Method of controlling the adhesion of cast lenses to the mold

A method of increasing the adhesion of a cast polymer lens to a resinous lens mold by subjecting the resinous mold material to high internal shear force to alter the molecular structure of the resinous mold material to provide for greater bonding between the mold and lens material.

FIELD OF THE INVENTION 
The use of plastic materials for making optical lense has increased rapidly 
for the past ten years. This is due to the availability of better plastic 
materials and the physical advantages of the plastic resins for specific 
applications such as ophthamic lenses. The technology for the production 
of high quality plastic lenses has not kept pace with the material supply 
industry. It is important to advance both areas if the full potential is 
to be realized. 
Plastic lenses offer many advantages over glass lenses. They are much 
lighter in weight and resist breakage. The cost of making high quality 
lenses has been high due to the problems caused by the shrinkage of the 
monomer when polymerized, which often breaks the expensive mold. 
STATE OF THE ART 
The current lens molds are fabricated from steel or glass, each mold is 
individually ground and polished to the required specifications. To 
achieve accurate reproduction of the bifocal and toric molds is most 
difficult and expensive. 
An object is to provide a process for making inexpensive molds which may be 
made to identical specifications. 
Another object is to provide a process whereby standard masters may be used 
to produce a large quantity of replica molds. 
The adhesion of the replica mold to the lens material may be increased by 
subjecting the heated mold material to extreme internal shear forces 
during processing.

THE LENSES ARE MADE AS FOLLOWS 
A master positive mold is made from glass or stainless steel or other 
materials which will withstand the molding temperatures. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
It has been discovered that the adhesion between the resinous mold material 
and the lens material can be increased by subjecting the heated resinous 
mold material to high shear forces such as passing the heated material 
through a small orifice of from 0.2 m/m to 5 m/m in cross sectional area, 
at high pressures of 5,000 to 50,000 pounds per square inch and at high 
velocities. The high internal shear forces produced upon passing through 
the orifice changes the molecular structure by cleaving some of the 
molecular chains to create attachment sites to which the monomer lens 
material will attach itself upon polymerization. 
The master mold, 1 FIG. 11, is placed in a sleeve, 4 FIG. 1, a molding 
grade of a resinous material such as polyimide, polycarbonate, 
polymethylpentene, polyethylene, polypropylene, nylon or other molding 
material which has been shear treated is placed in the sleeve, 4 FIG. 1. 
The sleeve and its contents are heated to the softening point of the 
molding material, pressure is applied to form the lens mold, 3 FIG. 1. The 
sides of the master mold, 1 FIG. 1, have been cut to a smaller diameter to 
provide the opening, 5 FIG. 1. When sufficient heat and pressure have been 
applied, the molding compound, 3, will fill the area around the positive 
mold, 1, forming a cup-like cavity with a curved optical surface, 2 FIG. 
1, at the bottom. Either injection or compression molding may be used to 
produce the lens molding container. The lens container 3 FIG. 1, is 
removed from the molding sleeve, 4 FIG. 1, and the optical mold, 1 FIG. 1, 
is also removed. 
CASTING THE OPTICAL SURFACE 
A liquid or syrup monomer material containing a suitable catalyst, 6 FIG. 
2, is placed over the optical surface, 2 FIG. 2, and covered to prevent 
evaporation with a cover, 7 FIG. 2, an air space, 8 FIG. 2, is provided. 
The liquid monomer is polymerized to form a solid. Microwave energy or 
heat may be used to speed the polymerization process. Thermosetting and 
crosslinked materials may be used to produce lenses which are 
dimensionally stable. This process is suitable for the production of soft 
contact lenses which cannot be made by compression or injection molding 
techniques. 
CUTTING THE SECOND OPTICAL SURFACE 
It is not necessary to remove the hardened plastic lens material, 6 FIG. 3, 
from the mold, 3 FIG. 3, before cutting the convex curve, 9 FIG. 3. The 
mold, 3 FIG. 3, may be placed in a suitable lathe and curvature, 9 FIG. 3, 
cut and polished. The finished lens, 6 FIG. 4, having the molded concave 
surface, 2, and the convex curvature, 9, which was cut and polished 
without being removed from the disposable mold, 3 FIG. 4. The cup-like 
device has served as a container for the monomer, 6 FIG. 2, provided the 
molded optical surface which for contact lens production may be two or 
more segments providing the required optical zone , peripheral curves and 
lens diameter. The cup-like mold, 3 FIG. 3, also serves as the holding 
block to facilitate cutting to the required thickness. The thickness of 
the cup bottom may be measured before adding the liquid monomer and 
measurements may be taken during the cutting operation and the lens 
thickness determined by subtracting the thickness of the cup bottom. The 
cup. 3 FIG. 3, which adheres strongly to the lens also serves as a holding 
fixture during the polishing operation. After the lens is processed to the 
required specifications, the lens is removed by sharply flexing the 
holding fixture, 3 FIG. 4, separating the finished lens from its support. 
Various modifications can be made without departing from the spirit of this 
invention or the scope of the appended claims. The constants set forth in 
the disclosure are given as examples and are in no way final or binding. 
In view of the above, it will be seen that the several objects of the 
invention are achieved and other advantages are obtained. As many changes 
could be made in the above construction and method without departing from 
the scope of the invention, it is intended that all matter contained in 
the above description shall be interpreted as illustrative and not in a 
limiting sense.