JP3243901B2 - Conductive roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive roll, and more particularly to a conductive roll requiring low hardness or flexibility and conductivity, such as a developing roll and a charging roll used in an electrophotographic copying machine and a facsimile. Things.

[0002]

2. Description of the Related Art Conductive rolls such as developing rolls and charging rolls used in electrophotographic copying machines and facsimile machines are required to have low hardness or flexibility and conductivity. In order to satisfy these requirements, a conductive layer having a structure in which a rubber layer made of a conductive rubber material having a low hardness is provided on an outer peripheral surface of a predetermined shaft body (core bar) with a predetermined thickness has been conventionally used. Rolls are used. Specifically, as the conductive rubber material, a rubber material such as EPDM, SBR, and NR is mixed with an electronic conductive agent such as carbon black and metal powder, and the volume resistivity is adjusted to 10 ⁶ Ωcm or less. At the same time, a large amount of a softening agent such as a process oil or a liquid polymer is further blended to have a hardness of about 30 ° to 50 ° (Hs: J
ISA) is used which is adjusted to a low level.

However, in a conductive roll provided with only such a rubber layer, for example, when used as a developing roll, a low molecular weight component (softening agent, etc.) in the rubber upon contact with the photosensitive drum is exposed to the surface of the photosensitive drum. In this case, the photosensitive drum is contaminated or rubber sticks to the photosensitive drum, which often impairs the function of the photosensitive drum.

On the other hand, in order to prevent sticking and contamination caused by the rubber layer, it is considered to provide a thin resin coating layer on the roll surface. However, when the resin hardness is high, the roll hardness increases. Problem. For this reason, conventionally, as a material for forming the coating layer, a thermoplastic urethane resin and the like having excellent flexibility, good adhesion to rubber, low tackiness, and excellent storage stability have been provided. Thermoplastic elastomers are used.

However, since the thermoplastic elastomer has a relatively large coefficient of friction, it has a problem that the toner easily and physically adheres. Therefore, a phenomenon (toner filming) in which the toner adheres to and spreads on the roll surface due to long-term or continuous use occurs, and as a result, the toner is not sufficiently charged or the toner is hardly placed on the roll. was there. In addition, since the thermoplastic elastomer has a relatively large network of molecular chains, a long-term use causes a problem that low-molecular-weight components (softeners and the like) in the rubber permeate the coating layer and cause bleeding and blooming. There have been problems that the toner is hardly 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 an object of the present invention is to prevent toner from adhering to a conductive roll and to provide a stable toner for a long period of time. An object of the present invention is to obtain a chargeability, suppress bleed and bloom, and prevent contamination of the photosensitive drum.

[0007]

In order to solve the above problems, the gist of the present invention is to provide a base layer made of a conductive elastic body on an outer peripheral surface of a shaft, To polyurethane thermoplastic elastomers
A material for forming a coating layer obtained by blending an amino resin
A conductive roll provided with a coating layer formed of a polyurethane-based thermoplastic elastomer crosslinked with an amino resin and formed by using the same .

In the present invention, preferably, the coating layer is made conductive by blending an electronic conductive agent or an ionic conductive agent. More preferably, the coating layer is made of an inorganic powder or an organic powder. Matting will result in the blending. Preferably, the coating layer has a thickness of 1 to 100 μm.
It is formed in the thickness of.

[0009]

In summary, in the conductive roll according to the present invention, the coating layer provided on the base layer is formed of a polyurethane thermoplastic elastomer crosslinked with an amino resin. In other words, this resin material reduces the coefficient of friction while effectively suppressing the increase in hardness by amino-crosslinking the polyurethane-based thermoplastic elastomer to increase the crosslinking density, thereby reducing the network of the 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 reduced, the adhesion of the toner is reduced, and the occurrence of toner filming can be prevented. It is possible to obtain stable toner charging properties over a long period of time. Further, since the network of the polyurethane thermoplastic elastomer molecular chains becomes denser, bleeding and blooming of low molecular weight components (softening agent and the like) in the rubber are suppressed, so that the toner chargeability is favorably maintained, Cracks can be prevented and contamination of the photosensitive drum can be prevented.

[0010]

FIG. 1 shows an example of a conductive roll according to the present invention. Here, 10 is a shaft (core), and 12 is a base layer made of a conductive elastic body. The base layer 12 is formed of the same material as that of the related art. For example, an elastic material such as EPDM, SBR, or NR 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 to process oil, liquid polymer, or the like. A large amount of a softening agent having a hardness of about 30 ° to 50 ° (H
s: Materials adjusted to JIS A) are used.

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

The polyurethane thermoplastic elastomer (hereinafter abbreviated as TPU) used as a material for forming the coating layer 14 includes various types such as ether type, ester type and caprolactone type. Can also be used. In addition, in handling, it is preferable to dissolve in a solvent such as a general-purpose organic solvent (ketone or toluene) or water. Further, it may or may not have a hydroxyl group or an amine group at the molecular terminal. And the molecular weight is
When used as a paint, a smaller one is desirable, and usually about 50,000 or less. Also, a filler such as a conductive agent or an inorganic powder or an organic powder described below 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, there is no particular limitation on the amino resin blended to crosslink the TPU, and urea resin,
Any of melamine resin, benzoguanamine resin and the like can be appropriately selected and used. Further, the blending amount is desirably 1 to 20% by weight with respect to TPU from the viewpoint of maintaining flexibility. The crosslinking with the amino resin reduces the friction coefficient of the TPU, reduces the adhesion of the toner, and reduces the network of the TPU molecular chain, thereby effectively suppressing the bleeding and bloom of the low molecular weight component in the rubber. It will be done.

In the conductive roll, the volume resistivity of the coating layer 14 is set so as to prevent the toner from being excessively charged or causing a leak 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
Various known conductive agents are blended and filled as necessary. Specifically, carbon black,
Electronic conductive agents such as graphite, metal powder, and conductive metal oxides, and ionic conductive agents such as polyvalent metal salts and quaternary ammonium salts are used. However, metal powder is not desirable because it is disadvantageous in terms of dispersibility and leak prevention.

Further, when it is desired to improve the transportability of the toner in the conductive roll, the TPU is blended with an inorganic powder or an organic powder, and then filled, so that the roll surface is frosted (the surface is made uneven). ) Is effective, whereby the coefficient of friction can also be advantageously reduced. Specifically, as the inorganic powder, silica,
Powders such as talc, wollastonite (calcium metasilicate), mica, clay, and molybdenum disulfide can be used. As organic powders, powders of nylon resin, fluorine resin, acrylic resin, urethane resin, etc. are used. Among them, those having good solvent resistance are desirable. In addition, matte is to get the effect enough,
Usually, the surface roughness Ra of the coating layer 14 is set to be 0.1 μm or more.
A powder having a particle size of about 1 to 10 μm is blended at a ratio of 50 parts by weight or less to 100 parts by weight of the TPU. If necessary, the filler may be subjected to a surface treatment using a silane coupling agent or the like.

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

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

In the conductive roll having such a configuration, since the coating layer 14 provided on the base layer 12 is formed of an amino-crosslinked polyurethane-based thermoplastic elastomer, the friction coefficient is low. Since toner does not easily adhere, stable toner charging properties can be obtained over a long period of time. Further, since the cross-linking density of the coating layer 14 is high, bleed and bloom of low molecular weight components (such as a softener) from the base layer 12 can be suppressed, and contamination of the photosensitive drum can be prevented.

[0019]

Hereinafter, typical examples of the present invention will be described to clarify the present invention more specifically. However, the present invention imposes no restrictions on the description of such examples. It goes without saying that you don't receive anything. In addition, the present invention, in addition to the following examples, and in addition to the above-described specific description, various modifications based on the knowledge of those skilled in the art, unless departing from the spirit of the present invention,
It should be understood that modifications, improvements and the like can 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
1 part by weight of a vulcanization accelerator (PZ) was blended to prepare a base layer forming material. Using this material, a base layer having a thickness of 3 mm was formed on the outer peripheral surface of a cored bar (diameter: 6 mm) by die molding to prepare a test roll. The base layer had a hardness of 25 ° (Hs: JIS A) and an electric resistance of 1 × 10 ⁴ Ω.

Next, various coating layer forming materials were prepared in accordance with the composition shown in Table 1 below, and methyl ethyl ketone, toluene and n-butanol were respectively mixed in a ratio of 3:
It was dissolved in a solvent mixed at a ratio of 1: 1 (volume ratio) to prepare a coating solution having a predetermined viscosity. However, in Example 4, DMF was used as the solvent because the ether-based TPU did not dissolve in the solvent. Then, using each of the obtained coating liquids, 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) in a thickness shown in Table 1 below, to obtain a desired 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]

With respect to each of the conductive rolls thus obtained, the roll electric resistance (Ω) and the roll hardness (Hs: JIS)
A), the coefficient of friction (μk) was measured, and the deterioration of the toner chargeability with time and the presence or absence of contamination of the photosensitive drum were examined by the following method. 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 roll surface and the core metal.

Deterioration of toner chargeability with time Each conductive roll was attached to an actual machine as a development roll, and the number of rotations until the toner charge amount became 60% of the initial value was examined.

Contamination of photosensitive drum Each conductive roll is pressed against the photosensitive drum (load: 1 k
g) After leaving for one month, observe the photosensitive drum surface,
The presence of contamination was examined.

[0026]

[Table 2]

As is clear from the results in Table 2, in Examples 1 to 9 in which the coating layer was formed with the TPU crosslinked with the amino resin, the coefficient of friction was small and the initial chargeability of the toner was maintained for a long period of time. Can be done. In addition, contamination of the photosensitive drum can be prevented well, and low hardness or flexibility can be obtained. On the other hand, in Comparative Example 1 having only the base layer, the coefficient of friction was large, and the toner charging property was significantly deteriorated by only one rotation, and the photosensitive drum was also contaminated. In Comparative Examples 2 and 3, in which the coating layer was formed with TPU not crosslinked with an amino resin, the coefficient of friction was slightly reduced, and the toner chargeability was slightly improved, but the photosensitive drum was contaminated.

[Brief description of the drawings]

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

[Explanation of symbols]

 10 Shaft 12 Base layer 14 Coating layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-266109 (JP, A) Maki et al., Illustrated Plastic Glossary, Japan, Nikkan Kogyo Shimbun, September 30, 1987, First Edition, 6th edition, Page 514, lines 4 to 10 (58) Fields investigated (Int. Cl. ⁷ , DB name) F16C 13/00 G03G 15/08 501 G03G 15/02 101

Claims (4)

(57) [Claims] 1. A base layer made of a conductive elastic body is provided on an outer peripheral surface of a shaft body, and a poly- layer is provided on an outer peripheral surface of the base layer.
Amino resin for urethane-based thermoplastic elastomer
Formed using the coating layer forming material obtained by blending
A conductive layer provided with a coating layer made of a polyurethane-based thermoplastic elastomer crosslinked with an amino resin. 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 matted by blending an inorganic powder or an organic powder. 4. The conductive roll according to claim 1, wherein said coating layer has a thickness of 1 to 100 μm.