Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2000-08-09
2002-06-25
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S446000, C428S447000, C428S480000, C528S015000, C528S031000, C528S032000, C525S446000, C106S287130, C106S287140
Reexamination Certificate
active
06410134
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an aqueous silicone coating composition having an excellent pot life; and to a polyester release film coated by said composition on at least one surface thereof, which is used as a temporary support substrate for an adhesive coated article.
BACKGROUND OF THE INVENTION
Polyesters such as polyethylene terephthalate (PET) are known to possess good chemical stability, physical and mechanical strength, heat resistance, durability, chemical resistance, weather resistance and electrical insulation property; and, therefore, have been widely used in manufacturing various articles including medical devices, capacitors, photographic films, packing and labeling materials, and magnetic recording media.
In addition, a silicone-coated polyester film may be used as a release substrate for adhesive coated articles such as adhesive tapes and peel-off label stickers. A silicone-coated polyester film having high strength, transparency and chemical resistance is particularly desirable in such applications.
Silicone-coated release films are produced by coating a substrate film with a solvent-based or solventless silicone composition. The use of a solvent-based silicone composition, however, induces the problem of releasing harmful organic solvents to the environment, while the coating obtained using a solventless silicone composition which usually has a high viscosity is undesirably thick, which leads to economic disadvantages.
Accordingly, there have been a number of studies to develop aqueous silicone coating compositions.
Canadian Patent No. 1,120,176 discloses an aqueous silicone emulsion consisting of: 1) a diorganopolysiloxane having silicon bonded vinyl groups in their terminal units, 2) an organopolysiloxane having at least three silicon-bonded hydrogen atoms per molecule, and 3) a catalytic amount of a platinum catalyst which promotes the addition of the silicon-hydrogen bonds to the vinyl groups. Similar aqueous-based silicone compositions containing polyvinyl alcohol and alkylphenyl polyglycol ether as emulsifying agents are disclosed in Canadian Patent No. 1,246,270, European Patent Publication No. 484,001, U.S. Pat. Nos. 5,095,067; 5,104,927; 4,791,029; 3,900,617; and 5,777,017.
However, release films coated with the aqueous silicone emulsions mentioned above have poor chemical resistance and unsatisfactory storage stability.
U.S. Pat. No. 5,672,428 teaches an aqueous silicone coating composition comprising: 1) an alkylvinylpolysiloxane containing vinyl groups, 2) a platinum or tin complex catalyst, 3) a glycidoxysilane, and 4) an alkylhydrogenpolysiloxane. Release films coated with this silicone composition exhibit improved chemical and rub-off resistances, but the productivity of this method is not good because the pot life of the composition is severely reduced.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a silicone coating composition having a good pot life, which is capable of forming a coating having good release property, improved rub-off and chemical resistances.
It is another object of the present invention to provide a polyester release film of which at least one surface is coated with the composition.
In accordance with one aspect of the present invention, there is provided an aqueous silicone coating composition comprising an alkylvinylpolysiloxane; 1.5 to 10 percent by weight, based on the amount of the alkylvinylpolysiloxane, of an alkylhydrogenpolysiloxane; 10 to 500 ppm, based on the amount of the alkylvinylpolysiloxane, of a platinum complex catalyst; and 0.5 to 20 percent by weight, based oil the amount of the alkylvinylpolysiloxane, of a water-soluble polyester resin.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, there is provided an aqueous silicone coating composition comprising an alkylvinylpolysiloxane, an alkylhydrogenpolysiloxane, a platinum complex catalyst and a water-soluble polyester resin.
The alkylvinylpolysiloxane which may be used in the present invention is a straight- or branched-chain type, wherein preferred is the straight-chain type. The straight-chain type alkylvinylpolysiloxane has two or more of R
2
groups per molecule on the average and a mean viscosity of 10 to 30,000 mm
2
/sec, preferably 200 to 7,000 mm
2
/sec at 25° C. Divinylpolydimethylsiloxane having two vinyl groups in its terminal units is most preferably employed in the present invention.
The alkylhydrogenpolysiloxane employed in the present invention is a straight-chain, branched-chain or ring type, wherein preferred is the straight-chain type. The straight-chain type alkylhydrogenpolysiloxane has two or more silicon-bonded hydrogen atoms per molecule on the average and a mean viscosity of 10 to 1,000 mm
2
/sec, preferably 10 to 100 mm
2
/sec at 25° C. Polymethylhydrogensiloxane having a hydrogen content of at least 1 weight % is most preferably employed in the present invention. The alkylhydrogenpolysiloxane may be employed in an amount ranging from 1.5 to 10 parts, preferably 2 to 5 parts by weight based on 100 parts by weight of the alkylvinylpolysiloxane.
The alkylvinylpolysiloxane and alkylhydrogenpolysiloxane are cross-linked and cured by inducing a hydrosilation reaction therebetween, the hydrosilation reaction being accelerated by a platinum catalyst such as platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex. The platinum complex catalyst may be employed in an amount ranging from 10 to 500 ppm based on the weight of the alkylvinylpolysiloxane.
Aqueous silicone emulsions comprising such alkylvinylpolysiloxanes, alkylhydrogenpolysiloxanes and platinum catalysts are commercially available, for example from Dow Corning(Midland, Mich.), GE Silicone(Waterford, N.Y.) and Rhone Poulenc, Inc.(Rockwell, S.C.) under the trade names of Syl-Off 7900/7922, SM 3000/3010 and 71822/71823, respectively. These emulsions are composed of two separate emulsions, i.e., a first emulsion containing an alkylvinylpolysiloxane and an alkylhydrogenpolysiloxane, and a second emulsion, an alkylvinylpolysiloxane and a platinum catalyst.
The water-soluble polyester resin employed in the present invention is water soluble or water dispersible, and contains a controlled amount of ester bonds formed between a dicarboxylic acid having hydrophilic groups and a diol in its main chain.
The amount of the dicarboxylic acid units having hydrophilic groups is preferably below 15 mol %, more preferably 5 to 15 mol %, based on the total dicarboxylic acid units present in the water-soluble polyester resin, wherein examples of hydrophilic groups are alkali metal sulfonate and alkali metal carboxylate groups. Other dicarboxylic acid units are derived from such conventional dicarboxylic acids as dimethylterephthalic acid, terephthalic acid, dimethylisophthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, diphenoxyethanedicarboxylic acid, biphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, anthracenedicarboxylic acid and &agr;, &bgr;-bis(2-chlorophenoxy)ethane-4,4′-dicarboxylic acid, among which a combination of dimethylterephthalic acid or terephthalic acid and isophthalic acid(50~80:20~50(mol %)) is preferred.
Examplary diols which are used in preparing the water-soluble polyester resin include: ethylene glycol, 1,4-butanediol, propylene glycol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol, among which a combination of ethylene glycol and 1,4-butanediol is preferred.
The water-soluble polyester resin of the present invention has a number average molecular weight of less than 50,000, preferably below 25,000, and it may be employed in an amount ranging from 0.5 to 20 parts, preferably 1 to 10 parts by weight based on 100 parts by weight of the alkylvinylpolysiloxane. When the amount of the water-soluble resin used is less than 0.5 parts by weight, the strength of coated film becomes unsatisfactory, while at an amount of more than 20 parts by weight, the forc
Park Eung-Sik
Won Jong-Seob
Chen Vivian
Rosenman & Colin LLP
SKC Limited
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