Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1999-12-22
2001-11-06
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C524S261000, C524S265000, C524S267000, C524S588000, C524S730000, C524S773000, C522S099000
Reexamination Certificate
active
06312818
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to materials useful with release coatings, that is, coatings which release materials that would ordinarily be adherent. In particular, this invention relates to adhesion-enhancing additives for release coatings.
When labels, stamps, decorative laminates, transfer tapes, or the like are coated with an adhesive, it is desirable that the substrate, on which the labels (for example) are stored be easily peeled away when the label is ready for use. However, it is also important that the adhesive quality of the label not be derogated by removal from the substrate. This can be accomplished by coating the substrate with a release coating, commonly a silicone release coating. Silicone release coatings on paper, polyethylene, Mylar and other substrates also provide non-stick surfaces for food handling and industrial packaging applications.
Epoxy functionalized polyorganosiloxanes have proved especially useful as release coatings. While these polymers show good adhesion to substrates such paper, they show poorer adhesion to plastic films such as polyethylene, polypropylene, polystyrene and polyester. Release coatings must have good adhesion to the substrate, or the coating may be removed during the manufacturing process or along with the adhesive when the label is removed from the substrate. One method to improve adhesion to plastic films is to employ an adhesion promoter, also known as an anchorage additive. However, few adhesion promoters are known.
U.S. Pat. No. 5,567,764 discloses the use of trialkoxysilane or trialkoxysiloxane containing alkenyl functional polyorganosiloxanes as adhesion promoters for addition cure release coatings. In addition cure release coatings, crosslinking is effected in the presence of a metal catalyst, such as platinum, palladium, rhodium, ruthenium, or iridium. This is in contrast to ultraviolet (UV) cure release coatings, which are cationically crosslinked in the presence of a UV light and a photoinitiator. When 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and vinyltriacetoxysilane are used in UV cure release coatings, the achieved anchorage is not consistent and the release coatings rub off. Accordingly, there remains a continuing need in the art for adhesion promoters which will provide consistent anchorage of UV cure release coatings to substrates, particularly to plastic films.
SUMMARY OF THE INVENTION
A release coating composition is provided, comprising
(a) a cationically curable functionalized polyorganosiloxane;
(b) a photoinitiator; and
(c) an adhesion promoter having the following formula (1):
wherein R
1
to R
3
and R
7
to R
9
are independently alkyl, alkoxy, aryl, aryloxy or alkenyl hydrocarbon or halohydrocarbon groups having from 1 to 20 carbon atoms, R
4
and R
6
are independently alkyl, aryl, or alkenyl hydrocarbon or halohydrocarbon groups having from 1 to 20 carbon atoms, and R
5
is an alkyl, aryl, or alkenyl hydrocarbon or halohydrocarbon group having from 1 to 20 carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION
A curable release coating composition comprises at least one cationically curable functionalized polyorganosiloxane, a photoinitiator and an anchorage additive of the following formula (1):
wherein R
1-3
and R
7-9
are independently alkyl, alkoxy, aryl, aryloxy or alkenyl halohydrocarbon functional groups having from 1 to 20 carbons, and R
4
and R
6
are independently alkyl, aryl, or alkenyl hydrocarbon or halohydrocarbon groups having from 1 to 20 carbon atoms and R
5
is an alkyl, aryl, or alkenyl hydrocarbon or halohydrocarbon group having from 1 to 20 carbon atoms.
The invention further comprises the release coating composition applied to a substrate, preferably a plastic film.
The cationically curable functionalized polyorganosiloxane has functional groups which are cationically crosslinkable. Exemplary cationically curable functionalized polyorganosiloxanes include epoxy functionalized polyorganosiloxanes, alkenyl ether functionalized polyorganosiloxanes, or a mixture thereof.
Suitable epoxy functionalized polyorganosiloxanes are described, for example, in U.S. Pat. No. 4,421,904 to Eckberg et al., which is incorporated by reference herein. Eckberg discloses cationically curable, precrosslinked, dialkylepoxy chain-stopped polydialkylalkylepoxysiloxane copolymers wherein the polysiloxane units contain lower alkyl substituents, preferably methyl groups. The epoxy functionality is obtained when certain of the hydrogen atoms on the polysiloxane chain of a polydimethyl-methylhydrogensiloxane copolymer are reacted in a hydrosilation addition reaction with a vinyl functional siloxane cross-linking fluid and other organic molecules which contain both ethylenic unsaturation and epoxide functionality. Ethylenically unsaturated species will add to a polyhydroalkylsiloxane to form a copolymer in the presence of a catalytic amount of platinum and/or rhodium metal. Although this addition reaction is the cure mechanism for other silicone compositions, in this case, a controlled amount of this cross-linking is permitted to take place in a silicone precursor fluid or intermediate, and this is referred to as “pre-crosslinking”. Pre-crosslinking of the precursor silicone fluid means that there has been partial cross-linking or cure of the composition and offers the advantages of enabling swift ultraviolet light initiated cure with a low energy expenditure and without any need for a solvent.
The ultraviolet curable epoxy functional silicone intermediate fluid comprises a pre-crosslinked epoxy functional dialkylepoxy chain-stopped polydialkylalkylepoxysiloxane copolymer silicone fluid which is the reaction product of a vinyl- or allylic-functional epoxide and a vinyl functional siloxane cross-linking fluid having a viscosity of approximately 1 to 100,000 centipoise at 25° C. with a hydrogen functional siloxane precursor fluid having a viscosity of approximately 1 to 10,000 centipoise at 25° C. in the presence of an effective amount of precious metal catalyst for facilitating an addition cure hydrosilation reaction between the vinyl functional cross-linking fluid, vinyl functional epoxide, and hydrogen functional siloxane precursor fluid.
The vinyl- or allylic-functional epoxide may be a cycloaliphatic epoxy compound such as 4-vinylcyclohexeneoxide, allylgycidyl ether or glycidyl acrylate, vinylnorbornene monoxide, and dicyclopentadiene monoxide.
The precious metal catalyst can be selected from the group of platinum-metal complexes, which includes complexes of ruthenium, rhodium, palladium, osmium, iridium and platinum.
The vinyl functional siloxane cross-linking fluid can be selected from the group consisting of dimethylvinyl chain-stopped linear polydimethysiloxane, dimethylvinyl chain-stopped polydimethyl-methylvinyl siloxane copolymer, tetravinyltetramethylcyclotetrasiloxane and tetramethyldivinyldisiloxane. The hydrogen functional siloxane precursor fluid can be selected from the group consisting of tetrahydortetramethylcyclotetrasiloxane, dimethylhydrogen chain-stopped linear polydimethylsiloxane, dimethylhydrogen chain-stopped polydimethyl-methyl-hydrogen siloxane copolymer and tetramethyldihydrodisiloxane.
These polymers are suitable for cure in the presence of a free radical photoinitiator (b) and UV or electron beam (EB) radiation. Suitable photoinitiators include, but are not limited to, onium salts of an element of Groups 15 to 17 of the Periodic Table with weakly nucleophilic or non-nucleophilic anions, as disclosed in Eckberg et al., and U.S. Pat. No. 5,340,898 to Cavezzan et al., which are incorporated herein by reference. Exemplary photoinitiators are bis-aryliodonium salts having the following formula (2):
wherein R is an alkyl, alkoxy or haloalkyl radical having from 1 to 20 carbon atoms, preferably a dodecyl moiety, and n is in integer in the range from 1 to five, preferably 1, and X is B(C
6
F
5
)
4
, CF
3
SO
3
, SbF
6
, AsF
6
, PF
6
, or BF
4
.
Adhesion promoters (c) have the following f
Lapinski Melania I.
Rubinsztajn Slawomir
Dawson Robert
General Electric Company
Zimmer Marc S.
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