Acrylic-based pressure sensitive

Polymers for Advanced Technologies 14, No.7, July 2003, p.502-7 ACRYLATE-BASED PRESSURE SENSITIVE ADHESIVE IN FABRICATION OF TRANSDERMALTHERAPEUTIC SYSTEM Tipre D N Vavia P R Mumbai,Uni versity... 

Polyvinyl alcohol is added to acrylate copolymer emulsions, which are usually surfactant-stabilized, to alter or improve their adhesive performance. Many emulsions of this type are used as components of water-based pressure-sensitive emulsions - typically, a tacky adhesive for paper can be prepared by dissolving polyvinyl alcohol in a 2-elhylhexylacrylate copolymer emulsion. 

POLYMER EMULSIONS BASED ON PURE ACRYLICS FOR PRESSURE SENSITIVE ADHESIVES... 

The acrylic-type pressure-sensitive adhesives are often partly cross-linked, partly linear in composition. Theory and data available suggest that the cross-linked component should be only very lightly cross-linked, so that the Rg calculated from Me of the cross-linked portion is larger than the Rg based on Me of the linear portion see Section 10.2 (93,94), especially Figure 10.11. Then the linear polymer can enter the network structure through reptation, developing physical bonds. 

Pressure sensitive adhesive tapes are used for holding and anchoring lead wires to the outer wrap of transformer coils, capacitor wrapping, protection of leads and coils, and other similar applications. Adhesive transfer films are used to hold insulating material in position. Natural rubber based pressure sensitive adhesives have poor solvent resisitance unless they are cross-linked. Many modifications are possible. Synthetic rubber has better stability than natural rubber and better solvent and ozone resistance. Acrylic pressure sensitive adhesives have the best balance of properties. They maintain their... 

These empirical relationships along with the glass transition temperature data estabhshed for homopolymers (Table 9.1) allow polymer chemists to determine the optimal position of the glass transition temperature and then design adequate emulsion polymer compositions to fulfill end-users requirements. n-Butyl acrylate (T = -54°C) and 2-ethylhexyl acrylate (Tg = -85°C), for example, are widely used as the major components of water-based pressure-sensitive adhesives. Vinyl acetate and n-butyl acrylate copolymer latexes with a weight ratio of about 80 20 Tg = 8°C) are a primary choice for inte-... 

Heteroatom functionalized terpene resins are also utilized in hot melt adhesive and ink appHcations. Diels-Alder reaction of terpenic dienes or trienes with acrylates, methacrylates, or other a, P-unsaturated esters of polyhydric alcohols has been shown to yield resins with superior pressure sensitive adhesive properties relative to petroleum and unmodified polyterpene resins (107). Limonene—phenol resins, produced by the BF etherate-catalyzed condensation of 1.4—2.0 moles of limonene with 1.0 mole of phenol have been shown to impart improved tack, elongation, and tensile strength to ethylene—vinyl acetate and ethylene—methyl acrylate-based hot melt adhesive systems (108). Terpene polyol ethers have been shown to be particularly effective tackifiers in pressure sensitive adhesive appHcations (109). 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

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. 

Pressure-sensitive adhesives (PSAs) based on acrylic, natural rubber and silicone are employed primarily for ease of application. To name Just a few applications, PSAs bond decals to surfaces, interior decorative surfaces to interior panels, interior trim pieces in place directly or hook and loop tape for the same purpose, structural shims in place during manufacturing and acoustic (sound deadening) materials to body skin interior surfaces. Tape products with pressure-sensitive adhesive on one or both surfaces are used for such functions as cargo compartment sealing, as a fluid barrier to prevent spills and leaks in the lavatories and... 

Polystyrene-PDMS block copolymers4l2), and poly(n-butyl methacrylate-acrylic acid)-PDMS graft copolymers 308) have been used as pressure sensitive adhesives. Hot melt adhesives based on polycarbonate-PDMS segmented copolymers 413) showed very good adhesion to substrates with low surface energies without the need for surface preparation, such as etching. 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

Silicone release liners are used as a nonadhering surface to which adhesive materials, such as, for example, pressure-sensitive adhesives, can be laminated. UV curable release coatings are based on poly(dimethylsiloxane) oligomers functionalized with acrylate or epoxy groups and are mostly coated onto papers or thin films. 

One of the most popular uses of radiant curing is the advancement (viscosity increase) or crosslinking of pressure-sensitive adhesives. These applications have been satisfied mostly with acrylate-based adhesive systems. With epoxy-based adhesives, the main applications are electrical and electronic components, the bonding of large aerospace structures such as composites, and the bonding of transparent substrates such as glass and plastic. 

The influence of parameters such as crosslinking agent aluminium acetylacetonate content, introduction time of monomers, amount of reactor charge, distribution of N-vinyl caprolactam (VC), diverse crosslinkers, viscosity and molar mass of the synthesised pressure-sensitive adhesives (PSA) and solvent balance and transfer agent kind and content on such important parameters of PS A as shrinkage, plasticity, adhesion to steel and deformation are examined. Synthesised pressure-sensitive adhesives based on acrylic polymers and containing 2-ethylhexyl acrylate (2-EHA), methyl acrylate (MA), acrylic acid (AA) and VC are used for production of self-adhesives containing PVC carrier. 4 refs. 

The primary mode of bonding for a pressure-sensitive adhesive is not chemical or mechanical but rather a polar attraction to the substrate. This always requires pressure to achieve sufficient wet-out onto the surface thereby providing adequate adhesion. The four main varieties of pressure-sensitive adhesives are derived from rubber-based, acrylic, modified acrylic and silicone formulations. Release liners are used to carry the sticky label and enable it to be printed. The release liners are normally paper, treated with a very thin silicone coating to allow the label to be peeled away easily without tearing. Some transfer of the silicone into the adhesive is inevitable. 

Gelva [Solutia], TM for a family of acrylic multipolymer products designed for high-performance, pressure-sensitive adhesive applications where skin adhesion, high temperature and/or diffi-cult-to-adhere-to surface are involved. Provided for both solvent and water based grades. 

Devices are secured to the skin by use of a skin-compatible pressure-sensitive adhesive, usually based on silicones, acrylates or polyisobutylenes. These adhesives are evaluated by shear-testing and assessment of rheological parameters (Musolf 1987). Standard rheological tests include creep compliance (measurement of the ability of the adhesive to flow into... 

The backing material and release liner can be fabricated from a variety of materials including polyvinylchloride, polyethylene, polypropylene, ethylene-vinyl acetate and aluminium foil. The most important property of these materials is that they are impervious to both drug and formulation excipients. The most useful backing materials conform with the skin and provide a balanced resistance to transepidermal water loss, which will allow some hydration of the stratum corneum, yet maintain a healthy subpatch environment. The release liners are usually films or coated papers and must separate easily from the adhesive layer without lifting off any of the pressure-sensitive adhesive. Silicone release coatings are used with acrylate and rubber-based adhesive systems, and fluorocarbon coatings with silicone adhesives. 

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. 

One of the newer developments in adhesives is the growing use of ultraviolet light or electron beam radiation to cure adhesives. Adhesives designed for UV- or E-beam curing are usually pressure sensitive or hot-melt systems based on acrylates, functional rubbers, or epoxidized rubbers, and use special UV or EB lamps to provide the cure. These systems can provide greatiy improved heat resistance compared to hot melts, and avoid the soivent emission problems of some of the solvent-based systems with which they compete. 

Acrylic adhesives first appeared about 1937 the acrylic resins may be considered as belonging to the vinyl family [1, p. 305], Today, acrylic adhesives appear in many forms as both pressure-sensitive and non-pressure sensitive formulations in organic solvent and emulsion forms as monomer and polymer cements as anaerobics as cyanoacrylates as so-called reactive or honeymoon two-part systems and as radiation curing formulations. Commercial production of acrylic polymers began in the late 1920s, but it was not until 1958 that the first aerylie sealant was developed [10, p. 226]. The solvent-based acrylic sealants were first introdueed to the eonstruction industry in about 1960 ... 

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. 

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