CS254383B1 - A method for the preparation of prefabricates for the production of contact lenses by mechanical treatment - Google Patents

Abstract

Method for preparing preforms for the production of contact lenses by mechanical processing of the polymerization of a monomer mixture in the presence of radical initiators, in which the monomer mixture is polymerized in the presence of a water-miscible solvent and the obtained preform is subjected to swelling extraction in the swollen state.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the preparation of prefabricated elements for the manufacture of contact lenses by mechanical treatment of conventional and multivalent materials. The term prefabricated material means a xerogel cast both in the form of buttons and in the form of contact lenses produced in closed molds by the cast molding method and the like.

Contact lenses, as is known, are nowadays mainly produced in two ways. The centrifugal casting method produces lenses directly in the swollen state (cf. latents no. 108 895, 116 260) by polymerizing the monomer mixture in a rotating form in the presence of a solvent.

The second method uses the classical method of machining xerogel prefabricated elements (buttons) prepared by radical polymerization resp. copolymerization of vinylic hydrophilic monomers in the absence of a solvent. The precast prepared in this way can be further machined and polished only if the glass transition temperature Tg of the material is sufficiently high so that the surface to be machined is in the glass state for the entire machining time.

This condition is not sufficiently fulfilled for multicellular copolymers whose more hydrophilic comonomers have a Tg lower than the temperature in the machined layer of the precast. For example, a crosslinked copolymer of monoethylene glycol monomethacrylate with diethylene glycol monomethacrylate from 55 wt. % water after swelling is no longer mechanically workable into an optically matching contact lens.

Another disadvantage of the present process is the slow polymerization rate in the high conversions of the polymerization system. In this way, most of the prefabricated products thus prepared contain residues of monomers and oligomers which are washed away from the equilibrium swollen contact lens. As a result, there is a loss of material from the finished product and hence changes in the swollen contact lens parameters due to deformations in the base curves. These defects are particularly noticeable in such polymer systems where two or more vinyl monomers having copolymers having unsuitable copolymerization parameters are copolymerized so that up to 20% of the solubles can be determined in the final xerogel block by sol-gel analysis, which in some cases are clearly shown as homopolymers of individual poorly copolymerizing monomers. However, each percent of monomeric and low molecular weight fractions in such a block decreases the glass transition temperature Tg by about 6 ° C, which makes or precludes mechanical machining of the precast products.

The above disadvantages are eliminated by a process for the preparation of prefabricated parts for the production of contact lenses by mechanical treatment of polymerization of the monomer mixture in the presence of free radical initiators, in which the monomer mixture is polymerized . As the water-miscible solvent, glycerin, water, glycols and derivatives thereof, aliphatic alcohols containing 1 to 7 carbon atoms, dimethylformamide, dimethylsulfoxide, dimethylacetamide, diacetine or mixtures thereof and the like are preferably used.

The solvent is preferably added to the polymerization mixture in an amount of up to 60% by weight, preferably 20 to 30% by weight. The swelling agent may be water, aliphatic alcohols containing 1 to 7 carbon atoms, dimethylsulfoxide, dimethylformamide, glyderin, etc. The extraction may preferably be carried out at elevated temperature, preferably near the boiling point of the swelling agent used. The extraction is preferably carried out successively with different swelling agents. The prefabricated material is thereby freed of any polymerization solvent from the remainder of the monomers, oligomers or homopolymers of one or more of the poorly copolymerizing copolymers.

The drying can advantageously be carried out by transferring the swollen prefabricated product to an oven where, in an atmosphere of superheated steam of water or a hydrophilic shoe, above the Tg of the respective copolymer, preferably in the range of 102-180 ° C, optionally in the presence of air or inert gas to constant weight, cooled, eventually dried again to constant weight, transferred to a desiccator, where it is stored above the desiccant until processing into a contact lens.

The advantage of this process is that not only allows the low molecular weight components to be washed thoroughly as described above, compared to the method used to prepare prefabricated parts for contact lenses from different types of xerogels, but also provides a more structured internal cross-link tension, which is retained during drying and after re-swelling of the contact lens produced from the thus-prepared xerogels due to the arrangement of the cross-linking structure, a network is obtained. without internal voltage, which is evident in polarized light. This process also ensures a high conversion of polymerizing components over time compared to the preparation of solvent-free xerogel materials.

The advantage of drying the swollen prefabricates in superheated steam is that the polymerization solvent is discharged from the three-dimensional structure under conditions of perfect mobility of the polymer chains and their side segments (i.e., above the Tg of the gel). maintaining the external dimensions and angles of the dried prefabricate relative to the swollen at a given initial composition of the polymerization mixture.

However, it is also possible to dry the swollen prefabricates freely in air under laboratory conditions, followed by drying to constant weight (dehumidification), preferably again in superheated steam. This method is economically demanding, but time consuming.

The prefabricated elements are perfectly relaxed, free of all unwanted water or water. alcohol-soluble fractions and ready to be machined into contact lenses. That is, as stated above, with each percent of washed solubles (low molecular weight and uncrosslinked homopolymers), the Tg of the xerogels increases by about 6 ° C, resulting in improved machining properties and polishing of the material. The process according to the invention ensures that the finished contact lens of the thus prepared precasts is free of any material loss after prolonged extraction with water or alcohol and hence also without any changes in the optical parameters. The relationship between the parameters of the prefabricated xerogel replica and the prefabricated prefabricate clearly implies that by swelling the xerogel replica all dimensions are increased by the same factor.

In the following, the invention is illustrated in more detail by means of exemplary embodiments.

He did

80% wt. % Of 2-hydroxyethyl methacrylate containing 0.4 wt. % ethylene glycol dimethacrylate and 20 wt. glycerin was polymerized in the presence of 0.1 wt. of diisopropyl percarbonate at 60 ° C for 16 hours in the casting mold on the buttons. After this time, the prefabricated product was transferred to a wash liquor (also in soxlet extractors) where it was washed with distilled water at 60 ° C until its swollen weight did not increase further (while checking the last extractions of the UV extractant) spectroscopy). The swollen gel prefabricated product was then transferred to a 135 ° C oven containing a porous ceramic plate soaked with 50 ml of distilled water.

This created an atmosphere enriched with preheated steam in the oven. The precast was dried to constant weight. From this perfectly dried xerogel prefabricated, a contact lens with an optical power of - 5.5 D, a diameter of 14.4 mm, a center radius of 8.70 and a center thickness of 0.20 mm was made in a swollen state.

Example 2

The precast prepared and washed with water according to Example 1 was placed in a thermostatically controlled drying cabinet at a temperature of 165 ° C, into which a stream was fed to the same temperature of superheated steam produced in the evaporator. This created an atmosphere of pure superheated steam.

The result after complete drying of the precast was the same as in Example 1.

Example 3

The procedure was as in Example 1 except that the steam was generated by an excess amount of ethanol. The result was as successful as in the previous examples.

Attaches% wt. % blend of 80 wt. % diethylene glycol methacrylate and 20 wt. % Of 2-hydroxyethyl methacrylate containing 0.2 wt. % ethylene glycol dimethyl acrylate and 0.4 wt. of diethylene glycol dimethacrylate was mixed with 20% by weight of glycerin. This mixture was polymerized in the presence of 0.1% by weight of diisopropyl percarbonate at 60 ° C for 16 hours in a casting mold on buttons.

After this time, the precast product obtained was transferred to a washing bath and further processed according to Example 1 with the same result.

Example 5

The precast prepared according to Example 4 was transferred to a wash liquor where it was washed with distilled water at 60 ° C until its swelling weight did not increase further (while checking the last extractions of the extractant by UV spectroscopy). The swollen gel prefabricated product was then left to air under laboratory conditions and dried to constant weight for a long time. It was then briefly transferred to a 135 ° C oven containing a porous ceramic plate, soaked with 50 ml of distilled water. This created an atmosphere enriched in the oven enriched with superheated steam. The prefabricate was thus dehumidified - dried to constant weight. A contact lens with an optical power of 5.5 D, a diameter of 14.4 mm, a center radius of 8.70 and a center thickness of 0.20 mm in a swollen state was produced from this xerogel precast.

Claims (7)

SUBJECT OF THE INVENTION Process for the preparation of prefabricated parts for the production of contact lenses by mechanical treatment of polymerization of a monomer mixture in the presence of free-radical initiators, characterized in that the monomer mixture is polymerized in the presence of a water-miscible solvent and subjected to swollen product. 2. The process of claim 1 wherein the water-miscible solvent is glycerin, water, glycols and derivatives thereof, aliphatic alcohols containing 1 to 7 carbon atoms, dimethylformamide, dimethylsulfoxide, dimethylacetamide, diaoetin, isopropanol, or mixtures thereof. 3. The process according to claim 1, wherein the water-miscible solvent is added to the polymerization mixture in an amount of up to 60% by weight. 4. The process of claims 1 to 3 wherein the swelling agent is water, aliphatic alcohols containing 1 to 7 carbon atoms, dimethylsulfoxide, dimethylformamide and glycerin. 5. Process according to claims 1 to 4, characterized in that the extraction is carried out at an elevated temperature, preferably at a temperature close to the boiling point of the swelling agent used. 6. The process of claim 1, wherein the swollen precast product is heated above the glass transition temperature Tg of the respective copolymers in a swelling agent vapor atmosphere, optionally in the presence of air or an inert gas, after which it is cooled and dried. 7. A process as claimed in any one of claims 1 to 6, wherein the extraction is carried out successively with different swelling agents.