layer provided on the base layer is formed of a polyurethane-based thermoplastic elastomer crosslinked with an amino resin. That is, this resin material amino-crosslinks the polyurethane-based thermoplastic elastomer to increase the crosslink density, thereby effectively suppressing an increase in hardness, lowering the coefficient of friction, and forming a network of polyurethane-based thermoplastic elastomer molecular chains. It is more dense. Therefore, in the conductive roll according to the present invention, since the friction coefficient of the coating layer is lowered, the adhesion of the toner is reduced and the occurrence of toner filming can be prevented, so that the deterioration of the toner charging property with time is reduced, It is possible to obtain stable toner chargeability for a long period of time. In addition, since the network of the polyurethane-based thermoplastic elastomer molecular chain becomes dense, bleeding and bloom of low-molecular weight components (softening agent etc.) in the rubber are suppressed, and toner chargeability is maintained well, and The generation of cracks can be prevented, and further, the contamination of the photosensitive drum can be prevented.

[0010]

SPECIFIC STRUCTURE By the way, FIG. 1 shows an example of a conductive roll according to the present invention. Here, 10 is a shaft body (core metal), and 12 is a base layer made of a conductive elastic body. The base layer 12 is made of the same material as the conventional one. For example, an elastic material such as EPDM, SBR, NR, etc. is mixed with an electronic conductive agent such as carbon black or metal powder to adjust the volume resistivity to 10 ⁶ Ωcm or less, and further process oil or liquid polymer. A large amount of the softening agent is blended to have a hardness of about 30 ° to 50 ° (H
s: A material adjusted to as low as JIS A) is used.

On the outer peripheral surface of the base layer 12,
Thus, the coating layer 14 made of the amino-crosslinked polyurethane-based thermoplastic elastomer is formed.

Here, as the thermoplastic polyurethane elastomer (hereinafter abbreviated as TPU) used as the material for forming the coating layer 14, there are various types such as ether type, ester type, caprolactone type, and any of them. Momo can be used. In terms of handling, a general-purpose organic solvent (ketone-based or toluene-based) or a solvent dissolved in a solvent such as water is preferable. Further, it may or may not have a hydroxyl group or an amine group at the molecular end. And the molecular weight is
When it is used as a paint, the smaller the size is, the more preferable it is usually about 50,000 or less. Further, a filler such as a conductive agent or an inorganic powder or an organic powder described later is blended,
In the case of dispersing, it is desirable that the molecular weight is large, and it is usually 10,000 or more.

On the other hand, the amino resin compounded to crosslink the TPU is not particularly limited, and urea resin,
Any of melamine resin, benzoguanamine resin and the like can be appropriately selected and used. Further, the blending amount thereof is preferably 1 to 20% by weight with respect to TPU from the viewpoint of maintaining flexibility. By the cross-linking with the amino resin, the friction coefficient of TPU is lowered, the adhesion of toner is reduced, and the network of TPU molecular chain is reduced, so that bleeding and bloom of low molecular weight components in rubber are effectively suppressed. Will be done.

Further, in the conductive roll, the volume resistivity: Rv of the coating layer 14 is prevented so that the toner is not excessively charged or leaks when a voltage is applied.
Is 10 ² to 10 ¹⁰ Ωcm, more preferably 10 ⁴ to 10 ⁸
It is desirable to adjust to Ωcm. Therefore, the TPU
If necessary, various known conductive agents may be blended and filled in. Specifically, carbon black,
Electronic conductive agents such as graphite, metal powder and conductive metal oxides, and ion conductive agents such as polyvalent metal salts and quaternary ammonium salts are used. However, metal powder is not very desirable because it is disadvantageous in terms of dispersibility and leak prevention.

Further, in order to improve the transportability of the toner in the conductive roll, the TPU is blended with an inorganic powder or an organic powder to fill the roll surface to make the surface of the roll matte (the surface is made uneven). ) Is effective, whereby the coefficient of friction can also be advantageously reduced. Specifically, as the inorganic powder, silica,
Powders of talc, wollastonite (calcium metasilicate), mica, clay, molybdenum disulfide, etc. can be used. As the organic powder, nylon resin, fluororesin, acrylic resin, urethane resin, etc. powder can be used. Among them, those having good solvent resistance are desirable. In addition, in order to obtain the effect sufficiently,
Usually, the surface roughness Ra of the coating layer 14 is made to be 0.1 μm or more.
The powder having a particle size of about 1 to 10 μm is blended at a ratio of 50 parts by weight or less with respect to 100 parts by weight of TPU. If necessary, the filler may be surface-treated with a silane coupling agent or the like.

In order to obtain the conductive roll shown in FIG. 1, first, the conductive elastic body is used to form the base layer 12 on the outer peripheral surface of the shaft body 10 by a known molding method such as mold molding. To mold. Then, using the TPU material,
The coating layer 14 is formed on the outer peripheral surface of the base layer 12 by an extrusion method or a coating method such as dipping.

The thickness of each layer of the conductive roll is appropriately determined depending on the use of the roll, but the base layer 12 is usually formed to have a thickness of about 2 to 10 mm. On the other hand, if the coating layer 14 is too thin, the effect of the filler and the effect of suppressing the bleeding and blooming due to the mesh are reduced, while if it is too thick, the roll hardness becomes too hard and the amount of contact with the photoreceptor decreases. Usually, it is formed to have a thickness of 1 to 100 μm, preferably about 10 to 50 μm.

In the conductive roll having such a structure, the coating layer 14 provided on the base layer 12 is formed of the amino-crosslinked polyurethane-based thermoplastic elastomer, so that the friction coefficient is low. Since the toner does not easily adhere, it is possible to obtain a stable toner charging property for a long period of time. In addition, since the coating layer 14 has a high crosslink density, bleeding and blooming of low molecular weight components (softening agent, etc.) from the base layer 12 can be suppressed, and contamination of the photosensitive drum can be prevented.

[0019]

EXAMPLES Hereinafter, representative examples of the present invention will be shown to clarify the present invention in more detail. However, the present invention is not limited by the description of such examples. Needless to say, it is not something to receive. Further, in addition to the following specific examples, in addition to the following embodiments, the present invention includes various modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention.
It should be understood that modifications, improvements, etc. may be made.

Examples 1 to 9 and Comparative Examples 1 to 3 First, NBR: 100 parts by weight, liquid NBR: 10 parts by weight, zinc white: 5 parts by weight, stearic acid: 1 part by weight, acetylene black: 50 parts by weight, Plasticizer (DOP): 70
Parts by weight, sulfur: 0.5 parts by weight, vulcanization accelerator (DM): 2
By weight, a vulcanization accelerator (PZ): 1 part by weight was mixed to prepare a base layer forming material. Then, using this material, a base layer having a thickness of 3 mm was formed on the outer peripheral surface of the core metal (diameter: 6 mm) by die molding, and a test roll was produced. The hardness of the base layer was 25 ° (Hs: JIS A) and the electric resistance was 1 × 10 ⁴ Ω.

Next, various materials for forming the coating layer were prepared according to the blending composition shown in Table 1 below, and methyl ethyl ketone, toluene and n-butanol were added in the amount of 3: 3, respectively.
It was dissolved in a solvent mixed at a ratio of 1: 1 (volume ratio) to prepare a coating liquid having a predetermined viscosity. However, in Example 4 only, DMF was used as the solvent because the ether-based TPU was not soluble in the solvent. Then, using each of the obtained coating liquid, by a known dipping method,
A coating layer was formed on the outer peripheral surface of the test roll (on the outer peripheral surface of the base layer) with the thickness shown in Table 1 below to obtain a target conductive roll. However, in Comparative Example 1, the coating roll was not provided and the test roll was left as it was. The electric resistance of the coating layer of each conductive roll was as shown in Table 1 below.

[0022]

[Table 1]

For each conductive roll thus obtained, the roll electrical resistance (Ω) and roll hardness (Hs: JIS
A) and the friction coefficient (μk) were measured, and the deterioration of the toner charging property with time and the presence or absence of contamination of the photosensitive drum were examined by the methods described below, and the results are shown in Table 2 below. The electric resistance of the roll is the electric resistance between the 1 cm ² electrode formed on the surface of the roll and the core metal.

Deterioration of Toner Charging Property with Time Each conductive roll was attached as a developing roll to an actual machine, and the number of rotations until the toner charge amount reached 60% of the initial amount was examined.

Contamination of the photosensitive drum Press each conductive roll against the photosensitive drum (load: 1 k
g) After leaving it for 1 month, observe the surface of the photosensitive drum,
The presence or absence of contamination was investigated.

[0026]

[Table 2]

As is clear from the results of Table 2, in Examples 1 to 9 in which the coating layer was formed of TPU crosslinked with the amino resin, the friction coefficient was small and the initial toner chargeability was maintained for a long time. Can be done. Further, the contamination of the photosensitive drum is favorably prevented, and the low hardness and the flexibility are also favorable. On the other hand, in Comparative Example 1 including only the base layer, the friction coefficient was large, and the toner charging property was significantly deteriorated after only one rotation, and the photosensitive drum was also contaminated. Further, in Comparative Examples 2 and 3 in which the coating layer was formed of TPU that was not crosslinked with the amino resin, the friction coefficient was slightly small and the toner charging property was slightly improved, but the photosensitive drum was contaminated.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an example of a conductive roll according to the present invention.

[Explanation of symbols]

 10 Shaft 12 Base layer 14 Coating layer

Claims (4)

[Claims] 1. A base layer made of a conductive elastic body is provided on the outer peripheral surface of a shaft body, and a coating layer made of a polyurethane-based thermoplastic elastomer crosslinked with an amino resin is provided on the outer peripheral surface of the base layer. Conductive roll characterized in that 2. The conductive roll according to claim 1, wherein the coating layer is made conductive by blending an electronic conductive agent or an ionic conductive agent. 3. The conductive roll according to claim 1, wherein the coating layer is matte by blending an inorganic powder or an organic powder. 4. The conductive roll according to claim 1, wherein the coating layer has a thickness of 1 to 100 μm.