Thermoplastic Foam Substrates

Some solvent cements and solvent-containing adhesives, such as pressure-sensitive adhesives (PSAs), will collapse thermoplastic foams by dissolving the cell walls. In such cases water-based adhesives based on SBR or polyvinyl acetate, or 100%-solids adhesives are often used (1). 

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Thermosetting Foam Substrates Most thermosetting plastics are not particularly difficult to bond. Obviously, solvent cementing is not suitable for bonding thermosets to themselves, since they are not soluble. In some cases solvent solutions can be used to join thermoplastics to thermosets. In general, adhesive bonding is the only practical method of joining a thermoset to itself or to a non-plastic material. Epoxies or modified epoxies are the most widely used adhesives for thermosets (1). 

The Hquid monomers are suitable for bulk polymerization processes. The reaction can be conducted in a mold (casting, reaction injection mol ding), continuously on a conveyor (block and panel foam production), or in an extmder (thermoplastic polyurethane elastomers and engineering thermoplastics). Also, spraying of the monomers onto the surface of suitable substrates provides insulation barriers or cross-linked coatings. 

Hotmelt adhesives are thermoplastics that are processed free of solvents in the melted state and are therefore known as hotmelts. Since the adhesives are 100% solids, no volatile components can be released. No incineration and/or ventilation systems are required to dispose of the solvents. These adhesives are used to fill larger gaps and therefore often function as both adhesives and sealants. Foamed hotmelt adhesives comprise a special category They are capable of filling large gaps with very little material while still bonding the substrates. 

Polypropylene (PP) in various forms (filled, unfilled, reinforced, rubber blended) finds the greatest usage of all automotive plastics. Its consumption is likely to accelerate as a result of new laws requiring recyclability, and because of the weight and cost reductions it offers. New fabrication techniques may also contribute to growth. For example, the monomaterial sandwich construction techniques developed by fabricators yield rugged and lightweight PP-based instrument and door panels. These parts consist of a sandwich of reinforced or neat PP substrate, a cross-linked PP foam, and a thermoplastic polyolefin elastomer (TPO) cover. 

A recent development is the use of more than one adhesive on the same substrate. For example, a cross-linkable acrylic adhesive can be applied on a close-cell polyurethane foam, and the sheet adhesive can be used to mount autobody side-moldings. A two-sided film or sheet can be made to contain a thermoplastic adhesive on one side to bond to the auto-carpet fibers and another adhesive on the opposite side to bond to the polypropylene body and console panels. 

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