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
2003-01-16
2004-11-30
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S205000, C525S217000, C525S221000, C525S222000, C525S225000, C525S230000
Reexamination Certificate
active
06825278
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to modified pressure sensitive adhesives (PSAs) having improved adhesion properties. In another aspect, the invention concerns a novel process for producing such modified PSAs. The inventive modified PSAs are useful as, for example, tapes, labels, stickers, decals, decorative vinyls, laminates, and wall coverings.
BACKGROUND OF THE INVENTION
Pressure sensitive adhesives (PSAs) are useful in many applications for bonding a flexible material to another surface. PSAs may be classified according to the chemical composition (i.e., the main elastomer) used in the adhesive formulation. The largest class of PSAs in use today are polyacrylates. A distinct and advantageous feature of polyacrylates is that they are tacky without compounding with tackifying resins. A further advantage is that polymerization of acrylic monomers does not require expensive equipment.
Acrylic PSAs are typically produced either by emulsion or solution polymerization. Emulsion polymerization is by far the most important process for producing acrylic PSAs because acrylic dispersions are environmentally safe, easy to handle, and economical. Further, acrylic dispersions from emulsion polymerization exhibit good adhesive properties, coatability at very high speeds, and favorable die-cutting properties.
The adhesion properties of the acrylic PSA dispersions resulting from emulsion polymerization are greatly influenced by the type and relative quantities of monomers employed in the polymerization process. Most pressure sensitive acrylic adhesives are formed from acrylic esters that yield soft tacky polymers of low glass transition temperature (T
g
). The primary monomers used to form acrylic PSAs are alkyl acrylates and methacrylates of 4 to 17 carbon atoms. In particular, butyl acrylate, 2-ethylhexyl acrylate, and iso-octyl acrylate are known monomers which can be polymerized to yield soft and tacky homopolymers. However, homopolymers are not generally used for pressure sensitive adhesives. Rather, homopolymers are typically modified by copolymerization with at least a small portion of other comonomers. Copolymerization with other monomers is a universally used technique to vary adhesive properties. Typically, the main monomer (i.e., alkyl acrylates and methacrylates of 4 to 17 carbon atoms) are copolymerized with a modifying monomer (typically a second acrylic ester) and/or monomers with functional groups (e.g., acrylic, methacrylic, itaconic acids and their amides). The functional groups may affect a wide range of properties and also provide crosslinking sites. Polar comonomers, in particular carboxyl groups, which are used in comparatively small amounts can have a strong impact on the adhesion properties. In general, a typical pressure sensitive acrylic polymer composition is derived from the following monomers: main monomer (50-98%), modifying monomer (10-40%), and monomer with functional groups (0.5-20%).
It is commonly known that the adhesion properties of PSAs can be varied by the grafting or crosslinking of polymers. Crosslinking typically improves the creep and shear resistance of PSAs. However, crosslinking is usually accompanied by a decrease in tack and peel. Generally, crosslinking increases the shear and tensile moduli, and especially its elastic component, at the expense of the viscous one. Thus, there exists a need for PSAs, and methods for producing such PSAs, that exhibit improved shear strength without a significant reduction in peel and tack.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a method of making a modified pressure sensitive adhesive (PSA) is provided. The method comprises forming a monomer mixture comprising a main monomer; polymerizing the monomer mixture to thereby form a polymerized mixture comprising a base polymer having units derived from the main monomer; and after substantial completion of the polymerizing step, reacting a modifying polymer comprising units derived from a n-vinyl lactam with the polymerized mixture in the presence of a free-radical initiator to thereby form a modified mixture comprising a modified polymer.
In accordance with another embodiment of the present invention, a method of making a modified PSA is provided. The method comprises forming a monomer mixture comprising an ethylenically unsaturated acid ester having a glass transition temperature less than about 0° C. and an ethylenically unsaturated acid; emulsion polymerizing the ethylenically unsaturated acid ester and the ethylenically unsaturated acid to thereby form an acidic polymerized mixture comprising a base copolymer, wherein the base copolymer comprises 50 to 98 weight percent of units derived from the ethylenically unsaturated acid ester and 0.1 to 20 weight percent of units derived from the ethylenically unsaturated acid; after at least about 80 weight percent of the ethylenically unsaturated acid ester has been polymerized, adding polyvinyl pyrrolidone to the polymerized mixture to thereby form a modified mixture comprising a modified polymer; and neutralizing the modified mixture to a pH of at least about 7.0 to thereby form a neutralized mixture.
In accordance with still another embodiment of the present invention, a method of making a modified PSA is provided. The method comprises copolymerizing a main monomer and a functional monomer via emulsion polymerization to thereby form a polymeric backbone having a carboxylic functional group; and after substantial completion of the copolymerization step, reacting a polyvinyl pyrrolidone polymer with the polymeric backbone to thereby chemically bind the polyvinyl pyrrolidone polymer to the backbone at the carboxylic functional group.
In accordance with yet another embodiment of the present invention, a modified polymer composition suitable for use in PSAs is provided. The modified polymer composition comprises a polymeric backbone comprising main units derived from a main monomer having a glass transition temperature of less than about 0° C. in homopolymerized form and functional units derived from a functional monomer having a carboxylic functionality. The modified polymer composition further comprises a modifying polymeric moiety that has been chemically bound to at least one of said functional units of said polymeric backbone. Prior to being chemically bound to the functional unit, the modifying polymeric moiety was a modifying polymer comprising units derived from a n-vinyl lactam.
The inventive modified PSA and process for making such modified PSA provide an adhesive composition having a substantially improved shear strength without significant reduction in peel and tack.
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the present invention concerns a method of making a pressure sensitive adhesive (PSA), wherein the method comprises: (1) preparing a monomer mixture comprising one or more polymerizable monomers; (2) polymerizing the monomer mixture to form a polymerized mixture; (3) modifying the polymerized mixture with a modifying polymer; and (4) neutralizing the resulting modified mixture.
Generally the monomer(s) employed in the monomer mixture can be any ethylenically unsaturated monomer that is capable of undergoing polymerization or copolymerization according to the present invention. Examples of suitable ethylenically unsaturated monomers are, for example, alkyl esters (e.g., (meth)acrylic acid esters); ethylenically unsaturated carboxylic acids; the nitriles, vinyl and vinylidene halides, and amides of unsaturated carboxylic acids; mono- and polyunsaturated hydrocarbon monomers; vinyl esters (e.g., vinyl esters of C
1
to C
6
saturated monocarboxylic acids); vinyl ethers; and amino monomers. By convention, the parentheticals used herein designate optional content (i.e., (meth)acrylate means “acrylate” or “methacrylate”).
Examples of (meth)acrylic acid esters suitable for use in the present invention include C
1
-C
17
alkyl(meth)acrylates. Typical (meth)acrylic esters include methyl(meth)acrylate, ethyl(meth)acrylate, isopropyl (meth)acrylat
Bernatova Olga
Havranek Jiri
Holub Pavel
Horalek Jiri
Moudra Edita
Nutter Nathan M.
Resolution Specialty Materials LLC
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