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
2000-05-05
2002-07-16
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...
C524S837000, C524S862000, C428S447000, C526S279000, C528S024000, C528S025000, C528S028000, C528S032000, C106S287150
Reexamination Certificate
active
06420480
ABSTRACT:
TECHNICAL FIELD
This invention relates to silicone acrylate latex polymers and in particular to silicone acrylate latex polymers prepared by emulsion polymerization and useful as release coatings.
BACKGROUND OF THE INVENTION
Generally, conventional release coating compositions are solvent-based polymers. They are typically prepared using solution polymerization in organic solvents. In an attempt to meet many environmentally driven standards to reduce or replace volatile organic solvents, efforts have been directed towards the development of waterborne release coatings and low adhesion backsize coatings. Furthermore, reducing and/or eliminating solvents has added economical advantage. However, many of the aqueous release coatings described in the literature are not completely solvent-free systems.
Many of the existing waterborne release coatings involve processes where solvents are used during the polymerization. These processes then require an additional step of distillation or other process(es) to remove the solvents. The drawbacks of this technology are the low solids, the use of solvent during production that raises environmental issues, and the long time required to remove the solvent to invert into water which can result in increased costs. The use of solvents is not desirable due to environmental, economic, and safety reasons.
Thus, there is a need to provide waterborne release coatings that are essentially solvent free, while at the same time providing desirable release, writability, printability, and aging characteristics.
SUMMARY OF THE INVENTION
Briefly, in one aspect of the present invention, polymer latices are provided that are useful as release coatings for pressure-sensitive adhesive (PSA) coated paper and tapes. In yet another aspect, coated articles comprising a layer of the polymer latex compositions of the present invention are provided.
With the ever-present environmental concern to eliminate organic solvents, the use of 100% solids and water-based release coatings is becoming more desirable. The latices of the present invention are waterborne, which is an advantage over the more conventional release coating compositions that are usually comprised of solvent-based polymers, and possess good and stable release characteristics.
The waterborne polymer latices of the present invention comprise:
(a) latex particles, wherein the latex particles are the polymerization reaction product comprising:
(1) about 15 to about 45 percent by weight of a silicone containing monomer;
(2) about 25 to about 85 percent by weight of one or more short chain alkyl acrylate or alkyl methacrylate monomers, wherein the alkyl group contains less than about 12 carbon atoms;
(3) 0 to about 15 percent by weight of one or more carboxylic acid functional monomers; and
(4) 0 to about 15 percent by weight of one or more nitrogen containing monomers; such that the combination of components (3) and (4) is greater than 0% by wt, preferably is in the range of greater than 0% to 30% by wt., and more preferably, is in the range of greater than 0% to 15% by wt.;
(b) an effective amount of an emulsifier or an emulsifier mixture;
(c) water; and
(d) optionally, one or more additives.
Silicone containing monomers useful in forming the polymer latices of the present invention can be defined as mercapto functional silicone macromolecular chain transfer agents or silicone-containing macromonomers.
Additives for the above-identified compositions can include fillers, coalescing agents, defoamers, and the like.
The present invention takes advantage of the emulsion polymerization process where all the monomers react to form a polymer in an aqueous medium. The novelty of the invention is the ability to incorporate monomers that provide or contribute to good release characteristics but also have low water solubility (i.e.—silicone-containing monomers). This is accomplished by using a mini-emulsion process that includes a homogenization step rather than a conventional emulsion polymerization approach that does not require any homogenization.
The latices of the present invention provide release during the removal of an adhesive coated sheet of paper from a pad or during unwinding of pressure-sensitive adhesive coated tapes, such as clear tapes, masking tape, packaging tape, etc. Furthermore, the latices advantageously provide for high readhesion, that is, a readhesion in the range of 80% or greater, without the necessity of additional processing to remove free silicone from the latices.
Advantageously, the water-based latices of the present invention are prepared without the use of organic solvents. The release coatings obtained possess good release, writability, printability, and aging properties for conventional pressure-sensitive adhesives.
In another aspect of the present invention, a coated sheet material is provided comprising a flexible sheeting and a release coating covering at least a portion of one major surface of the flexible sheet wherein the release coating is formed by coating the above-described waterborne silicone acrylate latex polymer, which has been diluted as necessary for coating. The coated article thus obtained possesses excellent release, writability, printability, and aging properties.
DESCRIPTION OF THE PREFERRED EMBODIMENTS(S)
Waterborne Release Coating Composition
The latices of the present invention are comprised of a polymer dispersed within an aqueous phase that is stabilized with an emulsifier. The latices are prepared by emulsion copolymerization of silicone containing monomers. The latices provide release during the removal of adhesive coated sheets of paper from a pad or during the unwinding of pressure-sensitive adhesive coated tapes, and the like.
Monomers
Silicone Containing Monomers
Silicone containing monomers useful in forming the polymer latices of the present invention include mercapto functional silicone macromolecular chain transfer agents such as pendant functional mercaptopolydiorganosiloxane copolymers that are described by the following general formula (1):
wherein:
R
1
, R
2
, and R
3
are monovalent moieties that can independently be the same or different and are selected from the group consisting of alkyl, aryl, alkylaryl, alkoxy, alkylamino, hydroxyl, hydrogen, fluoroalkyl, divalent linking groups and are most preferably alkyl moieties;
R
4
, R
5
, and R
6
are monovalent moieties that can independently be the same or different and are selected from the group consisting of alkyl, aryl, alkylaryl, alkoxy, alkylamino, hydroxyl, hydrogen, fluoroalkyl and are most preferably alkyl moieties;
z can range from 1 to about 16, preferably 1 to 5 and is most preferably 3;
x and y are integers of at least one and the sum of x+y is an integer of 10 or greater; and y can range from 0.5 to about 80% of (x+y); preferably from 1-20% of (x+y) and most preferably from 3.5-14% of (x+y).
A most preferred additive is commercially available from Shin-Etsu, Inc. Akron, Ohio, under the commercial designation of “X-22-980” wherein R
1
, R
2
, R
3
, R
4,
R
5
, and R
6
=CH
3
, y=3.5 to 4.5% of (x+y), z=3, and the number average molecular weight (Mn)=8000. Additional most preferred additives of varying values of R, x, y, and z are available from Huls America, Inc. (Piscataway, N.J.)
The term silicone containing monomer as used herein also includes silicone macromonomers having the general formula (2):
wherein:
X is a polymerizable vinyl group;
Y is a divalent linking group selected from the group consisting of —CH
2
—, —CH
2
—CH
2
—, and —CH
2
—CH
2
—CH
2
—;
m is 20 to 2000;
each R is independently selected from the group consisting of hydrogen, C
1-8
alkyl, aryl, and alkoxy.
Preferably the formulas of the silicone macromonomer are selected such that X is selected from the group consisting of:
Preferably, the macromonomer is represented by the general formula (4):
wherein m is 100 to 150, (prepared according to procedures described in U.S. Pat. No. 4,728,571). This monomer is referred to herein as “SiMac”.
Preferably the latices o
3M Innovative Properties Company
Dawson Robert
Peters Carolyn V.
Zimmer Marc S.
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