Cast sheet

Poly(methyl methacrylate) Cast sheet Impact- modified Heat- resistant ... 

Three bulk polymerization processes are commercially important for the production of methacrylate polymers batch cell casting, continuous casting, and continuous bulk polymerization. Approximately half the worldwide production of bulk polymerized methacrylates is in the form of molding and extmsion compounds, a quarter is in the form of cell cast sheets, and a quarter is in the form of continuous cast sheets. 

Many lens casters use the term hard-resin lenses for DADC products companies and trade names include American Optical (Aoflte ), Cobum (Supremacy I), Optical Radiation (Orcoflte), and Silor Optical (Orma 1000). Additional information can be obtained from the Optical Manufacturers Association, Falls Church, Va. Cast sheets of homopolymer and copolymers are suppHed by the SGL Homalite Company, Foster Grant, and others. 

Extruded sheet is cheaper than cast sheet but because there is some residual molecular orientation, is somewhat less satisfactory optically and more difficult to machine. On the other hand, no doubt a function of its lower molecular weight, it may be thermoformed more easily. 

Currently, these tests are of no practical value to the designer and the only approach to the problem of scratch, mar, and abrasion resistance is to simulate actual performance needs. For optical purposes, a cast sheet in the allyl family of plastics known as CR39 has been used as a standard of comparison in evaluating scratch and mar resistance of a material. The CR39 is used for eye lenses and other optical products where the advantages of plastics are a consideration. Coatings have been developed for polycarbonate, acrylics, and other plastics that dramatically improve the scratch and mar resistance of these materials. 

Conan DuPont s trade-name for their mineral filled acrylic continuous cast sheet material. This wear resistant and attractive material is used for consumer s kitchen counter... 

Properties Poly(methyl methacrylate) Cast sheet Impact- modified Heat- resistant Alkyd, molded Acrylic poly(vinyl chloride) alloy styrene-poly(vinyl chloride) alloy... 

Cast and extruded sheets, cell-cast sheets, stretched sheets, films down to 50 microns laminated protective surfaces on ABS, PVC or other plastic sheets that are thermo-formed into parts requiring resistance to outdoor weathering for residential siding and transformer housings... 

Cast and extruded sheets, cell-cast sheets for greenhouses... 

ISO 1628-6 1990 Plastics - Determination of viscosity number and limiting viscosity number - Part 6 Methyl methacrylate polymers ISO 7823-1 2003 Plastics - Poly(methyl methacrylate) sheets - Types, dimensions and characteristics - Part 1 Cast sheets... 

ISO 7823-3 2003 Plastics - Poly(methyl methacrylate) sheets - Types, dimensions and characteristics - Part 3 Continuous cast sheets ISO 8257-1 1998 Plastics - Poly(methyl methacrylate) (PMMA) moulding and extrusion materials - Part 1 Designation system and basis for specifications ISO 8257-2 2001 Plastics - Poly(methyl methacrylate) (PMMA) moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties ISO 12017 1995 Plastics - Poly(methyl methacrylate) double- and triple-skin sheets - Test methods... 

Extreme care has to be exercised to avoid contaminating the tape-cast sheets with dust which would seriously reduce yield and impair reliability, and a high level of cleanliness, including clean room standards, are required for processing the thinner layers. 

Major markets for casting sheets exist. Cast sheet is made in a batch process within a mold or cell or continuously between stainless steel belts. Basically the processing cells consist of two pieces of polished (or tempered) plate glass slightly larger in area than the finished sheet is to... 

An important advantage of the method is the elimination of the severe problems of handling and breakage of large sheets of costly glass that make up the cells. Cell-cast sheet has superior optical properties and light transmittance as well as smoother surfaces. The continuous process provides more uniform thickness and has less tendency to form warped sheet. 

Figures 29 and 30 show typical growth rates for two high molecular cast sheets PMMA, one of them being frequency sensitive and the other one not frequency sensitive.

Fig. 29. Growth rates da/dn versus 8K, at 23 °C for a high molecular cast sheet PMMA showing frequency sensitivity (0.1, 1,11 and 100 Hz test). (PMMA Plexiglas G from Rohm and Haas company, USA). From Refs. and courtesy of Society of Plastics Engineers Edn.

Fig. 30. Growth rates da/dn versus 8Ki at 23 °C for another high molecular cast sheet PMMA that does not show frequency sensitivity (0.4, 2, 10 and 50 Hz test). (PMMA 233 from Rohm Company (Germany) From Ref. courtesy Dr. Dietrich Steinkopff Verlag...

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