Molding compound

The main difference with un-reinforced or filled thermoplastic compounding is the treatment of the screw to limit its wear. The screw profile will also be optimized for glass filament thermoplastic compounding, more particularly in terms of the mixing forces after the introduction of the 

Testing method D1238 D955 D696 Cl 77 D792 D570 

Ultra high molecular weight-PE HOPE 30% Gfr Polymide Polymide 30% Gfr Polyethylene sulfide Polypropylene (PP) PP 10-40% talc PP 10-30 Gfr High impact polystyrene Styrene acrylonitrile (SAN) 

SAN 20 Gfr Styrene maleic anhydride (SMA) Polystyrene Polyurethane Polysulfone Polysulfone 20% 

Notes Gfr, Glass fiber filled Cfr, carbon fiber filled Mf, 

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Aromatic polyester Unsaturated polyester Alkyd molding compounds ... 

HDPE, high density polyethylene PP, polypropylene EVA, ethylene—vinyl alcohol SMC, sheet-molding compound ERP, fiber-reinforced plastic LDPE, low density polyethylene PE, polyethylene BMC, bulk mol ding compound TPE, thermoplastic elastomer. 

Lubricants. Process aids or lubricants promote smooth and rapid extmsion and calendering, prevent sticking to extmders or calender roUs, and impart good release properties to molding compounds. In some cases use of lubricants allow slightly lower processing temperatures (see Vinyl polymers). 

Uncured resins are skin sensitizers and contact should be avoided, as weU as breathing the vapor, mist, or dust. Novolak-based pulverized products generally contain hexamethylenetetramine, which may cause rashes and dermatitis. PhenoHc molding compounds and pulverized phenoHc adhesives must be controUed as potentially explosive dusts. In addition, they contain irritating or toxic additives. 

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. 

PhenoHc sheet-molding compound is seeing increased use in interior and exterior appHcations in mass transit. The trains in service on the English Channel tunnel have several panels made from phenoHc SMC which had to meet the strict European safety standards for fire and smoke generation. 

Some amino resins are used as additives to modify the properties of other materials. For example, a small amount of amino resin added to textile fabric imparts the familiar wash-and-wear quaUties to shirts and dresses. Automobile tires are strengthened by amino resins which improve the adhesion of mbber to tire cord (qv). A racing sailboat may have a better chance to win because the sails of Dacron polyester have been treated with an amino resin (1). Amino resins can improve the strength of paper even when it is wet. Molding compounds based on amino resins are used for parts of electrical devices, botde and jar caps, molded plastic dinnerware, and buttons. 

The term amino resin is usually appHed to the broad class of materials regardless of appHcation, whereas the term aminoplast or sometimes amino plastic is more commonly appHed to thermosetting molding compounds based on amino resins. Amino plastics and resins have been in use since the 1920s. Compared to other segments of the plastics industry, they are mature products, and their growth rate is only about half of that of the plastics industry as a whole. They account for about 3% of the United States plastics and resins production. 

Melamine resins were introduced about ten years after the Beetle molding compound. They were very similar to those based on urea but had superior quaHties. Henkel in Germany was issued a patent for a melamine resin in 1936 (7). Melamine resins rapidly supplanted urea resins and were soon used in molding, laminating, and bonding formulations, as well as for textile and paper treatments. The remarkable stabiHty of the symmetrical triazine ring made these products resistant to chemical change once the resin had been cured to the insoluble, cross-linked state. 

Amino molding compounds can be compression, injection, or transfer molded. Urea molding compound has found wide use and acceptance in the electrical surface wiring device industry. Typical appHcations are circuit breakers, switches, wall plates, and duplex outlets. Urea is also used in closures, stove hardware, buttons, and small housings. Melamine molding compound is used primarily in dinnerware appHcations for both domestic and institutional use. It is also used in electrical wiring devices, ashtrays, buttons, and housings. 

To make a decorated plate, the mold is opened shortly after the main charge of molding compound has been pressed iato shape, the decorative foil is laid ia the mold on top of the partially cured plate, ptinted side down, and the mold closed again to complete the curing process. The melamiae-treated foil is thus fused to the molded plate and, as with the decorative lamiaate, the overlay becomes transparent so that the ptinted design shows through yet is protected by the film of cured resia. 

The excellent electrical properties, hardness, heat resistance, and strength of melamine resias makes them useful for a variety of iadustrial apphcatioas. Some represeatative properties of amino resia molding compounds, including the industrial-grade melamines, are Hsted in Table 2. 

Table 2. Typical Properties of Filled Amino Resin Molding Compounds...

In 1989 quantity costs, which reflect the lowest cost, of urea molding compounds, were approximately 1.41 /kg ( 0.035/in. for black and brown colors, 1.58/kg ( 0.039/in.for white and ivory special colors are somewhat higher in price. The approximate cost of cellulose-filled melamine molding compound is 1.74/kg ( 0.043/in. ). Glass fiber-filled melamine sells for 7.70/kg ( 0.22/in. ). 

Amino molding compounds are produced worldwide. The following Hst represents the major suppHers. 

Phenohc resins (qv), once a popular matrix material for composite materials, have in recent years been superseded by polyesters and epoxies. Nevertheless, phenohc resins stiU find considerable use in appHcations where high temperature stabiHty and fire resistance are of paramount importance. Typical examples of the use of phenoHc resins in the marine industry include internal bulkheads, decks, and certain finishings. The curing process involves significant production of water, often resulting in the formation of voids within the volume of the material. Further, the fact that phenoHcs are prone to absorb water in humid or aqueous conditions somewhat limits their widespread appHcation. PhenoHc resins are also used as the adhesive in plywood, and phenohc molding compounds have wide use in household appliances and in the automotive, aerospace, and electrical industries (12). 

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