UV-curable fresnel lens resin composition, fresnel lens, and back projection screen

Abstract: The invention relates to a UV-curable Fresnel lens resin composition comprising a (meth)acrylate containing a hydroxyl group and an aromatic ring (A1), a urethane group-containing (meth)acrylate (A2) comprising an aromatic diol, an aromatic ring-containing monofunctional (meth)acrylate (A3), and a photopolymerization initiator (B) for the formation of a Fresnel lens on a sheet or plate made of a methyl methacrylate (co)polymer ; to a Fresnel lens formed by UV cure of said composition ; and to a rear projection screen including a sheet or plate carrying said Fresnel lens. The Fresnel lens has high refractive index, antistatic properties and is satisfactory in adhesion to a sheet or plate.

Description: FIELD OF THE INVENTION The present invention relates to a UV-curable Fresnel lens resin composition, a Fresnel lens, and a rear projection screen. More particularly, the invention relates to a UV-curable Fresnel lens resin composition showing good adhesion to a sheet or plate made of a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate with one or more other acrylate or methacrylate (hereinafter referred to collectively as methyl methacrylate (co)polymer); a Fresnel lens comprising a resin formed by UV cure of said composition in situ on said sheet or plate; and a rear projection screen including a sheet or plate carrying said Fresnel lens. DESCRIPTION OF THE PRIOR ART The Fresnel lens heretofore used for the fabrication of a rear projection screen is manufactured typically by casting a UV-curable resin composition between a mold and a transparent resin sheet or plate made of a methyl methacrylate (co)polymer, and exposing the resin composition to ultraviolet light, and thereby curing it. With the recent trend toward reduced thickness of projection television devices, a demand exists for resins with high refractive indices and accordingly a variety of UV-curable resin compositions have been proposed (e.g. Japanese Kokai Publications Hei-5-65318, Hei-5-155944, Hei-5-247156, and USP-5453452). However, the proposed UV-curable resin compositions are unsatisfactory in the adhesion to a sheet or plate made of a methyl methacrylate (co)polymer, and require a primer on the sheet or plate. Moreover, the lens obtainable from any of those UV-curable resin compositions has the problem of static deposition of dust particles. As compositions which can be used without the aid of a primer and yet show improved adhesion to a sheet or plate, the following compositions 1 ○ and 2 ○ were proposed. On the other hand, as compositions solving the above-mentioned problem of static deposition of dust particles, the following composition 3 ○ has been proposed. 1 ○ A composition comprising diacrylate or dimethacrylate of a low molecular hydrocarbon diol (e.g. EP-510754A1) 2 ○ A composition comprising an epoxy acrylate or methacrylate(e.g. Japanese Kokai Publication Hei-5-310871) 3 ○ A UV-curable resin composition having antistatic properties (e.g. Japanese Kokai Publications Hei-1-302201 and Hei-3-157412) However, any of these compositions 1 ○ to 3 ○ has the drawback that an attempt to insure sufficiently high adhesion to a sheet or plate results in a reduced refractive index and/or poor scratch resistance of the lens surface owing to embrittlement of the resin, so that it has been impossible to obtain a Fresnel lens meeting all the requirements of acceptable adhesion, refractive index, and scratch resistance. It is an object of the present invention to provide a UV-curable resin composition capable of providing a Fresnel lens satisfactory in all the parameters of adhesion to a sheet or plate, refractive index, and scratch resistance. It is a further object of the present invention to provide a UV-curable resin composition capable of providing a Fresnel lens further having antistatic properties. It is a still another object of the present invention to provide a Fresnel lens having all of the above-mentioned characteristics. It is a further object of the present invention to provide a rear projection screen including a Fresnel lens sheet or Fresnel lens plate carrying a Fresnel lens having all of said desirable characteristics. SUMMARY OF THE INVENTION The above objects have been accomplished by the present invention which provides the following UV-curable resin composition [1a]; Fresnel lens [2a]; and rear projection screen [3a]. [1a] UV-curable resin composition A UV-curable Fresnel lens resin composition for use in the formation of a Fresnel lens on a sheet or plate made of a methyl methacrylate (co)polymer, said resin composition comprising (A1) an acrylate or methacrylate (herein after referred to collectively as (meth)acrylate) containing hydroxyl group and aromatic ring; (A2) a urethane group-containig (meth)acrylate having a moiety of an aromatic diol (a1) represented by the following general formula: wherein Ph represents 1,4-phenylene group, R 1 , R 2 and R 3 each represents hydrogen atom or methyl group, m and n each represents an integer of 1 to 15, and (m+n) is equal to 2 to 20; (A3) an aromatic ring-containing monofunctional (meth)acrylate; and (B) a photopolymerization initiator. [2a] Fresnel lens A Fresnel lens comprising a resin formed by UV cure of composition [1a] in situ on a sheet or plate made of a methyl methacrylate (co)polymer. [3a] Rear projection screen A rear projection screen comprising a Fresnel lens sheet or Fresnel lens plate carrying the Fresnel lens [2a] as disposed on a sheet or plate made of a methyl methacrylate (co)polymer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing one example of a rear projection screen. In Fig. 1, the reference numeral 1 stands for a rear projection screen, 2 for a Fresnel lens sheet or Fresnel lens plate, 3 for a lenticular lens sheet, 4 for a light absorbing layer, 5 for a Fresnel lens, and 6 for a sheet or plate made of a methyl methacrylate (co) polymer. DETAILED DESCRIPTION OF THE INVENTION The composition [1a] of the present invention is a UV-curable resin composition for use in the formation of a Fresnel lens on a sheet or plate made of a methyl methacrylate (co)polymer, namely a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate with one or more other (meth)acrylates. The composition [1a] is a UV-curable resin composition of the urethane group-containing (meth)acrylate type which may be supplemented with a phosphate (C2). With this composition, the resin formed by UV radiation cure is a (meth)acrylate resin. The urethane group-containig (meth)acrylate (A2) in the composition [1a] of the invention has moiety of an aromatic diol (a1). The aromatic diol (a1) is an addition product of a bisphenol with alkylene oxide as can be seen from the above general formula (1). The bisphenol mentioned above includes such species as bisphenol A, bisphenol F, and bisphenol AD. The alkylene oxide includes such species as ethylene oxide (briefly, EO), propylene oxide (briefly, PO) and these may be used in combination to give an EO-PO random addition product or an EO-PO block addition product. Each of m and n in general formula (1), both representing the number of moles of alkylene oxide added, is an integer of usually 1 to 15 and preferably 1 to 7, and (m+n) is usually 2 to 20 and preferably 2 to 12. If (m+n) is within said range, the scratch resistance of the lens available on cure of the composition will be good and the refractive index of the cured composition will be high. The addition product of the bisphenol with alkylene oxide can be produced typically by a known process such as a prosess that EO and/or PO are added to a bisphenol by addition reaction in the presence of a basic catalyst. The composition [1a] of the present invention comprises, as mentioned above, a (meth)acrylate containing hydroxyl group and aromatic ring (A1), a urethane group-containing (meth)acrylate (A2), an aromatic ring-containing (meth)acrylate (A3), and a photopolymerization initiator (B) as essential components. The (meth)acrylate containing hydroxyl group and aromatic ring (A1) includes but is not limited to (A11) 2-hydroxy-3-phenoxypropyl (meth)acrylate, (A12) 2-hydroxy-3-(2'-, 3'-, or 4'-methylphenoxy)propyl (meth)acrylate, (A13) (meth)acryloyloxyethyl (meth)acryloyloxy-2-hydroxypropyl phthalate, and (A14) the addition product of a bisphenol (e.g. bisphenol A, bisphenol F, or bisphenol S) glycidyl ether with a (meth)acrylate. Preferred among them are said (A11) and said (A12), both of which have low viscosity values. The urethane group-containing (meth)acrylate (A2) includes but is not limited to (A21) the reaction product of an organic polyisocyanate (b2) with a hydroxyl group-containing (meth)acrylate (b3) and an aromatic diol (a1), (A22) the reaction product of (b2) with (b3) and a polyester polyol (b1) derived from (a1) and a dicarboxylic acid (a2), (A23) the reaction product of (b2) with (b3) and the combination of (a1) and (b1). Preferred among them is (A22). The dicarboxylic acid (a2) includes but is not limited to maleic acid, fumaric acid, succinic acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, and acid anhydrides thereof. Preferred among them are maleic acid, fumaric acid, succinic acid and adipic acid. The polyester polyol (b1) can be obtained from an aromatic diol (a1) and a dicarboxylic acid (a2) under the known esterification conditions. The OH/COOH equivalent ratio for the production of the polyester polyol (b1) is generally 2.0 to 1.05 and preferably 2.0 to 1.5. The diol as a constituent of a urethane group-containing (meth)acrylate (A2) is said (a1) and/or said (b1) but where necessary a third diol can be used in conjunction. The third diol is preferably one having a molecular weight of not more than 400. The use of a diol with a molecular weight of more than 400 is undesirable, since the refractive index will be seriously decreased. The third diol includes but is not limited to ethylene glycol, propylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,4-butanediol, 1,6-hexanediol, polyethylene glycol (degree of polymerization: 2 to 9), polypropylene glycol (degree of polymerization: 2 to 6), and polycaprolactonediol (degree of polymerization: 2 or 3). The proportion of the third diol, if used, is generally not more than 30 weight % and preferably not more than 10 weight %, based on the weight of (a1). The organic polyisocyanate (b2) as a constituent of said urethane group-containing (meth)acrylate (A2) includes but is not limited to (b21) 2,4-tolylene diisocyanate, (b22) 2,6-tolylene diisocyanate, (b23) xylylene diisocyanate, (b24) 4,4'-diphenylmethane diisocyanate, (b25) isophorone diisocyanate, (b26) dicyclohexylmethane diisocyanate, (b27) hexamethylene diisocyanate, and (b28) the modification products thereof (e.g. carbodiimides, urethodiones, biurets, isocyanurates, etc.). In addition, optional combinations of the above compounds can also be mentioned. Preferred, among them, are (b21), (b22), (b23) and (b24) and combinations of two or more of them. The hydroxyl-containing (meth)acrylate (b3) as a constituent of said urethane group-containing (meth)acrylate (A2) includes but is not limited to (b31) 2-hydroxyethyl (meth)acrylate, (b32) 2-hydroxypropyl (meth)acrylate, (b33) 4-hydroxybutyl (meth)acrylate, (b34) 2-hydroxy-3-butoxypropyl (meth)acrylate, and (b35) 2-hydroxy-3-phenoxypropyl (meth)acrylate. Preferred, among them, are (b31) and (b32). There is no particular limitation on production method for said (A2) but a typical process comprises reacting said (a1) and/or said (b1) with said (b2) in the known manner for urethane-forming reaction and, then, reacting with (b3). The number average molecular weight of a urethane group-containing (meth)acrylate (A2) is generally 2,000 to 10,000 and preferably 3,000 to 8,000. If the number average molecular weight is within the range of 2,000 to 10,000, sufficient flexibility will be obtained and the viscosity of the resin composition will be sutable for not causing air entrapment to ensuring the lens functions. The refractive index (25 °C ) of said (A2) is generally not less than 1.52 and preferably not less than 1.53. The aromatic ring-containing monofunctional (meth)acrylate (A3) includes but is not limited to (A31) phenyl (meth)acrylate, (A32) benzyl (meth)acrylate, (A33) a (meth)acrylate of addition product of phenol with EO and/or PO (number of moles of EO and/or PO added: 1 to 6), (A34) a (meth)acrylate of addition product of nonylphenol with EO and/or PO (number of moles of EO and/or PO added: 1 to 6), and (A35) a (meth)acrylate of addition product of dodecylphenol with EO and/or PO (number of moles of EO and/or PO added: 1 to 6). Preferred, among them, are (A33), (A34) and a combination thereof. The composition [1a] of the present invention may contain 20 to 60 weight % of said (A1) and preferably 30 to 50 weight %, 10 to 50 weight % of said (A2) and preferably 20 to 40 weight %, and 5 to 50 weight % of said (A3) and preferably 10 to 40 weight %. Using said (A1) in a proportion of 20 to 60 weight % may be attainable of satisfactory adhesion to a sheet or plate and of the viscosity suitable for preventing air entrapment in moulding to make sure of the lens functions. Using said (A2) in a proportion of 10 to 50 weight % may be attainable of flexibility and scratch resistance and also of the viscosity suitable for preventing air entrapment in moulding to make sure of the lens functions. Using said (A3) in a proportion of 5 to 50 weight % will ensure suitable viscosity and adhesion to a sheet or plate. In the composition [1a] of the present invention, the urethane group-containing (meth)acrylate (A2) as it is alone shows antistatic properties, but there are cases that (A2) alone ensures only inadequate antistatic properties. In order to realize sufficient antistatic properties with (A2) alone, it must be incorporated in an increased proportion but it occasionally causes deterioration of adhesion. In such cases, where necessary, the antistatic properties can be improved by using a phosphate (C2) of the following general formula (2) in combination with said (A2), whereby the objective performance can be obtained. This phosphate (C2) contributes to improve scratch resistance of the cured composition and, at the same time, functions as a mold release agent [R(OCH 2 CH 2 ) s O] t PO(OH) (3-t) wherein R represents alkyl group containing 5 to 16 carbon atoms, s represents an integer of 1 to 4, t represents an integer of 1 or 2. Referring to general formula (2), R is an alkyl group containing 5 to 16 carbon atoms. With R inside the above carbon number range, sufficient antistatic performance can be obtained. The symbol s stands for an integer of 1 to 4. If s is equal to zero, the phosphate (C2) will be insoluble in the composition of the invention or, even if soluble, will tend to separate out during storage. If the value of s is 5 or more, the required antistatic properties will not be fully expressed. The symbol t represents an integer of 1 or 2. If t is equal to zero, said (C2) will remain insoluble in the composition [1a] of the invention. If t is equal to 3, antistatic properties will not be fully expressed. The phosphate (C2) can be obtained by adding EO to an aliphatic alcohol of 5 to 16 carbon atoms in a known manner and reacting the addition product further with either phosphoric acid or a derivative thereof (e.g. diphosphorus pentaoxide). The aliphatic alcohol of 5 to 16 carbon atoms mentioned above is a straight-chain monohydric alcohol or a branched monohydric alcohol, which includes n-hexyl alcohol, n-octyl alcohol, 2-ethylhexyl alcohol and n-lauryl alcohol, to mention just a few preferred species. The proportion of the phosphate (C2), when used, in the composition [1a] of the present invention is preferably 0.1 to 2.0 weight % and more preferably 0.3 to 1.5 weight %. In using the proportion of 0.1 to 2.0 weight % of (C2), appreciable antistatic propertis and adhesion to a sheet or plate will be insured. For improving adhesion further, among other purposes, a plasticizer (C3) with a solubility parameter in the range of 10.0 to 11.5 may be optionally incorporated in the composition [1a] of the present invention. The solubility parameter (briefly, SP) of plasticizer (C3) is 10.0 to 11.5 and preferably 10.5 to 11.2. SP value of (C3) within the above range will realize improvement in adhesion. The SP values mentioned in this specification are the values calculated in accordance with Polymer Engineering and Science, 14 (2), 147 (1974). The plasticizer (C3) includes but is not limited to the following species. Dimethyl phthalate (SP 10.90) Diethyl phthalate (SP 10.54) Dibutyl phthalate (SP 10.07) Butyl benzyl phthalate (SP 10.74) Dicyclohexyl phthalate (SP 10.39) Ethyl phthalyl ethyl glycolate (SP 10.75) Butyl phthalyl butyl glycolate (SP 10.17) Triphenyl phosphate (SP 10.73) Tricresyl phosphate (SP 10.46) Diphenyl cresyl phosphate (SP 10.54) Polyethylene glycol dibenzoate (degree of polymerization of ethylene glycol; 1 to 12) (SP 11.15 to 10.02) Polypropylene glycol dibenzoate (degree of polymerization of propylene glycol; 1 to 4) (SP 10.89 to 10.04) Preferred, among them, are species with high refractive indices such as dimethyl phthalate, butyl benzyl phthalate, triphenyl phosphate, tricresyl phosphate and diphenyl cresyl phosphate. The proportion of plasticizer (C3), if used, in the composition [1a] of the present invention is 1 to 20 weight % and preferably 3 to 15 weight %. In using the (C3) in the proportion of 1 to 20 weight %, sufficient improvement can be obtained in adhesion to a sheet or plate and the hardness of the cured composition will be sufficent to provide the lens with dimensional stability. In the composition [1a] of the present invention, one or more (meth)acrylate monomers other than said (A1), said (A2), and said (A3) can be employed where necessary. The other (meth)acrylate monomers mentioned above may, for example, be the following species. Tetrahydrofurfuryl (meth)acrylate Methoxyethyl (meth)acrylate Ethoxyethyl (meth)acrylate Butoxyethyl (meth)acrylate Glycidyl (meth)acrylate Isobornyl (meth)acrylate 2-Hydroxyethyl (meth)acrylate 2-Hydroxypropyl (meth)acrylate 4-Hydroxybutyl (meth)acrylate 2-Hydroxy-3-butoxypropyl (meth)acrylate Ethylene glycol di(meth)acrylate 1,2- or 1,3-Propylene glycol di(meth)acrylate Diethylene glycol di(meth)acrylate 1,6-Hexanediol di(meth)acrylate Neopentyl glycol di(meth)acrylate Di(meth)acrylate of a bisphenol (e.g. bisphenol A, bisphenol F, or bisphenol S) or di(meth)acrylate of the addition product of the bisphenol with alkylene oxide Trimethylolpropane tri(meth)acrylate Pentaerythritol tetra(meth)acrylate Dipentaerythritol hexa(meth)acrylate Alkylene oxide-modified trimethylolpropane tri(meth) acrylate Alkylene oxide-modified pentaerythritol tetra(meth) acrylate Alkylene oxide-modified dipentaerythritol hexa(meth) acrylate The proportion of such other (meth)acrylate monomer or monomers to the total weight of (A1), (A2) and (A3) combined is usually not more than 30 weight % and preferably not more than 20 weight %. The photopolymerization initiator (B) as an essential component of composition [1a] of the present invention includes but is not limited to benzoin alkyl ethers, benzyl dimethyl ketal, 1-hydroxycyclohexylphenylketone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, benzophenone, methylbenzoyl formate, isopropylthioxanthone. These may be combindly used. The proportion of the photopolymerization initiator (B) is usually 0.1 to 10 weight % and preferably 0.5 to 6 weight %, based on the total composition weight of composition [1a]. Where necessary, a thermal polymerization inhibitor, antifoaming agent, leveling agent, coupling agent, antistatic agent, ultraviolet absorber, and other known additives can be selectively incorporated in composition [1a]. The viscosity of the composition [1a] according to the present invention is preferably 500 to 5,000 cps at the casting temperature. If the viscosity on casting is within the above range, air cells will not be entrapped in the molding and hence will not impair less functions. The refractive indices (25 °C ) of the cured resins from the composition [1a] of the present invention is usually not less than 1.54 and preferably not less than 1.55. Moreover, the surface resistivities of these cured resins are usually not more than 10 13 Ω and preferably not more than 10 12 Ω. Since the composition [1a] of the present invention can thus be tailored to yield cured resins with refractive indices not less than 1.54, sufficiently short focal lengths can be realized when they are applied to the manufacture of Fresnel lens. Moreover, because the compositions have been provided with antistatic properties, no static electricity is generated in the assembling of a lens sheet or a lens plate so that improved handling workability can be expected with no deposits of dust. The composition [1a] of the present invention can be cured by UV irradiation. There is no particular limitation on the type of UV irradiation equipment but a high-pressure mercury lamp or a metal halide lamp can be used as a radiation source. As shown in Fig. 1, the rear projection screen 1 of the invention comprises a sheet or plate 6 made of a methyl methacrylate (co)polymer and the Fresnel lens 5 formed by the UV curing of the composition [1a] of the invention in situ on the light emergence surface of said sheet or plate 6, and a lenticular lens sheet 3 comprising lenticular lenses arranged on both incidence and emergence surfaces and having light absorbing layer 4 in the non-light-converging(non-light emerging) zones formed on the emergence surface as the projected light is converged by the lenticular lenses on the incidence surface in such a manner that the Fresnel lens 5 is juxtaposed with the lenticular lenses on the incidence surface of lenticular lens sheet 3. The Fresnel lens 5 is directly formed on the sheet or plate 6 by UV cure of said composition [1a] without interposition of an adhesive layer such as a primer layer on the sheet or plate 6. The sheet or plate thus constitued by disposing thereon the Fresnel lens of the present invention may be refered to as the Fresnel lens sheet or Fresnel lens plate in the specification. The rear projection screen 1 of the present invention comprises the Fresnel lens sheet or Fresnel lens plate 2 carrying the Fresnel lens 5 formed by curing the composition [1a] of the invention, and in addition to the use in combination with the lenticular lens sheet 3 as illustrated in Fig. 1, it can be used in combination with various other alternative screen lens sheets. The sheet or plate 6 is made of a methyl methacrylate (co)polymer, viz. a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate with one or more other alkyl (meth)acrylates the carbon number of the alkyl moiety of which are usually 1 to 18. The methyl methacrylate content of said sheet or plate is usually not less than 70 weight % and preferably not less than 80 weight %. If the proportion of methyl methacrylate is within said range, adequate adhesion to the cured composition of the invention will be insured. The sheet or plate 6 made of a methyl methacrylate (co) polymer can be formed by the known molding technique such as injection molding, extrusion molding, or casting. The thickness of the sheet or plate may be ranged from 0.5 to 5 mm. Production of the Fresnel lens sheet or Fresnel lens plate can be carried out typically by a process which comprises applying the composition [1a] of the invention to a Fresnel lens mold, superimposing said sheet or plate on said composition under application of pressure to avoid entrapping of air, irradiating the assemblage with ultraviolet light to cure the composition [1a] followed by releasing from the mold. EXAMPLES The following examples illustrate the present invention in further detail and should by no means be construed as defining the scope of the invention. In the examples, all parts are by weight. Examples of Synthesis 1 to 3 Using the components (a1), (a2), (b2) and (b3) according to the formulas (weight ratios) indicated in Table 1, urethane group-containing acrylate (A2-1 to A2-3) were produced by the following method. The refractive index (25 °C ) of each sheet was determined with an Abbe refractometer (manufactured by Atago). The results are shown in Table 1. Synthetic process A four-necked flask equipped with a stirrer, condensor and thermometer was charged with the indicated amounts of (a1) and (a2) and 0.025 part of dibutyltin oxide and the dehydrative esterification reaction was carried out at 10 mmHg and 200 °C for 8 hours. To the resulting polyester (b1) was added the indicated amount of (b2) and the reaction was further carried out at 80 to 90 °C for 2 hours. Then, the indicated amount of (b3) was added and the reaction was further carried out at 80 to 90 °C for 3 hours. In this manner, urethane group-containing acrylates (A2-1 to A2-3) were synthesized. Example of Synthesis 1 2 3 Symbol A2-1 A2-2 A2-3 a1 Bisphenol A EO (10 mol)addition product Bisphenol A EO (6 mol)addition product Bisphenol A EO (4 mol)addition product Amount of a1 401 400 400 a2 Maleic anhydride Succinic acid Succinic acid Amount of a2 29.4 48.0 72.8 b2 Xylylene diisocyanate Tolylene diisocyanate Tolylene diisocyanate Amount of b2 69.2 86.0 79.0 b3 Hydroxyethyl acrylate Hydroxyethyl acrylate Hydroxyethyl acrylate Amount of b3 15.8 21.0 33.8 Number average mol. wt. 7,480 6,120 4,050 Refractive index(25°C) 1.546 1.537 1.550 In the table, EO stands for ethylene oxide and PO for propylene oxide. Comparative Examples of Synthesis 1 and 2 Using the diol, (b2), and (b3) in accordance with the formulas (weight ratios) shown in Table 2, control urethane group-containing acrylates (UA-1 and UA-2) were synthesized by the following comparative method of synthesis. The refractive index (25 °C) of each urethane group-containing acrylate synthesized is shown in Table 2. Comparative method of synthesis The same reactor as used for the above-described method of synthesis was charged with the indicated amounts of diol and (b2) and the reaction was carried out at 80 to 90°C for 2 hours. Then, the indicated amount of (b3) was added and the reaction was further carried out at 80 to 90°C for 3 hours. In this manner, urethane group-containing acrylates (UA-1 and UA-2) were obtained. Comparative Example of Systhesis 1 2 Symbol UA-1 UA-2 Diol Bisphenol A EO (40 mol) addition product Polycaprolactonediol(Mw=2,000) Amount of diol 398 400 b2 Tolylene diisocyanate Isophorone diisocyanate Amount of b2 51.2 44.4 b3 Hydroxyethyl acrylate Hydroxyethyl acrylate Amount of b3 21.9 46.4 Number average mol. wt. 4,995 2,676 Refractive index (25°C) 1.517 1.484 Examples 1 to 5 According to the formulas (weight ratios) shown in Table 3, resin compositions [1a] of the invention (Examples 1 to 5) were prepared. The viscosity of each sample at 35°C was measured with a BL viscosimeter (manufactured by Tokyo Keiki). In addition, 50 µm films were prepared and irradiated with 1000 mJ/cm 2 of ultraviolet light to provide cured films and the refractive index of each film at 25 °C was determined. The viscosity (35 °C ) and refractive index of each film are shown in Table 4. Comparative Examples 1 to 3 According to the formulas (weight ratios) shown in Table 3, comparative resin compositions (Comparative Examples 1 to 3) were prepared. The viscosity (35 °C) and refractive index of each cured composition are shown in Table 4. Test Example 1 Using the resin compositions of Examples 1 to 5 and Comparative Examples 1 to 3, Fresnel lenses were prepared by the following test method and tested for adhesion to a sheet, mold releasability, and scratch resistance. The results are shown in Table 4. Test method Each of the UV-curable resin compositions shown in Table 3 was applied, in a thickness of 50 to 150µm, onto a chrome-plated Fresnel lens mold (50 cm× 50 cm) by the dispenser controlled at 35 °C, and a 2 mm-thick sheet made of a methyl methacrylate copolymer (Sumipex HT(trade name), manufactured by Sumitomo Chemical) was superimposed on the dispensed resin composition in the mold under application of pressure with care exercised to avoid air entrapment. Then, using a high-pressure mercury lamp, the UV-curable resin was cured by 1,000 mJ/cm 2 of UV light and the mold was then released to provide a Fresnel lens. The mold releasability and the performance parameters of each Fresnel lens were evaluated as follows. (1) Mold releasability: The ease of release from the mold in the production of the Fresnel lens Criteria ○: Easy to release × : Difficult to release, with deformation ensuing (2) Air entrapment: The presence or absence of air cells in the Fresnel lens Criteria ○ : no air cells × : Air cells (3) Adhesion: The degree of adhesion of the UV-cured resin composition to the sheet The sample is crosshatched with a knife at 1 mm/pitch (10× 10) and a cellophane tape was set in position and peeled off at an angle of 90 degrees. The degree of exfoliation of the cured resin from the sheet was evaluated. Criteria ○ : not exfoliated × : Exfoliated (4) Scratch resistance: Scratchability of the Fresnel lens Criteria ○: Scratching with the finger nail leaves no mark × : Scratching with the finger nail leaves a mark Example Comparative Example 1 2 3 4 5 1 2 3 A1 Aronix M-5700 50 50 45 30 30 10 50 50 A2 A2-1 25 30 A2-2 30 A2-3 40 40 40 UA-1 30 UA-2 30 A3 Aronix M-101 15 20 20 35 50 10 Aronix M-111 15 20 NK Ester A-400 10 10 Viscoat 195 10 5 B Darocur 1173 2 2 2 2 2 2 2 2 In the table, each component means as follows: Aronix M-5700 : (trade name) 2-Hydroxy-3-phenoxypropyl acrylate, manufactured by Toagosei Chemical Industry Co. Ltd. Aronix M-101 : Phenoxy diethylene glycol acrylate, (trade name) manufactured by Toagosei Chemical Industry Co. Ltd. Aronix M-111 : Nonylphenoxy ethylene glycol acrylate, (trade name) manufactured by Toagosei Chemical Industry Co. Ltd. NK Ester A-400: (trade name) Polyethylene glycol diacrylate, manufactured by Shin Nakamura Kagaku Viscoat 195 : (trade name) 1,4-Butanediol diacrylate, manufactured by Osaka Yuki Kagaku Darocur 1173 : (trade name) 2-Hydroxy-2-methyl-1-phenylpropan-1-one, manufactured by Ciba-Geigy Example 6 to 10 In accordance with the formulas (weight ratios) shown in Table 5, resin compositions (1a) each containing a plasticizer (C3) according to the invention (Examples 6 to 10) were prepared. The viscosity of each sample at 35 °C was measured with a BL viscosimeter (manufactured by Tokyo Keiki). In addition, 50 µm films were prepared and irradiated with 1000 mJ/cm 2 of ultraviolet light to provide cured sample films and the refractive index of each film at 25 °C was determined. The viscosity (35°C) and refractive index of each film are shown in Table 6. Test Example 2 Using the resin compositions of Examples 6 to 10, Fresnel lenses were prepared in accordance with the same test method as Test Example 1 and evaluated for adhesion to a sheet, mold releasability, and scratch resistance. The results are shown in Table 6. Examples 6 7 8 9 10 A1 Aronix M-5700 50 40 30 40 40 A2 A2-1 30 35 40 A2-2 30 30 A2-3 A3 Aronix M-101 15 20 20 20 Aronix M-111 15 C3 Tricresyl phosphate 5 5 10 5 Dimethyl phthalate 10 NK Ester A-400 5 Viscoat 195 5 B Darocur 1173 2 2 2 2 2 Example of Synthesis 4 An autoclave equipped with a stirrer, condensor and thermometer was charged with 558 parts of lauryl alcohol followed by addition of 264 parts of ethylene oxide at 50 °C and the reaction was conducted at 200 °C for 2 hours. To the resulting alcohol (822 parts), 137 parts of diphosphorus pentaoxide was added and the reaction was further carried out at 80 to 90°C for 2 hours to provide a phosphate (C2-1). Example of Synthesis 5 In the same autoclave as used in Example of Synthesis 4, 520 parts of octyl alcohol was reacted with 176 parts of ethylene oxide at 50 °C and, then, with 280 parts of diphosphorus pentaoxide to provide a phosphate (C2-2). Comparative Example of Synthesis 3 A four-necked flask equipped with a stirrer, condensor and thermometer was charged with 400 parts of lauric acid. After 300 parts of triethanolamine was added at room temperature, the reaction was carried out at room temperature for 2 hours to provide lauric acid triethanolamine salt (LA-1). Examples 11 to 15 According to the formulas (weight ratios) shown in Table 7, resin compositions [1a] (Examples 11 to 15) each containing a phosphate (C2) were prepared. The viscosity (35°C) of each composition was measured with a BL viscosimeter (manufactured by Tokyo Keiki). In addition, 50 µm-thick films were prepared and irradiated with ultraviolet light at 1000 mJ/cm 2 to provide cured films and the refractive index (25°C) of each cured film was determined. The viscosity (35 °C) and cured refractive index values are shown in Table 8. Test Example 3 Using the resin compositions of Examples 11 to 15, Fresnel lenses were prepared by the same method as Test Example 1 and evaluated for adhesion to a sheet, mold releasability, and scratch resistance. The evaluation of antistatic properties was made by the following test method. The results are shown in Table 8. Antistatic test After conditioning to a temperature of 25 °C and a humidity of 60%, the surface resistivity of each Fresnel lens was measured with Ultra High Resistance Meter (manufactured by Advantest). Example Comparative Example 11 12 13 14 15 1 2 3 A1 Aronix M-5700 50 40 30 40 40 50 40 40 A2 A2-1 30 30 40 30 30 A2-2 30 35 30 Aronix M-101 20 30 20 25 20 20 Aronix M-111 25 30 NK Ester A-400 5 10 Viscoat 195 10 C2 C2-1 0.3 0.5 0.5 C2-2 0.5 1.0 LA-1 1.0 3.0 B Darocur 1173 2 2 2 2 2 2 2 2 The UV-curable Fresnel lens resin composition of the present invention has the following advantages. 1) Excellent adhesion to a sheet or plate made of a methyl methacrylate homopolymer or a copolymer of methyl methacrylate with one or more other (meth)acrylates. 2) Easily moldable into Fresnel lens and other optical parts. 3) Providing a cured resin with a refractive index as high as 1.54 or higher and excellent chemical resistance, toughness, heat resistance, and cold resistance. 4) The cured resin is highly antistatic. Having the above-mentioned advantages, the composition of the present invention is of great utility value as a Fresnel lens material. The rear projection screen of the present invention includes the Fresnel lens sheet or Fresnel lens plate formed by curing the above UV-curable resin composition and, therefore, has an excellent Fresnel lens with high scratch resistance. Therefore, there is no risk of damage or injury even on contact with other lens sheets during transport or assembly and it is no longer necessary to treat the surface by, for example, applying silicone oil or the like between the Fresnel lens sheet or Fresnel lens plate and the lenticular lens sheet. Furthermore, the rear projection screen of the present invention has a highly antistatic Fresnel lens surface so that no deposit of dust occurs in assembly, thus contributing to improved workability. In addition, since the refractive index of the rear projection screen is as high as at least 1.54, it is possible to manufacture Fresnel lenses of short focal length to reduce the distance between the rear projection screen and the light source, thus permitting the design and manufacture of low-profile, compact projection television devices of large screen size.

Claims: A UV-curable Fresnel lens resin composition for use in the formation of a Fresnel lens on a sheet or plate made of a methyl methacrylate (co)polymer, characterized in that said resin composition comprises (A1) a (meth)acrylate containing a hydroxyl group and an aromatic ring; (A2) a urethane group-containing (meth)acrylate having a moiety of an aromatic diol (a1) represented by the following general formula: wherein Ph represents a 1,4-phenylene group, R 1 , R 2 and R 3 each represent a hydrogen atom or a methyl group, m and n each represent an integer of 1 to 15, and (m+n) is equal to 2 to 20; (A3) an aromatic ring-containing monofunctional (meth)acrylate; and (B) a photopolymerization initiator. The composition according to claim 1 wherein (A2) is a reaction product of an organic isocyanate (b2) with a hydroxyl group-containing (meth)acrylate (b3) and a polyester polyol (b1) derived from (a1) and a dicarboxylic acid (a2). The composition according to claim 2 wherein (a2) is at least one dicarboxylic acid selected from the group consisting of maleic acid, fumaric acid, succinic acid, adipic acid and the acid anhydrides thereof. The composition according to any one of claims 1-3 which contains 20 to 60 weight % of (A1), 10 to 50 weight % of (A2), 5 to 50 weight % of (A3), and 0.1 to 10 weight % of (B). The composition according to any one of claims 1-4 which further contains (C3) a plasticizer with a solubility parameter in the range of 10.0 to 11.5, preferably in a proportion of 1 to 20 weight %. The composition according to any one of claims 1-5 which further contains (C2) a phosphate represented by the following general formula (2), preferably in a proportion of 0.1 to 2.0 weight % : [R(OCH 2 CH 2 ) s O] t PO(OH) (3-t) wherein R represents an alkyl group containing 5 to 16 carbon atoms, s represents an integer of 1 to 4, and t represents an integer of 1 or 2. A Fresnel lens comprising a resin formed by UV cure of the composition claimed in any one of claims 1-6 in situ on a sheet or plate made of a methyl methacrylate (co)polymer. A rear projection screen comprising a Fresnel lens sheet or Fresnel lens plate carrying the Fresnel lens according to claim 7 as disposed on a sheet or plate made of a methyl methacrylate (co)polymer.

Inventors: HONDA MAKOTO, OKUBO MICHIHARU, OSAWA FUTOSHI, YAMASHITA TSUTOMU, HONDA, MAKOTO, OKUBO, MICHIHARU, OSAWA, FUTOSHI, YAMASHITA, TSUTOMU, Honda, Makoto, c/0 Dainippon Printing Co., Ltd., Okubo, Michiharu, Sanyo Chemical Industries, Ltd., Osawa, Futoshi, c/0 Dainippon Printing Co., Ltd., Yamashita, Tsutomu, Sanyo Chemical Industries, Ltd
Applicants: DAINIPPON PRINTING CO LTD, SANYO CHEMICAL IND LTD, DAINIPPON PRINTING CO., LTD., SANYO CHEMICAL INDUSTRIES, LTD.
Application year: 1996
Main classification: G02B1
IPC codes: G02B1, G03B21, G02B3