JP6870429B2 - Resin solution and method for manufacturing optical film using it - Google Patents

Description

The present invention relates to a resin solution suitable for producing an optical film such as a retardation film and an optical film obtained by using the resin solution.

Many optical films are used in liquid crystal displays and organic EL displays in order to improve display characteristics. In particular, the retardation film plays a major role in improving contrast when viewed from the front or at an angle, and compensating for color tone.

As the conventional retardation film, a stretched film such as a cellulosic polymer, polycarbonate or cyclic polyolefin is used. In particular, a film made of a cellulosic polymer such as a triacetyl cellulose film is widely used because it has good adhesion to polyvinyl alcohol as a polarizer.

However, an optical film made of a cellulosic polymer has some problems. For example, a cellulose-based film is processed into an optical film having a retardation value suitable for various displays by adjusting stretching conditions, and the three-dimensional refractive index of the film obtained by uniaxial or biaxial stretching of a cellulosic film. The rate is ny ≧ nx> nz, and in order to produce an optical film having a three-dimensional refractive index other than that, for example, ny> nz> nx or ny = nz> nx. A special stretching method is required, such as adhering a heat-shrinkable film to one or both sides of the film, heat-stretching the laminate, and applying a shrinking force in the thickness direction of the film. It is also difficult to control (see, for example, Patent Documents 1 to 3). Here, nx is the refractive index in the phase-advancing axis direction (the direction with the smallest refractive index) in the film surface, ny is the refractive index in the slow-phase axial direction (the direction with the largest refractive index) in the film surface, and nz is the film surface. Indicates the refractive index of the outside (thickness direction).

Further, the cellulosic film is generally produced by the solvent casting method, but since the cellulosic film formed by the casting method has an out-of-plane phase difference (Rth) of about 40 nm in the film thickness direction, the liquid crystal in the IPS mode. There are problems such as color shift occurring in displays and the like. Here, the out-of-plane phase difference (Rth) is a phase difference value represented by the following equation.

Rth = [(nx + ny) /2-nz] × d
(In the formula, nx indicates the refractive index in the phase-advancing axis direction in the film surface, ny indicates the refractive index in the slow-phase axial direction in the film surface, nz indicates the refractive index outside the film surface, and d indicates the film thickness. )
Further, a retardation film made of a fumaric acid ester resin has been proposed (see, for example, Patent Document 4).

However, the three-dimensional refractive index of the stretched film made of the fumaric acid ester resin is nz> ny> nx, and in order to obtain the optical film exhibiting the above three-dimensional refractive index, laminating with another optical compensation film or the like is performed. is required.

Therefore, as an optical film exhibiting the above three-dimensional refractive index, a resin composition and an optical film using the same have been proposed (see, for example, Patent Documents 5 to 7).

Further, the retardation film is generally used as an antireflection layer for a reflective liquid crystal display device, a touch panel or an organic EL, and in this application, a retardation film having a larger retardation especially in a longer wavelength region (hereinafter referred to as a retardation film). , "Reverse wavelength dispersion film") is required.

For example, when an inverse wavelength dispersion film is used as the retardation film of the circularly polarizing plate for organic EL, the retardation is preferably about 1/4 of the measurement wavelength λ, and the retardation at 450 nm and the retardation at 550 nm. The ratio of Re (450) / Re (550) is preferably close to 0.81.

Patent Documents 5 to 7 propose films that express ny <nz <nx and inverse wavelength dispersion in a single layer, but by changing only the composition and blend ratio of a material having negative birefringence. There was no description about producing an optical film having more excellent phase difference characteristics by controlling the three-dimensional refractive index and the inverse wavelength dispersion and making the solvent used for film formation suitable. ..

Japanese Patent No. 2818983 Japanese Unexamined Patent Publication No. 5-297223 Japanese Unexamined Patent Publication No. 5-323120 Japanese Unexamined Patent Publication No. 2008-64817 WO2014 / 196552 WO2016 / 060115A Japanese Unexamined Patent Publication No. 2014-224926

The present invention has been made in view of the above problems, and an object of the present invention is to provide a resin solution capable of producing an optical film that can be suitably used for a retardation film or the like, and a production method using the same.

As a result of diligent studies to solve the above problems, the present inventors have found that a resin solution containing a specific polymer and a specific solvent solves the above problems, and have completed the present invention.

That is, the present invention is a resin solution containing a polymer A exhibiting positive birefringence, a polymer B exhibiting negative birefringence, and an organic solvent, wherein the organic solvent is −OR (where R is carbon). It indicates a linear or branched alkyl of numbers 1 to 5.) It is a single solvent of an aromatic solvent having a group or a mixed solvent of an aromatic solvent and a non-aromatic solvent having a −OR group. Moreover, the present invention relates to a resin solution characterized in that the solubility parameter δ obtained by the Polymer method for the organic solvent is 17 to 23 (J / cm ³ ) ^1/2.

Hereinafter, the present invention will be described in detail.

The resin solution of the present invention contains a polymer A exhibiting positive birefringence, a polymer B exhibiting negative birefringence, and an organic solvent. In the present invention, the resin solution is a resin solution obtained by dissolving a polymer A exhibiting positive birefringence and a polymer B exhibiting negative birefringence in an organic solvent, whereby when a film is formed, it is formed. It is a film that expresses ny <nz <nx and inverse wavelength dispersion in a single layer. In the present invention, it is also possible to knead the powder, pellets, etc. of each polymer and then dissolve them in an organic solvent.

The polymer A of the present invention is not particularly limited as long as it is a polymer exhibiting positive birefringence.

Since the polymer A imparts high compatibility with the polymer B, it is preferable to exhibit hydrogen-bonding interactions between different molecules. Therefore, it is preferable to have a functional group capable of forming a hydrogen bond such as a hydroxyl group, a carboxylic acid group, a carbonyl group, an ether group, an amino group, a cyano group and a urea group.

From the viewpoint of thermal stability, the Tg _A of the polymer A is preferably 120 ° C. or higher.

Examples of the polymer A include cellulose-based polymers, polyester-based polymers, polycarbonate-based polymers, polyarylate-based polymers, polysulfone (including polyethersulfone) -based polymers, polyester-based polymers, polyethylene-based polymers, norbornene-based polymers, and cycloolefin-based polymers. Examples thereof include polymers, acrylic polymers, and urethane-based polymers. Of these, cellulosic polymers and acrylic polymers are preferable, cellulose ethers are more preferable, and cellulosic ethers represented by the following general formula (1) are particularly preferable because they have good solubility in general-purpose solvents and have a wide compatibility range. preferable.

(In the formula, R ₁ , R ₂ , and R ₃ each independently indicate hydrogen or a substituent having 1 to 12 carbon atoms.)
I.

Hereinafter, cellulose ether, which is a particularly preferable cellulosic polymer, will be described as the polymer A used in the optical film of the present invention.

The cellulose ether is a polymer in which β-glucose units are linearly polymerized, and a part or all of the hydroxyl groups at the 2-position, 3-position and 6-position of the glucose unit is etherified, for example. Alkyl cellulose (methyl cellulose, ethyl cellulose, propyl cellulose, etc.), hydroxyalkyl cellulose (hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), aralkyl cellulose (benzyl cellulose, trityl cellulose, etc.), cyanoalkyl cellulose (cyanethyl cellulose, etc.), carboxyalkyl cellulose (carboxy) Methyl cellulose, carboxyethyl cellulose, etc.), carboxyalkyl alkyl cellulose (carboxymethyl methyl cellulose, carboxymethyl ethyl cellulose, etc.), aminoalkyl cellulose (aminoethyl cellulose, etc.) and the like.

The degree of substitution of the hydroxyl group of cellulose via the oxygen atom is the rate at which the hydroxyl group of cellulose is etherified (100% etherification is the degree of substitution 3) for each of the 2-, 3-, and 6-positions. This means that the total degree of substitution DS of the ether group is preferably 1.5 to 3.0 (1.5 ≦ DS ≦ 3.0), more preferably 1.5 to 3.0 (1.5 ≦ DS ≦ 3.0), because it has good solubility in an organic solvent. It is 1.8 to 2.8. The cellulosic polymer preferably has a substituent having 1 to 12 carbon atoms. Examples of the substituent having 1 to 12 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decanyl group, a dodecanyl group, an isobutyl group and a t-butyl group. , Cyclohexyl group, phenonyl group, benzyl group, naphthyl group and the like. Among these, a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group, which are alkyl groups having 1 to 5 carbon atoms, are particularly preferable. The cellulosic polymer used in the present invention may have only one type of ether group or may have two or more types of ether groups. It may have an ester group in addition to the ether group.

Cellulose ether is generally synthesized by alkali-decomposing cellulose pulp obtained from wood or cotton and etherifying the alkali-decomposed cellulose pulp. As the alkali, hydroxides of alkali metals such as lithium, potassium and sodium, ammonia and the like can be used, and sodium hydroxide is particularly preferable. The alkali is generally used as an aqueous solution.

Alkalineized cellulose pulp is preferably etherified by contact with methyl chloride or a mixture of methyl chloride and propylene oxide. Depending on the type of cellulose ether, alkyl halides (methyl chloride, ethyl chloride, etc.), aralkyl halides (benzyl chloride, trityl chloride, etc.), halocarboxylic acids (monochloroacetic acid, monochloropropionic acid, etc.), alkylene oxides (ethylene oxide, etc.) An etherifying agent such as propylene oxide) is used. These etherifying agents can be used alone or in combination of two or more. Ordinary etherifying agents include alkyl halides, epoxides and the like, and specifically include, for example, methyl chloride, ethyl chloride, ethylene oxide, propylene oxide, butylene oxide, and mixtures thereof.

If necessary, after completion of the reaction, depolymerization treatment may be carried out with hydrogen chloride, hydrogen bromide, hydrochloric acid, sulfuric acid or the like to adjust the viscosity.

Cellulose-based polymers have excellent mechanical properties and excellent molding processability during film formation. Therefore, the number average in terms of standard polystyrene obtained from the elution curve measured by gel permeation chromatography (GPC). preferably has a molecular weight (Mn) is ^{1 × 10 3 ~1 × 10 6} , further preferably ^{5 × 10 3 ~2 × 10 5} .

The polymer B of the present invention is not particularly limited as long as it is a polymer exhibiting negative birefringence.

Examples of the polymer B include a polymer obtained by polymerizing an ethylenically unsaturated monomer.

As ethylenically unsaturated monomer units: As vinyl esters, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprate, vinyl laurate, vinyl myristate, palmitin. Vinyl acid, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl laurate, etc .; as acrylic acid esters, for example, methyl acrylate, acrylic acid. Ethyl, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-) , I-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic Cyclohexyl acid, acrylic acid (2-ethylhexyl), phenylacrylic acid, benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic Acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, etc .; methacryl As an acid ester, the above acrylic acid ester is changed to a methacrylic acid ester; as an unsaturated acid, for example, acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, silicic acid, fumaric acid, etc.; As styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, isopropylstyrene, chloromethylstyrene, methoxystyreneacetoxystyrene, vinylphenol, chlorostyrene, dichlorostyrene, bromostyrene, cyanostyrene, nitrostyrene, methyl vinylbenzoate. Esters and the like; as monomers having a fused ring composed of two or more aromatic rings in the side chain, for example, vinylnaphthalene, vinylpyrene, vinylazulene, vinylcarbazole, vinylfluorene, etc .; as silicon-containing vinyl-based monomers, for example, vinyl Trimethoxysilane, vinyl triethoxysilane, etc .; as a nitrogen-containing vinyl-based monomer, for example, vinyl Pyrrolidone, vinylpyridine, acrylonitrile, methacrylonitrile and the like; fumaric acid ester; cinnamic acid ester and the like can be mentioned. The polymer composed of the above monomers may be a copolymer or a homopolymer. Of these, as the polymer B according to the present invention, a polymer having a carboxylic acid group or a hydroxyl group in the side chain is preferable because it has good solubility in a general-purpose solvent and has a wide compatibility range, and a (meth) acrylic acid ester. Polymers containing residue units, silicic acid ester residue units, and fumaric acid ester residue units are more preferable, and ester-based polymers containing silicic acid ester residue units and / or fumaric acid ester residue units are particularly preferable.

Hereinafter, as the polymer B used in the optical film of the present invention, an ester-based polymer containing a particularly preferable cinnamic acid ester residue unit and / or fumaric acid ester residue unit will be described.

In the present invention, the positive and negative of birefringence are defined as shown below.

Negative birefringence means that the stretching direction is the phase-advancing axis direction, and positive birefringence means that the direction perpendicular to the stretching direction is the phase-advancing axis direction.

That is, when uniaxially stretched, the refractive index in the axial direction orthogonal to the stretching axis is small (phase-advancing axis: perpendicular to the stretching direction) is a polymer showing positive birefringence, and when uniaxially stretched, the refractive index in the stretching axial direction is small. (Phase-advancing axis: stretching direction) is called a polymer showing negative birefringence.

When used as an optical film application, as an ester-based polymer exhibiting negative birefringence, negative birefringence is highly exhibited and the optical compensation film can be thinned, so that the Kay represented by the following general formula (2) can be achieved. It is preferable that the ester-based polymer contains a dermal acid ester residue unit and / or a fumaric acid ester residue unit represented by the following general formula (3).

(In the formula, R ₄ represents hydrogen or an alkyl group having 1 to 12 carbon atoms. X represents a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group and a phenyl group. Alternatively, it indicates an alkoxy group having 1 to 12 carbon atoms.)

(In the formula, R _{5 and} R ₆ each independently represent hydrogen or an alkyl group having 1 to 12 carbon atoms.)
The ester polymer exhibiting negative birefringence is a residue unit of a monomer copolymerizable with the monomer, with 100 mol% of the monomer related to the ester residue unit exhibiting negative birefringence. It may contain 0 to 20 mol%.

Examples of the residue unit of the monomer copolymerizable with the monomer related to the ester residue unit exhibiting negative birefractive property include styrene residues such as styrene residue and α-methylstyrene residue; Acrylic acid residue; Methacrylic acid residue; Vinyl ester residue such as vinyl acetate residue and vinyl propionate residue; Vinyl ether such as methyl vinyl ether residue, ethyl vinyl ether residue and butyl vinyl ether residue Residues; N-substituted maleimide residues such as N-methylmaleimide residue, N-cyclohexylmaleimide residue, N-phenylmaleimide residue; acrylonitrile residue; methacrylonitrile residue ;; silicic acid residue; ethylene Olefin residues such as residues and propylene residues; vinyl pyrrolidone residues; one or more such as vinyl pyridine residues can be mentioned.

Ester-based polymers that exhibit negative birefringence have particularly excellent mechanical properties and excellent molding processability during film formation. Therefore, from the elution curve measured by gel permeation chromatography (GPC). preferably the number average molecular weight of standard polystyrene obtained (Mn) is of ^{1 × 10 3 ~5 × 10 6} , further preferably ^{5 × 10 3 ~2 × 10 5} .

As a method for producing an ester-based polymer exhibiting negative birefringence, any method may be used as long as the ester-based polymer can be obtained, and it can be produced by radical polymerization. Examples of monomers copolymerizable with esters exhibiting negative birefractive properties include styrenes such as styrene and α-methylstyrene; acrylic acids; methacrylic acid; vinyl esters such as vinyl acetate and vinyl propionate. Vinyl esters such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; N-substituted maleimides such as N-methylmaleimide, N-cyclohexyl maleimide, N-phenylmaleimide; acrylonitrile; methacrylonitrile; silicic acid; ethylene , Olefins such as propylene; vinylpyrrolidone; one or more kinds such as vinylpyridine.

In the present invention, the ratio of the composition of the polymer A and the polymer B is preferably 30 to 99% by weight of the polymer A and 70 to 1% by weight of the polymer B from the viewpoint of the expression of the phase difference.

The organic solvent of the present invention is a single solvent or an aromatic solvent of an aromatic solvent having a −OR (where R indicates a linear or branched alkyl having 1 to 5 carbon atoms) group and −OR. It is a mixed solvent with a non-aromatic solvent having a group. In the present invention, the organic solvent is a single solvent of an aromatic solvent having a −OR group or a mixed solvent of an aromatic solvent and a non-aromatic solvent having a −OR group. It is possible to improve the expression of the phase difference, and an optical film suitable as the retardation film can be obtained. Here, in the present invention, when an aromatic solvent having no -OR group is used alone, or when a non-aromatic solvent having a -OR group is used alone, the optical characteristics are inferior. Further, when the number of carbon atoms of the alkyl of R in the −OR group exceeds 5, the volatility is low and the productivity is inferior. When R in the −OR group is cyclic alkyl, due to the formation of peroxide or the like, Since problems such as yellowing and embrittlement of the film occur, an optical film suitable as a retardation film cannot be obtained.

The organic solvent of the present invention has a solubility parameter δ determined by the Fedor method of 17 to 23 (J / cm ³ ) ^1/2 . In the present invention, it has been found that the solubility parameter δ can be improved when the solubility parameter δ is within the range according to the present invention when the specific single solvent or mixed solvent is used, and the solubility parameter δ is the present invention. When it is out of the range of, it becomes difficult to improve the expression of the phase difference.

For the method of calculating the solubility parameter δ by the method of Fedor, for example, PROPERTIES OF POLYMERS THEIR CORLERATION WITH CHEMICAL STRUCTURE; W. VAN KREVELEN, ELSEVIER, p. It can be calculated by the method described in 189-200 (1990). When two or more solvents are used, the solubility parameter of the solvent is defined as the arithmetic mean at each weight ratio.

The organic solvent according to the present invention is not particularly limited as long as it satisfies the requirements of the previous term, but is excellent in optical properties, and therefore includes an aromatic solvent and a non-aromatic solvent represented by the following general formula (4). It is preferable that it is a mixed solvent of.

(In the formula, R _{7 and} R ₈ each independently represent an alkyl group having 1 to 5 carbon atoms.)
The boiling point of the organic solvent according to the present invention is preferably 200 ° C. or lower, more preferably 170 ° C. or lower so that residual solvent does not easily remain in the film forming step.

Regarding the specific organic solvent according to the present invention, examples of the single solvent include aromatic hydrocarbon solvents such as methoxybenzene and ethoxybenzene.

Regarding the specific organic solvent according to the present invention, examples of the mixed solvent include aromatic hydrocarbon solvents such as benzene, toluene, xylene and mesitylen; aromatic halogenated hydrocarbon solvents such as chlorobenzene and dichlorobenzene; phenol and roses. Examples thereof include a mixed solvent of an aromatic solvent such as a phenol solvent such as chlorophenyl and a non-aromatic solvent such as an ester solvent such as methyl acetate, ethyl acetate, butyl acetate, methyl butyrate, ethyl butyrate and butyl butyrate. ..

The viscosity of the resin solution of the present invention can be adjusted by adjusting the molecular weight of the polymer, the concentration of the polymer, and the type of solvent. The viscosity of the resin solution is not particularly limited, but is preferably 50 to 30,000 cps, more preferably 100 to 20,000 cps, and particularly preferably 300 to 10,000 cps in order to facilitate film coatability. When coating as a polymer solution, the polymer A and the polymer B are mixed in a total amount of 5 to 60% by weight, preferably 10 to 50% by weight, based on 100% by weight of the solvent in terms of viscosity. Is good.

The resin solution of the present invention may contain an antioxidant in order to improve thermal stability. Examples of antioxidants include hindered phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, lactone-based antioxidants, amine-based antioxidants, hydroxylamine-based antioxidants, and vitamin E-based antioxidants. Examples thereof include antioxidants and other antioxidants, and these antioxidants may be used alone or in combination of two or more.

The resin solution of the present invention may contain a hindered amine-based light stabilizer or an ultraviolet absorber in order to enhance weather resistance. Examples of the ultraviolet absorber include benzotriazol, benzophenone, triazine, benzoate and the like.

The resin solution of the present invention contains other polymers, surfactants, polymer electrolytes, conductive complexes, pigments, dyes, antistatic agents, antiblocking agents, lubricants, etc., as long as the gist of the invention is not exceeded. May be good.

Any method may be used for producing the film using the resin solution of the present invention, but it is preferable to produce the film by the solution casting method. Here, the solution casting method is a method in which a resin solution is cast on a support substrate and then heated to evaporate the solvent to obtain a film. The coating method is not particularly limited, and a normal method can be adopted. For example, the T-die method, the doctor blade method, the bar coater method, the slot die method, the lip coater method, the reverse gravure coating method, the microgravure method, the spin coating method, the brush coating method, the roll coating method, the flexographic printing method and the like can be mentioned. .. The supporting base material used is not particularly limited, but for example, polyester or polycarbonate, polystyrene, polyethylene or polypropylene, polyvinyl chloride or polyvinylidene chloride, triacetyl cellulose or polyvinyl alcohol, polyimide or polyallylate, polysulfone or poly Examples thereof include a polymer base material made of ether sulfone, an epoxy resin or the like, a glass base material such as a glass plate or a quartz substrate, a metal base material such as aluminum, stainless steel or a ferrotype, and an inorganic base material such as a ceramics substrate. The base material is preferably a polymer base material or a metal base material.

The drying method in the drying step of the coating solution is not particularly limited, and ordinary heating means can be adopted. For example, a hot air blower, a heating roll, a far infrared heater and the like can be mentioned.

From the viewpoint of drying time, appearance, and phase difference development, the drying step is preferably two or more steps of a first low temperature drying step and a second high temperature drying step, and particularly preferably three or more steps. The first low temperature drying step may be divided into two or more steps, and the second high temperature drying step may be divided into two or more steps. Specifically, the first drying step is preferably 20 to 79 ° C., more preferably 30 to 79 ° C., and particularly preferably 40 ° C. to 79 ° C. The amount of residual solvent with respect to the resin solution component after the completion of the first drying step is preferably 3 to 50% by weight, more preferably 5 to 30% by weight. By sufficiently reducing the amount of residual solvent after the completion of the first drying step, the appearance is improved and the phase difference can be controlled. The drying temperature of the second drying step is preferably 80 ° C. to 220 ° C., more preferably 80 ° C. to 200 ° C. Setting the first half of the second drying step to 80 to 120 ° C. and the second half to 130 ° C. or higher can be preferably selected from the viewpoint of shortening the drying time and controlling the phase difference. In particular, the residual solvent before drying at 130 ° C. or higher is preferably 3 to 30% by weight, more preferably 4 to 20% by weight, and particularly preferably 5 to 15% by weight.

As a method for producing an optical film using the resin solution of the present invention, for example, the resin solution may be cast on a base material, dried by heating, and then peeled off from the base material.

The film obtained by the resin solution of the present invention is preferably used as an optical film. Hereinafter, the optical film according to the present invention will be described.

The optical film using the resin solution of the present invention preferably has a thickness of 5 to 200 μm, more preferably 10 to 100 μm, and more preferably 20 to 20 μm, from the viewpoint of the handleability of the film and the compatibility of the optical member with thinning. 80 μm is particularly preferable.

The phase difference characteristics of the optical film using the resin solution of the present invention differ depending on the target optical film. For example, the in-plane retardation (Re) represented by the following formula (1) is preferably 60 to 300 nm. , More preferably 80 to 300 nm, particularly preferably 80 to 280 nm, and the Nz coefficient represented by the following formula (2) is preferably 0.30 to 0.95, still more preferably 0.35 to 0.65. Particularly preferably, those having a value of 0.45 to 0.55 and the like can be mentioned. The phase difference characteristic at this time is measured using a fully automatic birefringence meter (manufactured by Oji Measuring Instruments Co., Ltd., trade name KOBRA-21ADH) under the condition of a measurement wavelength of 589 nm.

Re = (ny-nx) x d (1)
Nz = (ny-nz) / (ny-nx) (2)
Rth = [(nx + ny) /2-nz] × d (3)
(In the formula, nx indicates the refractive index in the phase-advancing axis direction in the film surface, ny indicates the refractive index in the slow-phase axial direction in the film surface, nz indicates the refractive index outside the film surface, and d indicates the refractive index of the film. Indicates the thickness.)
The wavelength dispersion characteristic of the optical film of the present invention is preferably 0.60 <Re (450) / Re (550) <1.05, and more preferably 0.70 <Re (450) in order to suppress color shift. ) / Re (550) <1.02, and particularly preferably 0.75 <Re (450) / Re (550) <1.00.

The optical film of the present invention has a light transmittance of preferably 85% or more, more preferably 90% or more in order to improve the brightness.

The optical film of the present invention has a haze of preferably 2% or less, more preferably 1% or less, and particularly preferably 0.5% or less in order to improve contrast.

The optical film obtained by using the production method of the present invention is preferably uniaxially stretched or unbalanced biaxially stretched in order to exhibit an in-plane retardation (Re). As a method for stretching an optical film, a longitudinal uniaxial stretching method by roll stretching, a horizontal uniaxial stretching method by tenter stretching, an oblique stretching method, an unbalanced sequential biaxial stretching method by a combination of these, and an unbalanced simultaneous biaxial stretching method are used. A method or the like can be used, but any stretching method may be used as long as it is stretched to at least a uniaxial method.

The thickness of the optical film at the time of stretching is preferably 10 to 200 μm, more preferably 15 to 150 μm, and particularly preferably 15 to 110 μm from the viewpoint of ease of stretching treatment and compatibility with thinning of the optical member.

The stretching temperature is not particularly limited, but is preferably 50 to 200 ° C., more preferably 100 to 180 ° C., because good phase difference characteristics can be obtained. The draw ratio of uniaxial stretching is not particularly limited, but 1.05 to 4.0 times is preferable, and 1.1 to 3.5 times is more preferable, because good retardation characteristics can be obtained. The draw ratio of unbalanced biaxial stretching is not particularly limited, but 1.05 to 4.0 times is preferable in the length direction, and 1.1 to 3.5 times, because the optical compensation film has excellent optical characteristics. The magnification is more preferable, and the optical compensation film having excellent optical characteristics is obtained. Therefore, 1.01 to 1.2 times is preferable in the width direction, and 1.05 to 1.1 times is further preferable. The in-plane phase difference (Re) can be controlled by the stretching temperature and the stretching ratio.

The optical film using the resin solution of the present invention can be laminated with a film containing another resin, if necessary. Examples of other resins include polyether sulfone, polyarylate, polyethylene terephthalate, polynaphthalene terephthalate, polycarbonate, cyclic polyolefin, maleimide-based resin, fluorine-based resin, cellulose-based resin, and polyimide. It is also possible to stack a hard coat layer and a gas barrier layer.

According to the present invention, it is possible to provide a resin solution that can be suitably used for a retardation film or the like, and it is useful for an optical film for a liquid crystal display, an antireflection film for a circularly polarizing plate used for an organic EL or the like. ..

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.

The physical properties shown in the examples were measured by the following methods.

<Polymer analysis>
^{The structural analysis of the polymer was determined by proton nuclear magnetic resonance spectroscopy (1} H-NMR) spectral analysis using a nuclear magnetic resonance measuring device (manufactured by JEOL Ltd., trade name: JNM-GX270).

^{1 When the} composition ratio analysis was difficult from the H-NMR spectrum analysis, the fumaric acid monoester concentration was determined according to the JIS K 2501 (2003 version) petroleum product and lubricating oil-neutralization value test method.

<Measurement of number average molecular weight>
Measured at 40 ° C. using a gel permeation chromatography (GPC) apparatus (manufactured by Toso, trade name: C0-8011 ( _{equipped with column GMH HR-} H)) using tetrahydrofuran or dimethylformamide as a solvent. Then, it was calculated as a standard polystyrene conversion value.
<Measurement of Tg>
The glass transition temperature was determined using a differential scanning calorimeter (manufactured by SII, trade name: DSC6220) in a scanning range of −40 ° C. to 200 ° C. according to a method for measuring the transition temperature of JIS K 7121 (2012 edition) plastic.
<Measurement of residual solvent amount>
The film after the completion of the subject drying step was dissolved in a solvent and measured using a gas chromatography (GC) apparatus (manufactured by Shimadzu, trade name: GC-14A).
<Measurement of light transmittance and haze of film>
For the light transmittance and haze of the produced film, use a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., trade name: NDH2000), measure the light transmittance with JIS K 7361-1 (1997 version), and measure the haze. Measurements were made in accordance with JIS-K 7136 (2000 version).

<Measurement of phase difference characteristics>
The phase difference characteristic of the optical film was measured using light having a wavelength of 589 nm using a sample tilt type automatic birefringence meter (manufactured by Oji Measuring Instruments, trade name: KOBRA-WR).

<Measurement of wavelength dispersion characteristics>
Using a sample tilt type automatic birefringence meter (manufactured by Oji Measuring Instruments, trade name: KOBRA-WR), the ratio of the phase difference Re (450) due to light with a wavelength of 450 nm and the phase difference Re (550) due to light with a wavelength of 550 nm is optical. The wavelength dispersion characteristics of the film were measured.

Synthesis example 1
In a glass ampoule having a capacity of 75 mL, 42 g of diisopropyl fumarate, 7.7 g of monoethyl fumarate and 0.66 g of tert-butyl peroxypivalate as a polymerization initiator were placed, and after repeating nitrogen substitution and depressurization, the mixture was sealed under reduced pressure. did. This ampoule was placed in a constant temperature bath at 55 ° C. and held for 24 hours for radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved in 200 g of tetrahydrofuran. This polymer solution was added dropwise to 4 L of hexane to precipitate, and then vacuum dried at 80 ° C. for 10 hours to obtain 27 g of a diisopropyl fumarate / monoethyl fumarate copolymer. The number average molecular weight of the obtained polymer was 53,000, the diisopropyl fumarate residue unit was 82 mol%, and the monoethyl fumarate residue unit was 18 mol%. Tg was 175 ° C.

Synthesis example 2
In a glass ampoule with a capacity of 75 mL, 6.7 g of monoethyl fumarate, 37 g of diisopropyl fumarate, 6.1 g of n-propyl 4-methoxycinnamate and 2,5-dimethyl-2,5-di (2-di) as a polymerization initiator 1.48 g of ethylhexanoylperoxy) hexane was added, and after repeating nitrogen substitution and depressurization, the mixture was sealed under reduced pressure. This ampoule was placed in a constant temperature bath at 60 ° C. and held for 48 hours for radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved in 50 g of tetrahydrofuran. This polymer solution was added dropwise to methanol / water = 70/30 (% by weight / wt%) to precipitate, washed with 2 kg of methanol / water = 70/30 (% by weight / wt%), and then at 80 ° C. for 10 hours. By vacuum drying, 26 g of a monoethyl fumarate / diisopropyl fumarate / n-propyl copolymer 4-methoxysilicate was obtained. The number average molecular weight of the obtained polymer was 32,000, monoethyl fumarate residue unit 15 mol%, diisopropyl fumarate residue unit 72 mol%, and n-propyl fumarate n-propyl residue unit 13 mol%. there were. No Tg was observed within the scanning range, and it is estimated that the temperature is 200 ° C. or higher.

Synthesis example 3
In a glass ampoule with a capacity of 75 mL, 6.3 g of monoethyl fumarate, 15 g of diisopropyl fumarate, 29 g of ethyl 4-methoxycinnamate and 2,5-dimethyl-2,5-di (2-ethylhexanoylper) as a polymerization initiator Oxy) 1.48 g of hexane was added, and after repeating nitrogen substitution and depressurization, the mixture was sealed under reduced pressure. This ampoule was placed in a constant temperature bath at 60 ° C. and held for 48 hours for radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved in 50 g of tetrahydrofuran. This polymer solution was added dropwise to 2 kg of methanol / water = 60/40 (% by weight / wt%) to precipitate, washed with 2 kg of methanol / water = 60/40 (% by weight / wt%), and then 10 at 80 ° C. By vacuum drying for hours, 31 g of a monoethyl fumarate / diisopropyl fumarate / ethyl 4-methoxysilicate copolymer was obtained. The number average molecular weight of the obtained polymer was 38,000, monoethyl fumarate residue unit 22 mol%, diisopropyl fumarate residue unit 40 mol%, and ethyl 4-methoxysilicate residue unit 38 mol%. .. No Tg was observed within the scanning range, and it is estimated that the temperature is 200 ° C. or higher.

Synthesis example 4
A 4-cyanostyrene-2-hydroxyethyl methacrylate random copolymer (composition 80:20 (mol ratio), number average molecular weight 28,000) was synthesized by the solution polymerization method described in Japanese Patent Application No. 5-2058. Tg was 141 ° C.
<Cellulosic ether>
Ethyl cellulose as cellulose ether (ETHOCEL standard (ETHOCEL standard) 100 manufactured by Dow Chemical Co., Ltd., molecular weight Mn = 55,000, molecular weight Mw = 176,000, Mw / Mn = 3.2, total degree of substitution DS = 2.5, Tg : 123 ° C. and Dow Chemical Etocell Standard (ETHOCEL standard) 300, molecular weight Mn = 91,000, molecular weight Mw = 284,000, Mw / Mn = 3.1, total degree of substitution DS = 2.5, Tg: 123 ° C.) was used.
<Cellulose ester>
Cellulose acetate butyrate as a cellulose ester (manufactured by Eastman Chemical, CAB-381-2, Mn = 40,000, butyryl group = 57 mol%, acetyl group = 33 mol%, total degree of substitution DS = 2.70, Tg: 133 ° C.) was used.

Example 1
Ethyl cellulose (ETHOCEL standard manufactured by Dow Chemical Co., Ltd.) as a cellulosic polymer, molecular weight Mn = 55,000, molecular weight Mw = 176,000, Mw / Mn = 3.2, total substitution degree DS = 2.5, 93 g of Tg: 123 ° C.) and 57 g of the diisopropyl fumarate / monoethyl fumarate copolymer obtained in Synthesis Example 1 are dissolved in a toluene / butyl acetate = 80/20 (weight ratio) solution to provide a 15% by weight resin solution. Then, it was poured onto a polyethylene terephthalate film with a coater, dried in a safety oven (manufactured by ESPEC, trade name: SPH-201) at 40 ° C. for 5 minutes, and then dried at 140 ° C. for 5 minutes to obtain a film having a thickness of 60 μm and a width of 150 mm. ..

The obtained film was cut into 50 mm squares and uniaxially stretched 2.0 times at 140 ° C. by an automatic biaxial stretching device (manufactured by Imoto Seisakusho, trade name: IMC-16A1 type). The phase difference characteristics and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

The obtained optical film had high light transmittance, small haze, excellent transparency, and optical characteristics aimed at in-plane retardation (Re) and Nz coefficient.

Example 2
81 g of ethyl cellulose used in Example 1 and 69 g of monoethyl fumarate / diisopropyl fumarate / n-propyl copolymer 4-methoxysilicate obtained in Synthesis Example 2 were added to toluene / ethyl acetate / p-xylene = 55/10. Dissolve in a / 35 (weight ratio) solution to make a 15% by weight resin solution, sprinkle it on a polyethylene terephthalate film with a coater, dry it in a safety oven at 40 ° C. for 15 minutes, then dry it at 155 ° C. for 5 minutes, film thickness 75 μm, width 150 mm. Film (resin composition) was prepared. The obtained film was cut into 50 mm squares and uniaxially stretched 2.0 times at 140 ° C. by a stretching machine. The phase difference characteristics and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

The obtained optical film had high light transmittance, small haze, excellent transparency, and optical characteristics aimed at in-plane retardation (Re) and Nz coefficient.

Example 3
A film was prepared in the same manner as in Example 2 except that the solvent was methoxybenzene. The results are shown in Table 1.

The obtained optical film had high light transmittance, small haze, excellent transparency, and optical characteristics aimed at in-plane retardation (Re) and Nz coefficient.

Example 4
Ethyl cellulose (ETHOCEL standard manufactured by Dow Chemical Co., Ltd.) 300, molecular weight Mn = 91,000, molecular weight Mw = 284,000, Mw / Mn = 3.1, total substitution degree DS = 2.5, Tg: 123 ° C. ) 84 g, 66 g of the monoethyl fumarate / diisopropyl fumarate / ethyl 4-methoxysilicate copolymer obtained in Synthesis Example 3 was dissolved in toluene: ethyl acetate: p-xylene = 45: 20: 35 (weight ratio). Then, the resin solution was made into a 15% by weight, and the film was sprinkled on a polyethylene terephthalate film with a coater, dried in a safety oven at 40 ° C. for 12 minutes and then dried at 155 ° C. for 5 minutes to prepare a film (resin composition) having a thickness of 75 μm and a width of 150 mm. .. The obtained film was cut into 50 mm squares and uniaxially stretched 2.0 times at 140 ° C. by a stretching machine. The phase difference characteristics and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

The obtained optical film had high light transmittance, small haze, excellent transparency, and optical characteristics aimed at in-plane retardation (Re) and Nz coefficient.

Example 5
Styrene acetate butyrate (manufactured by Toluene Chemical, CAB-381-2, Mn = 40,000, butyryl group = 57 mol%, acetyl group = 33 mol%, total substitution degree DS = 2.70, Tg: 133 ° C.) 140 g and 10 g of the 4-cyanostyrene-2-hydroxyethyl methacrylate random copolymer obtained in Synthesis Example 4 were dissolved in toluene: ethyl butyrate = 8: 2 (weight ratio) to prepare a 15% by weight resin solution for safety. After drying in an oven at 40 ° C. for 15 minutes, it was dried at 155 ° C. for 5 minutes to prepare a film (resin composition) having a film thickness of 110 μm and a width of 150 mm. The obtained film was cut into 50 mm squares and uniaxially stretched 2.0 times at 130 ° C. by a stretching machine. The phase difference characteristics and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

The obtained optical film had high light transmittance, small haze, excellent transparency, and optical characteristics aimed at in-plane retardation (Re) and Nz coefficient.

Comparative Example 1
A film was prepared in the same manner as in Example 1 except that the solvent was n-hexane / butyl acetate = 80/20 (weight ratio). The results are shown in Table 1.

The obtained optical film was a film having a large haze and low transparency, and did not have the desired optical characteristics for the in-plane phase difference (Re) and the Nz coefficient.

Comparative Example 2
A film was prepared in the same manner as in Example 1 except that the solvent was n-hexane / butyl acetate = 20/80 (weight ratio). The results are shown in Table 1.

The obtained optical film was a film having a large haze and low transparency, and did not have the desired optical characteristics for the in-plane phase difference (Re) and the Nz coefficient.

Comparative Example 3
A film was prepared in the same manner as in Example 5 except that the solvent was n-hexane / ethyl acetate = 80/20 (weight ratio). The results are shown in Table 1.

The obtained optical film was a film having low light transmittance, a large haze, and low transparency, and did not have the desired optical characteristics in terms of in-plane phase difference (Re) and Nz coefficient.

Comparative Example 4
140 g of cellulose acetate butyrate used in Example 5 and 10 g of 4-cyanostyrene-2-hydroxyethyl methacrylate random copolymer obtained from Synthesis Example 4 were used in a twin-screw extruder (TEX30-SS manufactured by Japan Steel Works, Ltd.). ) Was melt-kneaded at 200 ° C. to pelletize. Then, the obtained pellets were heat-press molded to obtain a film having a thickness of 75 μm.

The obtained film had low light transmittance, large haze, low transparency, and was brittle, and the phase difference could not be measured.

Comparative Example 5
84 g of ethyl cellulose used in Example 1 and 66 g of a monoethyl fumarate / diisopropyl fumarate / ethyl 4-methoxysilicate copolymer obtained in Synthesis Example 3 were dissolved in butyl acetate to prepare a 15% by weight resin solution. After drying in a safety oven, a film (resin composition) having a film thickness of 110 μm and a width of 150 mm was prepared. The obtained film was cut into 50 mm squares and uniaxially stretched 2.0 times at 130 ° C. by a stretching machine. The phase difference characteristics and wavelength dispersion characteristics of the obtained optical film were measured. The results are shown in Table 1.

The obtained optical film was a film having a large haze and low transparency, and did not have the desired optical characteristics for the in-plane phase difference (Re) and the Nz coefficient.

Comparative Example 6
84 g of the ethyl cellulose used in Example 1 and 66 g of the monoethyl fumarate / diisopropyl fumarate / ethyl 4-methoxysilicate copolymer obtained in Synthesis Example 3 were added to toluene and stirred to prepare a 10% by weight resin solution. Attempts were made to make adjustments, but gelation did not result in a uniform solution.

The present invention provides a resin solution that can be suitably used for retardation films and the like, and a method for producing an optical film using the resin solution. In particular, a film having a controlled three-dimensional refractive index and wavelength dispersibility can be produced by subjecting a film obtained from the resin solution of the present invention to a process such as stretching, and an optical film for a liquid crystal display, an organic EL, or the like can be produced. It is useful for antireflection films for circularly polarizing plates used in the above.

Claims (5)

It contains at least one residue unit in the group consisting of a cellulose-based polymer A exhibiting positive birefractive properties, a (meth) acrylic acid ester residue unit, a siliceous ester residue unit, and a fumaric acid ester residue unit. A resin solution containing a polymer B exhibiting negative birefractive properties and an organic solvent, wherein the organic solvent is −OR (where R represents a linear or branched alkyl having 1 to 5 carbon atoms. ) A single solvent of an aromatic solvent having a group or a mixed solvent of an aromatic solvent and a non-aromatic solvent having a −OR group, and the solubility parameter δ obtained by the Ester method for the organic solvent is A resin solution characterized by being 17 to 23 (J / cm ³ ) ^1/2. The resin solution according to claim 1, wherein the polymer A is a cellulosic polymer represented by the following general formula (1).

(In the formula, R ₁ , R ₂ , and R ₃ each independently indicate hydrogen or a substituent having 1 to 12 carbon atoms.) Claimed that the polymer B is an ester-based polymer containing a cinnamic acid ester residue unit represented by the following general formula (2) and / or a fumaric acid ester residue unit represented by the following general formula (3). Item 2. The resin solution according to Item 1 or 2.

(In the formula, R ₄ represents an alkyl group having 1 to 12 carbon atoms. X represents a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, a phenyl group or a carbon. The number 1 to 12 of the alkyl group or the alkoxy group is shown.)

(In the formula, R ₅ and R ₆ each independently represent hydrogen or an alkyl group having 1 to 12 carbon atoms.) The resin solution according to any one of claims 1 to 3 , wherein the mixed solvent is a mixed solvent of an aromatic solvent and a non-aromatic solvent represented by the following general formula (4).

(In the formula, R ₇ and R ₈ each independently represent an alkyl group having 1 to 5 carbon atoms.) A method for producing a transparent optical film, which comprises casting the resin solution according to any one of claims 1 to 4 onto a base material, drying the resin solution, and then peeling the resin solution from the base material.