Composite ophthalmic lenses and their manufacture

This invention is directed to the fabrication of composite lenses consisting of a transparent thermoset polymer exhibiting an index of refraction of at least 1.58 and a thin glass element of essentially constant thickness adhered to the front surface of the polymer without the use of an adhesive, the glass element having a thickness not exceeding 0.3 mm and the thermoset polymer being an aromatic epoxy resin.

RELATED APPLICATION 
U.S. patent application Ser. No. 07/907,116, filed concurrently herewith by 
E. Firtion et al. under the title COMPOSITE OPHTHALMIC LENSES and assigned 
to the assignee of the present application, discloses the preparation of 
glass-plastic composite lenses comprising a thin glass element bonded to a 
relatively thick transparent lens or lens preform made of poly(diethylene 
glycol)bis(allyl carbonate) by a transparent adhesive layer of optical 
quality having an elastic modulus in the range of 0.13-1.0 MPa at 100% 
elongation and an elongation at rupture of at least 200%. 
BACKGROUND OF THE INVENTION 
The invention relates to new composite glass/plastic material ophthalmic 
lenses with a high index of refraction and their manufacturing. 
Composite lenses are desirable products to the extent that the part made of 
plastic material contributes lightness of weight and shock resistance 
while the glass part provides resistance to radiation, ability to receive 
a wide range of lasting surface treatments (anti-reflecting, reflecting, 
coloration) and, if necessary, lasting photochromism. 
Through European Patent Application No. 182,503 [which corresponds to U.S. 
Patent No. 4,679,918 (Ace)] for example, composite lenses are known which 
consist of a lens made of plastic material stuck to a glass element of 
constant thickness by means of a relatively thick elastomer adhesive 
layer. The disadvantage of such lenses is their relatively heavy weight 
and especially their excessive thickness, particularly at the edge in the 
case of negative power lenses, which makes them aesthetically not very 
attractive. 
Attempts have also been made to produce composite lenses by casting a 
liquid thermosetting plastic material onto a thin glass element, followed 
by heating with the intention of hardening the plastic material. This 
process has not been successful because of the great stresses exerted on 
the glass element by the plastic part during cooling because of the 
extensive contraction of the plastic material, stresses which cause the 
glass element to break or which bring about other redhibitory defects, as 
is explained in the preamble of French Patent No. 2,407,898 [which 
corresponds to U.S. Patent No. 4,227,950 (Spycher)]. 
As a solution to the problems encountered in prior techniques, French 
Patent No. 2,407,898 proposes a process of direct pouring for the 
production of a composite article which consists of a glass element 
connected to a thermosetting plastic material which exhibits a high degree 
of contraction, the composite article demonstrating low residual stresses 
between the glass element and the plastic element, which comprises the 
operations consisting of covering selected portions of the surface of the 
glass element with a thermoplastic adhesive with a hot gluing temperature 
higher than the minimum hardening temperature of the thermosetting plastic 
material; of pouring the thermosetting plastic material in liquid form 
over the portions of the surface of the glass element which were covered 
with the thermoplastic adhesive; of curing the thermosetting plastic 
material by heating the plastic material, the glass element, and the 
thermoplastic adhesive to a temperature lower than the hot gluing 
temperature of the thermoplastic adhesive, but higher than the minimum 
temperature of hardening of the thermosetting material; and of solidly 
connecting the cured thermosetting plastic material, the thermoplastic 
adhesive, and the glass element into a single glass-plastic material 
composite article by heating these components to a temperature higher than 
the hot gluing temperature of the thermoplastic adhesive. 
Composite lenses produced by this process have, however, not been developed 
industrially because of their complicated manufacturing process. 
There is, therefore, an unsatisfied need for composite lenses which are 
lightweight, not very thick, and which are easy and economical to 
manufacture. 
SUMMARY OF THE INVENTION 
The invention aims to provide new composite lenses produced by direct 
pouring which are light and not very thick. 
The invention also aims to provide new composite lenses produced by direct 
pouring, which have a high index of refraction, that is to say, at least 
1.58. 
More particularly, the invention relates to a composite lens consisting of 
a lens made of a transparent thermoset polymer with an index of refraction 
of at least 1.58 and a thin glass element of essentially constant 
thickness which sticks to the anterior surface of a thermoset aromatic 
epoxy resin; and 
the thermoset polymer is a thermoset aromatic epoxy resin; and 
the thin glass element has an essentially constant thickness of at most 0.3 
mm. 
The invention also relates to a process for manufacturing such a lens, 
characterized by the fact that it consists of pouring a thermosetting 
aromatic epoxy resin composition, which after curing forms a transparent 
aromatic epoxy resin with an index of refraction of at least 1.58, 
directly into the concave part of a thin preformed glass element with an 
essentially constant thickness of at least 0.15 mm and at most 0.3 mm; of 
applying onto the mass of poured thermosetting composition a counterform 
to shape the upper surface of said mass as desired; of subjecting the 
element-mass-counterform assembly to a thermal treatment which brings 
about the hardening of the thermosetting composition; of removing the 
counterform; and then of proceeding with trimming the edges of the lens. 
According to a particular embodiment, the thin glass element is a 
photochromic glass element. 
The invention results from the surprising discovery that, by combining the 
use of an aromatic epoxy resin with the use of an ultrathin glass element 
of essentially constant thickness, one can obtain composite lenses which 
are lightweight (and therefore comfortable to wear), and which are not 
very thick (and therefore aesthetically satisfactory). 
The choice of an epoxy resin was not obvious, because the epoxy resins are 
not currently used for commercially manufacturing ophthalmic lenses. 
Moreover, French Patent No. 2,407,898 clearly indicates in the preamble 
that the use of epoxy resin for the production of composite lenses by 
direct pouring had not allowed the obtaining of satisfactory results. 
The aromatic epoxy resins suitable for forming composite lenses of the 
invention are produced by curing thermosetting compositions which contain 
an aromatic diepoxide and a hardener chosen from the anhydrides of 
aromatic diacids and the aromatic diamines. 
It should be noted that the term "aromatic" as it is used in the present 
description, describes monomers and resins which are not necessarily 
entirely aromatic, but which can include, beside aromatic fragments, 
aliphatic and/or non-aromatic cyclic fragments. 
As examples of the aromatic diepoxides available in commerce, one can 
mention diglycidyl ether bisphenol A (abbreviated DGEBA) with the formula: 
##STR1## 
in which n=0 to 0.4, on the average, which is the preferred compound, and 
resorcinol diglycidyl ether (RDGE) with the formula: 
##STR2## 
As an example of an easily available aromatic diacid anhydride, one can 
mention phthalic anhydride. 
As examples of aromatic diamines available in commerce, one can mention 
4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 
m-phenylenediamine, xylylenediamine. 4,4'-diaminodiphenylsulfone and 
xylylenediamine are preferred. 
The thermosetting composition is obtained through careful mixing of the 
diepoxide with the hardener and possibly with a catalyst. 
PRIOR ART 
Besides U.S. Pat. No. 4,227,950 and U.S. Pat. No. 4,679,918 briefly 
reviewed above, attention is also called to U.S. Patent No. 4,793,703 
(Fretz, Jr.), U.S. Patent No. 5,064,712 (Fretz, Jr.), U.S. Pat. No. 
5,116,684 (Fretz, Jr. et al), U.S. patent application Ser. No. 07/682,479, 
filed Apr. 8, 1991, by D. Dasher et al. under the title HIGH INDEX ORGANIC 
LENS MEMBER, U.S. patent application Ser. No. 07/822,863, filed Jan. 21, 
1992 by D. Dasher et al. under the title OPHTHALMIC LENS METHOD, and U.S. 
patent application Ser. No. 07/624,055, filed Dec. 7, 1990 by R. S. 
Herndon et al. under the title COMPOSITE ARTICLE AND METHOD now U.S. Pat. 
No. 5,139,806. Each of the latter six disclosures is concerned with 
composite lens structures, but none describes the present inventive method 
of forming such structures without the use of an intermediate adhesive.

DESCRIPTION OF PREFERRED EMBODIMENTS 
As illustrated, ultrathin circular glass element 1, containing preformed 
central part 2 and an essentially flat flange 3, is placed on annular 
support 4, for example, made of polytetrafluoroethylene (Teflon.RTM.), so 
that it rests on said support only by its flange. Before pouring, one 
positions, on the periphery of central part 2, wedges 6 of appropriate 
thickness, four for example, equidistant from each other. Then one pours 
an appropriate quantity of thermosetting epoxy resin 5 into the concavity 
of central part 2. One then applies onto the mass of thermosetting 
composition counterform 7, for example made of glass or 
polytetrafluoroethylene, whose lower surface serves to give the posterior 
surface of the lens the desired shape. This can be a counterform whose 
lower surface 8 is flat, if one wishes to produce a semi-finished lens 
intended to be machined later, or it can be provided with a spherical or 
other profile, if one wishes to produce a finished lens. FIG. 1 
illustrates the case of the production of a finished lens with positive 
power, in which case the curvature of lower surface 8 of counterform 7 
must be less than the curvature of central part 2. FIG. 2 illustrates the 
case of the production of a finished lens with negative power, in which 
case the curvature of lower surface 8 of counterform 7 must be more 
accentuated than that of central part 2. 
The surface condition of lower surface 8 of the counterform must be as 
perfect as possible, and this lower surface 8 must have anti-sticking 
properties resulting, for example, from a treatment applied to the 
counterform, for example, with a Teflon.RTM. dispersion or a silicone 
solution, in order to facilitate removal of the counterform after 
hardening of composition 5. As a variant, the counterform could be 
produced entirely out of a material with anti-sticking properties, for 
example, out of polytetrafluoroethylene. 
The hardening of composition 5 can be brought about by heating the whole 
assembly consisting of the support 4, the glass element, the thermosetting 
composition, and the counterform in a furnace or oven according to a 
program of heating and cooling appropriate for the material used. After 
curing, one removes the counterform and the wedges, and one trims the 
edges of the composite lens to eliminate the flange and possible burrs of 
resin. 
The aromatic epoxy resins which constitute the organic part of the 
composite lenses of the invention have good properties of light 
transmission, an index of refraction of at least 1.58 and frequently on 
the order of 1.6, a good natural adhesion with regard to glass, a moderate 
volume contraction upon hardening, a relatively low thermal expansion 
coefficient, a low absorption of water, a low sensitivity to U.V. 
radiation, a high degree of hardness, and a temperature of vitreous 
transition usually over 100.degree. C., which makes them eminently useful 
in the application envisaged. 
The glass element must have a thickness of at most 0.3 mm and preferably a 
thickness of 0.20 to 0.25 mm, if one wishes to avoid breaking this element 
during hardening of the thermosetting epoxy resin composition. Thus, this 
composition, although its contraction with curing is moderate, when 
compared with other resins used in the field of optics, in any case 
undergoes a certain amount of shrinkage which causes thicker elements to 
break, for example, 0.8 mm thick elements. At thicknesses of 0.3 mm or 
less, however, it was surprisingly observed that the glass element 
acquired sufficient flexibility to bend without breaking with the 
geometric deformations generated by the shrinkage of the hardening epoxy 
resin. 
The glass element will usually consist of a sheet of ultrathin glass 
(called "microsheet"), of essentially constant thickness or "plano" that 
is to say, devoid of optical power. This glass element can be made of a 
colorless, colored, or photochromic mineral glass. 
A "microsheet" made of photochromic glass and its production are described 
in U.S. Pat. No. 4,168,339 (Kerko et al.). One can also produce a 
photochromic glass sheet of suitable thickness (.ltoreq.0.3 mm) from a 
thicker body by removal of material so as to reduce its thickness to the 
desired value by means of grinding and polishing. It is this last 
technique which is used to obtain the photochromic microsheet used in 
Example 3 below. 
The microsheet, originally flat, is cut in the form of a disk whose central 
part is preformed to the desired shape, which can be a spherical, 
non-spherical, or progressive shape, for example, by a process of hot 
forming under the action of an under pressure, until the disk is brought 
in contact with a perfectly polished mold. The glass must be formed while 
it is very viscous (10.sup.9 to 10.sup.11 Pa.s) in order to avoid 
glass-mold sticking. The operation is done under dust-free conditions to 
avoid or minimize surface defects. The resulting shaped disk then has a 
central part with the desired profile surrounded by an essentially flat 
flange which is intended to serve for support in the following operations. 
Other forming techniques could be used, for example, by application of 
centrifugal force. 
All glasses and photochromic glasses of optical quality are suitable. One 
can use, for example, transparent glass sold under the designation 0211 by 
the company Corning Incorporated, Corning, New York or photochromic glass 
sold under the designation Photogray Extra.RTM. by the same company. 
Although the epoxy resin has a good natural adhesion to the glass element, 
it is advantageous and recommended, in order to obtain the best results, 
to pretreat the surface of the glass element which is supposed to receive 
the thermosetting resin composition with an adhesion promoter. Such 
adhesion promoters are well known in the art and are available in 
commerce. The most current ones are silanes, particularly 
epoxyalkylalkoxysilanes such as glycidoxypropyltrimethoxysilane (sold 
under the commercial name A187 by the company Union Carbide, Danbury, 
Connecticut) or aminoalkylalkoxysilanes such as 
gamma-aminopropyltriethoxysilane (sold under the commercial designation 
All00 by the company Union Carbide). 
The following non-limiting examples are given for the purpose of 
illustrating the invention. 
In Examples 1, 2, and 4-11, circular transparent glass elements cut from a 
microsheet made of Corning 0211 glass and then preformed were used; 
whereas in Example 3 a preformed circular photochromic glass element with 
a thickness of 0.2-0.25 mm obtained by removal, using abrasives, of 
material from a semi-crude disk with the desired curvature made of 
Photogray Extra.RTM. photochromic glass with a thickness of 2-2.5 mm was 
used. 
The preformed glass elements had an overall diameter of 118 mm; the useful 
central part had a diameter of 70 mm. Three types of elements were 
prepared, of which the central parts had a radius of curvature of 69.5, 
105.6, and 170 mm, respectively. 
All the elements were covered, after careful cleaning, by centrifugal 
coating of 2900 rpm for 20 seconds, with an adhesion promoter obtained by 
mixing 1 wt% "A 187" silane sold by the company Union Carbide, 98 wt% 
ethanol, and 1 wt% distilled water, and aging of the resulting mixture for 
2 hours in order to hydrolyze it. The cleaning operation consisted of 
brushing the glass element with an aqueous solution of a surfactant, of 
rinsing by brushing with distilled water, of additionally rinsing the 
element by immersing it in distilled water, and of drying the element by 
centrifugation. After the covering operation, the hydrolysate applied on 
the glass element was condensed by heating to 100.degree. C. for 2 hours. 
EXAMPLE 1 
Preparation of Thermosetting Aromatic 
Epoxy Resin Compositions 
Thermosetting aromatic epoxy resin compositions A) to C) were prepared by 
carefully mixing the ingredients indicated at 40.degree. C. and under 
vacuum, until homogeneity was obtained. 
A) 3.65 parts by weight 4,4' -diaminodiphenylsulfone with an equivalent 
weight of amino groups of 62; and 
10 parts by weight DGEBA (diglycidyl ether bisphenol A) sold under the 
commercial name DER 332 by the company, Dow Chemical Co., Midland, 
Michigan; 
B) 2 parts by weight xylylenediamine; and 10 parts by weight of the DGEBA 
described in A). 
C) 10 parts by weight of the DGEBA described in A), 7.5 parts by weight 
phthalic anhydride, and 0.01 parts by weight dimethylbenzylamine 
(catalyst) . 
EXAMPLES 2-11 
Manufacturing of Composite Lens 
Compositions A) and C) of Example 1 were used to manufacture composite 
lenses by the process described above in reference to FIGS. 1 and 2. The 
quantities of poured composition ranged from 6.5 g for the least 
corrective lenses to 25 g for the most corrective lenses. Immediately 
after pouring, the counterform which had previously received an 
application of silicone RTV 141 (sold by company Rhone-Poulenc, 
Courberole, France) by centrifugal coating, followed by hardening by 
heating, in order to give it anti-sticking properties, was positioned. The 
poured material was then thermoset. The following table indicates the type 
of composite lenses produced, the conditions of curing of the epoxy resin, 
the properties of the hardened epoxy resin, and the results of certain 
tests conducted on the resulting lens. These tests were the following: 
Drop Ball Test 
This test, developed by the American Food and Drug Administration (FDA), 
consists of dropping a 16 g steel ball from a height of 1.27 m onto the 
convex surface of the lens. If the lens gets through the test without 
breaking, it successfully passes the test. 
Test of Resistance to Atmospheric Agents 
This test consisted of maintaining the composite lens samples in a climatic 
enclosure at 50QC and 98% relative humidity for 2 weeks. 
Temperature Cycle Test 
This test consisted of putting the composite lens samples for the indicated 
period of time in an enclosure in which the temperature varied from -40 to 
+80.degree. C. and returned to -40.degree. C. in the space of 2 hours. 
Test of Resistance to Boiling Water 
This test consisted of putting the samples in a water bath at room 
temperature, which was progressively brought to a boil, and of then 
keeping the samples for 2 hours in the boiling water. 
TABLE 
__________________________________________________________________________ 
EXAMPLE NO. 
1 2 3 4 5 
__________________________________________________________________________ 
Poured Composition 
B B B B B 
Type of Lens SF SF F, -6, 8D 
F, +2D F, +3, 5D 
Lens Thickness (mm) 
Max. 8 Max. 10 1.65 at center 
3.0 at center 
4.6 at center 
Hardening Conditions 
Hold 36 hr 
Hold 16 hr at 
Hold 16 hr at 
Hold 16 hr at 
Hold 16 hr at 
at 105- TA+, Hold 5 hr 
TA+, Hold 5 hr 
TA+, Hold 5 hr 
TA+, Hold 5 hr 
110.degree. C. 
at 110.degree. 
at 110.degree. C. 
at 110.degree. C. 
at 110.degree. C. 
PROPERTIES OF EPOXY 
RESIN: 
Refractive Index 
1.623 1.597 1.597 1.597 1.597 
Shore Hardness D 
88 88 88 88 88 
Vitreous Transition 
118 122 122 122 122 
Temperature .degree.C. 
Shrinkage With 0.3-0.4 0.3-0.4 0.3-0.4 0.3-0.4 0.3-0.4 
Polymerization % 
RESULTS OF TESTS: 
Resistance to Atmos- 
X X X X X (1 mo.) 
pheric Agents 
Temperature Cycle 
X X X X X 
Test 
Boiling Water Test 
ND ND X ND ND 
Drop Ball Test ND ND ND ND ND 
__________________________________________________________________________ 
EXAMPLE NO. 
7 8 9 10 11 
__________________________________________________________________________ 
Poured Composition 
B B B C B 
Type of Lens F, +5D F, -2D Toric, -1,7, +2, 
SF F, -6D 
9D cylinder 4,6 
Lens Thickness (mm) 
7.5 at center 
1.6 at center 
3.7 at center 
4.8 at center 
1.6 at center 
Hardening Conditions 
Hold 16 hr at 
Hold 16 hr at 
Hold 16 hr at 
Hold 16 hr at 
Hold 16 hr at 
TA+, Hold 4 hr 
TA+, Hold 5 hr 
TA+, Hold 5 hr 
96.degree. C. + Hold 2 
10.degree. C. + Hold 
1 hr 
at 10.degree. C.+, Hold 
at 110.degree. 
at 110.degree. C. 
at 150.degree. C. 
at 50.degree. C. + 
Hold 2 
2 hr at 130.degree. C. hr at 100.degree. C. 
PROPERTIES OF EPOXY 
RESIN: 
Refractive Index 
1.597 1.597 1.597 1.597 1.597 
Shore Hardness D 
88 88 88 88 88 
Vitreous Transition 
122 122 122 150 118 
Temperature .degree.C. 
Shrinkage With 0.3-0.4 0.3-0.4 0.3-0.4 ND 0.3-0.4 
Polymerization % 
RESULTS OF TESTS: 
Resistance to Atmos- 
X X X X X 
pheric Agents 
Temperature Cycle 
X X X X X 
Test 
Boiling Water Test 
X X X ND ND 
Drop Ball Test X X ND ND ND 
__________________________________________________________________________ 
Abbreviations: 
SF = semifinished 
F = finished 
Max = maximum thickness in mm for a semifinished lens 
D = diopter 
TA = room temperature 
X = successfully passes the test 
ND = not determined 
hr = hours 
The composite lenses of the invention are finer and lighter than the 
composite lenses that can be obtained according to the teachings of French 
Patent No. 2,407,898, supra or U.S. Pat. No. 4,227,950, supra. They are in 
fact capable of rivaling the classical lenses made of plastic material 
with a high index (n =1.6) with regard to weight, and the classical glass 
lenses with high index (meeting the European standards in force) with 
regard to the thickness in the center (positive lenses) or the thickness 
at the edge (negative lenses). 
It goes without saying that the embodiments described are only examples and 
that one could modify them, particularly by substitution of equivalent 
techniques, without consequently leaving the scope of the invention.