Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-10-01
2003-04-08
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S261000, C524S267000, C524S588000, C524S837000, C525S477000, C528S034000, C528S500000, C528S501000, C528S50200C
Reexamination Certificate
active
06545086
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
This invention is related to silicone pressure sensitive adhesive compositions, and particularly to such compositions in the form of aqueous dispersions or emulsions. Silicone pressure sensitive adhesives are used for example in paper coatings, as release modifying additives to organic pressure sensitive adhesives and in medical and personal care applications.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,791,163 (Dec. 13, 1988) describes an aqueous emulsion comprising an organic pressure sensitive adhesive and a silicone pressure sensitive adhesive. Japanese Patent 07331220 (Dec. 19, 1995) describes an aqueous silicone emulsion adhesive composition comprising an alkenyl organopolysiloxane, a resin comprising triorganosiloxy units and SiO
2
units (MQ resin), an organohydrogenpolysiloxane, an emulsifier and a platinum catalyst.
U.S. Pat. No. 5,612,400 (Mar. 18, 1997) describes a silicone pressure sensitive adhesive composition comprising 100 parts of an organopolysiloxane of viscosity at least 500000 cps, 60 to 300 parts of a MQ resin having 0.2 to 5 percent silicon-bonded hydroxyl radicals and a ratio of 0.6-1.2:1 triorganosiloxy units to SiO
2
units, and 20-2500 parts of a linear or cyclic volatile organosiloxane fluid of boiling point 95-250° C.
U.S. Pat. No. 5,330,747 (Jul. 19, 1994) and U.S. Pat. No. 5,451,610 (Sep. 19, 1995) describe personal care preparations, particularly eye cosmetics such as mascara, comprising a trimethylsilyl-endblocked benzene-soluble resinous copolymer containing silicon-bonded hydroxyl radicals, a silanol-endblocked polydiorganosiloxane fluid and a phenyl-containing polysiloxane fluid of viscosity 5-60000 centiStokes at 25° C. The composition can optionally contain a volatile silicone such as hexamethyldisiloxane or octamethylcyclotetrasiloxane.
BRIEF SUMMARY OF THE INVENTION
A pressure sensitive adhesive emulsion according to the invention comprises a disperse silicone phase emulsified in a continuous water phase in the presence of a surfactant, wherein the disperse silicone phase comprises 40 to 80 percent by weight of a silicone pressure sensitive adhesive, which is the product of mixing a silanol-terminated polydiorganosiloxane of Tg below −20° C. with a silanol-containing silicone resin of Tg above 0° C., dispersed in 60 to 20 percent by weight of a volatile silicone fluid having a boiling point below 300° C., the emulsion being substantially free of any non-silicon-containing volatile organic material.
The invention also includes a process for the production of a pressure sensitive adhesive emulsion comprising mixing the silicone pressure sensitive adhesive defined above, the volatile silicone fluid having a boiling point below 300° C., and a surfactant, and adding water optionally containing surfactant while shearing to form an emulsion.
The invention also includes a process for the production of a pressure sensitive adhesive emulsion comprising mixing the silicone pressure sensitive adhesive defined above with the volatile silicone fluid having a boiling point below 300° C. and adding the resulting mixture to an aqueous solution of a surfactant while shearing.
The invention further includes methods for the production of a pressure sensitive adhesive emulsion of reduced volatile content, wherein an emulsion as defined above is subjected to steam stripping, or is contacted with a hydrophobic pervaporation membrane, or is heated with removal of volatile material while adding water to the emulsion to compensate for water which is removed.
These and other features of the invention will become apparent from a consideration of the detailed description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
The silicone pressure sensitive adhesive generally comprises the product of mixing a silanol-terminated polydiorganosiloxane of Tg below −20° C. lightly crosslinked with a silanol-containing silicone resin of Tg above 0° C. The organic substituents of the silanol-terminated polydiorganosiloxane are generally alkyl groups having 1 to 6 carbon atoms or phenyl groups. Preferably at least 80 percent of the organic substituents are methyl groups. Most preferably the silanol-terminated polydiorganosiloxane is a dimethylhydroxy-terminated polydimethylsiloxane. The silanol-terminated polydiorganosiloxane preferably has a viscosity of at least 0.1 Pa.s and can have viscosity up to 30000 Pa.s or higher. It can for example be prepared by the method of U.S. Pat. No. 5,319,120.
The silanol-containing silicone resin is generally a non-linear siloxane resin and preferably consists of siloxane units of the formula R′
a
SiO
4−a/2
wherein R′ denotes a hydroxyl, hydrocarbon or hydrocarbonoxy group and wherein a has an average value of from 1 to 1.8. The resin preferably consists of monovalent trihydrocarbonsiloxy (M) groups of the formula R″
3
SiO
1/2
and tetrafunctional (Q) groups SiO
4/2
wherein R″ denotes a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably a methyl group. The number ratio of M groups to Q groups is preferably in the range 0.5:1 to 1.2:1 (equivalent to a value of a in the formula R′
a
SiO
4−a/2
of 1.0 to 1.63), and is more preferably 0.6:1 to 0.9:1. The silicone resin preferably contains at least 0.2 percent by weight up to about 3 or 5 percent silicon-bonded hydroxy radicals. These are preferably present as dimethylhydroxysiloxy (HO)(CH3)
2
SiO
1/2
units.
The silicone pressure sensitive adhesive preferably comprises 20 to 80 parts by weight, preferably 30 to 60 parts, of the silanol-terminated polydiorganosiloxane of Tg below −20° C., and 80 to 20 parts by weight, preferably 70 to 40 parts, of the silanol-containing silicone resin of Tg above 0° C. Most preferably the silicone pressure sensitive adhesive is the product of mixing 30 to 60 parts by weight of a silanol-terminated polydiorganosiloxane of Tg below −20° C. and viscosity 0.1-30000 Pa.s at 25° C. with 40 to 70 parts by weight of a silanol-containing silicone resin of Tg above 0° C. comprising monovalent trihydrocarbonsiloxy (M) groups of the formula R″
3
SiO
1/2
and tetrafunctional (Q) groups SiO
4/2
wherein R″ denotes a monovalent hydrocarbon group having 1 to 6 carbon atoms, the number ratio of M groups to Q groups being in the range 0.5:1 to 1.2:1.
The silanol groups of the polydiorganosiloxane generally undergo some condensation reaction with the silanol groups of the silicone resin so that the polydiorganosiloxane is lightly crosslinked by the silicone resin (that is, polydiorganosiloxane chains are bonded together through resin molecules to give chain branching and entanglement and/or a small amount of network character) to form the silicone pressure sensitive adhesive. A catalyst, for example an alkaline material such as ammonia, ammonium hydroxide or ammonium carbonate can be mixed with the silanol-terminated polydiorganosiloxane and the silicone resin to promote this crosslinking reaction. It may for example be preferred, particularly for personal care and medical applications, that the silanol-terminated polydiorganosiloxane has a viscosity in the range 1-100 Pa.s at 25° C. and is crosslinked with the aid of a catalyst. The amounts of silanol-terminated polydiorganosiloxane and silanol-containing silicone resin are preferably such that the Tg of the product of mixing is between −15 and 15° C. (T at tan delta maximum). The silanol-containing silicone resin preferably lowers the rubbery plateau modulus (G′ at Tg+30° C.) of the blend below 7E+05 dyne/cm2; this is an indication that the network character is due to light crosslinking as discussed above rather than extensive crosslinking.
The silicone pressure sensitive adhesive produced by mixing the silanol-terminated polydiorganosiloxane and sil
Dawson Robert
DeCesare Jim L.
Dow Corning Corporation
Zimmer Marc S
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