Composite sheet laminates

Composite-Based Laminates. Grade CEM-1 are laminates with continuous-filament glass cloth surfaces and a cellulose core, all with a flame-resistant epoxy resin binder. With good punching practice, sheets up to and including 2.4 mm (0.094 in.) in thickness may be punched at temperatures not less than 23°C (73°F). These laminates meet UL94 V-0 when tested in accordance with UL94. 

Typical of the temporary or manufacturing aid coating systems is the RISTON dry film photoresist for printed circuit (PC) board fabrication. This was the first of these systems developed. The RISTON product stmcture and the basic steps in its use are shown in Figure 2. It consists of a photopolymer sheet laminated between a Mylar cover sheet and a polyolefin separation sheet. It is manufactured as a continuous web (see Coating PROCESSES, survey), and is suppHed in roUs of varying width and photopolymer composition. 

This polymer film composition can be extruded into a polymer film sheet laminated to or co-extruded with a thermoplastic synthetic resin sheet to make a thermoformable inner liner. The ther-moformable inner liner is thermoformed, trimmed, and nested in a spaced relationship within an outer wall element, after which a polymer foam is injected to the space between the inner liner and the outer wall element. 

In laminating or coating, a preformed solid film of plastic is bonded with glue or adhesive directly onto the material to be laminated. Composite films of cellulose and poly(ethylene), for example, are produced in this way. In these composite films, the cellulose protects from foreign odors and the poly(ethylene) assures water-tightness. Composite films of poly(isobutylene) and poly(ethylene) are used in the construction of chemical apparatus made of steel. Poly(ethylene) takes care of the protection against corrosion, and poly(isobutylene), with adhesives, the adhesion to steel. Steel sheet laminated with PVC can be processed as normal, but is noncorrosive in the absence of any further treatment. Metal aircraft parts are often coated with films of poly(tetrafluoroethylene). Poly(tetrafluoroethylene) is difficult to wet, and this decreases the tendency to ice over. 

Packaging (qv) represents the largest market area for film and sheeting materials (15). It is a complex market with so many categories that it is difficult to get an accurate measure of end usage for specific materials (16). The stmcture of the marketplace which uses both monolayers of film, as well as converted composite stmctures and laminates, adds to the complexity. The ultimate user or packager may purchase raw film direcdy from a manufacturer, or use the same film laminated to one or more other films or substrates through a converter. The converter may buy film or extmde his own supply. Resin sales to film producers do not always correlate with their film sales, because of scrap and yield losses. 

Composites. The history of phenoHc resin composites goes back to the early development of phenoHc materials, when wood flour, minerals, and colorants were combined with phenoHc resins to produce mol ding compounds. In later appHcations, resin varnishes were developed for kraft paper and textile fabrics to make decorative and industrial laminates. Although phenoHcs have been well characterized in glass-reinforced composites, new developments continue in this area, such as new systems for Hquid-injection molding (LIM) and sheet-molding compounds (SMC). More compHcated composite systems are based on aramid and graphite fibers. 

ARALL laminates, a family of hybrid composites consisting of aramid fibers bonded with epoxy between 0.3 mm thick aircraft ahoy sheets, were introduced in the 1980s (53). The laminates have lower density than even the new Al—Li ahoys and are greatly superior to monolithic aluminum sheet in resisting the growth of fatigue cracks. ARALL laminates have been specified for aircraft stmcture which is subjected to cycHc tension loads (see Laminates). 

Wood (qv) is arguably the oldest building material used by humans to constmct their dweUings. It is a natural product obtained from trees, used in both stmctural and decorative appHcations. The chemical composition of wood is largely cellulose (qv) and lignin (qv). Today there are a variety of composite or reconstituted wood products, such as plywood, particle board, wood fiber boards, and laminated stmctural beams, where small pieces of wood or wood fiber are combined with adhesives to make larger sheets or boards (see Laminates). 

Plastic laminated sheets produced in 1913 led to the formation of the Formica Products Company and the commercial introduction, in 1931, of decorative laminates consisting of a urea—formaldehyde surface on an unrefined (kraft) paper core impregnated with phenoHc resin and compressed and heated between poHshed steel platens (8,10). The decorative surface laminates are usually about 1.6 mm thick and bonded to wood (a natural composite), plywood (another laminate), or particle board (a particulate composite). Since 1937, the surface layer of most decorative laminates has been fabricated with melamine—formaldehyde, which can be prepared with mineral fiUers, thus offering improved heat and moisture resistance and allowing a wide range of decorative effects (10,11). 

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