WO2008092597A2

WO2008092597A2 - Polymerizable liquid composition and process for the production of organic glass of the polyurethane type

Info

Publication number: WO2008092597A2
Application number: PCT/EP2008/000523
Authority: WO
Inventors: Fiorenzo Renzi; Roberto Forestieri; Andrea Vecchione; Willem Bos
Original assignee: Acomon Ag
Priority date: 2007-01-30
Filing date: 2008-01-23
Publication date: 2008-08-07
Also published as: WO2008092597A3; ITMI20070146A1

Abstract

The present invention relates to a polymerizable liquid composition and a process for the production of organic glass of the polyurethane type, which envisages a casting and polymerization process of polymerizable liquid compositions, comprising the following phases: a) mixing two components (A) and (B), wherein component (A) consists of a mixture of a cyclo-aliphatic diisocyanate monomer and a pre-polymer obtained by reaction between said cyclo- aliphatic diisocyanate monomer and one or more polyols and two or more hydroxyl groups and component (B) con- sists of one or more polyols; b) addition of a polymerization catalyst to the polymerizable liquid composition obtained in phase a); c) mixing for a time varying from 5 to 10 minutes, at an absolute pressure ranging from 5 to 10 mbar and a temperature ranging from 10°C to 25°C; d) filling one or more moulds and polymerization of the liquid composition by thermal treatment.

Description

POLYMERIZABLE LIQUID COMPOSITION AND PROCESS FOR THE PRODUCTION OF ORGANIC GLASS OF THE POLYURETHANE TYPE

The present invention relates to a polymerizable liquid composition and a process for the production of organic glass, having good optical and physico-mechanical properties, starting from polymerizable liquid compositions; it also relates to said compositions and the organic glass obtained from the polymerization of said compositions . More specifically, the process for the production of organic glass having good optical and physico-mechanical properties according to the present invention is applied to polymerizable liquid compositions essentially consisting of two components of which the first component (A) contains free isocyanate groups, whereas the second component (B) contains hydroxyl groups.

The state of the art already describes numerous materials which have been developed for applications in the optical field, in particular for applications which re- quire high transparency and the absence of colouring. Mineral glass has been the most widely-used material in the past, but more recently, it has been substituted by- plastic polymeric materials which are lighter, have an improved impact strength and are easy to produce. There are various types of commercially available polymeric materials, all having strong and weak points. Thermoplastic materials, for example, such as polymethylmethacrylate or polycarbonate have the problem of low resistance to contact with most chemical products and sol- vents and a poor processability, as they tend to melt during mechanical processings such as milling, turning, punching, grinding and polishing. Polycarbonate, moreover, has a high birefringence and chromatic aberration phenomena which make it unsuitable for high-quality opti- cal applications.

For ophthalmic applications, thermosetting organic glass obtained from the polymerization of ADC, known with the name of Allyl Diglycol Carbonate (ADC) is of particular commercial interest due to its specific mechanical properties of aging resistance and processability, as described for example by F. Strain, in "Encyclopedia of Chemical Processing and Design" , First Edition, Dekker Inc., New York, Vol. 11, page 452 onwards; and in "Encyclopedia of Polymer Science and Technology" (1964), Vol. 1, page 799 onwards, Interscience Publishers, New York. The commercial success of ADC is due not only to the good properties of the polymerized products, but also to the production technique of the end-products, which is relatively simple, known as casting. By operating with this technique, the liquid compositions containing the polymerization initiator are poured into the cavity of a mould obtained by coupling two glass elements, separated by a distancing washer made of a suitable material. The liquid compositions are then subjected to polymerization by thermal treatment with a gradual temperature increase, generally ranging from 30⁰C to HO⁰C, with polymerization times which generally vary from 10 hours to 100 hours. At the end of the above treatment, the moulds are opened and the polymerized end-products are recovered.

The use of ADC, however, has various drawbacks which make the production process of the end-products based on this composition risky from the point of view of safety and also economically onerous.

The polymerization reaction of the monomer in question is in fact normally carried out in the presence of peroxide initiators belonging to the group of dialkyl- peroxydicarbonates, such as diisopropylperoxydicarbonate (IPP) . IPP is commercially available, diluted in a variable concentration in the monomer. This solution, which reduces the dangerousness associated with the thermal instability of the peroxide, does not, however, solve the problem of transportation and storage of the peroxide at unfavourable temperatures. This solution also has the disadvantage of considerably increasing the quantity of initiator to be stored and managed daily and the operating costs . In addition, once prepared, the solution of monomer with the catalyst must be used in short times to avoid premature polymerization reactions, or, again to avoid this problem, the casting must be effected at a low temperature (about 0⁰C) . It can be easily deduced that this critical aspect represents a serious complication of the production process described above.

Finally, although the organic glass deriving from the polymerization of ADC has good optical and physico- mechanical properties, as previously specified, over the years the demand on the market for end-products having further enhanced optical and mechanical properties has increased considerably, in particular with reference to transparency, high toughness and impact strength. Alternative casting processes such as UV-curing, are much more rapid and allow thermosetting organic glass to be obtained starting from multifunctional acrylic or methacrylic monomers. These materials, however, have a low impact strength and resistance to abrasion and poorer optical properties with respect to the polymer obtained by polymerization of ADC.

Materials having a high impact strength based on polyurethane-urea polymers have recently been proposed, specifically for the field of ophthalmic lenses and as an alternative to polycarbonate, as described in international patent application WO03/044071. The lenses produced with these materials, however, still have, as in the case of polycarbonate, problems of processing, poor colourability with the immersion technique and, in addi- tion, the lenses obtained tend to become yellow with time due to oxidation reactions.

Finally, as the pot life of the mixture is very short (less than a minute) , the use of sophisticated and costly mixing/dispensing equipment or even more sophisti- cated machines which use a known transformation technique such as RIM (Reaction Injection Molding) , is indispensable for the preparation of end-products.

An objective of the present invention is therefore to overcome the drawbacks of the compositions and proc- esses according to the state of the art, by producing new organic glass having all the favourable characteristics of some already-existing materials, in particular the excellent optical properties, processability and dyeability of the ADC polymer, but at the same time having an en- hanced toughness and impact strength.

Furthermore, an objective of the present invention is also to find a process for the production of organic glass, i.e. end-products, starting from new material, which is simple and inexpensive. The present invention allows both objectives to be achieved. It relates, in fact, to a simple casting process for the production of transparent end-products made of thermosetting plastic material of the polyurethane type having excellent physico-mechanical properties starting from polymerizable liquid compositions which form a further object of the present invention.

Said polymerizable liquid compositions consist of two components (A) and (B) in a weight ratio varying from 1.2:1 to 2.2:1, wherein component (A) consists of a mix- ture of a cyclo-aliphatic diisocyanate monomer and a pre- polymer obtained by reaction between said cyclo-aliphatic diisocyanate monomer and one or more polyols having two or more hydroxyl groups per molecule and a molecular weight ranging from 200 to 2,000 g/mole; with a weight ratio between cyclo-aliphatic diisocyanate monomer and prepolymer which is such that the final weight percentage of the free isocyanate groups in said component (A) varies from 20% to 30% with respect to the total weight of component (A) ; and component (B) consists of one or more polyols having a molecular weight ranging from 200 to 2,000 g/mole and a functionality varying from 2 to 5.

The process for the production of organic glass of the present invention consists of a casting process for the production of organic glass starting from polymeriz- able liquid compositions of the polyurethane type, which comprises the following phases: a) mixing two components (A) and (B) in a weight ratio varying from 1.2:1 to 2.2:1, wherein component (A) consists of a mixture of a cyclo-aliphatic diisocyanate monomer and a prepolymer obtained by reaction between said cyclo-aliphatic diisocyanate monomer and one or more polyols having two or more hydroxyl groups per molecule and a molecular weight ranging from 200 to 2000 g/mole; with a weight ratio between cyclo-aliphatic diisocyanate monomer and prepolymer which is such that the final weight percentage of the free isocyanate groups in said component (A) varies from 20% to 30% with respect to the total weight of component (A) ; and component (B) consists of one or more polyols having a molecular weight ranging from 200 to 2,000 g/mole and a functionality varying from 2 to 5 ; b) addition of a polymerization catalyst to the po- lymerizable liquid composition obtained in phase a) ; c) mixing for a time varying from 5 to 10 minutes, at an absolute pressure ranging from 5 to 10 mbar and a temperature ranging from 10⁰C to 3O⁰C; d) filling one or more moulds and polymerization of the liquid composition by thermal treatment with temperatures ranging from 30 to 110⁰C and with polymerization times varying from 1 hour to 10 hours.

An object of the present invention also relates to the organic glass obtained by the casting process and polymerization of said compositions.

Finally, a further object of the present invention relates to the end-products or optical articles obtained by the casting process and polymerization of the poly- merizable composition, such as, for example, ophthalmic lenses and solar filters, protective screens, display windows, manifolds and solar and photovoltaic panels, substrates for optical disks, display panels and video- terminals .

The casting and polymerization process according to the present invention, apparently similar to the conventional ADC process well-known to experts in the field, provides two surprising advantages with respect to this known process: a first advantage is represented by a sufficiently long stability of the polymerizable composition at temperatures close to room temperature, which also allows the filling of a significant number of moulds and contemporaneously relatively short polymerization times, generally shorter than those necessary for ADC polymerization.

The polyurethane thermosetting plastic materials obtained with the casting and polymerization process ac- cording to the present invention, have excellent optical properties and excellent processability, similar to those which characterize the ADC polymer, but with respect to the latter, they have a much higher impact strength and toughness. These characteristics make the material suit- able for the manufacturing of complex end-products which could not be produced with the ADC polymer.

The quantity of catalyst in the process according to the present invention is optimized so as to obtain a final concentration which allows a sufficiently long pot life of the solution and a reduced polymerization time in an economically advantageous mould. DETAILED DESCRIPTION OF THE PRESENT INVENTION

As already specified, the present invention relates to a casting and polymerization process of polymerizable liquid compositions of the polyurethane type for the pro- auction of organic glass having good optical and physico- mechanical properties.

The polyurethane polymerizable liquid composition according to the present invention consists of component (A) and component (B) . Component A

Component (A) of the polymerizable composition according to the present invention consists of a mixture of a cyclo-aliphatic diisocyanate monomer and a prepolymer obtained by reaction between said cyclo-aliphatic diisocyanate monomer and one or more polyols having two or more hydroxyl groups per molecule and a molecular weight ranging from 100 to 2,000 g/mole, preferably from 100 to 1000 g/mole. The weight ratio between cyclo-aliphatic diisocyanate monomer and prepolymer in component (A) of the composition according to the present invention is such that the final weight percentage of the free isocy- anate groups in said component (A) varies from 20% to 30% with respect to the total weight of component (A) . The cyclo-aliphatic diisocyanate monomer of component (A) of the composition according to the present invention is selected from cyclohexane diisocyanate, methyl cyclohexanediisocyanate , bis ( isocyanatemethyl ) cyclohexane, 4 , 4 ' -methylene bis (cyclohexylisocyanate) , 3- isocyanate methyl-3 , 5 , δ-trimethylcyclohexylisocyanate commonly known as isophorondiisocyanate, 2,5(6) diisocy- anatemethylbicyclo (2 , 2 , 1) heptane and bis (isocyanate- methyl) cyclohexane . The cyclo-aliphatic diisocyanate monomer of component (A) of the composition of the pre- sent invention is preferably selected from 4 , 4 ' -methylene (bis (cyclohexylisocyanate) and bis (isocyanatemethyl) - cyclohexane .

The polyol used for the synthesis of the prepolymer of component (A) is at least a polyol having two or more hydroxyl groups per molecule and a molecular weight ranging from 100 to 2,000 g/mole, preferably from 100 to 1,000 g/mole.

Polyols useful according to the present invention are polyols selected from, for example, ethyleneglycol , propyleneglycol, diethyleneglycol, 1 , 4-butanediol , neopentylglycol, 1 , 6-hexandiol, trimethylolpropane, glycerin, pentaerythritol, dipentaerythritol, etc., or they can be selected from groups consisting of polyester polyols, polycaprolactone polyols, polyether polyols, poly- carbonate polyols or mixtures thereof, and in the case of several polyols, these are independently selected from the groups indicated above, described for example in High Polymers, Vol. XVI; "Polyurethane Chemistry and Technology", of Saunders and Frisch, Interscience Publishers, New York, Vol. I, pages 32-42, 44-54 (1962) and Vol. II, pages 5-6, 198-199 (1964) ; and "Developments in Polyure- thanes" , Vol. I, J. M. Burst, ed. , Applied Science Publishers, pages 1-76 (1978) .

The polyester polyols are preferably selected from esters of polyols having from 2 to 10 carbon atoms, such as, for example, ethyleneglycol, propyleneglycol, di- ethyleneglycol, 1, 4-butanediol, neopentylglycol, 1,6- hexanediol and dicarboxylic acids having from 4 to 10 carbon atoms such as, for example, adipic acid, succinic acid and sebacic acid. Among these, the most preferred are adipic esters of 1, 4-butanediol, 1, 6-hexanediol and 1 , 10 -decanediol .

The polycaprolactone polyols are preferably reaction products of E-caprolactone with a low-molecular-weight polyol having from 2 to 10 carbon atoms preferably selected from 1, 4-butanediol, 1, 6-hexanediol, 1,10- decanediol and neopentylglycol .

The polyether polyols are preferably polytetrame- thyleneglycol (PTMG) or the condensation product of a polyol, more preferably glycerin or trimethylolpropane, with ethylene oxide and/or propylene oxide having a molecular weight ranging from 200 to 1,000 g/mole or mixtures thereof.

The polycarbonate polyols are preferably aliphatic polycarbonates containing 1, 4-butanediol, 1, 6-hexanediol , 1, 10-decanediol, trimethylolpropane or neopentylglycol units.

The synthesis of the prepolyraer of component (A) is carried out at temperatures ranging from 90 to 110⁰C, by progressively adding the polyol to the cyclo-aliphatic diisocyanate in an inert nitrogen atmosphere. The reaction trend is followed by determining the concentration of residual isocyanate by titration. The quantity of polyol reacted is such that the final weight percentage of free isocyanate groups in component (A) ranges from 20% to 30% by weight with respect to the total weight of component (A) , corresponding to a final concentration of cyclo-aliphatic diisocyanate monomer in component (A) generally ranging from 50% to 90% by weight with respect to the total weight of component (A) .

This high concentration of diisocyanate monomer allows very low viscosity values to be obtained with respect to analogous products of the known art and this characteristic, combined with other specific characteris- tics of the casting technique according to the present invention which will be described hereunder, avoids the use of sophisticated and costly machinery for the production of optical end-products. This characteristic is also essential in the particular production process of organic glass, object of the present invention, by a manual cast- ing process, similar to that of the ADC process with IPP, manual casting meaning a casting not assisted by sophisticated mixing/dispensing machines.

Detaching agents or other additives can be incorpo- rated in component (A) in this phase. Component (B)

Component (B) of the polymerizable composition according to the present invention consists of one or more polyols having a molecular weight ranging from 100 to 2,000 g/mole and preferably from 100 to 1,000 g/mole and a functionality ranging from 2 to 5 and preferably between 2 and 3.

The polyols of component (B) are selected from the polyols already listed in the definition of component (A) above.

The polyol of component (B) can be indifferently the same as or different from that used for the synthesis of the prepolymer of component (A) .

In order to favour the chemical compatibility be- tween components (A) and (B) , however, the polyols of both components are preferably the same or at least belong to the same chemical family.

For the same reason, the two components (A) and (B) preferably have similar and sufficiently low viscosities. The organic glass and optical articles according to the present invention are prepared by the polymerization reaction of components (A) and (B) according to suitable weight ratios generally ranging from 1.2:1 and 2.2:1, in the presence of appropriate catalysts and additives. The catalyst used for the production process of organic glass according to the present invention is preferably a catalyst of the metallic type, wherein the catalyst is selected from tin, zinc, bismuth, titanium, zirconium and mercury. In particular, the catalyst is se- lected from salts of said metals such as dibutyl tin di- laurate, bismuth nitrate, zinc naphthenates , phenyl mercury neodecanoate .

The preferred catalyst is phenyl mercury neodecanoate . The additives can be incorporated in component (A) or in component (B) or in both before the mixing phase a) or they can be added during the mixing phase a) of the two components. Non-limiting examples of these additives are detaching agents such as alkyl phosphates or non- ionic fluorinated surface-active agents, dyes, comprising photochromatic dyes, bluing agents, UV absorbers of the benzotriazole family, such as for example, Tinuvin 571 of Ciba, IR absorbers, light stabilizers of the Hals type such as, for example, the commercial product Lowilite 76 of Chemtura, antioxidants, such as, for example, the coπi- mercial product Anox BF of Chemtura.

A further improvement in the mechanical properties such as hardness, impact strength and abrasion resistance can be obtained by the addition of inorganic nano- particles based on salts, or preferably based on zinc oxide, cerium oxide, silicon oxide, aluminum oxide, titanium oxide or zirconium oxide.

As already specified, the casting and polymerization process of the polymerizable liquid compositions of the polyurethane type according to the present invention is, in some of its aspects, similar to the conventional process used for ADC.

With respect to the latter, the most significant variant is that the catalyst which promotes the polymeri- zation reaction is added to the mixture of components (A) and (B) immediately before pouring into the mould, i.e. in phase c) of the process according to the present invention.

This contemporaneously and surprisingly gives two particularly favourable and apparently contradictory results, i.e.: a high stability of the polymerizable liquid composition during the mixing phase of the two components (as can be seen in the graph of Example 1 below, where it can be observed that at room temperature, even after a considerable period of time, in the order of 20 hours af- ter the preparation of the mixture, there is no significant increase in the viscosity) , whereas the processes for the polyurethane systems of the state of the art envisage stability in the order of a few minutes and, con- temporaneously, relatively short polymerization times in the mould and generally lower than those necessary for the polymerization of ADC as can be seen in the following experimental examples.

The high stability of the polymerizable liquid com- position according to the present invention is the fundamental requisite for allowing the use of the manual casting process, i.e. not assisted by sophisticated mixing/dispensing machinery as, in order to obtain, for example, a lens free of optical defects (such as flow lines, tensioning etc.), relatively long mixing times of components (A) and (B) are necessary, in the order of 1 hour. This cannot be achieved if the addition of the catalyst is effected at the beginning of the mixing of components (A) and (B) , as the relatively rapid increase in the viscosity makes the homogenization of the solution and filling of the moulds extremely difficult.

The addition and dissolution of small quantities of catalyst in a subsequent phase, on the contrary, is an extremely simple and rapid process, in the order of a few minutes. This allows a sufficiently long time for the mixing of components (A) and (B) before the addition of the catalyst and also a sufficiently long time during which the viscosity of the polymerizable composition remains sufficiently low to allow the filling phase of the moulds, the latter being an operation which, in any case, must be completed in reasonable times. For this purpose, the quantity of polymerizable composition to be prepared in relation to the concentration of catalyst charged must be suitably planned. More specifically, the production process of organic glass according to the present invention envisages a casting and polymerization process of the polymerizable liquid composition based on polyurethanes which comprises the following phases : a) mixing two components (A) and (B) in a first mixer, in a weight ratio varying from 1.2:1 to 2.2:1, wherein component (A) consists of a mixture of a cyclo- aliphatic diisocyanate monomer and a prepolymer obtained by reaction between said cyclo-aliphatic diisocyanate monomer and one or more polyols having two or more hy- droxyl groups per molecule and a molecular weight ranging from 100 to 2,000 g/mole; with a weight ratio between cyclo-aliphatic diisocyanate monomer and prepolymer which is such that the final weight percentage of the free iso- cyanate groups in said component (A) varies from 20% to 30% with respect to the total weight of component (A) ; and component (B) consists of one or more polyols having a molecular weight ranging from 100 to 2,000 g/mole and a functionality varying from 2 to 5. Said first phase a) is carried out without the addition of the catalyst. Additives such as UV-absorbers, dyes, detaching agents etc. can be added in this step, if not previously added in the single components. The mixing phase a) is carried out at a temperature close to room temperature (20-30⁰C) and an absolute pressure of 5-10 mbar until a homogeneous mixture is obtained. This normally requires a time ranging from about 1 hour to about 3 hours in relation to the quantity of product and type of mixer used. The mixture thus obtained, can be pre- served at a temperature close to room temperature for several hours without any significant increase in viscosity. At lower temperatures, the stability of the catalyst-free mixture increases further. During mixing under vacuum, the complete degassing of the solution takes place, which ensures the production of bubble-free polymerized optical articles.

Phase a) is followed by phase b) in which the polymerization catalyst is added to the polymerizable liquid composition obtained in phase a) , said phase b) can be effected after transferring the solution obtained in phase a) to a second mixer having a lower capacity with respect to the first mixer. The liquid composition of phase a) can be subjected to a filtration process to eliminate possible dispersed contaminants which would jeopardize the optical quality of the end-product. Filters which can be used for the purpose are cartridge filters made of polypropylene or nylon with a porosity of 0.5-1 absolute microns.

Alternatively, it is possible to avoid the use of a second mixer and effect the addition of the catalyst in the first and only mixer, once the complete homogeniza- tion of the two components has been obtained.

As already mentioned, phase b) envisages the addition of the catalyst; the catalyst is added in such a quantity as to obtain a final concentration which allows a sufficiently long pot life of the solution and a reduced polymerization time in the mould, which is economically advantageous.

The optimum concentration of catalyst ranges from 50 to 2,000 ppm depending on the type of catalyst. In particular, in the case of phenyl mercury neodecanoate , which is the preferred catalyst, the optimum concentration ranges from 50 to 300 ppm.

The mixing phase c) of the polymerizable composi- tion, in the process according to the present invention, is carried out for a time ranging from 5 to 10 minutes. Said phase c) is preferably effected at an absolute pressure of 5-10 mbar, at a temperature ranging from 10 to 25°C and for a sufficient time for obtaining a homogene- ous mixture. The mixing time necessary normally ranges from 5 to 10 minutes approximately.

Phase d) envisages the filling of the moulds or pouring into the mould and polymerization of the liquid composition for thermal treatment with temperatures rang- ing from 30 to 110⁰C and with polymerization times ranging from 1 hour to 10 hours.

Alternatively or additionally, the filtration of the liquid composition can be effected immediately before pouring into the mould. Moulds made of various materials such as glass or metals, can be used for the casting. Glass moulds are traditionally used for ophthalmic lenses,- metal moulds, however, offer various advantages such as, for example, a better capacity of dispersing the heat deriving from the polymerization reaction. Suitable metallic moulds can be made of stainless steel, nickel, aluminum, copper, chromium, silver and gold.

The liquid compositions are then subjected to polymerization by means of thermal treatment preferably with a gradual temperature increase ranging from 4O⁰C to 110⁰C, with polymerization times which generally range from 1 hour to 10 hours, preferably from 2 to 8 hours.

It is evident from the above description that the casting and polymerization process according to the present invention offers two substantial advantages with re- spect to the ADC casting technique; 1) the preparation of the polymerizable composition is carried out at room temperature; 2) the polymerization times are a half or a third, thus allowing the use of a more limited number of moulds which is used several times during the day. At the same time, the process according to the present invention does not have the disadvantages of the polyurethane and polyurethane-urea systems currently available which require the use of sophisticated mixing machinery. Furthermore, the shrinkage observed during the polymerization in the process according to the present invention is lower than 2%, also facilitating the casting of optical articles having a complex shape.

The polymers obtained with the polymerizable compo- sition and the process according to the present invention have a high transparency, excellent mechanical properties and processability .

A further object of the present invention also relates to end-products or optical articles obtained with the casting and polymerization process of the polymeriz- able compositions described above, such as for example ophthalmic lenses, sun lenses, Fresnel lenses, protective screens, display windows, solar and photovoltaic panels, optical guides, components for mobile telephones, sub- strates for optical disks, display panels and video- terminals, transparent tubes. These articles can also be produced by processing with tools starting from drafts or semi-processed products.

Said end-products or optical articles can be surface hardened with scratch-proof paints or they can be made anti-reflecting with the techniques and materials normally used for ADC end-products.

The advantages of the casting and polymerization technique of the polymerizable compositions according to the present invention, which envisages the delayed addition of a small quantity of catalyst or polymerization initiator, will appear evident from the following experimental examples which should in no way be considered as limiting the scope of the invention. In these examples, flat plates and neutral ophthalmic lenses were prepared by assembling, as previously described, glass moulds and distancing washers made of plasticized polyvinylchloride, ethylene-vinylacetate copolymer (EVA) , low density polyethylene (LDPE) , or an- other suitable material, compatibly with the processing conditions .

The polymerizable liquid compositions were then subjected to polymerization by means of thermal treatment in a forced circulation oven, with a gradual temperature rise as described in the following experimental examples .

The physico-mechanical properties were determined on the polymerized products or organic glass thus obtained; in particular, the following characteristics were determined on the flat plates: (a) Optical characteristics

Refraction index (n^D ₂o) : measured with an Abbe re- fractometer (ASTM D- 542) ;

Yellow index (YI) , (ASTM D- 1925) , determined with a Macbeth 1500 Plus spectrophotometer and defined as: YI = 100/Y • (l,277x - 1.06Z)

Light transmittance (ASTM D-1003) , determined with a Macbeth Colour i5 spectrophotometer, and expressed as a tristimulus value Y;

Haze % (ASTM D-1003) , determined with a Macbeth CoI- our i5 spectrophotometer.

(b) Physical and mechanical characteristics

Density: determined with hydrostatic scales at a temperature of 20⁰C (ASTM D-792) ;

Rockwell hardness (M) measured with a Rockwell du- rometer (ASTM D- 785) ; Unnotched Izod impact strength (ASTM D-256 modified) ;

Deflection temperature under load 1.82 MPa (HDT) (ASTM D-648) . The following properties were determined on the neutral lenses :

(c) Dyeability

The capacity of the material was determined, to adsorb a dye on the surface by immersion of a neutral lens in an aqueous bath in which the dye BPI gray was dispersed.

For this purpose, the lens was immersed in said dye bath for 15-30 minutes at temperatures ranging from 80 to 85°C and, after rinsing with demineralized water, the transmittance of the lens was determined by measuring the chromatic coordinate Y as described by CIE (1931) Standard Observer.

(d) Chemical resistance

The formation of defects in samples of flat plates was evaluated after immersion for 5 minutes in the following solvents: acetone, ethyl alcohol, H₂SO₄ (aqueous solution at 40%) and NaOH (aqueous solution at 10%) .

The advantages deriving from the casting and polymerization process of the polymerizable compositions ac- cording to the present invention with respect to proc- esses and compositions of the known art which in some cases are provided for comparative purposes, are evident from the following examples. EXAMPLE 1 a) Preparation of Component (A)

Component (A) was prepared starting from: 4 , 4 ' -methylene bis (cyclohexylisocyanate) , trade-name Desmodur W of Bayer AG, having a concentration and content of isocyanate groups equal to about 32% by weight; - alkoxylated trimethylolpropane, trade-name POLYOL R3530 of Perstorp, having a hydroxyl number equal to 530 mg KOH/g and nominal molecular weight equal to 310 g/mole .

262 g (1 mole) of Desmodur W were charged at room temperature into a three-necked jacketed flask, equipped with a thermometer and magnetic stirrer. A vacuum of about 2 mbar, broken with anhydrous nitrogen, was then applied. This operation was repeated 3 times so as to create an inert atmosphere .

37.2 g (0.12 moles) of POLYOL R3530 were then added slowly under stirring and a nitrogen seal at 100⁰C. The quantity of polyol added was such that at the end of the reaction, the concentration of non-reacted isocyanate groups is equal to about 24%-26%.

The reaction was carried out at this temperature for about 8 hours, controlling with time the content of re- sidual isocyanate groups by titration.

At the end of the reaction, the reaction mixture was cooled and filtered on a polypropylene filter of 1 micron thus obtaining about 290 g of a liquid product having the following characteristics:

Viscosity (25°C) : 450 cSt; Density (20⁰C): 1.09 g/ml; Free isocyanate: 25.2%; Apha colour: 10. The product thus obtained is a mixture of 4,4'- methylene bis (cyclohexylisocyanate) monomer as main component, the remaining part consisting of adducts of said cyclo-aliphatic diisocyanate with alkoxylated trimethy- lolpropane . b) Preparation of component (B)

Component (B) is the same polyol used in the synthesis of component (A) indicated under point a), i.e. alkoxylated trimethylolpropane (POLYOL R3530 of Perstorp) to which an optical bluing agent has been added (SoI- vaperm Violet RSB of Clariant, Color Index Solvent Violet 23, solution at 10% in the polyol) in a concentration equal to 0.02% by weight with respect to the total weight of component (B) . c) Casting 180 g of component (A) and 100 g of component (B) previously prepared, were charged into a two-necked jacketed flask, equipped with a thermometer and magnetic stirrer, and the whole solution was mixed at 23⁰C for about 1 hour at an absolute pressure of 5 mbar. The degassed solution thus obtained was subsequently filtered on a 1 micron polypropylene filter. It has the following properties:

Viscosity (25°C) : 600 cSt; Density (20⁰C) : 1.07 g/ml ; - Refraction index (n^D ₂₀) : 1.484;

Apha colour: 8.

0.03 g of catalyst (phenyl mercury neodecanoate) and 1.4 g of a detaching agent of the alkyl phosphate type (trade-name "Zelec UN" of Stepan) were then added to this solution, in quantities equal to about 0.01% by weight and 0.5% by weight with respect to the total weight of components (A) and (B) .

The polymerizable composition thus obtained was mixed for a further 5 minutes at 23⁰C and at an absolute pressure of 5 mbar and then poured into the moulds. d) Polymerization and evaluation of the polyurethanes obtained

The above composition, called Composition (1) , was subjected to polymerization by thermal treatment in a forced circulation oven, with a gradual temperature in- crease from 4O⁰C to 105⁰C in 7 hours (precisely from 40 to 60⁰C in 2 hours, from 60 to 105⁰C in 3 hours, followed by 2 hours in isotherm at 105⁰C) and the characteristics indicated in Table 1 were determined on the organic glass thus obtained, compared with the corresponding characteristics of an ADC polymer obtained with IPP at 3% by weight and a polymerization cycle having a duration of 20 hours with a progressive increase in temperature from 40 to 80⁰C. Table 1

^<a) plate thickness = 5 mm

The transparent polyurethanes according to the present invention have excellent optical and physico- mechanical properties. In particular, the Haze and Light transmittance values are practically equal to those of the ADC polymer and are better than those of the polyure- thane-urea systems of the known art.

As previously indicated, the catalyst-free composi- tion has a high stability at temperatures close to room temperature, as shown by the graph of Figure 1, where it is evident that even 20 hours after the preparation of the mixture, there is no significant increase in viscosity. With the addition of the catalyst, a progressive increase in the viscosity can be observed (see the graph of Figure 2) . Remaining with concentration values of the catalyst within the range of 200-300 ppm, however, it is possible to maintain the viscosity of the composition at sufficiently low values for a sufficiently long time to allow the filling of a significant number of moulds. EXAMPLE 2

The liquid compositions Nr. (2) , (3) , (4) and (5) of

Table 2 were prepared, polymerizable according to the present invention into organic glass having good optical and physico-mechanical properties. These compositions envisage the same component (A) as Example 1 whereas component (B) consists of mixtures of alkoxylated trimethylol- propane, diethyleneglycol and neopentylglycol in the ratios indicated in Table 3. Table 2

Table 3

In Table 3 it is evident that the addition of diethyleneglycol and neopentylglycol in component (B) causes a reduction in the viscosity of said component, reaching values close to that of 450 cSt of component (A) and thus facilitating the mixing of the two components.

1.4 g of Zelec UN, 0.02 g of the optical bluing agent of Example 1 and 0.03 g of phenylmercuryneode- canoate were added to compositions (2) , (3) , (4) and (5) , after mixing for about 1 hour at room temperature and at an absolute pressure of 0.5 mbar. The compositions thus obtained were mixed for a further 5 minutes under vacuum and the glass moulds were subsequently filled.

Neutral lenses having a thickness of 2 mm were then prepared with the above compositions, by polymerization in a forced circulation oven, with a gradual temperature increase from 60⁰C to 110⁰C in 4 hours (precisely from 60 to 110⁰C in 3 hours, followed by 1 hour in isotherm at 110⁰C) and, the characteristics indicated in Table 4 were determined on the organic glass thus obtained. Table 4

Flat plates having a thickness of 3 mm and 5 mm were also prepared with compositions (3) and (5) by polymerization under the conditions previously indicated and the characteristics specified in Table 5 were determined on the organic glass thus obtained. Table 5

^(a) plate thickness = 5 mm

From examining Tables 4 and 5, it is evident that the addition of diethyleneglycol and/or neopentylglycol to component (B) does not produce any significant variation in the polymerization properties with respect to those of composition (1) according to the present invention, with the advantage, with respect to this, of a lower viscosity and higher stability with time (see the graph of Figure 3 which compares the viscosity increase curves with time at 23⁰C) . Example 3

Semi-processed monofocal lenses were prepared with the liquid composition (3) of Table 2 according to the casting process of Example 1 and, comparatively, with the casting technique of the known art which envisages the addition of the catalyst in the initial step.

The polymerizable liquid compositions, containing 100 ppm of the catalyst phenyl mercury neodecanoate, were prepared according to the procedure indicated in Table 6 and were subsequently injected into moulds by pressuriza- tion with nitrogen at 1 bar (g) .

These compositions where then subjected to the polymerization process under the conditions indicated in Example 1, after which semi-processed monofocal lenses having a diameter of 75 mm and a weight of 60 grams were obtained, with the yields indicated in Table 6. Table 6

As is evident, with the casting technique according to the present invention, a yield of 95% to lenses without optical defects is obtained, against a yield of 15% to lenses without optical defects of the casting technique of the known art .

The results of a further comparative test are indicated in Table 7. Table 7

120 semi-processed lenses were injected, with the casting technique according to the present invention, over a period of approximately 90 minutes before the op- eration became difficult due to the increase in viscosity of the mixture .

With the known art, under the same conditions, it was only possible to inject 18 lenses with a much lower yield in terms of optical quality. Example 4

The liquid compositions Nr. (6) and (7) of Table 8 were prepared, polymerizahle according to the present invention into organic glass having good optical and phys- ico-mechanical properties. These compositions envisage the same component (A) as Example 1 whereas component (B) consists of mixtures of alkoxylated trimethylolpropane and trimethylolpropane, in the ratios indicated in Table 9. Table 8

Table 9

1.4 g of Zelec UN, 0.02 g of the optical bluing agent of Example 1 and 0.03 g of phenylmercuryneode- canoate were added to compositions (6) and (7) , after mixing for about 1 hour at room temperature and at an absolute pressure of 0.5 mbar. The compositions thus obtained were mixed for a further 5 minutes under vacuum and the glass moulds were subsequently filled.

Flat plates having a thickness of 3 mm and 5 mm were also prepared with said compositions by polymerization under the conditions previously indicated and the characteristics specified in Table 10 were determined on the organic glass thus obtained. Table 10

^(a) plate thickness = 5 mm

From examining Table 10, it is evident that the addition of trimethylolpropane to component (B) allows to obtain a significant increase of HDT with respect to those of composition (1) according to the present invention, without significantly worsening the other properties of polymerized products and. in particular, Izod impact strength.

Claims

1. A polymerizable liquid compositions comprising two components (A) and (B) in a weight ratio varying from 1.2:1 to 2.2:1, wherein component (A) consists of a mix- ture of a cyclo-aliphatic diisocyanate monomer and a pre- polymer obtained by reaction between said cyclo-aliphatic diisocyanate monomer and one or more polyols having two or more hydroxyl groups per molecule and a molecular weight ranging from 100 to 2,000 g/mole; with a weight ratio between cyclo-aliphatic diisocyanate monomer and prepolymer which is such that the final weight percentage of the free isocyanate groups in said component (A) varies from 20% to 30% with respect to the total weight of component (A) ; and component (B) consists of one or more polyols having a molecular weight ranging from 100 to 2,000 g/mole and a functionality varying from 2 to 5.

2. The composition according to claim 1, characterized in that the cyclo-aliphatic diisocyanate monomer of component (A) is selected from cyclohexane diisocyanate, methyl cyclohexanediisocyanate, bis (isocyanatemethyl) - cyclohexane, 4 , 4 ' -methylene bis (cyclohexylisocyanate) , 3- isocyanate methyl-3 , 5 , 5-trimethylcyclohexylisocyanate commonly known as isophorondiisocyanate, 2,5(6) diisocy- anatemethylbicyclo (2, 2, 1) heptane and bis (isocyanate- methyl) cyclohexane .

3. The composition according to claim 1, characterized in that the cyclo-aliphatic diisocyanate monomer of component . (A) is selected from 4 , 4 ' -methylene bis (cyclohexylisocyanate) and bis (isocyanatemethyl) - cyclohexane

4. The composition according to claim 1, characterized in that the polyol of the prepolymer of component (A) or of component (B) is at least a polyol having two or more hydroxyl groups per molecule and a molecular weight rang- ing from 100 to 1,000 g/mole .

5. The composition according to claim 1, characterized in that the polyol or polyols are independently selected from ethyleneglycol, propyleneglycol, diethyleneglycol, 1, 4-butanediol, neopentylglycol, 1 , 6-hexandiol, trimethy- lolpropane, glycerin, pentaerythritol, dipentaerythritol, and/or from groups consisting of polyester polyols, poly- caprolactone polyols, polyether polyols, polycarbonate polyols and mixtures thereof .

6. The composition according to claim 5, characterized in that the polyester polyols are selected from esters of polyols having from 2 to 10 carbon atoms and dicarboxylic acids having from 4 to 10 carbon atoms.

7. The composition according to claim 5, characterized in that the polyester polyols are adipic esters of 1,4- butanediol, 1, 6-hexanediol and 1, 10-decanediol .

8. The composition according to claim 5, characterized in that the polycaprolactone polyols are reaction products of E-caprolactone with a low-molecular-weight polyol having from 2 to 10 carbon atoms preferably selected from 1, 4-butanediol, 1, 6-hexanediol, 1, 10-decanediol and neopentylglycol .

9. The composition according to claim 5, characterized in that ths polyether polyols are polytetramethylenegly- col (PTMG) or the condensation product of a polyol, pref- erably glycerin or trimethylolpropane, with ethylene oxide and/or propylene oxide having a molecular weight ranging from 100 to 1,000 g/mole or mixtures thereof.

10. The composition according to claim 5, characterized in that the polycarbonate polyols are aliphatic polycar- bonates containing 1, 4-butanediol, 1, 6-hexanediol , 1, 10- decanediol, trimethylolpropane or neopentylglycol units.

11. The- composition according to claim 1 or claim 4, characterized in that component (B) consists of one or more polyols having a functionality ranging from 2 to 3.

12. The composition according to claim 1, characterized in that .the polyol of component (B) is indifferently the same as or different from that used for the synthesis of the prepolymer of component (A) .

13. A process for the production of organic glass which envisages a casting and polymerization process of poly- merizable liquid compositions of the polyurethane type, which comprises the following phases: a) mixing two components (A) and (B) in a weight ratio varying from 1.2:1 to 2.2:1, wherein component (A) consists of a mixture of a cyclo-aliphatic diisocyanate monomer and a prepolymer obtained by reaction between said cyclo-aliphatic diisocyanate monomer and one or more ^T^O1^ΛΛO1Ξ havin^g two or more Ix^drox^l crouds τ">er molecule and a molecular weight ranging from 100 to 2,000 g/mole,^■ with a weight ratio between cyclo-aliphatic diisocyanate monomer and prepolymer which is such that the final weight percentage of the free isocyanate groups in said component (A) varies from 20% to 30% with respect to the total weight of component (A) ; and component (B) consists of one or more polyols having a molecular weight ranging from 100 to 2,000 g/mole and a functionality varying from 2 to 5 ; b) addition of a polymerization catalyst to the po- lymerizable liquid composition obtained in phase a) ; c) mixing for a time varying from 5 to 10 minutes, at an absolute pressure ranging from 5 to 10 mbar and a temperature ranging from 10⁰C to 30⁰C; d) filling one or more moulds and polymerization of the liquid composition by thermal treatment with tempera- tures ranging from 30 to 110⁰C and with polymerization times varying from 1 hour to 10 hours.

14. The process according to claim 13, characterized in that the polymerizable liquid composition is a composition according to any of the claims from 2 to 12.

15. The process according to claim 13 or 14, characterized in that the polymerization catalyst is a catalyst of the metallic type, wherein the metal is selected from tin, zinc, bismuth, titanium, zirconium and mercury.

16. The process according to claim 15, characterized in that the catalyst is selected from salts of said metals such as dibutyl tin dilaurate, bismuth nitrate, zinc naphthenates, phenyl mercury neodecanoate .

17. The process according to claim 15, characterized in that the catalyst is phenyl mercury neodecanoate.

18. The process according to claim 13 or 14, characterized in that the concentration of catalyst ranges from 50 to 2,000 ppm .

19. The process according to claim 17, characterized in that the concentration of phenyl mercury neodecanoate ranges from 50 to 300 ppm.

20. The process according to claim 13 or 14, characterized in that possible additives are incorporated into component (A) or component (B) or both before the mixing phase a) or they are added during the mixing phase a) of the two components.

21. The process according to claim 20, characterized in that the additives are detaching agents, dyes, bluing agents, UV absorbers, IR absorbers, light stabilizers and/or antioxidants .

22. The process according to claim 20, characterized in that the additive consists of inorganic nanoparticles based on salts, or preferably based on zinc oxide, cerium oxide,- silicon oxide,- aluminum oxide, titanium oxide or zirconium oxide.

23. The process according to claim 13 or 14, characterized in that the mixing phase a) is carried out at a temperature close to room temperature (20-30⁰C) and an absolute pressure of 5-10 mbar until a homogeneous mixture is reached.

24. The process according to claim 13 or 14, characterized in that phase a) is carried out for a time ranging from about 1 hour to about 3 hours .

25. The process according to claim 13 or 14, characterized in that phase b) for the addition of the catalyst is carried out in the same mixer in which phase a) is effected or in a second mixer, possibly preceded by a filtration process.

26. The process according to claim 13 or 14, characterized in that phase d) is carried out for a time ranging from 2 to 8 hours.

27. Organic glass obtained by means of the process according to one of the claims from 13 to 26.

28. End-products or optical articles obtained from the processing of the organic glass according to claim 27.

29. End-products or optical articles according to claim 28, such as ophthalmic lenses and solar filters, protective screens, display windows, manifolds and solar and photovoltaic panels, substrates for optical disks, display panels and video-terminals .