Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1999-02-04
2001-03-13
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S031000, C528S032000, C528S033000
Reexamination Certificate
active
06201092
ABSTRACT:
This invention relates to addition curing type silicone compositions which in the cured state have improved heat resistance and form firm bonds to various substrates of resins and metals and which are applicable as the adhesive to electric and electronic parts and automotive parts.
BACKGROUND OF THE INVENTION
For providing addition curing type silicone adhesives which are bondable to a variety of substrates, attempts were made to add tackifiers (or adhesion agents) to curable silicone resins so that the resin might become more adhesive. For example, JP-B 21026/1978 corresponding to U.S. Pat. No. 3,699,072 discloses an addition curing type silicone rubber composition comprising an organohydrogensiloxane having alkoxysilyl groups, and JP-B 13508/1978 corresponding to U.S. Pat. No. 4,077,943 discloses an addition curing type silicone rubber composition comprising an organohydrogensiloxane having epoxy groups.
The prior art addition curing type silicone adhesives, however, are difficultly self-bondable to some substrates, especially resins. Primers must be applied before the silicone adhesives can be bonded. Such difficultly bondable resins are polycarbonates and polyphenylene sulfites. Nowadays, there is an increasing demand for addition curing type silicone adhesives capable of self-bonding to such resins.
As prior art approaches for producing addition curing type silicone adhesives capable of self-bonding to difficultly bondable resins, the addition of nitrogen compounds is known from JP-B 147963/1977. Also developed was a technique of using alkoxysilanes as a tackifier and adding organic tin compounds, organic titanium compounds or organic aluminum compounds as a hydrolytic catalyst.
These techniques, however, are not satisfactory since they can affect the curing of addition curing type silicone adhesives. More particularly, when nitrogen compounds are added to the addition curing type silicone adhesives, these compounds significantly inhibit the catalysis of platinum atom serving as the addition reaction catalyst, resulting in unstable curing. When organic tin compounds, organic titanium compounds or organic aluminum compounds are added, these compounds can deactivate organohydrogensiloxanes in the addition curing type silicone adhesives and act to cleave siloxane bonds in the silicone polymers at elevated temperatures, causing to reduce the heat resistance of the cured composition.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a novel and improved addition curing type silicone composition having improved curing stability, thermal stability and adhesion which cures into a product capable of firm adhesion to difficultly bondable resins.
We have found that when an addition curing type silicone composition comprising (A) an organopolysiloxane having at least two alkenyl groups each attached to a silicon atom in a molecule, (B) an organohydrogenpolysiloxane having at least two hydrogen atoms each attached to a silicon atom in a molecule, and (C) a platinum catalyst is further blended with (D) a (meth)acryloxyalkyl-modified organopolysiloxane having a linear or cyclic organopolysiloxane structure and a viscosity of 5 to 10,000 centipoise at 25° C. as an adhesion promoter, the (meth)acryloxyalkyl-modified organopolysiloxane quickly diffuses into the composition (that is, into the organopolysiloxane matrix) and (meth)acryl groups in its molecule have high affinity to various substrates. Then the (meth)acryloxyalkyl-modified organopolysiloxane is successful in providing the composition with improved adhesion without adversely affecting the curing and thermal stability of the composition. There is obtained an addition curing type silicone composition which in the cured state forms firm bonds to difficultly bondable resins such as polycarbonates and polyphenylene sulfites.
Accordingly, the present invention provides an addition curing type silicone composition comprising
(A) 100 parts by weight of an organopolysiloxane having at least two alkenyl groups each attached to a silicon atom in a molecule, represented by the following average compositional formula (1):
R
1
a
R
2
b
SiO
(4−a−b)/2
(1)
wherein R
1
is a substituted or unsubstituted monovalent hydrocarbon group free of an aliphatic unsaturated bond, R
2
is an alkenyl group, letter a is a number of 1.4 to 2.0, b is a number of 0.0001 to 0.5, and the sum of a and b is from 1.9 to 2.05,
(B) an organohydrogenpolysiloxane having at least two hydrogen atoms each attached to a silicon atom in a molecule, represented by the following average compositional formula (2):
R
3
c
H
d
SiO
(4−c−d)/2
(2)
wherein R
3
is a substituted or unsubstituted monovalent hydrocarbon group free of an aliphatic unsaturated bond, letter c is a number of 0.7 to 2.0, d is a number of 0.005 to 1.2, and the sum of c and d is from 0.8 to 3.0, in an amount to provide 0.4 to 10 silicon atom-attached hydrogen atoms per alkenyl group in the composition,
(C) a catalytic amount of a platinum catalyst,
(D) 0.0001 to 3 parts by weight of a (meth)acryloxyalkyl-modified organopolysiloxane having a linear or cyclic organopolysiloxane structure and a viscosity of 5 to 10,000 centipoise at 25° C.
DETAILED DESCRIPTION OF THE INVENTION
Component (A) of the addition curing type silicone composition according to the invention is the main component of the composition and an organopolysiloxane having at least two alkenyl groups each attached to a silicon atom in a molecule, represented by the following average compositional formula (1):
R
1
a
R
2
b
SiO
(4−a−b)/2
(1)
wherein R
1
is a substituted or unsubstituted monovalent hydrocarbon group free of an aliphatic unsaturated bond, R
2
is an alkenyl group, letter a is a number of 1.4 to 2.0, b is a number of 0.0001 to 0.5, and the sum of a and b is from 1.9 to 2.05. Preferably, a is a number of 1.9 to 2.0, b is a number of 0.001 to 0.1, and the sum of a and b is from 1.95 to 2.02.
With respect to molecular structure, the organopolysiloxane of formula (1) may be linear, partially branched or cyclic. It may be a homopolymer consisting of identical siloxane units or a copolymer consisting of two or more different siloxane units. Most often, it is a linear diorganopolysiloxane having a backbone portion consisting essentially of recurring diorganosiloxane units and blocked with a triorganosiloxy unit at each end. The alkenyl group in the molecule may be attached to either the silicon atom at the end of the molecular chain or a silicon atom midway the molecular chain or both. When the physical properties of the cured product is taken into account, the organopolysiloxane should preferably have alkenyl groups attached to the silicon atoms at the both ends of the molecular chain.
In formula (1), R
1
represents substituted or unsubstituted monovalent hydrocarbon groups free of an aliphatic unsaturated bond, preferably having 1 to 12 carbon atoms, especially 1 to 8 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl, isopropy, butyl, isobutyl, tert-butyl, hexyl, 2-ethylhexyl, octyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and substituted ones of these hydrocarbon groups wherein all or some of the hydrogen atoms are replaced by halogen atoms such as fluorine atoms and chlorine atoms or nitrile groups, typically substituted alkyl groups such as trifluoropropyl, chloromethyl, and cyanoethyl. The R
1
groups may be the same or different. It is preferred from the standpoints of chemical stability and ease of synthesis that all R
1
groups are methyl although some of the methyl groups may be replaced by phenyl or trifluoropropyl groups if necessary for particular properties.
R
2
represents alkenyl groups preferably having 2 to 8 carbon atoms, especially 2 to 4 carbon atoms, for example, vinyl, allyl, propenyl, isopropenyl, butenyl, isobutenyl, hexenyl, and
Dawson Robert
Peng Kao Liang
Shin-Etsu Chemical Co. , Ltd.
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