Nov. 15, 2002
Acrylic thermoplastics are known for their crystal clarity and outstanding weatherability.

Acrylic thermoplastics are known for their crystal clarity and outstanding weatherability. They are available in cast sheet, rod, and tube; extruded sheet and film; and compounds for injection molding and extrusion.

Cell-cast sheet is produced in several sizes and thicknesses. The largest sheets available are 120 144 in., in thicknesses from 0.030 to 4.25 in. Continuous cast material is supplied as flat sheet to in. thick, in widths to 9 ft. Acrylic sheet cast by the continuous process (between stainless-steel belts) is more uniform in thickness than cell-cast sheet. Cell-cast sheet, on the other hand, which is cast between glass plates, has superior optical properties and surface quality. Also, cell-cast sheet is available in a greater variety of colors and compositions. Cast acrylic sheet is supplied in general-purpose grades and in ultraviolet-absorbing, mirrored, super-thermoformable and cementable grades, and with various surface finishes. Sheets are available in transparent, translucent, and opaque colors.

Acrylic film is available in 2, 3, and 6-mil thicknesses, in clear form and in colors. It is supplied in rolls to 60 in. wide, principally for use as a protective laminated cover over other plastic materials.

Injection-molding and extrusion compounds are available in both standard and high-molecular-weight grades. Property differences between the two formulations are principally in flow and heat resistance. Higher molecular-weight resins have lower melt-flow rates and greater hot strength during processing. Lower molecular-weight grades flow more readily and are designed for making complex parts in hard-to-fill molds. Also available are high-impact molding grades, which provide the same transparency and weatherability as the conventional acrylics.

Properties: Acrylic plastics transmit and control light, resist weather, are stable against discoloration, and have superior dimensional stability and an excellent combination of structural and thermal properties. Clear acrylic plastic is as transparent as the finest optical glass. It has a light transmittance of 92%, exceptionally low haze level of approximately 1%, and an index of refraction of 1.49 -- high enough for use in lenses and other optical applications.

Colorants produce a full spectrum of transparent, translucent, or opaque colors. Most colors can be formulated for long-term outdoor durability. Acrylics are normally formulated to filter ultraviolet energy in the 360-nm and lower band. Other formulations are opaque to UV light or provide reduced UV transmission.

Mechanical properties of acrylics are high for short-term loading. However, for long-term service, tensile stresses must be limited to 1,500 psi to avoid crazing or surface cracking.

The moderate impact resistance of standard formulations is maintained even under conditions of extreme cold. High-impact grades have considerably higher impact strength than standard grades at room temperature, but impact strength decreases as temperature drops. Special formulations ensure compliance with Underwriters' Laboratories standards for bullet resistance.

Although acrylic plastics are among the most scratch resistant of the thermoplastics, normal maintenance and cleaning operations can scratch and abrade them. Special abrasion-resistant sheet is available that has the same optical and impact properties as standard grades.

Toughness of acrylic sheet, as measured by resistance to crack propagation, can be improved severalfold by inducing molecular orientation during forming. Jet-aircraft cabin windows, for example, are made from oriented acrylic sheet.

Acrylic sheet and moldings resist solutions of inorganic acids and alkalies and aliphatic hydrocarbons such as VM&P naphtha, as well as most detergent solutions and cleaning agents. They are attacked, however, by chlorinated and aromatic hydrocarbons, esters, and ketones.

Transparency, gloss, and dimensional stability of acrylics are virtually unaffected by years of exposure to the elements, salt spray, or corrosive atmospheres. These materials withstand exposure to light from fluorescent lamps without darkening or deteriorating. They ultimately discolor, however, when exposed to high-intensity UV light below 265 nm. Special formulations resist UV emission from light sources such as mercury-vapor and sodium-vapor lamps.

Applications: Cast acrylic sheet is used in aircraft, boat, mass transit, architectural, and protective glazing; internally illuminated outdoor signs, lighting diffusers, and skylights; and product prototypes and demonstration models. Special ultraviolet-absorbing grades are used for document preservation in museums and for various photographic applications.

Acrylic film is used as a laminated protective surface on ABS, PVC, or other plastic sheet that is thermoformed into parts requiring resistance to outdoor weathering. Examples include motorcycle shrouds, recreational-vehicle panels, residential siding, and transformer housings.

Acrylic moldings are used for light-control lenses in lighting fixtures, camera lenses, vending-machine parts, and appliance panels, knobs, and housings. Automotive applications include lenses for taillights and parking lights, instrument panels, nameplates, medallions, and dials. A modified molding compound contains an impact modifier to increase toughness. Parts molded from these durable transparent materials include automotive dials, housewares, piano keys, medical instruments, and toys.

Specially formulated acrylic sheet is available for deeply formed components such as tub-shower units, which are subsequently backed with glass-fiber-reinforced polyester. Chemical resistance of this sheet is superior to that of conventional sheet.

Sheet extruded from the high-impact molding grade is used for signs, thermoformed products, toys, and glass-fiber-polyester-backed components such as camper tops, furniture, and recreational-vehicle bodies.

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