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
2000-03-20
2001-07-31
Cain, Edward J. (Department: 1714)
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
Reexamination Certificate
active
06268426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conductive fluorosilicone rubber composition providing a conductive fluorosilicone rubber which is particularly small in tension set, rich in rubber elasticity, and excellent in heat resistance.
2. Description of the Prior Art
Conductive elastomers are broadly used in, for example, rubber contacts, static electricity, removal of electricity, shield of electromagnetic waves, and materials for various conductive rolls. As raw materials of the conductive elastomers, there are used various materials such as silicone, polyurethane, polyethylene, polypropylene and natural rubbers, depending on properties such as rubber strength, abrasion, and fire retardance which are required in accordance with the purposes of the conductive elastomers to be used.
As methods for rendering electrical conductivity to elastomers, there are used an electron transfer type in which a conductive carbon or a conductive metal powder is mixed, and an ion conductive type in which an ion conductive agent such as a lithium ion conductive agent is mixed. Generally speaking, the electron transfer type is broadly used.
Among the conductive elastomers, the conductive silicone rubber is excellent in properties such as heat resistance, cold resistance, and weatherability, so that it is used in rubber contacts and materials for business machines. Especially, a fluorosilicone rubber having a 3,3,3-trifluoropropyl group at its side chain is excellent in not only the above properties but also solvent resistance. There is a defect that addition of carbon to the fluorosilicone rubber for providing the same with electric conductivity results in lowering of mechanical strength and rubber elasticity. Particularly, the rubber elasticity typically represented by tension set is extremely lowered and heat deterioration is increased, so that there occurs a problem in use as diaphragms, O-rings or oil seal materials, which are typical parts of the fluorosilicone rubber, as parts of transportation or parts of petroleum-related apparatus and instrument.
In the case of the ion conductive fluorosilicone rubber, it is required to add a large amount of a transmitting substance (binder) for the ion conductive agent to the fluorosilicone rubber. This causes hindrance in crosslinking of the rubber material and decrease in the mechanical strength of a cured rubber. Thus, any practical product has not been known yet.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a conductive fluorosilicone rubber composition which upon curing, forms a conductive fluorosilicone rubber small in tension set, rich in rubber elasticity, and excellent in heat resistance.
Earnest studies have been made in order to accomplish the above object, and as a result, it has been found that the above object can be accomplished by using a graphitization-treated carbon black as a conductive carbon.
Thus, the present invention provides a conductive fluorosilicone composition comprising:
(A) An organopolysiloxane having a polymerization degree of at least 100 and represented by the following average compositional formula:
R
a
(CF
3
CH
2
CH
2
)
b
SiO
[4-(a+b)]/2
(1)
wherein R is an unsubstituted monovalent hydrocarbon group, a is a number ranging from 0.8 to 1.8, b is a number ranging from 0.2 to 1.2, and a and b are numbers satisfying a+b=1.95 to 2.05 and b/(a+b)=0.1 to 0.6,
(B) a graphitization-treated carbon black, and
(C) a curing agent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in more detail below.
[(A) Organopolysiloxane]
The organopolysiloxane used as component (A) in the present invention is represented by the following average compositional formula (1):
R
a
(CF
3
CH
2
CH
2
)
b
SiO
[4-(a+b)]/2
(1)
wherein R is an unsubstituted monovalent hydrocarbon group, a is a number ranging from 0.8 to 1.8, b is a number ranging from 0.2 to 1.2, and a and b are a numbers satisfying a+b=1.95 to 2.05 and b/(a+b)=0.1 to 0.6.
The unsubstituted monovalent hydrocarbon group R includes, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group; an alkenyl group such as a vinyl group, an allyl group and a butenyl group; a cycloalkyl group such as a cyclohexyl group; an aryl group such as a phenyl group, a tolyl group and a naphthyl group; an aralkyl group such as a benzyl group and a 2-phenylethyl group. Preferred are a methyl group and a vinyl group. Preferably, an alkenyl group, such as a vinyl group is contained in an amount of 0.01 to 2 mole %. Where a plurality of the R's are present in the molecule, they may be the same or different.
The a which represents the proportion of the group R is a number ranging from 0.8 to 1.8, the b which represents the proportion of the 3,3,3-trifluoropropyl group (CF
3
CH
2
CH
2
—) is a number ranging from 0.2 to 1.2, and the a+b which represents the total of both ranges from 1.95 to 2.05. Further, the ratio of the 3,3,3-trifluoropropyl group to the total of both, b/a+b, ranges from 0.1 to 0.6, preferably from 0.2 to 0.6.
Although it is basically preferred that the molecular structure of the organopolysiloxane represented by the above formula (1) is linear, a part of the molecular structure may be branched. The structure may be formed of only a repeating unit represented by
wherein R is as defined in respect of the formula (1), or may be formed of a blockpolymer comprising a repeating unit represented by
wherein R is as defined in respect of the formula (1), and a repeating unit represented by
wherein R is as defined in respect of the formula (1).
The terminal end is preferably blocked with
wherein R is as defined in respect of the formula (1), or
wherein R is as defined in respect of the formula (1).
The polymerization degree is preferably 100 to 20,000, more preferably 1,000 to 10,000, because a good processability is obtained.
[Graphitization-treated carbon black]
In the present invention, the graphitization-treated carbon black is used as component (B). The graphitization-treated carbon black is obtained by treating a carbon black at a high temperature until the carbon black has a graphite structure. Particularly, preferred is a graphitization-treated carbon black having an average particle diameter of 200 nm or less which has been obtained by subjecting a carbon black such as the furnace black or the thermal black which are originally manufactured by combustion to heat-treatment at 1,500 to 4,000° C. Particularly preferred is a graphitization-treated carbon black containing a volatile matter in an amount of 0.6% by weight or less. Herein, the volatile matter is measured according to JIS K-6221-1982 (Testing method for carbon black for rubbers).
Carbon blacks are manufactured by various manufacturing processes which are known as, for example, the contact process, the furnace process or the thermal process. Typical carbon blacks include furnace black, acetylene black, ketjen black, channel black and so on. However, when the carbon black thus obtained is used as it is, the resulting cured fluorosilicone rubber is lowered in rubber elasticity and heat resistance as well as mechanical strength represented by tension set. This is presumably because a trifluoropropyl group-containing organopolysiloxane is slow in crosslinking compared to methylvinylpolysiloxanes conventionally used, and in addition because reactive ingredients, such as a carboxyl group, a lactone, a phenol, a quinone or an active hydrogen, present on, for example, the surface of the carbon black inhibits crosslinking of the organopolysiloxane.
In the present invention, the graphitization-treated carbon black is used to remove the inhibitory for crosslinking.
The graphitization treatment presumably promotes the growth (graphitization) of crystallites of carbon black and the decomposition and removal of the reactive ingredients present
Hirabayashi Satao
Nakamura Tsutomu
Cain Edward J.
Pillsbury & Winthrop LLP
Shin-Etsu Chemical Co. , Ltd.
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