Plastic lenses

Light-focusing plastic rods and other optical devices with graduated refractive indexes may use DADC and other monomers (29). Preparation and properties of plastic lenses from CR-39 are reviewed in reference 30. 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

Vinyl neopentanoate is used in the preparation of adhesives and binders (44—46), optical materials for plastic lenses (47), gas permeable membranes for oxygen enrichment (48), and in coating appHcations (49,50). 

Eyeglass frames made of cellulose acetate plasticized with diglycerol esters do not exhibit opaqueness at the frame-lens junction with polycarbonate plastic lenses (146,147). 

Although the proposed appHcations for photochromic systems are numerous, few have received broad use. By far, the most successful commercial apphcation is the use of photochromic silver halide-containing glasses in prescription eyewear. The convenience of having lenses that darken automatically upon exposure to sunlight has proven appealing to spectacle wearers (35). With the increasing penetration of plastic lenses into the ophthalmic market, the desire for plastic photochromic ophthalmic lenses has also increased, and considerable effort has been spent on the discovery of photochromic systems for plastic eyewear. 

Hard lenses can be defined as plastic lenses that contain no water, have moduli in excess of 5 MPa (500 g/mm ), and have T well above the temperature of the ocular environment. Poly(methyl methacrylate) (PMMA) has excellent optical and mechanical properties and scratch resistance and was the first and only plastic used as a hard lens material before higher oxygen-permeable materials were developed. PMMA lenses also show excellent wetting in the ocular environment even though they are hydrophobic, eg, the contact angle is 66°. 

The ophthalmic applications for plastics lenses include contact lenses which are now made of acrylic plastics. Another material for this application is a special hydrophillic acrylic polymer used in soft contact lenses. These lenses are much more comfortable than rigid contact lenses. 

Spirooxazine compounds are useful in the field of plastic lenses, such as sunglasses and ski goggles. The plastic photochromic sunglasses have been in the marketplace since the early 1980s, and their market share is presently ca. 70%. The excellent lightfastness of the spironaphthooxazine series makes such applications possible, compared to other photochromic compounds. 

Plastic lenses are best when lightweight and clear vision are important. They offer the widest range of bifocal designs. 

The free world market for cerium-oxide based polishing compounds is not large—approximately 4400 metric tons per year—, and we do not see a substantial growth potential despite the 11% annual growth in sales of spectacle lenses. The reason is twofold first, faster more efficient polishing compounds are available which can be used in slurry concentrations one-half that of a few years ago second, fully half the market for ophthalmic glass lenses has been captured by plastic lenses of CR-39 polymer. Cerium oxide is ineffective in polishing this material specially treated alumina or stannic oxide are used. 

Polythiocarbonate urethanes, (I), prepared by Watanabe et aL (1) having molecular weights 2500 Da had favorable refractive indexes and Abbe numbers and were used in plastic lenses. 

Dicthylcncglycol-lm-(allylcarbonatc). marketed as C.R-39 . is finding increasing use where optical transparency is required. It is the primary material used in the manufacture of plastic lenses for eyewear because of its light weight, dimensional stability, abrasion resistance, and dye-ability. Other applications for this product include instrument panel covers, camera filters, and myriad glazing uses. In these applications, the solvent and chemical resistance of die material are important. 

Often, however, we are not too interested in actually stretching a polymeric material. An engineer might ask questions such as these. In designing plastic lenses for the exterior lights on our automobiles, which optically clear plastics are the least likely to crack when struck by stones thrown up by other cars "Which plastic will best resist breakage when used as a bumper in an automobile Which elastomer will provide adequate protection against sharp objects and have the desired resilience when used in a tire ... 

Acrylic fibers are by far the major end use for acrylonitrile. They find use primarily in fabrics for clothing, furniture, draperies, and carpets. The second largest consumer of acrylonitrile is acrylonitrile-butadiene-styrene (ABS) and styrene acrylonitrile (SAN) resins. ABS is useful in industrial and construction applications, and the superior clarity of SAN makes it useful in plastic lenses, windows, and transparent household items. 

Dr. Crano received a B.S. degree in Chemistry in 1957 from Notre Dame and M.S. and Ph.D. degrees from Case Western Reserve University in 1959 and 1962, respectively. He joined PPG Industries in 1961, and had spent his entire career with that firm, at first in various roles in the Chemical Research Development area. In 1974 PPG began research upon means to impart photochromic properties to ophthalmic lenses made from plastics, in particular from poly(allyl diglycol carbonate), CR-39 . Plastic lenses command over 85% of the total ophthalmic market in the US, principally because a lightweight plastic product is more comfortable to wear and permits more attractive fashion designs. 

To date, organic photochromic compounds have been used for the autorej lation of ophthalmic plastic lenses and for little else. But chiral photochromii compounds hold more information than nonchiral or racemic photochromic compounds, so they have a great advantage over them. When a photochromic com ii pound is used as a switch, its chiral derivative will be even more useful. 

Protective clothing, usually lab coats, should be worn at all times in the laboratory. Protective glasses should be worn when using hazardous chemicals. For many purposes normal reading glasses (preferably with plastic lenses) will offer sufficient protection, but this does not apply to contact lenses which make the eye difficult to wash in case of accident. Gloves and masks should be worn when needed. 

Polycarbonates are a class of thermoplastic polymers that are used in the plastic lenses of eyeglasses and in the shells of bicycle helmets. A polycarbonate is made from the reaction of bisphenol A (BPA) with phosgene (COCl2) ... 

The commercialization of the first pharmaceutical quality lens care products occurred in the 1950s. Harry Hind, a pharmacist and founder of the Barnes-Hind Company, has been credited as one of the first to develop and commercialize a wetting and storage solution for the rigid PMMA plastic lenses. Prior to his efforts, the literature mentions formulation of a saline solution containing sodium bicarbonate to be used with scleral lenses made from glass. 

Scheme 100 Compared structures of two monomers for the fabrication of optical plastic lenses.

Laboratoryware, plastics Ladders, plastics Lamp bases, plastics Lamp shades, plastics Lenses, plastics except ophthalmic or optical Lifejackets, plastics Liferafts, nonrigid plastics Lock washers, plastics Machine nuts, plastics Microwaveware, plastics Molding of plastics for the trade, except foam Monofilaments, plastics not suited for textile use Netting, plastics Nuts, plastics... 

W. M6hl, U. Lange, V. Paquet, Optical Coatings on Plastic Lenses by PICVD-Techinque, Proc. SPIE, Optical Interference Coatings, Vol. 2253, (1994) 486-491. 

PERSONAL PROTECTION wear long rubber aprons, long rubber gauntlets, high rubber boots, and wide plastic face shield wear plastic lensed eye goggles wear positive pressure self-contained breathing apparatus. 

Solids play a very important role in our lives. The concrete we drive on, the trees that shade us, the windows we look through, the paper that holds this print, the diamond in an engagement ring, and the plastic lenses in eyeglasses are all important solids. Most solids, such as wood, paper, and glass, contain mixtures of various components. However, some natural solids, such as diamonds and table salt, are nearly pure substances. 

---