IE48438B1 - A process for producing lenses or other optical means - Google Patents

Abstract

Lenses made of synthetic resins are made by casting a catalyzed monomer which is polymerized up to the hardening point by warming it within a mold formed from two or more glass lenses, assembled together by means of a perimetric gasket and a spring, wherein the shrinkage of the polymer being formed is compensated through catalyzed monomer kept in presence of air outside of the mold, from where it may flow into the interior of the mold in which there is no air. The monomer may be diethylene- glycol-bis-alkyl-carbonate.

Description

The present invention relates to a process for the production of lenses and other optical means from a polymerizable synthetic resin, through a continuous compensation casting.

In the last few decades the technological world has been paying considerable attention to research seeking molding methods based on the mold polymerization of one or more monomers, likely to produce solids having certain special characteristics.

The optical industry in particular has sought to produce lenses or other optical means by such a method: in practice, the various technologies aim at overcoming the disadvantages of the phenomena occurring during the polymerization process, in particular by studying the physical and chemical characteristics of the product with reference to the theoretically optimal polymer; the physical and chemical characteristics of the product with reference to the polymer obtained; and the shape of the product.

These technologies have been directed, in particular, towards the casting of thermosetting polymers, as the latter offer physical and chemical characteristics and other advantages better suited, when used as optical means, for instance lenses, than thermoplastic polymers. By now diethyleneglycol-bis-allylcarbonate (and its copolymers) having the formula: ch2 - ch2-o~co-o-ch2-ch =ch2 •ch2 - ch2- o-co-o-ch2-ch=ch2 better known under the trademark CR - 39 have entered into general use. The latter, with the addition of a catalyzer (or rather, of a free-radicals starter) polymerizes to an homopolymer or to a copolymer.

The preferred starter is the isopropyl-dicarbonateperoxide having the formula: CH.

CH-O-CO-O-O-CO-O-CH CH.

CH, known as I.P.P. The latter, in fact allows polymerization to take place at a lower temperature and within a shorter time than benzoyl-peroxide or other peroxides, which may also be used. In practice, known casting ..-.-- :.3d« for .ra-i.v 2 'srs cf C/--32 5? its copclyaers : . : .is :;v :rtro- j: / ::: of one cr sore ceti'yzsc ;; rrs, «·;·.·;-? in '/ /! itv;5 tr y’-spt’ytQ: ttc ·. ·:/; J.·-.·-.. -sa,·:'.' f.V3 gltSI ’2.3 2Ss i -, -:--. - - :.-- ' :vic:;j-id '.;o: si & lie-.-.. ·-·;·· ct’er b, :. jatt'c-i icacer :- The , · . -- . · s'.ti the -- -a..· .cr.c--.-s in order tc cctcii· a satisfactory :--. ?·. t-e ·:- .-v; ss paration; to ths same end it may .-: ac: a -.1/ difcvsb!3. Ths catalyzed sioncmer, intro:,ci2 as a fluid info ::: mold thus formed,solidifies the eno of a heating cycle, producing a strong c-vee dimensional sr-icksj-s (1-1% in the case of the CP. - 39 hofflopolyffis r), Thus a further function of the spring is continuously t0 squeeze the spacer gasket separating the lenses for «lag tlie «eld, until the fluid reaches the interraaciate al state, to avoid ths leakage cf fluid monomer from -.,: e mold. On the other hand, after t-.e gel phase has oeer rsacnsd, the pressure of the ;; spring.stresses the tharwonlastic or the spacer gasket to facilitate ere adnerenc’ of the mould to the polymer. Such a ε+res? say be considered as a squeezing of the spacer or as an expansion of ths gasket.

The adherence of tbs aide tc the polymer is required to avoid possible breakag-; of ths polymer or of the mold due to the strteg csv, ions which occur when the polymer shrinks, and to avoid, at least on the usable surface of the polymer, the introduction of air bubbles which, by hindering the polymerization would cause irreparable damage to the product.

Lenses thus obtained, made of CR-39 or its copolymers, typically have faulty perimeters,due to air bubbles. Air leakages, even after the gel phase has ended, may cause air bubbles and cavities, or the formation of a soft perimetral region in the polymer, or a possible chemical reaction between the gasket material and the catalyzed monomer. A feature common to all processes, however, is an appreciable reduction in the diameter of a lens made of CR-39 and its copolymers, with respect to the diameter of the lenses forming the mold. This is due to the following reasons: (A) the diameter of the internal mold cavity is reduced by the space occupied by the sealing spacer gasket.

(B) the three dimensional shrinkage of the polymer also involves the perimeter region, thus further reducing the diameter of the product,particularly in the case of negative or diverging lenses.

(C) possible faults at the perimeter (air bubbles 8 4 3 8 air suctions and a region of soft polymer) equally reduce the usable diameter by the affected depth.

These faults generally occur in the perimeter region 5 because it is generally preferred to position the molds with their concave side uppermost; positioning the molds with their convex side uppermost would give rise to the same faults at the centre of the lenses, thus making them worthless. Concavity and convexity of the mould are referred to the shape of the lens formed thereby.

After the sealing spacer gasket has been removed the opening of the mold is carried out by introducing a wedge into the slot previously occupied by the spacer, and using it as a lever between the two glass lenses, which normally adhere to the polymer. The polymeric lens thus extracted is complete, so far as the surfaces are concerned, but strongly stressed due to the shrinkage. Toachieve stress relief the lens has then to be submitted to a heat treatment.

This treatment, or stress relieving, is currently applied to all molded plastics materials, to glass, and to metals. The duration of the treatment, to obtain the desired effect, depends upon the temperature, related to the state of stress existing in the product and to the degree of polymerization of the polymer.

The above discussion aims to provide preliminary information on the prior art related to the polymerization process. It is a summary of experimental researches, carried out by the author,and of documents deriving from patents. Among the latter the following are mentioned: US-PS2.403.112/US-PS2.464.062/US-PS 3.171.869/US-PS3.038.21O/US-PS 2.964.501/FR-PS2.171.073/FR-PS 1.541.889/FR-PS1.204.627/FR-PS 1.462.519DE.-PS1.062.003/GB-PS 1.402.573 The present invention takes into consideration the numerous disadvantages of a technical and/or of an economical nature, which occur in the production of lenses or other optical menas made of plastics such as CR-39 and its copolymers. The present invention seeks to solve the problem of producing lenses or other optical means from plastics such as CR -39 and its copolymers. In arriving at the present invention consideration has been given to the following 8 4 3 8 aspects: a) the chemical basic preparation of the components; b) the ways and the means of polymerization; c c) the shape of the articles,obtainable without □ any reduction in size; d) the possible unification of the polymerization cycles for all given thicknesses; e) the obtaining of a polymer foreseen according , to special absorption and transmission requirements of the electro-magnetic energy.

In the following,it is to be understood that any monomer referred to could be replaced by a copolymer of the same, with any catalyzers or starters likely to ., be used, when the same reasoning,methods and devices ι ϋ are applied to solve the same problems or to attain the same aims, and when the same results are obtained, even if only partially.

According to one aspect of the present invention 20 a process for producing lenses or other optical means from a thermosetting plastics material comprises the steps of forming a tubular sleeve of substantially indeformable plastics material which is chemically compatible with the monomer and stable at the temperature of polymerization,positioning mold halves within the said sleeve at the required distance from each other so that they define, together with the lateral wall of the sleeve, a cavity having a diameter equal to that of the mold halves, the position of each mold half within the sleeve being maintained only by frictional contact between the rim of the mold half and the wall of the sleeve, introducing into the mold cavity a catalyzed thermosetting monomer to fill the said mold cavity and partly fill a compensation reservoir in communication therewith, submitting the said mold to homogeneous heating whereby to polymerise the monomer which undergoes an initial expansion and contraction stage followed by gelling with an associated shrinkage and subsequent hardening, the said compensation reservoir permitting a flow of the monomer out from and then back into the mold during the initial expansion and contraction stages prior to gelling, and the frictional engagement of the mold halves in the tubular sleeve permitting relative approach of these mold halves when the shrinkage associated with gelling takes place; and subsequently removing the sleeve and the mold halves from the lens thus formed when polymerisation of the monomer has been completed.

According to another aspect the present invention provides molding apparatus for producing lenses or other optical means from a thermosetting plastics material, comprising a tubular sleeve of substantially 8 J 3 8 indeformable plastics material which is stable at the temperature of polymerisation of the said thermosetting plastics material, and at least two mold halves shaped to fit into the said sleeve with a frictional engagement sufficient to retain the mold halves in position against the forces exerted by dimensional changes in the thermosetting plastics material before it has gelled,and to allow the mold halves to move within the sleeve under the action of forces exerted by dimensional changes in the thermosetting plastics material after the gel stage has been reached, and a reservoir for the thermosetting plastics material, which reservoir communicates with the mold cavity between the said two mold halves in the said sleeve.

Diethyleneglycol-bis-allyl-carbonate, or CR-39 is available on the market at a high purity grade i.e. about 99.150%. Gas chromatographic analysis indicates the presence of allyl-carbonate and of a not well identified substance (Fig.1) During the column separation performed on occasion of the above mentioned analysis, it was established that the impurities are more volatile,that is they have shorter retention times than the monomer. A series of experiments was then carried out to eliminate the impurities and the following was discovered: - the allyl carbonate is eliminated when the E monomer is heated to a temperature of 50-90°C; - this elimination is possibly due to a partial polymerization of the allyl carbonate as may be analytically determined by observing the area referring to the above-mentioned unidentified product; - the latter may,as a consequence, be considered as a polymer of the allyl carbonate.

The above was confirmed during the heating of the monomer, carried out deliberately for a longer time, at a temperature of 90°C,in static tanks. As the elimination of the allyl carbonate was partially suppressed, due to the tanks staticity, the analysis of the monomer revealed an appreciable increase of the polymer, caused by the allyl carbonate. These facts having been ascertained, a purifying system of the monomer was set up, as indicated in following example: EXAMPLE No.l The monomer CR-39 was gradua11v warmed up, at 8 J '3 ϋ Lerilpe id Iu i\.: ill . l· t; f'dfljjc of CH/ Ήι Ϊ. filt: ρ a « L1 a I C H Jill li d t i on v t the d I i y I tdi Luui ΰ c4>Lu hit-J at all the above mentioned tempeiatmes uas obviously related to the ratio;» of the tins·-» the i LinpefUtut e and tj the q lldii t i I treated. lil practice at a lower tempo ra tin o , d h/iiyar durutlui» Gf the operation was required; whereas at a hijhfei temperature the treatment was uOmpletcd id j sibiui· it duration, inns, fcr example , wi th : ------Quantity litre; ot the treated fliunijiiier Ch . 1 Average tempera!Ute /U°L I ttt α ί. ί tUa pur ί ud tmr hours t the warming up t ί mu and ί l.u l ΐ bid the gradua1 cooling down to r U U Iti t. ci fll p g l d I h « U . - - Strength of the monomer, before treatment: 59,158 (Fig -1) — -Strength uf Lhe iiiGnOmer s of t.cf treat men t: y9,484(Fig. 4)- li y i ii G ill*, ii Mia ? . « b 1 J , 1 . ί Ctilp’- t ι. I U « «i 3 bG yGbo> iindfci a*.tive el j i r h»9 tn fluid and a u Ce ί ¢. t ci t c tho a IΊ iii f lb t I u»i U, q» *· d 1«4 I 1. g - ΐ in the ranye of homogenize the of allyl carbonate, the latter was partially eliminated in accordance with the ratio of the time, the temperature and the quantity treated (as in example No.l). Thus for instance: -Quantity of the treated monomer CR-39:1 litre; -Average temperature: 70°C for a time period of four hours + the warming up time and the time for gradual cooling down to room temperature; -Strength of the monomer before treatment: 99,158 (Fig.l.).

•Strength of the monomer after treatment 99.713 (Fig.3).

Example No.3 By heating the monomer CR-39, according to the conditions described in Example No.l, but carrying out the operations under vacuum, we obtained: -Quantity of the treated monomer CR-39: 1 litre; -Average temperature: 70°C for 4 hours + the warming up time and the time of the gradual cooling down to room temperature; -Strength of the monomer before treatment 99,158(Fig.1) -Strength of the monomer after treatment: 99,686.(Fig.4) & 4 3 is EXAMFlE No.4 3/ heating the monomer CR-39, according to the conditions described in the Example No.2, but zarrying out the operation under vacuum conditions, va obtained; _____Quantity of the treated monomer CR-39:1 litre ----Average temperature: 70°C for 4 hours + the warming up time and the time of the gradual cooling down to room temperature; — Strength of the monomer, before treatment: 59,158 (Fig.l) _____Strength of the monomer after treatment: 1030( Fig.5) EXAMPLE No.5 By heating of the monomer according to the ,- conditions described in the Examples Mo.1,2,3 and the total dehydration of the monomer,was also obtained. Spectrophotometric analysis in the visible spectrum ?rom 400 to 700 nm. give for the thus purified monomer 1R-39, outstanding linearity and transmission.

, STARTER As a generally accepted rule isopropyldicarbonateperoxide, Known under the commercial name of Ϊ.Ρ.Ρ. , is added to the monomer CR-39, in a percentage of 3%. This percentage has been adopted in all processes, tnough a higher or a lower percentage may be adopted, for special purpose.

Even if commercial I.P.P. may be considered as pure, being an industrial product which is difficult to synthesize and handle.it contains in practice spurs of water and free chlorine ions.

The above may be observed from an infrared spectrophotometric analysis (Fig.6). To start a series of tests aiming at ascertaining the influence of the chlorine ions on the polymerization,within the framework of the present invention,isopropyldicarbonate-peroxide was synthesized by reaction between sodium peroxide and isopropyl-chloroformiate (previously purified up to 99,99%). The product obtained was used, after 1,2,3,4,5 water Teachings. Each leaching produced an appreciable reduction of the chlorine ions. By polymerizing the monomer CR -39, with the addition of 3% of isopropyl-dicarbonate-peroxide (obtained from the abovementioned repetitive Teachings) with a gradual heating cycle of 15 hours from +40°C to +110°C,we obtained: _ after 1 leaching only: a frankly yellow polymer __after 2 leachings: a yellow polymer; —- after 3 Teachings: a pale yellow polymer: 8-138 _after 4 leacbings: a straw-yel 1 ow polymer; _after 5 leachings: a colourless polymer.

It was thus ascertained that the yellowing of the oolymer is due to the content of chlorine ions.

On the other hand when leaching the isopropyidicarbonate-peroxide with water we separated a lighter fraction of the same product partially degraded due to deoxygenation.

To obtain an isopropyl-dicarbonate-peroxide with the highest grade of purity from free chlorine ions and degraded deoxygenated fractions,we followed the following sequence of operations.

EXAMPLE No.6 In a bain-marie, cooled to +9°C we melted 100 gr. of commercial I.P.P. having a melting point of fusion of +8°C. We added HgO cooled to +9°C,in which some drops of pyridin had been dissolved.

After stirring and decanting, the phases were separated. 2.' We then washed twice, with Hg9 isopropyl48438 dicarbonate-peroxide and carefully separated,together with the water, the lighter fraction of the isopropyldicarbonate-peroxidejcorresponding to the partially degraded or deoxygenated product. At this point a purified I.P.P. had been obtained (Fig.7) EXAMPLE No.7 When the I.P.P. purified according to the above described method (Example No.6) was frozen again and afterwards brought to melting,we observed a melting point of +9°C (instead of +8°C of the starting material) EXAMPLE No.8 Two test samples were prepared with the same CR-39 monomer, catalyzed under the same polymerization conditions, but respectively, with the addition of 3% of _Commercial I.P.P.; and _I.P.P.purified according to the method described in Example No.6 above; this showed the following differences,at 53°C, after 4 hours of gradual induced heating from 40°: _in the test sample containing commercial I.P.P. the monomer was present in the polymer in a percentage of 52%; and — ir. the test sample containing I.P.P., purified according to the described method, the monomer was present in the polymer, in percentage of 34%.

In ether words, the use of purified I.P.P. {as compared with that of commercial I.P.P.) causes a higher catalytic activity, likely to allow a given polymeric value to be obtai ned wi th: -- reduced percentages of the starter, -- shorter reaction times, and -- lower temperatures.

Furthermore, the test sample, obtained from purified I.P.P. was perfectly colourless.

ADDITIVES -The addition to the monomers of additives which absorb U.V. radiation allow the protection of polymers from degradation caused by the said radiation.

As the U.V. absorbers are not easily soluble, the following drawbacks may be observed in the polymer according to the quality and quantity of the absorber used: 2o - optical distortion (diffraction and dispersion) due to the unsatisfactory distribution of the absorbers, within the monomer; --yellow,green yellow, orange yellow colour of the product; -transmission interference in the visible electromagnetic spectrum.

With reference to the present invention we selected as absorber the 2-(2-hydroxy-5-methylphenyl) benzotriazole.

To establish the optimal quantity of the said U.V. absorber to be added to the monomer CR-39, with respect to the interferences likely to be caused in the polymer by such addition, so far as the transmission of the visible light is concerned, and the solution methods T0 the following operation were performed.

EXAMPLE No.9 We obtained a highly satisfactory solution and distribution of 2-(2-hydroxy-5-methyl-phenyl) benzotriazole, in the percentage of 0,0125% in the T5 purified monomer CR-39 (or catalyzed with I.P.P.) by inducing to the containers! trasonic frequencies in the range of 20 -70 «Hertz. The selected percentage of 0,0125% of 2-(2-hydroxy-5-methyl-phenyl) benzotriazole caused in the polymer CR-39, on test samples of 4mm of thickness, a good U.V. absorption and an almost linear transmission in the visible field (Fig.8).

Example 10 with the use of ultrasonics we obtained a perfect solution and distribution of 2(2-hydroxy-5-methyl-pheny1) benzotriazole in the monomer CR-39, both pure or catalyzed with I.P.P., „ in the selected percentage of 0,0100%. The latter percentage of additive gave rise to polymer spectra close to what has seen described in Example No.9 on test samples of 6mm of thi ckness.

Example No.11 κ With the use of ultrasonics, it was possible to obtain a perfect solution and distribution of 2(2-hydroxy-5mechyl-pheny1) benzotriazole , in the monomer CR-39, both pure or catalysed with I.P.P., in the selected percentage of 0,0150%. This percentage of addition gave rise to /5' spectra in the polymer which were close to those described in Example No.9, on test samples of 2 mm in thickness.

Example No.12 With the use of ultrasonics it was possible to obtain a perfect solution and distribution of a very high percentage of 2-(2-hydroxy-5-methyl-phenyl) benzotriazole with respect to those described in the Examples No.9,10,and 11 above, both in the pure monomer or catalyzed with I.P.P. or with benzoylperoxide. It was thus possible to obtain the preparation of easily tested concentrates, which later on were diluted in the desired percentage, in large quantities of pure or catalyzed monomer.

EXAMPLE No.13 CATALYSIS _Under mechanical stirring we mixed: -CR 39 monomer, purified and dehydrated as indicated in examples Nos.1,2,3, and 4 with -3% of I.P.P. purified as in Example No.6 above and -0,0125% of 2-(2-hydroxy-5-methyl-phenyl) benzotriazole, as in Examples Nos.9 and 12 above, the whole being filtered,under decompression.

EXAMPLE No.14 Using ultrasonic induction a quantity of CR-39 monomer, purified and dehydrated as indicated in Examples Nos.1,2,3, and 4 above was mixed with 3% of I.P.P. purified as in Example No.6 above,and 0.0125% of 2-(2-hydroxy-5-methyl-phenyl) benzotriazole, as in Examples Nos.9 and 12 above, the while being filtered under decompression. (38 EXAMPLE (io.15 With CR-39 monomer, catalyzed and with the addition of additive, as indicated in the Examples (ios.13 and 14 above, and submitted to a polymerization heating cycle we obtained practically colourless transparent polymers. The latter, in comparison with polymers obtained with current preparation techniques, had a quicker and more uniform polymerization cycle, with reference to the reactive saturation within a time X,for iq heating cycles V and thickness T. Furthermore,these polymers snowed outstanding physicochemical charactersstics, as observed through thermal differential calorimetric analysis, and tests of chemical i nerti a. i5 It may be observed that the methods described in the examples above are an improvement or a variant of the techniques which have been used up to now, whereas the proportions of the components correspond to values which may be modified, even though foll2o owing the same techniques.

PRINCIPLE OF CONTINUOUS MOLDS COMPENSATION — The shrinkage of CR-39 polymer and its copolymers, causes— as a rule -the need for introducing devices.previously of an empirical nature,to compensate such shrinkage. Generally,to reduce shrinkage, polymerization has been carried out with variable heating cycles, according to the thickness of the polymer. Other devices relate to the ways of assembling the molds and/or to intermediate manipulations .

As a rule, with the increase in the thickness of the polymer the duration of the heating cycles was extended as much as possible; the molds filled with the catalyzed monomer were kent at a low temperature (about 40°C) for a long span of time,to slow down the speed of the reaction and to reduce as far as possible, the negative effects of the shrinkage of the polymers.

Within the framework of the present invention we found a satisfactory solution to the problem through a continuous molds compensation, wherein the cavities which occurred in previous techniques during the polymerization due to the shrinkage of the polymer are avoided. The above is possible as the CR-39 monomer, and its copolymers, with addition of peroxide or percarbonate as catalyzer, polymerize only partially and in any case very slowly, in the presence of air, and remain in a fluid state for a long time. 8 4 3 8 We assembled as follows, molds for the casting of optical lenses.

EXAMPLE No.16 Two or more glass lenses, were introduced into 5 a tubular sleeve of polyethylene (or of a different material, which would not react with the catalyzed monomer). The diameter of the tube was kept within such dimensions as to give rise to sliding friction and to allow the positioning of the lenses at the desired distance from each other. Thus one or more cavities were created by the lenses’curvature.(Fig. 9 in which 1 is the tubular sleeve;2 are the lenses 3 is the cavity).

EXAMPLE No.l/ Two or more glass lenses were introduced into a tubular sleeve, as in Example No.16 above, of such a diameter to give rise to friction between the lenses and the sleeve. Beforehand we had introduced or created in the tubular sleeve a spacer having a desired length and a minimum thickness, to cause the interruption of the sliding of the lenses , (Fig.10 wherein: 1 is the tubular sleeve; are the lenses; 3 is the cavity;4 is the spacer.) 2b EXAMPLE NO.18 Two or more glass lenses were slid down a tubular sleeve, as in Example No.16 above, the diameter of the tube being the same as that of the lenses. A spacer had been introduced or cast beforehand in the tube, as in Example No.17 above.

EXAMPLE No.19 Molds prepared according to Examples Nos.16,17 and 18 above, were filled with CR-39 monomer,catalyzed according to Examples Nos.13 and 14 above, and positioned with their convex side upwards. Catalyzed monomer was also introduced into the perimetric channel, partially defined by the surface of the uppermost lens, and partially defined by the internal wall of the tube. (See Fig.11 and Fig.12 wherein: 1 is the tube; 2 are the lenses; 5 is the catalyzed monomer) .

EXAMPLE No.20 Molds prepared according to Examples Nos.16,17 and IS above, were filled with CR-39 monomer,catalyzed according to Examples Nos.13 and 14 above, and positioned with their concave side upwards. Catalyzed monomer 8 4 3 8 was introduced into the internal cavity of the upper most lens, to reach up to the internal wall of the tube. (Fig.13 and Fig.14 wherein: 1 is the tube; are the lenses; 5 is the catalyzed monomer).

EXAMPLE No.21 Molds prepared according to Example Nos.16,17 and 18 above,were filled with CR-39 monomer,catalyzed according to Examples Nos.13 and 14 above and positioned horizontally, according to Examples Nos 1C 19 and 20 above. The tubular sleeves were provided with, or formed as, a receptacle with the internal cavity of the molds. The receptacle was also filled with the catalyzed monomer. This receptacle was made by totally or partially covering the perimeter of the tube inside and/or outside (Fig.15 and Fig. wherein: 1 is the tube;2 are the lenses; 5 is the catalyzed monomer; 6 is the receptacle).

EXAMPLE No.22 Molds prepared according to the Examples Nos.16, 17 and 18 above, were filled with CR-39 monomer, catalyzed according to Examples Nos,13 and 14 above, and positioned vertically. The exterior of the tubular sleeve was provided with, or formed as, a receptacle communicating with the internal cavity of the molds. This receptacle was also filled with the catalyzed monomer. (Fig.17, wherein: 1 is the tubular sleeve; 2 are the lenses; 5 is the catalyzed monomer; is the receptacle).

EXAMPLE No.22 Molds prepared according to the Examples Nos. 16,17 and 18 above, were filled with Cr-39 monomer,catalyzed according to Examples Nos. 13 and 14 above, and positioned vertically. The exterior of the tubular sleeve was provided with, or formed as, a receptacle communicating with the internal cavity of the molds. This receptacle was also filled with the catalyzed monomer. (Fig.17,wherein: 1 is the tubular sleeve; are the lenses; 5 is the catalyzed monomer; 6 is the receptacle.) EXAMPLE No.23 All the molds prepared and positioned as indicated in the Examples above, the cavities of which correspond to the shapes of different types of lens (vertical, convergent,divergent,cylindrical, lenticular,bifocal, prismatic etc.) were subjected,in an oven,to the same heating cycle of 15 hours.(Fig.18).The vertical stroke appearing in the cycle,indicates, as will be further explained, the moment where springs were applied to the ο 48 438 molds, that is when the gel phase of the monomer had been completed. The perfectly polymerized lenses thus obtained, showed finished surfaces and various curves and thicknesses. Their diameter was practically equal c to that of the glass lenses forming the simple or multiple molds (with a very 1ow diametral shrinkage equal, on average to 0.7%).

It was thus experimentally confirmed that the continuous compensation had operated in all the different arrangements described in the Examples above, establishing a continuous flow of polymerizable monomer from the outside into the inside of the molds, and compensating the shrinkage of the cast material whilst preventing the creation of air bubbles which would have caused the separation of the polymer from the mold.

Ths flow from the exterior to the interior had been made possible by means of preformed passages or through capillarity. The polymers thus obtained had a particularly homogeneous aspect.

Self-Positioning Spring - Many CR-39 lenses, available on the market, when examined with polarized light, show tensions which cannot be removed, even by submitting the polymers to heat48438 treatment. Within the framework of the present invention we considered the convenience of applying a pressure on the lenses forming the mold, after the polymer had reached the gel phase. It was then decided to introduce a spring capable of applying pressure to any kind of curved or plane surface, and to position itself through homogeneous contact on the whole of the support surface, to avoid localized high pressure, likely to cause the braking of the molds or of the polymers, or unacceptable pressures on the polymers themselves.

Example No.24 We build such springs to press lightly on the molds; they can be fitted in place quickly and easily by means of the compression of levers 7,8, causing the resilient opening of the pressures 9,10. The latter, consisting of small cups 11,12 shaped as a meniscus, may pivot in all directions around pivots 13,14. These springs adapt to all types of mold assemble including curves and various planes and by means of the pivoting of the small cups, afford a perfect adherence, so as to be able to exert an even pressure which is very useful to the production of regular polymers. (Fig.19 and Fig.20). 8 4 3 8 Example No.25 Springs as in Example No.24 above, but provided with only one small cup. (Fig.21).

Opening of the Molds - Lenses made of CR-39 and its copolymers,is strongly adherent to the casting mold, thus the separation from each other is a problem which is difficult to solve, particularly within the framework of the present invention. In fact, as the diameter of the cast polymer obtained is practically equal to the molds, it is impossible to achieve a mechanical separation by means of a wedge or a similar tool. It was determined, however that ultrasonic frequencies in the range of 20-70 KHertz, induced in a tank filled with water, in which the molds had been immersed, after the polymerization of their content, caused the separation of the polymers from the molds.

Example No.26 To separate the polymer from the glass lenses forming the molds, the latter were immersed in warm water baths, after which ultrasonic frequencies in the range of 20-70 «Hertz were induced.

In all cases, after some minutes, the polymer separated from the molds. The duration of the operation depending upon the bath temperature; it was shorter for a higher temperature and vice versa.

Example No.27 To carry out at the same time the separation of the polymer obtained from the glass lenses constituting the molds, and a first washing of the latter, the molds were immersed in warm baths of water solution of any type of cleansing substance (such as detergent,detersive, degreasing, emulsifying or saporification agent,sol vent acid or alkaline substance). In every case, within some minutes from the induction to the bath of ultrasonic frequencies, in the range of 20-70 «Hertz, the polymer separated from the molds: the relation between the duration of the operation the bath temperature was the same as indicated in the Example No.26.

From the above it appears evident that the described process and/or means constituting the subject of the present invention, which allow the production of quality lenses or other optical devices, made of CR -39 and its Β ί ϋ Β copolymers, may be directly or indirectly related to the wnole field of applications of cast homopolymers and copolymers with reference to the casting of any type of product, and the applicability or the selection of ζ any kind of polymerizable resin.lt also clearly appears that the examples - though referring to specific embodiments of the present invention, cannot be considered as limiting the latter. It is underlined that the process as a whole, attains in a synergistic manner, the advantages obtained by means of each described operation or means, with respect to their individual functions.

Claims (16)

1. A process for producing lenses or other optical means from a thermosetting plastics monomer, comprising the steps of forming a tubular sleeve of a substantially indeformable plastics material which is chemically compatible with the monomer and stable at the temperature of polymerization,positioning mold halves within the said sleeve at the required distance from each other so that they define, together with the lateral wall of the sleeve, a cavity having a diameter equal to that of the mold halves, the position of each mold half within the sleeve being maintained only by frictional contact between the rim of the mold half and the wall of the sleeve, introducing into the mold cavity a catalyzed thermosetting monomer to fill the said mold cavity and partly fill a compensation reservoir in communication therewith, submitting the said mold to homogeneous heating whereby to polymerise the monomer which undergoes an initial expansion and contraction stage followed by gelling with an associated shrinkage and subsequent hardening,the said compensation reservoir permitting a flow of the monomer out from and then back into the mold during the initial expansion and contraction stages prior to gelling, and the frictional engagement of the mold halves in the tubular sleeve permitting relative approach of these mold halves when the shrinkage associated with gelling takes place; and subsequently removing the sleeve and the mold halves from the 'ens thus formed when polymerisation of the monomer 5 nas been completed.

2. A process as claimed in Claim 1, wherein the saia monomer is diethyleneglycol-bis-allyl-carbonate.

3. A process as claimed in Claim 2, wherein the said monomer includes polymers thereof. 10 4. A process as claimed in any of Claims 1 to 3 wherein di ethylene-glycol-bis-allyl-carbonate catalyzed with isopropyl dicarbonate-peroxide is used as the monomer. 5. A process as claimed in any of Claims 1 to 4, 15 wherein the said monomer is diethylene-glycol-bisallvl-carbonate catalyzed with isopropyl dicarbonate peroxide, to which 2-(2-hydroxy-5-methyl-phenyl) benzotriazole is added, as an U.V. absorbed addi ti ve. 20 5. A process as claimed in any of Claims 1 to 5 wherein the catalyzed monomer is submitted to a heating cycle of 15 hours with a gradual temperature increase of from about + 40°C to 110°C.

4. 84-3 8 7. A process as claimed in any of Claims 1 to 6, wherein the compensation reservoir is formed by modification of a portion of the tubular sleeve. 8. A process as claimed in any of Claims 1 to 6,

5. Wherein the mold halves are located one above the other within the tubular sleeve and the compensation reservoir is constituted by a volume within the tubular sleeve, above the upper mold half.

6. 9. A process as claimed in any of Claims 1 to 6,

7. 10 wherein the compensation reservoir is located close to and outside the tubular sleeve, in an axial position therealong corresponding to the cavity delimited by the two mold halves. 10. A process as claimed in any preceding Claim 15 wherein, after the gel stage of the monomer has been reached, compressing springs are applied to press the two mold halves towards one another.

8. 11. A process as claimed in Claim 10, wherein the compressing springs which are applied to the 20 mold halves, are provided with a contact cup freely pivotally mounted on a pivot. ί 8 4 3 8

9. 12. A process as claimed in any preceding Claim , in which the removal of the lens from the mold halves is obtained by immersing the casting assembly in a warm liquid bath and subjecting it to ultrasonic 5 frequencies lying between 20 and 70 KHz.

10. 13. A process as claimed in Claim 12, wherein the liquid in the bath is an aqueous solution of a detergent substance.

11. 14. A process for producing lenses or other 10 optical means,as claimed in Claim 1 and substantially as hereinbefore described in the examples and with reference to the accompanying drawings.

12. 15. Molding apparatus for producing lenses or other optical means from a thermosetting plastics 15 material,comprising a tubular sleeve of substantially indeformable plastics material which is stable at the temperature of polymerisation of the said thermosetting plastics material,and at least two mold halves shaped to fit into the said sleeve with 20 a frictional engagment sufficient to retain the mold halves in position against the forces exerted by dimensional changes in the thermosetting plastics material before it has gelled, and to allow the mold halves to move within the sleeve under the action of forces exerted by dimensional changes in the thermosetting plastics material after the gel stage has been reached, and a reservoir for the thermosetting plastics material, which reservoir 5 communicates with the mold cavity between the said two mold halves in the said sleeve.

13. 16. Molding apparatus as claimed in Claim 15, in which the said reservoir is constituted by a volume within the said sleeve on the side of one 10 of the mold halves remote from the mold cavity between the two mold halves and communication between the mold cavity and the reservoir takes place by capillarity between the rim of the adjacent mold half and the inner surface of the sleeve. 15

14. 17. Molding apparatus as claimed in Claim 15, in which the reservoir is formed externally of the sleeve and communicates with the mold cavity through at least one preformed passage traversing the sleeve wall. 20

15. 18. Molding apparatus substantially as hereinbefore described with reference to Figures 9 to 21 of the accompanying drawings.

16. 19. Lenses and optical means when made by the process as claimed in any of Claims 1 to 14.