Room temperature curable organopolysiloxane compositions

Details Room temperature curable organopolysiloxane compositions Room temperature curable organopolysiloxane compositions

2002-06-28

2004-05-25

Peng, Kuo-Liang (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C525S477000, C528S034000, C528S901000

Reexamination Certificate

active

06740725

ABSTRACT:

This invention relates to one-part room temperature curable organopolysiloxane compositions having improved electrical properties, especially resistance to electrolytic corrosion.
BACKGROUND OF THE INVENTION
In the prior art, one-part room temperature curable organopolysiloxane compositions are applied to circuit boards for electric and electronic applications and used as the moisture-proof and anti-fouling coat. A problem arises that the cured organopolysiloxane compositions experience a decline of insulation resistance upon application of voltage in a hot humid environment.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a one-part room temperature curable organopolysiloxane composition which has eliminated the drawbacks of the prior art compositions, and cures into a product which is resistant to electrolytic corrosion in that no decline of insulation resistance occurs upon application of voltage in a hot humid environment.
It has been found that a room temperature curable organopolysiloxane composition comprising (a) an organopolysiloxane having a specific structure, (b) a alkenoxysilane or substituted alkenoxysilane or a partial hydrolyzate thereof, and (c) a siloxane or a partial hydrolyzate thereof cures into a product which does experience no decline of insulation resistance upon application of voltage in a hot humid environment and is resistant to electrolytic corrosion.
Accordingly, the present invention provides a room temperature curable organopolysiloxane composition comprising
(a) 100 parts by weight of an organopolysiloxane having the following general formula (I):
 wherein R
1
is hydrogen, a substituted or unsubstituted alkyl radical or a substituted or unsubstituted alkenyl radical, R
2
is independently a substituted or unsubstituted monovalent hydrocarbon radical, X is an oxygen atom or a divalent hydrocarbon radical, a is 0, 1 or 2, and n is an integer of at least 10,
(b) 1 to 30 parts by weight of a substituted or unsubstituted alkenoxysilane having the following general formula (II):
 wherein R
3
is a substituted or unsubstituted monovalent hydrocarbon radical, R
4
and R
5
are each independently hydrogen or a substituted or unsubstituted monovalent hydrocarbon radical, and x is 3 or 4, or a partial hydrolyzate thereof, and
(c) 0.01 to 10 parts by weight of a siloxane containing per molecule at least one monovalent radical having the general formula (III):
 wherein R
6
, R
7
, R
8
and R
9
each are hydrogen or a monovalent hydrocarbon radical, and y is an integer of 1 to 6, at least two silicon atoms, and at least three radicals selected from the group consisting of alkyl, alkoxy and alkenoxy radicals, or a partial hydrolyzate thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Component (a) serving as the base in the composition of the invention is an organopolysiloxane having the following general formula (I).
Herein, R
1
is hydrogen, a substituted or unsubstituted alkyl radical, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, or a substituted or unsubstituted alkenyl radical, preferably having 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms. R
2
which may be the same or different is a substituted or unsubstituted monovalent hydrocarbon radical, preferably having 1 to 10 carbon atoms. X is an oxygen atom or a divalent hydrocarbon radical, preferably having 1 to 10 carbon atoms. The letter “a” is 0, 1 or 2, and n is an integer of at least 10.
More particularly, of the radicals represented by R
1
, suitable alkyl radicals include, but are not limited to, methyl, ethyl, propyl, and butyl, and substituted ones of these alkyl radicals in which some or all of the hydrogen atoms are substituted with halogen atoms, cyano or the like, for example, halogenated alkyl radicals such as chloromethyl, trichloropropyl and trifluoropropyl and cyanoalkyl radicals such as 2-cyanoethyl, 3-cyanopropyl and 2-cyanobutyl. Of these, methyl and ethyl are preferred. Suitable alkenyl radicals include alkenyl radicals such as vinyl, allyl and isopropenyl, and substituted ones of these alkenyl radicals in which some or all of the hydrogen atoms are substituted with aryl radicals (e.g., phenyl), such as phenylethenyl. Of these, isopropenyl and vinyl are preferred. It is preferred that “a” be 2 where R
1
is hydrogen, and “a” be 0 or 1 where R
1
is an alkyl or alkenyl radical.
The hydrocarbon radicals represented by R
2
include, but are not limited to, alkyl radicals such as methyl, ethyl, propyl, isopropyl, butyl, 2-ethylbutyl and octyl; cycloalkyl radicals such as cyclohexyl and cyclopentyl; alkenyl radicals such as vinyl and allyl; aryl radicals such as phenyl, tolyl, xylyl, naphthyl, biphenyl and phenanthryl; aralkyl radicals such as benzyl and phenylethyl; and substituted ones of the foregoing radicals in which some or all of the hydrogen atoms are substituted with halogen atoms, cyano or the like, for example, halogenated hydrocarbon radicals such as chloromethyl, trichloropropyl, trifluoropropyl, bromophenyl and chlorocyclohexyl, and cyano hydrocarbon radicals such as 2-cyanoethyl, 3-cyanopropyl and 2-cyanobutyl. Of these, methyl is preferred.
X is an oxygen atom or an alkylene radical such as methylene, ethylene and propylene, with the oxygen and ethylene being preferred.
Preferably, the organopolysiloxane is capped with a hydroxyl radical at either end of its molecular chain, especially with one hydroxyl radical at each end of its molecular chain.
In formula (1), n is an integer of 10 or greater. The organopolysiloxane preferably has a viscosity of about 25 to 1,000,000 centistokes (cSt) at 25° C., and more preferably about 500 to 500,000 cSt at 25° C.
Component (b) serving as a curing agent in the inventive composition is an alkenoxysilane or substituted alkenoxysilane having the following general formula (II) or a partial hydrolyzate thereof.
Herein, R
3
is a substituted or unsubstituted monovalent hydrocarbon radical, preferably having 1 to 10 carbon atoms. R
4
and R
5
which may be the same or different are hydrogen or substituted or unsubstituted monovalent hydrocarbon radicals, preferably having 1 to 10 carbon atoms. The letter x is 3 or 4.
More particularly, suitable hydrocarbon radicals represented by R
3
include alkyl, alkenyl, aryl and other radicals as exemplified above for R
2
. The monovalent hydrocarbon radicals represented by R
4
and R
5
include alkyl, alkenyl and other radicals as exemplified above for R
2
.
Illustrative, non-limiting examples of the alkenoxysilane (b) include methyltrivinyloxysilane, methyltri(isopropenyloxy)silane, vinyltri(isopropenyloxy)silane, phenyltri(isopropenyloxy)silane, propyltri(isopropenyloxy) silane, tetra(isopropenyloxy)silane, methyltri(1-phenylethenyloxy)silane, methyltri(1-butenyloxy)silane, methyltri (1-methyl-1-propenyloxy)silane, methyltri(1,4-dimethyl-1,3-pentadienyloxy)silane and partial hydrolyzates thereof.
Usually, the alkenoxysilane (b) is added in an amount of 1 to 30 parts, preferably 3 to 20 parts, and more preferably 3 to 10 parts by weight per 100 parts by weight of the organopolysiloxane (a). Less than 1 part of component (b) effects insufficient crosslinking, failing to provide the desired rubbery elasticity in the cured state. More than 30 parts of component (b) entails an increased shrinkage factor upon curing, resulting in poor mechanical properties.
Component (c) serving as a curing catalyst in the inventive composition is a siloxane or a partial hydrolyzate thereof. The siloxane should contain per molecule at least one monovalent radical having the general formula (III), at least two silicon atoms, and at least three radicals selected from among alkyl, alkoxy and alkenoxy radicals.
Herein R
6
, R
7
, R
8
and R
9
each are hydrogen or a monovalent hydrocarbon radical, preferably having 1 to 10 carbon atoms, and y is an integer of 1 to 6. Examples of the monovalent hydrocarbon radicals represented by R
6
, R
7
, R
8
and R
9
include those exemplified above for R
2
.
Preferably, the siloxane (c) has the followi

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