Plastics joining application

The welded joint differs from all others in that an attempt is made to produce a continuity of homogeneous material which may or may not involve the incorporation of a filler material. There are a large variety of processes by which this may be achieved, most of which depend upon the application of thermal energy to bring about a plastic or molten state of the metal surfaces to be joined. The more common processes used are classified in Table 9.6. 

Product design with plastics, A practical manual , Joseph B. Dyn Industrial Press Inc. (1983) ISBN 0831111410. A classic, applied, practical plastic design book. Topics covered include (1) introduction to the application of plastics, (2) description and derivation of short term and long term properties, (3) polymer formation, variation, and characteristics, (4) product design features, (5) designing the plastic product, (6) joining... 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

Heat sealing A method of joining plastic films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically. 

The reactive hotmelt adhesives retain a high level of flexibility and dynamic load-bearing capacities even after crossUnking and are used to join plastics to one another as well as to wood (furniture industry), glass (construction industry), aluminum (sandwich elements), and painted surfaces. Typical applications include window casement sheathing, foil laminations, clip fasteners, bookbinding, textile... 

The percentage of solids in the dispersion adhesives is 35-55%, in some cases as much as 70%, the rest is water, which after the adhesive application must either be completely evaporated (ventilation time) or diffuse into the joined parts (wood, textiles, concrete, foams, leather). The film formation temperature in types containing plasticizers and flexibilizing additives is lower than in types that are free of plasticizers. Additives, so-called high boilers (ethyl glycol, ethyl glycol acetate, ethylhexanol), are used to bring the film formation temperature down. 

Apart from liquids, also solids, such as metals, glasses and plastics have surface tension. Due to the stiffness of these materials, it is invisible to the eye, but metrologically determinable. Thus, with the application of the adhesive, two partners with different surface tensions are joined - depending on the material of the adherend and the adhesive. 

THEODORE E. TABOR Is a native of Montana, where he obtained a B.A. degree In chemistry from the University of Montana-Mlssoula. He was a National Defense Education Act fellow at Kansas State University, where he obtained his Ph.D. degree In chemistry. He Joined the Dow Chemical Company In Midland, Mich., and has held various positions In Dow s R D organization, a part of corporate R D. His research areas Include organic reaction mechanisms, applications of chlorinated solvents In textile processing, and the development of flame retardants for textiles and plastics. He Is a member of the ACS and has held numerous positions In the Midland Section, Including the chairmanship of the section. 

---