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CR – 39 LENSES

MADE BY: SWATI PANARAFROM : BHARTIMAIYA COLLEGE OF

OPTOMETRY2nd YEAR 4th SEMESTER

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CR - 39

• It is also called as Columbia resin or allyl diglycol carbonate.

• CR – 39 or allyl diglycol carbonate is a plastic polymer commonly used in manufacture of eyeglass lenses.

• It was developed by Pittsburgh Plate Glass industries.

• It is the thermosetting material.

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• CR stands for Columbia Resin & it is 39th formula of a thermosetting plastic developed by the Columbia resin project of PPG industries back in 1940.

• “CR” stands for Columbia Resin, and the number 39 denotes the type of Columbia Resin used.

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• COLUMBIA RESIN batch no. 39• Petroleum derivative from polyester

group• Chemically diallyglycol carbonate • Refractive index = 1.498• Specific Gravity = 1.32• Abbe value = 58• Transparency = 92.2 %• UV cutoff = 355 nm

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• For years CR- 39 was used without anti scratch coating.

• Now, however, most CR-39 lenses come with an anti scratch coating, making the material much more scratch resistant.

• For smaller, high velocity, sharply pointed objects, CR-39 lenses perform better than chemically tempered glass.

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• CR-39 plastic lenses do not fog up as easily as glass lenses.

• Whereas welding or grinding spatter will pit or permanently stick to glass lenses, it does not adhere to plastic lens material.

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• The material is highly impact resistant and carries high transparency.

• Multiple tinting and coating is possible. • only drawback is weak resistant to

abrasion.

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ADVANTAGES

• High impact resistance• Light in weight• Resistance to chemicals and solvents• Resistance to heat & temperature

fluctuations • Available in photo chromic glasses• U.V. protection• Can be tinted & coated• Inexpensive

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characteristics

• Lightness• Impact resistance• Chemical inertness• Resistance to pitting• Resistance to fogging• Tint ability• Versatility in optical design

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DISADVANTAGES

• Low scratch resistance i.e. scratches are easily formed

• Increase thickness• Index variability with temperature• Inferior photo chromic properties• Surface abrasion• Warp age upon glazing

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• Can yellow with age • Softer material surface – scratches

more easily• Lower refractive index and variability

with temp.

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•THANK YOU