Wet-stick adhesives

Details Wet-stick adhesives Wet-stick adhesives

1999-08-13

2002-08-27

Seidleck, James J. (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...

C525S217000, C525S218000, C525S221000, C525S222000, C525S241000, C428S041300, C428S041500, C428S3550CN, C428S3550AC, C524S442000, C524S492000, C524S500000, C156S327000, C156S330900

Reexamination Certificate

active

06441092

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to a pressure-sensitive adhesive and more particularly to a pressure-sensitive adhesive that includes a mixture of a pressure-sensitive adhesive component and a film-forming component. Significantly, such pressure-sensitive adhesives provide bond formation useful for adhesion to skin or like delicate surfaces, even when such surfaces are wet.
BACKGROUND OF INVENTION
Pressure-sensitive adhesive articles and the like 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 coated 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, so-called “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 (Takamoto, et al.) and EP 91800 (Potter, et al.). These 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-ethylehxyl 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 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-carboxyethyl acrylate, itaconic acid, sulfoethyl acrylate, and the like. Addition of these hydrophilic acidic comonomers in minor amounts (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 skin adhesion in some applications, there is still a need for articles having good initial wet skin adhesion in other applications, preferably, on the order of the same article's initial dry skin 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) a pressure-sensitive acrylate adhesive comprising:
(i) at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbons on average that, when homopolymerized, preferably has a glass transition temperature of less than about 10° C. (referred to herein as monomer A); and
(ii) at least one copolymerized monoethylenically unsaturated reinforcing monomer that, when homopolymerized, preferably has a glass transition temperature of at least about 10° C. (referred to herein as monomer B); and
(b) a film-forming component comprising:
(i) at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbons on average; and
(ii) at least one copolymerized hydrophilic acidic monomer.
Advantageously, the pressure-sensitive adhesive in accordance with the present invention adheres to wet skin.
The acrylate copolymer for the pressure-sensitive adhesive component is preferably formulated to have a resultant T
g
of less than about 25° C. and more preferably, less than about 10° C. The film-forming polymer component is preferably formulated to have a resultant T
g
of less than about 70° C. The glass transition temperatures of the homopolymers of the monomers and the pressure-sensitive adhesive are typically accurate to within ±5° C. and are measured by differential scanning calorimetry
Preferably, the wet-stick pressure-sensitive adhesive of the present invention includes a (meth)acrylic acid ester monomer of the pressure-sensitive adhesive component having the following general formula:
wherein R
1
is H or CH
3
and R
2
is a linear or branched hydrocarbon group of about 4 to about 14 carbon atoms optionally including one or more heteroatoms. More preferably, the (meth)acrylic acid ester monomer is selected from the group of n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, lauryl acrylate, and mixtures thereof. Preferably, the (meth)acrylic acid ester monomer is present in the pressure-sensitive adhesive component in an amount of about 85 wt-% to about 99 wt-%, based on the total weight of the copolymerizable monomers.
Preferably, a wet-stick adhesive of the present invention includes a hydrophilic acidic monomer that is an ethylenically unsaturated carboxylic acid, an ethylenically unsaturated sulfonic acid, an ethylenically unsaturated phosphonic acid, or mixtures thereof. More preferably, the hydrophilic acidic monomer is an ethylenically unsaturated carboxylic acid. Preferably, the hydrophilic acidic monomer is present in the film-forming component in an amount of about 1 wt-% to about 50 wt-%, based on the total weight of copolymerizable monomers.
A wet-stick pressure-sensitive adhesive of the present invention can further include an additive selected from the group consisting of a plasticizer, a tackifier, a pigment, glass beads, polymeric beads, fibers, a reinforcing agent, silica, a toughening agent, a fire retardant, an antioxidant, a stabilizer, or mixtures thereof. Additionally, the wet-stick pressure-sensitive adhesive of the present invention can be crosslinked.
Another aspect of the present invention provides an article comprising a backing and a wet-stick pressure-sensitive adhesive comprising:
(a) a pressure-sensitive adhesive component comprising:
(i) at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbons on average; and
(ii) at least one copolymerized monoethylenically unsaturated reinforcing monomer; and
(b) a film-forming component comprising:
(i) at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbons on average; and
(ii) at least one copolymerized hydrophilic acidic monomer.
Preferably, the article adheres to wet skin. More preferably, the article has an initial wet skin adhesion of at least about 0.8 N/dm. Additionally, an article preferably has an initial wet skin adhesion at least about 65% of an initial dry skin adhesion.
A further aspect of the prese

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