Latex adhesives contact bonding

Latex Adhesive Applications. Polychloroprene latex adhesives have a long history of use in foil laminating adhesives, facing adhesives, and constmction mastics. Increasingly stringent restrictions on the emission of photoreactive solvents has heightened interest in latex compounds for broader apphcations, particularly contact bond adhesives. Table 10 makes a general comparison of solvent and latex contact bond adhesives (158). 

Table 10. Comparison of Latex and Solvent Contact Bond Adhesives ...

Latex adhesives Latex adhesives are based on polymer latexes and require that the polymers be near their Tg so that they can flow and provide good surface contact when the water evaporates. It is not surprising that the same polymers that are useful as latex paints are also useful as latex adhesives (such as PMMA). Latex adhesives are widely employed for bonding pile to carpet backings. 

Solvent solutions and latex cements require the removal of the solvent from the adhesive before bonding can take place. This is accomplished by simple or heat-assisted evaporation. Some of the stronger or more environmentally resistant rubber-based adhesives require an elevated-temperature cure. Only slight pressure is usually required with pressure-sensitive adhesives (PSAs) to obtain a satisfactory bond. These adhesives are permanently tacky and flow under pressure, thus they provide intimate contact with the adherend surface. 

Latex (emulsion) adhesives. In contact with water, adhesive bonds with latex adhesives may release surfactants, which will have the effect of lowering surface tension and changing the thermodynamic work of adhesion. Some latices based on copolymers of vinyl acetate were dried to give films which were then immersed in small quantities of water. The surface tensions (/w) fell from 72.8 mN m to values in the range 39-53 mN m in the first hour and then remained fairly static [76]. Measurements of interfacial tensions against n-hexadecane showed the dispersion components of surface tension remained essentially constant but polar components were reduced into the range 6-20 mN m ... 

Latex 750 a contains medium gel, slow crystallizing polymer which gives an excellent combination of flexibility, dry tack, heat-reactivity and cohesive strength. It is used primarily in contact bond adhesives. 

Neoprene Latex 115 reacts slowly with zinc oxide in adhesive form, causing a gradual increase in the adhesive gel content. In contact bonding, where gel content directly affects the contactability of dry films, it is suggested that adhesives be used within six months. 

The second formulation is a contact bond adhesive based on Neoprene Latex 115. It provides good cohesive strength development because of the reactivity of Latex 115. For best results, it should be used within six months after formulation. 

These materials are based on polymer latexes made by emulsion polymerization. They flow easily while the continuous water phase is present and dry by evaporation of the water, leaving behind a layer of polymer. In order that the polymer particles coalesce to form a continuous joint and be able to flow to contact the adherend surfaces, the polymers used must be above their glass transition temperature at use temperature. These requirements are similar to those for latex paints, so it is not surprising that some of the same polymers are used in both applications, for example, styrene-butadiene copolymers and poly(vinyl acetate). Nitrile and neoprene mbbers are used for increased polarity. A familiar example of a latex adhesive is white glue, basically a plasticized poly(vinyl acetate) latex. Latex adhesives have displaced solvent-based adhesives in many applications because of their reduced pollution and fire hazards. They are used extensively for bonding pile and backing in carpets. 

Contact bonding In this method, both surfaces are coated and the adhesive is permitted to become dry to the touch. Within a given time, these surfaces are pressed together and near-ultimate bond strength is immediately achieved. In this method, both surfaces may be nonporous. Neoprene latex adhesives are commonly utilized in contact bonding... 

Aqueous dispersions are used in fiber bonding, paper coating, friction and abrasive appHcations, and laminates and wood bonding. PhenoHc dispersions improve the strength of latex-contact adhesive appHcations. Epoxy-modified phenoHc dispersions are prepared by dispersion of the phenoHc epoxy resin. The systems are used for baked primer appHcations and bonding requirements. Minimum baking conditions are 20 min at 150°C (25). 

Polymeric materials are commonly used for bonding materials. Impact or contact adhesives are mainly based on highly crystalline polychloroprene (Neoprene), NR latex is used as a flexible adhesive very suitable for use with fabrics. Rigid adhesives based on materials such as polystyrene cement, epoxy resin or cyanoacrylates are suitable for bonding of rigid materials. The bond is provided by intramolecular forces between the adhesive and the adherend. Adiabatic... 

Uses ABS latex for waterproof and greaseproof coatings, ieather finishes, paints, paper coatings, and nonwoven binders and saturation food pkg. adhesives in resin-bonded filters for food contact Regulatory FDA21CFR 175.105,177.2260 Properties Sp.gr. 1.01 vise. 28 cps pH 10.3-11.0 surf. tens. 48 dynes/ cm (29 C) 3942% solids Hycai 1578X1 [Noveon]... 

Hazardous Decomp. Prods. CO, CO2, acrid fumes NFPA Health 2, Flammability 3, Reactivity 2 Uses Monomer for synthesis of nitrile rubber, PVAc emulsions, PVOH, EVA copolymers, vinyl chloride-vinyl acetate copolymers, PVBI, and vinyl acetate-acrylonitrile copolymers in polymerized form for plastic masses, films, lacquers, latex paints, adhesives, textile finishing, safety glass interlayers textile hand modifier binder for paper coatings esterification for food starch modified film-former in cosmetics food pkg. adhesives resinous/polymeric food-contact coatings for polyolefin films food-contact paper/paperboard, ionomeric resins, copolymers, laminates, resin-bonded filters, textiles... 

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