a Brite/Euram CRAFT project involving a group of SMEs in the optical sector,
two Research Institutes and a University, set out to find a more effective
means of applying scratch-resistant coatings to spectacle lenses. In doing
so, it also identified a significantly larger potential market in the
treatment of display covers for GSM telephones and other portable devices.
chemical vapour deposition (PECVD) is a technique wherein a plasma cloud
is set up near the surface of a substrate such that pre-cursor gases are
decomposed into chemically active molecules which then bombard and coat
the substrate's surface. The nature of the resulting coating depends in
part on the combination of pre-cursor gases. The technique is usually
employed to deposit coatings onto hard substrates. For the PLASCOAT consortium,
the challenge was to extend the application of PECVD to softer plastic
materials such as the polycarbonate and CR39 (diethyleneglycol-bis-allylcarbonate)
used in the production of ophthalmic spectacle and sunglass lenses. The
aim was to improve scratch resistance, to reduce reflectivity and increase
hydrophobicity. During the course of the project, its original leader,
FACT Optique, was acquired by the Finnish company Savcor
Coatings - which had a particular interest in producing display covers
for the GSM market. Consequently, polymethyl methacrylate (PMMA), a material
widely used for this application, was added to the list of target polymers
were several good reasons to look at the PECVD process. One was to
find a replacement for current lacquering methods, which involve the
use of environmentally objectional solvents. Another was to reduce
manufacturing costs by increasing production speeds and improving
reproducibility. Finally, it was expected that superior protection
could double the lifetime of lenses, while multiple coatings would
enhance their multifunctionality.
order to add a hard silicon-based scratch-resistant layer to a soft
plastic, a technique was developed whereby the composition of the
coating was varied progressively as the deposition proceeded. This
allowed a smooth transition from a polymer-like structure that bonded
effectively to the substrate, to a tough, oxide-like outer protective
surface, with a total layer thickness of around 10 mm.
The partners also demonstrated that scratch coatings on polycarbonate
and CR39 were compatible with antireflective treatments applied
by widely-used ion-assisted deposition and sputtering techniques.
coating of PMMA proved less successful, as no reliable adhesive
could be found. Hydrophobic coating was also abandoned, due to a
lack of commercial interest.
further problem was in adapting the process to ophthalmic lenses,
which vary in their curvature according to the required vision correction
properties. PECVD is essentially best suited to volume production,
involving the placement of a metallic cathode behind the lens. This
cathode must fit the lens closely in order to ensure that the vaporised
coating deposits evenly on the plastic surface. Consequently, the
handling of mixed batches of lenses requiring individually optimised
cathodes would not be a cost-effective option.
towards an industrial technology for coating sunglasses has been
considerable, and the outlook for the coating of display covers
is equally promising. Italian research partner CETEV
(Centro Technologie del Vuoto) played a major role in the project,
having built a prototype deposition machine, now installed at Savcor,
essentially the main project deliverable. They were also instrumental
in the strategic reorganisation of the project as it changed directions
from an ophthalmic to a GSM application. Other industrial SME participants
include Nuova Ottica Omi, which will install a hybrid plating/PECVD
plant for coating sunglasses, Laboratorio Ottica Salvatore Vitale
which plans to continue collaborating with CETEV, to perfect a process
for one-step antiscratch/antireflective treatment. If this can be
accomplished, it could well become economically feasible to coat
progressive ophthalmic lenses - which have an intrinsically high
added value, thus justifying the cost of treatment in smaller batches.
Other project participants included French SME Biophy Research and
the University of Catania.
prototype reactor is now working well, delivering homogeneous and
reproducible coatings on substrates with surface areas of up to
more than 1 m2. Its design is robust, and will readily
accommodate extensions for automated loading and unloading.
is now able to produce GSM display covers at a rate of 20-30,000
per week, and expects to be able to move towards a targeted 1 million
per week within around one year. This would open the door to an
industry with a potential annual turnover of 100
million. However, penetration of the market will depend on the company's
success in persuading telephone manufacturers to introduce the new
present, PMMA is the preferred material for display covers. Untreated,
it is a little more transparent than polycarbonate. But coating
the latter polymer also adds a degree of antireflectivity, which
largely eliminates the difference - while wear resistance is a remarkable
2 000 times greater than that of uncoated PMMA.
Savcor has also identified another interesting niche application
in the coating of 1.2 metre-long polycarbonate tubes that form the
covers of inspection lights used when servicing aero engines. These
have been accepted by the British Royal Air Force, and are now in
According to Savcor's Dr. Kaj Pischow, PLASCOAT was very worthwhile
for all of the partners, with excellent co-operation and a positive
outcome in terms of an innovative and readily exploitable technology.
and development in the area of surface coating is covered within
the New materials and production technologies
project under BRITE-EURAM
Plasma Enhanced Chemical Vapour Deposition of Hard Coatings on
BRST-CT98-5307, PLASCOAT, start 1 October 1998, duration 24 months