Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-11
2002-10-01
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S496000, C252S511000
Reexamination Certificate
active
06458883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conductive rubber composition, and a manufacturing method and a conductive rubber member thereof. More particularly, it relates to a conductive rubber composition having a low hardness and a low distortion, and exhibiting a small range of variations in its volume specific resistance value and low dependence on environment, and a manufacturing method thereof. Further, it relates to a conductive rubber member obtained using this composition and used in image forming apparatuses such as electrophotographic apparatuses and electrostatic recording apparatuses.
The present invention provides wide application in rubber members used in auto parts, hoses, belts, various rolls for copiers, facsimiles, printers, and the like, footwear, AV devices, OA devices, sealants, and the like, especially, various rubber members used in printers by means of electrophotography, electrostatic recording, and the like.
2. Prior Art
In recent years, semi-conductive elastic rolls have received attention as transferring members, and contact charging members with respect to toners of dry electrophotographic apparatuses with advances in electrophotographic technology. Thus, they are used for developing rolls, transferring rolls, and the like. The semi-conductive members used for such applications are required not only to have prescribed electric resistance values, but also to exhibit a small range of positional variations in electric resistance and low dependence of the electric resistance on the applied voltage, and to vary less in electric resistance when continuously energized. They are further required to have a narrow range of variations in electric resistance values even for environmental changes ranging from low temperature and low humidity to high temperature and high humidity.
In general, conductivity (volume specific resistance value: 1×10
6
&OHgr;·cm or less) is imparted by mixing of carbon black and the like. Accordingly, with a conventional method, the dosage thereof is increased, and hence the viscosity of the system is increased, thereby interfering with the processability and raising the hardness. Consequently, the contact area with a photosensitizing drum decreases, entailing a problem in printing properties. For preventing this, there is known a conductive rubber composition having a prescribed electric resistance and hardness, and suitable as a rubber material for electrically conductive blades used in image forming apparatuses such as electrophotographic copying machines and electrostatic recording apparatuses (Japanese Patent Laid-Open Publication No. Hei-10-87897). This composition contains a vulcanized product of a rubber component A (epoxy containing rubber, and the like.), a rubber component B (SBR, NBR, and the like.) vulcanized by a different mechanism from the case of the rubber component A, and conductive particles. The conductivity and hardness are adjusted in a prescribed range by increasing the concentration of the conductive particles in the rubber component B. However, a considerable portion of the conductive particles transfers toward the rubber component A during kneading. Accordingly, it is difficult to impart the desired conductivity with stability. Further, the composition requires two types of vulcanizing agents each having a different vulcanization mechanism. Thus, two-step vulcanization is required to be carried out, resulting in a complicated procedure. Further, in WO97/03122, there is disclosed a method for manufacturing a conductive rubber composition, which comprises: a step of kneading a rubber component (A), a rubber component (B) to be vulcanized by a different mechanism from the case of the rubber component (A), and the vulcanizing agent of the rubber component (A) to vulcanize only the rubber component (A), and a step of subsequently adding the vulcanizing agent of the rubber component (B), and conductive particles thereto. However, this method also entails insufficient dispersion of the conductive particles, resulting in variations in conductivity.
Further, when a plasticizer and a softening agent are added in large amounts to achieve lower hardness, insufficient dispersion of a conductivity imparting agent unacceptably occurs, resulting in variations in conductivity.
[Problems to be Solved by the Invention]
The present invention has been achieved in view of the foregoing. It is therefore an object of the present invention to provide a conductive rubber composition which not only shows a prescribed electric resistance value, but also varies less in electric resistance, and has a narrow range of variations in electrical resistance values even for environmental changes ranging from low temperature and low humidity to high temperature and high humidity, and is excellent in low hardness and low compression set. It is a further object of the present invention to provide a method for manufacturing such a conductive rubber composition, and a conductive rubber member obtained using this composition.
SUMMARY OF THE INVENTION
The present inventors have conducted a rigorous study, and consequently they have found that the objects of the present invention can be achieved by providing the following conductive rubber composition. That is, the composition contains a crosslinked particulate polymer (A1), an uncrosslinked polymer (A2, generally a linear polymer), and a conductivity imparting agent (B), and the aforesaid conductivity imparting agent (B) is unevenly distributed and the more conductivity imparting agent (B) exist in the uncrosslinked polymer (A2) than in the crosslinked particulate polymer (A1) by starting the kneading at such a temperature that the Moony viscosity of the uncrosslinked polymer is equal to or less than the Moony viscosity of the crosslinked particulate polymer. The present invention has been achieved based on this finding.
A conductive rubber composition, according to a first aspect of the present invention, is characterized by comprising: a crosslinked particulate polymer (A1), an uncrosslinked polymer (A2), and a conductivity imparting agent (B), wherein the aforesaid crosslinked particulate polymer (A1) is a nonpolar polymer, the aforesaid uncrosslinked polymer (A2) is a polar polymer, and the aforesaid conductivity imparting agent (B) is unevenly distributed and the more conductivity imparting agent (B) exist in the uncrosslinked polymer (A2) than in the crosslinked particulate polymer (A1).
A method for manufacturing a conductive rubber composition, according to a second aspect of the present invention, is characterized by comprising: a step of starting the kneading of the composition at such a temperature (T° C.) wherein the following expression (1) holds, the aforesaid composition comprising a crosslinked particulate polymer (A1), an uncrosslinked polymer (A2), and a conductivity imparting agent (B), the crosslinked particulate polymer (A1) being a nonpolar polymer, and the uncrosslinked polymer (A2) being a polar polymer, where the temperature (T° C.) denotes the temperature at which kneading is started, that is, it is not a temperature during kneading, but it virtually represents the set temperature of a kneading machine:
Moony viscosity (T° C.) of the uncrosslinked polymer (A2)/Moony viscosity (T° C.) of the crosslinked particulate polymer
(A1)≦1.0 (1)
Each of these Moony viscosities is individually determined for the crosslinked particulate polymer and the uncrosslinked polymer at the fourth minute after preheating each polymer for 1 minute at a prescribed temperature, and then rotating it for 4 minutes at 2 rpm using a rotor.
A conductive rubber member, according to a third aspect of the present invention, is characterized by being obtained by vulcanizing the aforesaid conductive rubber composition and used in an image forming apparatus.
[Effect of the Invention]
According to the rubber composition of the present invention, there can be provided a conductive rubber member (rubber sheet, and the lik
Kita Kiyonori
Takashima Masaaki
Tsuneyoshi Minoru
Yamazaki Takao
JSR Corporation
Lee Rip A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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