Abstract: An extruded hollow thermoplastic board, which includes a pair of flat and parallel sheets spaced apart and interconnected by extending ribs, generally has a plurality of depression bands in the areas where the flat sheets and extending ribs are joined. The bands, which negatively affect the surface flatness, are especially apparent for crystalline thermoplastic materials. A hollow thermoplastic board, which effectively reduces the depth of the depression bands by inclusion of locationally fixed gas pockets in the rib area during production, is disclosed in the present invention. The hollow thermoplastic board of the present invention substantially enhances the surface smoothness and is highly beneficial to applications such as printing, lamination and graphic art. The present invention also provides a method for production of the hollow thermoplastic boards of smooth surfaces.

Abstract: An extruded hollow thermoplastic board, which includes a pair of flat and parallel sheets spaced apart and interconnected by extending ribs, generally has a plurality of depression bands in the areas where the flat sheets and extending ribs are joined. The bands, which negatively affect the surface flatness, are especially apparent for crystalline thermoplastic materials. A hollow thermoplastic board, which effectively reduces the depth of the depression bands by inclusion of locationally fixed gas pockets in the rib area during production, is disclosed in the present invention. The hollow thermoplastic board of the present invention substantially enhances the surface smoothness and is highly beneficial to applications such as printing, lamination and graphic art. The present invention also provides a method for production of the hollow thermoplastic boards of smooth surfaces.

Abstract: The present invention discloses an apparatus for regulating chamber pressure in a process chamber by a closed-loop control method utilizing a pressure sensor, a pressure controller and an inverter for regulating the rotational speed of an exhaust blower such that the exhaust pressure in a factory exhaust conduit can be substantially controlled at a constant value. The present invention novel method and apparatus allows a more stable chamber pressure to be maintained in an APCVD or LPCVD chamber, while substantially reduces the possibility of particulate contamination on a throttle valve that is mounted juxtaposed to the process chamber and thus minimizing any back-fill contamination problems.

Abstract: A method of rotationally molding blends of polymers of good flow to produce articles of high impact resistance, high stress crack resistance, smooth surfaces, and the absence of excessive warpage in which the blend is placed in a rotational mold which is then biaxially rotated about two perpendicular axes while heating the mold and contents and then cooling the mold and contents to about room temperature while maintaining this biaxial rotation followed by removing the resulting article. The disclosure also includes the rotationally molded shaped structures resulting from this method with these structures having high impact resistance, high stress crack resistance, smooth surfaces and the absence of excessive warpage.

Abstract: Terephthalic acid is esterified with an alkylene glycol by heating in a first stage one mole of the acid with at least about 1.2 moles of the glycol and 0.01 to 1.0% based on the weight of the acid of a volatile organic base at a temperature between 240.degree. and 320.degree. C and at a pressure above the vapor pressure of the glycol at the reaction temperature until about 75-85% of the acid groups initially present in the terephthalic acid have been esterified, and then maintaining the reaction mixtures from the first stage in a second stage at a temperature between 240.degree. to 320.degree. at a pressure less than that of the said first stage until at least about 95% of the acid groups initially present in the terephthalic acid have been esterified.

Abstract: A three component blend of polymers comprising a polyethylene homopolymer or ethylene-alkene copolymer with an ethylene-vinyl acetate copolymer and either an ethylene-propylene copolymer or an ethylene-propylene-diene terpolymer. These three component blends are particularly suitable for rotational molding of shaped structures as they have synergistic properties of environmental stress crack resistance and high impact strength of the finished products. The disclosure also includes shaped structures comprising these blends.