PROCESS FOR THE PREPARATION OF SUBSTITUTES FOR OPTICAL GLASSES AND POLYMERIZABLE LIQUID COMPOSITION SUITABLE TO THAT PURPOSE

Abstract: Substitute for optical glasses are obtained by submitting to polymerization, in the presence of a free-­ radical initiator and in bulk, a polymerizable liquid composition containing: - monomer diethyleneglycol bis(allylcarbonate); - oligomer diethyleneglycol bis(allylcarbonate); - monomer tris(hydroxyethyl)isocyanurate tris(allylcarbon­ ate).

Description: The present invention relates to a polymerizable liquid composition on the basis of allylcarbonates, and to the conversion of said mixture into substitutes for optical glasses, having high optical and mechanical characteristics. The invention relates also to the substitutes for optical glasses thus obtained. In the field of the substitutes for optical glasses, the products of polymerisation of glycols bis(allylcarbonates) are interesting, such as, e.g., those disclosed in EP-A-0 035,304, and among these, the products from diethyleneglycol bis(allylcarbonate) polymerization are considerably interesting from the industrial viewpoint, and this in view of the optical and mechanical characteristics of such polymerizates. In particular, according to the prior art, mixtures of diethyleneglycol bis(allylcarbonate) and of a free-radical polymerization initiator are polymerized in glass moulds having a shape corresponding to the shape of the article which is to be manufactured, by operating by the casting technique. Such articles as flat sheets, ophthalmic lenses and safety lenses are thus produced. However, the use of diethyleneglycol bis(allylcarbonate) shows some limitations in the application field of the replacement of optical glasses. For example, it is not much suitable to the production of high-diopter lenses and of lenses having sharp curvature changes, such as Fresnel's lenses and lenticular lenses, and this because of its high shrinkage. Such a shrinkage causes the occurrence of stress phenomena which cause the separation from the mould, and sometimes breakage phenomena. In particular applications of high commercial interest, for example in the production of protecting shields, solar panels, lenses for hunters, and so forth, substitutes for optical glasses having impact strength higher than that made possible by the polymerizates of diethyleneglycol bis(allylcarbonate) are required. Thus, EP-A-0114080 filed on July 25, 1984 a polymerizable liquid composition is disclosed, which is constituted by an oligomer of a bis(allylcarbonate) of a dihydroxy alcohol and by a monomer of a bis(allylcarbonate) of a dihydroxy alcohol or of a tris(allylcarbonate) of a trihydroxyalcohol and/or of an acrylic or vinyl monomer. These compositions give rise to polymerizates suitable for use as substitutes for optical glasses, satisfactory both as regards the shrinkage phenomena during the polymerization step, and the physical and mechanical characteristics of the same polymerizates. However, these liquid compositions have often viscosity values higher than 3.0 · 10⁻⁴ m²/s (300 centistokes) at 25°C and such a characteristic thereof can create difficulties in their conversion into manufactured articles, during their processing by the casting technique. It resulted hence desirable to have available compositions of allylcarbonates liquid and sufficiently fluid under room conditions to overcome the processing difficuties previously briefly mentioned and polymerizable, under the usual polymerization conditions, with low shrinkage, in the production of substitutes for optical glasses having improved characteristics, in particular as regards the impact resistance. It has been found now that such a requirement can be fulfilled when the substitutes for the optical glasses are prepared by the casting technique, by starting from a polymerizable liquid allylcarbonate composition consisting of the following components: from 10% to 50% by weight of component (A) which is the monomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of at least 10:1; from 20% to 70% by weight of component (B) which is an oligomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of 2:1, said oligomer product having the formula: wherein R is the radical of diethylene glycol and n has a value, or an average value, of from 2 to 5; from 5% to 50% by weight of component (C) which is the monomer product of tris(hydroxyethyl )isocyanurate tris(allylcarbonate) resulting from the reaction of diallylcarbonate with tris(hydroxyethyl )isocyanurate in the presence of a basic catalyst in a molar ratio of at least 10:1, and a free-radical initiator in an amount of from 1% to 6% by weight relative to the total weight of said (A), (B) and (C) components, said composition having a kinematic viscosity at 25°C lower than 0,00025 m²/s (250 cSt). The component (A) of the polymerizable liquid composition is a monomer of diethyleneglycol bis(allylcarbonate), definable by the formula: wherein R is the diethyleneglycol radical. This component is prepared by the reaction between diallylcarbonate and diethyleneglycol in molar ratio to each other of at least 10/1, operating in the presence of a basic catalyst, for example according to as disclosed in EP-A-0 035,304. Under these conditions, a reaction product constituted by at least 80-90% by weight of compound (I), the residual percentage being constituted by oligomers of diethyleneglycol bis(allylcarbonate). Thus, the component (A) of the polymerizable liquid composition can be constituted by the compound (I) only, or by a mixture containing at least 80-90% by weight of compound (I), the residual percentage being constituted by its oligomers. In the preferred form of embodiment the component (A) is present in the polymerizable liquid composition in an amount of from 15 to 45% by weight. The component (B) of the polymerizable liquid composition is an oligomer or a mixture of oligomers of diethyleneglycol bis(allylcarbonate), definable by the formula: wherein R is the diethyleneglycol radical and n has a value, or an average value, of from 2 to 5. This component is prepared by the reaction between diallylcarbonate and diethyleneglycol in molar ratio to each other of the order of 2/1, operating in the presence of a basic catalyst, similarly to the preceding component (A). Under these conditions, an essentially oligomeric reaction product corresponding to the above formula (II) is obtained, with an n average value of 3 and constituted by at least 60-70% by weight by oligomers, the residual percentage being constituted by monomer diethyleneglycol bis(allylcarbonate). In the preferred form of embodiment, the component (B) is present in the polymerizable liquid composition in an amount of from 30 to 60% by weight. The component (C) of the polymerizable liquid composition is a monomer of tris(hydroxyethyl)isocyanurate tris(allylcarbonate), definable by the formula: This component is prepared by the reaction between diallylcarbonate and tris(hydroxyethyl)isocyanurate in molar ratio to each other of at least 10/1, operating in the presence of a basic catalyst, similarly to as for the preceding component (A). Under these conditions, a reaction product constituted by at least 60-70% by weight of compound (III) is obtained, the residual percentage being constituted by oligomers of tris(hydroxyethyl)isocyanurate tris(allylcarbonate). Thus, the component (C) of the polymerizable liquid composition can be constituted by the compound (III) only, or by a mixture containing at least 60-70% by weight of compound (III), the residual percentage being constituted by its oligomers. In the preferred form of embodiment the component (C) is present in the polymerizable liquid composition in an amount of from 10 to 45% by weight. The polymerizable liquid composition of the present invention contains moreover one or more polymerization initiators, soluble in the same composition, and able to generate free radicals within a temperature range of from 30 to 120°C. Non limiting Examples of such initiators are diisopropylperoxydicarbonate,dicyclohexylperoxydicarbonate, disec.butylperoxydicarbonate, dibenzoylperoxide and tert-butylperbenzoate. In the preferred form of embodiment, the polymerization initiator is present in an amount of from 3 to 5,5% by weight, relatively to the total of the weights of components (A), (B) and (C). The polymerizable liquid composition on the present invention can additionally contain one or more conventional additives, such as stabilizers, release agents, dyes, pigments and U.V. absorbers or I.R. absorbers however in an overall amount not greater than 1% by weight relatively to the total of the weights of components (A), (B) and (C). The polymerizable liquid composition of the present invention has viscosity values lower than 2.5 · 10⁻⁴ m²/s (250 centistokes) at 25°C and typically comprised within the range of from 0.5 · 10⁻⁴ to 2.0 · 10⁻⁴ m²/s (50 to 200 centistokes) at 25°C. These viscosity values render the same composition particularly suitable to the processing by the casting technique, according to which the composition is poured into moulds of shape corresponding to the shape of the article which is to be manufactured, operating at a temperature lower than the decomposition temperature of the free-radical initiator, and the composition is then polymerized inside the mould. In particular, said polymerization is carried out by heating the polymerizable liquid composition at a temperature of from 30 to 120°C. The corresponding polymerization times vary within a range from 3 to 100 hours. In this polymerization, the volume shrinkage phenomena are very limited, the shrinkage being in any cases lower than about 10% by volume. Thus, those stress phenomena, which cause the separation of the polymerizate from the mould and the breakage of the same polymerizate are avoided. Furthermore, such polymerizates have a set of such optical and mechanical characteristics as to make them particularly useful as substitutes for optical glasses. Among the mechanical characteristics, the impact strength, which is in any case higher than 12 kJ/m² (12 kg/cm²), is particularly good. In the following experimental Examples, reported to only exemplifying and not limitative purpose, the following components have been used for the polymerizable liquid composition. (A) monomer of diethyleneglycol bis(allylcarbonate): product of the reaction between diallylcarbonate and diethyleneglycol in molar ratio to each other of 12/1, by operating as disclosed in EP-A-0 035,304. This product contains 85-90% by weight of diethyleneglycol bis(allylcarbonate) (I), the residual percentage being constituted by oligomers of the same; (B) oligomers of diethyleneglycol bis(allylcarbonate): product of the reaction between diallylcarbonate and diethyleneglycol in molar ratio to each other of 2/1, operating as disclosed in the above mentioned European Pat. Appln.. This product corresponds to the above formula (II) with n average value of 3, the monomer content being of the order of 35% by weight. (C) monomer of tris(hydroxyethyl)isocyanurate tris(allylcarbonate):product of the reaction between diallylcarbonate and tris(hydroxyethyl)isocyanurate in molar ratio to each other of 12/1, operating as disclosed in the above mentioned European Pat. Appln.. This product contains 75% by weight of tris(hydroxyethyl)isocyanurate tris(allylcarbonate) (III), the residual percentage being constituted by oligomers of the same. The components (A), (B) and (C) are mixed with each other in the proportions which are indicated hereunder, and to the mixture dicyclohexylperoxydicarbonate (DCPD) is then added in a constant amount of 5.2% by weight relatively to the total of the weights of (A), (B) and (C). The compositions thus obtained are poured, at room temperature (20-25°C), into moulds constituted by two glass sheets of dimensions of 20×20 cm, provided with a gasket of plastified polyvinylchloride of 3.2 mm in thickness. The polymerization is carried out in oven with forced air circulation, at the temperature of 48°C for 72 hours. At the end the sheets are removed from the moulds and are maintained at 110°C during the following two hours, to the purpose of destroying the possibly unreacted catalyst and releasing the stresses frozen during the polymerization step. The technological characteristics of the polymerizates thus obtained are reported in the following Tables. In particular, the following characteristics have been determined: a) Optical characteristics refractive index (n 20 / D ) by Abbe refractometer (ASTM D-542); % Haze and % transmittance in the visible band: measured by using Hazegard XL-211 marketed by Gardner Co. (ASTM D-1003); Yellow Index (YI), defined as: as measured by the Gardner XL-805 Colorimeter (ASTM D-1925). b) Physical and mechanical characteristics Density, as determined by hydrostatic balance at the temperature of 20°C (ASTM D-792); Volume shrinkage on polymerization, calculated by the following equation: Rockwell Hardness (M), as measured by Rockwell Durometer (ASTM D-785); Ultimate tensile strength and flexural elastic modulus (ASTM D-790); Abrasion strength,Taber method (ASTM D-1044 modified), carried out by using a pair of cs-10F grinding wheels and with a load of 500 g on both of them. The results are expressed as the ratio between the number of passages necessary to produce a 10% increase in Haze for the sample under test, and for a reference sample of poly(methylmetacrylate) (PMMA). IZOD Impact strength without notch (ASTM D-256 modified). c) Thermal characteristics High-load Deflection Temperature (HDT) (°C/1.8 2 MPa), (ASTM D-648). Example 1 A polymerizable liquid composition according to the invention (Test 1) and two comparative polymerizable liquid compositions (Tests 2 and 3) are prepared. These compositions are reported in Table 1, together with their viscosity and density values. These compositions are polymerized and in Table 3 the characteristics are reported of the thus obtained polymers. Example 2 Polymerizable liquid compositions are prepared according to the invention (Tests from 4 to 12) and in Table 2 the same compositions are reported, together with their viscosity and density values. These compositions are polymerized and in Table 4 the characteristics of the polymers thus obtained are reported. Composition Test 1 Test 2 Test 3 Density (g/cm³) 1.337 1.311 1.352 Volume Shrinkage (%) 9.6 12.1 7.8 n 20 / D 1.5036 1.5004 - YI 1.2 0.8 1.2 Haze (%) 0.15 0.1 0.5 Transmittance in visible band (%) 93.1 93.3 93 Rockwell Hardness (M) 99 97 99 Flexural Modulus (MPa) 2800 2300 2500 Flexural ultimate tensile strength (MPa) 100 78 90 Izod Impact Resistance modified (KJ/m²) 12.8 8 14.3 Taber Abrasion Strength (xPMMA) 16 17 15 HDT (°C) 70 66.3 57

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, LI, LU, NL, SE A liquid polymerizable allylcarbonate composition for the preparation of optical glass substitutes, consisting of the following components: from 10% to 50% by weight of component (A) which is the monomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of at least 10:1; from 20% to 70% by weight of component (B) which is an oligomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of 2:1, said oligomer product having the formula: wherein R is the radical of diethylene glycol and n has a value, or an average value, of from 2 to 5; from 5% to 50% by weight of component (C) which is the monomer product of tris(hydroxyethyl)isocyanurate tris(allylcarbonate) resulting from the reaction of diallylcarbonate with tris(hydroxyethyl)isocyanurate in the presence of a basic catalyst in a molar ratio of at least 10:1, and a free-radical initiator in an amount of from 1% to 6% by weight relative to the total weight of said (A), (B) and (C) components, said composition having a kinematic viscosity at 25°C lower than 0,00025 m²/s (250 cSt). Composition according to Claim 1, wherein component (A) contains from 80% to 90% by weight of the monomeric diethyleneglycol bis(allylcarbonate), the residual percentage being oligomers of diethyleneglycol bis(allylcarbonate). Composition according to Claim 1, wherein component (B) is defined by the formula: wherein R is the radical of diethylene glycol and n has an average value of 3. Composition according to Claim 1, wherein component (C) is the monomer product of the reaction of diallylcarbonate with tris(hydroxyethyl)isocyanurate in the presence of a basic catalyst in a molar ratio of 12:1, said component (C) containing from 60% to 70% by weight of the monomer of tris(hydroxyethyl)isocyanurate tris(allylcarbonate), the residual percentage being oligomers of tris(hydroxyethyl)isocyanurate tris(allylcarbonate). Composition according to Claim 1, wherein said composition comprises from 15% to 45% by weight of component (A), from 30% to 60% of component (B) and from 10% to 45% by weight of component (C). Composition according to Claim 1, wherein said free-radical initiator is selected from diisopropylperoxydicarbonate; dicyclohexylperoxydicarbonate; di-sec.butylperoxydicarbonate; dibenzoylperoxide, and tert.butylperbenzoate. Composition according to Claim 1, wherein said composition contains said free-radical initiator in an amount of from 3% to 5,5% by weight relative to the total weight of components (A), (B) and (C). Composition according to Claim 1, wherein said composition additionally contains stabilizers, release agents, dyes, pigments, UV-radiation absorbers and IR-radiation absorbers, in an overal amount not greater than 1% relative to the total weight of the components (A), (B) and (C). Process for preparing optical glass substitutes comprising the steps of: combining the following components into a polymerizable composition: from 10% to 50% by weight of component (A) which is the monomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of at least 10:1; from 20% to 70% by weight of component (B) which is an oligomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of 2:1, said oligomer product having the formula: wherein R is the radical of diethylene glycol and n has a value, or an average value, of from 2 to 5; from 5% to 50% by weight of component (C) which is the monomer product of tris(hydroxyethyl)isocyanurate tris(allylcarbonate) resulting from the reaction of diallylcarbonate with tris(hydroxyethyl)isocyanurate in the presence of a basic catalyst in a molar ratio of at least 10:1, and a free-radical initiator in an amount of from 1% to 6% by weight relative to the total weight of said (A), (B) and (C) components, said composition having a kinematic viscosity at 25°C lower than 0,00025 m²/s (250 cSt); pouring said polymerizable composition into moulds shaped correspondingly to an article which is to be manufactured; maintaining said polymerizable composition at a temperature lower than the decomposition temperature of said free-radical initiator, and polymerizing said polymerizable composition at a temperature of from 30°C to 120°C for a time of from 3 hours to 100 hours. Claims for the following Contracting State : AT Process for preparing optical glass substitutes characterized in that it comprises the steps of: combining the following components into a polymerizable composition: from 10% to 50% by weight of component (A) which is the monomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of at least 10:1; from 20% to 70% by weight of component (B) which is an oligomer product of the reaction between diallylcarbonate and diethyleneglycol in the presence of a basic catalyst and in a molar ratio of 2:1, said oligomer product having the formula: wherein R is the radical of diethylene glycol and n has a value, or an average value, of from 2 to 5; from 5% to 50% by weight of component (C) which is the monomer product of tris(hydroxyethyl)isocyanurate tris(allylcarbonate) resulting from the reaction of diallylcarbonate with tris(hydroxyethyl)isocyanurate in the presence of a basic catalyst in a molar ratio of at least 10:1, and a free-radical initiator in an amount of from 1% to 6% by weight relative to the total weight of said (A), (B) and (C) components, said composition having a kinematic viscosity at 25°C lower than 0,00025 m²/s (250 cSt); pouring said polymerizable composition into moulds shaped correspondingly to an article which is to be manufactured; maintaining said polymerizable composition at a temperature lower than the decomposition temperature of said free-radical initiator, and polymerizing said polymerizable composition at a temperature of from 30°C to 120°C for a time of from 3 hours to 100 hours. Process according to Claim 1, characterized in that component (A) contains from 80% to 90% by weight of the monomeric diethyleneglycol bis(allylcarbonate), the residual percentage being oligomers of diethyleneglycol bis(allylcarbonate). Process according to Claim 1, characterized in that component (B) is defined by the formula: characterized in that R is the radical of diethylene glycol and n has an average value of 3. Process according to Claim 1, characterized in that component (C) is the monomer product of the reaction of diallylcarbonate with tris(hydroxyethyl)isocyanurate in the presence of a basic catalyst in a molar ratio of 12:1, said component (C) containing from 60% to 70% by weight of the monomer of tris(hydroxyethyl)isocyanurate tris(allylcarbonate), the residual percentage being oligomers of tris(hydroxyethyl)isocyanurate tris(allylcarbonate). Process according to Claim 1, characterized in that said composition comprises from 15% to 45% by weight of component (A), from 30% to 60% of component (B) and from 10% to 45% by weight of component (C). Process according to Claim 1, characterized in that said free-radical initiator is selected from diisopropylperoxydicarbonate; dicyclohexylperoxydicarbonate; di-sec.butylperoxydicarbonate; dibenzoylperoxide, and tert.butylperbenzoate. Process according to Claim 1, characterized in that said composition contains said free-radical initiator in an amount of from 3% to 5,5% by weight relative to the total weight of components (A), (B) and (C). Process according to Claim 1, characterized in that said composition additionally contains stabilizers, release agents, dyes, pigments, UV-radiation absorbers and IR-radiation absorbers, in an overal amount not greater than 1% relative to the total weight of the components (A), (B) and (C).

Inventors: GAGLIARDI, CLAUDIO, RENZI, FIORENZO, RIVETTI, FRANCO, ROMANO, UGO
Applicants: ENICHEM SYNTHESIS S.P.A.
Application year: 1986
Main classification: C08F218
IPC codes: G02B1, C08F218, C08F18