Wet-stick adhesives, articles, and methods

Details Wet-stick adhesives, articles, and methods Wet-stick adhesives, articles, and methods

1999-08-13

2003-02-11

Szekely, Peter (Department: 1714)

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...

C524S277000, C525S924000, C525S187000, C525S404000, C525S411000, C525S412000, C428S3550AC, C602S052000, C424S448000

Reexamination Certificate

active

06518343

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to a pressure-sensitive adhesive and more particularly to a pressure-sensitive adhesive containing a poly(alkylene oxide) copolymer that provides bond formation useful for adhesion to wet surfaces, such as skin or like delicate surfaces.
BACKGROUND OF INVENTION
Pressure-sensitive adhesive (PSA) articles are used in a wide variety of applications where there is a need to adhere to skin, for example, medical tapes, wound or surgical dressings, athletic tapes, surgical drapes, or tapes or tabs used in adhering medical devices such as sensors, electrodes, ostomy appliances, or the like. A concern with many of these adhesive articles is the need to balance the objective of providing sufficiently high levels of adhesion to wet skin as well as to dry skin. Thus, pressure-sensitive adhesives that adhere to wet or moist surfaces, particularly skin, are referred to as “wet-stick” adhesives.
One approach in the art to providing pressure-sensitive adhesive articles for application to wet skin has been the use of pattern coated adhesives. A discontinuous adhesive coating on a backing allows the skin to breathe, at least in the areas of the backing not coated with adhesive. This approach is disclosed in U.S. Pat. No. 4,595,001 (Potter, et al.) and U.S. Pat. No. 5,613,942 (Lucast, et al.), as well as EP 353972 (Takemoto, et al.) and EP 91800 (Potter, et al.). These patent documents generally teach intermittent coating of adhesives onto different backings.
(Meth)acrylate pressure-sensitive adhesives are attractive materials for many applications. (Meth)acrylates are known for their optical clarity, oxidative resistance, and inherently tacky nature. Inherently tacky (meth)acrylate pressure-sensitive adhesives (i.e., materials that require no additives such as tackifying resins) are typically formulated predominately from acrylic acid ester monomers of nontertiary alcohols. Examples of such monomers include n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, isodecyl acrylate and dodecyl acrylate. When these (meth)acrylate monomers are polymerized, the homopolymers have a glass transition temperature (Tg) of less than about 10° C. This low Tg is a necessary property in (meth)acrylate materials that exhibit tack at room temperature. Such (meth)acrylate polymers are hydrophobic in nature and, without modification, are generally unsuitable as wet-stick adhesives.
A means to increase the hydrophilic character of (meth)acrylate polymers is to copolymerize the (meth)acrylate monomers with hydrophilic acidic comonomers, such as acrylic acid, methacrylic acid, beta-carboxyethyi acrylate, itaconic acid, sulfoethyl acrylate, and the like. Addition of these hydrophilic acidic comonomers in minor amounts (e.g., about 1 weight percent to about 15 weight percent) can also enhance the internal or cohesive strength of the PSA. This increased polymer reinforcement, however, can diminish the tack of the hydrophilic acidic comonomer-containing (meth)acrylate copolymer.
At higher acidic comonomer levels, (meth)acrylate copolymers can dramatically lose their tack and become highly hydrophilic. When exposed to water, the moisture helps to transform these highly acidic, low tack compositions into tacky materials that are suitable as wet-stick adhesives used in many medical applications. When the water is allowed to evaporate, however, these adhesives lose their pressure-sensitive tack. Thus, although this provides suitable wet-stick adhesion in some applications, there is still a need for articles having good initial wet-stick adhesion in other applications, preferably, on the order of the same article's initial dry-stick adhesion.
SUMMARY OF INVENTION
Briefly, in one aspect of the present invention, a wet-stick pressure-sensitive adhesive is provided wherein the pressure-sensitive adhesive comprises:
(a) at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester monomer, wherein the (meth)acrylic acid ester monomer when homopolymerized has a Tg of less than about 10° C.;
(b) at least one copolymerized hydrophilic acidic monomer; and
(c) at least one nonreactive poly(alkylene oxide) copolymer comprising at least two copolymerized alkylene oxides, at least one of which is hydrophilic (e.g., ethylene oxide) and at least one of which is hydrophobic (e.g., propylene oxide).
In another embodiment is an article that includes a backing and a wet-stick pressure-sensitive adhesive as described above. The adhesives of the present invention adhere to wet surfaces, preferably and advantageously, to wet skin. The glass transition temperature of the adhesive is preferably at least about 10° C. The glass transition temperatures of the homopolymers and adhesive are typically accurate to within ±5° C. and are measured by differential scanning calorimetry.
Yet another embodiment is a method of making a wet-stick pressure-sensitive adhesive. The method includes combining under conditions effective to cause polymerization: at least one monoethylenically unsaturated (meth)acrylic acid ester monomer, which when homopolymerized, has a Tg of less than about 10° C.; at least one hydrophilic acidic monomer; and at least one nonreactive poly(alkylene oxide) copolymer comprising at least two copolymerized alkylene oxides, at least one of which is hydrophilic and at least one of which is hydrophobic.
A method of using an adhesive article is also provided. The method involves: providing an adhesive article comprising a backing and a wet-stick pressure-sensitive adhesive layer disposed thereon, wherein the wet-stick pressure-sensitive adhesive comprises: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester monomer, wherein the (meth)acrylic acid ester monomer when homopolymerized has a Tg of less than about 10° C.; at least one copolymerized hydrophilic acidic monomer; and at least one nonreactive poly(alkylene oxide) copolymer comprising at least two copolymerized alkylene oxides, at least one of which is hydrophilic and at least one of which is hydrophobic; and adhering the adhesive article to skin.
As used herein in this application:
“pressure-sensitive adhesive” or “PSA” refers to a viscoelastic material that displays aggressive tackiness and adheres well to a wide variety of substrates after applying only light pressure (e.g., finger pressure). An acceptable quantitative description of a pressure-sensitive adhesive is given by the Dahlquist criterion, which indicates that materials having a storage modulus (G') of less than about 4.0×10
5
Pascals (measured at room temperature) have pressure sensitive adhesive properties;
“wet-stick adhesive” refers to a material that exhibits pressure-sensitive adhesive properties when adhered to at least a wet surface, preferably, to both wet and dry surfaces, particularly skin;
“(meth)acrylate monomers” are acrylic acid esters or methacrylic acid esters of nontertiary alcohols, the alcohols preferably having about 4 to 14 carbon atoms;
“hydrophilic acidic monomers” are water soluble ethylenically unsaturated, free radically reactive monomers having carboxylic acid, sulfonic acid, or phosphonic acid functionality and are copolymerizable with the (meth)acrylate monomers;
“hydrophilic alkylene oxides” are monomers that are polymerizable to oligomers or homopolymers that are soluble in room-temperature (25° C.) water at 10% by weight;
“hydrophobic alkylene oxides” are monomers that are polymerizable to oligomers or homopolymers that are insoluble in room-temperature water at 10% by weight;
“copolymer” includes a polymer of any length (including oligomers) of two or more types of polymerizable monomers, and therefore includes terpolymers, tetrapolymers, etc., which can include random copolymers, block copolymers, or alternating copolymers; and
“nonreactive” refers to components that do not contain free radically reactive ethylenically unsaturated groups that could co-react with the comonomers or functionalities or significantly inhibit the polymerization of these

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