Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-07-12
2004-02-24
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S446000, C524S860000, C524S861000, C524S862000
Reexamination Certificate
active
06696161
ABSTRACT:
This invention relates to silicone compositions capable of adhering to plastic film substrates independent of the type of plastic film, and release films using the same.
BACKGROUND OF THE INVENTION
In the coating art, there are known a variety of silicone release compositions for use in preventing any sticking or adhesion between substrates of paper, plastics or the like and pressure-sensitive adhesives. Of these, solvent type silicone compositions have been widely used because of release properties and relatively low substrate selectivity.
However, the demand for solventless silicone compositions is now increasing from the safety and health standpoints. A number of solventless silicone compositions are known in the art as described in JP-A 49-47426, JP-A 50-141591, JP-B 52-39791 and JP-A 57-77395. These compositions adhere well to paper and laminated paper, but do not adhere well to plastic films.
It was then proposed to blend certain silanes or siloxanes in organopolysiloxane for imparting self-adhesiveness thereto (see JP-B 46-2187 and JP-B 52-9469). Since these compositions cure through condensation reaction, which requires elevated temperatures, they are unsuited for plastic films.
JP-A 63-27560 and JP-A 6-293881 disclose silicone compositions based on an organovinylpolysiloxane having branching points within the molecule, which adhere well to polyolefin film substrates without a need for solvents. However, these silicone compositions raise the problem that they fail to establish satisfactory bonds when applied to polyester film substrates.
SUMMARY OF THE INVENTION
An object of the invention is to provide a silicone composition which cures in the absence of a solvent into a coating that adheres well to plastic film substrates independent of the type of plastic film. Another object is to provide a release film using the same.
It has been found that when first and second organopolysiloxanes specified below are combined, the resulting silicone composition, despite a solventless system, is able to cure into a coating that firmly adheres to plastic film substrates independent of the type of plastic film.
The present invention provides a silicone composition comprising
(A) 100 parts by weight of a first organopolysiloxane having the following average compositional formula (1):
wherein R
1
is alkenyl, R
2
is a monovalent hydrocarbon radical, R
3
is hydrogen or alkyl, m, n and p are such positive numbers in the range: 0.6≦(n+p)/m≦1.5 and 0≦p/(n+p)≦0.05 that the organopolysiloxane has a viscosity at 25° C. of 5 to 100 mPa·s,
(B) 10 to 100 parts by weight of a second organopolysiloxane having the following general formula (2):
wherein R
4
is a monovalent hydrocarbon radical, at least two of the entire R
4
radicals are alkenyl, t is a number from 0 to 15, q, r, s and t are such numbers that the organopolysiloxane has a viscosity at 25° C. of from 100 mPa·s to a 30% toluene dilute-solution viscosity of 20,000 mPa·s,
(C) 30 to 100 parts by weight of an organohydrogenpolysiloxane having at least two hydrogen atoms each directly attached to a silicon atom per molecule, and
(D) a catalytic amount of a platinum group metal catalyst.
The present invention also provides a release film in which a cured coating of the silicone composition is formed on a plastic film substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(A) First Organopolysiloxane
The first organopolysiloxane is the most important component in the silicone composition of the invention and has the following average compositional formula (1).
Herein R
1
is alkenyl, R
2
is a monovalent hydrocarbon radical, and R
3
is hydrogen or alkyl. Suitable alkenyl radicals represented by R
1
are those having 2 to 8 carbon atoms, such as vinyl, allyl, butenyl, pentenyl and hexenyl. Suitable monovalent hydrocarbon radicals represented by R
2
are those having 1 to 8 carbon atoms, for example, alkenyl radicals such as vinyl, allyl, butenyl and pentenyl as exemplified for R
1
, alkyl radicals such as methyl, ethyl and propyl, aryl radicals such as phenyl, aralkyl radicals such as benzyl, and substituted ones of the foregoing radicals in which some or all of the hydrogen atoms are substituted with halogen atoms. Suitable alkyl radicals represented by R
3
are those having 1 to 6 carbon atoms, such as methyl, ethyl and propyl.
The subscripts m, n and p are such positive numbers that the first organopolysiloxane has a viscosity at 25° C. of 5 to 100 mPa·s, preferably 10 to 50 mPa·s. The value of (n+p)/m is from 0.6 to 1.5, and preferably from 0.8 to 1.2. If (n+p)/m<0.6, the adhesion to plastic film declines. If (n+p)/m>1.5, which indicates a higher proportion of R
2
SiO
3/2
units, it is difficult to synthesize such organopolysiloxanes. The value of p/(n+p) is from 0 to 0.05, and preferably from 0 to 0.03. If p/(n+p)>0.05, which indicates a higher content of hydroxyl or alkoxy radicals, the resulting silicone composition becomes less curable.
As described above, the first organopolysiloxane has a viscosity at 25° C. of 5 to 100 mPa·s. A viscosity of less than 5 mPa·s detracts from curability whereas a viscosity of more than 100 mPa·s detracts from adhesion.
The first organopolysiloxane should preferably have a vinyl value of 0.5 to 2.25 mol/100 g, and more preferably 0.5 to 1.0 mol/100 g.
The first organopolysiloxane can be prepared, for example, by subjecting a trialkoxymethylsilane and a dialkenyltetramethyldisiloxane or hexamethyldisiloxane in an alcohol solvent to cohydrolysis in the presence of an acid catalyst, neutralizing, removing the alcohol by-product, washing with water, and removing the unreacted reactants.
(B) Second Organopolysiloxane
The second organopolysiloxane is a component that largely governs the release force of a cured coating of the silicone composition. By altering the structure and substituents of this component, the release properties of the cured coating can be controlled. The second organopolysiloxane has the following general formula (2).
Herein R
4
is a monovalent hydrocarbon radical, preferably those radicals of 1 to 8 carbon atoms, as exemplified above for R
2
. At least two of the entire R
4
radicals should be alkenyl.
The subscripts q, r, s and t are such numbers that the second organopolysiloxane has a viscosity at 25° C. in a range from 100 mPa·s to a 30% toluene dilute-solution viscosity of 20,000 mPa·s, and especially in a range from 200 mPa·s to a 30% toluene dilute-solution viscosity of 5,000 mPa·s, while t is in the range: 0≦t≦15, and especially 0≦t≦6. If the viscosity of the second organopolysiloxane is less than 100 mPa·s, the resulting silicone composition becomes less viscous and less effective to apply to film substrates. If the 30% toluene dilute-solution viscosity exceeds 20,000 mPa·s, the resulting silicone composition becomes too viscous and less efficient to apply.
The second organopolysiloxane may be used singly or in admixture of two or more. Preferably, the second organopolysiloxane contains 10 to 50% by weight based on the entire second organopolysiloxane of an organopolysiloxane having a 30% toluene dilute-solution viscosity of 1,000 to 10,000 mPa·s at 25° C. and especially 2,000 to 5,000 mPa·s at 25° C., and a vinyl value in average molecule of at least 0.02 mol/100 g, more preferably 0.02 to 0.2 mol/100 g, and even more preferably 0.02 to 0.08 mol/100 g. The preferred second organopolysiloxane ensures that the resulting silicone composition provides a cured coating having satisfactory adhesion, release properties and wear resistance. It is preferred to use an organopolysiloxane having a viscosity at 25° C. of 200 to 1,000 mPa·s and a vinyl value of 0.01 to 0.10 mol/100 g as the remainder of the second organopolysiloxane.
An appropriate amount of the second organopolysiloxane blended is 10 to 100 parts by weight, and preferably 10 to 50 parts by weight, per 100 parts by weight of the first organopolysiloxane. With less than 10 parts of the second organopolysiloxane, the release force of cured coat
Irifune Shinji
Ogawa Masahiko
Dawson Robert
Feely Michael J
Shin-Etsu Chemical Co. , Ltd.
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