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United States Patent 
[li] 4,382,902  May 10,1983
 METHOD FOR MOLDING CONTACT
LENSES USING ULTRAVIOLET ENERGY
 Inventor: Bernard Feurer,
 Assignee: Alcon Pharmaceuticals Limited, Cham, Switzerland
 Appl. No.: 238,962
 Filed: Feb. 27,1981
 Foreign Application Priority Data
Feb. 28, 1980 [FR] France 80 04750
 Int. C1.3 B29D 11/00
 U.S. Q 264/1.4; 264/25;
 Field of Search 264/1.4, 25, 337;
 References Cited
U.S. PATENT DOCUMENTS
3,171,869 3/1965 Weinberg 264/1.4
3,983,083 9/1976 Kaetsu et al 264/1.4
4,073,577 2/1978 Hofer 264/1.4
4,113,224 9/1978 Clark et al ... 264/1.4
4,166,088 8/1979 Neefe 264/1.4
4,209,289 6/1980 Newcomb et al. 425/410
FOREIGN PATENT DOCUMENTS
55-132221 10/1980 Japan 264/1.4
Primary Examiner—James B. Lowe
Attorney, Agent, or Firm—Shlesinger, Arkwright,
Garvey & Dinsmore
The invention relates to a fabrication process for molding a contact lens evincing the required optical properties.
This method consists in designing a mold (1,2) with a high thermal inertia, transparent to, or little absorbing electromagnetic waves with wavelengths between 1 micron and 10-6 microns, in developing a base composition from polymerizing double-bond monomers which are absorbing with respect to these waves and in securing the polymerization of the composition inside the closed mold by irradiating with the above-cited electromagnetic waves at a power density such as to keep the temperature approximately less than 40° C. at the mold level.
11 Claims, 4 Drawing Figures
U.S. Patent May 10, 1983 Sheet 1 of 2 4,382,902
U.S. Patent May 10, 1983 Sheet 2 of 2 4,382,902
METHOD FOR MOLDING CONTACT LENSES
USING ULTRAVIOLET ENERGY
The invention relates to a fabrication method for 5 molding a contact lens which is a finished product with the required optical properties for placement on an eye and ensuring the desired corrections.
It is known that the contact lenses are conventionally made by machining blanks or disks obtained by poly- 10 merizing a synthetic monomeric composition; these disks or blanks as a rule are obtained by polymerizing in molds without there being any attending particular difficulties, as the optical surfaces are machined thereafter. 15
This machining of disks to impart the final shape with the required optical properties to the lenses represents a costly, delicate and lengthy operation, requiring numerous and specialized personnel. To eliminate this machining operation, it has already been suggested to directly 20 produce by molding these contact lenses, by providing for the polymerization of the base composition in a closed mold which renders as a hollow the final shape of the lens to be obtained.
However this type of fabrication runs into a problem 25 which is exceedingly difficult to resolve practically when desiring to achieve lenses of which the surfaces have the required optical properties and the rims are thin enough and of a proper contour to be physiologically supported by the eye. In fact, during the polymeri- 30 zation, which as a rule is carried out at a temperature of 60° to 70° C, detachments of the lens material from the mold are observed, with the formation of minute pockets between the lens and the mold walls. The lenses so made cannot be used, so that, regardless of their seem- 35 ing interest, these molding methods to-date have failed to be commercially profitable.
The experts who have considered this problem have explained the lens detachment and the formation of pockets as a shrinkage phenomenon that would be expe- 40 rienced by the hot material during polymerization.
Thus, in the French patent application number 77.08393, there is an attempt to resolve this problem by designing a special mold provided with elastic lips around its periphery of which the function is to fill the 45 empty space that tends to appear around the lens, in order to prevent lens detachment and the formation of pockets, as mentioned above.
A certain improvement is obtained, which reinforces the thesis that the difficulties are due to material shrink- 50 age during polymerization.
However, the method described in the above cited patent application requires the design of special molds of which the very thin elastic lips are likelt to degrade rapidly. Moreover, and most of all, the rim of the lens 55 made in such molds as a rule will be relatively thick and rather irregular. When emplaced, such lenses suffer from the drawback that they are frequently moved by the action of the lids catching on their rims.
Furthermore, in some methods, non-hermetic molds 60 have been used, with open rims at their periphery, where these methods consist in pouring excess material, which can be drained through the open rims, into the molds (for instance French Pat. No. 2,270,082). However these methods require working the lenses again to 65 machine their rims following molding. Also, in this kind of procedure, the molding implementation is far more complex and delicate, as the polymerization must take
place progressively from the center to the rims of the mold. As a rule, the polymerizing conditions are so adjusted that it will take place in two phases, first an onset of polymerization at the center of the mold (during which polymerization of the rims is avoided), and then peripheral polymerization.
The object of the present invention is a fabrication method by molding, of the above cited type, wherein a base composition is polymerized in a hermetic mold consisting of two parts hermetically closing one against the other and rendering in hollow shape the form of the desired lens.
Another object of the invention is to solve the molding problem cited above, without the drawbacks of the known solutions.
Another object of the invention in particular is to allow fabrication in a single stage by molding a lens in a closed mold to obtain a lens with optical surfaces and thin rims, and appropriate properties.
Another object of the invention is to provide a method which can be implemented in simple-structure molds that do not risk rapid wear.
To that end, the fabrication method of this invention to make a corneal lens of suitable optical quality by polymerizing a base composition in a closed mold consists of:
designing a mold of a material which is transparent to or little absorbing the electromagnetic waves of a length approximately between 1 micron and 10~6 microns, where said mold has a thermal inertia much higher than that of the base composition amount required to make a lens;
developing a base composition from one or more polymerizing double-bond monomers, with the property of absorbing the above cited electromagnetic waves;
and securing the polymerization of the composition inside the closed mold by irradiating the set with electromagnetic waves with the above cited lengths and with a power density adjusted to maintain a temperature at the mold level which is less than approximately 40° C. When implementing such a method, it is observed that the lens material remains applied against the mold and perfectly hugs its shape, both in the central regions and at the rim of the lens. Upon completion of the polymerization, the lens evinces an optically satisfactory surface, also and particularly regular rims which reproduce the undeforming geometry of the mold at that level. Due to a proper mold shape, these rims therefore may be slight in thickness, progressively decreasing in conformity with the requirements placed on the corneal lenses, and this result is reproducible in the course of mass moldings of lenses.
Very likely the explanation of this unexpected result is in the two following facts: on one hand, contrary to what was believed, the pocket formation in the conventional methods arises at least in part as much from the hot differential expansions of the mold and of the base composition as from latter's shrinkage, and on the other hand, the shrinkage of the base composition during a low-temperature polymerization by itself is insufficient to cause detachment.
The method of the invention results in the dissipation of the energy required to polymerize at the core of the lens material by avoiding heating it excessively, and especially by avoiding heating the mold, which practi