Stock material or miscellaneous articles – Composite – Of polycarbonate
Patent
1987-04-15
1988-08-30
Buffalow, Edith
Stock material or miscellaneous articles
Composite
Of polycarbonate
4284233, 4284237, 428913, 428480, 528 66, 528 76, 528 77, A61F 116
Patent
active
047676710
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an antimist coating for glass or plastics substrates such as polycarbonate substrates which in use are susceptible to misting and to methods for applying such coatings. More particularly the invention relates to antimist coatings formed from hydrophilic polyurethanes.
The problem of the misting of automobile, train and aeroplane windows, as well as of lenses used in eye glasses, safety glasses, binoculars and cameras and of safety visors and other transparent surfaces made of glass or plastics such as polycarbonate is well known. The occurrence of misting is particularly dangerous when the substrate involved forms part of a safety device, such as safety goggles, glasses, screens or visors in which misting of the substrate by moist breath or external water vapour can lead to accidents. There is therefore a requirement for a transparent antimist coating having high light transmission and minimal optical distortion. Antifogging coatings formed from hydrophilic polyacrylate polymers and copolymers have been described in for example British Pat. Nos. 1205767, 1260948 and 1498345, and U.S. Pat. Nos. 3,488,215, 3,515,579, 3,520,949 and 3,635,756. However, such coatings have not been found to be entirely satisfactory through suffering from one or more of the following disadvantages (a) that when hydrated the coatings were soft and were therefore susceptible to abrasion and scratching both in use and when being cleaned; (b) that when saturated the coating was not sufficiently well adhered to the substrate and readily delaminated. This was particularly true when the substrate was glass or a plastics substrate such as polycarbonate, a particularly severe disadvantage in the case of the latter substrate as polycarbonate is widely used in safety goggles, visors and screens because of its high impact resistance; (c) the curing temperature required for the coating process involving acrylates is high, usually in excess of 80.degree. C. which is expensive to operate and requires long heating and cooling periods which makes the process of manufacturing slow: (d) when dry and not plasticised by absorbed water, the coatings were relatively brittle and were susceptible to cracking if flexed.
U.K. Pat. No. 1423269 and U.S. Pat. Nos. 4,018,939 and 3,935,367 disclose nonfogging film coatings comprising a block copolymer containing alternating blocks of polyurethane and hydrophilic polyacrylate. The copolymer is adhered to the substrate by subjecting the substrate to a controlled exposure to UV irradiation either before or after the nonfogging coating has been cast onto it. The coatings used in the present invention do not require this extra manufacturing step.
U.S. Pat. No. 4,467,073 and International Patent Application No. WO 86/00916 describe an anti-fog liquid coating composition formed by complexing or reacting surfactants with hydrophilic polymers which has been cross linked with isocyanate prepolymers. The hydrophilic polymers employed include polyvinyl-pyrrolidone and copolymers thereof and polydimethylacrylamide. The patents do not disclose or suggest the use of hydrophilic polyurethanes as is required in the present invention. The patents do not disclose hydrophilic polymers having the water content, when hydrated, of the hydrophilic polyurethanes used in the present invention. The hydrophilic polyurethanes used in the present invention do not contain or require the presence of surfactants to be effective.
U.S. Pat. Nos. 4,079,160 and 4,435,450 describes abrasion resistant polyurethane coatings which may be applied to glass or polymeric substrates. However, antifogging coatings or the use of hydrophilic polyurethanes is not disclosed or suggested.
U.S. Pat. Nos. 4,156,067 and 4,255,550 describe polyurethane polyether resins which contain carboxylic acid groups and hydroxyl groups in the polymer back bone. Such polyurethanes are described as being suitable inter alia as antifog coatings. However, these polymers are described as being soluble under alkaline conditions which may preclude the
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Howes John G. B.
Parker Robert S. R.
Buffalow Edith
Smith and Nephew Associated Companies p.l.c.
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