TWI627191B - Resin composition for optical material, optical film and liquid crystal display device - Google Patents

Abstract

An object of the present invention is to provide a resin composition which is small in birefringence due to an external force and which can be applied to the production of an optical element, an optical film obtained by using the resin composition, and a liquid crystal display device using the same, wherein Providing a polymer (A) obtained by using (meth)acrylic acid or an alkyl (meth)acrylate, and having the following general formula (1) (In the formula, A ¹ and A ^{2 are each} independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms. R ¹ to R ^{4 are each} independently an alkyl group having 1 to 3 carbon atoms. A resin composition for an optical material of the compound (B) in which X ¹ and X ^{2 are each} independently a divalent linking group.

Description

Resin composition for optical material, optical film, and liquid crystal display device

The present invention relates to a resin composition which is small in variation in birefringence due to an external force, can be applied to the production of an optical element, and an optical film which can be obtained by using the resin composition, and a liquid crystal display device using the same.

Recently, as the display market has expanded, for example, there has been an increasing demand for images with higher definition, and optical materials that are not only transparent materials but also capable of imparting high optical characteristics are being sought.

Generally, a polymer material generates birefringence due to a difference in refractive index in a molecular main chain direction and a direction perpendicular thereto. It is necessary to strictly control the birefringence with the use. When used in a protective film for a liquid crystal polarizing plate, even if the total light transmittance is the same, a polymer material molded body having a small birefringence is required, and triethylene fluorene-based fibers are used. It is a representative material.

In the past, the size of the polymer optical material molded product required for the increase in the size of the liquid crystal display has increased in recent years. Therefore, in order to reduce the distribution of birefringence due to variations in external force, a double due to external force is being sought. A material with a small change in refraction.

It is possible to obtain a small change in birefringence due to external force The material of the product is a polymer optical material capable of obtaining a molded article having a small photoelastic coefficient, and among these materials, in particular, an acrylic resin is attracting attention as an inexpensive material. Specifically, a resin composition containing an acrylic resin and an aliphatic polyester resin as a plasticizer is known (for example, see Patent Document 1). However, even if the optical material disclosed in Patent Document 1 is used, it is difficult to obtain an optical film having a sufficiently small photoelastic coefficient.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] International Publication No. 2006/077776

An object of the present invention is to provide a resin composition which is small in birefringence due to an external force and which can be applied to the production of an optical element, an optical film which can be obtained by using the resin composition, and a liquid crystal display using the same Device.

As a result of intensive studies, the present inventors have found that a composition containing a compound containing an acrylic resin and a compound having a biphenyl skeleton and having a structure in which a terminal of the compound is terminated with a hydrocarbon group and an aryl group can be used. Further, an optical element having a small change in birefringence due to an external force is obtained; the resin composition is particularly suitable for producing an optical film; the optical film can be suitably used as an element for manufacturing a liquid crystal display device; and the present invention has been completed.

That is, the present invention provides a resin composition for an optical material, which comprises a polymer (A) which can be obtained by using (meth)acrylic acid or an alkyl (meth)acrylate, and which has the following formula ( 1) (In the formula, A ¹ and A ^{2 are each} independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms. R ¹ to R ^{4 are each} independently an alkyl group having 1 to 3 carbon atoms. The compound (B) represented by X ¹ and X ^{2 are each} independently a divalent linking group.

Moreover, the present invention provides an optical film comprising the resin composition for an optical material.

Furthermore, the present invention provides a liquid crystal display device comprising the optical film.

According to the present invention, an acrylic resin which is an inexpensive material can be used, and a resin composition which can be applied to the production of an optical element with a small change in birefringence due to an external force can be provided. By using this resin composition, an optical film having a small change in birefringence due to an external force can be easily obtained. Then, by using the optical film, it is possible to obtain a liquid crystal display device which is less likely to change the visual condition of the screen due to an external force.

[Formation of the Invention]

The polymer (A) used in the present invention can be obtained by using (meth)acrylic acid or an alkyl (meth)acrylate, and specifically, it can be (meth)acrylic acid or alkyl (meth)acrylate. The ester is an essential component and is obtained by polymerization using other polymerizable monomers as needed. Examples of the (meth)acrylic acid or the alkyl (meth)acrylate include acrylic acid; methacrylic acid; cyclohexyl methacrylate; t-butylcyclohexyl methacrylate; methyl methacrylate; An alkyl methacrylate; an alkyl acrylate such as methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate or 2-ethylhexyl acrylate.

Among the polymers (A) used in the present invention, in particular, a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and other monomers can obtain a film having good optical properties, and the economy is also Good and good.

Examples of the other monomer include (meth)acrylic acid esters other than (meth)acrylic acid or methyl methacrylate; aromatic vinyl compounds such as styrene, vinyltoluene, and α-methylstyrene; a cyanide vinyl group such as acrylonitrile or methacrylonitrile; a maleimide such as N-phenyl maleimide or N-cyclohexylmethyleneimine An unsaturated carboxylic acid anhydride such as maleic anhydride; an unsaturated acid such as maleic acid or the like.

A monomer such as an aromatic vinyl compound, a vinyl cyanide group, a maleimide group, an unsaturated carboxylic acid anhydride or an unsaturated acid as the other monomer, even if methacrylic acid is not used In the case of a methyl ester, it can also be used in a range which does not impair the effects of the present invention.

When a polymer as the polymer (A) is obtained by copolymerizing the aforementioned methyl methacrylate and other monomers, as an other monomer, an aromatic vinyl compound can obtain an optical film excellent in heat resistance and economy. Preferably, styrene and α-methylstyrene are particularly preferred. The amount of the aromatic vinyl compound to be used is preferably 1 to 50 parts by mass, more preferably 2 to 30 parts by mass, per 100 parts by mass of the methyl methacrylate.

Moreover, as the other monomer, an effect of obtaining an optical film having excellent heat resistance by using an unsaturated carboxylic acid anhydride can be expected. Among the unsaturated carboxylic acid anhydrides, maleic anhydride is particularly preferred. The amount of the unsaturated carboxylic acid anhydride to be used is preferably from 1 to 100 parts by mass, more preferably from 5 to 90 parts by mass, per 100 parts by mass of the methyl methacrylate.

The polymer (A) used in the present invention may be used alone (meth)acrylic acid or alkyl (meth)acrylate, or two or more kinds thereof may be used in combination. Further, the other monomers may be used singly or in combination of two or more.

The polymer (A) used in the present invention has a weight average molecular weight of 50,000 to 200,000, and is preferable because a molded article such as an optical film having strength can be obtained, and a resin composition having sufficient fluidity and good moldability is preferable. Good for 70,000~150,000.

Further, the polymer (A) used in the present invention preferably has a number average molecular weight of from 15,000 to 100,000, preferably from 20,000 to 50,000.

In the present invention, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values measured by GPC and converted to polystyrene. The measurement conditions of GPC are as follows.

[GPC measurement conditions]

Measuring device: "HLC-8220 GPC" manufactured by Tosoh Corporation

Pipe column: Guard column "HHR-H" (6.0mmI.D.×4cm) from Tosoh Corporation + "TSK-GEL GMHHR-N" manufactured by Tosoh Corporation (7.8mmI.D) .×30cm)+TSK-GEL GMHHR-N (7.8mmI.D.×30cm) manufactured by Tosoh Corporation + "TSK-GEL GMHHR-N" manufactured by Tosoh Corporation (7.8mmI.D.× 30cm) + "TSK-GEL GMHHR-N" manufactured by Tosoh Corporation (7.8mmI.D.×30cm)

Detector: ELSD ("ELSD2000" by Alltech)

Data Processing: "CPC-8020 Type II Data Analysis Version 4.30" by Tosoh Corporation

Measurement conditions: column temperature 40 ° C

Developing solvent Tetrahydrofuran (THF)

Flow rate 1.0ml/min

Sample: A product (5 μl) which was filtered with a 1.0% by mass of a tetrahydrofuran solution in terms of a resin solid content by a microfilter.

Standard sample: The following monodisperse polystyrene of a known molecular weight was used in accordance with the above-mentioned "GPC-8020 Type II Data Analysis Version 4.30" measurement operation manual.

(monodisperse polystyrene)

"A-500" made by Tosoh Corporation

"A-1000" made by Tosoh Corporation

"A-2500" made by Tosoh Corporation

"A-5000" made by Tosoh Corporation

"F-1" made by Tosoh Corporation

"F-2" made by Tosoh Corporation

Tosoh Corporation's "F-4"

"F-10" made by Tosoh Corporation

"F-20" made by Tosoh Corporation

Tosoh Corporation's "F-40"

"C-80" made by Tosoh Corporation

"C-128" made by Tosoh Corporation

"C-288" made by Tosoh Corporation

Tosoh Corporation's "F-550"

As a method of producing the polymer (A) used in the present invention, various polymerization methods such as casting polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, anionic polymerization, and the like can be used. Among the production methods, in particular, bulk polymerization and solution polymerization are preferred because a polymer having a small amount of fine foreign matter can be obtained. When solution polymerization is carried out, a solution in which a mixture of raw materials is dissolved in a solvent of an aromatic hydrocarbon such as toluene or ethylbenzene can be used. When the polymerization is carried out by bulk polymerization, the polymerization can be initiated by irradiation of free radicals and ionizing radiation generated by heating as usual.

As the initiator used in the above polymerization reaction, any of the initiators used in the radical polymerization can be usually used, for example, an azo compound such as azobisisobutyronitrile can be used; benzammonium peroxide, lauric peroxide An organic peroxide such as hydrazine or hexanobutylperoxy-2-ethyl hexanoate. When the polymerization is carried out, when the polymerization is carried out at a high temperature of 90 ° C or higher, since the solution polymerization is usually carried out, the 10-hour half-life temperature is 80 ° C. The peroxide which is soluble in the organic solvent to be used, the azobis initiator, and the like are preferable, and specific examples thereof include 1,1-bis(t-butylperoxy)-3,3. , 5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-bis(benzhydrylperoxy)hexane, 1,1-azobis (1 - cyclohexanecarbonitrile, 2-(aminomethyl sulfhydryl) isobutyronitrile, and the like. These initiators are used in the range of 0.005 to 5% by mass.

When the polymer (A) used in the present invention is polymerized, a molecular weight modifier may be used as needed. The molecular weight modifier may be any one used in usual radical polymerization, and examples thereof include thiol compounds such as butanol, octyl mercaptan, dodecyl mercaptan, and 2-ethylhexyl thioglycolate. Very good. These molecular weight modifiers can be added in a concentration range such that the degree of polymerization is controlled within the above range.

The compound (B) used in the present invention is, for example, the following formula (1) (In the formula, A ¹ and A ^{2 are each} independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms. R ¹ to R ^{4 are each} independently an alkyl group having 1 to 3 carbon atoms. X ¹ and X ^{2 are each} independently represented by a divalent linking group, and include a bisphenol skeleton. The effect of reducing the absolute value of the photoelastic coefficient of the acrylic resin can be expected by having a bisphenol skeleton. In addition, by terminating the terminal ends with the above A ¹ and A ² , a resin composition having good stability such as stability and stability can be obtained.

X ¹ and X ² in the compound (B) containing the bisphenol skeleton used in the present invention may be the same or different. Examples of the above X ¹ and X ² include an ester group, an ether group, a thioether group, an amine group, and an imido group. Among them, an ester group or an ether group is preferred from the viewpoint of compatibility with an acrylic resin.

Examples of the alkyl group having 1 to 8 carbon atoms as a specific example of the above A ¹ and A ² include a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a second butyl group, and the like. Tributyl, n-pentyl, isopentyl, third pentyl, cyclopentyl, n-hexyl, isohexyl, 2-hexyl, dimethylbutyl, ethylbutyl, cyclohexyl, heptyl, octyl Wait. As the aryl group having 6 to 18 carbon atoms, a phenyl group, a benzyl group, a tolyl group, a 2,4,6-trimethylphenyl group, a tert-butylphenyl group, a 2,4-di-third group can be exemplified. Phenylphenyl, 2,6-di-t-butylphenyl, naphthyl and the like. Among them, a phenyl group and a tolyl group are preferred from the viewpoint of a resin composition having good stability such as storage stability.

As a specific example of the compound (B) to be used in the present invention, for example, a compound represented by the following formula can be obtained by, for example, being able to easily obtain the effects of the present invention.

(In the formula, L ¹ and L ^{2 are each} independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms. R ¹ to R ^{4 are each} independently an alkyl group having 1 to 3 carbon atoms. )

The compound represented by the above formula (1-1) can be, for example, an epoxy compound having a bisphenol skeleton, a monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms, or a carbon number of 7 to 18 Obtained by the reaction of an aromatic monocarboxylic acid. In addition, the compound represented by the above formula (1-2) can be, for example, an epoxy compound having a bisphenol skeleton, and a monool having an alkyl group having 1 to 8 carbon atoms or an alkoxide derivative thereof. It is obtained by reacting an aromatic monool having 6 to 18 carbon atoms.

As the epoxy compound having a bisphenol skeleton, a diglycidyl ether type epoxy compound which can be obtained by a reaction of a bisphenol and epichlorohydrin can be exemplified. As a specific example of the epoxy compound, 3,3',5,5'-tetramethyl-4,4'-diglycidoxy bisphenol can be used (commercially available from Nippon Epoxy Resin Co., Ltd.) A bisphenol epoxy compound such as "jER YX-4000" (epoxy equivalent: 180 to 192).

Examples of the monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms include acetic acid, propionic acid, butyric acid, caproic acid, and octanoic acid. Examples of the aromatic monocarboxylic acid having 7 to 18 carbon atoms include benzoic acid, dimethylbenzoic acid, trimethylbenzoic acid, tetramethylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, and diastereomer. Propylbenzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, methoxybenzoic acid, ethoxybenzoic acid, propoxybenzoic acid, cyanobenzoic acid, fluorobenzoic acid, nitrobenzoic acid, 4-phenylbenzene Formic acid, 4-(3-methylphenyl)benzoic acid, 4-(4-methylphenyl)benzoic acid, 4-(3,5-dimethylphenyl)benzoic acid, 2-methyl-4 -Phenylbenzoic acid, 2,6-dimethyl-4-phenylbenzoic acid, 2,6-dimethyl-4-(3,5-dimethylphenyl)benzoic acid, naphthoic acid, nicotine Acid, furancarboxylic acid, 1-naphthoic acid, 2-naphthoic acid, and the like. The monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms and the aromatic monocarboxylic acid having 7 to 18 carbon atoms may be used singly or in combination of two or more kinds. Further, in the present invention, the number of carbon atoms of the "monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms" also includes the number of carbon atoms of the carbonyl group in the number. Further, the number of carbon atoms of the "aromatic monocarboxylic acid having 7 to 18 carbon atoms" is also included in the number of carbon atoms of the carbonyl group.

Examples of the monoalcohol having an alkyl group having 1 to 8 carbon atoms include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, second butanol, tert-butanol, and n-pentane. Alcohol, isoamyl alcohol, third pentanol, cyclopentanol, n-hexanol, isohexanol, cyclohexanol, heptanol, octanol, and the like. Examples of the aromatic monool having 6 to 18 carbon atoms include phenol, benzyl alcohol, methylphenol, 2,4,6-trimethylphenol, tert-butylphenol, and 2,4-di-3rd. Phenolic, 2,6-di-t-butylphenol, 1-naphthol, 2-naphthol, and the like.

As described above, the compound represented by the formula (1-1) can be borrowed It is obtained, for example, by reacting an epoxy compound having a bisphenol skeleton, a monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms or an aromatic monocarboxylic acid having 7 to 18 carbon atoms.

Further, the compound represented by the formula (1-2) can be, for example, an epoxy compound having a bisphenol skeleton, and a monool having an alkyl group having 1 to 8 carbon atoms or an aromatic having 6 to 18 carbon atoms. It is obtained by reacting a monoalcohol. The reaction temperature in the reaction of the epoxy compound with the monocarboxylic acid and the monoalcohol is preferably in the range of 80 to 130 ° C, preferably in the range of 100 ° C to 115 ° C. The reaction time is preferably in the range of 10 to 25 hours. Further, the ratio of the epoxy compound to the monocarboxylic acid and the monool is defined by the number of moles of the epoxy group of the epoxy compound, the molar number of the monocarboxylic acid, and the molar ratio of the monool ( The epoxy group molar number / (the molar number of the monocarboxylic acid or the molar number of the monool) is preferably in the range of 1/0.9 to 1.1.

In the reaction of the epoxy group of the epoxy compound with the carboxyl group of the monocarboxylic acid or the hydroxyl group of the monoalcohol, a catalyst may be used as needed. As the catalyst, a phosphine compound such as trimethylphosphine, triethylphosphine, tributylphosphine, trioctylphosphine or triphenylphosphine; 2-methylimidazole, 2-ethylimidazole, 2- Imidazole compound such as isopropyl imidazole, 2-ethyl-4-methylimidazole, 4-phenyl-2-methylimidazole; triethylamine, tributylamine, trihexylamine, triamylamine, triethanolamine , dimethylaminoethanol, triethylenediamine, dimethylaniline, dimethylbenzylamine, 2-(dimethylaminomethyl)phenol, 1,8-diaziridine (5,4,0) An amine compound such as undecene-7; a pyridine compound such as dimethylaminopyridine or the like. The catalyst is preferably used in an amount of 0.05 to 1 part by mass based on 100 parts by mass of the total of the epoxy compound and the aromatic monocarboxylic acid.

Among the compounds represented by the above formula (1-1) and the compound represented by the formula (1-2), in particular, since L ¹ and L ² are each a phenyl group or a tolyl group, compatibility with an acrylic resin is good. And good. Among them, particularly in the compound represented by the formula (1-1), it is preferred that L ¹ is a phenyl group or a tolyl group.

Further, in the compound represented by the formula (1-1) and the compound represented by the formula (1-2), R ¹ to R ⁴ are each a methyl group and become a phase with the polymer (A). Good solubility of the compound.

The property state of the compound (B) used in the present invention varies depending on factors such as composition, and is usually liquid, solid, paste or the like at normal temperature.

The content of the compound (B) in the resin composition for an optical material of the present invention depends on the photoelastic coefficient of the polymer (A) to be used, but from the viewpoint of being able to reduce the absolute value of the photoelastic coefficient of the resin composition, It is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of the polymer.

The optical film of the present invention is characterized by comprising the resin composition for an optical material of the present invention. The optical film of the present invention has a characteristic that the photoelastic coefficient is very small, and specifically, the absolute value of the photoelastic coefficient is 2.0 × 10 ^-12 /Pa or less, preferably 1.0 × 10 ^-12 /Pa or less. Therefore, the optical film of the present invention has a small photoelastic coefficient, and as a result, it is possible to provide a liquid crystal display device in which the change in birefringence due to an external force is small and it is difficult to change the visual condition of the screen due to an external force.

In the present invention, the photoelastic coefficient is measured by the method shown below.

<Method for Measuring Photoelastic Coefficient (C _R )>

An optical film obtained by stretching was used as an example of the optical film of the present invention, and the optical film was cut at a width of 15 mm in the extending direction to obtain a measurement sample. The measurement sample was fixed to a tensile clamp for photoelastic measurement (manufactured by Oji Scientific Instruments Co., Ltd.), and the load at the time of tensile measurement of the sample was changed from 127.3 g ‧ f to 727.3 g ‧ f per 100 g ‧ f The difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.) measured the change in the in-plane phase difference at 588 nm when each load was applied. The measurement was carried out in an environment of 23 ° C and a relative humidity of 55%.

The composition for an optical material of the present invention can be used for the production of various molded articles for optics. Among them, in particular, a film-form molded body (optical film) can be produced by using the composition for an optical material of the present invention. In the optical film, for example, an optical film which extends at least in the uniaxial direction and has an absolute value of the photoelastic coefficient of 2 (×10 ^-12 /Pa) or less can be applied to a phase difference of a retardation film or the like and requires stress. The use of the characteristics of the resulting birefringence change is small. The retardation film is preferably an optical film having an absolute photoelastic coefficient of 1 (×10 ^-12 /Pa) or less, and preferably has an absolute photoelastic coefficient of 0.5 (×10 ^-12 /Pa) or less. Optical film. The stretching ratio in the TD direction and the MD direction of the optical film is appropriately selected depending on the purpose, and an optical film having a small isotropic birefringence can be obtained by adjusting the amount of the compound (B) to a large birefringence. Phase difference film.

The polymer other than the polymer (A) can be mixed to the resin composition for an optical material of the present invention in a range not impairing the object of the present invention. As the polymer other than the above polymer (A), for example, Polyolefin such as polyethylene or polypropylene; styrene resin such as polystyrene or styrene acrylonitrile copolymer; polydecylamine, polysulfurized benzene resin, polyetheretherketone resin, polyester resin, polyfluorene, A thermoplastic resin such as polyphenylene ether, polyimide, polyether quinone, or polyacetal; and a thermosetting resin such as a phenol resin, a melamine resin, a polyoxyxylene resin, or an epoxy resin. These may be mixed in one type or in combination of two or more types.

Further, any additive can be blended according to various purposes within a range that does not significantly impair the effects of the present invention. The kind of the additive is not particularly limited as long as it is a blender generally used for a resin or a rubbery polymer. As the additive, a pigment such as an inorganic filler or iron oxide; a slip of stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, and ethyl bis-stearylamine can be exemplified. Release agent; softener/plasticizer for alkane-based processing oil, naphthenic processing oil, aromatic processing oil, alkane, organopolyoxyalkylene, mineral oil, etc.; hindered phenolic antioxidant, phosphorus heat Antioxidant such as stabilizer, lactone thermal stabilizer, vitamin E thermal stabilizer; light stabilizer for hindered amine light stabilizer, benzoate light stabilizer; benzophenone ultraviolet absorber ,three It is a UV absorber such as a UV absorber or a benzotriazole-based UV absorber; a flame retardant; an antistatic agent; a reinforcing agent for organic fibers, glass fibers, carbon fibers, metal whiskers, etc.; a coloring agent, other additives or the like Mixtures, etc.

The resin composition for an optical material of the present invention may contain the polymer (A) and the compound (B), and the production method thereof is not particularly limited. Specifically, for example, a single-axis extruder, a twin-screw extruder, a Bancher mixer, a Brabender, and various kneading machines can be used. The melt kneading machine or the like obtains the polymer (A) and the compound (B), and a method of melt-kneading the above-mentioned additives as needed.

The optical film of the present invention is characterized by containing the resin composition for an optical material of the present invention. In order to obtain the optical film of the present invention, a method such as extrusion molding, tape casting, or the like can be used. Specifically, for example, an optical film in an unstretched state can be extruded by using an extruder or the like which has a T-die, a circular die, or the like. When the optical film of the present invention is obtained by extrusion molding, the resin composition for an optical material of the present invention obtained by melt-kneading the polymer (A) or the compound (B) in advance may be used. The polymer (A) and the compound (B) are melt-kneaded at the time of extrusion molding and directly extruded. Further, the polymer (A) and the compound (B) can be dissolved in the solvent by using a solvent in which the polymer (A) and the compound (B) are dissolved, thereby obtaining a spinning solution (doping) Solution) An optical film of the present invention in an unstretched state is obtained by a solution casting method of tape casting.

Hereinafter, the solution casting method will be described in detail. The optical film obtained by the solution casting method exhibits substantially optical isotropic properties. The film exhibiting optical isotropy can be used for an optical material such as a liquid crystal display, and particularly, it is used for a protective film for a polarizing plate. Further, the film obtained by the above method is less likely to have unevenness on the surface and good surface smoothness.

The foregoing solution casting method generally comprises the first step of dissolving the aforementioned polymer (A) and the aforementioned compound (B) in an organic solvent and casting the obtained resin solution on a metal support; tree The second step of forming a thin film by distilling off and drying the organic solvent contained in the fat solution; and then removing the film formed on the metal support from the metal support and heating and drying the third step.

As the metal support used in the first step, a metal such as an endless belt or a barrel can be exemplified, and for example, a stainless steel can be used and the surface thereof can be mirror-finished.

When the resin solution is cast on the metal support, in order to prevent foreign matter from being mixed into the obtained film, it is preferred to use a resin solution filtered through a filter.

The drying method in the second step is not particularly limited, and for example, air having a temperature in the range of 30 to 50 ° C is blown onto the upper side and/or the lower side of the metal supporting body to allow the cast resin solution to be cast. A method of forming a film on the metal support by evaporating 50 to 80% by mass of the organic solvent.

Next, in the third step, the film formed in the second step is peeled off from the metal support, and is heated and dried at a temperature higher than the second step. As the heating and drying method, for example, a method of raising the temperature stepwise at a temperature of 100 to 160 ° C is preferable because a good dimensional stability can be obtained. By heating and drying under the above-described temperature conditions, the organic solvent remaining in the film after the second step can be almost completely removed.

In the first step to the third step, the organic solvent can also be recovered and reused.

An organic solvent which can be used when the polymer (A) and the compound (B) are mixed and dissolved in an organic solvent, The solvent is not particularly limited, and examples thereof include solvents such as chloroform, dichloromethane, and chlorinated methane.

The concentration of the polymer (A) in the resin solution is preferably 10 to 50% by mass, preferably 15 to 35% by mass.

The film thickness of the optical film of the present invention is preferably in the range of 20 to 120 μm, preferably in the range of 25 to 100 μm, and particularly preferably in the range of 25 to 80 μm.

In the present invention, it is possible to obtain, for example, an extended optical which is longitudinally uniaxially stretched in the mechanical traveling direction and transversely uniaxially extended in the direction perpendicular to the mechanical direction of the optical film obtained in the above-described method, as needed. film. Further, biaxial stretching can be obtained by a sequential biaxial stretching method in which a roll extension and a tenter is extended, a simultaneous biaxial stretching method by a tenter stretching, a biaxial stretching method by a tubular extension, or the like. Extended film. The stretching ratio is preferably 0.1% or more and 1000% or less in at least one direction, more preferably 0.2% or more and 600% or less, and particularly preferably 0.3% or more and 300% or less. By designing in this range, it is possible to obtain an extended optical film which is preferable from the viewpoints of birefringence, heat resistance and strength.

The optical film of the present invention can be applied as an optical material to a polarizing plate protective film used for a display such as a liquid crystal display device, a plasma display, an organic EL display, a field emission display, or a rear projection television, or a quarter wave. A phase difference film such as a sheet, a half wave plate, a viewing angle control film, a liquid crystal optical compensation film, or the like, and a front panel of a display. Further, in addition to the above, the resin composition for an optical material of the present invention can be used in the field of an optical communication system, an optical exchange system, and an optical measurement system. In waveguide paths, lenses, optical fibers, substrates for optical fibers, cladding materials, lenses for LEDs, lens covers, and the like.

[Examples]

Hereinafter, the present invention will be more specifically described based on the examples. Parts and % in the examples are based on mass unless otherwise specified.

Synthesis Example 1 [Synthesis of Compound (B)]

299 g of tetramethylbiphenol type epoxy resin (epoxy equivalent 187), 195 g of benzoic acid and 1 g of triphenylphosphine were placed in a 1 liter four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen introduction tube. The reaction was carried out at 115 ° C for 20 hours as a catalyst to obtain a compound (B1) represented by the above formula (1-1). The compound (B1) had an acid value of 0.7 and a hydroxyl group value of 178.

Synthesis Example 2 (ibid.)

299 g of tetramethylbiphenol type epoxy resin (epoxy 187), 195 g of phenol and 1 g of triphenylphosphine were placed in a 1 liter four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen introduction tube. The catalyst was reacted at 115 ° C for 20 hours to obtain a compound (B2) represented by the above formula (1-2). The compound (B2) had an acid value of 0.7 and a hydroxyl group value of 178.

Synthesis Example 3 (ibid.)

In a 1 liter four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen introduction tube, 299 g of tetramethylbiphenol type epoxy resin (epoxy 187), 217 g of p-toluic acid, and 1 g of triphenyl group were placed. The phosphine was used as a catalyst and reacted at 115 ° C for 24 hours to obtain a compound (B3) represented by the above formula (1-1). The compound (B3) had an acid value of 0.2 and a hydroxyl group value of 171.

Synthesis Example 4 [Comparison of Comparative Control Polyester Resin (b')]

1 liter of internal volume with thermometer, stirrer and reflux condenser Into the four-necked flask, 341 g of ethylene glycol and 659 g of adipic acid were added. Next, tetraisopropyl titanate was added in an amount of 30 ppm based on the total amount of ethylene glycol and adipic acid, and the mixture was heated to 220 ° C while stirring under a nitrogen stream, and the reaction was carried out for 24 hours to obtain a number average molecular weight of 1,100 and an acid value of A comparative polyester resin (b'1) of 0.19 and a hydroxyl group of 112 was used.

Synthesis Example 5 (ibid.)

A number average molecular weight of 11,000 was obtained in the same manner as in Synthesis Example 3, except that 770 g of succinic acid, 595 g of 1,2-propanediol, and 60 ppm of tetraisopropyl titanate were used with respect to the total amount of succinic acid and 1,2-propanediol. A comparative control polyester resin (b'2) having an acid value of 0.7 and a hydroxyl value of 8.

Example 1 (Preparation of resin composition for optical materials)

100 parts of acrylic resin (A1) [methyl methacrylate / maleic anhydride / styrene = 50 / 40 / 10 (mole ratio) copolymer, number average molecular weight 27,800], 5 parts of polyester resin ( B1) is added to a mixed solvent containing 270 parts of methyl chloride and 30 parts of methanol and dissolved to obtain a resin composition (spinning solution) for an optical material of the present invention.

The spinning solution was cast on a glass plate to have a thickness of 0.5 mm, dried at room temperature for 16 hours, dried at 50 ° C for 30 minutes, and further dried at 100 ° C for 60 minutes to obtain an unextended film having a thickness of 100 μm. film.

The obtained unstretched film is uniaxially stretched at a glass transition temperature (Tg) of the resin composition (1) for an optical material determined by a differential scanning calorimeter (DSC) at a temperature of 5 ° C (stretching ratio) 2 times, elongation speed 100% / min), making stretch film (1). Among them, the measurement of the Tg using a differential scanning calorimeter (DSC) was carried out in accordance with the following conditions.

<Measurement conditions of glass transition temperature Tg>

A differential scanning calorimeter DSC822e (manufactured by METTLER TOLEDO Co., Ltd.) was used. Specifically, 5 mg of the resin composition was placed in a light aluminum pan, and the temperature was raised from 25 ° C to 150 ° C (first round) at 10 ° C per minute under a nitrogen atmosphere, and once quenched to 0 ° C, again at 10 ° C per minute. The temperature was raised from 0 ° C to 150 ° C (second round). The glass transition temperature Tg is determined from the DSC curve obtained in the second round by the midpoint method.

The optical properties of the obtained stretched film (1), specifically, in-plane birefringence (Δn), out-of-plane birefringence (ΔP), photoelastic coefficient (C _R ), and fog were evaluated according to the method shown below. degree. The evaluation results are shown in Table 1.

<Evaluation method of in-plane birefringence (Δn) and out-of-plane birefringence (ΔP)>

Using the phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.), in-plane birefringence (Δn) and out-of-plane birefringence (ΔP) were calculated according to the following formula except that the refractive index at 588 nm was obtained.

In-plane birefringence (Δn)=(n _x )-(n _y )

In-plane birefringence (ΔP)=[(n _x )+(n _y )]/2-(n _z )

[(n _x ): refractive index in the extending direction, (n _y ): refractive index in the direction perpendicular to the extending direction, (n _z ): refractive index in the thickness direction of the film]

Further, the measurement was carried out in an environment of 23 ° C and 55% relative humidity.

<Evaluation method of photoelastic coefficient (C _R )>

The stretched film is fixed to a tensile clamp for photoelastic measurement in a stretch film cut at a width of 15 mm in parallel with the extending direction (Prince Measurement Machine) In the in-plane phase difference (Re), the phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.) was used to measure the in-plane phase difference of 588 nm from the change load of 127.3 g ‧ f to 727.3 g ‧ f per 100 g ‧ )The change. The measurement was carried out in an environment of 23 ° C and 55% relative humidity. The in-plane phase difference (Re) is calculated according to the following formula.

Re=(n _x -n _y )×d

[(n _x ): refractive index in the extending direction, (n _y ): refractive index in the direction perpendicular to the extending direction, d: film thickness (μm)]

For the measured values, the stress (σ) is plotted on the horizontal axis and the in-plane phase difference (Re) is plotted on the vertical axis, and the photoelastic coefficient (C _R ) is calculated from the linear slope of the linear range by the least square approximation. The smaller the absolute value of the slope, the closer the photoelastic coefficient is to 0, indicating that the optical film due to the external force has a smaller change in birefringence.

<Evaluation of haze>

The NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd. was used in accordance with JIS K 7136.

Examples 2 to 8 and Comparative Examples 1 to 6

Optical films (2) to (8) and comparative control were obtained in the same manner as in Example 1 except that the resin composition (spinning liquid) for optical materials was obtained under the blending and stretching conditions shown in Tables 1 to 2. Extend the film (1') to (5'). The same evaluation as in Example 1 was carried out, and the results are shown in Tables 1 to 2.

Notes to Table 1

Not measurable: The haze of the film is large and the optical properties cannot be measured.

Notes to Table 2

Acrylic film (A2): copolymer of methyl methacrylate/α-methylstyrene = 93/7 (mole ratio), number average molecular weight 30,000

Not measurable: The haze of the film is too large to measure the optical properties.

The optical film obtained by using the optical resin composition of the present invention is a film having a small optical elastic modulus and a small change in birefringence due to an external force. On the other hand, the optical film of the comparative example has a large absolute value of the optical elastic coefficient and a large change in birefringence due to an external force.

Claims (8)

A resin composition for an optical material, which comprises a polymer (A) obtained by using (meth)acrylic acid or an alkyl (meth)acrylate, and a compound represented by the following formula (1) ( B), In the formula, A ¹ and A ^{2 are each} independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms; and R ¹ to R ^{4 are each} independently an alkyl group having 1 to 3 carbon atoms; ¹ and X ^{2 are each} independently a divalent linking group, and the content of the compound (B) is 1 to 10 parts by mass based on 100 parts by mass of the polymer (A). The resin composition for an optical material according to claim 1, wherein the compound (B) is represented by the following formula (1-1) or formula (1-2), In the formula, L ¹ and L ^{2 are each} independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms; and R ¹ to R ^{4 are each} independently an alkyl group having 1 to 3 carbon atoms. The resin composition for an optical material according to claim 2, wherein the L ¹ and L ² are each a phenyl group or a tolyl group. The resin composition for an optical material according to claim 3, wherein the R ¹ to R ⁴ are each a methyl group. The resin composition for an optical material according to claim 1, wherein the polymer (A) is obtained by using methyl methacrylate. An optical film comprising the resin composition for an optical material according to any one of claims 1 to 5. The optical film of claim 6, which is for polarizing plate protection. A liquid crystal display device having the optical film of claim 6 or 7.