WO2006022545A1

WO2006022545A1 - Curable liquid resin composition

Info

Publication number: WO2006022545A1
Application number: PCT/NL2005/000615
Authority: WO
Inventors: Satoshi Futami; Takeo Shigemoto; Komiya Zen
Original assignee: Jsr Corporation
Priority date: 2004-08-25
Filing date: 2005-08-25
Publication date: 2006-03-02
Also published as: JP2006063144A

Abstract

To provide a photocurable resin composition capable of producing a cured product having excellent heat resistance, showing an extremely small amount of deformation, and useful as an optical part. A photocurable resin optical part forming composition, comprising: (A) 20-60 wt % of a urethane (meth)acrylate oligomer obtained by reacting a polyol, a polyisocyanate, and a hydroxyl group-containing (meth)acrylate, the polyol having a branched structure, including a hydroxyl group at each branched chain terminal, and having a value obtained by dividing the molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals of 100-2,000; (B) 30-70 wt % of a polymerizable monofunctional compound; and (C) 0.01-10 wt % of a radical photoinitiator.

Description

CURABLE LIQUID RESIN COMPOSITION

Technical field

The present invention relates to a photocurable resin composition. More particularly, the present invention relates to a photocurable resin composition useful for forming an optical part such as a lens of a lens sheet such as a prism lens sheet that is used for a backlight of a liquid crystal display, a Fresnel lens sheet or a lenticular lens sheet that is used for a screen of a projection TV or the like, or a backlight using such sheets.

Background Art

Lenses such as a Fresnel lens and a lenticular lens have been manufactured by using a press-forming process or a casting process. However, these processes require a long time for manufacturing the lens, thereby resulting in poor productivity. In order to solve such a problem, a method of manufacturing lenses using a UV-curable resin has recently been studied. Specifically, the method comprises injecting a UV-curable resin composition into a mold having a lens shape placed on a transparent resin substrate, and curing the composition by applying ultraviolet rays from the side of the substrate, whereby a lens can be manufactured in a short time.

A hard lens sheet may be warped (also referred to as "curling") during production, or the lens shape may be deformed under such use conditions where the lens is used at a high temperature of about 6O⁰C, and is then cooled to room temperature. As a result, the resulting image may be distorted. In particular, since notebook type personal computers or the like are provided with two lens sheets in order to improve luminance, a lens sheet showing only a small amount of curling has been required. A reduction in the amount of curling of a lens sheet by utilizing a large amount of monofunctional monomers in place of polyfunctional monomers in the resin has been proposed in Japanese Patent Application Laid-open No. 2004-51941.

However, since the degree of crosslinking is reduced due to a decrease in the amount of polyfunctional monomers, heat resistance is decreased.

Problems to be Solved by the Invention Accordingly, an object of the present invention is to provide a p^:hotocurable resin composition capable of producing a cured product having excellent heat resistance, showing an extremely small amount of deformation, and which cured product is useful as an optical part.

Means for Solving the Problem

As a result of extensive studies, the present inventors have found that a reduction in the amount of curling and an increase in heat resistance can be achieved by using a composition having specific components. This finding has led to the completion of the present invention.

Specifically, the present invention provides a photocurable resin suitable for forming an optical part composition, comprising: (A) 20-60 wt% of a urethane (meth)acrylate oligomer obtained by reacting a polyol, a polyisocyanate, and a hydroxyl group-containing (meth)acrylate, the polyol having a branched structure, including a hydroxyl group at each branched chain terminal, and having a value obtained by dividing the molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals of 100-2,000;

(B) 30-70 wt% of a polymerizable monofunctional compound; and

(C) 0.01-10 wt% of a radical photoinitiator; and also provides an optical part obtained by curing the composition.

Effect of the Invention

The cured product of the photocurable resin composition according to the present invention can form a lens sheet exhibiting high heat resistance and showing only a small amount of .curing.

Best Mode for Carrying out the Invention

The present invention will be described below in detail. The urethane (meth)acrylate oligomer (A) used in the photocurable resin composition of the present invention (hereinafter also referred to as "composition of the present invention") has functions of reducing warping and improving heat resistance (softening point) of a cured product obtained by curing the composition of the present invention. The urethane (meth)acrylate oligomer (A) is obtained by reacting (a) a polyol having a branched structure, including a hydroxyl group at each branched chain terminal, and having a value obtained by dividing the molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals of 100-2,000 (hereinafter also referred to as "polyol (a)"), (b) a polyisocyanate, and (c) a hydroxyl group-containing (meth)acrylate. The urethane (meth)acrylate oligomer is obtained by reacting the polyol (a), polyisocyanate (b), and hydroxyl group-containing (meth)acrylate (c) at a specific raw material molar ratio. A urethane bond (-CONH-) formed by a hydroxyl group of the polyol (a) and an isocyanate group of the isocyanate (b) provides toughness to the cured product. Moreover, since the polyol (a) has three or more hydroxyl groups, the composition forms a cured product having a network structure.

As the reaction method, a method of reacting the polyol (a), the polyisocyanate (b), and the hydroxyl group-containing (meth)acrylate (c) all together; a method of reacting the polyisocyanate (b) with the hydroxyl group-containing (meth)acrylate (c), and reacting the resulting product with the polyol (a); a method of reacting the polyisocyanate (b) with the hydroxyl group-containing (meth)acrylate (c), reacting the resulting product with the polyol (a), and further reacting the resulting product with the hydroxyl group-containing (meth)acrylate (c); and the like can be given. In the reaction of these compounds, it is preferable to use a urethanization catalyst such as copper naphthenate, cobalt naphthenate, zinc naphthenate, di-n-butyltin dilaurate, triethylamine, 1 ,4-diazabicyclo[2.2.2]octane, or 2,6,7-trimethyl-1 ,4-diazabicyclo[2.2.2]octane in an amount of 0.01-1 part by weight for 100 parts by weight of the total reactant. The reaction temperature is usually 10-90⁰C, and preferably 30-80⁰C.

In the present invention, the polyol (a) has a branched structure, includes a hydroxyl group at each branched chain terminal, and has a value obtained by dividing the molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals of 100-2,000. As specific examples of the polyol, a polyol (a1) obtained by ring-opening polymerization of a sugar such as glycerin or sorbitol and at least one compound selected from ethylene oxide, propylene oxide, and butylene oxide can be given.

The polyol has a value of 100-2,000, and still more preferably of 100- 1 ,000 as obtained by dividing the number average molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals. The number average molecular weight of the entire polyol (a1) is preferably 300-5000, more preferably 500- 4000, and particularly preferably 800-1000, although the number average molecular weight of the polyol (a1) is not limited thereto.

The "value obtained by dividing the molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals" means the average - A -

molecular weight of the branched chains. The molecular weight of the polyol used herein refers to the polystyrene-reduced number molecular weight determined by gel permeation chromatography.

The polyol (a1) contains three or more branched chain terminal in one molecule, and preferably contains 3-6 branched chain terminals.

As commercially available products of the polyol (a1), So-1000, So- 800, Sanix TP-400, Sanix GL-3000, Sanix GP-250, Sanix GP-400, Sanix GP-600, Sanix GP-1000, Sanix GP-3000, Sanix GP-3700M, Sanix GP-4000, Sanix GEP-2800, Newpole TL4500N, Uniol TG-1000, and Uniol TG-4000 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Asahi Glass Urethane Co., Ltd., Sanyo Chemical Industries, Ltd., and Nippon Oil and Fats Co., Ltd. can be given.

As the polyiosocyanate (b), a diisocyanate is preferable. As examples of the diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1 ,3- xylylene diisocyanate, 1 ,4-xylylene diisocyanate, 1 ,5-naphthalene diisocyanate, m- phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylphenylene diisocyanate, 4,4'-biphenylene diisocyanate, 1 ,6-hexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexylisocyanate), 2,2,4-trimethylhexamethylene diisocyanate, bis(2-isocyanatoethyl)fumarate, 6-isopropyl-1 ,3-phenyl diisocyanate, A- diphenylpropane diisocyanate, lysine diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, tetramethylxylylene diisocyanate, 2,5(or 6)-bis(isocyanatemethyl)-bicyclo[2.2.1]heptane, and the like can be given. Of these, 2,4-tolylene diisocyanate and isophorone diisocyanate are particularly preferable. The polyisocyanate (b) may be used either individually or in combination of two or more.

As examples of the hydroxyl group-containing (meth)acrylate (c), 2- hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, 1 ,4-butanediol mono(meth)acrylate, 2-hydroxyalkyl(meth)acryloyl phosphate, 4-hydroxycyclohexyl (meth)acrylate, 1 ,6-hexanediol mono(meth)acrylate, neopentyl glycol mono(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolethane di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, (meth)acrylates shown by the following formulas (1) and (2), a compound obtained by the addition reaction of (meth)acrylic acid with a glycidyl group- containing compound such as an alkyl glycidyl ether, allyl glycidyl ether, glycidyl (meth)acrylate, and the like can be given.

Of these hydroxyl group-containing (meth)acrylates, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are preferable.

CH₂= CR¹- COOCH₂CH₂^ OCOCH₂CH₂CH₂CH₂CH^- OH { 1 )

CH₂=CR¹~COOCH₂CH(0H)CH₂-O — (^ h ( 2 )

wherein R¹ represents a hydrogen atom or a methyl group, and n is an integer of 1-15. The hydroxyl group-containing (meth)acrylate (c) may be used either individually or in combination of two or more.

The urethane (meth)acrylate oligomer (A) is added to the curable liquid resin composition of the present invention in an amount of preferably 20-60 wt%, and still more preferably 30-50 wt%. If the amount is less than 20 wt%, applicability may be impaired. If the amount exceeds 60 wt%, the amount of curling of the lens sheet is increased.

The curable liquid resin composition of the present invention may further include a urethane (meth)acrylate other than the component (A). As examples of such a urethane (meth)acrylate, a urethane (meth)acrylate obtained by reacting a diol, a diisocyanate, and a hydroxyl group-containing (meth)acrylate compound, or a urethane (meth)acrylate obtained by reacting a diisocyanate and a hydroxyl group- containing (meth)acrylate compound can be given.

When adding the urethane (meth)acrylate oligomer other than the component (A), the total amount of the component (A) and the urethane (meth)acrylate oligomer other than the component (A) is within 20-60 wt% of the composition. As examples of the urethane (meth)acrylate obtained by reacting the diol, diisocyanate, and hydroxyl group-containing (meth)acrylate compound, the reaction product of a polyol other than the polyol (a1) (hereinafter referred to as "polyol (a2)"), the diisocyanate (b), and the hydroxyl group-containing (meth)acrylate (c) can be given. The components (b) and (c) are the same as those described for the component (A).

The polyol (a2) may be a polyol other than the polyol (a1) or a mixture of polyols. Examples of the polyol (a2) include aliphatic or cyclic polyether diols, polyester diols, polycarbonate diols, and polycaprolactone diols. There are no specific limitations to the manner of polymerization of the structural units of these polyols. These polyols may be any of a random polymer, a block polymer, and a graft polymer. As examples of the aliphatic polyether diols, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, polyether polyols obtained by ring-opening copolymerization of two or more ion-polymerizable cyclic compounds, and the like can be given. As examples of the ion-polymerizable cyclic compound, cyclic ethers such as ethylene oxide, propylene oxide, 1 ,2-butylene oxide, butene-1 -oxide, isobutene oxide, 3,3-bischloromethyloxetane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, cyclohexene oxide, styrene oxide, epichlorohydrin, glycidyl methacrylate, allyl glycidyl ether, allyl glycidyl carbonate, butadiene monoxide, isoprene monoxide, vinyloxetane, vinyltetrahydrofuran, vinylcyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether, and glycidyl benzoate can be given. Moreover, a polyether polyol obtained by ring- opening copolymerization of the above ion-polymerizable cyclic compound with a cyclic imine such as ethyleneimine, cyclic lactonic acid such as beta-propyolactone or glycolic acid lactide, or dimethylcyclopolysiloxane may also used. As examples of specific combination of two or more ion-polymerizable cyclic compounds, a combination of tetrahydrofuran and propylene oxide, tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, tetrahydrofuran and ethylene oxide, propylene oxide and ethylene oxide, butene-1 -oxide and ethylene oxide, a ternary copolymer of tetrahydrofuran, butene-1 -oxide, and ethylene oxide, and the like can be given. The ring-opening copolymer of these ion-polymerizabie cyclic compounds may be either a random copolymer or a block copolymer.

These polyether polyols are commercially available as EXCENOL 1020 (manufactured by Asahi Glass Urethane Co., Ltd.), PTMG 650, PTMG 1000, PTMG 2000 (manufactured by Mitsubishi Chemical Corp.), PEG 1000, Unisafe DC1100, DC1800 (manufactured by Nippon Oil and Fats Co., Ltd.), PPTG 2000, PPTG 1000, PTG 400, PTGL 2000 (manufactured by Hodogaya Chemical Co., Ltd.), and Z- 3001-4, Z-3001-5, PBG 2000A, PBG 2000B (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

As examples of the cyclic polyether polyol, alkylene oxide addition diol of bisphenol A, alkylene oxide addition diol of bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, alkylene oxide addition diol of hydrogenated bisphenol A, alkylene oxide addition diol of hydrogenated bisphenol F, alkylene oxide addition diol of hydroquinone, alkylene oxide addition diol of naphthohydroquinone, alkylene oxide addition diol of anthrahydroquinone, 1 ,4-cyclohexanediol and alkylene oxide addition diol thereof, tricyclodecanediol, tricyclodecanedimethanol, pentacyclopentadecanediol, pentacyclopentadecanedimethanol, and the like can be given. Of these, alkylene oxide addition diol of hydrogenated bisphenol A, alkylene oxide addition diol of bisphenol A, and tricyclodecanedimethanol are preferable. These polyols are commercially available as Uniol DA400, DA700, DA1000, DB400 (manufactured by Nippon Oil and Fats Co., Ltd.), N1162 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), tricyclodecanedimethanol (manufactured by Mitsubishi Chemical Corp.), and the like.

As examples of the polyester polyol, polyester polyols obtained by reacting a polyol with a dibasic acid can be given. Examples of the above polyols include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1 ,6-hexanediol, neopentyl glycol, 1 ,4- cyclohexanedimethanol, 3-methyl-1 ,5-pentanediol, 1 ,9-nonanediol, and 2-methyl-1 ,8- octanediol. As examples of the dibasic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid, sebacic acid, and the like can be given. These polyester diols are commercially available as Kurapol P-2010, PMIPA, PKA-A, PKA-A2, PNA-2000 (manufactured by Kuraray Co., Ltd.), and the like. As examples of the polycarbonate polyol, polycarbonate of polytetrahydrofuran, polycarbonate of 1 ,6-hexanediol, and the like can be given. As commercially available products of the polycarbonate polyol, DN-980, 981, 982, 983 (manufactured by Nippon Polyurethane Industry Co., Ltd.), PC-8000 (manufactured by PPG), PC-THF-CD (manufactured by BASF), and the like can be given. As examples of the polycaprolactone diol, polycaprolactone diols obtained by reacting ε-caprolactone and a diol such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1 ,2-polybutylene glycol, 1 ,6-hexanediol, neopentyl glycol, 1 ,4-cyclohexanedimethanol, or 1 ,4-butanediol can be given. These diols are commercially available as Placcel 205, 205AL, 212, 212AL, 220, 220AL (manufactured by Daicel Chemical Industries, Ltd.), and the like.

The polyol (a2) other than those illustrated above may also be used. As examples of such other polyols, ethylene glycol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, neopentyl glycol, 1 ,4-cyclohexanedimethanol, dimethylol compound of dicyclopentadiene, tricyclodecanedimethanol, beta-methyl-gamma-valerolactone, hydroxy-terminated polybutadiene, hydroxy-terminated hydrogenated polybutadiene, castor oil-modified polyol, diol-terminated compound of polydimethylsiloxane, polydimethylsiloxanecarbitol-modified diol, and the like can be given.

A diamine may be used in combination with the polyol (a1) instead of the polyol (a2). As examples of the diamine, ethylenediamine, tetramethylenediamine, hexamethylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, diamine containing a hetero atom, polyether diamine, and the like can be given.

As the polyol (a2), a polyether diol, alkylene oxide addition diol of bisphenol A, and alkylene oxide addition diol of hydrogenated bisphenol A are preferable. These diols are commercially available as PTMG 650, PTMG 1000, PTMG 2000 (manufactured by Mitsubishi Chemical Corp.), Uniol DA400, DA700, DA1000, DB400 (manufactured by Nippon Oil and Fats Co., Ltd.), and N1162 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

The number average molecular weight of the polyol (a2) is 300- 5,000, preferably 300-2,000, and more preferably 300-1 ,000.

As specific examples of the urethane (meth)acrylate, other than the component (A), obtained by reacting a diisocyanate and a hydroxyl group-containing (meth)acrylate compound, a reaction product of hydroxyethyl (meth)acrylate and 2,4- tolylene diisocyanate, a reaction product of hydroxyethyl (meth)acrylate and 2,5 (or 6)- bis(isocyanatemethyl)-bicyclo[2.2.1]heptane, a reaction product of hydroxyethyl (meth)acrylate and isophorone diisocyanate, a reaction product of hydroxypropyl (meth)acrylate and 2,4-tolylene diisocyanate, and a reaction product of hydroxypropyl (meth)acrylate and isophorone diisocyanate and the like can be given.

A polymerizable monofunctional compound is added to the liquid curable resin composition of the present invention as the component (B). As examples of the polymerizable monofunctional compound, N-vinylpyrrolidone, lactams containing a vinyl group such as N-vinylcaprolactam, (meth)acrylates containing an alicyclic structure such as isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and dicyclopentanyl (meth)acrylate, benzyl (meth)acrylate, 4- butylcyclohexyl (meth)acrylate, acryloylmorpholine, vinyl imidazole, vinyl pyridine, 2- hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, benzyl(meth)acrylate, phenoxyethyl(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, diacetone(meth)acrylamide, isobutoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, t- octyl(meth)acrylamide, dimethylaminoethyl (meth)acrylate, diethylaminoethyl

(meth)acrylate, 7-amino-3,7-dimethyloctyl (meth)acrylate, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, hydroxybutyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, 2-ethylhexyl vinyl ether, and compounds shown by the following formulas (3) to (6) can be given.

CH₂=CR²-CO-(R³O)_ra-R⁴ ( 3 ) O

wherein R² represents a hydrogen atom or a methyl group, R³ represents an alkylene group having 2-6, and preferably 2-4 carbon atoms, R⁴ represents a hydrogen atom or an alkyl group having 1-12, and preferably 1-9 carbon atoms, and m indicates an integer of 0-12, and preferably of 1-8.

wherein R⁵ represents a hydrogen atom or a methyl group, R⁶ represents an alkylene group having 2-8, and preferably 2-5 carbon atoms, R⁷ individually represents a hydrogen atom or a methyl group, and p is preferably an integer of 1-4.

wherein R⁸, R⁹, R¹⁰, and R¹¹ individually represent a hydrogen atom or a methyl group, and q is an integer of 1-5.

Of these polymerizable monofunctional compounds (B), N- vinylpyrrolidone, a vinyl group-containing lactam such as N-vinylcaprolactam, or acryloylmorpholine is preferable.

These polymerizable monofunctional compounds (B) are commercially available as IBXA (manufactured by Osaka Organic Chemical Industry Co., Ltd.), Aronix M-111 , M-113, M-114, M-117, TO-1210, Aronix M-110 (manufactured by Toagosei Co., Ltd.), and the like.

The polymerizable monofunctional compound (B) is used in an amount of preferably 30-70 wt%, and more preferably 40-60 wt% of the total amount of the curable liquid resin composition of the present invention.

As examples of the radical photoinitiator (C), acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2- phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'- dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2- methylpropan-1 -one, 2-hydroxy-2-methyl-1 -phenylpropan-1 -one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1-[4- (methylthio)phenyl]-2-morpholino-propan-1-one, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, an initiator shown by the following formula (7), and the like can be given.

wherein r represents an integer of 1-5.

As examples of commercially available products of the radical photoinitiator (C), lrgacure 184, 369, 651 , 500, 819, 907, 784, 2959, CG1 1700, CGI 1750, CGI 11850, CG24-61 , Darocur 1116, 1173 (manufactured by Ciba Specialty Chemicals Co., Ltd.), Lucirin LR8728 (manufactured by BASF), Ubecryl P36 (manufactured by UCB), KIP 150 (manufactured by Lamberti Co.), and the like can be given. Of these, Irgacure184 and KIP 150 are preferable, with KIP 150 being particularly preferable in order to improve heat resistance and reduce warping.

The radical photoinitiator (C) is used in an amount of preferably 0.01- 10 wt%, and particularly preferably 0.5-7 wt% of the composition. The upper limit of the amount is preferable from the viewpoint of curing characteristics of the composition, mechanical and optical characteristics and handling of the cured product and the like. The lower limit of the amount is preferable in order to prevent a decrease in curing speed.

The composition of the present invention preferably further includes (D) a (meth)acrylate having two or more functional groups (hereinafter referred to as "the (meth)acrylate (D)"). It is still more preferable that at least part of the component (D) include a (meth)acrylate having three or more functional groups from the viewpoint of the strength of the resulting cured product. As examples of the (meth)acrylate (D), a (meth)acrylate of a polyhydric alcohol having three or more hydroxyl groups, such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane trioxyethyl(meth)acrylate, and tris(2-acryloyloxyethyl)isocyanurate, and the like can be given. These compounds may be used either individually or in combination of two or more.

As examples of commercially available products of the (meth)acrylate (D), Aronix M305, M309, M310, M315, M320, M350, M360, M408 (manufactured by Toagosei Co., Ltd.), Viscoat #295, #300, #360, GPT, 3PA, #400 (manufactured by Osaka Organic Chemical Industry Co., Ltd.), NK Ester TMPT, A-TMPT, A-TMM-3, A- TMM-3L, A-TMMT (manufactured by Shin-Nakamura Chemical Co., Ltd.), Light Acrylate TMP-A, TMP-6EO-3A, PE-3A, PE-4A, DPE-6A (manufactured by Kyoeisha Chemical Co., Ltd.), Kayarad PET-30, GPO-303, TMPTA, TPA-320, DPHA, D-310, DPCA-20, DPCA-60 (manufactured by Nippon Kayaku Co., Ltd.), and the like can be given.

The (meth)acrylate (D) is added in an amount of preferably 3-20 wt%, and particularly preferably 5-10 wt% of the composition. The lower limit of the amount is preferable in view of heat resistance of the cured product. The upper limit is preferable from the viewpoint of maintaining a reduction in warping.

The composition of the present invention may further include a photosensitizer. As examples of the photosensitizer, triethylamine, diethylamine, N- methyldiethanoleamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl A- dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl A- dimethylaminobenzoate, and the like can be given. As commercially available products of the photosensitizer, Ubecryl P102, 103, 104, 105 (manufactured by UCB), and the like can be given. Various additives such as antioxidants, coloring agents, UV absorbers, light stabilizers, silane coupling agents, heat polymerization inhibitors, leveling agents, surfactants, preservatives, plasticizers, lubricants, solvents, fillers, aging preventives, wettability improvers, and coating surface improvers may optionally be added to the composition of the present invention, insofar as the characteristics of the composition are not adversely affected.

The composition of the present invention is cured by applying radiation, or by applying radiation and heat. Radiation used herein refers to infrared rays, visible rays, ultraviolet rays, X-rays, electron beams, α-rays, β-rays, γ-rays, and the like. It is particularly preferable that a cured product obtained by curing the composition of the present invention by applying radiation have the following properties. Specifically, the refractive index of the cured product at 25⁰C is preferably 1.50 or more, and still more preferably 1.55 or more. If the refractive index is less than 1.50, sufficient frontal brightness may not be secured when forming a prism lens sheet using the composition of the present invention. The softening point of the cured product is preferably 5O⁰C or more, and particularly preferably 52⁰C or more. If the softening point of the cured product is less than 5O⁰C, heat resistance may be insufficient.

A cured product obtained by curing the composition of the present invention is particularly useful as a prism lens of a liquid crystal display shown in Figure 1.

Examples

The present invention is described below in more detail by examples. However, the present invention is not limited to these examples. In the examples, "part(s)" refers to "part(s) by weight".

Preparation example of urethane (meth)acrylate oligomer (A) Synthesis of A-1 A reaction vessel equipped with a stirrer was charged with 42.961 g of isophorone diisocyanate, 0.024 g of 2,6-di-t-butyl-p-cresol, 0.08 g of dibutyltin dilaurate, and 0.008 g of phenothiazine. The mixture was cooled with ice to 1O⁰C or less with stirring. After the dropwise addition of 22.448 g of hydroxyethyl acrylate at 2O⁰C or less, the mixture was allowed to react for one hour with stirring. After the addition of 34.479 g of polypropylenehexaol with a number average molecular weight of 1000 ("So-1000" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), the mixture was stirred at 70-75⁰C for three hours. The reaction was terminated when the residual isocyanate content became 0.1 wt% or less. The resulting liquid resin is called "oligomer A-1".

Synthesis of A-2

A reaction vessel equipped with a stirrer was charged with 27.676 g of 2,4-tolylene diisocyanate, 0.024 g of 2,6-di-t-butyl-p-cresol, 0.08 g of dibutyltin dilaurate, and 0.008 g of phenothiazine. The mixture was cooled with ice to 1O⁰C or less with stirring. After the dropwise addition of 18.451 g of hydroxyethyl acrylate at 2O⁰C or less, the mixture was allowed to react for one hour with stirring. After the addition of 53.761 g of polypropylenetriol with a number average molecular weight of 1000 ("Uniol TG-1000" manufactured by Nippon Oil and Fats Co., Ltd.), the mixture was stirred at 70-75⁰C for three hours. The reaction was terminated when the residual isocyanate content became 0.1 wt% or less. The resulting liquid resin is called "oligomer A-2".

Synthesis of A-3

A reaction vessel equipped with a stirrer was charged with 10.460 g of 2,4-tolylene diisocyanate, 0.024 g of 2,6-di-t-butyl-p-cresol, 0.080 g of dibutyltin dilaurate, and 0.008 g of phenothiazine. The mixture was cooled with ice to 1O⁰C or less with stirring. After the dropwise addition of 6.973 g of hydroxyethyl acrylate while controlling a solution temperature at 2O⁰C or less, the mixture was allowed to react for one hour with stirring. After the addition of 82.455 g of polypropylenetriol with a number average molecular weight of 4,000 ("Uniol TG-4000" manufactured by Nippon Oil and Fats Co., Ltd.), the mixture was stirred at 70-75⁰C for three hours. The reaction was terminated when the residual isocyanate content became 0.1 wt% or less. The resulting liquid resin is called "oligomer A-3".

Synthesis of A'-1

A reaction vessel equipped with a stirrer was charged with 33.264 g of 2,4-tolylene diisocyanate, 0.024 g of 2,6-di-t-butyl-p-cresol, 0.08 g of dibutyltin dilaurate, and 0.008 g of phenothiazine. The mixture was cooled with ice to 1O⁰C or less with stirring. After the dropwise addition of 22.176 g of hydroxyethyl acrylate at 2O⁰C or less, the mixture was allowed to react for one hour with stirring. After the addition of 44.448 g of ethylene oxide addition diol of hydrogenated bisphenol A with a number average molecular weight of 400 (N1162 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), the mixture was stirred at 70-75⁰C for three hours. The reaction was terminated when the residual isocyanate content became 0.1 wt% or less. The resulting liquid resin is called "oligomer A'-1".

Synthesis of A'-2

A reaction vessel equipped with a stirrer was charged with 35.454 g of 2,4-tolylene diisocyanate, 0.024 g of 2,6-di-t-butyl-p-cresol, 0.08 g of dibutyltin dilaurate, and 0.008 g of phenothiazine. The mixture was cooled with ice to 10⁰C or less with stirring. After the dropwise addition of 23.636 g of hydroxyethyl acrylate at 2O⁰C or less, the mixture was allowed to react for one hour with stirring. After the addition of 40.854 g of alkylene oxide addition diol of bisphenol A with a number average molecular weight of 400 ("DA400" manufactured by Nippon Oil and Fats Co., Ltd.), the mixture was stirred at 70-75⁰C for three hours. The reaction was terminated when the residual isocyanate content became 0.1 wt% or less. The resulting liquid resin is called "oligomer A'-2".

Synthesis of A'-3 A reaction vessel equipped with a stirrer was charged with 22.099 g of 2,4-tolylene diisocyanate, 0.024 g of 2,6-di-t-butyl-p-cresol, 0.08 g of dibutyltin dilaurate, and 0.008 g of phenothiazine. The mixture was cooled with ice to 1O⁰C or less with stirring. After the dropwise addition of 14.732 g of hydroxyethyl acrylate at 2O⁰C or less, the mixture was allowed to react for one hour with stirring. After the addition of 63.057 g of polypropylene glycol with a number average molecular weight of 1 ,000 ("Excenol 1020" manufactured by Asahi Glass Urethane Co., Ltd.), the mixture was stirred at 70-75⁰C for three hours. The reaction was terminated when the residual isocyanate content became 0.1 wt% or less. The resulting liquid resin is called "oligomer A'-3".

Examples 1-4 and Comparative Examples 1-5

A photocurable resin composition was prepared by mixing each component at a ratio shown in Table 1. A cured product was obtained by the resulting composition under the following conditions. The properties of the resulting cured product were evaluated according to the following evaluation methods. The results are shown in Table 1.

Evaluation method for cured product properties

1. Measurement of refractive index

The photocurable resin composition obtained in each of the examples and comparative examples was applied to a glass plate using an applicator bar, and irradiated with ultraviolet rays at a dose of 1.0 J/cm² in air to obtain a cured film with a thickness of 200 μm. The refractive index of the cured film at 25⁰C was measured using an Abbe refractometer (manufactured by Atago Co., Ltd.) according to JIS K 7105. 2. Evaluation of transparency

The photocurable resin composition obtained in each of the examples and comparative examples was applied to a 125 μm-thick polyethylene terephthalate (PET) film using an applicator bar so that the applied composition had a thickness of 40 μm. The applied composition was exposed to ultraviolet rays at a dose of 250 mJ/cm² in a nitrogen atmosphere to obtain a cured film. The transparency of the resulting cured film was observed with the naked eye to determine the presence or absence of abnormalities such as foreign matters, coating unevenness, repelling, cloudiness, and loss of transparency. A cured film showing no abnormalities was rated as "Good", and a cured film showing at least one of these abnormalities was rated as "Bad".

3. Evaluation of heat resistance A cured film was obtained in the same manner as in the transparency evaluation. The cured film was cut into a square 1 cm x 1 cm. A columnar quartz rod with a diameter of 5 mm was pressed against the specimen at a load of 20 gf using a thermal mechanical analysis (TMA) system (manufactured by Seiko Instruments Inc.) while changing the temperature to measure the amount of displacement of the thickness of the test specimen. The temperature increase rate was set at 5°C/min.

The amount of displacement is increased with the temperature increase. The inflection point at which the amount of displacement is decreased was measured as the softening point (⁰C). If the inflection point is low, the lens shape may be deformed at a high temperature. Therefore, a case where the inflection point was less than 5O⁰C was judged as "Bad", and a case where the inflection point was 5O⁰C or more was judged as "Good". The softening point (⁰C) is shown in Table 1 as the heat resistant temperature of the lens sheet.

4. Measurement of warping A cured film was obtained in the same manner as in the transparency evaluation. The sample was cut into a square 8 cm x 8 cm and placed on a flat desk with the cured film on the upper side. The heights of the four corners of the sample from the desk were measured. The average value of the heights was defined as the amount of warping. If the amount of warping exceeds 10 mm, when forming a lens sheet using the curable composition of the present invention, optical properties such as luminance may be affected due to curling of the lens. Therefore, a case where the amount of warping exceeded 10 mm was judged as "Bad", a case where the amount of warping was 10 mm or less was judged as "Fair", and a case where the amount of warping was 5 mm or less was judged as "Excellent". Before the measurement of warping, the sample was allowed to stand in a thermo-hygrostat at a temperature of 23⁰C and relative humidity of 50% overnight after irradiation with ultraviolet rays. The measurement was conducted immediately after heating the resulting sample at 85⁰C for 30 minutes.

Table 1

The detail of the components (B) to (D) shown in Table 1 are as follows. Light Ester PO: Phenoxyethyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd.)

KIP150: Radical photoinitiator (manufactured by Lamberti) (the structural formula is given below)

wherein r represents an integer of 1-5. Aronix M315: Tris(2-hydroxyethyl)isocyanuric acid acrylate (manufactured by Toagosei Co., Ltd.)

As is clear from Table 1 , the cured product of the composition including the components (A), (B), (C), and (D) of the present invention in amounts specified in the present invention has excellent heat resistance, shows a small amount of warping and deformation, and has a refractive index as high as 1.50 or more. Therefore, the cured product is particularly useful as an optical part.

In Comparative Example 4, since the amount of the component (A) is more than 60 wt%, warping of the cured product is increased.

In Comparative Example 1 and 3, since the urethane (meth)acrylate oligomer including the polyol (a2) having no branched structure is used, the inflection point is decreased to less than 5O⁰C so that the softening point is also decreased. In Comparative Example 2, since the polyol used in the urethane (meth)acrylate oligomer has no branched structure, warping of the cured product is increased, although the heat resistance is excellent. In Comparative Example 5, the amount of the component (B) is less than 30 wt%, warping of the cured product is increased.

On the other hand, the cured products obtained in Examples 1 to 4 of the present invention exhibit excellent heat resistance and a small amount of warping. These results show that a cured product obtained by curing the photocurable resin composition having a specific composition according to the present invention exhibits excellent heat resistance and shows a small amount of curling.

Industrial Applicability

A cured product of the photocurable resin composition of the present invention exhibits excellent heat resistance and shows a small amount of deformation while maintaining a high refractive index. Therefore, the cured product is particularly useful as an optical part such as a prism lens sheet.

Since the cured product of the photocurable resin composition of the present invention has a high refractive index, the cured product is particularly useful as a lens sheet which allows light emitted from a backlight of a liquid crystal display to perpendicularly (dorectly) enter the viewer's field of vision.

Brief Description of the Drawings

Fig. 1 shows an example of applying a prism lens sheet to a liquid crystal display as an application example of a cured product obtained by curing a composition according to the present invention.

Explanation of Symbols 1 : Substrate 2: Lens of prism lens sheet

Claims

1 A photocurable resin suitable for forming an optical part composition, comprising: (A) 20-60 wt% of a urethane (meth)acrylate oligomer obtained by reacting a polyol, a polyisocyanate, and a hydroxyl group-containing (meth)acrylate, the polyol having a branched structure, including a hydroxyl group at each branched chain terminal, and having a value, obtained by dividing the molecular weight of the polyol by the number of hydroxyl groups at the branched chain terminals, of 100-2,000;

(B) 30-70 wt% of a polymerizable monofunctional compound; and

(C) 0.01-10 wt% of a radical photoinitiator.

2 The composition according to claim 1, further comprising: (D) 3-20 wt% of a (meth)acrylate having two or more functional groups. 3 The composition according to claim 1 or 2, wherein at least part of the component (D) is a (meth)acrylate compound having three or more functional groups.

4 The composition according to any of claims 1 to 3, wherein the optical part is a

Fresnel lens sheet, lenticular lens sheet, or prism lens sheet. 5 Optical part obtained from the composition according to any one of claims 1-4.