JPH11158377A - Silicone rubber composition and fixing roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition having a low hardness, excellent in thermal conductivity, further heat resistance and low compression set properties and suitable as a covering material for a fixing roll by compounding a thermosetting type silicone rubber with zinc oxide having a specified particle diameter. SOLUTION: This composition is obtained by compounding (A) 100 pts.wt. thermosetting type silicone rubber with (B) 100-1,000 pts.wt. zinc oxide having 2-50 μm average particle diameter. The component A is usually composed of a polyorganosiloxane which is a base polymer, a curing agent and, as necessary, a silica powder, an additive, etc. For example, dicumyl peroxide is preferred as the curing agent from the viewpoint of corrosiveness for metals when utilizing a cross-linking method with an organic peroxide vulcanizing agent. The zinc oxide treated with a silane-based or a titanate-based coupling agent, stearic acid, etc., is preferably used as the component B from the viewpoint of the low compression set properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermally conductive silicone rubber composition, and more particularly, to a silicone rubber composition having low hardness and excellent thermal conductivity and heat resistance, which is used for fixing toner in electrophotographic equipment. An object of the present invention is to provide a silicone rubber composition capable of obtaining a long-term stable image when used as a coating material for a roll.

[0002]

Technical background of the invention and its problems Silicone rubber is
It has excellent electrical insulation, heat resistance, weather resistance, and flame retardancy, and has been used as a coating material for a fixing roll or a pressure roll of a fixing unit of a copying machine or a laser beam printer. In particular, recently, with the spread of color copying, the hardness of the fixing roll has also been required to be low, and a type in which a fluororesin is coated on a thermally conductive silicone rubber, which cannot be achieved with conventional metals or fluororesins, has been widely adopted. ing. The silicone rubber used here is required to have low hardness and high thermal conductivity, and furthermore, to be constantly exposed to a high temperature of 150 ° C. to 200 ° C., to be required heat resistance and low compression set. As the silicone rubber, those proposed in JP-A-3-221982, JP-B-64-25993, and JP-B-6-43820 have been used. These conventionally used silicone rubbers contain silica, alumina, magnesia or the like as a filler. However, silica has a problem that it has a low thermal conductivity and cannot be reduced in hardness when highly filled. In addition, magnesia has a problem that the surface is hydrated by moisture in the air and the heat resistance of the silicone rubber is reduced. Furthermore,
Although the cause of alumina is unknown, it has been difficult to reduce the compression set. Japanese Patent Application Laid-Open No. 8-12889 proposes a conductive metal oxide as a filler, and includes conductive zinc oxide. Among them, tin oxide or the like is used to impart conductivity. The solution has a problem that tin adversely affects the heat resistance of the silicone rubber. Further, in order to impart conductivity, the particle diameter is 0.01
Although it is required that the particle size is about 1 μm, the addition of zinc oxide having such a particle size is not suitable for this application because it has an adverse effect on lowering the hardness and compression set of silicone rubber.

[0003]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned problems of the prior art, and has a low hardness, excellent thermal conductivity, excellent heat resistance and low compression set, and a coating of a fixing roll. It is intended to provide a silicone rubber composition suitably used as a material.

[0004]

The present inventors have conducted intensive studies to provide a silicone rubber composition suitable for coating a fixing roll with respect to the above-mentioned problems, and as a result, it has been found that a specific zinc oxide can be added to a heat-curable silicone rubber. They have found that they are extremely effective, and have completed the present invention. That is, the present invention provides a silicone rubber composition comprising 100 to 1000 parts by weight of zinc oxide having an average particle diameter of 2 to 50 μm per 100 parts by weight of a heat-curable silicone rubber, and the silicone rubber composition. Is a fixing roll characterized in that a fixing material is used as a coating material.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The heat-curable silicone rubber used in the present invention is not particularly limited as long as it is a generally used heat-curable silicone rubber, and a polyorganosiloxane serving as a base polymer and silica powder, an additive, a curing agent, etc. , But need not contain silica powder or additives. The polyorganosiloxane of the base polymer is an average unit formula: R ¹ _a SiO _{(4-a) / 2} (where R ¹ is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02), which is mainly used in the form of a straight chain, a part of which is a branched chain,
A three-dimensional structure may be formed, and a homopolymer,
It may be a copolymer or a mixture thereof. Examples of the substituted or unsubstituted monovalent hydrocarbon group bonded to a silicon atom of the polyorganosiloxane include an alkyl group such as a methyl group, an ethyl group and a propyl group; a vinyl group, an allyl group and a butadienyl group. Alkenyl group;
Cycloalkenyl groups such as phenyl group, xenyl group and naphthyl group; alkylaryl groups such as benzyl group;
Examples thereof include unsubstituted hydrocarbon groups such as an alkylaryl group such as a tolyl group and a xylyl group, and substituted hydrocarbon groups such as a chloromethyl group and a 3,3,3-trifluoropropyl group. As the monovalent hydrocarbon group bonded to the silicon atom, a methyl group is mainly used, and from the viewpoint of heat resistance and workability, it is preferable that 93 mol% or more is a methyl group. Further, as a cross-linking group, it is preferable to have a vinyl group, and from the viewpoint of mechanical strength and cross-linking property, it may be contained in an amount of 0.001 to 5% based on the total number of organic groups, and particularly preferably 0.02 to 2%. Is preferable. In addition, as a molecular chain terminal of the polyorganosiloxane, a hydroxyl group, an alkoxy group, or a triorganosilyl group is exemplified, and a triorganosilyl group is more preferable. Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, and a methyldiphenylsilyl group. The average degree of polymerization of the polyorganosiloxane is in the range of 1,000 to 20,000, preferably 3000 to 1500.
0, particularly preferably 5000 to 10,000. If the degree of polymerization is too small, it is difficult to obtain a sufficient mechanical strength, while if it is too large, it is difficult to mix the compound into the system.

[0006] Silica powder should not be blended if a low-hardness rubber cured product is desired, but may be used if high strength is required. In the present invention, known materials such as fumed silica, wet silica, and calcined silica generally used for compounding silicone rubber and the like are used, but are not particularly limited. These finely divided silica-based fillers may be used as they are,
Those surface-treated with silane, polyorganosiloxane, hexaorganodisilazane or the like may be used, or they may be reacted with these treating agents in-process. The amount of the silica powder is not particularly limited, but is preferably about 1 to 200 parts by weight, preferably 5 to 60 parts by weight, per 100 parts by weight of the polyorganosiloxane in order to improve the strength and processability. It is preferably about parts by weight.

The curing agent is appropriately selected according to the reaction mechanism for obtaining the rubber elastic body. As the reaction mechanism, a crosslinking method with an organic peroxide vulcanizing agent and a method by an addition reaction are known, and it is well known that a preferable combination with a curing catalyst or a crosslinking agent is determined by the reaction mechanism. is there. In the case of a crosslinking method using an organic peroxide, the curing catalyst may be benzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, di- Various organic peroxide vulcanizing agents such as t-butyl peroxide and the like are used. In particular, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5- Di-t-butylperoxyhexane and di-t-butyl peroxide are preferred. In addition, these organic peroxide vulcanizing agents are used as one kind or as a mixture of two or more kinds. The amount of the organic peroxide is preferably in the range of 0.05 to 15 parts by weight based on 100 parts by weight of the polyorganosiloxane base polymer. If the compounding amount of the organic peroxide is less than 0.05 parts by weight, the vulcanization is not sufficiently performed, and if the compounding amount exceeds 15 parts by weight, not only no further special effect is obtained, but also the obtained silicone rubber molding is obtained. This is because it may adversely affect the physical properties of the body. When applying an addition reaction, as a curing agent,
Platinum catalysts such as chloroplatinic acid for curing, platinum olefin complex, platinum vinyl siloxane complex, platinum carbon, platinum triphenylphosphine complex, etc. are used. However, an organopolysiloxane having an average number exceeding two is used. Among the curing agents, the compounding amount of the curing catalyst is preferably in the range of 1 to 1000 ppm in terms of platinum atomic weight based on 100 parts by weight of the polyorganosiloxane base polymer. If the amount of the curing catalyst is less than 1 ppm in terms of the amount of platinum atoms, curing will not proceed sufficiently, and if it exceeds 1000 ppm, no particular improvement in curing speed can be expected. The amount of the crosslinking agent is preferably such that the number of hydrogen atoms bonded to silicon atoms in the crosslinking agent is 0.5 to 4.0 with respect to the alkenyl groups in the polyorganosiloxane base polymer, and more preferably. The quantity is 1.0 to 3.0. When the amount of hydrogen atoms is less than 0.5, curing in the composition does not proceed sufficiently, and the hardness of the composition after curing becomes low. The physical properties and heat resistance of the composition are reduced.

[0008] In addition to the above-mentioned components, the composition of the present invention may further include, for example, ground quartz,
Silica-based filler such as diatomaceous earth, dimethyl silicone oil for low hardness, processing aid for improving workability, various additives such as titanium oxide, iron oxide, cerium oxide, vanadium oxide, chromium oxide, etc. Metal oxides,
A pigment, a heat-resistant agent, a flame-retardant-imparting agent and the like can be added as long as the properties of the composition of the present invention are not impaired.

The filler, zinc oxide, which is a feature of the present composition, has a particle size characteristic of the present invention. Conventionally, zinc oxide having a particle diameter of about 0.01 to 1 μm has been used as a filler for rubber. On the other hand, in the present invention, zinc oxide having an average particle diameter of 2 to 50 μm is selectively used. The particle diameter is important for lowering the hardness, and is effective at 2 μm or more. When it was smaller than 2 μm, the result was that the rubber hardness was significantly increased. Further, when the particle diameter exceeded 50 μm, the strength of the silicone rubber was remarkably reduced. The preferred particle size is 3 to 30 μm, particularly 5 to 30 μm. Although zinc oxide may be used as it is, it is preferable to use a zinc oxide surface-treated with a silane-based or titanate-based coupling agent, dimethylpolysiloxane oil, stearic acid, or the like, from the viewpoint of low compression set. As the surface treatment method, zinc oxide surface-treated in advance may be used, or a method in which a surface treatment agent is mixed together when preparing the composition of the present invention. The amount of zinc oxide is preferably 100 to 1000 parts by weight, more preferably 150 to 700 parts by weight, per 100 parts by weight of the thermosetting silicone rubber. If the amount is too small, the desired thermal conductivity cannot be obtained, and if it is too large, the strength and workability are significantly reduced.

The silicone rubber composition of the present invention can be obtained by uniformly mixing the above-mentioned components at room temperature. If necessary, components other than the curing agent are first mixed with a planetary mixer, kneader or the like for 100 to 200 times. Within 1 ° C
After heat treatment for 4 hours, an organic peroxide may be added and mixed.

The silicone rubber composition of the present invention is suitably used for applications requiring thermal conductivity and the like, and is particularly formed into a fixing roll by coating and curing by a conventional method, and exhibits extremely good performance.

[0012]

As described above, the silicone rubber composition of the present invention has low hardness, low compression set, excellent heat conductivity, and excellent heat resistance, so that a long-term stable image can be obtained when used as a fixing roll coating material. Can be.

[0013]

EXAMPLES Hereinafter, the present invention will be described more specifically by way of Examples.
Although described, the present invention is not limited to these. In the following examples, parts are parts by weight. Example 1 (CH ₃ ) ₂ SiO unit 99.9 mol%, (CH ₃ ) (CH ₂ = CH) SiO unit 0.12
% Of a polyorganosiloxane having a degree of polymerization of 6000, the end of which is blocked with a dimethylvinylsilyl group, 350 parts of zinc oxide having an average particle diameter of 10 μm, 1 part of vinyltriethoxysilane, and 1 part of cerium hydroxide. Kneaded with a kneader mixer until uniform. Thereafter, heat treatment was performed at 150 ° C. for 2 hours. To this silicone rubber composition, 1.5 parts of dicumyl peroxide as a curing agent was mixed with a two-roll mill until uniform, to obtain a silicone rubber base polymer. This silicone rubber base polymer was press-vulcanized at 170 ° C. for 10 minutes to obtain a cured silicone rubber sheet. This silicone rubber sheet was evaluated for physical properties (hardness, heat resistance, compression set) according to JIS K6301. The thermal conductivity was measured with a (Shotherm QTM-DII rapid thermal conductivity meter). Example 2 A sample was prepared and evaluated in the same manner as in the silicone rubber compound of Example 1, except that the amount of zinc oxide was changed to 150 parts. Example 3 A sample was prepared and evaluated in the same manner as in the silicone rubber compound of Example 1, except that vinyltriethoxysilane was not blended. Example 4 A sample was prepared and evaluated in the same manner as in the silicone rubber compound of Example 1, except that zinc oxide having an average particle diameter of 20 μm was used. Comparative Example 1 A sample was prepared and evaluated in the same manner as in the silicone rubber compound of Example 1, except that 250 parts of crushed quartz having an average particle diameter of 5 μm was used instead of zinc oxide. Comparative Example 2 A sample was prepared and evaluated in the same manner as in the silicone rubber compound of Example 1, except that 300 parts of ultra-low active magnesium oxide having an average particle diameter of 2 μm was used instead of zinc oxide. Comparative Example 3 In the silicone rubber compound of Example 1, an average particle diameter of 0.5 μm was used instead of zinc oxide having an average particle diameter of 10 μm.
A sample was prepared and evaluated in the same manner except that 350 parts of zinc oxide was used. Comparative Example 4 A sample was prepared and evaluated in the same manner as in the silicone rubber compound of Example 1, except that alumina having an average particle diameter of 10 μm was used instead of zinc oxide. Table 1 shows the results.

[0014]

[Table 1]

Claims (2)

[Claims] 1. A zinc oxide having an average particle size of 2 to 50 μm is added to 100 to 1000 parts by weight of a heat-curable silicone rubber.
A silicone rubber composition characterized by being compounded by weight. 2. A fixing roll using the silicone rubber composition according to claim 1 as a coating material.