Organic glass with high refractive index

Abstract: Novel organic glass with a high refractive index comprising a copolymer of (a) a diallyl isophthalate monomer, (b) an allyl benzoate monomer and (c) a diester of maleic acid and/or diester of fumaric acid monomer, which also shows excellent light resistance and excellent other physical properties such as excellent moldability, high impact resistance, high dimension stability, excellent mechanical processing properties, excellent dyeability and excellent hard coating property, and is useful as a material for optical or optoelectronic parts such as lenses, prisms, reflecting mirror and window materials.

Description: This invention relates to an organic glass with a high refractive index suitable as a material for optical parts, more particularly to a novel organic glass with a high refractive index comprising a copolymer of (a) a diallyl isophthalate monomer, (b) an allyl benzoate monomer and (c) a diester of maleic acid monomer and/or a diester of fumaric acid monomer, which also has excellent other physical properties such as excellent light resistance, high impact resistance, high dimension stability, excellent mechanical processing properties, excellent dyeability and excellent hard coating property (e.g. excellent adhesion of coating glass film) and is useful as a material for optical parts such as lenses and prisms. Organic glass has been noticed as a material for optical parts, particularly lens because of its light weight in comparison with inorganic glass, and organic glass comprising a polymer of diethylene glycol bis(allyl carbonate) or methyl methacrylate has been used as a lens material. Among known organic glasses, organic glass comprising a polymer of diethylene glycol bis(allyl-carbonate) (CR-39) has lightweight and other excellent physical properties such as high impact resistance, high dimension stability, excellent mechanical processing properties, excellent dyeability and excellent hard coating property, and hence, the demand thereof has rapidly increased for using it as a lens material for eyeglasses, i.e. for correcting one's eyesight instead of using inorganic glass in about the last ten years. Although the organic glass comprising a polymer of diethylene glycol bis(allyl carbonate) has excellent properties as optical materials as mentioned above, it has a refractive index of 1.499 which is lower than that of the conventional crown glass (inorganic glass) (its refractive index is 1.523). When this organic glass is used as a lens material for eyeglasses, it must be made thicker in comparison with an inorganic glass material, so that the material loses its merit of lightweight and further the eyeglasses becomes unattractive. This tendency becomes stronger with increase of diopter of lens. Accordingly, the conventional organic glass is not necessarily suitable as a lens material for eyeglasses. In order to eliminate these drawbacks of the conventional organic glass, there have recently been developed various lens materials comprising diallyl phthalate polymers or bisphenol A derivatives which have higher refractive index, for examples polymers of 2,2-bis(4-methacryloxyethoxyphenyl)propane or 2,2-bis(4-methacryloxyethoxy-3,5-dibromophenyl)propane but these lens materials having a high refractive index are somewhat disadvantageous in exhibiting less impact resistance and less processability and hence are still not necessarily satisfactory as a lens material for eyeglasses. It is disclosed in JP-A-81318/1984 that an organic glass comprising a copolymer of diallyl phthalate and unsaturated alcohol esters of benzoic acid (e.g. allyl benzoate) has an improved impact resistance and is useful as a lens material for eyeglasses. Although this organic glass is quite excellent in molding properties, impact resistance and mechanical processing properties, it has disadvantages such as extremely high yellowing by outdoor exposure, and hence, it is still unsatisfactory as a lens for eyeglasses. In order to improve the light resistance and to prevent the undesirable yellowing, an ultraviolet stabilizer is usually incorporated, but the organic glass comprising the above-mentioned copolymer is still not necessarily satisfactory in terms of light resistance even by incorporation of the conventional ultraviolet stabilizer. It is also disclosed in US-A-2,964,501 that a terpolymer of (1) 78-98 % of an ester of a glycol with an acid ester of a monohydric alcohol (e.g. diethylene glycol bis(allyl carbonate), (2) 1-20 % of a diester of a monohydric alcohol (e.g. diallyl phthalate) and (3) 0.25-10 % of a dialkyl ester of an alkenedioic acid (e.g. dialkyl esters of maleic acid, fumaric acid, itaconic acid, or citraconic acid) is useful as a lens material. However, this literature does not teach the improvement of light resistance of the product due to the incorporation of (3). It is further disclosed in JP-A-15813/1988 and 43911/1988 that a resin prepared by copolymerizing (A) 10-95 % of one or more vinyl-containing aromatic carboxylic acid ester monomer (e.g. diallyl phthalate), (B) 5-50 % of a diacrylate monomer (e.g. polyethylene glycol diacrylate) and (C) 1-80 % of an unsaturated dibasic acid diester monomer containing an aromatic ring in the ester group is useful as a plastic lens material. However, these literatures do not teach the improvement of light resistance of the product, either. It is the object of the present invention to provide a novel organic glass which has a high refractive index as well as excellent mechanical properties, chemical properties and optical properties without the drawback of yellowing by light exposure and which is useful as a material for optical parts such as lens and prisms. This object could be achieved on the basis of the finding that a copolymer of three monomer components of a diallyl isophthalate monomer, an allyl benzoate monomer and a diester of maleic acid and/or a diester of fumaric acid monomer showed a highly improved light resistance as well as excellent molding properties, a high impact resistance and excellent processing properties. The subject matter of the invention therefore is a novel organic glass with a high refractive index of at least 1.54 comprising a copolymer of the components (a) a diallyl isophthalate monomer, (b) an allyl benzoate monomer, and (c) a diester of maleic acid monomer and/or a diester of fumaric acid monomer, which are used in a ratio of 40 to 80 wt.%, more preferably 50 to 70 wt.%, of (a) component, 10 to 35 wt.%, more preferably 10 to 30 wt.%, of (b) component, and 5 to 50 wt.%, more preferably 10 to 30 wt., of (c) component. The diallyl isophthalate monomer (a) may be diallyl isophthalate itself or a combination thereof with a small amount of diallyl orthophthalate and/or diallyl terephthalate. The allyl benzoate monomer (b) includes allyl benzoate or methallyl benzoate which may optionally be substituted on the benzene ring by a straight chain or branched chain alkyl group having 1 to 6 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl and n-hexyl (e.g. allyl o-toluylate, allyl m-toluylate, allyl p-toluylate and allyl p-tert-butylbenzoate) or a straight chain or branched chain alkoxy group having 1 to 6 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, isopentyloxy, neopentyloxy, tert-pentyloxy and hexyloxy (e.g. allyl p-methoxybenzoate and allyl 3,4,5-trimethoxybenzoate). This component (b) is effective for improving the impact resistance of the diallyl isophthalate without deteriorating its high refractive index. The diester of maleic acid and/or diester of fumaric acid monomer (c) includes diesters of maleic acid or diesters of fumaric acid with an alkyl group having 1 to 8 carbon atoms (e.g. methyl, ethyl, propyl, butyl, pentyl and hexyl) or with a cyclohexyl, phenyl or benzyl group. Preferred esters are diethyl maleate, di-n-butyl maleate, diethyl-fumarate or di-n-butyl fumarate as well as diesters of maleic acid or fumaric acid with an alkyl group having 1 to 8 carbon atoms or with a cyclohexyl, phenyl or benzyl group in which at least one of the ester group is a phenyl or benzyl group. This component (c) is each used alone or in a combination thereof and is effective for improving light resistance of the organic glass comprising the above components (a) and (b). As mentioned above, the component (b) is effective for improving impact resistance of the cured product, and hence, when it is used in an amount of less than 10 wt.%, the effect for improving the impact resistance is insufficient, and on the other hand, when the amount is over 35 wt.%, the product shows unfavorably lower heat distortion temperature and hence shows inferior dimension stability and processability. The component (c) has an excellent light resistance by itself and can impart the excellent light resistance to the cured product. When the component (c) is used in an amount of less than 5 wt.%, the above excellent properties cannot sufficiently be transferred to the cured product, and on the other hand, when the amount is over 50 wt.%, the refractive index of the cured product is disadvantageously lowered. Since the component (c) affects the refractive index of the cured product as mentioned above, the degree of the effect being depending on the kind of compound (c), i.e. the alcohol moiety of the ester, the amount of the component (c) should carefully be determined within the range of less than 50 wt.% so that the cured product has the refractive index not less than the lower limit (i.e. 1.54) of the organic glass. The component (a) should be used in an amount of at least 40 wt.% in order to provide the copolymer with three dimensional crosslinking, insolubility and infusibility, chemical resistance, and heat resistance and dimension stability in practical or processing viewpoint. The copolymer of the organic glass of the invention may further be incorporated with an appropriate amount of diethylene glycol bis(allylcarbonate) as an additional component within the range capable of providing the refractive index of not less than 1.54 so that the organic glass of the invention can be treated by the conventional hard coating process in order to improve the surface hardness as used for the conventional optical material produced from diethylene glycol bis(allylcarbonate). The organic glass of this invention can be prepared by copolymerizing the above components (a) to (c) by any conventional method, for example by casting method, in the presence of a polymerization initiator. The copolymerization can also be carried out with irradiation of ionizing radiation such as X-ray, α-ray, β-ray, and γ-ray, or ultraviolet. The organic glass with a high refractive index of this invention comprising the copolymer of diallyl isophthalate, allyl benzoate, and a diester of maleic acid and/or diester of fumaric acid maintains high refractive index due to diallyl isophthalate and shows excellent light resistance as well as other excellent physical properties, such as excellent moldability, high impact resistance, high dimension stability, excellent mechanical processing properties, excellent dyeability, and excellent hard coating property. Accordingly, the organic glass with a high refractive index of the invention is useful as a material for producing optical or optoelectronic parts such as lens, prisms, reflecting mirrors and window materials, particularly lens for eyeglasses. The organic glass of the invention has also the advantage that it can be treated by the conventional hard coating process as used for making the conventional optical material produced from diethylene glycol bis(allylcarbonate). This invention is illustrated by the following Examples and Reference Examples but should not be construed to be limited thereto. Examples 1-9 and Reference Examples 1-5 To a mixture of each monomer of the components (a) to (c) as shown in Table 1 is added diisopropyl peroxydicarbonate (4 parts by weight) as a polymerization initiator, and the mixture is poured into a casting mold made of two glass-made circular plates (diameter 70 mm) and a gasket of ethylene-vinyl acetate copolymer wherein the mixture is polymerized. The polymerization reaction is carried out by heating the mixture in a circulating hot air oven at 40°C for 5 hours, and thereafter, raising gradually the temperature from 40°C to 80°C over a period of 11 hours and keeping the temperature at 80°C for 2 hours, and then cooling gradually to 60°C. After the polymerization reaction, the molded product is released from the casting mold and subjected to heat-treatment at 110°C for 2 hours. The molded product thus obtained was subjected to the following tests. The test results are shown in Table 2. (1) Transmittance It was measured by a luminous transmittance photometer as to a circular test plate (thickness: 2 mm). (2) Refractive index It was measured by Abbe refractometer as to the test plate as used in the above (1) which was cut and polished. The index was measured on two crossed surfaces of the polished test plate. (3) Surface hardness It was measured according to JIS K-5400 under a load of 9,8 N (1 kgf) on the test plate as used in the above (1), and the hardness was shown by the pencil scratch hardness. (4) Impact resistance It was measured in accordance with the standard of FDA (Food and Drug Administration, Rules and Regulations §801,410) as to two set of circular specimens (each 10 lenses) having spherical surface (radius: 120 mm, thickness: 2 mm and diameter: 70 mm) but having no dioptric power. A steel ball weighting 16 g or 25 g was allowed to drop onto each specimen from a height of 127 cm, and the ratio of not broken specimens to 10 specimens was shown. (5) Dyeability The test plate as used in the above (1) was dipped in a brown color dyeing bath at 92°C for 10 minutes, and thereafter, the luminous transmittance was measured like in the above (1). (6) Light resistance Light resistance test was carried out as to the test plate (thickness: 2 mm) as used in the above (1) with a fademeter (UV strength: 1 mW/cm², wave length: 320-390 nm) as prescribed in JAS (Japanese Agricultural Standard) as a light resistance tester. Yellowing by light irradiation was measured as to transmitted light using a color difference meter and indicated as index of color space (b*) (defined in CIE 1976) wherein larger figure shows denser yellow. In the above Table 1, the abbreviations mean as follows: DAIP: diallyl isophthalate ABZ: allyl benzoate ABBZ: allyl p-tert-butylbenzoate DEM: diethyl maleate DBM: di-n-butyl maleate PBZM: propylbenzyl maleate DEF: diethyl fumarate DBF: di-n-butyl fumarate PBZF: propylbenzyl fumarate CR-39: diethylene glycol bis(allylcarbonate) UVS: 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (UV stabilizer) As is clear from the above test results, the organic glass of this invention had highly improved light resistance as compared with the organic glasses of Reference Examples, maintained the high refractive index and further showed excellent properties necessary for optical parts (e.g. lens) such as excellent dyeability, impact resistance, etc. Table 2 shows that the organic glass of this invention had higher refractive index than that of the conventional CR-39.

Claims: An organic glass with a high refractive index of at least 1.54 which comprises a copolymer of (a) a diallyl isophthalate monomer, (b) an allyl benzoate monomer, and (c) a diester of maleic acid and/or diester of fumaric acid monomer in the ratio of 40 to 80 wt.% of the diallyl isophthalate monomer (a), 10 to 35 wt.% of the allyl benzoate monomer (b) and 5 to 50 wt.% of the diester of maleic acid and/or diester of fumaric acid monomer (c). The organic glass according to claim 1, wherein the ratio of the monomers are 50 to 70 wt.% of the diallyl isophthalate monomer (a), 10 to 30 wt.% of the allyl benzoate monomer (b) and 10 to 30 wt.% of the diester of maleic acid and/or diester of fumaric acid monomer (c). The organic glass according to claim 1, wherein the allyl benzoate monomer (b) is allyl benzoate or methallyl benzoate which may optionally be substituted on the benzene ring by a straight chain or branched chain alkyl group having 1 to 6 carbon atoms or a straight chain or branched chain alkoxy group having 1 to 6 carbon atoms. The organic glass according to claim 3, wherein the allyl benzoate monomer (b) is allyl benzoate or allyl p-tert-butylbenzoate The organic glass according to claim 1, wherein the diester of maleic acid and/or diester of fumaric acid monomer (c) is a diester of maleic acid or fumaric acid with an alkyl alcohol having 1 to 8 carbon atoms. The organic glass according to claim 5, wherein the diester of maleic acid or diester of fumaric acid monomer (c) is diethyl maleate, di-n-butyl maleate, diethyl fumarate or di-n-butyl fumarate. The organic glass according to claim 1, wherein the diester of maleic acid and/or diester of fumaric acid monomer (c) is a diester of maleic acid or fumaric acid with an alkyl group having 1 to 8 carbon atoms, or with a cyclohexyl, phenyl or benzyl group in which at least one of the ester groups is a phenyl or benzyl group.

Inventors: FUJIO YOSHIHARU, MATSUKUMA KANEMASA, FUJIO, YOSHIHARU, MATSUKUMA, KANEMASA
Applicants: DAISO CO LTD, DAISO CO., LTD.
Application year: 1990
Main classification: C08F218
IPC codes: C08F218, C08F222, G02B1, C08F18, C08F22