JPS61201A - Polymerization of monomer mixture for manufacture of contactlens by centrifugal molding - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for polymerizing monomer mixtures in the manufacture of contact lenses by centrifugal casting.

For example, U.S. Percent Liver No. 3,699,089, No. 3.40
No. 8,429, No. 3,822,089 and No. 4.15
The manufacture of contact lenses by centrifugal casting, as described in No. 3,349, is useful in cases where the time required for almost complete polymerization of the monomer mixture is very short, i.e., at most a few minutes. In particular, it has been found to be very effective.

This is particularly the case when polymerizing monomer mixtures containing methacrylic esters as a basic component. However, with the development of new materials that have very high permeability, especially to oxygen, types of polymers that form very slowly from a given monomer can be created, and in such cases The monomer is almost completely converted into a gel after many hours. In such a case, the productivity of the continuous casting machine is almost inversely proportional to the polymerization time, resulting in a decrease in productivity.

Therefore, the main advantage of centrifugal casting is lost.

1. The method according to the invention comprises a precast monomer mixture which still contains some unpolymerized monomer components, but which, after precrosslinking, is solidified in a mold for the production of a precast product having the stable shape of the final contact lens. The carousel type (carro+t, s
et) By using a column-type centrifugal casting apparatus, the centrifugal casting method can be used very economically in the manufacture of contact lenses, even for monomer mixtures that polymerize very slowly. It is something. In the next operation, these precasts are exposed to polymerization properties without rotation for a period of time necessary to achieve complete polymerization conversion δ. In the first step, characterized by the rotation of the mold, photopolymerization according to the invention, i.e. a photocatalyst activated by irradiation, e.g. alkyl esters of 2,2-jethoxyacetophenone or benzoin (alkyl being methinopeethyl, isopropyl, rubutyl, 5ec- photopolymerization with peroxide-type catalysts (e.g. diisopropyl peroxocarbonate, ammonium persulfate, dibenzole peroxide, etc.) is used, but in the second stage when the template containing the photochemically polymerized mixture is stationary. or unstable azo compound type catalysts (azobisisobutyronitrile etc.)
A thermal polymerization induced by the presence of is used. Both types of catalyst for the first stage as well as for the final stage are already added simultaneously to the starting monomer mixture. constantly rotating,
The monomer mixture is exposed to light in a mold at room temperature until a gel state is obtained, and then the mold containing this gel is heated for 50 to 50 minutes without rotation until the complete conversion is completed. Heat to a temperature of 100°C. Advantageously, the amount of photopolymerization catalyst is in the range from 0.05 to 5N, and the amount of thermal polymerization catalyst is preferably from 0.05 to 5% by weight. The photopolymerization catalyst is largely decomposed and consumed during photopolymerization, whereas the thermal polymerization (second stage) catalyst remains intact during photopolymerization, which proceeds at low temperatures. In special cases, catalysts are used which are capable of initiating the radical polymerization both photochemically and thermally, for example photochemically unstable azo compounds.

Equipment used in a wide variety of methods is useful in carrying out this method. The simplest device is to use a protective gas stream (e.g. pure nitrogen or carbon dioxide) after the mold containing the preliminarily wetted material leaves a carousel-type or column-type continuous manufacturing device and undergoes each inspection. in a countercurrent flow into a container that is flushed with a protective gas. Such a container containing a large number (several thousand) of molds is then hermetically sealed and placed in a box heated to a constant temperature and held there for a period of time necessary for the polymerization to be nearly complete. do. Finally, the lens is removed from the mold and processed as usual. This simple method involves casting the lenses in a uniform mold and collecting them for second stage processing in a large container, allowing for large series of uniformly molded lenses without the need for lens sorting. Particularly suitable for the production of

In other systems, where the mold bank exiting the centrifugal casting machine is held until completion of the process, the cast discharge device from the centrifugal casting machine passes through the irradiation zone and contains the already gelled prepolymer. consisting of an arrangement in which the molds to be produced are periodically slid from a rotating polymerization column by means of a sliding gate over an opening, through which they fall into a tubular magazine located below the opening and through which a gentle upward flow of protective gas flows. . The mold charge magazine is then hermetically sealed and held in a heated thermostat to carry out the final polymerization.

An advantage of the above method is that the arrangement of the molds in the magazine is well suited for semi-automated processing in the subsequent inspection and measurement steps.

Another advantage of this method is that the prepolymerized lens is encapsulated in a relatively small space between the closely-fitting molds, reducing evaporation of volatile components of the polymerizing mixture at elevated temperatures. That's true.

Another arrangement of this device is to place the prepolymerized lens-containing mold into
It consists in that the second stage can also be carried out continuously by pushing along a heated protective gas-filled tunnel.

Advancement of the mold takes place either by stepwise movement in heated tracks or by the smooth movement of a conveyor belt. This method is only used if the second mounting stage does not require an extremely long heating period. Otherwise, the length required to advance the mold train becomes too large and the equipment monitoring and maintenance requirements become high.

As an example of a slowly polymerizing monomer mixture, it is possible to use a mixture containing vinylpyrrolidone as the main monomer, as well as small amounts of hydrophobic monomers, such as for example butyl methacrylate, allyl methacrylate, allyl methacrylate oligomers, etc. . When mixtures of these monomers are added to the powder with non-polymerizable mixtures and almost completely polymerized in the presence of a photocatalyst, these mixtures can be exposed to effective radiation for 1 hour, even in the presence of the most effective photocatalysts. or more exposure. Therefore,
The capacity of the expensive equipment for continuous centrifugal casting is very low, with only 5 to 20 cast lenses per hour being released into the irradiation zone from a machine with 5 to 20 rotating molds. Only. However, if the mixture has already transformed into a non-flowing gel, 3 to 5 minutes may be sufficient to polymerize 3 to 5 lenses under the same polymerization conditions; One hundred molds can be passed through the photopolymerization device in the course of one hour, and in the final stage, the following operations as described above can lead to an entirely polymerized lens with minimal production costs.

The invention is explained in more detail by means of an example: Example In a conventional apparatus for continuous spin casting of contact lenses using photoinitiated polymerization, 100 parts by volume of hydroxyethyl methacrylate (HEMA), 0.3 parts by volume of ethylene dimethacrylate were added. Part by volume, 10q6 aqueous solution of ammonium persulfate 0
．． Monomer mixture 25 consisting of 2 parts by volume, 0.4 parts by volume of benzoin ethyl ether and 15 parts by volume of glycerol.
A mold (sagittal depth 3.5 mm, sharp edge diameter 13 mm and center radius 8.33 mm) containing μl was loaded. The rate of passage of the mold through the spin casting apparatus at room temperature is determined by the rate of passage of the mold (38
The speed was kept constant such that the irradiation (5 revolutions/min) required 30-50 seconds. The mold leaving the rotating region of the sl-'/casting chamber is incompletely polymerized but already contains sufficiently crosslinked monomers that gravity does not change the shape of the contact lens. The molds collected in boxes (each containing about 1,000 molds) were kept at a temperature of 65-70° C. for 10-20 hours under a pure nitrogen atmosphere. Polymerization proceeded under these conditions and complete conversion occurred. Soak in water as usual.

The lens was removed from the mold, examined, and then stored in a physiological solution.

This arrangement allows expensive and sophisticated spin casting equipment to be used 5 to 10 times more efficiently than with conventional photopolymerization alone. When using only well-known photopolymerization,
Several times longer irradiation times were required in the rotating region for complete conversion.

(5 other people)

Claims (1)

[Claims] 1) In a method for polymerizing a monomer mixture in the manufacture of contact lenses by centrifugal casting, a photopolymerization catalyst whose catalytic effect is induced by irradiation at room temperature, and a photopolymerization catalyst whose catalytic effect is induced by elevated temperature. A thermal polymerization catalyst is added to the monomer mixture, and the monomer mixture is then exposed to light in a constantly rotating mold at room temperature until it reaches a gel state, and then exposed to light at 50-100°C without rotating the gel-containing mold. A method consisting of heating at a temperature until complete polymerization conversion is achieved. 2) The method according to claim 1, wherein the photocatalyst is an alkyl ether of benzoin (alkyl is methyl, ethyl, isopropyl, n-butyl or sec-butyl). 3) The method according to claim 1, wherein the photocatalyst is 2,2-diethoxyacetophenone. 4) The method according to claim 1, wherein the thermal polymerization catalyst is a peroxide type catalyst. 5) The method of claim 4, wherein the peroxide type catalyst is selected from the group consisting of diisopropyl peroxocarbonate, ammonium persulfate and dibenzoyl peroxide. 6) The method according to claim 1, wherein the thermal polymerization catalyst is selected from unstable azo compounds. 7) The method according to claim 6, wherein the thermal polymerization catalyst is azobisisobutyronitrile. 8) The method according to claim 1, wherein the photopolymerization catalyst is added in an amount of 0.05 to 5% by weight. 9) The method according to claim 1, wherein the thermal polymerization catalyst is added in an amount of 0.05 to 5% by weight.