Acrylic functional organopolysiloxanes and radiation-curable...

Details Acrylic functional organopolysiloxanes and radiation-curable... Acrylic functional organopolysiloxanes and radiation-curable...

1999-07-27

2001-05-29

Dawson, Robert (Department: 1712)

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

Synthetic resins

From silicon reactant having at least one...

C528S015000, C528S031000, C522S099000, C428S447000

Reexamination Certificate

active

06239246

ABSTRACT:

This invention relates to acrylic functional organopolysiloxanes useful as a main component in back coating agents for adhesive tapes and release paper coating agents for adhesive labels, and radiation-curable compositions comprising the same.
BACKGROUND OF THE INVENTION
One common approach taken for the purpose of preventing adhesion and bond between a substrate such as paper, converted paper or plastic film and a pressure-sensitive adhesive material is to apply a curable silicone composition onto the substrate surface and cure the coating with heat, UV or electron beams. The coated substrate is generally known as a release sheet.
The composition from which a releasable cured film is formed is required to cure at a low temperature and within a short time from the standpoints of productivity and energy saving and also in consideration of its application to less heat resistant substrates. Especially from the standpoint of preventing the substrate from deforming by heat, it is advantageous to cure a coating with radiation such as electron beams or ultraviolet rays into a cured film.
One useful method for preparing a composition for forming a releasable cured film is to cure an organopolysiloxane having (meth)acrylate groups by irradiating electron beams. The release of a cured film from a tacky material depends on the (meth)acrylate group content of the (meth)acrylate group-containing organopolysiloxane. The cured film requires a greater peeling force as the content of (meth)acrylate groups increases.
On the other hand, at least a certain amount of (meth)acrylate groups is necessary in order to quickly form a cured film. No cured film can be formed if the (meth)acrylate group content is reduced. Also, (meth)acrylate groups contribute to the phenomenon that a cured film firmly bonds to the substrate. An organopolysiloxane having a reduced (meth)acrylate group content cannot form a releasable film on the substrate because the cured film will readily separate from the substrate.
As understood from the foregoing, the releasable cured film involves contradictory release, cure, and substrate bond behaviors. It is difficult to find a compromise between light peeling and formation of a satisfactory cured film.
JP-A 7-316517 discloses that a cured film ensuring light peeling and age stability is obtainable by mixing an organopolysiloxane having (meth)acrylate groups with a non-reactive organopolysiloxane. In this cured film, however, the non-reactive organopolysiloxane which has not been incorporated in the crosslinked structure migrates from the surface of the cured film to a surface in contact therewith, detracting from the residual bonding force and ball tack, that is, the tack of a self-adhesive layer.
SUMMARY OF THE INVENTION
An object of the invention is to provide an acrylic functional organopolysiloxane which offers light release and good retention of adhesion and is radiation curable. Another object of the invention is to provide a radiation-curable composition comprising the same.
The invention provides an acrylic functional organopolysiloxane obtained by effecting addition reaction between (A) an organopolysiloxane having acrylic functional groups and (B) an organopolysiloxane having a hydride (SiH) group at either end to induce partial crosslinking. This acrylic functional organopolysiloxane is useful as a main component in back coating agents for adhesive tapes and release paper coating agents for adhesive labels. A radiation-curable composition comprising the organopolysiloxane as a main component is lightly releasable, ensures good retention of adhesion, and upon exposure to radiation, forms a cured film.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The acrylic functional organopolysiloxane of the invention is obtained by effecting addition reaction between (A) an organopolysiloxane having acrylic functional groups and (B) an organopolysiloxane having a hydride group at either end to induce partial crosslinking.
The organopolysiloxane (A) is preferably an organopolysiloxane having acrylic functional groups represented by the following average compositional formula (1):
A
x
R
1
y
SiO
(4−x−y)/2
  (1)
wherein A is —R
2
OCOCR
3
═CH
2
or —OR
2
OCOCR
3
═CH
2
wherein R
2
is an alkylene group of 1 to 10 carbon atoms, and R
3
is hydrogen or methyl; R
1
, which may be the same or different, is a monovalent hydrocarbon group, of 1 to 10 carbon atoms; x is from 0.002 to 1.50, y is 0 to 3.0, and the sum of x and y is from 1.5 to 2.5.
Preferred examples of the C
1
-C
10
alkylene group represented by R
2
are methylene, ethylene and propylene groups.
The groups represented by R
1
are substituted or unsubstituted monovalent C
1
-C
10
hydrocarbon groups, for example, alkyl groups such as methyl, ethyl, propyl and butyl, cycloalkyl groups such as cyclohexyl, aryl groups such as phenyl and tolyl, aralkyl groups such as benzyl and phenylethyl, and substituted ones of these groups in which some or all of the hydrogen atoms attached to carbon atoms are replaced by hydroxyl groups, cyano groups or halogen atoms, such as hydroxypropyl, cyanoethyl, 1-chloropropyl and 3,3,3-trifluoropropyl. Alkyl and aryl groups are desirable as R
1
groups when the release of the acrylic functional organopolysiloxane in the cured state is taken into account.
Among the organopolysiloxanes of formula (1), those of the following formulae (3) to (7) are preferred.
In formulae (3) to (7), p is an integer of at least 2, preferably 2 to 100 and more preferably 2 to 50, q is an integer of at least 0, preferably 0 to 1,000 and more preferably 0 to 500. Letters r and t are integers of at least 0 and the sum of r+t is an integer of at least 2, preferably 2 to 100 and more preferably 2 to 50; s and u are integers of at least 0 and the sum of s+u is an integer of at least 0, preferably 0 to 2,000 and more preferably 0 to 1,000; and m is an integer of 0 to 3.
The organopolysiloxane (A) generally has a viscosity of 10 to 10,000 centistokes at 25° C. and preferably 50 to 1,000 centistokes at 25° C.
Specific examples of the organopolysiloxane (A) are given below.
The organopolysiloxane (A) may be used alone or in admixture of two or more.
The organopolysiloxane having a hydride group at either end (B) is preferably one represented by the following average compositional formula (2):
H(R
2
SiO)
n
SiR
2
H  (2)
wherein R, which may be the same or different, is a monovalent hydrocarbon group of 1 to 10 carbon atoms, and n is a positive number so that the organopolysiloxane has a viscosity of 1 to 1,000,000 centistokes at 25° C.
Illustrative of the groups represented by R are substituted or unsubstituted monovalent C
1
-C
10
hydrocarbon groups, for example, alkyl groups such as methyl, ethyl, propyl and butyl, cycloalkyl groups such as cyclohexyl, aryl groups such as phenyl and tolyl, and substituted ones of these groups in which some or all of the hydrogen atoms attached to carbon atoms are replaced by hydroxyl groups, cyano groups or halogen atoms, such as hydroxypropyl, cyanoethyl, 1-chloropropyl and 3,3,3-trifluoropropyl. Alkyl and aryl groups are desirable as R groups when the release of the acrylic functional organopolysiloxane in the cured state is taken into account. Further preferably, at least 80 mol % of the R groups in the entire siloxane units are methyl groups. The letter n is a positive number, preferably at least 2, so that the organopolysiloxane has a viscosity of 1 to 1,000,000 centistokes, especially 50 to 1,000 centistokes at 25° C.
Illustrative examples of the organopolysiloxane (B) are given below.
H(Me
2
SiO)
50
SiMe
2
H
H(Me
2
SiO)
100
SiMe
2
H
H(Me
2
SiO)
200
SiMe
2
H
H(Me
2
SiO)
100
(Ph
2
SiO)
20
SiMe
2
H
Herein, Me is methyl and Ph is phenyl.
The organopolysiloxane (B) may be used alone or in admixture of two or more.
For reaction, the organopolysiloxane having acrylic functional groups (A) and the organopolysiloxane having a hydride group at either end (B) are preferably used in a molar ratio (B)/(A) from 99/1 to 5/95 and especially from 98/2 to 20/

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