Page 101 - The Indian Optician Digital Edition September-October 2021
P. 101
The “ink” which is used is a plastics monomer
one such which is available is similar to MR 6
in its optical properties an HDDA (Hexanediol
diacrylate) which is capable of rapid cure when
exposed to Ultra Violet radiation. Each layer
of ink is sprayed in the form of micro-droplets
the size of which is only about 20 micrometres
(microns) with a volume of just 6 picolitres. It
will be appreciated that if each droplet is only
20 micrometres, a one millimetre thick layer of
deposition requires 50 layers of ink! Each layer
must be cured after each deposition.
The reduction in the length of each layer
depends upon its position in the build-up of
FIGURE 1 TWO-DIMENSIONAL PRINTING
A) PRINTING ON PAPER monomer. In the case of a plus lens, each layer is
B) PRINTING ON ACETATE SHEET about 2 micrometres smaller than the previous
layer at the commencement of the deposition,
the difference increasing to about 30 microns
manufacturing technology is destined to
replace current free form processing. Additive near the pole of the surface.
manufacturing refers to 3D printing of The first company to market a 3D Printer
ophthalmic lenses which is already available specifically for spectacle lens production
from a few manufacturers mainly in the USA. and, of course, all the technology required to
The manufacturing technique is similar to manufacture the lenses, Luxexcel, is based in
that of using an ordinary printer connected to the Netherlands. At present, their equipment
a computer (Figure 1). The common printing permits 4 lenses per hour to be produced. You
machine prints text and reproduces diagrams in can see more of their current offerings on their
the correct position on the page. When printing website, www.luxexcel.com.
on paper, the ink is absorbed by the paper Figure 3 shows their 3D Printing equipment,
(Figure 1a). the VisionPlatform, a single machine which
However, one could also print on acetate offers a full production run in one piece of
sheet as teachers used to do in the days before equipment.
PowerPoint and similar drawing aids. In this The process, developed by Luxexcel, begins
case, the acetate sheet does not absorb the ink with the custom lens design and surface
which instead sits on top of the acetate and, of
course, can be overprinted several times. Each
print builds up the thickness of ink on the sheet
(Figure 1b).
Exactly the same process can be used for
printing a spectacle lens. In the case of a plano-
convex lens it would be built up as shown in
Figure 2, each layer being a fraction less in
length than the previous layer and is seen to
build to make the profile of a convex surface.
The same process can be used to build up a
concave surface, now leaving an ever-increasing FIGURE 2 THREE-DIMENSIONAL PRINTING A PLANO-
gap between the centre and edges of the CONVEX LENS IN SIDE AND TOP ELEVATIONS
A) BUILDING UP THE SURFACE LAYER BY LAYER
surface with each layer. B) THE COMPLETE PLANO-CONVEX LENS
97 | LENS TALK
