WO2015046009A1 - Resin composition for optical materials, optical film and liquid crystal display device - Google Patents

Abstract

The present invention provides a resin composition for optical materials, which contains (A) a polymer obtained using a (meth)acrylic acid or a (meth)acrylic acid alkyl ester and (B) a compound represented by general formula (1), for the purpose of providing: a resin composition that is small in birefringence change by an external force and is suitable for use in the production of an optical member; an optical film which is obtained using this resin composition; and a liquid crystal display device which uses this optical film. (In the formula, each of A¹ and A² independently represents an alkyl group having 1-8 carbon atoms or an aryl group having 6-18 carbon atoms; each of R¹-R⁴ independently represents an alkyl group having 1-3 carbon atoms; and each of X¹ and X² independently represents 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 that is small in change of birefringence due to an external force and can be suitably used for manufacturing an optical member, an optical film obtained using the resin composition, and a liquid crystal display device using the same.

Recently, for example, with the expansion of the display market, there has been a growing demand for clearer images, and there is a demand for optical materials with higher optical properties than simple transparent materials.

Generally, a polymer generates birefringence because its refractive index is different between the molecular main chain direction and the direction perpendicular thereto. Depending on the application, it is required to strictly control this birefringence. In the case of a protective film used for a polarizing plate of a liquid crystal, a polymer material having a smaller birefringence even if the total light transmittance is the same. A molded body is required, and triacetyl cellulose is used as a typical material.

Under these circumstances, in recent years, as the liquid crystal display becomes larger and the polymer optical material molding required for it becomes larger, the birefringence change due to the external force is reduced in order to reduce the birefringence distribution caused by the bias of the external force. There is a need for materials with a small size.

A material from which a molded product with a small change in birefringence due to external force can be obtained, that is, a polymer optical material from which a molded product with a small photoelastic coefficient can be obtained. Among these materials, an acrylic resin is used as an inexpensive material. Attention has been paid. Specifically, a resin composition containing an acrylic resin and an aliphatic polyester resin as a plasticizer is known (see, for example, 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.

International Publication No. 2006/077776 Pamphlet

The problems to be solved by the present invention are a resin composition that can be suitably used for the production of an optical member with a small change in birefringence due to an external force, an optical film obtained using the resin composition, and the same. It is to provide a liquid crystal display device.

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

That is, the present invention relates to a polymer (A) obtained by using (meth) acrylic acid or (meth) acrylic acid alkyl ester, and the following general formula (1):

(Wherein 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 8 carbon atoms) And X ¹ and X ² are each independently a divalent linking group.)
The resin composition for optical materials characterized by containing the compound (B) represented by these is provided.

The present invention also provides an optical film comprising the resin composition for optical materials.

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

According to the present invention, it is possible to provide a resin composition that uses an acrylic resin that is an inexpensive material and has a small change in birefringence due to an external force and can be suitably used for manufacturing an optical member. By using this resin composition, an optical film having a small change in birefringence due to an external force can be easily obtained. By using this optical film, it is possible to obtain a liquid crystal display device in which the appearance of the screen is hardly changed by an external force.

The polymer (A) used in the present invention is obtained using (meth) acrylic acid or (meth) acrylic acid alkyl ester. Specifically, (meth) acrylic acid or (meth) acrylic acid alkyl ester is essential. As required, it can be obtained by polymerization in combination with other polymerizable monomers. Examples of the (meth) acrylic acid or the (meth) acrylic acid alkyl ester include, for example, acrylic acid; methacrylic acid: methacrylic acid alkyl ester such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, methyl methacrylate; methyl acrylate, Examples thereof include alkyl acrylates such as ethyl acrylate, butyl acrylate, isopropyl acrylate and 2-ethylhexyl acrylate.

Among the polymers (A) used in the present invention, a film in which a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and other monomers is excellent in optical properties can be obtained, and economically. Is also preferable because of its superiority.

Examples of the other monomer include (meth) acrylic acid or (meth) acrylic acid esters other than methyl methacrylate; aromatic vinyl compounds such as styrene, vinyltoluene and α-methylstyrene; acrylonitrile, methacrylic acid Examples thereof include vinyl cyanides such as nitrile; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; unsaturated acids such as maleic acid and the like.

Monomers such as aromatic vinyl compounds, vinyl cyanides, maleimides, unsaturated carboxylic acid anhydrides and unsaturated acids exemplified as the other monomers may be used even when methyl methacrylate is not used. It can be used as long as the effects of the present invention are not impaired.

In the case of obtaining a polymer to be used as the polymer (A) by copolymerizing the methyl methacrylate with another monomer, aromatic vinyl compounds are excellent in heat resistance and economy as the other monomer. From the viewpoint of obtaining an optical film, styrene and α-methylstyrene are more preferable. Here, the amount of the aromatic vinyl compound used is preferably 1 to 50 parts by mass and more preferably 2 to 30 parts by mass with respect to 100 parts by mass of methyl methacrylate.

In addition, as the other monomer, an effect of obtaining an optical film having excellent heat resistance can be expected by using unsaturated carboxylic acid anhydrides. Of the unsaturated carboxylic acid anhydrides, maleic anhydride is preferred. Here, the amount of the unsaturated carboxylic acid anhydride to be used is preferably 1 to 100 parts by mass and more preferably 5 to 90 parts by mass with respect to 100 parts by mass of methyl methacrylate.

For the polymer (A) used in the present invention, (meth) acrylic acid or (meth) acrylic acid alkyl ester may be used alone, or two or more kinds may be used in combination. The other monomers may be used alone 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, which can provide a molded product such as a strong optical film, has sufficient fluidity, and has good moldability. It is preferable because an excellent resin composition can be obtained, and more preferably 70,000 to 150,000.

In addition, the number average molecular weight of the polymer (A) used in the present invention is preferably 15,000 to 100,000, and more preferably 20,000 to 50,000.

Here, in the present invention, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values converted to polystyrene based on GPC measurement. The measurement conditions for GPC are as follows.

[GPC measurement conditions]
Measuring device: “HLC-8220 GPC” manufactured by Tosoh Corporation
Column: Guard column “HHR-H” (6.0 mm ID × 4 cm) manufactured by Tosoh Corporation + “TSK-GEL GMHHR-N” (7.8 mm ID × 30 cm) manufactured by Tosoh Corporation + Tosoh Corporation “TSK-GEL GMHHR-N” (7.8 mm ID × 30 cm) + Tosoh Corporation “TSK-GEL GMHHR-N” (7.8 mm ID × 30 cm) + Tosoh Corporation “TSK- GEL GMHHR-N "(7.8 mm ID x 30 cm)
Detector: ELSD ("ELSD2000" manufactured by Oltec)
Data processing: “GPC-8020 Model II data analysis version 4.30” manufactured by Tosoh Corporation
Measurement conditions: Column temperature 40 ° C
Developing solvent Tetrahydrofuran (THF)
Flow rate: 1.0 ml / min Sample: A 1.0% by mass tetrahydrofuran solution in terms of resin solid content filtered through a microfilter (5 μl).
Standard sample: The following monodisperse polystyrene having a known molecular weight was used in accordance with the measurement manual of “GPC-8020 Model II Data Analysis Version 4.30”.

(Monodispersed polystyrene)
“A-500” manufactured by Tosoh Corporation
“A-1000” manufactured by Tosoh Corporation
“A-2500” manufactured by Tosoh Corporation
"A-5000" manufactured by Tosoh Corporation
“F-1” manufactured by Tosoh Corporation
“F-2” manufactured by Tosoh Corporation
“F-4” manufactured by Tosoh Corporation
“F-10” manufactured by Tosoh Corporation
“F-20” manufactured by Tosoh Corporation
“F-40” manufactured by Tosoh Corporation
“F-80” manufactured by Tosoh Corporation
“F-128” manufactured by Tosoh Corporation
“F-288” manufactured by Tosoh Corporation
“F-550” manufactured by Tosoh Corporation

As a method for producing the polymer (A) used in the present invention, for example, various polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization and anionic polymerization can be used. Among the production methods, bulk polymerization and solution polymerization are preferable because a polymer with a small amount of minute foreign matters can be obtained. When solution polymerization is performed, a solution prepared by dissolving a mixture of raw materials in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. In the case of polymerization by bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation as is usually done.

As the initiator used in the polymerization reaction, any initiator generally used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile; benzoyl peroxide, lauroyl peroxide, t-butyl An organic peroxide such as peroxy-2-ethylhexanoate is used. When the polymerization is carried out at a high temperature of 90 ° C. or higher, solution polymerization is generally used, so that the 10-hour half-life temperature is 80 ° C. or higher and the peroxide is soluble in the organic solvent used. And azobis initiators are preferred. Specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di ( Benzoylperoxy) hexane, 1,1-azobis (1-cyclohexanecarbonitrile), 2- (carbamoylazo) isobutyronitrile and the like can be mentioned. These initiators are used in the range of 0.005 to 5% by mass.

When polymerizing the polymer (A) used in the present invention, a molecular weight modifier may be used as necessary. As the molecular weight regulator, any one used in general radical polymerization is used, and for example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate are particularly preferable. These molecular weight regulators are 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 represented by the following general formula (1)

(Wherein 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 8 carbon atoms) And X ¹ and X ² are each independently a divalent linking group.)
As shown, it contains a biphenol skeleton. By having a biphenyl skeleton, the effect of reducing the absolute value of the photoelastic coefficient of the acrylic resin can be expected. Further, since the terminal is sealed with the A ¹ and A ^2, an excellent resin composition stability such as storage stability.

X ¹ and X ² in the compound (B) used in the present invention (including the biphenol skeleton) may be the same or different. Examples of X ¹ and X ² include an ester group, an ether group, a thioether group, an amino group, and an imino group. Among these, an ester group or an ether group is preferable because of compatibility with an acrylic resin.

Specific examples of A ¹ and A ² include alkyl groups having 1 to 8 carbon atoms such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl. Group, t-butyl group, n-pentyl group, isopentyl group, t-pentyl group, cyclopentyl group, n-hexyl group, isohexyl group, 2-hexyl group, dimethylbutyl group, ethylbutyl group, cyclohexyl group, heptyl group, octyl Groups and the like. Examples of the aryl group having 6 to 18 carbon atoms include phenyl group, benzyl group, tolyl group, 2,4,6-trimethylphenyl group, tert-butylphenyl, 2,4-ditertiarybutylphenyl group, 2, Examples thereof include 6-ditertiary butylphenyl group and naphthyl group. Especially, since it becomes a resin composition excellent in stability, such as storage stability, a phenyl group and a tolyl group are preferable.

Specific examples of the compound (B) used in the present invention are preferably exemplified by, for example, compounds represented by the following general formula since the effects of the present invention can be obtained and obtained easily.

(Wherein 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 8 carbon atoms) 3 alkyl groups.)

The compound represented by the general formula (1-1) includes, for example, an epoxy compound having a biphenyl skeleton, a monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms, or an aromatic having 7 to 18 carbon atoms. It can be obtained by reacting with a monocarboxylic acid. The compound represented by the general formula (1-2) includes, for example, an epoxy compound having a biphenyl skeleton, a monoalcohol having an alkyl group having 1 to 8 carbon atoms, or an alkoxide derivative thereof, and 6 to 6 carbon atoms. It can be obtained by reacting with 18 aromatic monoalcohols.

Examples of the epoxy compound having a biphenyl skeleton include a diglycidyl ether type epoxy compound obtained by a reaction between biphenols and epichlorohydrin. As a specific example of this epoxy compound, 3,3 ′, 5,5′-tetramethyl-4,4′-diglycidyloxybiphenyl (commercially available product “jER YX-4000” manufactured by Japan Epoxy Resin Co., Ltd.) Biphenol type epoxy compounds such as epoxy equivalent of 180 to 192)) can be used.

Examples of the monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms include acetic acid, propionic acid, butanoic acid, hexanoic acid, octanoic acid and the like. 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, cumic acid, o-toluic acid, m-toluic acid, p-toluic acid, anisic acid, ethoxybenzoic acid, propoxybenzoic acid, cyanobenzoic acid, fluorobenzoic acid, nitrobenzoic acid, 4-phenylbenzoic 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, nicotinic acid, furoic acid, 1-naphthalenecarboxylic acid, 2-naphthalene Bonn 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 can be used alone or in combination of two or more. In the present invention, the number of carbon atoms of the “monocarboxylic acid having an alkyl group having 2 to 8 carbon atoms” includes the number of carbon atoms of the carbonyl group. The number of carbon atoms of the carbonyl group is also included in the number of carbon atoms of the “aromatic monocarboxylic acid having 7 to 18 carbon atoms”.

Examples of the monoalcohol having an alkyl group having 1 to 8 carbon atoms include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutyl alcohol, sec-butyl alcohol, t-butyl alcohol, and n-pentanol. , Isopentyl alcohol, t-pentyl alcohol, cyclopentanol, n-hexanol, isohexanol, cyclohesanol, heptanol, octanol and the like. Examples of the aromatic monoalcohol having 6 to 18 carbon atoms include phenol, benzyl alcohol, methylphenol, 2,4,6-trimethylphenol, tert-butylphenol, 2,4-ditertiary butylphenol, 2,6- Examples include ditertiary butylphenol, 1-naphthol, and 2-naphthol.

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

In addition, the compound represented by the general formula (1-2) includes, for example, an epoxy compound having a biphenyl skeleton, a monoalcohol having an alkyl group having 1 to 8 carbon atoms, or an aromatic monovalent having 6 to 18 carbon atoms. It can be obtained by reacting with alcohol. The reaction temperature for reacting the epoxy compound with the monocarboxylic acid or the monoalcohol is preferably in the range of 80 to 130 ° C, more preferably in the range of 100 to 115 ° C. The reaction time is preferably in the range of 10 to 25 hours. The charging ratio between the epoxy compound and the monocarboxylic acid or monoalcohol is the ratio of the number of moles of epoxy groups in the epoxy compound to the number of moles of monocarboxylic acids or moles of monoalcohol (number of moles of epoxy groups). ) / (Number of moles of monocarboxylic acid or number of moles of monoalcohol) 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 necessary. Examples of the catalyst include phosphine compounds such as trimethylphosphine, triethylphosphine, tributylphosphine, trioctylphosphine, and triphenylphosphine; 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-ethyl-4-methyl Imidazole compounds such as imidazole and 4-phenyl-2-methylimidazole; triethylamine, tributylamine, trihexylamine, triamylamine, triethanolamine, dimethylaminoethanol, tritylenediamine, dimethylphenylamine, dimethylbenzylamine, 2 -(Dimethylaminomethyl) phenol, amine compounds such as 1,8-diazabicyclo (5,4,0) undecene-7; Such as emission compounds. These catalysts are preferably used in an amount of 0.05 to 1 part by mass with respect to 100 parts by mass in total of the epoxy compound and the aromatic monocarboxylic acid.

Among the compounds represented by the general formula (1-1) and the compounds represented by the general formula (1-2), those in which L ¹ and L ² are each a phenyl group or a tolyl group are compatible with an acrylic resin. Is preferable because it is good. Of these, compounds represented by general formula (1-1) in which L ¹ is a phenyl group or a tolyl group are more preferable.

Further, in the compound represented by the general formula (1-1) and the compound represented by the general formula (1-2), R ¹ to R ⁴ each have a methyl group compatible with the polymer (A). It is preferable because it becomes a compound excellent in.

The properties of the compound (B) used in the present invention vary depending on factors such as composition, but are usually liquid, solid, paste, etc. at room temperature.

The content of the compound (B) in the resin composition for optical materials of the present invention depends on the photoelastic coefficient of the polymer (A) used, but the absolute value of the photoelastic coefficient of the resin composition can be reduced. The amount is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass with respect to 100 parts by mass of the polymer.

The optical film of the present invention contains the resin composition for optical materials of the present invention. The optical film of the present invention has a characteristic that the photoelastic coefficient is extremely small. Specifically, the absolute value of the photoelastic coefficient is 2.0 × 10 ⁻¹² / Pa or less, more preferably 1.0 × 10 ^−12. / Pa or less. As described above, the optical film of the present invention has a small photoelastic coefficient. As a result, a change in birefringence due to an external force is small, and a liquid crystal display device in which the appearance of the screen is hardly changed by the external force can be provided.

In the present invention, the photoelastic coefficient was measured by the following method.
<Measuring method of photoelastic coefficient ( _CR )>
An optical film obtained by stretching is used as an example of the optical film of the present invention, and this optical film is cut out in a stretching direction with a width of 15 mm to obtain a measurement sample. This measurement sample is fixed to a photoelasticity measurement tension jig (manufactured by Oji Scientific Instruments Co., Ltd.), and the weight at which the measurement sample is pulled every 100 g · f from 127.3 g · f to 727.3 g · f is changed. The in-plane phase difference change at 588 nm when each weight is applied is measured by a phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments). Measurement is performed in an atmosphere of 23 ° C. and 55% relative humidity.

By using the composition for optical materials of the present invention, it can be used for production of various optical molded articles. Especially, the composition for optical materials of this invention can be used for manufacturing a film-form molded object (optical film). In the optical film, for example, an optical film that is stretched at least in a uniaxial direction and has an absolute value of a photoelastic coefficient of 2 (× 10 ⁻¹² / Pa) or less requires a phase difference such as a phase difference film. Therefore, it can be suitably used for applications that require a small change in birefringence due to the above. The retardation film is preferably an optical film having an absolute value of photoelastic coefficient of 1 (× 10 ⁻¹² / Pa) or less, and an absolute value of photoelastic coefficient of 0.5 (× 10 ⁻¹² / Pa) or less. An optical film is more preferable. The stretching ratio in the TD direction and the MD direction of such an optical film is appropriately selected depending on the purpose, and by adjusting the amount of the compound (B), birefringence from an optically isotropic optical film having a small birefringence. Large retardation film can be obtained.

In the resin composition for an optical material of the present invention, a polymer other than the polymer (A) can be mixed as long as the object of the present invention is not impaired. Examples of polymers other than the polymer (A) include polyolefins such as polyethylene and polypropylene; styrene resins such as polystyrene and styrene acrylonitrile copolymers; polyamides, polyphenylene sulfide resins, polyether ether ketone resins, polyester resins, And thermoplastic resins such as polysulfone, polyphenylene oxide, polyimide, polyetherimide, and polyacetal; and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin. These may mix 1 type and may mix 2 or more types.

Furthermore, any additive can be blended according to various purposes within a range that does not significantly impair the effects of the present invention. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers. Examples of additives include pigments such as inorganic fillers and iron oxides; lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, and ethylene bisstearamide; mold release agents; paraffinic processes Softeners and plasticizers such as oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane, mineral oil; hindered phenol antioxidant, phosphorus heat stabilizer, lactone heat stabilizer, vitamin Antioxidants such as E-based heat stabilizers; Light stabilizers such as hindered amine light stabilizers and benzoate light stabilizers; UV absorption such as benzophenone UV absorbers, triazine UV absorbers, and benzotriazole UV absorbers Agent; flame retardant; antistatic agent; organic fiber, glass fiber, carbon fiber, metal Reinforcing agents such as Isuka; coloring agents, other additives, or mixtures thereof.

The resin composition for an optical material of the present invention may contain the polymer (A) and the compound (B), and the production method is not particularly limited. Specifically, for example, the polymer (A) and the compound (B) and, if necessary, the above additives are melt kneaded in a single screw extruder, twin screw extruder, Banbury mixer, Brabender, various kneaders, etc. It can be obtained by a melt kneading method using a machine.

The optical film of the present invention contains the resin composition for optical materials of the present invention. In order to obtain the optical film of the present invention, for example, techniques such as extrusion molding and cast molding are used. Specifically, for example, an unstretched optical film can be extruded using an extruder equipped with 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 optical materials of the present invention obtained by melting and kneading the polymer (A) and the compound (B) in advance can be used. It is also possible to melt and knead the polymer (A) and the compound (B) at the time of molding and to perform extrusion molding as it is. In addition, using a solvent that dissolves the polymer (A) and the compound (B) component, the polymer (A) and the compound (B) are dissolved in the solvent to obtain a so-called dope solution. The optical film of the present invention in an unstretched state can also be obtained by a solution casting method (solvent casting method) in which casting is performed.

Hereinafter, the solution casting method will be described in detail. The optical film obtained by the solution casting method substantially exhibits optical isotropy. The film showing optical isotropy can be used for an optical material such as a liquid crystal display, and is particularly useful as a protective film for a polarizing plate. Moreover, the film obtained by the said method cannot form an unevenness | corrugation on the surface, and is excellent in surface smoothness.

The solution casting method generally includes a first step of dissolving the polymer (A) and the compound (B) in an organic solvent and casting the obtained resin solution on a metal support, The second step of distilling off the organic solvent contained in the stretched resin solution and drying to form a film, followed by peeling the film formed on the metal support from the metal support and drying by heating. It consists of 3 steps.

Examples of the metal support used in the first step include endless belt-shaped or drum-shaped metal supports, for example, stainless steel with a mirror-finished surface can be used. .

When casting the resin solution on the metal support, it is preferable to use a resin solution filtered with a filter in order to prevent foreign matters from entering the film obtained.

The drying method in the second step is not particularly limited. For example, it is included in the cast resin solution by applying air in a temperature range of 30 to 50 ° C. to the upper surface and / or the lower surface of the metal support. Examples thereof include a method of evaporating 50 to 80% by mass of an organic solvent to form a film on the metal support.

Next, the third step is a step in which the film formed in the second step is peeled off from the metal support and is heated and dried under a temperature condition higher than that in the second step. As the heat drying method, for example, a method in which the temperature is raised stepwise under a temperature condition of 100 to 160 ° C. is preferable because good dimensional stability can be obtained. The organic solvent remaining in the film after the second step can be almost completely removed by heating and drying under the temperature condition.

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

The organic solvent that can be used when the polymer (A) and the compound (B) are mixed and dissolved in an organic solvent is not particularly limited as long as they can be dissolved, and examples thereof include chloroform and methylene dichloride. And a solvent such as methylene chloride.

The concentration of the polymer (A) in the resin solution is preferably 10 to 50% by mass, more 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, more preferably in the range of 25 to 100 μm, and particularly preferably in the range of 25 to 80 μm.

In the present invention, for example, the unstretched optical film obtained by the above-described method is stretched by uniaxially stretching in the mechanical flow direction and transversely uniaxially stretching in the direction orthogonal to the mechanical flow direction, as necessary. The obtained optical film can be obtained. Moreover, the stretched film biaxially stretched can be obtained by stretching by a sequential biaxial stretching method of roll stretching and tenter stretching, a simultaneous biaxial stretching method by tenter stretching, a biaxial stretching method by tubular stretching, or the like. The draw 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 more preferably 0.3% or more and 300% or less. Especially preferred. By designing in this range, a stretched optical film preferable in terms of birefringence, heat resistance and strength can be obtained.

The optical film according to the present invention includes, as an optical material, 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, a rear projection television, a quarter wavelength plate, and a half. It can be suitably used for a retardation film such as a wave plate, a viewing angle control film, a liquid crystal optical compensation film, a display front plate and the like. In addition, the resin composition for optical materials of the present invention is also used in the fields of optical communication systems, optical switching systems, and optical measurement systems, such as waveguides, lenses, optical fibers, optical fiber substrates, coating materials, and LED lenses. It can also be used for lens covers and the like.

Hereinafter, the present invention will be described more specifically based on examples. Unless otherwise indicated, parts and% in the examples are based on mass.

Synthesis Example 1 [Synthesis of Compound (B)]
Add 299 g of tetramethylbiphenol type epoxy resin (epoxy equivalent 187), 195 g of benzoic acid and 1 g of triphenylphosphine as a catalyst to a 1 liter four-necked flask equipped with a thermometer, stirrer, reflux condenser and nitrogen inlet tube. The mixture was reacted at 115 ° C. for 20 hours to obtain the compound (B1) represented by the general formula (1-1). The acid value of the compound (B1) was 0.7, and the hydroxyl value was 178.

Synthesis example 2 (same as above)
To a 1 liter four-necked flask equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet tube was added 299 g of tetramethylbiphenol type epoxy resin (epoxy equivalent 187), 195 g of phenol and 1 g of triphenylphosphine as a catalyst, By reacting at 115 ° C. for 20 hours, the compound (B2) represented by the general formula (1-2) was obtained. The acid value of the compound (B2) was 0.7, and the hydroxyl value was 178.

Synthesis example 3 (same as above)
To a 1 liter four-necked flask equipped with a thermometer, stirrer, reflux condenser and nitrogen inlet tube was added 299 g of tetramethylbiphenol type epoxy resin (epoxy equivalent 187), 217 g of paratoluic acid and 1 g of triphenylphosphine as a catalyst. And a reaction at 115 ° C. for 24 hours to obtain a compound (B3) represented by the general formula (1-1). The acid value of the compound (B3) was 0.2, and the hydroxyl value was 171.

Synthesis Example 4 [Synthesis of polyester resin for comparison (b ′)]
A four-necked flask having an internal volume of 1 liter equipped with a thermometer, a stirrer and a reflux condenser was charged with 341 g of ethylene glycol and 659 g of adipic acid. Furthermore, tetraisopropyl titanate was added at 30 ppm with respect to the total amount of ethylene glycol and adipic acid, the temperature was raised to 220 ° C. with stirring under a nitrogen stream, and the reaction was allowed to proceed for 24 hours. A comparative polyester resin (b′1) having a value of 0.19 and a hydroxyl value of 112 was obtained.

Synthesis example 5 (same as above)
The number average molecular weight was 11, as in Synthesis Example 3 except that 770 g of succinic acid, 595 g of 1,2-propylene glycol, and 60 ppm of tetraisopropyl titanate were used with respect to the total amount of succinic acid and 1,2-propylene glycol. A comparative polyester resin (b′2) having an acid value of 0.7 and a hydroxyl value of 8 was obtained.

Example 1 (Preparation of resin composition for optical material)
Acrylic resin (A1) [methyl methacrylate / maleic anhydride / styrene = 50/40/10 (molar ratio) copolymer, number average molecular weight 27,800] 100 parts, polyester resin (B1) 5 parts, It melt | dissolved in addition to the mixed solvent which consists of 270 parts of methylene chloride and 30 parts of methanol, and obtained the resin composition for optical materials (dope liquid) of this invention.

The dope solution was cast on a glass plate to a thickness of 0.5 mm, dried at room temperature for 16 hours, then dried at 50 ° C. for 30 minutes, and further at 100 ° C. for 60 minutes to obtain a film thickness of 100 μm. An unstretched film was obtained.

The obtained unstretched film was uniaxially stretched at a temperature of glass transition temperature (Tg) + 5 ° C. of the resin composition for optical materials (1) obtained by a differential scanning calorimeter (DSC) (stretching ratio: 2 times, stretching speed: 100) % / Min) to prepare a stretched film (1). Here, the measurement of Tg using a suggestion scanning calorimeter (DSC) followed the following conditions.

<Measurement conditions for glass transition temperature Tg>
A differential scanning calorimeter DSC822e (manufactured by METTTLER TOLEDO) was used. Specifically, 5 mg of the resin composition was put in a lightweight aluminum pan, heated in a nitrogen atmosphere from 25 ° C. to 150 ° C. at a rate of 10 ° C. per minute (1 run), rapidly cooled to 0 ° C., once again, 0 The temperature was raised from 10 ° C. to 150 ° C. at a rate of 10 ° C. per minute (2nd run). The glass transition temperature Tg was determined by the midpoint method from the DSC curve obtained from 2nd run.

The obtained stretched film (1) was evaluated for optical properties, specifically, in-plane birefringence (Δn), out-of-plane birefringence (ΔP) photoelastic coefficient (C _R ), and haze according to the following methods. The evaluation results are shown in Table 1.

<Evaluation method of in-plane birefringence (Δn) and out-of-plane birefringence (ΔP)>
Using a phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments), the refractive index at 588 nm was determined, and in-plane birefringence (Δn) and out-of-plane birefringence (ΔP) were determined according to the following equations.
In-plane birefringence (Δn) = (n _x ) − (n _y )
Out-of-plane birefringence _{(ΔP) = [(n x} ) + (n y)] / 2- (n z)
[(N _x ): refractive index in the stretching direction, (n _y ): refractive index in the direction orthogonal to the stretching direction, (n _z ): refractive index in the film thickness direction]
The measurement was performed in an atmosphere at 23 ° C. and 55% relative humidity.

<Evaluation method of photoelastic coefficient ( _CR )>
A stretched film obtained by cutting the stretched film with a width of 15 mm in parallel with the stretching direction is fixed to a tensile jig for photoelasticity measurement (manufactured by Oji Scientific Instruments Co., Ltd.) and 100 g · f from 127.3 g · f to 727.3 g · f. The change in in-plane retardation (Re) at 588 nm when the weight was changed every time was measured with a phase difference measuring device KOBRA-WR (manufactured by Oji Scientific Instruments). The measurement was performed in an atmosphere of 23 ° C. and 55% relative humidity. The in-plane retardation (Re) was obtained according to the following formula.
Re = (n _x −n _y ) × d
[(N _x ): refractive index in the stretching direction, (n _y ): refractive index in the direction orthogonal to the stretching direction, d: film thickness (μm)]

With respect to the measured values, stress (σ) is plotted on the horizontal axis and in-plane phase difference (Re) is plotted on the vertical axis, and the photoelastic coefficient (C _R ) is obtained from the slope of the straight line in the linear region by least square approximation. It shows that a photoelastic coefficient is near 0, so that the absolute value of inclination is small, and it shows that it is an optical film with a small change of birefringence by external force.

<Evaluation of haze>
It was based on JIS K 7136 using NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd.

Examples 2 to 8 and Comparative Examples 1 to 6
Optical films (2) to (8) and comparative stretching were performed in the same manner as in Example 1 except that a resin composition for optical material (dope solution) was obtained under the blending and stretching conditions shown in Tables 1 to 2. Films (1 ′) to (5 ′) were obtained. The same evaluation as in Example 1 was performed, and the results are shown in Tables 1 and 2.

Footnotes in Table 1 Unmeasurable: The haze of the film was so large that optical properties could not be measured.

Footnotes in Table 2 Acrylic film (A2): Copolymer of methyl methacrylate / α-methylstyrene = 93/7 (molar ratio), number average molecular weight 30,000)
Inability to measure: The optical properties could not be measured because the haze of the film was large.

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 external force.

Claims (9)

1. Polymer (A) obtained by using (meth) acrylic acid or (meth) acrylic acid alkyl ester, and the following general formula (1)
   

   

   (Wherein 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 8 carbon atoms) And X ¹ and X ² are each independently a divalent linking group.)
   The resin composition for optical materials characterized by containing the compound (B) represented by these.
2. The compound (B) is represented by the following general formula (1-1) or general formula (1-2):
   

   

   (Wherein 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 8 carbon atoms) 3 alkyl groups.)
   The resin composition for optical materials according to claim 1, represented by:
3. The resin composition for an optical material according to claim ² , wherein each of L ¹ and L ² is a phenyl group or a tolyl group.
4. The resin composition for an optical material according to claim 3, wherein each of R ¹ to R ⁴ is a methyl group.
5. The resin composition for an optical material according to claim 1, wherein the content of the compound (B) is 1 to 10 parts by mass with respect to 100 parts by mass of the polymer (A).
6. The resin composition for an optical material according to claim 1, wherein the polymer (A) is obtained using methyl methacrylate.
7. An optical film comprising the resin composition for an optical material according to any one of claims 1 to 6.
8. The optical film according to claim 7, which is used for protecting a polarizing plate.
9. A liquid crystal display device comprising the optical film according to claim 7 or 8.