Standard Cr39 1.50 Index Lenses
Standard Lens
1.50 Index Cr39 Plastic Thickness Comparison Chart
Our standard lenses are single vision 1.50 index Cr 39 plastic resin they are adequate for most people.
They are made exactly to your prescription and are suitable for general wear.
Cr39 1.50 index plastic lenses have been widely used for many years now, these lenses can be tinted from the very pale fashion shades right up to deep dark sunglass shades.
Lenses can also be hard coated to reduce scratching and antireflection coated to reduce internal surface reflections, improving the clarity of vision.
The only real drawback is in higher powers where the lens thickness can be poor cosmetically, in these situations a higher index lens material is recommended.
Unfortunately high 1.59, 1.60, 1.67, 1.74 index materials cannot be tinted by the same means as Cr39 resin, the process of tinting is usually carried out by the lens manufacturer and is very costly by comparison to standard Cr39 1.50 index plastic resin lenses, for this reason alone Budgetspex don't offer tinting of high index lenses.
Return to topThere is only one CR-39 monomer, and it only comes from PPG.All Cr39 lenses originate with PPG's CR39 monomer. |
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The Beginning
By the time World War II began, the plastics revolution was already well underway.
Polystyrene resins had been produced commercially since 1937 and nylon, the first highperformance
engineering plastic, was also a product of the 1930’s.
As the war began,both the Allies and the Axis powers faced severe shortages of natural raw materials.
The plastics industry turned out to be a rich source of acceptable substitutes. Realization ofthis fact led to concentrated efforts by industry to develop other new plastics.
PPG Industries – known as Pittsburgh Plate Glass Company until 1965 – began searchingfor a way to create an allyl resin with low-pressure thermosetting properties. Rohm &Haas had already developed Plexiglas® resin and DuPont had invented Lucite® resin,both thermoplastic materials. Pittsburgh Plate Glass Co. owned a subsidiary company inBarberton, Ohio called Columbia Southern Chemical Company where a research teamwas assigned responsibility for investigating clear resins. They called this project “Columbia Resins”.
The team isolated compounds and identified them by code numbers. By May 1940, one of the compounds showed real promise.
This particular resin was an allyl diglycolcarbonate (ADC) monomer that Pittsburgh Plate Glass Co. trademarked under the material’s batch name – CR-39™.
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The 39th Compound |
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The 39th attempt was the most promising because it offered unique characteristics.
Among them was the fact that the resin could be combined with multiple layers of cloth,paper and other materials to produce exceptionally strong laminated products capable of being molded into a variety of reinforced shapes. This discovery marked the beginning of what would come to be a major new industry7 called “reinforced plastics”.
The first commercial use for CR-39 monomer involved combining the resin with fiberglass to form a molded fuel tank for the B-17 bomber. Fuel tanks were molded of materials laminated with CR-39 resin and lined with special rubber compound that became self-sealing when the tank was pierced by bullets or shell fragments.
Replacing conventional fuel tanks with tanks laminated Using CR-39 resin made it possible to greatly reduce the plane’s weight, extending the bomber’s range and contributing substantially to the war effort.
Another innovative use for CR-39 resin in aircraft was production of transparent tubes embedded in fuel lines running through the flight engineers’ compartment, providing the crew a visible gage to indicate fuel flow to each engine.
These tubes made of CR-39 resin replaced glass tubes which often shattered during combat, spraying gasoline throughout the cockpit.
There was also some minor use of CR-39 resin for making lenses during the war, but the lenses produced were ½” to ¾” thick and primarily used for reflector and searchlight applications.
The War Ends
When the war ended in 1945, all government contracts were cancelled and Pittsburgh Plate Glass Co.’s Barberton plant ended up with a railroad tank car full of CR-39 resin, all that was left from wartime production.
The 38,000 pounds of resin remaining in the tank car represented a costly investment for the company, so a search was launched for markets that could use it. CR-39 resin remains a liquid until a catalyst is added, but eventually will harden on its own. In the early days, no one knew how long that selfcuring process would take.
They did know that when it happened, instead of an expensive railroad tank car, they would end up with a useless steel-encased slab of plastic.
Return to topThe Search for Peacetime Uses
A variety of industries were contacted in a search to find customers for the leftover CR-39 resin.
The ophthalmic industry indicated some initial interest, particularly because of the material’s resistance to impact. One company – Univis Lens Company – was interested enough to set up a special research department to try to develop plastic eyeglass lenses.
Univis was a leading lens producer investing large sums in an attempt to produce plastic lenses from CR-39 resin. Eventually, they abandoned the project, but following successful production of plastic lenses by Armorlite, SOLA and Essilor, Univis eventually became a major plastic lens producer.
Until 1960-61, PPG’s primary CR-39 resin sales were for flat sheet applications.
These sheets of transparent plastic were used for personal safety equipment and clothing such as welding helmets, industrial goggles, gas masks, etc.
Another widespread use during postwar years was for windshields of industrial crane cabs and other vehicles used in industrial plants.
As the optical industry gradually learned how to cast lenses from CR-39 resin, and how to edge and surface these new lenses, sales to the optical industry grew slowly but steadily until 1975 when more than 90 percent of PPG’s CR-39 resin sales were to the optical trade. In 1975, PPG predicted that plastic lenses – at that time representing 15 percent of all eyewear in the U.S. – would grow to 30 percent by 1978.
Today, plastic lenses represent more than 80 percent of the U.S. market.
PPG employees who tried to sell the contents of that tank car full of CR-39 resin in 1946 uncovered two important facts. First, CR-39 monomer was remarkably stable with an amazingly long shelf life. The solidifying they feared never came to pass. Second, there was indeed a viable market for a stable, transparent, impact-resistant material for producing spectacle lenses.
About the Author
Joseph L. Bruneni (1925-2004) was the author of “LOOKING BACK, an illustrated history of the American Ophthalmic Industry,” a hard cover book published in 1994 and still in print. He was a frequent contributor to most of the major optical trade publications and wrote regularly-appearing columns in a number of them. He served as a special consultant to the Optical Laboratories Association (OLA), was a member of the Ocular Heritage Society and served as an assistant professor teaching ophthalmic optics at the Southern California College of Optometry.
CR-39 (Reg. U.S. Pat. & Tm. Off.) is a trademark of PPG Industries, Inc.
Return to topMarketing Lenses with CR-39™ Resin |
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To establish plastic lenses as a viable alternative to glass, SOLA first had to convince eyecare professionals in Australia.
One of the early marketing promotions the company implemented was making thousands of clip-on sunglasses with plano lenses and building them into batches of five.
These bundles were shipped to hundreds of opticians and optometrists throughout Australia.
One pair was free, and the other four were billed at a special low price.
The end result was a steadily growing acceptance of lenses with CR-39 resin in Australia.
SOLA soon realized that, as big as Australia was, the Australian market could not support the kind of manufacturing plant they envisioned for themselves.
As a result, they focused on export sales, expanding to Japan, the United Kingdom, Italy, Brazil, and finally, the United States in 1975.
At this time, the U.S. lens market was still dominated by glass lenses, representing 70 percent of the market.
As a result, SOLA’s marketing efforts during the ‘70s were devoted to aggressively converting the market to lighter, more impact-resistant lenses.
By 1983, the U.S. market was over 50 percent plastic and by 1992, more than 80 percent.
Return to topEssilor International and CR-39 Resin |
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Georges Lissac, founder of the Lissac Company in 1931, later created SIL (Societe Industrielle de Lunetterie) in 1946 and a separate company, LOS (Lentilles Ophtalmiques Speciales), in 1948.
These two companies included frame and lens research and development, manufacturing and distribution operations.
Rene Grandperret, with LOS, developed an early interest in plastic lenses, dating back to the late 1940’s. In 1952, LOS introduced the ORMA® 500 lens made from Plexiglas® resin, marking the beginning of plastic spectacle lenses in France.
Lenses made from Plexiglas® resin were only marginally successful because of the familiar problem of scratching. LOS eventually found what they decided was the ideal resin in the United States and began experimenting with PPG’s CR-39 monomer.
After years of continuing research, LOS eventually mastered the difficulties of casting lenses from CR-39 monomer and introduced the ORMA® 1000 lens with CR-39 resin in 1956.
This lens was patented and introduced worldwide in 1959. In 1969, Lissac formed a French company from existing business divisions with the now familiar name of Silor.
Eventually, Silor merged with Essel, another significant French ophthalmic company, to become Essilor International.
Return to topPlastic
Lissac’s early attempts at producing plastic lenses were with Plexiglas® resin cast in molds instead of using heat compression.
The lenses were reasonably impact-resistant but very susceptible to scratching and yellowing with age.
These early plastic lenses, called ORMA® 500 lenses, were used primarily for children.
One day, Lissac’s Grandperret received a transparent sheet that seemed to have interesting mechanical and optical properties.
The material had good transparency and resistance to scratching 40 times that of Plexiglas® resin.
The commercial name was Homalite®, and it was made of CR-39 resin.
In l953, Grandperret ordered a half liter of CR-39® resin for experiments.
Many production methods for casting lenses with CR-39 resin were tried.
One involved partially polymerizing the lens and removing it from the mold to continue polymerization in a large pan.
Later, polymerization in the mold was tried.
General consensus deemed that molding lenses with CR-39 resin would never be adaptable to bifocals.
By this time, both the English and the French were convinced that the ultimate answer would be a lens made of Plexiglas® resin covered with a veneer of CR-39 resin for scratch protection.
Grandperret tried a radiochemical process for linking Plexiglas® and CR-39 resins, but the resulting lenses were unsatisfactory.
Return to topOptical Laboratories and CR-39 Resin |
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Converting lens production from glass lenses to casting lenses from CR-39 monomer involved a variety of new technologies, equipment and skills for lens manufacturers.
For a number of years, most lens manufacturers maintained two diversely different production lines, one for glass and one for plastic. As lenses made from CR-39 resin came to dominate the market, lens manufacturers began dropping out of the glass market altogether.
This changing market impacted optical laboratories in even more dramatic ways.
At the time Armorlite began producing lenses made from CR-39 resin, no labs had the ability to surface plastic lenses.
They learned to edge plastic lenses, but they had no experience with grinding and polishing them.
Armorlite, the first successful manufacturer of plastic lenses, eventually set up a surfacing laboratory to provide practitioners with surfaced lenses.
They were convinced this was the only way they could create a market for their new plastic lenses.
By now, laboratories began to receive occasional orders for post-cataract lenses made from CR-39 resin.
It seemed obvious that labs would eventually have to surface this new material.
As it turned out, the role of convincing and teaching labs to process lenses with CR-39 resin fell in the unlikely hands of a World War II pilot named Forbes Robertson who was hired to Armorlite in 1959 to sell lenses.
Robertson was convinced that the only way to build national demand for lenses made from CR-39 resin was to get labs surfacing plastic lenses as quickly as possible.
Among the first companies to take up plastic surfacing at Robertson’s urging were Uhlemann Optical, Boll & Lewis and White Haines, and Opti-Craft. Opti-Craft soon became Armorlite’s best customer.
Their sales efforts, in effect, opened up the whole West Coast for Armorlite.
Other wholesale laboratories began surfacing plastic lenses in the hopes of salvaging business they were losing to Opti-Craft.
Aggressive labs across the country began experimenting, trying any way they could think of to surface plastic.
Most surfacing problems were created because labs wanted to process plastic the way they did glass.
Surfacing blocks were small in diameter and designed for glass, offering no support beyond the center of the lens.
Plastic lenses flexed during surfacing, creating multiple waves and distortion. Eventually, Coburn Optical – producer of surfacing equipment – came out with larger blocks and eliminated one cause of distortion.
Robertson was convinced that plastic lenses would only succeed if labs cold process them on equipment they already owned.
The problem came in convincing labs that to do this, they had to completely clean the existing equipment and maintain a degree of cleanliness they weren’t used to.
Another issue was that heat created problems when surfacing plastic.
Air-conditioned labs were comparatively rare at that time, and Robertson continually urged that plastic production lines had to be air-conditioned.
Eventually, this was accepted, and experienced labs began to process glass and plastic on separate production lines with air conditioning for the plastic line.
Return to topThe Fate of Glass
Initially, labs concentrated their plastic production on producing post-cataract lenses.
Plastic lenses were too new and too prone to scratching for most patients, but with post-cataract patients, it was a different story.
During that period before the development of inter-ocular lenses, two factors made lenses cast from CR-39 resin an ideal lens for post-cataract patients.
The first was weight.
Strong plus lenses of 10 to 14 diopters were extremely heavy when made up in glass.
The second factor was the recent development of sophisticated aspheric post-cataract design that proved extremely difficult and costly to produce in glass.
A good set of glass molds, however, could replicate the most sophisticated aspheric curves over and over in CR-39 resin.
It was comparatively easy for labs to convince doctors and consumers of the advantages of lightweight plastic lenses for cataract patients.
Expertise gained with cataract lenses helped establish plastic lenses for all patients.
The fate of glass lenses was largely sealed when the Food and Drug Administration (FDA) decreed in 1972 that all glass lenses sold in the United States would have to be a minimum of 2.2 mm at their thinnest point, be heat-treated or chemically tempered and pass a drop ball test performed by the lab or the person edging the lenses.
Previously, most glass lenses had centers or edges well under 1.5mm.
This new ruling effectively meant that glass lenses would be 30 to 50 percent heavier than in the past.
This couldn’t have happened at a worse time for glass because frame styles were just starting to grow in size.
These factors effectively combined to give lenses made from CR-39 monomer the boost that would ultimately make CR-39 resin the dominant lens material in the United States.
The rest, as they say, is history.
CR-39 9Reg. U.S. Pat. & Tm. Off.) is a trademark of PPG Industries, Inc.
Return to topThe Continuing Evolution of CR-39™ Resin –
Photochromic Plastic
Almost from the day photochromic glass lenses were first introduced, lens manufacturers received requests for a photochromic lens made in a lightweight plastic.
During the entire fifty years CR-39™ resin has been used for ophthalmic lenses, PPG researchers have continually searched for ways to increase its versatility.
The most dramatic result of this continuing research was the development of an effective photochromic process based on a variation of CR-39 resin called CR-307™ monomer.
The story of how Transitions® lenses evolved is best told in timeline fashion, beginning in 1973.
1973
The first reported work on photochromics by PPG takes place at the company’s Barberton Technical Center in 1973.
From then until 1980, photochromic research and development became part of a number of different CR-39 monomer projects.
Efforts remained comparatively low-key, and no synthesis of new compounds was involved.
1981
American Optical introduces their Photolite lens.
The industry excitement prompted by this product release galvanized the scientists at PPG into another flurry of photochromic research. The lens turns out to be a commercial failure because of poor properties, short lifetime and an unattractive blue color.
An new specialist with a background in photochromics is added to PPG’s staff, and synthesis of new photochromics combined with testing of known photochromics in matrix from CR-39 monomer begins.
1983 – Pyridobenzoxazines
This year is a photochromic milestone because of the discovery of a new family of photochromics called pyridobenzoxazines.
This year also marks the discovery of the unique imbibition process for incorporating photochromic properties in polymers and copolymers made from CR-39 monomer.
1984
PPG starts a joint venture with Intercast-Europe to manufacture and sell photochromic sunlenses called Attiva.
These are still manufactured by Intercast, using PPG’s blue photochromics.
Research in this technology continued, and in 1985, production of Attiva lenses reached 3,150 per day.
In 1986, marketing of the Visenza lens, an all-PPG venture, begins.
A variety of prototype lens systems were produced and tested on PPG employees and consumers during the next three years.
1986 – Transitions
PPG authorizes $1 million for testing the technical and marketing feasibility of plastic photochromic lenses.
Between July 1987 and May 1988, the company assesses the acceptance of prototype lens systems through employee and consumer use tests.
In the fall of 1987, 30 persons wear the lenses for one month.
A typical comment about those primitive lenses comes from one wearer, “They worked pretty well…could get a lot darker, and, boy, are they an ugly yellow in the bleached state.”
In 1988, a pair is given to another employee to wear on a trip to Hawaii. His comment, “If you can’t make them get any darker, you’re out of business.” Additional consumer-use tests are conducted in Minneapolis, Miami and San Diego, and gradually, the responses improve.
1988
On May 1, PPG gives the go-ahead to proceed to the next step, which consists of setting up test markets for the new photochromic lenses in Vermont and southern New Hampshire.
This is considered a milestone by the company’s ophthalmic photochromics group.
Later, additional test markets are established in Memphis and Pittsburgh.
1990
Substantial progress is made, and by 1990, Transitions Optical Inc. (TOI) is formed and a manufacturing facility established in Pinellas Park, FL, for producing photochromic lenses.
By this time, PPG invested more than $8.5 million in developing the new Transitions photochromic lens.
To firm up the industry’s shaky confidence in such a new technology, TOI offers a patient satisfaction guarantee on their new lenses. During the first three years of distribution, return rates run less than one percent.
Other plastic photochromic lenses have been introduced, but none have enjoyed the success of Transitions comfort lenses, dating back to their introduction in 1990.
Transitions® lenses are made of a lightweight polymer, similar to CR-39 resin.
1992
The first Transitions lenses formulation is replaced by the new Transitions Plus lens.
This second generation provides greater activation speed, darkening more and faster than the original lens. In 1993, Transitions Plus lenses receive the prestigious Optical Laboratories Associates (OLA) Award for Best Lens Treatment.
1996
The newest generation of Transitions lenses is unveiled to the eyecare profession.
The result is overwhelming approval of Transitions III lenses which darken faster, darken more and achieve a true gray color that most consumers prefer.
This newest TOI product is also available in mid-index, opening a totally new market for photochromic plastic lenses.
2002
The debut of Next Generation Transitions, 1.50 marks the first time that a company has brought to market a 1.50 photochromic lens that is virtually indistinguishable indoors from clear lenses, with the outdoor darkness of sunglasses, and with a record-breaking speed of performance.
CR-39 9Reg. U.S. Pat. & Tm. Off.) is a trademark of PPG Industries, Inc.
Return to top| Lens Thickness Comparison | -6.00 | +4.00 | ||
| 1.50 Index Our standard lens is single vision 1.5 index Cr 39 plastic resin and is adequate for most people |  |
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| 1.56 Index The tensile strength of this index is lower than any other in general, although some brands have overcome this problem. It is slightly thinner than 1.50 but its lack of strength renders it unusable for Rimless. |  |
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| 1.60 Index Our lowest priced thinner lens. |  |
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| 1.67 Index Our mid priced thinner lens i |  |
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| 1.74 Index |  |
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As you can see demonstrated in the above chart, the saving in lens thickness is most dramatic when used in high minus prescriptions
CR-607™ Monomer
CR-607 monomer, developed as a new substrate for TransitionsÒ lenses, produces lenses with superior photochromic performance. CR-607 monomer was designed to give casters an easy replacement for CR-307 monomer.
Since CR-607 monomer has similar polymerization shrinkage and the same refractive index as CR-307 monomer, it should not require new molds.
CR-630™ Monomer
The casting of CR-630 monomer is virtually identical to the casting of CR-607 monomer with the exception of the initiator used. CR-607 monomer is used with 100% IPP, and CR-630 monomer has been specially formulated to be used with a pre-mix of 10% IPP in CR-39™ monomer
Return to topHIRI™ Resin
Lenses made from HIRI casting resin are both thinner and lighter than those made of conventional plastic or glass because of the resins higher refractive index (1.56) and lighter weight.
Properly fabricated lenses made from HIRI resin are optically uniform, with no waves or inclusions, and they give less chromatic aberration than polycarbonate lenses. Although designed primarily as a lighter and easier-to-cast and high-refractive index alternative to CR-39 monomer, HIRI resin may be used in any application that requires a versatile, easily processed thermosetting resin.
CR-424™ UV Curable Monomer
Lenses made from CR-424 monomer act as the substrate for manufacturing mid-index Transitions lenses.
With a refractive index of 1.554 and a density of 1.20, lenses made from CR-424 monomer are thin and light in addition to being photochromic.
CR-27™ Premix
CR-27 is an initiator premix mixture of 27% Di-isopropyl Peroxydicarbonate (IPP) and 73% CR-39 (Diethylene Glycol Bisallyl Carbonate).
CR-607, CR-630, HIRI, CR-424 and CR-27 (Reg. U.S. Pat. & Tm. Off.) are trademarks of PPG Industries, Inc.