Finished ophthalmic lens comprising an optical smooth coating over a rough-surfaced base

A cut and/or ground ophthalmic lens surface is finished to optical smoothness and clarity by direct coating with a transparent liquid material which is curable into a clear, tough and tenacious laminate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to the manufacture of ophthalmic lenses and has 
particular reference to the finishing of cut and/or ground lens surfaces. 
2. Discussion of the Prior Art: 
Ophthalmic lens surfaces which are machined to prescription curvatures with 
cutting tools and/or loose abrasives exhibit tool and/or abrasive marks 
which produce the well-known "gray" effect needing to be removed by 
further working. 
Heretofore, removal of machined surface roughness has required fine 
grinding and polishing operations which are time consuming, tedious and 
costly to perform and require large investment in capital equipment. 
Additionally, in the manufacture of plastic opthalmic lenses which are 
conventionally fine ground and polished, it is considered desirable, if 
not necessary, to incur the additional manufacturing time and cost of 
covering the polished surfaces with a tough and optically clear material 
for enhancement of scratch resistance as disclosed in U.S. Pat. Nos. 
3,986,997 and 4,127,697, for example. 
In view of the aforesaid drawbacks of prior art high capital equipment 
cost, undue expenditure of manufacturing time and other high costliness of 
finishing machined ophthalmic lens surfaces, it is a principal object of 
this invention to provide a lens surface finishing operation which 
obviates the need for much, if not all, of the traditional finishing 
equipment and procedures and wherewith an optimum optically clear, highly 
scratch resistant lens surface may be produced simply, rapidly and 
economically. 
More specifically, it is an object of the invention to provide optically 
clear finishes on machined lens surfaces without the need for lens 
polishing operations; and 
Another object is to accomplish the foregoing with simultaneous provision 
of end product high scratch resistance. 
Other objects and advantages of the invention will become apparent from the 
following description. 
SUMMARY OF THE INVENTION 
The foregoing objects and their corollaries are accomplished by coating a 
machine cut or ground surface of an ophthalmic lens substrate with a 
liquid material, e.g. a pigment-free aqueous composition, which will cure 
into a tough tenacious and highly scratch resistant optically clear 
laminate. By such means, the surface roughness of the machined lens 
surface, whether glass or plastic, may be smoothly covered with the 
coating material to eliminate the effect of light scattering and afford 
optimum transparency. 
Details of the invention will become more readily understood by reference 
to the following description when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the drawings, FIG. 1 is an illustration of an ophthalmic lens 10 having 
a concave surface 12 machined to prescription curvature, e.g. by 
fly-cutting, diamond tool generating or loose abrasive surfacing. As such, 
surface 12 is left with a roughness which may comprise randomly sized and 
shaped peaks and depressions. All such and other forms of roughness 
produced by machine cutting or abrading cause scattering of incident light 
which renders the lens translucent and of "gray" finish. This well-known 
"gray" finish (i.e. translucency), not being of optical quality and 
completely unacceptable for ophthalmic use, requires working to optical 
smoothness for optimum clarity. To this end, the present invention 
eliminates the traditional final steps of fine grinding and polishing and, 
instead, dips, sprays, spin coats, doctors or otherwise applies an 
optically clear coating 14 to surface 12. 
Coating 14 is so formulated as to initially flow in low viscosity liquid 
form into the aforesaid roughness of surface 12 and be curable, e.g. with 
application of heat, into an optically clear, tough and tenacious 
laminate. 
FIG. 2 is an illustration of a dip-coated lens wherein the coating 14 
surrounds the lens substrate 16 and FIG. 3 illustrates a single surface 
coating 14' applied by spraying, pouring, flow or spin coating, doctoring 
or other such means of application. 
The invention is applicable to all forms of ophthalmic lens media including 
thermosetting and thermoplastic materials of which allyl diglycol 
carbonate, polymethylmethacrylate and polycarbonate are exemplary. Optical 
quality styrene and cellulosic plastics such as cellulose acetate and 
cellulose propionate are further adaptable to coating according to the 
invention, as is glass. 
A pigment-free aqueous coating composition and a number of specific 
examples thereof which are suitable for performing the aforesaid function 
and end product are disclosed in U.S. Pat. No. 3,986,997 together with 
methods of application. The coating is a pigment-free aqueous coating 
composition comprising a dispersion of colloidal silica in lower aliphatic 
alcohol-water solution of the partial condensate of a silanol of the 
formula RSi(OH).sub.3 in which R is selected from the group consisting of 
alkyl radicals of 1 to 3 inclusive carbon atoms, the vinyl radical, the 
3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and the 
gamma-methacryloxypropyl radical, at least 70 weight percent of the 
silanol being CH.sub.3 Si(OH).sub.3, said composition containing 10 to 50 
weight percent solids consisting essentially of 10 to 70 weight percent 
colloidal silica and 30 to 90 weight percent of the partial condensate. 
Lenses coated according to the disclosure of U.S. Pat. No. 3,986,997 may 
also incorporate tie coatings such as are set forth in U.S. Pat. No. 
4,127,697. 
Other suitable priming and coating compositions, with methods of 
application, are disclosed in assignee's co-pending application Ser. No. 
897,317 filed on Apr. 18, 1978 in the names of Don H. Rotenberg et al., 
and now U.S. Pat. No. 4,173,490 and continuation-in-part application Ser. 
No. 948,595 filed on Oct. 4, 1978, and now U.S. Pat. No. 4,229,228. These 
coating compositions are hydrolysis products of about 35 to 70 weight 
percent tetraethyl orthosilicate and 55 to 20 weight percent of a silane 
selected from the group consisting of methyltrimethoxysilane, 
methyltrietheoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, 
dimethyldimethoxysilane, dimethyldiethoxysilane and mixtures thereof and 
up to 20 weight percent of a siloxane having a reactive polar site. 
A further desirable coating composition is disclosed in Japanese 
application for Patent No. 52-26109 filed on Mar. 11, 1977 in the names of 
Masaharu Suzuki, et al by Toray Industries, Inc. of Tokyo, Japan and 
published on Sept. 28, 1978 under Disclosure No. 53-111336. This 
composition consists essentially of a mixture of one or more compounds 
selected from a group of compounds including one or both of epoxy group, 
and silanol and/or siloxane group (provided, in any case so selected that 
epoxy group, and silanol and/or siloxane group are included in the same 
molecule or different molecule); silica particle having a size of 1 to 100 
microns; and aluminum chelate compound of a general formula: 
EQU Al.XnY.sub.3-n 
wherein X is OL (L: lower alkyl), Y is at least a ligand derived from 
compounds of general formula M.sup.1 COCH.sub.2 COM.sup.2 (M.sup.1, 
M.sup.2 both lower alkyl) and a ligand derived from compounds of general 
formula M.sup.3 COCH.sub.2 COOM.sup.4 (M.sup.3 both lower alkyl) and n is 
0, 1 or 2. 
An ophthalmic lens substrate formed of allyl diglycol carbonate (CR39.RTM.) 
may also be primed for adequate bonding of the aforesaid coating 
compositions by dipping in an aqueous solution of sodium hydroxide 
maintained at a temperature of approximately 23.degree. C. followed by air 
drying at approximately 20.degree. C. This treatment of allyl diglycol 
carbonate lenses for subsequent coating purposes is set forth in U.S. Pat. 
No. 4,127,682 (Column 5, Example 1). U.S. Pat. No. 4,127,682 further sets 
forth a desirable pretreatment for optical elements formed of a 
polycarbonate (Column 6, Example 2). 
It has been determined that a thickness of coating 14 or 14' (FIGS. 2 and 
3) of approximately ten times the depth of machined surface roughness will 
produce a finish of optical quality. With an approximate depth of surface 
roughness of 0.8 micron and use of one or more of the coating compositions 
of U.S. Pat. No. 3,986,997, dip coating may be accomplished at room 
temperature with a lens withdrawal rate of approximately seven and 
one-half inches per minute from the coating solution and air drying for 
approximately 15 minutes. Final curing may be accomplished in 
approximately 8 hours with the lens subjected to a temperature of 
approximately 220.degree. F. This will provide a coating thickness of 
approximately 4 microns. 
Repeating the above procedure will provide the aforesaid coating thickness 
of approximately ten times the depth of original surface roughness, i.e. a 
final thickness of approximately 8 microns. 
Regarding the expressions "optical smoothness", "optical clarity" and 
"optical quality", those interested in detailed technical definitions 
thereof may refer to Optical Glassworking by F. Twyman published in 1955 
by Hilger and Watts Limited of London (pages 154 et seq.). Furthermore, 
the term "lens", as used herein, is intended to include all forms of such 
articles, i.e. whether in the configuration of blanks with only one side 
optically finished, both sides finished and/or uncut or cut to final 
diametral sizes and edge contours.