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Technical Info

Optical Materials Yellowness reduction Casting Yield Mould Adhesion Coatings IPP/ADC

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Casting Yield

Casting Yield and Monomer Shrinkage

Plastic lenses for ophthalmic application are manufactured by mixing optical monomers with hardening agents (initiators), and transferring the mixture to glass or metal moulds. These moulds are then heated for a period of time wherein a chemical reaction takes place (polymerization) that converts the liquid monomer into a hard polymer. During this process the liquid monomer shrinks as it is transformed into a hard glassy polymer. Standard hard resin or ADC monomer has a shrinkage of almost 13%. As a result, achieving a high casting yield may prove to be difficult, in particular for lenses with complex designs, like high power lenses, progressives and bi- and trifocals.

To solve shrinkage related problems, ACOMON has developed several specialized products with reduced shrinkage that can help to improve yield.

RAV 7NG with a shrinkage of 10%, has a significantly lower shrinkage compared to commercially available ADC monomers and can be used alone or mixed with standard monomers like RAV 7AT or RAV 700, to optimize the degree of shrinkage.

RAV 720 and RAV 717 are used to prevent seg line cracking, a defect in casting multifocal lenses. RAV 720 also is very powerful for preventing tinting failures, like ‘ferns’, ‘fern trees’ and ‘white arches’.

RAV 7MC, for the production of in-mass coloured sunlenses, and RAV 755, for the production of middle index lenses, have even lower shrinkage.

ACOMON’s goal is and has always been to help lens manufacturers by developing specialized monomers to improve casting yields.

RAVolution ®, our a latest development, has a record low shrinkage of less than 3%.

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