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
2001-03-16
2003-11-04
Wu, David W. (Department: 1713)
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...
C524S529000, C524S533000, C524S536000, C523S456000
Reexamination Certificate
active
06642298
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pressure sensitive adhesive formulations. In particular, the invention relates to a pressure sensitive adhesive formulation comprising an acrylic polymer grafted with an ethylene-butylene rubber macromer.
BACKGROUND OF THE INVENTION
Typical acrylic pressure sensitive adhesive formulations are copolymers of alkyl ester monomers, a functional monomer such as acrylic acid, and may be crosslinked using, for example, aluminum chelates. These adhesives are generally deficient in adhesion to low energy surfaces. While adhesives may be tackified with rosin esters to improve low surface energy adhesion, tackification results in loss of heat resistance and poor aging properties. Even though good aging properties are compromised, tackified acrylic dispersions are sufficient for some applications, e.g. most paper label uses and, indeed, have become the dominant paper label technology. These tackified acrylic adhesives, however, do not have sufficient resistance to degradation for most graphics and industrial tape applications in which acrylic solutions are conventionally used.
Rubber-resin formulations are often used to adhere to polyolefins and other low energy substrates. Typical compositions are natural rubber or styrene block copolymers tackified with rosin esters. These formulations provide excellent tack and cohesive strength but discolor and lose tack on aging due to oxidative and UV light induced degradation. Formulations of fully hydrogenated rubbers and resins, besides being more costly, generally do not have the required adhesive performance.
U.S. Pat. No. 5,625,005 discloses hybrid rubber-acrylic pressure sensitive adhesives described as having good UV resistance and aging characteristics along with high adhesion to non-polar surfaces. Despite this advancement in the art, there remains a need for improved polymer compositions which can be used to prepare pressure sensitive adhesives having sufficient adhesion and chemical resistance properties for applications such as industrial tapes and transfer films, and exterior graphics applications on low energy, difficult to adhere surfaces. The present invention addresses this need.
SUMMARY OF THE INVENTION
The invention provides adhesive formulations having outstanding coating characteristics, adhesion to a wide variety of substrates, including low energy surfaces, while maintaining these performance properties at higher temperatures in their dried state.
One aspect of the invention is directed to a pressure-sensitive adhesive comprising an acrylic polymer grafted with a rubber macromer. Preferred for use is an ethylene-butylene macromer. In one embodiment, the acrylic polymer comprises at least one low glass transition temperature (Tg) alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group and at least one monomer having a high glass transition temperature (i.e., a Tg greater than about 0° C.). In preferred embodiments of the invention the acrylic polymer may further comprise at least one hydroxy functional monomer and/or may also comprise at least one carboxy functional monomer. In a particularly preferred embodiment, a crosslinking agent, such as an aluminum or a titanium crosslinking agent, is used.
Another aspect of the invention is directed to a pressure-sensitive adhesive comprising an acrylic polymer comprising at least one low Tg alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group grafted with a rubber macromer, preferably, an ethylene-butylene macromer, the polymer being crosslinked using a titanium crosslinking agent. In a preferred embodiment, the acrylic polymer comprises, in addition to an alkyl acrylate monomer, at least one high Tg monomer, at least one hydroxy functional monomer and/or at least one carboxy functional monomer. The use of a titanium-containing metal alkoxide crosslinker has been discovered to impart excellent and unexpected high temperature performance.
Still another aspect of the invention is directed to a process of making a pressure-sensitive adhesive comprising an acrylic polymer grafted with a rubber macromer, preferably an ethylene-butylene macromer, wherein the macromer is substantially free of metal or strong acid. Preferably, the molecular weight of the macromer used to make the adhesive ranges from about 2,000 to about 10,000. The process comprises reacting an acrylic polymer component with a rubber macromer component, said macromer component being substantially free of catalyst used to prepare the macromer component.
Yet another aspect of the invention is directed adhesive articles, e.g., industrial tapes, transfer films, and the like, comprising a pressure sensitive adhesive hybrid polymer. In one particularly preferred embodiment, the hybrid polymer comprises an ethylene-butylene macromer, 2-ethylhexyl acrylate or similar low Tg acrylic monomer, methyl acrylate or similar high Tg monomer, and preferably a hydroxy functional monomer such as hydroxyethyl acrylate.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term “pressure-sensitive adhesive” refers to a viscoelastic material which adheres instantaneously to most substrates with the application of slight pressure and remains permanently tacky. A polymer is a pressure-sensitive adhesive within the meaning of the term as used herein if it has the properties of a pressure-sensitive adhesive per se or functions as a pressure-sensitive adhesive by admixture with tackifiers, plasticizers or other additives.
The adhesive polymer of the invention is a rubber-acrylic hybrid polymer comprising an acrylic polymer backbone grafted with rubber macromers including, but not limited to, ethylene-butylene macromers, ethylene-propylene macromers and ethylene-butylene-propylene macromers. In general, the hybrid polymers are made by copolymerizing alkyl acrylate ester monomers in the presence of a macromer containing a reactive acrylic or methacrylic end group. This leads to a comb-type copolymer having an acrylic backbone and side chains of macromer.
More specifically, acrylic polymer backbone contemplated for use in the practice of the invention is formed of acrylate monomers of one or more low Tg alkyl acrylates. Low transition temperature monomers are those having a Tg of less than about 0° C. Preferred alkyl acrylates which may be used to practice the invention have up to about 18 carbon atoms in the alkyl group, preferably from about 4 to about 10 carbon atoms in the alkyl group. Alkyl acrylates for use in the invention include butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, decyl acrylate, dodecyl acrylates, isomers thereof, and combinations thereof. A preferred alkyl acrylate for use in the practice of the invention is 2-ethyl hexyl acrylate.
The monomer system used to make the acrylic backbone polymer could be solely based on low Tg alkyl acrylate ester monomers, but is preferably modified by inclusion of high Tg monomers and/or functional comonomers, in particular carboxy-containing functional monomers, and/or, even more preferably, hydroxy-containing functional monomers.
High Tg monomer components which may be present, and in some embodiments are preferably present, include methyl acrylate, ethyl acrylate, isobutyl methacrylate, and/or vinyl acetate. The high Tg monomers may be present in a total amount of up to about 50% by weight, preferably from about 5 to about 50% by weight, even more preferably from about 10 to about 40% by weight, based on total weight of the hybrid polymer.
The acrylic backbone polymer may also comprise one or more functional monomers. Preferred are carboxy and/or hydroxy functional monomers.
Carboxy functional monomers will typically be present in the hybrid polymer in an amount of up to about 7% by weight, more typically from about 1 to about 5% by weight, based on the total weight of the monomers. Useful carboxylic acids preferably contain from about 3 to about 5 carbon atoms and include, among others, acrylic acid, methacrylic acid, itacon
Chandran Rama
Eaton Patrick S.
Foreman Paul B.
Shah Smita M.
Foulke Cynthia L.
Hu Henry S.
Wu David W.
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