Resin transfer molding phenolics

CompositGS. There has been substantial progress in improving the processability of phenolics in composite materials (104-106) to the point where a variety of materials are available for pultrusion, filament winding, and resin-transfer molding (see Composites, Fabrication). More complicated composite systems are based on aramid and graphite fibers. 

Coa sites Continuous Panel/Electrical Laminates/Filament Hinding/General Molded Products/Phenolic Holding/RTM (Resin Transfer Molding)/SMC/BMC/Spray-Up/Hand Lay-Up... 

Cooqposites Filaaent Winding, General Molded Products, Phenolic Holding, PreForm, Pultrusion, RTH (Resin Transfer Molding), SHC/BMC... 

Typical transfer molding compositions for encapsulation of electronic devices are mixtures of an epoxy novolac resin, a phenolic resin hardener, a catalyst, large amounts of inorganic filler (e.g., Si02) flame-retardant ingredients, internal lubricants, carbon black, and sometimes other additives such as getters to trap ionic impurities (34,35), corrosion-protection materials, and stress-relief ingredients. 

For RPs, electroformed molds are mainly useful for autoclave molding and for closed matched die molding (cold press, low-pressure hot press, resin injection, resin transfer, low-pressure phenolic molding, and resin casting) as well as for reinforced reaction injection molding (RKIM). Prototyping can also use this technique for mold-making. 

The novolacs are another class of epoxy resins. They are produced by reacting a novolac resin, usually formed by the reaction of o-cresol or phenol and formaldehyde with epichlorohydrin. Figure 3.5 shows the general structure. These materials are used as transfer molding powders, electrical laminates, and parts where superior thermal properties and high resistance to solvents and chemicals are required. 

Cyanate ester and phenolic triazine (PT). The cyanate ester resins have shown superior dielectric properties and much lower moisture absorption than any other structural resin for composites. The physical properties of cyanate ester resins are compared to those of a representative BMI resin in Table 2.33. The PT resins also possess superior elevated-temperature properties, along with excellent properties at cryogenic temperatures. They are available in several viscosities, ranging from a viscous liquid to powder, which facilitates their use in applications that use liquid resins such as filament winding and transfer molding. 

Weathering resistance in phenolic resins depends on their composition and processing Novolac-type transfer molding compounds are more resistant than resole molding compounds [32]. 

Phenolics Elastomers Powder, solutions Excellent thermal stability to over 300 F generally, and over 400 F in special formulations. Broad choice of resins. May be cast or compression, transfer, or injection molded. Precision potentiometers, RF connectors, heating panels. 

Durez . [OxyQiem/Durez] Phenolic, alkyd, or phthalate resins, some glass or mineral filled thermosets for tqpplics. incl. automrxive transmission parts and braking systems, communication products for compr., transfer, and inj. molding applies. 

Resinoid. piesinoid Engineering] Phenolic resin, some glass or fabric reinforced thetmoset fix inj transfer, and ctmipression molding. 

Molding Powders. Urea-formaldehyde resins are compounded with alpha-cellulose cotton fiber reinforcement to produce molding powders (4 percent) for compression, transfer, and injection molding. Typical molding conditions are 127 to 182°C and 2000 to 8000 psi. They are superior to phenolics in white color, electrical resistance, and low cost, but are limited by moisture sensitivity (Table 3.13). They are used primarily in electrical wiring devices such as wall outlets, receptacles, electric blanket controls, circuit breakers, and knob handles. Smaller amounts are used in bottle caps, housewares, buttons, and sanitary ware. 

Phenolic resins are available in various grades for compression, transfer, and injection molding. Major suppUers of phenolic resins include Cytec Fiberite (Enduron), Occidental (Durez), Plastics Engineering (Plenco), Lockport (Valite), Plaslok, Rogers, and Resinoid. 

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