Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-08-11
2002-05-14
Dawson, Robert (Department: 1752)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C528S024000, C528S031000, C528S032000, C528S015000, C525S477000, C525S479000
Reexamination Certificate
active
06387487
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to silicone compositions suitable for forming pressure sensitive adhesives. More particularly, the present invention relates to solventless or low-solvent, curable silicone compositions suitable for forming pressure sensitive adhesive compositions having excellent tack and adhesive properties.
The term “pressure sensitive adhesive” (PSA) as used herein refers to adhesives that can be adhered to a surface and yet can be stripped from the surface without transferring more than trace quantities of adhesive to the surface, and can be readhered to the same or another surface because the adhesive retains some or all of its tack and adhesive strength. Silicone pressure sensitive adhesives have excellent adhesive and cohesive strength and high tack as well as excellent heat resistance, cold resistance, electrical properties, and the like, which makes them applicable for use as electrical-insulating tape and for various pressure-sensitive products that must be resistant to hot and cold.
However, a drawback associated with silicone pressure sensitive adhesives is the use, handling, and emission of flammable and volatile organic compounds, e.g., organic solvents, in the preparation of the pressure sensitive adhesives from compositions containing high levels of organic solvent. Solvent is generally used for the purpose of reducing the viscosity of the composition to a level that renders the curable composition processable. While low-solvent compositions are known, their high temperature performance, particularly their lap shear, is deficient for some applications.
Silicone compositions capable of curing to form pressure sensitive adhesive compositions are known in the art.
U.S. Pat. No. 5,248,739 to Schmidt et al. generally describes pressure sensitive adhesive compositions comprising a resinous copolymer and a polydiorganosiloxane.
Commonly assigned U.S. Pat. No. 5,292,586 to Lin et al. generally describes solventless or low-solvent silicone pressure sensitive adhesive compositions comprising a resinous copolymer, a vinyl-endblocked polydiorganosiloxane, and a hydride-endblocked polydiorganosiloxane.
Commonly assigned U.S. Pat. No. 5,466,532 to Wengrovius et al. describes solventless or low-solvent silicone pressure sensitive adhesive compositions comprising a resinous copolymer, a vinyl-terminated polydiorganosiloxane, a hydrogen-terminated polydiorganosiloxane, and a hydrosilation catalyst.
Commonly assigned U.S. Pat. No. 5,576,110 to Lin et al. describes pressure sensitive adhesive compositions comprising (A) a resinous copolymer; (B) an alkenyl-containing polydiorganosiloxane having a viscosity of at least about 3000 centipoise at 25° C.; (C) a set of multi-functional silicones as crosslinker; (D) optionally, a reaction mixture of (A) and (B); (E) a hydrosilation catalyst; and (F) optionally, an organic solvent.
U.S. Pat. No. 5,916,981 to Cifuentes et al. generally describes a method for preparing pressure sensitive adhesive compositions comprising a hydroxyl-terminated polydiorganosiloxane; at least one soluble MQ resin; at least one silanol condensation catalyst; at least one solvent or plasticizer; and an organic peroxide or azo compound.
There remains a need for solventless or low-solvent pressure sensitive adhesive silicone compositions with improved high temperature properties.
BRIEF SUMMARY OF THE INVENTION
Excellent processing properties and high temperature performance are provided by a curable, low-solvent silicone coating composition comprising:
(A) about 20 to about 80 parts by weight of an alkenyl-terminated polydiorganosiloxane of formula (I)
R
2
R
1
2
SiO(R
1
2
SiO)
m
SiR
1
2
R
2
(I)
wherein each R
1
is independently an alkyl group having from 1 to about 10 carbon atoms or an aryl group, R
2
is an alkenyl group having from 1 to about 10 carbon atoms, and m has an average value of about 20 to about 2000;
(B) about 2 to about 80 parts by weight of a silanol-terminated polydiorganosiloxane of formula (II)
R
1
2
Si(OH)O(R
1
2
SiO)
p
SiR
1
2
(OH) (II)
wherein each R
1
is independently an alkyl group as defined above, and the average value of p is chosen to provide a viscosity of about 100,000 centipoise to about 750,000 centipoise;
(C) about 20 to about 80 parts by weight of a resinous copolymer containing R
3
SiO
1/2
units and SiO
4/2
units, where R is a hydrocarbon monovalent radical having from 1 to about 6 carbon atoms, said resinous copolymer having a molar ratio of R
3
SiO
1/2
units to SiO
4/2
units of about 0.6 to about 0.9;
(D) an organohydrogenpolysiloxane of formula (III)
R
3
2
HSiO(R
3
2
SiO)
q
SiHR
3
2
(III)
wherein each R
3
is independently an alkyl group having 1 to about 10 carbon atoms or an aryl group; q has an average value of 1 to about 300; the molar ratio of silicon-bonded hydrogen groups in (D) to silicon-bonded alkenyl groups in (A) being about 0.8:1 to about 1.5:1;
(E) a catalytic amount of a hydrosilation catalyst; and
(F) about 0.2 to about 6 parts by weight of a cross-linking agent comprising an organic peroxide or an organic azo compound;
wherein all parts by weight are based on the weight of the entire composition.
DETAILED DESCRIPTION OF THE INVENTION
A curable silicone coating composition with low solvent content and excellent processing properties comprises:
(A) about 20 to about 80 parts by weight of an alkenyl-terminated polydiorganosiloxane of formula (I)
R
2
R
1
2
SiO(R
1
2
SiO)
m
SiR
1
2
R
2
(I)
wherein each R
1
is independently an alkyl group having from 1 to about 10 carbon atoms or an aryl group, R
2
is an alkenyl group having from 1 to about 10 carbon atoms, and m has an average value of about 20 to about 2000;
(B) about 2 to about 80 parts by weight of a silanol-terminated polydiorganosiloxane of formula (II)
R
1
2
Si(OH)O(R
1
2
SiO)
p
SiR
1
2
(OH) (II)
wherein each R
1
is independently an alkyl group as defined above, and the average value of p is chosen to provide a viscosity of about 100,000 centipoise to about 750,000 centipoise;
(C) about 20 to about 80 parts by weight of a resinous copolymer containing R
3
SiO
1/2
units and SiO
4/2
units, where R is a hydrocarbon monovalent radical having from 1 to about 6 carbon atoms, said resinous copolymer having a molar ratio of R
3
SiO
1/2
units to SiO
4/2
units of about 0.6 to about 0.9;
(D) an organohydrogenpolysiloxane of formula (III)
R
3
2
HSiO(R
3
2
SiO)
q
SiHR
3
2
(III)
wherein each R
3
is independently an alkyl group having 1 to about 10 carbon atoms or an aryl group; q has an average value of 1 to about 300; the molar ratio of silicon-bonded hydrogen groups in (D) to silicon-bonded alkenyl groups in (A) being about 0.8:1 to about 1.5:1;
(E) a catalytic amount of a hydrosilation catalyst; and
(F) about 0.2 to about 6 parts by weight of a cross-linking agent comprising an organic peroxide or an organic azo compound;
wherein all parts by weight are based on the weight of the entire composition.
The use of alkenyl-terminated polydiorganosiloxane (A) and organohydrogenpolysiloxane (D) having two terminal hydride units per molecule increases the molecular weight of the cured composition, allowing the use of reduced solvent levels while maintaining a viscosity sufficiently low for coating.
Component (A) of the composition is an alkenyl-terminated polydiorganosiloxane having formula (I)
R
2
R
1
2
SiO(R
1
2
SiO)
m
SiR
1
2
R
2
(I)
wherein each R
1
is independently an alkyl group having 1 to about 10 carbon atoms or an aryl group, R
2
is an alkenyl group having 1 to about 10 carbon atoms, m has an average value of about 20 to about 2000, preferably about 90 to about 1200, more preferably about 120 to about 1000.
In formula (I), R
1
may be an alkyl group such as methyl, ethyl, or propyl, or an aryl group such as phenyl. Preferably, at least 99.5 percent and most preferably essentially 100 percent of all R
1
radicals are alkyl and most preferably methyl. R
2
may be an alkenyl group such as vinyl,
Greenberg Ronald A.
Griswold Roy M.
Horkay Ference
Lin Shaow B.
Townsend David F.
General Electric Company
Zimmer Marc S.
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