Impact acrylic dominates use in heavy gauge sheet (HGS) and polycarbonate has a solid hold on second place, but material supplier Eastman Chemical (Kingsport, TN) believes Kelvx, its new copolyester grade, could snag a larger share of the market at polycarbonate's expense. According to Eastman officials and some early users, the material rectifies copolyester (COPE) limitations such as its comparatively low heat-deflection temperature (HDT), and lower stiffness and notched Izod impact strength.
The HGS market is a substantial one with at least 200,000 tonnes/year demand in Europe alone, says Michael Hartmann, HGS marketing manager in the Cologne, Germany offices of Eastman. He estimates that acrylics have a 76 percent share of the market and polycarbonate about 16 percent, with Eastman's Spectar COPE, offered for about a decade, accounting for most of the remainder. Each material has its strengths and weaknesses. PC offers the best impact resistance but requires pre-drying and is expensive. High-impact acrylic brings strong scratch resistance and good light transmission, is easy to bond and fabricate, and is the least expensive of the three. It is more brittle than the other materials, however.
COPE thermoforms particularly well for deep definition, and its impact strength and chemical resistance top those of acrylics. But Spectar's HDT of 65C was often considered too low for outdoor use, admits Hartmann, leading processors to relegate it largely to indoor applications such as point-of-purchase displays (see article in June 2002 MP/MPI).
Eastman will not reveal details on Kelvx's molecular structure, saying only that it is a high-temperature copolyester material, but company officials seem to indicate that additives help achieve its higher heat resistance. Kelvx is supplied from Kingsport. Its pricing lands about 10 percent less than PC and about 10 percent more than Spectar, says Hartmann. Spectar pricing overlaps that of impact acrylics.
The heat-absorption temperature of Kelvx at 1.80 MPa (ISO 75 test) is 80C, equal to that of high-impact acrylics; PC's is higher, at about 130C. Hartmann notes that Kelvx's flexural modulus of 2150 MPa approaches that of PC and tops that of impact-modified acrylics, but that Kelvx's thermoforming temperature is between 150 and 170C, considerably lower than PC. Elongation at break is 15 percent.
Impact strength changes little between 23 and -10C, a critical factor, notes Hartmann, for its proposed outdoor use. Eastman has done flammability testing and says the material will earn a 94 V-2 rating using U.S. test UL 94. In Europe, processors, not material suppliers, must certify the sheet themselves, and each country requires its own testing (a pan-European test, long demanded by industry, is likely in the next few years). Willi Onklin, Kelvx technical manager, says a second grade, Kelvx VX, is offered for use in capstock layers to prevent yellowing during outdoor use. Both grades are about 1 percent more dense than PC, he says.
In an unusual arrangement for the supplier, Eastman is using toll extruders in China, Australia, and Latin America, and will market the sheet itself in those places, says David Speicher, regional business manager. In the U.S., processors Spartech Plastics (St. Louis, MO) and Sheffield Plastics (Sheffield, MA), market sheet made from the material, and in Europe, Makroform (Darmstadt, Germany) and Barlo Plastics (Geel, Belgium) market sheet using Kelvx. Other sheet extruders are also being contacted, says Speicher.
In Italy, thermoformer Caodura (Vicenza), has tested the material with good results, according to firm president Paolo Caodura. Once flammability testing in European countries is completed, which he expects to be late this year, Caodura will add Kelvx sheet to acrylic and PC, the other materials it forms. Caodura says the material's low thermoforming temperature produces cycle times 5 to 10 percent faster than PC, and the lack of a pre-drying requirement leads to even greater time savings. He says the material beats acrylics for impact resistance and parts definition.