Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-08-11
2002-12-24
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550AC, C428S3550BL, C525S071000, C525S080000
Reexamination Certificate
active
06497949
ABSTRACT:
FIELD OF INVENTION
This invention relates to adhesive blends comprising a hydrophilic pressure sensitive adhesive and a hydrophobic pressure sensitive adhesive, more particularly to dry- and wet-surface adhesion, which may be present in different layers in a multilayer structure.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesive (PSA) tapes have been used for more than half a century for a variety of marking, holding, protecting, sealing and masking purposes. Pressure-sensitive adhesive tapes comprise a backing or substrate, and a pressure-sensitive adhesive. Pressure-sensitive adhesives require no activation other than finger pressure, exert a strong holding force and should be removable from a smooth surface without leaving a residue.
Adhering to skin presents challenges to adhesive manufacturers due to the inherent variability of the properties of skin. Adhesion to skin is dependent upon many factors. These factors include but are not limited to the environment in which the recipient is located. For instance, adhesion to skin will vary on the same person depending upon the humidity. If the same person were tested for skin adhesion using a given adhesive in different climates, different adhesion results would be obtained depending upon if the person were located in an arid versus in a humid environment.
Furthermore, skin varies from individual to individual. One person may have extremely dry skin whereas another person may have oily skin. As well as varying from individual to individual, skin properties may vary on a given individual depending upon the location on the body. For instance, skin located on a hand may be considerably drier than skin located on a back or face. Therefore, it is very difficult to manufacture a skin adhesive that is suitable for environmental and individual variabilities.
Adhesive composition and performance are also dependent upon the intended use of the adhesive. Use of PSAs for masking tape, or pavement markings will differ from uses for medical applications. While all applications require some wet-stick capabilities, there will be different requirements for the applications. For example, some uses require a gentle adhesive, such as adherence to a sensitive area whereas other uses require a more aggressive adhesive, such as when it is necessary that the adhesive remain adhered for an extended period of time or if the adhesive is adhered to an area which is very mobile.
Medical adhesives are generally used in wound dressings, surgical drapes, bandages and tapes. These items are generally constructed of a backing coated with an adhesive. The performance of the adhesive is in part dependent upon the occlusivity of the backing. Backings are generally categorized by their porosity into either nonocclusive or occlusive backings. When occlusive backings are used to prepare bandages or the like for medical applications the resulting bandage typically does not adhere well to skin over extended time periods. This probably occurs because the bandage cannot release water vapor that causes retention of moisture and in turn causes the adhesive to lift from the skin.
Conformability and cohesiveness are inversely related properties and are considered when preparing or selecting adhesives for end-uses, particularly for medical articles and medical applications. It is desirable for a medical adhesive to conform to the terrain of the skin to which it is adhered. This enhances comfort to the wearer and also ensures a higher initial adhesion to the skin because the adhesive is able to flow into the skin's topography. However, if an adhesive is too conformable it may lack the necessary cohesiveness necessary to remove the article with the adhesive intact. If an adhesive lacks cohesive strength the adhesive on a bandage may split upon an attempt to remove the article leaving some adhesive residue adhered to the skin and some adhesive removed along with the bandage backing. This is unacceptable to most medical professionals and patients.
Pressure-sensitive adhesives require a delicate balance of viscous and elastic properties that result in a four-fold balance of adhesion, cohesion, stretchiness and elasticity. Pressure-sensitive adhesives generally comprise a polymer that is either inherently tacky or can be tackified with the addition of tackifying resins. They can be coated in solvent or as water-based emulsions to reduce the material viscosity to a level that is easily applied to a substrate of choice.
Generally, when additives are used to enhance properties of pressure-sensitive adhesives they are required to be miscible with the pressure-sensitive adhesive or to have some common blocks or groups to permit homogeneous blends to form at the molecular level. Pressure-sensitive adhesives have been modified to extend their applicability into new areas. Tackified thermoplastic elastomers have been dissolved in acrylic monomers and subsequently cured. Tackified thermoplastic elastomers have also been added to polymerized acrylic pressure-sensitive adhesives in solvent where each component contains a common segment to permit compatibility. Natural rubber has been added to polymerized acrylic pressure-sensitive adhesives in solvent and subsequently thermally cured. The general purpose is to combine the high shear properties of elastomers with the high tack performance of acrylics to achieve adhesion to both polar and nonpolar surfaces. Further improvements and better balance of properties continue to be sought.
Pressure sensitive adhesives that adhere to wet or moist surfaces, so-called hydrophilic or “wet-stick” adhesives, are useful in many industrial, commercial and consumer applications. In pharmaceutical and other medical fields, such hydrophilic adhesives are typically used for adhering articles such as tapes, bandages, dressings, and drapes to moist skin surfaces such as wounds or areas of the body prone to moistness. Hydrophilic adhesives also find use in outdoor or exterior applications, such as on roadway materials, traffic control signage, and marine or automotive coatings and surfaces. Labels for food containers and other products that are exposed to moisture due to condensation or subjected to water or ice immersion also must be coated with hydrophilic adhesives.
(Meth)acrylate pressure sensitive adhesives are attractive materials for many tape and label applications because of their hydrophilic character. Copolymerization of (meth)acrylate monomers with hydrophilic acidic comonomers can increase hydrophilic characteristics and can enhance the cohesive strength of the PSA. However, this increased cohesive strength generally diminishes 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, these adhesives lose their pressure-sensitive tack. Such compositions can also be useful as water-soluble or water dispersible adhesives. Water-dispersible or soluble (meth)acrylate copolymers can be formulated as repulpable adhesives used to splice dry paper rolls and designed to lose adhesive integrity and fully degrade when undergoing paper recycling operations.
When using high levels of acidic comonomers, it is difficult to effectively copolymerize these materials without a solvent, an aqueous reaction medium, or additives that promote interpolymerization of these monomers. Attempts to copolymerize these monomers in the absence of compatibilizing reaction media often results in heterogeneous materials dominated by glassy regions formed by the polymerization of the acidic comonomers and softer domains comprising the polymerized (meth)acrylate monomers. Thus, (meth)acrylate copolymers having high levels of acidic comonomers have traditionally been made using either solvent or water-
Clanton Anthony R.
Gieselman Melinda B.
Hyde Patrick D.
Ma Jingjing
Menzies Robert H.
3M Innovative Properties Company
Keehan Christopher M
Peters Carolyn V.
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