Polymerization catalyst for polythiourethanes, polymerizable liquid composition and process for the production of organic polythiourethane glass with a high refractive index

Abstract

Polymerizable liquid compositions containing three components (A), (B) and (C) are provided, wherein component (A) contains at least one cycloaliphatic diisocyanate monomer wherein the weight percentage of free isocyanate groups in component (A) ranges from about 20% to about 50% by weight with respect to the total weight of component (A); component (B) contains at least one polythiol having a molecular weight ranging from 50 to 1,200 g/moles and a functionality ranging from 2 to 5, the components (A) and (B) being present in a weight ratio varying from 0.5:1 to 2:1; and component (C) being a defined polymerization catalyst. A process for the production of organic glass using the polymerizable liquid composition is further provided.

Claims

1. A polymerizable liquid composition of polythiourethane, comprising three components (A), (B), and (C), wherein component (A) is selected from 4,4-methylene bis(cyclohexyl isocyanate) and bis(isocyanate methyl) cyclohexane; component (B) is selected from 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol and a mixture of 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol and ethylene glycol-di(3-mercaptopropionate), wherein said components (A) and (B) are present in a weight ratio varying from 0.5:1 to 2:1; component (C) being a catalyst for organic polythiourethane glass, wherein the catalyst does not contain organometallic compounds and consists of a mixture of a tertiary amine and a disubstituted phosphoric acid, wherein the component (C) is selected from a mixture of triethylamine and bis(2-ethylhexyl)phosphate and a mixture of methyl-1,2,2,6,6-pentamethyl-4 piperidinyl sebacate and bis(1,2,2,6,6-pentamethyl-4 piperidinyl)sebacate with bis(2-ethylhexyl)phosphate, wherein the tertiary amine and the disubstituted phosphoric acid are present in a molar ratio ranging from 1/1.3 to 1/20.

2. The polymerizable composition according to claim 1, wherein component (A) is 4,4-methylene bis(cyclohexyl isocyanate) and component (B) is a mixture of 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol and ethylene glycol-di(3-mercaptopropionate).

3. The polymerizable composition according to claim 1, wherein the quantity of component (C) ranges from 0.1 to 2% by weight with respect to the total weight of the polymerizable composition.

4. The polymerizable composition according to claim 3, wherein the quantity of component (C) ranges from 0.2 to 1.5% by weight with respect to the total weight of the polymerizable composition.

5. The polymerizable composition according to claim 1, wherein the catalyst consists of mixtures of triethylamine and bis(2-ethylhexyl)phosphate.

6. A process for the production of organic glass which provides a casting and polymerization process of the polymerizable liquid composition of polyurethane, according to claim 1, comprising the following phases: a mixing phase a) of components (A) and (C); a mixing phase b) of the solution obtained in the mixing phase a) and component (B), optionally in the presence of other additives; a filtration phase c) to remove any pollutants dispersed in the mixture, said filtration phase also being effected alternatively or additionally, on the single components (A) and (B) before the mixing phase b); a filling phase d) of a mould, wherein the mixture obtained at the end of phase c) is placed inside the mould; and a polymerization phase e) wherein the liquid composition placed in the mould, is polymerized by thermal treatment.

7. Organic glass obtained by the process according to claim 6.

8. Manufactured products or optical articles obtained by the processing of the organic glass according to claim 7.

9. Manufactured products or optical articles according to claim 8, selected from the group consisting of ophthalmic lenses, solar filters, Fresnel lenses, protective and safety shields, displays, substrates for optical disks, display panels and video display units, optical guides, components for mobile phones, transparent tubes.

Description

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(1) As already indicated, the present invention relates to a casting and polymerization process of polymerizable liquid compositions of the polythiourethane type for the production of organic glass with a high refractive index, having good optical and physico-mechanical properties.

(2) The polymerizable liquid composition according to the present invention is composed of component (A), component (B) and component (C).

(3) Component (A)

(4) Component (A) of the polymerizable composition according to the present invention contains at least one cycloaliphatic diisocyanate monomer or a mixture of cycloaliphatic diisocyanate monomers, wherein the weight percentage of free isocyanate groups in said component (A) ranges from about 20% to about 50% by weight with respect to the total weight of component (A) and, preferably, ranges from about 25% to about 40% by weight with respect to the total weight of component (A).

(5) Examples of cycloaliphatic diisocyanate monomers corresponding to component (A) of the composition according to the present invention are cyclohexane diisocyanate, methyl cyclohexane diisocyanate, bis(isocyanate methyl)cyclohexane, 4,4-methylene bis(cyclohexyl isocyanate), 4,4-isopropylidene bis(cyclohexyl isocyanate), 4,4-dicyclohexylmethane diisocyanate), bis(isocyanate cyclohexyl)methane, bis(isocyanatecyclohexyl)-2,2-propane, bis(isocyanatecyclohexyl)-1,2-ethane, 3-isocyanate methyl-3,5,5-trimethyl cyclohexyl isocyanate commonly known as isophorone diisocyanate, 2,5(6)diisocyanate-methylbicyclo(2,2,1)heptane and octahydro-4,7-methane-1H-indendylmethyldiisocyanate.

(6) The cycloaliphatic diisocyanate monomer of component (A) of the composition according to the present invention is preferably selected from 4,4-methylene bis(cyclohexyl isocyanate) and bis(isocyanate methyl)cyclohexane.

(7) Component (B)

(8) Component (B) of the polymerizable composition according to the present invention contains one or more polythiols having a molecular weight ranging from 50 to 1,200 g/moles and preferably from 100 to 1,000 g/moles and a functionality from 2 to 5 and preferably from 2 to 4, said polythiols being selected from polythiols having general formula (3):

(9) ##STR00004##
wherein:
R represents alkylidene groups having from 1 to 6 carbon atoms, the same or different; R1 represents alkyl groups having from 1 to 10 carbon atoms, the same or different; n ranges from 1 to 6; m varies from 1 to 6; p varies from 1 to 4; q is equal to 0 or 1 and p+q is equal to 4;
polythiols having general formula (4):

(10) ##STR00005##
wherein:
R represents an alkylidene group having from 1 to 6 carbon atoms; n ranges from 1 to 6; m ranges from 1 to 6; and/or polythiols having general formula (5):

(11) ##STR00006##
wherein:

(12) R1=(CH.sub.2).sub.nSH; R2=S(CH.sub.2).sub.nSH; R3=RS(CH.sub.2).sub.nSH; R is an alkyl group having from 1 to 10 carbon atoms and n ranges from 1 to 3.

(13) Examples of thiols having general formula (3), as component (B) of the polymerizable composition according to the present invention are: pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(thioglycolate), trimethylolpropane tris(thioglycolate), trimethylolpropane tris(3-mercaptopropionate).

(14) Examples of thiols having general formula (4), as component (B) of the polymerizable composition according to the present invention are: ethyleneglycol-di(3-mercaptopropionate), ethyleneglycol-di(2-mercaptoacetate), polyethyleneglycol-di(2-mercapto-acetate), polyethyleneglycol-di(3-mercaptopropionate), polypropyleneglycol-di(2-mercaptoacetate), polypropyleneglycol-di(3-mercaptopropionate).

(15) Examples of thiols having general formula (5), as component (B) of the polymerizable composition according to the present invention are: 2,3-bis((2-mercaptoethyl)thio)-1-mercaptopropane, 5,7-dimercaptomethyl-1,1-dimercapto-3,6,9-trithiaun-decane, 4,7-dimercaptomethyl-1,1-dimercapto-3,6,9-trithiaun-decane, 4,8-dimercaptomethyl-1,1-dimercapto-3,6,9-trithiaun-decane, 1,1,3,3-tetrakis(mercaptomethylthio)propane, 1,1,2,2-tetrakis(mercaptomethylthio)ethane.

(16) Examples of preferred thiols are 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol and a mixture of 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol and ethylene glycol-di(3-mercaptopropionate)

(17) Examples of components (A) and (B) preferably used are 4,4-methylene bis(cyclohexyl isocyanate), as component (A), ethylene glycol-di(3-mercaptopropionate), and 2,3-bis(2-mercaptoethyl)thio)-1-propanethiol, as component (B).

(18) The organic glass or optical articles according to the present invention are prepared by the polymerization reaction of components (A) and (B) according to suitable weight ratios which generally vary from 0.5:1 to 2:1, in the presence of a suitable catalyst which forms component (C) and possibly further additives such as those listed below.

(19) Component (C)

(20) Component (C) of the polymerizable liquid composition according to the present invention is a polymerization catalyst which does not contain organometallic compounds and consists of a mixture of a tertiary amine represented by the following general formula (1):

(21) ##STR00007##
wherein:
R1, R2 and R3, equal to or different from each other, represent a C.sub.1-C.sub.20 linear or branched aliphatic group, or a C.sub.3-C.sub.20 cycloaliphatic group, said groups possibly containing heteroatoms such as N, O, P, S, halogens; a disubstituted phosphoric acid having general formula (2):

(22) ##STR00008##
wherein:
R2 and R4, equal to or different from each other, represent a linear or branched C.sub.1-C.sub.20 aliphatic group, or a C.sub.3-C.sub.20 cycloaliphatic group;
R3 and R5, equal to or different from each other, represent a C.sub.1-C.sub.3 alkylidene group and m and p are equal to 0, 1 or 2;
the tertiary aliphatic amine and disubstituted phosphoric acid being present in a molar ratio varying from 1/1.3 to 1/20 and, preferably, from 1/1.5 to 1/15.

(23) Amine compounds having formula (1) which can be used for the purposes of the present invention are tertiary aliphatic amines such as, for example: triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, triisobutylamine, benzyldimethylamine, n-methyl-morpholine, dimethylcyclohexylamine, 1,2,2,6,6-pentamethyl-4-piperidinol, 1,2,2,6,6-pentamethyl-4-hydroxyethyl-4-piperidinol, dimethyldipropylenetriamine, pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl)ether, N-methyl morpholine, triethylenediamine, bicyclo-octane diamine (DABCO), etc.

(24) Sterically hindered amines such as amines known as HALS and in particular liquid tertiary amines, can also be used, such as, for example: methyl-1,2,2,6,6-pentamethyl-4-piperidinyl sebacate; mixtures of methyl-1,2,2,6,6-pentamethyl-4-piperidinyl sebacate and bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate; bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate; bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) sebacate.

(25) Examples of preferred amines according to the present invention are triethylamine, tri-n-propylamine, tri-isopropylamine, and mixtures of methyl-1,2,2,6,6-pentamethyl-4 piperidinyl sebacate (preferably 25% by weight) and bis(1,2,2,6,6-pentamethyl-4 piperidinyl) sebacate (preferably 75% by weight).

(26) Examples of disubstituted phosphoric acid having formula (2) which can be used for the purposes of the present invention are: dimethylphosphate, diethylphosphate, diisopropylphosphate, dibutylphosphate, dioctylphosphate, bis(2-ethylhexyl)phosphate, diisodecylphosphate, methoxyethyl-ethoxyethylphosphate, methoxyethyl-propoxyethylphosphate, ethoxyethyl-propoxyethyl phosphate, ethoxyethyl-butoxyethyl phosphate, di(methoxy-ethyl)phosphate, di(ethoxyethyl)phosphate, di(propoxy-ethyl)phosphate, di(butoxyethyl)phosphate, di(hexyloxy-ethyl)phosphate, di(decyloxyethyl) phosphate, di(methoxy-propyl)phosphate, di(ethoxypropyl)phosphate, di(propoxy-propyl)phosphate and/or mixtures of the same.

(27) The disubstituted phosphoric acid used in the catalyst and therefore in the polymerizable liquid composition and process according to the present invention is preferably selected from C.sub.8 diester of phosphoric acid, C.sub.10 diester of phosphoric acid and/or mixtures thereof.

(28) Examples of preferred catalysts are mixtures of triethylamine and bis(2-ethylhexyl)phosphate or mixtures of methyl-1,2,2,6,6-pentamethyl-4 piperidinyl sebacate (25% by weight) and bis(1,2,2,6,6-pentamethyl-4 piperidinyl)sebacate (75% by weight) with bis(2-ethylhexyl)phosphate.

(29) According to the present invention, the quantity of component (C) ranges from 0.1 to 2% by weight with respect to the total weight of the polymerizable composition and preferably from 0.2% to 1.5% by weight with respect to the total weight of the composition.

(30) Additives

(31) Further additives can be incorporated into component (A) or component (B) or both, before the mixing phase or they can be added during the mixing phase of the two components.

(32) Non-limiting examples of these additives are dyes, including photochromatic dyes, bluing agents, UV absorbers of the family of benzotriazoles, IR absorbers, antioxidants, anti-fog agents and radical scavengers.

(33) A further improvement in the mechanical properties such as hardness, impact strength and abrasion resistance can be obtained by the addition of inorganic nanoparticles based on salts, or preferably based on zinc oxide, cerium oxide, silicon oxide, aluminium oxide, titanium oxide or zirconium oxide.

(34) The polymerizable composition according to the present invention does not require the separate addition of internal mould release agents such as non-ionic fluorinated surfactants, non-ionic silicon surfactants, quaternary alkylammonium salts or monoesters of phosphoric acid, as it is in itself inherently provided with self-release properties.

(35) With the polymerizable liquid composition according to the present invention, it is consequently possible to produce articles having a high refractive index with excellent optical and physico-mechanical properties, on an industrial scale, by means of simple and inexpensive casting techniques.

(36) An object of the present invention also relates to the organic glass obtained with the casting and polymerization process of said compositions.

(37) Finally, a further object of the present invention relates to end-products or optical articles comprising the organic glass obtained with the casting and polymerization process of the polymerizable composition according to the present invention, as previously described, such as, for example, ophthalmic lenses and solar filters, Fresnel lenses, protective and safety shields, displays, substrates for optical disks, display panels and video display units, optical guides, components for mobile phones, transparent tubes.

(38) These end-products or optical articles can also be produced by processing with tool machines starting from semi-finished articles.

(39) Said end-products or optical articles can be surface hardened with antiscratch coatings or they can be made non-reflective with techniques and materials normally used for ADC end-products.

(40) As previously indicated, the extremely low viscosity values of the polymerizable compositions according to the present invention combined with a good pot-life of the composition itself, allow perfectly homogeneous mixtures of the various components to be obtained, consequently allowing defect-free optical end-products to be produced on an industrial scale.

(41) This characteristic is essential in particular for the production process of organic glass by means of the manual casting technique, object of the present invention, as, thanks to this, it is possible to fill a considerable number of moulds in short times, thus satisfying the fundamental requisite for industrial-type production.

(42) The polythiourethane thermosetting plastic materials, i.e. the organic glass obtained with the process according to the present invention, have excellent optical properties and an excellent processability, similar to those which characterize ADC polymers but, with respect to the latter, they are equipped with a much higher impact strength and toughness. These characteristics make the material suitable for the manufacturing of complex end-products which cannot be produced with ADC polymers.

(43) As already observed, the quantity of catalyst and the molar ratio between the two components tertiary amine and disubstituted phosphoric acid, can be defined and optimized in the process according to the present invention so as to obtain a pot-life of the polymerizable composition which varies from short to sufficiently long and, at the same time, obtain a reduced polymerization time in the mould, which is economically advantageous, and makes the catalyst and therefore the process according to the present invention suitable for industrial production, as will appear evident from the following experimental examples.

(44) In these examples, the pot-life at 25 C. of the polymerizable composition according to the present invention was evaluated by measuring the viscosity in consecutive times, starting from the preparation.

(45) Starting from the assumption that the processing of the mixture (in particular the filtration and filling of the mould) becomes too difficult if the viscosity increases to over 300 cStokes, the pot-life is defined, within the scope of the present invention, as the time range necessary for reaching this viscosity value. Consequently according to the previous definition, an adequate pot-life at 25 C. is equal to at least 2 hours.

(46) Flat sheets and ophthalmic lenses were prepared with the polymerizable liquid compositions of the following examples, using the casting technique in moulds assembled as previously described and using, depending on the specific cases, gaskets made of plasticized polyvinylchloride, low density polyethylene (LDPE), or another suitable material, compatibly with the processing conditions.

(47) In particular, it has been surprisingly found that, thanks to the use, as polymerization catalysts, of a specific mixture of tertiary amines (preferably trialkylamines) and disubstituted phosphoric acid (preferably alkylphosphates) in a precise molar ratio which must not be stoichiometric, but ranging from 1/1.3 to 1/20, it is possible to obtain a better control of the pot-life with respect to the reactivity, also obtaining a high flexibility degree in the catalysis of the reaction and in the mould release properties.

(48) 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 indicated in the following experimental examples.

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

(50) (a) Optical Characteristics

(51) Refraction index (n.sup.D.sub.20): measured with an Abbe refractometer (ASTM D-542);

(52) Yellow index (YI), (ASTM D-1925), determined with a Macbeth Colour i5 spectrophotometer and defined as:
YI=100/Y.Math.(1.277X1.06Z)

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

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

(55) (b) Physical and Mechanical Characteristics

(56) Density: determined with hydrostatic scales at a temperature of 20 C. (ASTM D-792);

(57) Rockwell hardness (M) measured with a Rockwell durometer (ASTM D-785);

(58) Unnotched Izod impact strength (ASTM D-256 modified);

(59) Deflection temperature under flexural load 1.82 MPa (HDT) (ASTM D-648).

(60) (c) Chemical Resistance

(61) The formation of defects in samples of flat plates was evaluated after immersion for 5 minutes in the following solvents: acetone, ethyl alcohol, H.sub.2SO.sub.4 (aqueous solution at 40%) and NaOH (aqueous solution at 10%).

(62) The advantages deriving from the casting and polymerization process of the polymerizable compositions according to the present invention with respect to processes and compositions of the known art which in some cases are provided for comparative purposes, are evident from the following examples

Example 1

(63) The composition nr. 1 was prepared according to the present invention, consisting of components (A), (B) and (C) in the quantities indicated in Table 1.

(64) Component (A)

(65) Component (A) consists of 4,4-methylene bis(cyclohexyl isocyanate).

(66) Component (B)

(67) Component (B) is obtained by mixing at 25 C. and 10 mbar of pressure: ethyleneglycol-di(3-mercaptopropionate) and 2,3-bis((2-mercaptoethyl)thio)-1-propanthiol.

(68) Component (C)

(69) Component (C) is obtained by mixing at 25 C., triethylamine and bis(2-ethylhexyl)phosphate.

(70) TABLE-US-00001 TABLE 1 Composition n 1 Component (A) H12MDI, g 1500 Component (B) GDMP, g 100 (mixture) DMPT, g 900 Component (C) TEA, g 0.82 (mixture) Bis(2-EHP),g 8.18 Molar ratio TEA/Bis(2-EHP) 1/3.1 Legend H12MDI = 4,4-methylene bis(cyclohexyl isocyanate) GDMP = ethyleneglycol-di(3-mercaptopropionate) DMPT = 2,3-bis((2-mercaptoethyl)thio)-1-propanthiol TEA = triethylamine Bis(2-EHP) = bis(2-ethylhexyl)phosphate
Casting (Manual Casting)

(71) 1,500 g of component (A) and 9 g of component (C) previously prepared and consisting of 0.82 g of TEA and 8.18 g of Bis(2-EHP) (molar ratio TEA/Bis(2-EHP)=1/3.1), were charged into a two-necked jacketed flask, equipped with a thermometer and magnetic stirrer.

(72) The whole solution was mixed at 25 C. for about 1 hour in an inert nitrogen atmosphere. 1,000 g of component (B) previously prepared, were added to the degassed and limpid solution thus obtained.

(73) The whole solution was mixed at 25 C. for about 30 minutes, at an absolute pressure of 10 mbar, obtaining a polymerizable composition according to the present invention, on which the pot-life was evaluated with time at 25 C., by means of viscosity measurements at the same temperature (Table 2).

(74) TABLE-US-00002 TABLE 2 Composition n 1 Initial Viscosity at 25 C. (cSt) 34 Viscosity after 1 hour at 25 C. (cSt) 64 Viscosity after 2 hours at 25 C. (cSt) 111 Viscosity after 3 hours at 25 C. (cSt) 177 Viscosity after 4 hours at 25 C. (cSt) 276

(75) The data indicate a pot-life higher than 4 hours and therefore suitable for the production of optical articles on an industrial scale with the manual casting technique.

(76) The polymerizable composition thus obtained was poured into glass moulds and subjected to polymerization in a forced circulation oven with a gradual temperature increase from 40 C. to 130 C. in 24 hours.

(77) At the end of the polymerization, upon opening the moulds, neutral lenses having a thickness of 2 mm and flat plates having a thickness of 3 mm were recovered, without any problems of pre-release or damage of the moulds, on which the characteristics indicated in Table 3 were determined.

(78) For comparative purposes, the same table also indicates the properties of the ADC polymer obtained by polymerization as previously described.

(79) TABLE-US-00003 TABLE 3 Composition n 1 ADC n.sup.D.sub.20 1.592 1.500 Abbe number 42 58 Density, 20 C., g/ml 1.225 1.311 YI.sup.(a) 0.50 0.80 Light transmittance, Y 91 92 Haze, % 0.1 0.1 Rockwell hardness.sup.(a) 112 97 Unnotched Izod impact strength, kJ/m.sup.2 108 25 HDT, C. 102 58 Chemical resistance Acetone No No (defects) C.sub.2H.sub.5OH H.sub.2SO.sub.4 NaOH

(80) The polythiourethane according to the present invention shows high refractive index values and a high Abbe number, excellent optical and physico-mechanical properties, the same or higher than those of the ADC polymer, in particular a density about 7% lower, an impact strength over 4 times higher and an HDT over 40 C. higher.

Example 2

(81) Following the procedure of Example 1, the compositions from nr. 2 to 5 were prepared according to the present invention, consisting of Components (A), (B) and (C) in the quantities and under the conditions indicated in Table 4.

(82) TABLE-US-00004 TABLE 4 Composition n 2 3 4 5 Component (A) H12MDI, g 1530 1500 1500 1500 Component (B) GDMP, g 50 100 100 (mixture) DMPT, g 1000 950 900 900 Component (C) TEA, g 0.9 0.75 1.0 0.68 (mixture) Bis(2-EHP)g 3.75 3.75 8.0 6.8 Molar ratio TEA/Bis(2-EHP) 1/1.3 1/1.5 1/2.5 1/3.1

(83) The initial viscosity was measured on the degassed and limpid solutions thus obtained, and subsequently the viscosity, at the same temperature, in consecutive times, obtaining the values indicated in Table 5.

(84) TABLE-US-00005 TABLE 5 Composition n 2 3 4 5 Initial Viscosity at 25 C. (cSt) 52 53 40 40 Viscosity after 1 hours at 25 C. 121 146 91 80 (cSt) Viscosity after 2 hours at 25 C. 250 274 182 128 (cSt) Viscosity after 3 hours at 25 C. 464 505 346 220 (cSt)

(85) The data indicate in each case a pot-life higher than 2 hours and consequently suitable for the production of optical articles on an industrial scale with the manual casting technique.

(86) From the data indicated in Table 5, it is also evident how the stability of the mixture according to the present invention can be varied, by modifying the concentration of the catalyst and molar ratio between the two components of the catalyst.

(87) The polymerizable compositions from nr. 2 to nr. 4 thus obtained were poured into glass moulds and subjected to polymerization in a forced circulation oven with a gradual temperature increase from 40 C. to 130 C. in 24 hours.

(88) At the end of the polymerization, upon opening the moulds, flat plates having a thickness of 3 mm were recovered, without any problems of pre-release or damage of the moulds, on which the characteristics indicated in Table 6 were determined, in which it can be seen that the transparent polythiourethanes according to the present invention have excellent optical and physico-mechanical properties, completely analogous to those obtained with the polymerizable compositions of Example 1 of the present invention.

(89) TABLE-US-00006 TABLE 6 Composition n 2 3 4 5 n.sup.D.sub.20 1.595 1.594 1.591 1.592 Abbe number 41 41 41 41 Density, 20 C., g/ml 1.221 1.226 1.226 1.225 Light transmittance, Y 91 91 91 91 Haze, % 0.13 0.11 0.10 0.13 Rockwell Hardness.sup.(a) 114 113 112 112 Unnotched Izod impact 85 94 106 105 strength, kJ/m.sup.2 HDT, C. 119 105 103 100 Chemical Acetone No No No No resistance C.sub.2H.sub.5OH (defects) H.sub.2SO.sub.4 NaOH

Example 3

(90) Composition nr. 6 was prepared according to the present invention, consisting of Components (A), (B) and (C) in the quantities indicated in Table 7.

(91) Component (C) is obtained by mixing the following products at 25 C.:

(92) methyl-1,2,2,6,6-pentamethyl-4-piperidinyl sebacate (25% by weight) and bis(1,2,2,6,6-pentamethyl-4 piperidinyl)sebacate (75% by weight);

(93) bis(2-ethylhexyl)phosphate (Bis(2-EHP)).

(94) TABLE-US-00007 TABLE 7 Composition n 6 Component (A) H12MDI, g 1500 Component (B) GDMP, g 100 (mixture) DMPT, g 900 Component (C) Mixture of tertiary amines, g 1.3 (mixture) Bis(2-EHP), g 7.8 Molar ratio (Tertiary amines)/Bis(2-EHP) 1/8.9

(95) The initial viscosity was measured on the degassed and limpid solution thus obtained, and subsequently the viscosity, at the same temperature, in consecutive times, obtaining the values indicated in Table 8.

(96) TABLE-US-00008 TABLE 8 Composition n 6 Initial Viscosity at 25 C. (cSt) 47 Viscosity after 1 hour at 25 C. 90 (cSt) Viscosity after 2 hours at 25 C. 145 (cSt) Viscosity after 3 hours at 25 C. 230 (cSt)

(97) The data indicate a pot-life higher than 2 hours and consequently suitable for the production of optical articles on an industrial scale with the manual casting technique.

(98) The polymerizable composition nr. 6 thus obtained was poured into glass moulds and subjected to polymerization in a forced circulation oven with a gradual temperature increase from 40 C. to 130 C. in 24 hours.

(99) At the end of the polymerization, upon opening the moulds, flat plates having a thickness of 3 mm were recovered, without any problems of pre-release or damage of the moulds, on which the characteristics indicated in Table 9 were determined, in which it can be seen that the transparent polythiourethane according to the present invention has excellent optical and physico-mechanical properties, completely analogous to those obtained with the polymerizable compositions of Example 1 of the present invention.

(100) TABLE-US-00009 TABLE 9 Composition n 6 n.sup.D.sub.20 1.591 Abbe number 42 Density, 20 C., g/ml 1.226 Light transmittance, Y 91 Haze, % 0.12 Rockwell Hardness.sup.(a) 112 Unnotched Izod impact strength, kJ/m.sup.2 104 HDT, C. 104 Chemical resistance Acetone No (defects) C.sub.2H.sub.5OH H.sub.2SO.sub.4 NaOH

Comparative Example 1

(101) The comparative compositions nr. 1C and nr. 2C consisting of Components (A), (B) and (C) in the quantities and under the conditions indicated in Table 10.

(102) TABLE-US-00010 TABLE 10 Comparative composition n 1C 2C Component( A) H12MDI, g 1500 1500 Component (B) GDMP, g 100 100 (mixture) DMPT, g 900 900 Component (C) TEA, g 0.9 0.9 (mixture) Bis(2-EHP), g 2.9 3.2 Molar ratio TEA/Bis(2-EHP) 1/1 1/1.1

(103) The viscosity was measured on the degassed and limpid solutions thus obtained, at 25 C. one hour after the preparation, which proved to be higher than 500 cStokes and consequently these compositions are not suitable for the production of optical articles on an industrial scale with the manual casting technique as their pot-life is much lower than 2 hours.

(104) The polymerizable composition nr. 1C thus obtained however was poured into glass moulds and subjected to polymerization in a forced circulation oven with a gradual temperature increase from 40 C. to 130 C. in 24 hours.

(105) At the end of the polymerization it was not possible to open the moulds and recover the polymer sheet due to the excessive adhesion to the glass of the mould.

Comparative Example 2

(106) The comparative compositions nr. 3 and nr. 4 of Table 11 were prepared operating according to what is described in patent application JP2008074957.

(107) TABLE-US-00011 TABLE 11 Component Comparative composition n 3 4 Diisocyanate m-xylylenediisocyanate, g 36.4 Mixture of 2,5-bis(isocyanate- 39.9 methyl)-bicyclo-[2.2.1]-heptane and 2,6-bis(isocyanatemethyl)-bicyclo- [2.2.1]-heptane, g Polithiol + Mixture of 4-mercaptomethy1-1,8- 33.6 amine dimercapto-3,6-dithiaoctane + triethylamine (1040 ppm), g Mixture of 4-mercaptomethy1-1,8- 33.6 dimercapto-3,6-dithiaoctane + triethylamine (1100 ppm), g Sulfonic Methanesulfonic acid, g 0.07 0.074 Acid

(108) Contrary to what is claimed in the above document, upon the addition of triethylamine, the immediate formation of a viscous gel was observed in both solutions, and consequently they are not suitable for the production of optical articles on an industrial scale.

(109) The same result was observed by inverting the order of the addition of the amine and sulfonic acid.