Polyester mold shrinkage

Besides high mechanical strength, polyester LCPs exhibit excellent thermal and chemical resistance, high heat deflection temperature, low mold shrinkage,... 

Trogamid T has low mold shrinkage and good dimensional stability. The weldability which is very good offers an obvious advantage over the crystalline polyesters and polyamides. 

Polyblends in which both phases are rigid are frequently called poly alloys. Poly (phenyl oxide) is blended with impact polystyrene to improve melt flow. Complete compatibility between the two phases is rare and was observed between poly (methyl methacrylate) and poly(vinylidene fluoride) by D. R. Paul and J. O. Altamirano. Thermoplastics are added to polyesters to reduce mold shrinkage. 

The primary motivations for blending the thermoplastic polyesters with other polymers are (a) to improve the solvent resistance and process-ability of amorphous polymers such as PC, styren-ics, PPE, etc., (b) to reduce the mold shrinkage of polyesters associated with their crystallization,... 

Refers to low profile RJ surfaces. These are special TS polyester compounds for RPs that are combinations of thermoset and thermoplastic materials. Although the term low profile and low-shrink are sometimes used interchangeably, there is a difference. Low-shrink contain up to 30wt% TP, while low-profile contain from 30-50wt% TP. Low-shrink offers minimum surface waviness on molded parts, as low as 25 pm (1 mil) per in mold shrinkage whereas low-profile offers no surface waviness of 0-12.7 pm (0-0.5 in) per in mold shrinkage. 

LCPs offer high strength and rigidity, reduced mold shrinkage, dimensional stability, excellent sol-vent/chemical resistance, wear resistance, high heat resistance, and inherent flame retardancy. Polyester... 

A variety of thermosetting resins are used in SMC. Polyesters represent the most volume and are available in systems that provide low shrinkage and low surface profile by means of special additives. Class A automotive surface requirements have resulted in the development of sophisticated systems that commercially produce auto body panels that can be taken direcdy from the mold and processed through standard automotive painting systems, without additional surface finishing. Vinyl ester and epoxy resins (qv) are also used in SMC for more stmcturaHy demanding appHcations. 

Alkyds. Alkyd resins consist of a combination of unsaturated polyester resins, a monomer, and fillers. Alkyd compounds generally contain glass fiber filler, but they may also include clay, calcium carbonate, alumina, and other fillers. Alkyds have good heat, chemical, and water resistance, and they have good arc resistance and electrical properties. Alkyds are easy to mold and economical to use. Postmolding shrinkage is small. Then-greatest limitation is extremes of temperature (above 175°C) and humidity. 

Epoxy polymers (including epoxy novolacs) have been designed to meet most of these requirements and are almost universally used in such encap-sulant applications. Epoxy polymers exhibit superior adhesion that in many cases eliminates the need for a barrier or junction coating. They have a low coefScient of thermal expansion low shrinkage and low injection velocity, which means that low transfer or injection pressures can be used. These polymers also possess excellent mechanical properties coupled with low moisture and gas permeability. Above all, they are cheap and readily available. Other transfer-molding materials used to a limited extent include silicones, phenolic materials, and even polyesters. Most molding formulations are highly filled (70-75%) with materials such as quartz, fused silica, short... 

Third generation. Highest levels of shrinkage control. Accuracy of mold reproduction and surface smoothness Dual thickening systems containing isocyanate prepolymers Saturated polyesters Saturated polyester blends with pol5rvdnyl chloride Polyurethanes... 

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