FR2561401A1 - PROCESS FOR THE POLYMERIZATION OF MIXTURES OF MONOMERS FOR THE PRODUCTION OF CONTACT LENSES BY CENTRIFUGAL MOLDING - Google Patents

Abstract

THE PROCESS CONSISTS OF SIMULTANEOUSLY CONFORMING AND PRE-POLYMERIZING THE MIXTURE OF MONOMERS BY PHOTOPOLYMERIZATION AT ROOM TEMPERATURE WHILE THE MIXTURE OF MONOMERS IS SUBJECT TO ROTATION, THEN, WITHOUT ROTATION, TO END THE POLYMERIZATION POLYMERIZATION BY TEMPERATURE POLYMERIZATION OF MONOMERS.

Description

The present invention relates to a polymerization process.

  sation of monomer mixtures for the production of

  contact lenses by centrifugal molding.

  The production of contact lenses by the centrifugal molding process, for example according to US Pat. Nos. 3,699,089, 3,408,429, 3,822,089 and 4,153,349, has been found to be highly effective, particularly in case the time required for the practically total polymerization of a mixture of monomers is very short, that is to say less than a few minutes. This is the case when it is a question of polymerizing mixtures of monomers containing methacrylic esters of glycols as basic components. However, the development of new materials with extraordinarily high permeability, in particular towards oxygen, has led to the use of certain types of polymers which are formed from particular monomers much slower to polymerize. to the point that some of them are only converted to a gel even after several hours. In this case, the productivity of continuous molding machines

  lowers because it is approximately inversely proportional

  tional to the duration of the polymerization. The advantage

  main of the centrifugal molding process is thus lost.

  The process according to the present invention allows a highly economical use of the centrifugal molding process for the production of contact lenses even with mixtures of slowly polymerizing monomers using the continuous molding equipment of the carousel or column type which has been employed so far for the production of pre-molds formed from mixtures of monomers

  pre-cured which contain a still substantial amount

  tial of unpolymerized monomer components, but which have the stabilized form of the final contact lens fixed by that of the mold after a preliminary crosslinking. These 3 pre-molds are exposed, in the following operation, and without undergoing rotation, to polymerization conditions

  for the time necessary to obtain a polymerization

  -2- full tion. In the first step, characterized by the rotation of the molds, photopolymerization according to the invention is used, that is to say that the polymerization is obtained by means of photocatalysts which become active under the effect of radiation, for example the diethoxy2,2 acetophenone or the alkyl ethers of benzoin, the term alkyl possibly being a methyl, ethyl, isopropyl, n-butyl, sec-butyl group, etc. while in the second

  stage, when the molds containing the photochemical mixture

  only pre-polymerized are at rest, thermal polymerization is used which is induced for example by

  presence of a peroxide catalyst (peroxocarbona-

  diisopropyl, ammonium persulfonate, dibenzoyl peroxide, etc.) or unstable azo compounds (azobisisobutyronitrile, etc.). The two types of catalysts, both for the first and for the second polymerization stages, are added simultaneously to the starting monomer mixture. The mixture of monomers is exposed to light in the mold in constant rotation at normal temperature until the mixture passes into the gel state then the mold containing the gel is heated without rotation to a temperature of 50 to 100 C until complete polymerization. The amount of photocatalyst is advantageously between 0.05% and 5% by weight. The amount of catalyst for thermal polymerization is preferably in the range from 0.05% to 5% by weight. The photocatalyst is decomposed and consumed for the most part during the photopolymerization, while the catalyst intended for thermal polymerization (second step) remains intact during the photopolymerization which takes place at a lower temperature. In special cases, a catalyst can be used which is capable of serving both as a photochemical and thermal catalyst in the context of radical polymerizations, for example the compounds

azo photochemically unstable.

  The implementation of the method can be done using equipment adapted in various ways. The simplest equipment consists of an arrangement in which the molds containing the prepolymerized mixture and leaving the continuous production apparatus of the carousel type or

  column, are dropped, after their respective inspection

  against a current of protective gas (for example nitrogen or pure carbon dioxide) in a container rinsed with the protective gas. This container, containing a large number (up to several thousand) of molds, is then hermetically sealed from air and placed in an enclosure heated to constant temperature where it is kept for the time necessary for polymerization. practically complete. The lenses are optionally removed from the molds and processed in the conventional manner. This simple procedure has been found to be particularly suitable for the production of large series of uniform type lenses which have been molded into identical molds assembled to undergo the second stage in

  large containers and which do not need to be sorted.

  Another equipment, in which the sequence of molds leaving the centrifugal molding apparatus is preserved during the completion of the polymerization consists in providing a mold discharge zone out of the apparatus where the molds which have just come pass into the radiation zone and which contain the already gelled prepolymer, periodically slide out of the rotating polymerization column by a slide located above an opening and fall through this opening into a tubular magazine placed under the opening and through which a moderate stream of protective gas is injected upwards. The loaded magazines are then hermetically closed from the air and kept in a thermostatic atmosphere to carry out the final polymerization. The arrangement of mussels in stores that

  best suited for partially automatic handling

  set for later stages of verification and measurement

  is that which is advantageously used according to the invention

tion.

256 140 1

  Another advantage of this process (de is Cpe. The ieuit i I 11 prepolymerized remains enclosed in a relatively small space between the molds as.s.-iijettis troit 'ei'nt and I': vai) ra'i tion of the components the volatile plums of the polymerization mixture are reduced to high temperature. Another possibility of equipment consists in also carrying out the second continuous step by forcing the halves containing the pre-polymerized lenses along a heated tunnel filled with protective gas. The advance of the molds is obtained either by a stepwise movement on a heated track, or by a gentle movement of a conveyor. This

  process can only be used if the second polymer

  sation does not require extemely long heating periods. Otherwise, the length needed for the row: t of moving molds would become too large for putlvo it

be monitored and maintained.

  As an example of slowly polymerizing monomers which can be used in such mixtures and which contain vinylpyrrolidone as the main component with a

  addition of a minor amount of hydrophobic monomers.

  there may be mentioned, for example, butyl methacrylate. allyl methacrylate, allyl methacrylate oligomers, etc. If mixtures of these monomers, in

  particular with the addition of an unpolymerized solvent;

  have to be practically polymerized

  complete in the presence of the most efficient photocatalysts

  these, their exposure to effective radiation takes an hour or more. Consequently, the capacity of the expensive apparatus for continuous centrifugal molding would be very low since only 5 to 20 molded lenses could be produced per hour or even less using the apparatus with 5. 20

  molds being rotated in the radiation area.

  On the other hand, it only takes three to five minutes under the same polymerization conditions to achieve the

  conversion from 3 to 10, when the mixture is d (ja.

  transformed into non-fluid gel, so that we can

  pass up to p) several hundred molds containing

  each a lens pre-polymerized through the photopolymerization apparatus for one hour and that they are brought to the final state of fully polymerized lenses in the subsequent operation described above, with the minimum production costs. The invention is described below with more

  details by reference. the following example.

Example.

  The conventional apparatus for continuous rotary molding of contact lenses using photopolymerization is loaded with cells having a sagittal depth of 3.5 mm, an external diameter of 13 mm and a radius in the center of 8.3 mm containing 25 microliters of mixture of monomers formed by parts by volume of hydroxyethyl methacrylate (HEMA), 0.3 parts by volume of ethylene dimethacrylate, 0.2 parts of a 10% aqueous solution of ammonium persulfate, 0.4 parts of benzoin ethyl ether and 15 parts of glycerol. The passage of the molds at room temperature through the rotary molding apparatus was maintained at a constant speed so that the exposure of the rotary molds (385 revolutions per minute) in the area illuminated by ultraviolet light take 30 to 50 seconds. The molds leaving the rotary zone of the rotary molding machine contain a gel of partially polymerized monomers but already sufficiently crosslinked, the shape of contact lens remains stable despite the gravity, The molds collected in enclosures under atmosphere of pure nitrogen in each containing about 1 mi] lier, are stored for 10 to 20 hours at a temperature between 65 and 70 C. Under these conditions, the polymerization is brought to an end. The lenses are then separated from the mold as usual by swelling in water and stored after inspection in a physiological solution. 31i. Using this arrangement, expensive and complicated centrifugal molding equipment is operated with an efficiency 5 to 10 times greater than that obtained with the well-known photopolymerization processes when used until complete polymerization, which request a

  much longer residence time in the rotation area.

-7-

Claims (7)

  1- Process for the polymerization of a mixture of monomers for the production of contact lenses by centrifugal molding, characterized in that a polymerization photocatalyst which is activated by radiation at ambient temperature, and a polymerization catalyst   thermal, which is activated by an increase in temperature   re, are added to the mixture of monomers, said mixture then being exposed to light in a rotating mold con.-taimenL.at room temperature until a gel is obtained after which the mold containing the gel is heated without rotation to a temperature of 50 to 100 C until a total polymerization.   2- A method according to claim 1, characterized in that the photocatalyst is a benzoin alkyl ether in which the term alkyl represents a methyl group,   ethyl, isopropyl, n-butyl, sec-butyl.   3- A method according to claim 1, characterized in that   that said photocatalyst is 2,2-diethoxy acetophenone.   4- A method according to claim 1, characterized in that said thermal polymerization catalyst is a peroxide catalyst.   - Method according to claim 4, characterized in that said peroxide type catalyst is selected from the group comprising diisopropyl peroxocarbonate,   ammonium persulfate and dibenzoyl peroxide.   6- A method according to claim 1, characterized in that said thermal polymerization catalyst is chosen among the unstable azo compounds.   7- A method according to claim 6, characterized in that said thermal polymerization catalyst is azobisisobutyronitrile. Method according to claim 1, characterized in that said photocatalyst is added in an amount of approximately 0.05 to 5% by weight.   9- Process according to claim 1, characterized in that said thermal polymerization catalyst is added   from 0.05% to 5% by weight.