Fluorinated curable compositions

Details Fluorinated curable compositions Fluorinated curable compositions

2002-02-20

2004-01-06

Wilson, D. R. (Department: 1713)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S479000, C528S015000, C528S028000, C528S031000, C528S032000, C528S043000

Reexamination Certificate

active

06673876

ABSTRACT:

This invention relates to fluorinated curable compositions which cure into gel products having adhesion and improved chemical and solvent resistance, and are suited for the potting, sealing and coating of electric and electronic parts.
BACKGROUND OF THE INVENTION
Cured gel products of silicone rubber have good electrically and thermally insulating properties, stable electric properties and flexibility. They are useful as potting and sealing materials for electric and electronic parts, and coating materials for protecting control circuit devices such as power transistors, ICs and capacitors from external, thermal and mechanical damages.
Typical silicone rubber composition examples forming such cured gel products are organopolysiloxane compositions of the addition curing type. The organopolysiloxane compositions of the addition curing type are known, for example, from JP-A 56-143241, 63-35655 and 63-33475 as comprising an organopolysiloxane having a vinyl group attached to a silicon atom and an organohydrogenpolysiloxane having a hydrogen atom attached to a silicon atom, wherein crosslinking reaction takes place in the presence of a platinum group catalyst to form a silicone gel.
However, silicon gels resulting from such organopolysiloxane compositions of the addition curing type are prone to degradation or swelling upon exposure to such chemicals as strong bases and strong acids or such solvents as toluene, alcohols and gasoline, often failing to maintain their performance.
As one solution to this problem, JP-A 11-116685 discloses a fluorochemical gel composition comprising a polyfluoro compound having two alkenyl groups and a divalent perfluoropolyether group in a molecule, an organohydrogenpolysiloxane having a hydrogen atom attached to a silicon atom, and a platinum group catalyst as well as a fluorochemical gel product resulting from curing thereof. This cured fluorochemical gel product exhibits better chemical and solvent resistance as desired than ordinary silicone gels, but is less adherent to substrates of electric and electronic parts.
Although the organohydrogenpolysiloxane is combined with the high molecular weight perfluoropolyether serving as the base in the above composition, the organohydrogenpolysiloxane is less compatible with the base, leaving problems of separation and unstable cure.
SUMMARY OF THE INVENTION
An object of the invention is to provide a fluorinated curable composition comprising compatible components which cures into a gel product having good substrate adhesion and improved chemical and solvent resistance.
It has been found that when a linear polyfluoro compound containing at least two alkenyl groups of the following general formula (1), a fluorinated organohydrogensiloxane of the following general formula (2) and a platinum group metal catalyst are blended in combination, these components are fully compatible with each other and the resulting fluorinated curable composition cures into a gel product having good substrate adhesion and improved chemical and solvent resistance.
Specifically, the invention provides a fluorinated curable composition comprising as essential components,
(A) a linear polyfluoro compound of the following general formula (1):
CH
2
═CH—(X)
a
-Rf
1
-(X)
a
—CH═CH
2
  (1)
wherein X is independently —CH
2
—, —CH
2
O—, —CH
2
OCH
2
— or —Y—NR
1
—CO— wherein Y is —CH
2
— or a divalent group represented by
and R
1
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group, Rf
1
is a divalent perfluoropolyether group, and “a” is independently equal to 0 or 1,
(B) a fluorinated organohydrogensiloxane of the following general formula (2):
wherein X and “a” are as defined above, Rf
2
is a monovalent perfluoropolyether group, Z is a divalent hydrocarbon group, Rf
3
is a divalent perfluoroalkylene or perfluoropolyether group, w and x each are an integer of up to 3, w+x is from 2 to 5, y is 0 or 1, and a+y is at least 1, and
(C) a catalytic amount of a platinum group metal catalyst.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the fluorinated curable composition of the invention, component (A) is a linear polyfluoro compound of the following general formula (1).
CH
2
═CH—(X)
a
-Rf
1
-(X)
a
—CH═CH
2
  (1)
Herein X is independently —CH
2
—, —CH
2
O—, —CH
2
OCH
2
— or —Y—NR
1
—CO— wherein Y is —CH
2
— or a divalent group represented by
and R
1
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group. Rf
1
is a divalent perfluoropolyether group. Letter “a” is independently equal to 0 or 1.
In formula (1), Rf
1
is a divalent perfluoropolyether group, and preferably selected from groups of the following formulae:
wherein p and q each are an integer of at least 1, p+q is from 50 to 200, and r is an integer of 2 to 6,
wherein r is an integer of 2 to 6, s is an integer inclusive of 0, t is an integer inclusive of 0, s+t is from 50 to 200, and
wherein u is an integer of 50 to 200 and v is an integer of 1 to 50.
Illustrative examples of Rf
1
are given below.
In formula (1), X is independently —CH
2
—, —CH
2
O—, —CH
2
OCH
2
— or —Y—NR
1
—CO—. Herein Y is —CH
2
— or a divalent group of the following formula.
R
1
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group. The monovalent hydrocarbon groups preferably have 1 to 12 carbon atoms, more preferably 1 to 10 carbon atoms. Illustrative are unsubstituted monovalent hydrocarbon groups, for example, alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, cyclohexyl and octyl, aryl groups such as phenyl and tolyl, and aralkyl groups such as benzyl and phenylethyl, and substituted monovalent hydrocarbon groups obtained by replacing some or all of the hydrogen atoms in the foregoing groups by halogen atoms such as fluorine.
The alkenyl groups in formula (1) are preferably vinyl, allyl and analogous groups having a —CH═CH
2
structure at the end. The alkenyl groups may be bonded to opposite ends of the backbone directly or via divalent linkage groups represented by X.
In formula (1), letter “a” is independently equal to 0 or 1.
It is preferred that the inventive composition have an appropriate flow so that the composition is useful in casting, potting, coating, impregnation and adhesion, and that its cured product have appropriate physical properties. From this standpoint, component (A) should preferably have a viscosity in the range of 5 to 100,000 mPa·s at 23° C. Depending on a particular application, component (A) having a most appropriate viscosity within the range is desirably used.
Component (B) is a fluorinated organohydrogensiloxane of the following general formula (2).
Herein X and “a” are as defined above, Rf
2
is a monovalent perfluoropolyether group, Z is a divalent hydrocarbon group, Rf
3
is a divalent perfluoroalkylene or perfluoropolyether group, w and x each are an integer of up to 3, w+x is from 2 to 5, y is 0 or 1, and a+y is at least 1.
The monovalent perfluoropolyether groups represented by Rf
2
are preferably those of the following formulae.
More illustrative examples of Rf
2
are given below.
In formula (2), X and “a” are as defined in formula (1) while X and “a” in formula (1) may be identical with or different from X and “a” in formula (2), respectively.
The divalent hydrocarbon groups represented by Z are preferably those of 1 to 10 carbon atoms, especially 1 to 5 carbon atoms, including alkylene groups such as methylene, ethylene, propylene, methylethylene and tetramethylene, and arylene groups such as phenylene.
Preferred examples of the divalent perfluoroalkylene and perfluoropolyether groups represented by Rf
3
are given below.
—C
m
F
2m
—  (m is an integer of 1 to 20, preferably 2 to 10.)
Subscripts w and x each are an integer of up to 3, satisfying 5≧w+x≧2, and y is 0 or 1, satisfying a+y>1.
The fluorinated organohydrogensiloxane (B) serves as a crosslinker and chain extender for component (A), and should preferably have at least two hydrosilyl groups (i.e., Si—H groups) in a molecule. For co

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