Room temperature curable silicone rubber composition

Details Room temperature curable silicone rubber composition Room temperature curable silicone rubber composition

2001-12-18

2003-05-20

Dawson, Robert (Department: 1712)

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...

C528S901000, C528S034000, C528S035000, C528S018000, C528S028000, C524S492000, C525S477000, C549S215000

Reexamination Certificate

active

06566443

ABSTRACT:

FIELD OF THE INVENTION
The present invention is a room temperature curable silicone rubber composition and more particularly a nonsagging and extrudable room temperature curable silicone rubber composition that exhibits an excellent and robust adherence to a variety of substrates when the composition is cured while in contact with the substrate.
BACKGROUND OF THE INVENTION
A large number of compositions are known within the art that cure at room temperature upon contact with atmospheric moisture to produce silicone rubber. Compositions of this type include alcohol-liberating room temperature curable silicone rubber compositions whose main components are alkoxysilyl-terminated diorganopolysiloxane and alkoxysilane. These alcohol-liberating room temperature curable silicone rubber compositions cure in the presence of an organotitanium compound catalyst with the liberation of alcohol. They are frequently used as sealants and adhesives for electrical/electronic instruments and devices and as sealants for building elements because they lack unpleasant odor and do not corrode metals (refer, for example, to Japanese Published (Kokoku or Examined) Patent Application Number Sho 39-27643 (27,643/1964) and Japanese Laid Open (Kokai or Unexamined) Patent Application Numbers Sho 55-43119 (43,119/1980) and Sho 62-252456 (252,456/1987)). Alcohol-liberating room temperature curable silicone rubber compositions of this type, however, are poorly adhesive to a variety of substrates, such as glass, plastics, and metals, and thus have been unable to provide fully satisfactory performance in some applications.
The inventors discovered that the above described problems can be solved by the admixture of two specific types of dry method silicas into an alcohol-liberating room temperature curable silicone rubber composition based on a special diorganopolysiloxane.
In more specific terms, the object of this invention is to provide a nonsagging and extrudable room temperature curable silicone rubber composition that exhibits an excellent and robust adherence to a variety of substrates when the composition is cured while in contact with the substrate.
SUMMARY OF THE INVENTION
The present invention is a room temperature curable silicone rubber composition comprising
(A) 100 weight parts diorganopolysiloxane comprising
(a-1) 20 to 100 weight parts diorganopolysiloxane described by general formula
 where R
1
and R
2
represent alkyl or alkoxyalkyl; R
3
is selected from the group consisting of monovalent hydrocarbyl, halogenated hydrocarbyl, and cyanoalkyl; a is 0 or 1; Y is selected from the group consisting of oxygen atom, divalent hydrocarbon group, and a group described by general formula
 where R
3
is defined as above and Z represents a divalent hydrocarbon group; and n is a positive number that produces a viscosity at 25° C. of from 20 to 1,000,000 mPa·s and
(a-2) 80 to 0 weight parts diorganopolysiloxane described by general formula
 where R
1
, R
2
, and R
3
are defined as above, R
4
is alkyl or alkenyl, and Y, a, and n are defined as above;
(B) 1 to 20 weight parts surface-hydrophobicized dry method silica;
(C) 1 to 20 weight parts non-surface-hydrophobicized dry method silica;
(D) 1 to 25 weight parts alkoxysilane described by general formula R
5
b
Si(OR
6
)
4-b
where R
5
represents monovalent hydrocarbyl, R
6
is alkyl or alkoxyalkyl, and b is 0 or 1, or the partial hydrolysis and condensation product thereof,
(E) 0.5 to 10 weight parts organotitanium compound; and
(F) 0.01 to 5 weight parts light stabilizer and/or ultraviolet absorber.
DESCRIPTION OF THE INVENTION
The present invention is a room temperature curable silicone rubber composition comprising
(A) 100 weight parts diorganopolysiloxane comprising
(a-1) 20 to 100 weight parts diorganopolysiloxane described by general formula
 where R
1
and R
2
represent alkyl or alkoxyalkyl; R
3
is selected from the group consisting of monovalent hydrocarbyl, halogenated hydrocarbyl, and cyanoalkyl; a is 0 or 1; Y is selected from the group consisting of oxygen atom, divalent hydrocarbon group, and a group described by general formula
 where R
3
is defined as above and Z represents a divalent hydrocarbon group; and n is a positive number that produces a viscosity at 25° C. of from 20 to 1,000,000 mPa·s and
(a-2) 80 to 0 weight parts diorganopolysiloxane described by general formula
 where R
1
, R
2
, and R
3
are defined as above, R
4
is alkyl or alkenyl, and Y, a, and n are defined as above;
(B) 1 to 20 weight parts surface-hydrophobicized dry method silica;
(C) 1 to 20 weight parts non-surface-hydrophobicized dry method silica;
(D) 1 to 25 weight parts alkoxysilane described by general formula R
5
b
Si(OR
6
)
4-b
where R
5
represents monovalent hydrocarbyl, R
6
is alkyl or alkoxyalkyl, and b is 0 or 1, or the partial hydrolysis and condensation product thereof;
(E) 0.5 to 10 weight parts organotitanium compound; and
(F) 0.01 to 5 weight parts light stabilizer and/or ultraviolet absorber.
To explain the present invention in greater detail, the diorganopolysiloxane (A) is the base component of the composition. The component (a-1) encompassed by component (A) is diorganopolysiloxane having hydrolyzable alkoxy or alkoxyalkoxyl at both molecular chain terminals. R
1
and R
2
in the preceding formula for this diorganopolysiloxane each represent alkyl such as methyl, ethyl, propyl, or butyl, or alkoxyalkyl such as methoxyethyl, ethoxyethyl, methoxypropyl, or methoxybutyl. R
3
is selected from the group consisting of monovalent hydrocarbyl, halogenated hydrocarbyl, and cyanoalkyl groups. R
3
can be, for example, alkyl such as methyl, ethyl, propyl, or butyl; cycloalkyl such as cyclopentyl or cyclohexyl; alkenyl such as vinyl or allyl; aryl such as phenyl, tolyl, or naphthyl; aralkyl such as benzyl, phenylethyl, or phenylpropyl; halogenated hydrocarbyl such as chloromethyl, trifluoropropyl, or chloropropyl; or cyanoalkyl such as &bgr;-cyanoethyl or &ggr;-cyanopropyl. Methyl is preferred among the preceding. Y and Z can each represent a divalent hydrocarbon group, for which alkylene is preferred, for example, methylene, propylene, and butylene. The subscript n represents a positive number that provides a viscosity at 25° C. of 20 to 1,000,000 mPa·s.
Component (a-2), which is diorganopolysiloxane having hydrolyzable alkoxy or alkoxyalkyl at only a single molecular chain terminal, functions to lower the modulus of the cured silicone rubber afforded by the present composition. R
1
, R
2
, R
3
, a, n, Y and Z in the preceding formula for component (a-2) have the same definitions as for component (a-1). R
4
is alkyl such as methyl, ethyl, propyl, or butyl, or alkenyl such as vinyl or allyl. Component (A) comprises from 20 to 100 weight parts component (a-1) and from 80 to 0 weight parts (a-2) wherein the total of the two is 100 weight parts. Larger component (a-1) contents should be used when it is desired to raise the modulus of the cured product, while larger component (a-2) contents should be used when it is desired to lower the modulus. In addition, component (A) may consist of only 100 weight parts component (a-1).
Component (B) is surface-hydrophobicized dry method silica. This component functions to impart mechanical strength to the present composition and to impart adherence to a variety of substrates. This dry method silica can be obtained by hydrophobicizing the surface of the non-surface-hydrophobicized dry method silica described below for component (C) using any of various hydrophobicizing agents. The hydrophobicizing agent can be exemplified by hexamethyldisilazane, tetramethyldivinyldisilazane, dimethyldichlorosilane, trimethylchlorosilane, trimethylsilanol, methylhydrogenpolysiloxanes, octamethylcyclotetrasiloxane, and silanol-terminated dimethylsiloxane oligomers. These hydrophobicizing agents induce surface hydrophobicization by reacting with the silanol present on the surface of the dry method silica. Component (B) can be prepared, for example, by adding the hydrophobicizing agent to the dry met

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