Thermoplastic resin adhesives

Although thermoplastic adhesives fall into many different chemical classes, they are all composed predominantly of Unear macromolecules. Most thermoplastic resins are capable of bonding a wide variety of substrates such as paper, wood, and leather. Some are capable of bonding rubbers, metals, and some plastics, without special surface treatment. The most notable exceptions are the silicone and fluorocarbon plastics.  

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Uses Coupling agent for mosf thermoset and thermoplastic resins adhesion promoter for solv., water-based, solventless, and powd. coating systems pigment treatment tood-contact coatings Features Esp. effective in PS, polyolefin, epoxy systems Regulatory FDA 21 CFR 175.300, when coupled with silica, as adjunct to epoxy resins in contact with nonacidic, aq. or dry solid foods at temps, below 88 C... 

Certain general categories are also listed, such as alloys, aromatic polymer, conductive, delayed-tack, elastomeric adhesives, anaerobic, film and tape adhesives, hot-melt adhesives, inorganic glues, microencapsulated adhesives, rubber-based adhesives, solvent-based systems, thermoplastic resin adhesives, thermosetting-resin adhesives, and water-based adhesives. 

Typical Applications Most thermoset and thermoplastic resins adhesion promoter used to couple inorganic fillers or reinforcing materials with resins surface pretreatment of fillers and relnforcers. 

A thermoplastic resin adhesive is one that melts or softens on heating and rehardens on cooling without (within certain temperature limits) undergoing chemical change. At temperatures above the melting point, an irreversible chemical change such as depolymerization or oxidative degradation could take place. When used as adhesives, thermoplastic resins are applied in the form of solutions, dispersions in water, or solids. They are usually set by solidification, which is a purely physical means. When applied as solution or dispersion, adhesion follows evaporation or absorption of the liquid... 

The cured polymers are hard, clear, and glassy thermoplastic resins with high tensile strengths. The polymers, because of their highly polar stmcture, exhibit excellent adhesion to a wide variety of substrate combinations. They tend to be somewhat britde and have only low to moderate impact and peel strengths. The addition of fillers such as poly (methyl methacrylate) (PMMA) reduces the brittleness somewhat. Newer formulations are now available that contain dissolved elastomeric materials of various types. These mbber-modifted products have been found to offer adhesive bonds of considerably improved toughness (3,4). 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

Goextrusions. In coextmsion, two or more thermoplastic resin melts are extruded simultaneously from the same die. Coextmsion permits an intimate layering in precisely the quantities required to function. Incompatible plastic materials are bonded with thermoplastic adhesive layers. Coextmded films may be made by extmsion-blowing or slot-casting of two, three, or more layers, eg, AB or ABA. Slot-casting is capable of combining up to 11 layers. 

Block copolymers have become commercially valuable commodities because of their unique stmcture—property relationships. They are best described in terms of their appHcations such as thermoplastic elastomers (TPE), elastomeric fibers, toughened thermoplastic resins, compatibilizers, surfactants, and adhesives (see Elastot rs, synthetic—thermoplastic). 

In some examples it is not necessary to prepare the organometallic-coupling agent R2MX2 beforehand. Thus coating glass fibres with a heptane or alcohol solution of titanium alkoxide promotes adhesion between the fibre and polymer, e.g., acrylic, polyolefins, polyester, polyamide and other thermoplastic resins. 

PVB combinations with the thermoplastic resins nitrocellulose or shellac have been used as sealers for wood finishing. In these applications the PVB component adds flexibility and adhesion. Tough, optically clear blends have been made with aliphatic polyurethanes. Thermosets are prepared with cross-linkers that form covalent bonds with hydroxy] groups. 

An acrylate-terminated polyurethane modified epoxy compound and a polyethylene polyamine homologue and fatty acid combination were formulated into a two-component adhesive system. The adhesive is useful for bonding various thermoplastic resins such as ABS, PC, PBT-PC blends, and PPO.22... 

The thermoplastic resins are usually blended with the epoxy resin in a solvent solution. Early researchers realized that to make this approach effective, it was necessary to increase the compatibility and interfacial adhesion of the thermoplastic modifier and the epoxy resins. The problem of poor miscibility of the thermoplastic resins and poor processabihty of the final product are the main reasons that these materials have not achieved commercial success. 

Reinforced thermoplastic parts are generally abraded and cleaned prior to adhesive bonding. However, special surface treatment such as used on the thermoplastic resin matrix may be necessary for optimum strength. Care must be taken so that the treatment chemicals do not wick into the composite material and cause degradation. It may not be a good idea to use chemical surface treatment without first verifying that the treatment does not degrade the substrate. 

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