Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-08-01
2002-12-10
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S148000
Reexamination Certificate
active
06492433
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improved ultraviolet light curable silicone release coating compositions. More particularly, it relates to novel additive blends of alkylphenols and alkyl vinyl ethers, which, when added to epoxysilicone polymers, provide for superior miscibility of polar onium salt photocatalysts in the epoxysilicone medium, and provide for superior release of the resulting photocured silicone coating from acrylic adhesives laminated thereto.
BACKGROUND OF THE INVENTION
Silicone coating compositions are used for many applications including release coatings, or adhesive coatings, designed to permit release of aggressive adhesives without denigration of the adhesive properties due to contact with the silicone surface. Other silicone coatings well known to those versed in the art include protective coatings and conformal coatings. Such coatings have often been applied to various substrates as dispersions in solvents such as low boiling aromatic and aliphatic organic compounds or as emulsions dispersed in water. In such cases it is necessary to apply considerable heat to both remove the dispersing agent and to accelerate crosslinking (curing) of the silicone that has been applied to the substrate. Application of silicone without solvent or water dispersing agents is a desirable improvement of the art in that removal of volatile organic solvent requires environmentally compliant technology that adds cost to the coating process without otherwise benefiting the coating process. Similarly, elimination of a thermal cure step in favor of a low temperature radiation crosslinking process permits use of film, plastic or other thin gauge substrate material for the silicone release coating which would otherwise be ruled out because such substrates cannot accommodate the heat required for conventional silicone release coating crosslinking.
Silicone compositions have long been in use for rendering surfaces non-adherent to materials which would otherwise adhere thereto. Epoxy-functional polydimethylsiloxanes (PDMS), when combined with compatible iodonium cationic type photocatalysts, are well known to those skilled in the art to be useful UV curable silicone release coatings. Such combinations of organofunctional silicone polymers and lipophilic iodonium photocatalysts have been taught in U.S. Pat. No. 4,279,717 and many other subsequent patents. Such coatings based on cationic photocurable epoxy-silicones have been shown to be readily coatable to thin, defect-free continuous films when applied to smooth paper or plastic film liners using 3 roll offset gravure or multiroll liquid film splitting techniques, and these coatings are quickly crosslinked by exposure to focused ultraviolet light to create low surface energy adhesive surfaces capable of release of organic pressure sensitive adhesives (PSA). A drawback to the cationic epoxysilicone based photocurable release coating systems has been their inability to provide long term stable release from commonly used aggressive acrylic PSA's, particularly if the adhesive is laminated to the silicone coating in-line, that is, as part of the converting process. While the precise cause of this performance deficiency is not established, it is thought that a significant post-cure of the epoxysilicone coating takes place which, when occurring in the laminate with the acrylic PSA, leads to chemical interactions of the silicone surface with the acrylic PSA which in turn leads to unstable release and even a lock-up of the silicone surface with the PSA. It is therefore clear that providing a means by which a photocured epoxysilicone release coating can consistently give low (premium) release of aggressive acrylic adhesives as a function of laminate aging is highly desirable.
The absence of solvent from a coating composition reduces the energy needed for crosslinking as well as the need for pollution abatement. But the absence of solvent leads to problems insofar as silicone release coatings are non-polar viscous materials that are immiscible with many polar additives including 'onium type cationic photocatalysts. Another problem associated with solvent-free silicone coatings is that the high viscosity associated with solvent free compositions is unsuited for many cost-effective coating techniques including direct gravure or indirect gravure coating. Such coating equipment is used for pattern coating of silicone to produce complex double release constructions and other specialty products. Vinyl ether monomers such as dodecylvinyl ether and the bis-vinyl ether of 1,4-cyclohexanedimethanol have been shown to be useful reactive diluents for photocurable epoxysilicone release coatings, capable of efficient reduction of viscosity and enhancement of photocure, as taught by Eckberg et al in U.S. Pat. No. 5,650,453. However, the presence of vinyl ethers in the cured epoxysilicone release coating gives rise to unstable release of the silicone coated liner from most acrylic and rubber based adhesives. Alkylphenols such as 4-dodecylphenol (DDP), in blends with certain alkanediols, have been shown to be effective reactive diluents for cationic photocure epoxysilicone release systems, as taught by Descorcie et al in U.S. Pat. No. 5,010,118. Also, the use of DDP or other alkylphenols in such cases for the enhanced miscibility of alkoxy-substituted bis-aryl iodonium and tris-phenyl sulfonium hexafluoroantimonates has been published. Phenol-substituted epoxysilicone terpolymers have been described as controlled release additives for UV epoxysilicone systems in Riding et al, U.S. Pat. No. 4,952,657.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that certain specific combinations of additives are miscible with photocurable silicone compositions and also act as compatibilizing agents for polar 'onium type cationic photocatalysts which are often incompletely miscible with nonpolar organofunctional silicones and which, unexpectedly, provide dramatic improvement in the stability of release of the resultant UV cured silicone coating from aggressive acrylic adhesives. The present invention provides for photocurable silicone release coating compositions that are efficiently photo-crosslinked, readily applied to film, paper, and glassine substrates, and which provide exceptionally stable release from aggressive adhesives. The compositions of the instant invention provide for a curable additive for catatonically photocurable silicone polymers, said additive selected from a first group consisting of vinyl ether monomers and a second group selected from a group of alkylphenol compounds.
The present invention therefore provides for an ultraviolet light or electron beam curable silicone coating composition comprising:
a) An epoxy functional silicone selected from the group consisting of:
MD
x
D
E
y
Q
z
T
u
D
Rf
j
M
M
E
D
x
D
E
y
Q
z
T
u
D
Rf
j
M
E
M
E
D
x
D
E
y
Q
z
T
u
D
Rf
j
M
And mixtures thereof; and where:
M=(CH
3
)
3
SiO
1/2
M
E
=(C
6
H
9
O(CH
2
)
2
)(CH
3
)
2
SiO
1/2
D=(CH
3
)
2
SiO
2/2
D
E
=(C
6
H
9
O)(CH
2
)
2
(CH
3
)SiO
2/2
D
Rf
=(CF
3
CH
2
CH
2
)(CH
3
)SiO
2/2
Q=SiO
4/2
T=(CH
3
)SiO
3/2
where j, x,y,z, and u are positive integers and j, z, and u may be zero and wherein said epoxy-functional silicone has a viscosity ranging from about 20 to about 100000 centistokes at 25° C. And, if preferred, a polydimethylsiloxane chainstopped with (poly)(carbinol) group-containing trialkylsiloxy species of the general formula:
M
BOH
D
v
M
BOH
Where D is as defined above, and M
BOH
=R
1
R
2
R
3
SiO
1/2
, with R
1
, R
2
, and R
3
each monovalent radicals and each independently selected from the group consisting of hydrogen, trifluoropropyl, monovalent hydrocarbon radicals, and (HO-alkyl)
n
— radicals such that each M
BOH
chainstopper unit includes at least one, and preferable more than one, (HO-alkyl) group;
b) an unsaturated ether compound selected from the group consisting of:
CH
2
═CH—O—(CH
2
)
11
CH
3
(CH
2
═CH—O—CH
2
)
2
—(C
6
H
10
)
CH
2
═
Nutter Nathan M.
Wheelock Kenneth S.
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