Polarizing prescription lenses and method of making

Apparatus and a method for adhering a flexible soft polarizing film to a curved surface, such as the convex surface of a prescription eyeglass to be made into a polarizing lens is disclosed. The method involves glass-casting, and preformation of the film in a manner calculated to have a minimum hardening/drying effect. Air is excluded during lamination without the need for a vacuum and the attendant complications.

TECHNICAL FIELD 
This invention relates to novel polarized prescription sunglasses and a 
method of making the same. 
BACKGROUND 
While the theoretical possibility of light polarizing filters was known 
from a very early time, it was not until Alvin and Mortimer Marks grew 
iodine crystals in the 1940's that useful polarizing materials were first 
made. Polarizing materials were discovered by William Bird Herapath and 
were announced in the London Philosophical Papers in the mid 1860's. 
Cellulose had been dyed with iodine by H. Amyronn and reported in 1919 in 
"Accidental Double Refraction in Celluloid in 6 Cellulose" and J. Conroy 
in 1876 reported that microscopic crystals of iodine polarized light. Many 
others dyed oriented fibers prior to 1930 and reported dichroic effects. 
Alvin and Mortimer Marks in the 1930's learned how to grow crystals which 
attached themselves in an oriented fashion to surfaces such as plastic or 
glass, and so produced continuous crystalline light polarizers. The new 
materials, for the first time, allowed the evaluation of the percentage of 
polarization in naturally polarized light phenomena such as glare, 
reflection, and the like. Several years later, Edwin Land contributed to 
the technology by initially using Herapath's iodo quinine sulphate as part 
of a plastic structure which incorporated minute crystals oriented by 
stretching. These new relatively inexpensive polarizing materials were 
almost immediately employed in a wide variety of applications, including, 
sunglasses, photography, scientific instrumentation, military hardware and 
so forth. 
Of all the potential applications of the new polarizing materials, perhaps 
the largest promised to be the application to eyewear. Indeed, the market 
in polarized non-prescription sunglasses in the United States is huge. 
Polarized prescription glasses were first introduced as flat laminated 
glass blanks that were then ground to prescription. These were costly and 
heavy to wear because of the thickness of glass required. Despite the fact 
that polarized prescription lenses, especially in the beginning, were 
relatively expensive as compared to non-polarizing tinted lenses, the same 
do have a substantial but small part of the market. Nevertheless, a much 
larger portion of the market can use prescription polarizing glasses. 
The various available alternative solutions have a number of problems. 
Clip-on polarizers present two extra surfaces for the collection of dust 
and other vision impairing matter. Clip-ons tend to be, by necessity, 
rather light in structure and are liable to breakage, blowing off in the 
wind, and other forms of instability. Accordingly, clip-on polarizers have 
never captured a portion of the market of prescription eyeglass wearers 
commensurate with the market share of polarizing non-prescription glasses 
as compared to tinted non-prescription glasses. 
Rather, the need for light attenuating prescription sunglasses has mostly 
been filled by tinted non-polarizing glasses. These are made by taking 
finished eyeglasses (in which the lenses have been ground to the desired 
prescription and further ground to fit the eyeglass frame) and coating the 
finished product with a filter material. While this material does not 
exhibit polarizing characteristics, and is thus far inferior to polarizing 
glasses in its operating characteristics, this method does offer the 
advantage of a simple efficient and reliable way of attenuating light 
input into the eyes of the wearer. 
However, a small portion of the light attenuating eyeglass market is taken 
by polarizing prescription sunglasses which are made by taking a glass or 
plastic blank of reduced thickness, adhering a polarizing film to one of 
its surfaces and covering the polarized film with yet another glass blank. 
This forms a sandwich comprising two layers of glass with a layer of 
polarizing material disposed therebetween. This product can also be made 
by injection molding of lens plastic around a polarizing filter. 
It is necessary to grind the edges of the lens blank to fit them to the 
eyeglass frame. This can only be done after the polarizing layer has been 
inserted into the sandwich. This grinding is typically done in the 
laboratory of the eyeglass retailer. Such "labs" purchase prescription 
polarizing blanks with a given prescription power for grinding to the 
particular frame shape to be matched. 
In the view of the fragile nature of the polarizing prescription lens, 
damage to the polarizing layer and/or the transparent sandwich members is 
likely to occur. The high cost of the blanks together with the 
above-described likelihood of damage have combined to make the polarizing 
sandwich lens somewhat impractical as an answer to the problem of 
providing polarized prescription sunglasses. Nevertheless, in the 
approximately fifty years since polarizing materials first became 
available, no other commercially viable solution has been proposed. 
DISCLOSURE OF INVENTION 
The invention, as claimed, is intended to provide a remedy. It solves the 
problem of how to provide an inexpensive effective polarizing prescription 
lens. The inventive method and apparatus overcome the disadvantages of 
prior art devices and methods involving likelihood of lens damage. In 
addition, the final product has the advantage of preventing ultraviolet 
radiation from passing through the eye as well as greatly reducing costs. 
Moreover, the inventive system may be applied to completely fabricated 
glasses made of glass, CR 39 or polycarbonate and even used glasses. CR-39 
glasses are the preferred base material as CR-39 tends to have the lowest 
internal stresses. Thus the consumer is presented with the possibility of 
converting an old pair of glasses to use as prescription sunglasses for a 
relatively inexpensive price as compared to the present situation of being 
forced to buy specially fabricated polarizing prescription glasses at 
relatively great cost. Accordingly, it is estimated that the present 
invention will, for a small fraction of the present cost of polarized 
prescription glasses result in substantially identically functioning 
products. 
The above is achieved by applying a polarizing film to a curved surface 
with a drop of liquid being used to exclude air from between the laminate 
and the lens. In this respect, it is noted that polarizing films because 
of their highly organized structure at the micron level present special 
handling problems and their adhesion to a surface curved in two orthogonal 
directions, as in the case of most prescription lenses, present a special 
problem addressed by the specialized procedure of the inventive method 
While laminating procedures for adhering a polarizing film to a curved 
surface are known, various problems have prevented commercialization of 
the procedure. See U.S. Pat. Nos. 2,354,692 and 3,300,436.

DETAILED DESCRIPTION 
As noted above, to make polarized prescription eyeglasses it has been 
necessary to obtain polarized blank lenses, into which the polarizing film 
has already been embedded (in a sandwich type arrangement to allow for 
grinding without affecting the polarizing material). Polarized blanks are 
considerably costlier than normal glass or plastic blanks. Therefore 
breakage and grinding errors become costly, yet are part and parcel of 
normal industry practice. Neither passing on, nor absorbing the cost of 
mistakes or defective materials is acceptable if one wishes to provide 
reasonably priced eye care. 
The objectives achieved by the invention are to not only eliminate the high 
costs caused by damaged polarized lenses but to also bring down the cost 
of polarized optical materials while reducing the possibility of defects 
or grinding errors. 
In accordance with the present invention, a casting composition for a 
polarized film is made in accordance with known techniques, such as those 
in U.S. Pat. No. 3,300,436 of Alvin and Mortimer Marks entitled Coating 
for Light Polarizing Materials. In accordance with the present invention, 
a polyvinyl butyral based casting composition is preferred, despite the 
customary use of polyvinyl alcohol in the art. This casting composition is 
filtered through a Pall Trinity 10 micron filter using a peristaltic pump 
with silicone tubing. The silicon tubing may be obtained from the Walter 
Cooling Company of Rosedale, N.Y. under catalog number Masterflex Code No. 
6411-18. The filter is available from Pall Trincor of New Jersey. 
Referring to FIG. 1, forty grams of filtered solution 8 is spun in an 
airtight chamber 10 at 700 rpm for 10 seconds (or for an additional 3 
seconds if a typical formula with a relatively large amount of iodine is 
present in the mixture). Spinning is performed on a 10".times.10" square 
glass plate 12 resting on a circular platen 14. Platen 14 is rotated by 
transparent shaft 16, which in turn is driven by pulleys 18 and 20 which 
are linked by timing belt 22 which reduces slippage. The system is driven 
by motor 24. 
The spinning time is controlled in the apparatus shown in FIG. 1 by 
comparison of the mixture color to a standard color. In particular, a 
light source 26 directly passes light through a filter standard 28 to a 
photocell 30 whose output is compared to the output of photocell 32, which 
receives light passed through spun solution 8. Comparison is done by 
control circuit 34 which stops spinning when the desired color density is 
reached. The use of an airtight chamber minimizes turbulence and eddy 
currents. Further reduction of these disturbances is achieved by using a 
circular platen 14 which has a diameter at least as great as the diagonal 
length of plate 12. The position of plate 12 on platen 14 is maintained by 
stops 36. 
The resulting spun film is then covered with a glass plate about 1/4" above 
the film to reduce evaporation and allow bubbles to rise while natural 
surface tension smooths out the film. 
Drying is allowed for 30 minutes in an air tight, dust-free container. This 
is followed by air drying until the color of the film changes from yellow 
to dark blue. The film is then slit 1/2" from two opposite edges and 
stretched in one direction to 5 to 6 times its original size, divided in 
half with a cut perpendicular to the direction of stretching. Each of 
these halves may then be cut in half again with the cutline in the middle 
of the half sheet and extending in the direction of stretching, and the 
quarters coming from a single half sheet placed on plastic plates 100 to 
correspond to a single pair of glasses (FIG. 2). A large center hole 102 
and two bolting holes 104 are defined by each plate 100. Double sided tape 
or glue disposed along the perimeter of the film and on the plastic plate 
is used to hold the film in a stretched position. Stretching is done at 
room temperature (20-22 degrees Centigrade) with a relative humidity of 
55% or less. 
The mounted and stretched film may be secured to finished or used eyeglass 
lenses, (whether spherical, astigmatic, or progressive), blank lenses 
(lenses with only the outside surface finished and usually round in 
shape), or finished blanks (so-called stock lenses which have two sides 
finished but which have not been fitted to an eyeglass frame). 
In accordance with the present invention a finished lens which may be 
spherical or aspherical and ready to go into an eyeglass frame and made of 
glass, CR-39 , polycarbonate or the like is subjected to surface treatment 
so that adhesion of the polarizing film may be achieved by means of an 
intrinsic bond between the surface of the lens and the 
butyral-lithium-iodine polysilicate complex formed by processing. 
The surface preparation formula contains: 
SURFACE PREATION FORMULA 
Sulphuric Acid (98.08%)--500 parts by weight 
Chromium Trioxide--1 part by weight 
Such surface preparation formula is placed on a glass concave surface which 
has a curvature close to that of the CR-39 lens to be treated. Then one 
lays the CR-39 lens onto the acid with the concave glass surface of the 
glass surface in contact with the convex lens surface for 20 seconds 
causing the acid to be distributed about the entire surface to be treated. 
The lens is then washed in water and dried. Work should be done in a 
ventilated area and a rubber apron, gloves and protective eye covering 
should be used when working with this acid mixture. Treatment of the 
surface may alternatively be accomplished by use of a plasma generator for 
up to 1 minute. Also, a combination of both these treatments may be used. 
One then measures the curvature of the lens with a lens gauge. The prepared 
lens 110 is then secured in place in an apparatus 200 shown in FIG. 3 by 
means of adhesive material 202 making sure that the lens axis and the film 
polarization direction are aligned so that the polarizing film 108 will 
maximally filter out reflected glare when the coated lens is inserted in a 
pair of finished sunglasses. 
One then places the base plate 100 with film 108 into apparatus 200, 
bringing the back of the film about 1/4 inch from the front etched surface 
of the lens to be coated. A vacuum is engaged in chamber 204 through tube 
206, gauge 208 and vacuum line 210 to achieve the curvature needed on the 
film to match the lens surface as shown in phantom lines. One then 
introduces a few cubic centimeters of distilled water (or other liquid) 
onto the film. It is noted that for relatively flat surfaces, a vacuum may 
not be necessary. 
Apparatus 200 includes a vacuum portion 212 and a mounting portion 214. 
Vacuum portion 212 comprises a Vacuum circuit made of vacuum line 206, 
gauge 208 and vacuum line 210 and is attached to a vacuum source whose 
pressure may be regulated. Gauge 208 includes a top flexible membrane 216 
which moves downwardly in response to the application of vacuum. This 
causes a follower 218 to also move down against the force of a spring 220. 
Spring 220 is fixed at one end to follower 218 and to a fixed point 222. 
Follower 218 is, in turn, pivotely connected to an indicator 224 which is 
pivoted at a point 226 and will give an indication calibrated to diopters 
of the power of a lens on a scale 228 in response to pressure which causes 
curvature of membrane 216 and a corresponding indication on the scale of 
the curvature of film 108 in response to the application of pressure. Thus 
it is possible using this apparatus to regulate the vacuum pressure to the 
point where the shape of deformed film 108 shown in FIG. 3 may be made to 
substantially match curvature of a lens surface to receive a polarized 
film layer. 
Support portion 214 comprises a pair of threaded members 230 which are 
secured to plate 100 by bolts 232 and knurled bolts 234. At the opposite 
end, bolts 236 act against a support 238 and springs 240 which bear 
against bolts 242 to provide an adjustable mounting for support 238. 
Support 238 includes a tube 240 which is biased in the direction toward 
support 238 by a spring 242 which is advanced by rotation of threaded 
member 244 which is secured to rotating knob 246. This causes advancement 
of square ram 248 whose outside shape matches the inner diameter of square 
tube 240 thus allowing advancement of ram 248 with a lens 110 mounted 
thereon toward film 108 without rotation of the film. In connection with 
this it is noted that plate 100 and vacuum chamber 212 are sealed to each 
other allowing the maintenance of a lower pressure within chamber 212 in 
order to deform film 108 into the shape illustrated in phantom lines in 
FIG. 3. Generally, the shape of the film must be very slightly less 
concave than the glass surface to be coated is convex. This allows the 
central point of the convex surface to be coated to be the first portion 
to contact the film. As the ram is advanced, it stretches the remainder of 
the film into contact. This stretching should be minimized so the 
difference in concavity should be as small as possible. If, on the other 
hand the surface of the film is slightly more concave, it will trap the 
liquid and the polarized coating will be defective. 
To achieve lamination one tightens the knob 246 to make contact between the 
film 108 with distilled water 250 on it and the lens to be coated. 
Alternatively to water 250 one may use any liquid that does not attack or 
otherwise adversely affect the polarizing film, or even an adhesive or 
other material. One then slightly tightens somewhat more than necessary 
for contact with film 108 to achieve good adhesion. The formed coating may 
then be checked by viewing through another polarizing filter to check the 
quality of the product. One then waits 45 minutes and removes the lens, 
with the attached film, along with the ram assembly from chamber 204. The 
lens is then placed face up in an air oven and baked for 15 minutes at 
77.degree. C. After baking one trims the film to the edge of the lens 
using sharp blade. 
The trimmed lens is removed from the ram and then baked, face up, for 2 
hours at 68 degrees C. and then allowed to air dry overnight 
(approximately 12 hours). A first silication solution is applied to the 
lens for 15 seconds to lock in the iodine. The lens is then spun briefly 
and air blown dry and placed under a heat lamp for 5 minutes. 
This first silication step can be done effectively at 60% relative humidity 
or less. Above 60% relative humidity the lens will become cloudy and the 
silication does not effectively stabilize the lens. The silication 
solution was formulated as follows: 
Butyl Alcohol--20 parts 
Tetraethylorthosilicate--80 parts 
Tetraethylorthosilicate is manufactured by Union Carbide, Coating Chemicals 
Division of Danbury, Conn. 
A silicate resin solution which serves the purpose of sealing the surface 
is then applied in a second silication step to the lens which is then 
briefly spun to spin of excess resin solution. The lens is then air dried 
under a heat lamp for 5 minutes. The lens is then placed in an oven for 2 
hours at 77 degrees centigrade. After two hours in the oven, the lens is 
cooled to room temperature. 
The second step silicate resin solution used was made by first forming a 
base which contained the following: 
Butyl Acetate--22.0 parts by weight 
Acetic Acid--7.0 parts by weight 
Toluene--17.0 parts by weight 
Methyl Isobutyl Ketone--48.0 parts by weight 
Butyl Lactate--25.0 parts by weight 
Normal Propanol--20.0 parts by weight 
XYSG--6.6 parts by weight 
Total--145.6 parts 
The base was then filtered through a 10 micron Pall filter. To 14 parts of 
base was added: 
Silbond (ethyl silicate pure)--3 parts 
Butyl Acetate--5 parts 
Toluene--5 parts 
Silbond is manufactured by Stauffer Chemical Co., Specialty Chemicals 
Division of Westport, Conn. 
Owen Illinois Hard Coat is then applied to the lens. The hard coat is 
modified by the addition of an additional catalyst which acts to overcome 
the iodine which it prevents escaping. The catalyst is included in the 
hard coat in the amount of 3% instead of 2%. The lens is then baked for 
four hours at approximately 82 degrees Centigrade. Of course, ultraviolet 
light cured commercially available hard coats may also be used. 
Matched lenses may be made by matching the amount of stretch of the 
polarizing film 310 as shown in FIG. 4. Here the film has been stretched 
by grasping edges 311 and 312 and pulling in the direction of arrows 313 
and 314 respectively. Stretching tends to be uniform perpendicular to the 
direction of stretch. Thus cutting along line 316 yields a pair of 
substantially matched film members 318 and 320. If desired cutting may be 
dispensed with and a two hole base plate 300 used, as shown in phantom 
lines. 
Specialized lenses may also be fabricated in accordance with the present 
invention. For example, bifocals with segments protruding cause the 
polarized film to disorient due to the build up of fluid, such as the 
softening fluid which is retained during processing. A solution to this 
problem is the application of the polarized film to the entire lens and 
then stripping of the film away from the bottom portion of the lens, which 
because of its shape causes the problem. Removal of the film is easily 
accomplished by cutting and lifting off the film before silication and/or 
baking results in firmly attaching the film to the CR-39 lens. The 
remaining portions of the process are the same. Alternatively, a smooth 
lens 410 as shown in FIG. 5, covered with film 412 can be cemented to, for 
example, a smooth or a bifocal member 414 to make bifocal, progressive 
single vision wafer lenses. 
Also, treating the surface of a blank with a plasma generator, or treating 
with NaOH or KOH will sufficiently etch the surface to cause polarized 
film to adhere. Likewise, the process is not limited to spinning polarized 
film on glass. The purpose of the spinning technique is to obtain 
uniformity and have a well finished surface. A glass wheel machine can 
also be used. 
The barrier coating silicate resin solution can also be over-coated with a 
photoresist coating then exposed to strong ultraviolet light where it 
becomes insoluble and prevents other hard coats from attacking the 
polarizing compositions. Catalysts monomers such as CR-39 can be molded 
over and in contact with the surface. 
While illustrative embodiments of the invention have been described, it is, 
of course, understood that various modifications will be obvious to those 
of ordinary skill in the art. Such modifications are within the spirit and 
scope of the invention which is limited and defined only by the appended 
claims.