Roll or roller – Concentric layered annulus – Specific composition
Reexamination Certificate
1999-10-25
2001-07-17
Cuda Rosenbaum, I (Department: 3726)
Roll or roller
Concentric layered annulus
Specific composition
C492S046000, C492S053000
Reexamination Certificate
active
06261214
ABSTRACT:
This invention generally relates to heat fixing rolls in heat fixing units in electrostatic recording apparatus such as electrophotographic copiers, printers and facsimile machines and more particularly, to silicone rubber compositions for use in forming the heat fixing rolls.
BACKGROUND OF THE INVENTION
Thermosetting liquid silicone rubber compositions are used in a variety of fields because they are readily moldable and after molding, have improved heat resistance and electrical insulating properties. Recently they are widely used in fixing rolls in plain paper copiers (PPC), laser beam printers and facsimile machines because of their heat resistance and parting properties.
Apparatus utilizing the electrophotographic process require means for transferring a toner image from a photoconductor drum to a paper sheet and fixing the toner image to the sheet. The most commonly used means for fixing the toner image is by passing a toner image-bearing paper sheet between a heating roll and a pressure roll rotating in close contact, thereby thermally fusing the toner image to the sheet for fixation. In this heat fusing process, the response of a copier or printer is generally accelerated by increasing the heat conductivity of the roll material. The roll materials having a high heat conductivity, however, naturally show rapid heat release. The current drive toward size reduction and cost reduction arises a need for a material having a low heat conductivity and hence, good heat insulation.
One typical such material is silicone rubber foam utilizing the low heat conductivity of gas. The silicone rubber foam is typically prepared by adding pyrolytic blowing agents. Alternatively, a silicone rubber composition is molded and cured in such a manner that hydrogen gas may evolve upon curing as a by-product whereby a foam is obtained. However, the addition of pyrolytic blowing agents has the problem that decomposition gases are toxic and odorous. Where a platinum catalyst is used as the curing catalyst, undesirably the blowing agent acts to retard curing. The method of utilizing hydrogen gas evolving upon curing suffers from the problems that hydrogen gas is explosive and the uncured composition requires careful handling during storage. Where silicone rubber foam is formed by injection molding a silicone rubber composition in a mold whereby the rubber is expanded in the mold, it is difficult to produce a silicone rubber foam having uniform micro-cells.
SUMMARY OF THE INVENTION
An object of the invention is to provide a silicone rubber composition which cures into silicone rubber having a low heat conductivity without raising the above-mentioned problems, and thus suitable for use in heat fixing rolls. Another object of the invention is to provide a heat fixing roll using the silicone rubber composition.
In a first aspect, the invention provides a silicone rubber composition comprising 100 parts by weight of a thermosetting organopolysiloxane composition and 0.1 to 200 parts by weight of a hollow filler having a mean particle size of up to 200 &mgr;m. This composition cures into silicone rubber having a low heat conductivity and good heat insulation and thus suitable as a silicone rubber layer on a heat fixing roll.
In a second aspect, the invention provides a heat fixing roll comprising a roll shaft, a silicone rubber layer formed on the outer circumferential surface of the shaft, and optionally a fluoro-resin layer surrounding the silicone rubber layer. The silicone rubber layer is a cured product of the silicone rubber composition defined above.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The silicone rubber composition for a heat fixing roll according to the invention is based on a thermosetting organopolysiloxane composition, in which a hollow filler is blended. The hollow filler acts such that gas-filled cells are created in a cured part to reduce the heat conductivity thereof like sponge rubber.
Exemplary hollow fillers include glass balloons, silica balloons, carbon balloons, alumina balloons, zirconia balloons, shirasu (or silicious) balloons, and plastic balloons such as phenolic resin balloons, acrylonitrile balloons, and vinylidene chloride resin balloons. Preferably, the hollow filler is formed of such a material that the hollow filler itself may have elasticity. Therefore, the preferred hollow filler is in the form of microballoons of a thermoplastic resin, especially microballoons formed of a homopolymer of vinylidene chloride, acrylonitrile, methacrylonitrile, an acrylate, or a methacrylate, or a copolymer of two or more of these monomers. An inorganic filler may be attached to a surface of such a hollow resin filler for the purpose of imparting strength thereto.
In order that the composition be reduced in heat conductivity to a full extent, the hollow filler should preferably have a true specific gravity of 0.01 to 1.0, more preferably 0.01 to 0.5, and especially 0.02 to 0.5. A filler with too low a true specific gravity would be difficult to formulate and handle, have an insufficient pressure resistance or strength to prevent crushing upon molding, and provide an insufficient weight reduction and heat conductivity reduction. A too high true specific gravity means that the material portion (or wall) of the hollow filler accounts for a greater proportion of the filler, which would provide an insufficient decline of heat conductivity.
The hollow filler In the form of microballoons has a mean particle size of up to 200 &mgr;m, preferably up to 150 &mgr;m, and more preferably up to 90 &mgr;m. Microballoons having a too large mean particle size can be crushed by the injection pressure during molding, leading to the undesired problems that the filled composition has an increased heat conductivity and an increased surface roughness when molded into a roll. The lower limit of the mean particle size of the hollow filler is not critical although it is usually 10 &mgr;m. and especially 20 &mgr;m. The mean particle size can be determined as a weight average value (or median diameter) by laser light diffractometry.
An appropriate amount of the hollow filler blended is 0.1 to 200 parts, preferably 0.2 to 150 parts, and more preferably 0.5 to 100 parts by weight per 100 parts by weight of the thermosetting organopolysiloxane composition. The hollow filler is preferably blended in an amount of 10 to 80% by volume, especially 15 to 75% by volume of the silicone rubber composition. A too low volumetric proportion of the hollow filler would lead to an insufficient decline of heat conductivity. With a too high volumetric proportion of the hollow filler, blending is difficult, and molded parts would lose rubber elasticity and become brittle.
The thermosetting organopolysiloxane composition may be any well-known thermosetting organopolysiloxane composition used in forming a silicone rubber layer on a heat fixing roll, which may be either of the organic peroxide curing type or of the addition reaction curing type. Preferred is a thermosetting organopolysiloxane composition of the addition reaction curing type, comprising as main components, (A) 100 parts by weight of an organopolysiloxane containing at least two alkenyl groups each attached to a silicon atom in a molecule, (B) 0.1 to 50 parts by weight of an organohydrogenpolysiloxane containing at least two hydrogen atoms each attached to a silicon atom in a molecule, and (C) a catalytic amount of an addition reaction catalyst.
Component (A) is an organopolysiloxane having on the average at least two alkenyl radicals in a molecule, represented by the average compositional formula (1).
R
1
a
SiO
(4−a)/2
(1)
Herein, R
1
is a substituted or unsubstituted monovalent hydrocarbon radical having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms. The R
1
radicals may be the same or different. Letter a is a positive number of 1.5 to 2.8, preferably 1.8 to 2.5, and more preferably 1.95 to 2.05.
Examples of the substituted or unsubstituted monovalent hydrocarbon radical attached to a silicon atom represented by R
1
include alkyl radicals su
Birch & Stewart Kolasch & Birch, LLP
Cuda Rosenbaum I
Shin-Etsu Chemical Co. , Ltd.
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