Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-12-18
2003-05-13
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C528S015000, C528S032000, C528S031000, C525S478000, C428S449000
Reexamination Certificate
active
06562469
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silicone composition intended for forming cured release coatings, and more specifically relates to a solventless silicone composition for forming cured release coatings that is capable of forming on the surface of various substrate materials, such as various paper materials, laminated paper, synthetic resin film, metal foil, etc., cured coatings that are releasable from tacky substances.
BACKGROUND OF THE INVENTION
Cured coatings consisting of curable silicone compositions in which organopolysiloxane is the main component exhibit tacky substance-releasing properties and have been utilized for peel-away liners of pressure sensitive adhesive tape and pressure sensitive adhesive sheets. It should be noted that, in addition to the release properties, compositions of this type are often required to exhibit slip properties for use at the interface between paper and paper, plastic film and plastic film, or between paper and plastic film, and between paper, plastic film and the human hand. For this reason, numerous silicone compositions of the organic solvent solution type, aqueous emulsion type, etc., have been proposed as silicone compositions for forming cured release coatings exhibiting characteristics of this kind. However, although compositions of the former organic solvent solution type possess superior release properties, slip properties, and curing characteristics, due to the large amount of the organic solvent required, they have various problems, such as atmospheric pollution, adverse influence on the health of workers, and considerable expenditures required for solvent recovery equipment. Also, a disadvantage of the latter compositions of the aqueous emulsion type is the need for heating at an elevated temperature for a prolonged period of time to form coatings, which results in low productivity. In addition, there are other disadvantages such as the limited use of high molecular weight organopolysiloxanes due to difficulties in their emulsification as well as inferior characteristics as compared with compositions of the organic solvent solution type, which are due to the use of emulsifying agents.
On the other hand, a composition comprising vinyl-containing diorganopolysiloxane having a viscosity of 50 to 4,000 mPa·s at 25° C., organohydrogenpolysiloxane having at least three hydrogen atoms bonded to silicon atoms per one molecule, a platinum catalyst, and an activity inhibitor (see Japanese Patent Publication No. Sho 52(1977)-047485) is an example of a solventless silicone composition for forming cured release coatings that does not utilize organic solvents or water. However, a disadvantage of cured coatings formed using this composition is their poorer slip properties as compared with coatings formed using the above-mentioned compositions of the organic solvent solution type, as a result of which their use has been limited. In addition, a solventless silicone composition comprising a mixture of 100 to 50 parts by weight of a vinyl-containing polysiloxane having both terminal ends of the molecular chain blocked by trialkylsiloxy groups and 0 to 50 parts by weight of a dimethylvinylsiloxy-endblocked vinyl-containing polysiloxane, a methylhydrogenpolysiloxane, and a platinum catalyst (see Japanese Patent Application Publication No. Hei 07(1995)-258606) is also known. Although the composition exhibited improvements in terms of slip properties, it was far from sufficient, and because its curability is low as well, the composition can not satisfy certain applications. For example, when the composition was used as a release agent for Kraft tape, due to the insufficient slip properties, when the tape was applied to corrugated fiberboard etc., frictional resistance between the tape and hands increased, as a result of which there were hand injuries or the force used for the application of the tape was insufficient and the pressure sensitive adhesive did not firmly adhere to the corrugated fiberboard and peeling occurred over time. In addition, there have been attempts to use methods, in which dimethylsiloxane oil, polyether-modified silicone oils, surface active agents, and waxes were added in order to improve slip properties, but their disadvantage was the decreased adhesive strength of the pressure sensitive adhesive agent due to the migration of some of the additives to the surface of the cured coating.
It is an object of the present invention to provide a silicone composition for forming cured release coatings which is superior in curability, and after curing is capable of forming on the surface of various substrate materials, such as paper and plastic film, cured coatings that possess superior release properties and slip properties and do not reduce the pressure sensitive adhesive characteristics of pressure sensitive substances.
SUMMARY OF THE INVENTION
The present invention relates to an essentially solventless silicone composition for forming cured release coatings comprising
(A) 100 parts by weight of a mixture comprising 99 to 90 parts by weight of (A-1) a linear diorganopolysiloxane having a viscosity of 5 to 1,000 mPa·s at 25° C., having both terminal ends of the molecular chain blocked by dimethylalkenylsiloxy groups, with an alkenyl group content of 0.2 of 10 mol % of all organic groups and 1 to 10 parts by weight of (A-2) a linear diorganopolysiloxane having a viscosity of 1,000 to 10,000 mPa·s at 25° C. and having both terminal ends of the molecular chain blocked by trimethylsiloxy groups and having at least two pendant alkenyl groups bonded to silicon atoms, with an alkenyl group content of 0.05 to 0.5 mol % of all organic groups,
(B) 3 to 50 parts by weight of an organohydrogenpolysiloxane having a viscosity of 1 to 1,000 mPa·s at 25° C. and having at least three silicon-bonded hydrogen atoms per molecule, and
(C) a catalytic amount of a platinum catalyst.
DESCRIPTION OF THE INVENTION
The present invention relates to an essentially solventless silicone composition for forming cured release coatings. The composition comprises
(A) 100 parts by weight of a mixture comprising 99 to 90 parts by weight of (A-1) a linear diorganopolysiloxane having a viscosity of 5 to 1,000 mPa·s at 25° C., having both terminal ends of the molecular chain blocked by dimethylalkenylsiloxy groups, with an alkenyl group content of 0.2 of 10 mol % of all organic groups and 1 to 10 parts by weight of (A-2) a linear diorganopolysiloxane having a viscosity of 1,000 to 10,000 mPa·s at 25° C., having both terminal ends of the molecular chain blocked by trimethylsiloxy groups and having at least two pendant alkenyl groups bonded to silicon atoms, with an alkenyl group content of 0.05 to 0.5 mol % of all organic groups,
(B) 3 to 50 parts by weight of an organohydrogenpolysiloxane having a viscosity of 1 to 1,000 mPa·s at 25° C. and having at least three silicon-bonded hydrogen atoms per molecule, and
(C) a catalytic amount of a platinum catalyst.
The composition of the present invention will now be explained in detail. Component (A-1), which is the main component of the present composition, is a linear diorganopolysiloxane having both terminal ends of the molecular chain blocked by dimethylalkenylsiloxy groups, with an alkenyl group content of 0.2 to 10 mol % of all organic groups of (A-1). Diorganopolysiloxanes described by general formula
are suggested as component (A-1). In the formula, R
1
and R
2
are alkenyl groups exemplified by vinyl, butenyl, hexenyl, octenyl, and decenyl. Among these, vinyl and hexenyl are preferable. R
3
is a monovalent hydrocarbon group other than alkenyl, exemplified by methyl, ethyl, butyl, and other alkyl groups; phenyl, tolyl, and other aryl groups; cyclohexyl and other cycloalkyl groups. The subscript x is an integer of 1 or greater and y is an integer of 0 or greater, preferably within such a range that 0≦y/(x+y)≦0.2. The value of (x+y) is such that the viscosity of (A-1) at 25° C. is 5 to 1,000 mPa·s and preferably within the range of 50 to 600 mPa·s. Exemplary of component (A-1) are
Kaiya Nobuo
Koyama Taku
Dawson Robert
Dow Corning Toray Silicone Co. Ltd.
Peng Kuo-Liang
Scaduto Patricia M.
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