Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 26 TUESDAY MORNING
JS1-TuM-INV-7 COATINGS FOR OPHTHALMIC LENSES. T. Vilajuana, Departamento
de I+D+I INDO, Sta. Eulàlia, 181 08902 L’Hospitalet de Llobregat, Barcelona. Spain. E-mail:
toni@indo.es
Since 1937 Indo is the leading company in the ophthalmic optics Spanish market, and one of the five
main European companies of the sector. The core activity of the company is the fabrication of spectacle
lenses, which represents more than 50% of the total turnover. The investment in R&D activities
was 2.5% of the sales income in 2005 and is planned to increase an additional 4% in 2006.
The main requirements of an ideal ophthalmic lens, are lightness, transparency, scratch resistance
and impact strength. Additionally, an ideal lens should be as thin as possible. Organic or polymeric
lenses have a clear advantage in terms of weight and impact resistance when compared to mineral
glass. Nevertheless, a polymeric lens can be more easily abraded than a mineral one. Particularly,
high refractive organic lenses can easily be scratched. For this reason, the application of anti-scratch
coatings has become necessary to increase the abrasion resistance of polymeric lenses. Typically, that
coating is a few micron layer of a composite based on a polysiloxane matrix containing silica
nanoparticles. This provides the required flexibility and toughness to obtain good scratch resistance
and optimum adhesion of the coating to the lens.
An additional benefit of some lenses is that they adapt to light conditions, changing its transmittance
according to the amount of light outdoors. The benefit of this photochromic lenses is that they provide
a dynamic adaptation to light conditions and a UV protection. This is due to the presence in the
lens of molecules that react with UV radiation. The absorption of UV radiation changes the molecule’s
steric configuration, and consequently absorbing visible light. This is why the lens becomes
dark brown or grey, etc. This process is reversible and in the absence of UV light, the lenses become
clear. Some polymer lenses are casted mixing these photochromic molecules with the lens monomer,
while others are applied a photochromic layer in the external surface of a clear lens.
Lenses reflect light, since they consist of two optical surfaces that are immersed in an environment of
different refractive index. The higher the difference, the more light is reflected. This light reflected is
perceived as ghost images that superpose to natural perception and reduce the quality of vision,
which contributes to increase fatigue. These reflections can be practically be reduced with the application
of an antireflective (AR) coating, typically composed of 5 to 7 layers of metal oxides.
The first AR coatings easily got dirty and the smudges and fingerprints were more visible and difficult
to remove. In fact, many patients found it difficult to keep clean. The application of a hydrophobic
and oleophobic topcoat is a big advantage for these lenses, since they stay cleaner longer than
previous ones. The composition of that layer is based on a mixture of perluorated hydrocarbons and
silica compounds that repeal water and grease.
Since lenses are produced in large quantities, additional concerns like uniformity of optical and mechanical
properties are important key factors in order to decide which technology is used to produce
these coatings. Lens reflectance, abrasion resistance, coating durability, hydrophobicity and photochromism
has to be tightly controlled.
Developing new polymer materials with better optical and mechanical properties requires the application
of complex coatings and technologies. The production of millions of them at a competitive
cost and in a personalised basis is the challenge of the leading ophthalmic optical companies.
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