Abrasion resistance polycarbonate

Abrasion-Resistant Polycarbonate Sheet. Abrasion-resistant polycarbonate sheet retains the extremely high impact properties and also provides resistance to abrasion. The surface coating also gives some added protection against weathering. 

The abihty of organically modified ceramics based on alumina, zkconia, titania, or siUca (and mixtures of each) to function as abrasion-resistant coatings has also been studied (62). Eor example, polycarbonate, when coated with an epoxy—aluminosihcate system, experiences a significant reduction in the degree of hazing induced by an abrader, as compared to uncoated polycarbonate. 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Acrylic Resins. The first synthetic polymer denture material, used throughout much of the 20th century, was based on the discovery of vulcanised mbber in 1839. Other polymers explored for denture and other dental uses have included ceUuloid, phenolformaldehyde resins, and vinyl chloride copolymers. Polystyrene, polycarbonates, polyurethanes, and acryHc resins have also been used for dental polymers. Because of the unique combination of properties, eg, aesthetics and ease of fabrication, acryHc resins based on methyl methacrylate and its polymer and/or copolymers have received the most attention since their introduction in 1937. However, deficiencies include excessive polymerization shrinkage and poor abrasion resistance. Polymers used in dental appHcation should have minimal dimensional changes during and subsequent to polymerization exceUent chemical, physical, and color stabiHty processabiHty and biocompatibiHty and the abiHty to blend with contiguous tissues. 

The acetal resins show superior creep resistance to the nylons but are inferior in this respect, to the polycarbonates. It is to be noted, however, that limitations in the load-bearing properties of the polycarbonates restrict their use in engineering applications (see Chapter 20). Another property of importance in engineering is abrasion resistance—a property that is extremely difficult to assess. Results obtained from various tests indicate that the acetal polymers are superior to most plastics and die cast aluminium, but inferior to nylon 66 (see also Section 19.3.6 and Chapter 18). 

The use of PBT as an engineering material is more a consequence of a balance of good properties rather than of a few outstanding ones. It does not possess the toughness of polycarbonate, the abrasion resistance of an aliphatic polyamide, the heat resistance of a polysulphone, polyketone or poly(phenylene sulphide) or... 

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. 

Lexan resins - [POLYCARBONATES] (Vol 19) -enhanced abrasion resistance [GLASSES, ORGANIC-INORGANIC HYBRIDS] (Vol 12) - [POLYCARBONATES] (Vol 19)... 

A comparison of the abrasive wear by Bohm (1990) found that the hard and more brittle plastics, such as polyacetals, polyamide-imide, and polycarbonates, are less abrasion resistant than softer and tougher materials such as the polyethylenes and polyurethanes. Table 7.2 details some comparative... 

D1SHP40L [GE Silicones] Primo used as adhesion promoter for weatherable abrasion-resistant silicone hardcoat on Lexan polycarbonate. 

Paints and Coatings. Ethoxysilanes are used in high temperature, zinc-rich paints (see Paint) (51,52). Methyl- and phenyltrialkoxysilanes are used to prepare abrasion-resistant coatings for plastics (53), particularly polycarbonate (54,55), and dielectric coatings and seals for high voltage electrical components, including television tubes. 

For example, the abrasion-resistant coatings based on a silicone-silica hybrid (33) have provided a scratch- and mar-resistant finish for polycarbonate as well as metals. The chemistry involved is discussed by Vincent, Kimball and Boundy (3iL). The coating consists of polysiloxane and silane-modified submicron silica particles, microscopically dispersed in the solution. The coating is then cured at elevated temperatures. Currently, this type of abrasion resistant coating is marketed in the U.S. by Dow Corning and General Electric Company. 

Surface modifications with plasmas have specific applications for systems requiring special protections, e.g., low surface energy or low wear resistance. Surface photopolymerization has yet to prove its value. The protection of a polymer surface with abrasion-resistant, silicone-silica hybrid material has demonstrated some utilities for polycarbonate or other optical materials. 

T. Wydeven developed a plasma process that significantly improves the hardness of optical lenses and, consequently, leads to greater scratch resistance (7. Vinyl-trimethoxysilane films were deposited on transparent polycarbonate lenses by plasma polymerization. The adherent, clear films protect the substrate from abrasion and also serve as antireflection coatings. Post-treatment of the vinyltrimethoxysilane films in an oxygen glow discharge fui ther improved the abrasion resistance. 

Many substrates, for example, many wood products, are provided with protective and decorative coatings of organic polymers, for example, radiation- or heat-curable polyacrylates, polyacrylate copolymers, polycarbonates or terephthalic resins, so as to improve gloss, dryness (no tack), and abrasion resistance and scratch resistance. 

Polytetrafluoroethylene is added to acetal, polycarbonate, and nylon to decrease friction and increase abrasion resistance. 

The temperature resistance of the polyarylates lies between polysulfone and polycarbonate. The polymer is flame retardant and shows good toughness and UV resistance. Polyarylates are transparent and have good electrical properties. The abrasion resistance of polyarylates is superior to polycarbonate. In addition, the polymer shows a very high recovery from deformation. However, the material is subject to environmental stress cracking, particularly in the presence of aromatic and aliphatic hydrocarbons. 

---