Resin is a hydrocarbon secretion from various plants, especially conifers. It is valued for its unique chemical structure and its use in latex paints and adhesives. As a mixture of many macromolecular compounds, it has different melting points.
Resin can be divided into natural resin and synthetic resin. There are a great many types of resin, widely used in light and heavy industries, and commonly seen in daily life — such as plastics, resin eyeglass lenses, coatings, etc. Resin lenses are optical lenses made from resin through chemical synthesis, processing and polishing.
Features
A. Low density Due to gaps between molecular chains, fewer molecules per unit volume result in low specific gravity and light weight — only about 1/3 to 1/2 the weight of glass lenses.
B. Moderate refractive indexCommon CR39 (allyl diglycol carbonate) has a refractive index of 1.497–1.504.On the market, common resin lenses include aspheric, ultra thin, hardened and coated lenses with a refractive index of 1.67.Many manufacturers now offer 1.74 high index resin lenses.
C.Surface hardness Lower than glass, so they are easily scratched by hard objects.They require hardening with silica, but still cannot reach the hardness of glass.Wearers must take good care of the lenses.
D.Good elasticity Organic molecular chains allow displacement, making resin lenses about 23–28 times more impact resistant than glass.Europe, the US and Japan prohibit children under 16 from wearing glass lenses.
E. Auxiliary functions Can be treated to provide protection against harmful rays, photochromic effects, and more.
F. Processability Excellent. Suitable for full rim, half rim and rimless frames.Permeable dyeing is available for custom colors.
G. Chemical resistance As an organic compound, resin lenses must not be used in acidic or alkaline environments.
H. Thermal properties Do not use above 60°C, as the anti reflective coating may crack or peel off.
I. PriceVaries by quality, function, brand and grade.
J. Lens thickness design According to U.S. FDA standards, the minimum center thickness can be 0.6 mm, but strength decreases accordingly.For safety, manufacturers in Europe, the US and Japan generally set the center thickness to at least 1.0 mm for prescriptions over ±1.00 D.
Advantages and Disadvantages
Resin lenses are optical lenses made of resin. Compared with glass lenses, they have unique advantages:
Light weight
Resin: 0.83–1.5 g/cm³Optical glass: 2.27–5.95 g/cm³
High impact resistance
Impact strength: 8–10 kg/cm², several times that of glass.Not easily broken, safe and durable.
Good light transmittance
Similar to glass in the visible light range;Slightly higher in the infrared range;In the ultraviolet range, transmittance drops below 0.4 μm, and almost all light below 0.3 μm is absorbed.
Low cost
After making one precision mold, lenses can be mass produced by injection molding, saving time and cost.
Meet special needs
Aspheric lenses are easy to produce with resin, but difficult with glass.
Disadvantages:
Lower surface wear resistance and chemical resistance than glass
Easier to scratch
Higher water absorption These can be improved by coating.
The main drawback is a high thermal expansion coefficient, low thermal conductivity and low softening temperature, making lenses prone to deformation and degraded optical performance.
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