Pressure sensitive adhesive acrylic dispersion

A. 2 ettl, Modification of acrylic dispersions, in Hatulbotdt of Pressure Sensitive Adhesive Technology, 2nd edn, D. Satas (ed.). Van Nostrand Rdnhtdd. New Ytnk, 1989. Ch. 16... 

Chem. Descrip. Aqueous dispersion of a thermoplastic acrylic polymer based on 2-ethylhexyl acrylate/ethylacrylate copolymer Uses Acrylic for mfg. of pressure-sensitive adhesives and self-adhesive... 

The ever-increasing raw material choice available to the adhesive formulator is demonstrated with particular reference to Hercules resin dispersions for the modification of acrylic latex polymer systems used in pressure sensitive adhesive formulations. The requirements of a tackil g resin are examined and the advantages afforded by such products from Hercules as Tacolyn 1070, Tacolyn 3179 and Res A-2603 are discussed, in terms of their ability to offer balances of peel, tack and shear and consistently high levels of stability, it is claimed. 5 refs. 

Pressure-sensitive adhesive dispersions are based primarily on special acrylic ester copolymers, again generally in combination with resins. In addition to suitable resins, two polymer bases are used primarily for hot-melt pressure-sensitive adhesives, namely, ethylene-vinyl-acetate copolymers and styrene-butadiene or styrene-isoprene block copolymers, which also are known as thermoplastic rubbers. 

The tack is the ability of a pressure sensitive adhesive to adhere immediately to a surface. A pressure sensitive adhesive with good tack forms the contact points necessary for adhesion of the tape or label after only brief contact with a substrate. Solvent based rubber adhesives can have very good tack, depending on the formulation. Acrylate solutions and dispersions, as well as hot-melt contact adhesives, meet the usual demands. 

Tape adhesives can be made thermally conductive by the dispersion of small articles of a conductive filler such as Saint-Gobain boron nitride (BN) PCTH3MHF and spherical aluminum oxide (AI2O3) available from Denka Corp. [42]. For example, 3M Corp offers pressure-sensitive adhesive (PSA) tapes filled with thermally conductive ceramic particles and flame retardant fillers. This product is designed with a thin polyester (PET) film and a soft acrylic polymer. It conforms to surfaces to which it adheres thus providing contact surface area for heat transfer [43]. 

Before adhesion occurs, wetting of the surface must occur, which implies that the molecules of the adhesives must come close with those of the surface to interact. After the solvent evaporates, a permanent bond sets between the surfaces to be joined. Pressure-sensitive adhesives are special nonreacting ones that do not lose their tackiness even when the solvent evaporates. This is because the polymer used is initially in the liquid stage and it remains so even after drying. The most common adhesive used industrially is polymer dispersion of a copolymer of 2-ethyl hexyl acrylate, vinyl acetate, and acrylic acid in water... 

For some applications, such as for repulpable type PSAs, it may be advantageous to incorporate high levels of acrylic acid because this makes the polymer more hydrophilic. At the same time, high levels of acid also improve the water-dispersibility of the adhesive, especially at higher pH where the acid groups are converted to the more water-soluble neutralized salt form. Since the high level of acid increases the of the resulting polymer, a non-tacky material results. To make the adhesive pressure sensitive, the polymer can be softened with water-dispersible or soluble plasticizers, such as polyethers [68]. 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

Self-adhesive labels can be applied to most materials wood, plastic, metal, glass, paper and board. As the adhesives are resin-based (plasticised thermoplastics), migration problems can occur when they are applied to certain plastics (PVC, LDPE, etc.). Adhesive systems for pressure sensitive labels include latex and acrylic bases and adhesives which may be applied as a hot melt, or via a solvent, emulsion or dispersion base. Water-based adhesives are currently increasing in use. 

Cross-linkable monomers may be included to make the formulated adhesive curable by catalysis, heat, or radiation, thereby improving the performance of the film, especially at higher temperatures. Since the dispersion has both toughness and tack built in, no further compounding is necessary, making pressure-sensitive acrylic dispersions the easiest products to work with. In most applications, however, the formulator will prefer to modify the properties to order, and use of tackifying resins added either in solution or as a dispersion is common. Vinyl ethers can again be used either as sole binders or as tackifiers to modify the properties of the base dispersion. 

Primal N-560 has been nsed to form a temporary pressure-sensitive film where required (Notman and Tennent, 1980). PBA, with a small amount of dibutyl phthalate plasticizer probably applied from a dispersion, is the adhesive on a paper tape used for temporary attachment of paper (Archival Aids). A specially formulated acrylic/styrene polymer was made and its solution emulsified for textile conservation (Bengtsson, 1975). 

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