Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-11-18
2001-10-09
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S015000, C528S032000, C528S031000
Reexamination Certificate
active
06300426
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solventless silicone composition intended for forming cured release films. More specifically, the invention relates to a silicone composition which, through the use of a cured organopolysiloxane film, imparts to the surfaces of various substrates, such as paper, synthetic resin film, or metal foil, release properties relative to tacky substances.
BACKGROUND OF THE INVENTION
Solventless silicone compositions are used as release liners of adhesive tapes and sheets for forming, cured films with an ability to release from adhesive substances. When these release films are peeled with low speed (below approximately 0.3 m/min), resistance to peeling is allowed in a wide range from low to high. However, when peeling is carried out with a high speed (50 m/min or higher), it is required that resistance to peeling be relatively low. Japanese Patent Application No. 2-187466 discloses a solventless silicone release coating composition prepared from an polyorganohydrogensiloxane, a platinum catalyst, and a mixture of polydiorganosiloxanes comprising a copolymer of dimethylsiloxane and methylvinylsiloxane and a copolymer of diphenylsiloxane, methylvinylsiloxane, and dimethylsiloxane with diphenylsiloxane units in an amount of 0.5 to 3.0 mole %. A drawback of this composition is high resistance to peeling and a decrease in residual adhesion of the adhesive material that has been applied onto the cured release film. For these reasons, the above composition was not always satisfactory in use. In Japanese Patent Application Nos. 9-125004, 10-158519, and 2-145649, is disclosed a composition comprising an uncured copolymer of methylhexenylsiloxane and dimethylsiloxane having both molecular terminals capped with trimethylsiloxy groups, a polyorganohydrogensiloxane, a platinum catalyst, and an organic solvent. Since the main component of this composition is a polydiorganosiloxane having hexenyl groups and comprising a rubber-like high-molecular-weight substance, it is required that the composition be diluted in an organic solvent. llowever, organic solvents not only are harmful to the health of the workers who work with such solvents, but also are costly since they require the use of various means to prevent evaporation of these solvents into the surrounding atmosphere. In addition, the use of the cured films produced from the aforementioned compositions is not always satisfactory. This is because, when peeling is carried out at high speed (exceeding approximately 50 m/min), it is difficult to ensure low resistance to peeling.
In Japanese Patent Application No. 7-258606 it was proposed to utilize solventless silicone release coating composition having a main component in the form of polyorganosiloxane having both molecular terminals capped with trialkylsiloxy groups and with two or more vinyl groups in a side chain. In Japanese Patent Publication 62-86061 was disclosed a silicone release coating composition having as its main component a polydiorganosiloxane having alkenyl groups containing 6 or more carbon atoms in one molecule. Although the aforementioned compositions are free of problems associated with the use of organic solvents and are not subject to decrease in the coefficient of residual adhesion in the adhesive material applied onto the cured release films, they still have high resistance to peeling when peeling is performed at a high speed (approximately 50 m/min or higher).
SUMMARY OF THE INVENTION
This invention relates to a silicone composition comprising: (A) a mixture of (i) a linear trimethylsiloxy-terminated polydiorganosiloxane containing at least 2 alkenyl groups having at least 4 carbon atoms and (ii) optionally a linear dimethylalkenylsiloxy-terminated polydiorganosiloxane, (B) a polyorganohydrogensiloxane, (C) a catalytic quantity of a platinum catalyst, and (D) an inhibitor.
It is an object of this invention to provide a solventless silicone release coating composition which makes it possible to form cured release films with low resistance to peeling when peeling is carried out at high speeds, and With the possibility of controlling the resistance to peeling between low and high values when peeling is carried out at low speeds.
It is also an object of this invention to produce a solventless silicone release coating composition which is not subject to a decrease in the coefficient of residual adhesion in the adhesive material applied onto a cured release film.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to a silicone composition comprising: (A) a mixture of (i) 40 to 100 wt % of a linear trimethylsiloxy-terminated polydiorganosiloxane having a viscosity of 50 to 5000 mm
2
/s at 25° C. and containing at least 2 alkenyl groups having at least 4 carbon atoms, the alkenyl groups comprising 0.2 to 10.0 mole % of all organic groups bonded to silicon atoms in the polydiorganosiloxane, and (ii) 0 to 60 wt % of a linear dimethylalkenylsiloxy-terminated polydiorganosiloxane having a viscosity of 50 to 5000 mm
2
/s at 25° C. and containing at least 2 alkenyl groups per molecule, the alkenyl groups comprising 0.2 to 10.0 mole % of all organic groups bonded to silicon atoms in the polydiorganosiloxane, (B) 3 to 50 parts by weight per 100 parts by weight of Component (A) of a polyorganohydrogensiloxane having at least 3 silicon-bonded hydrogen atoms per molecule and having a viscosity of 1 to 1000 mm
2
/s at 25° C., (C) a catalytic quantity of a platinum catalyst, and (D) an inhibitor.
The polydiorganosiloxane of Component A(i) is a linear-chain siloxane which is terminated with trimethylsiloxy groups and which contains in its side chain at least 2 alkenyl groups having 4 or more carbon atoms. Normally, the alkenyl group is bonded to a silicon atom. The alkenyl groups are exemplified by butenyl, 5-hexenyl, octenyl, and decenyl. It is preferred that the alkenyl group is the 5-hexenyl group. It is recommended that the alkenyl groups comprise 0.2 to 10 mole %, preferably 1.0 to 5.0 mole % of the total amount of organic groups bonded to silicon atoms in the polydiorganosiloxane. Silicon-bonded organic groups other than alkenyl groups are exemplified by monovalent hydrocarbon groups such as alkyl groups exemplified by methyl, ethyl, propyl, butyl, pentyl, and hexyl, aryl groups exemplified by phenyl, tolyl, and xylyl, aralkyl groups such as benzyl and phenethyl, with methyl being preferred. The polydiorganosiloxane of Component A(i) preferably is a trimethylsiloxy-terminated polydimethylsiloxane-polymethylalkenylsiloxane copolymer represented by the formula:
wherein R
1
is an alkenyl group having 4 or more carbon atoms, x and y are positive integers which satisfy the following conditions: 0.80≦x/(x+y)<0.99; 0.01<y/(x+y)≦0.20 and y≦2. If y/(x+y) is below 0.01, in the case of high-speed peeling, the resistance to peeling will be high. If, on the other hand, the above value exceeds 0.20, resistance to peeling will be high at both low- and high-speed peeling. It is preferable that y/(x+y) be within the range of 0.03 to 0.06. Furthermore, (x+y) should have a value that provides viscosity at 25° C. within the range of 50 to 5000 mm
2
/s, and preferably within the range of 100 to 2000 mm
2
/s.
The polydiorganosiloxane of Component A(ii) is a linear-chain siloxane which contains at least 2 alkenyl groups in its molecule and which is terminated with dimethylalkenylsiloxy groups. Normally, the alkenyl group is bonded to a silicon atom. The alkenyl groups are exemplified by vinyl, butenyl, 5-hexenyl, octenyl, and decenyl. It is especially preferred that the alkenyl group is selected from the group consisting of vinyl group and 5-hexenyl. It is recommended that the alkenyl groups comprise 0.2 to 10 mole %, preferably 1.0 to 5.0 mole % of the total amount of organic groups bonded to silicon atoms in the polydiorganosiloxane. Silicon-bonded organic groups other than alkenyl groups are exemplified by monovalent hydrocarbon groups such as alkyl groups exemplified by methyl, ethyl, propyl, butyl,
Koyama Taku
Togashi Atsushi
Yamada Takateru
Dawson Robert
Dow Corning Toray Silicone Company, Ltd.
Peng Kuo-Liang
Scaduto Patricia M.
Troy Timothy J.
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