JP7127327B2 - Cellulose resin composition and optical film using the same - Google Patents

Description

The present invention relates to a resin composition and a film using the same, and more specifically, a resin composition suitable for optical films for liquid crystal displays and organic ELs having excellent retardation characteristics, wavelength dispersion characteristics, and moisture and heat resistance. and an optical film using the same.

In recent years, the demand for display performance and durability has increased in various displays, and it is necessary to improve the response speed and compensate for a wider range of viewing angles such as contrast and color balance when viewing the displayed image from an oblique direction. is the issue. In order to solve these problems, VA (Vertical Alignment) method, OCB (Optical Compensated Bend) method, or IPS (In-Plane Switching) method display elements have been developed, and various letters are displayed according to each liquid crystal method. There is a demand for an optical compensation film material that exhibits gradation.

As conventional optical compensation films, stretched films such as cellulose-based resins, polycarbonates, and cyclic polyolefins have been used. In particular, stretched films made of cellulose-based resins such as cellulose acylate are widely used as optical compensation films for liquid crystal display devices because of their transparency, toughness, moisture permeability and low wavelength dispersion that are necessary for processing. .

However, optical compensation films made of cellulose-based resins have several problems. For example, a cellulose-based resin film is processed into an optical compensation film having a retardation value suitable for various displays by adjusting the stretching conditions, and the cellulose-based resin film is obtained by uniaxially or biaxially stretching The three-dimensional refractive index of the film is ny≧nx>nz, and an optical compensation film having other three-dimensional refractive indexes such as ny>nz>nx or ny=nz>nx is used. For production, a special stretching method is required, such as attaching a heat-shrinkable film to one or both sides of the film, heat-stretching the laminate, and applying shrinkage force in the thickness direction of the polymer film. It is also difficult to control the refractive index (retardation value) (see Patent Documents 1 to 3, for example). where nx is the refractive index in the fast axis direction in the film plane (direction with the smallest refractive index), ny is the refractive index in the slow axis direction in the film plane (the direction with the largest refractive index), and nz is the film plane. The refractive index of the outside (thickness direction) is shown.

Cellulose-based resin films are generally produced by a solvent casting method. A cellulose-based resin film formed by a casting method has an out-of-plane retardation (Rth) of about 40 nm in the film thickness direction. IPS mode liquid crystal displays have problems such as color shift. Here, the out-of-plane retardation (Rth) is a retardation value represented by the following formula.

Rth=[(nx+ny)/2−nz]×d
(wherein, nx is the in-plane refractive index in the fast axis direction, ny is the in-plane refractive index in the slow axis direction, nz is the out-of-plane refractive index of the film, and d is the film thickness. )
Also, a retardation film (optical compensation film) made of a fumaric acid ester resin has been proposed (see, for example, Patent Document 4).

However, the three-dimensional refractive index of a stretched film made of a fumaric acid ester-based resin is nz>ny>nx. etc. is necessary.

Accordingly, as an optical compensation film exhibiting the three-dimensional refractive index, a resin composition and an optical compensation film using the resin composition have been proposed (see, for example, Patent Documents 5 to 7). Although Patent Documents 5 to 7 have excellent performance as an optical compensation film, there is a demand for an optical compensation film that exhibits the desired Re with a thinner film.

Here, in general, the optical compensation film is also used as a reflective liquid crystal display device, a touch panel, or an antireflection layer of an organic EL. hereinafter referred to as a "reverse wavelength dispersion film"). For example, when a reverse wavelength dispersion film is used as an optical compensation film for a circularly polarizing plate for organic EL, the retardation is preferably about 1/4 of the measured wavelength λ, and retardation at 450 nm and retardation at 550 nm It is preferred that the ratio Re(450)/Re(550) be close to 0.81. In view of thinning of the display device, the reverse wavelength dispersion film to be used is also required to be thin. Various optical compensation films have been developed to meet the required properties as described above.

A retardation film containing a cellulose resin and a fumarate ester polymer has been proposed as a retardation film (optical compensation film) that exhibits the above three-dimensional refractive index and is used as a reverse wavelength dispersion film (for example, patent Reference 8). However, the retardation film described in Patent Document 8 has a problem in the durability of the resulting film in a high-temperature, high-humidity environment, and there is a demand for an optically-compensatory film that is highly stable under high-temperature, high-humidity conditions.

Japanese Patent No. 2818983 JP-A-5-297223 JP-A-5-323120 JP 2008-64817 A JP 2013-28741 A JP 2014-125609 A JP 2014-125610 A JP 2015-157928 A

The present invention has been made in view of the above problems, and its object is a film using a resin composition having excellent retardation characteristics and wavelength dispersion characteristics, highly stable optical under high temperature and high humidity to provide the film.

The present inventors have made intensive studies to solve the above problems, and found that a specific cellulose-based resin composition and an optical film using the same can solve the above problems, and have completed the present invention. rice field.

That is, the present invention comprises 50 to 98.99% by weight of a cellulose-based resin having a degree of substitution of 1.5 to 2.95 represented by the following general formula (1), and an ester-based resin exhibiting negative birefringence. The present invention relates to a resin composition characterized by containing 1 to 49.99% by weight of a resin and 0.01 to 5% by weight of a hydroxy group-reactive cross-linking agent.

(In the formula, R ₁ , R ₂ and R ₃ each independently represent hydrogen or a substituent having 1 to 12 carbon atoms.)
The contents of the present invention will be described in detail below.

The resin composition of the present invention is characterized by containing a specific cellulose-based resin, an ester-based resin exhibiting negative birefringence, and a hydroxy group-reactive cross-linking agent.

The cellulose resin contained in the resin composition of the present invention is represented by the following general formula (1).

(In the formula, R ₁ , R ₂ and R ₃ each independently represent hydrogen or a substituent having 1 to 12 carbon atoms.)
Examples of the cellulose-based resin of the present invention include cellulose ether, cellulose ether ester, and the like. The resin composition of the present invention may contain one or more of these cellulose resins.

In the cellulose-based resin of the present invention, the degree of substitution of the cellulose hydroxyl groups through oxygen atoms is such that cellulose hydroxyl groups are substituted at each of the 2-, 3-, and 6-positions. It means the ratio (when substituted by 100%, the degree of substitution is 3), and is 1.5 to 2.95, preferably 1.8 to 2.8, from the viewpoints of solubility, compatibility, and stretching processability. is.

Since the cellulose-based resin of the present invention has excellent mechanical properties and excellent moldability during film formation, it can be obtained from an elution curve measured by gel permeation chromatography (GPC). The number average molecular weight (Mn) in terms of standard polystyrene is preferably 1×10 ³ to 1×10 ⁶ , more preferably 5×10 ³ to 2×10 ⁵ .

The cellulose-based resin of the present invention is excellent in compatibility with ester-based resins exhibiting negative birefringence, has a large in-plane retardation Re, and is excellent in stretching workability. is preferred.

Cellulose ether, which is preferable as the cellulose-based resin in the present invention, will be described below.

Cellulose ether, which is the cellulose-based resin of the present invention, is a polymer in which β-glucose units are linearly polymerized. It is a partially or wholly etherified polymer. Cellulose ethers of the present invention include, for example, alkylcelluloses such as methylcellulose, ethylcellulose and propylcellulose; hydroxyalkylcelluloses such as hydroxyethylcellulose and hydroxypropylcellulose. aralkyl cellulose such as benzyl cellulose and trityl cellulose; cyanoalkyl cellulose such as cyanoethyl cellulose; carboxyalkyl cellulose such as carboxymethyl cellulose and carboxyethyl cellulose; cellulose, carboxyalkylalkylcellulose such as carboxymethylethylcellulose; aminoalkylcellulose such as aminoethylcellulose;

The degree of substitution (degree of etherification) of the hydroxyl groups of cellulose in the cellulose ether via oxygen atoms is means the ratio of etherification (100% etherification has a substitution degree of 3), and from the viewpoint of solubility, compatibility, and stretching processability, the total substitution degree DS of the ether group is preferably is between 1.8 and 2.8. From the viewpoint of solubility and compatibility, the cellulose ether preferably has a substituent of 1 to 12 carbon atoms. Examples of substituents having 1 to 12 carbon atoms include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decanyl group, dodecanyl group, isobutyl group and t-butyl group. , cyclohexyl group, phenonyl group, benzyl group, naphthyl group and the like. Among these, from the viewpoint of solubility and compatibility, methyl group, ethyl group, propyl group, butyl group and pentyl group, which are alkyl groups having 1 to 5 carbon atoms, are preferred. The cellulose-based polymer used in the present invention may have only one type of ether group, or may have two or more types of ether groups. Also, it may have an ester group in addition to the ether group.

Cellulose ethers are generally synthesized by alkaline decomposition of cellulose pulp obtained from wood or cotton and etherification of the alkaline decomposition cellulose pulp. Alkalis that can be used include hydroxides of alkali metals such as lithium, potassium and sodium, and ammonia. The alkalis are generally used as aqueous solutions. The alkalinized cellulose pulp is then etherified by contact with an etherification agent that is used according to the type of cellulose ether. Examples of the etherifying agent include alkyl halides such as methyl chloride and ethyl chloride; aralkyl halides such as benzyl chloride and trityl chloride; halocarboxylic acids such as monochloroacetic acid and monochloropropionic acid; ethylene oxide, propylene oxide and butylene. Alkylene oxides such as oxides can be mentioned, and these etherifying agents can be used alone or in combination of two or more.

If necessary, after completion of the reaction, depolymerization treatment may be performed with hydrogen chloride, hydrogen bromide, hydrochloric acid, sulfuric acid, or the like for viscosity adjustment.

The ester-based resin exhibiting negative birefringence contained in the resin composition of the present invention (hereinafter referred to as an ester-based resin exhibiting negative birefringence) is a resin having an ester residue unit exhibiting negative birefringence. As long as it is not particularly limited, the residue unit includes, for example, a (meth)acrylic acid ester residue unit, a cinnamic acid ester residue unit, a fumarate residue unit, etc., and one of these Or 2 or more types are mentioned.

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

Negative birefringence means that the drawing direction is the fast axis direction, and positive birefringence means that the direction perpendicular to the drawing direction is the fast axis direction. In other words, when uniaxially stretched, the refractive index in the direction perpendicular to the stretching axis is small (fast axis: the direction perpendicular to the stretching direction) is a resin that exhibits positive birefringence, and when uniaxially stretched, the refractive index in the stretching direction is small. (Fast axis: stretching direction) is called a resin exhibiting negative birefringence.

Ester-based resins exhibiting negative birefringence exhibit a large degree of negative birefringence, and the optical compensation film can be made thinner. / Or, it is preferably an ester-based resin containing a fumaric acid ester residue unit represented by the following general formula (3).

(In the formula, R ₄ represents an alkyl group having 1 to 12 carbon atoms. X and Y are each independently hydrogen, 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, a hydroxyl group, or 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.)
In the ester-based resin exhibiting negative birefringence, 0 mol% of monomers related to ester residue units exhibiting negative birefringence are copolymerizable with the monomer. ~20 mol% may be included.

Examples of the residue unit of the monomer copolymerizable with the ester residue unit showing negative birefringence include styrene residues such as styrene residues and α-methylstyrene residues; Acrylic acid residue; methacrylic acid residue; vinyl ester residue such as vinyl acetate residue and vinyl propionate residue; vinyl ether residue such as methyl vinyl ether residue, ethyl vinyl ether residue and butyl vinyl ether residue Residue; N-substituted maleimide residue such as N-methylmaleimide residue, N-cyclohexylmaleimide residue, N-phenylmaleimide residue; acrylonitrile residue; methacrylonitrile residue; cinnamic acid residue; ethylene residue olefin residues such as propylene residues; vinylpyrrolidone residues; vinylpyridine residues; , vinylcarbazole, vinylfluorene, and the like.

Ester-based resins exhibiting negative birefringence have particularly excellent mechanical properties and excellent molding processability during film formation. Therefore, the elution curve measured by gel permeation chromatography (GPC). The number average molecular weight (Mn) in terms of standard polystyrene obtained from the above is preferably 1×10 ³ to 5×10 ⁶ , more preferably 5×10 ³ to 2×10 ⁵ .

The composition ratio of the cellulose resin and the ester resin exhibiting negative birefringence in the resin composition of the present invention is 30 to 98.99% by weight of the cellulose resin and the ester exhibiting negative birefringence. 1 to 69.99% by weight of the system resin is preferred. When the cellulose-based resin is less than 30% by weight, or when the cellulose-based resin exceeds 98.99% by weight, it is difficult to control the retardation. Preferably, 30 to 98.99% by weight of cellulose resin and 10 to 69.99% by weight of ester resin exhibiting negative birefringence, more preferably 40 to 79.99% by weight of cellulose resin. % and 20 to 59.99% by weight of an ester resin exhibiting negative birefringence.

The ester resin exhibiting negative birefringence may be produced by any method as long as the ester resin can be obtained, and the ester resin can be produced by radical polymerization.

As the radical polymerization method, for example, any of bulk polymerization method, solution polymerization method, suspension polymerization method, precipitation polymerization method, emulsion polymerization method and the like can be employed.

The hydroxy group-reactive cross-linking agent in the present invention forms a cross-linked structure between cellulose-based resins by reacting with hydroxy groups. In the present invention, the elasticity of the film obtained by the crosslinked structure is improved, and the film has excellent durability in a high-temperature and high-humidity environment.

The hydroxy group-reactive cross-linking agent used in the present invention is not particularly limited as long as it is a compound having two or more groups in the molecule that can react with free hydroxy groups in the cellulose resin. Examples thereof include an isocyanate group, a carbodiimide group, a vinylsulfone group, an epoxy group, an oxazoline group, a melamine group, a dialdehyde group, and an ethyleneimine group.

In the present invention, the hydroxy group-reactive cross-linking agent is not particularly limited as long as it is a compound having two or more substituents reactive with a hydroxy group in the molecule. compounds, vinylsulfone group-containing compounds, epoxy group-containing compounds, oxazoline group-containing compounds, melamine group-containing compounds, dialdehyde group-containing compounds, and ethyleneimine group-containing compounds. Of these, isocyanate group-containing compounds, carbodiimide group-containing compounds, and oxazoline group-containing compounds are preferred, and isocyanate group-containing compounds are more preferred, in terms of pot life and reactivity.

Examples of the hydroxy-reactive cross-linking agent include polymers having terminal hydroxy-reactive cross-linkable groups such as isocyanate groups and epoxy groups, even if they are low-molecular-weight compounds; good too.

The isocyanate group-containing compound used in the present invention is not particularly limited as long as it is a compound having two or more isocyanate groups in the molecule. Compounds having two or more isocyanate groups in the molecule include, for example, 2,4-tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and xylylene diisocyanate having two isocyanate groups in the molecule. isocyanate having two or more and having an aromatic ring; aliphatic isocyanate having two or more isocyanate groups in the molecule such as n-butyl diisocyanate and hexamethylene diisocyanate; isocyanate groups such as hydrogenated TDI and hydrogenated MDI Examples include isocyanates having two or more in the molecule and hydrogenated aromatic rings, and particularly low coloring properties, and aliphatic isocyanates having two or more isocyanate groups in the molecule and hydrogen in the aromatic rings. Added isocyanates are more preferred.

In the present invention, polyisocyanates obtained by reacting these isocyanate group-containing compounds with active hydrogen group-containing compounds may be used as the hydroxy group-reactive cross-linking agents having isocyanate groups.

In addition, as the isocyanate group-containing compound, since the isocyanate group has a strong reaction activity and easily reacts with a compound having an active hydrogen at room temperature, the active isocyanate group is blocked with a blocking agent from the viewpoint of easy handling. More preferred are isocyanate compounds.

Examples of the blocking agent include phenolxylenolic acid, ethyl acetoacetate, methyl ethyl ketoxime, caprolactam, dimethylpyrazole, dimethyl malonate, and diisopropylamine. Among these, dimethylpyrazole, dimethylmalonate, diisopropylamine, ethyl acetoacetate, and methylethylketoxime-blocked isocyanate are preferred because of their relatively low dissociation temperature.

In addition, blocked isocyanate compounds are also available as commercial products such as BI7991, BI7992, BI7951, BI7960, BI7961, BI7982 (manufactured by Baxendene), Coronate BI-301, Coronate 2507, Coronate 2554 (manufactured by Tosoh Corporation). It is possible.

The carbodiimide group-containing compound used in the present invention is not particularly limited as long as it has two or more carbodiimide groups or tautomeric cyanamide groups in the molecule as functional groups. Examples of such carbodiimide compounds include dicyclohexylmethanecarbodiimide, dicyclohexylcarbodiimide, tetramethylxylylenecarbodiimide, urea-modified carbodiimide, etc. One or a mixture of two or more of these can be used.

Carbodiimide group-containing compounds are also available as commercial products such as Carbodilite V-05, Carbodilite V-05S, Carbodilite V-03, Carbodilite V-09GB (manufactured by Nisshinbo Co., Ltd.), and Stabaxol P (manufactured by Rhein Chemie). It is possible.

The oxazoline group-containing compound used in the present invention is not particularly limited as long as it has an oxazoline group as a functional group in the compound. An oxazoline group-containing copolymer obtained by copolymerizing a monomer containing at least one oxazoline group and at least one other monomer is preferred.
Monomers containing an oxazoline group include, for example, 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2- Oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc., and a mixture of one or more of these can also be used. Among them, 2-isopropenyl-2-oxazoline is suitable because it is easily available industrially.
In the oxazoline group-containing compound, at least one other monomer used for the oxazoline group-containing monomer is not particularly limited as long as it is a monomer copolymerizable with the oxazoline group-containing monomer. acrylic acid esters or methacrylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; acrylic acid , methacrylic acid, itaconic acid, unsaturated carboxylic acids such as maleic acid; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated amides such as acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide; Vinyl esters such as vinyl acetate and vinyl propionate; Vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; Olefins such as ethylene and propylene; Halogen-containing -α,β-unsaturated such as vinyl chloride, vinylidene chloride and vinyl fluoride Monomers; α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene can be mentioned, and these can be used singly or in combination of two or more.

Further, the oxazoline group-containing compounds include, for example, Epocross K-2020E, Epocross K-2010E, Epocross K-2020E, Epocross K-2030E, Epocross WS-300, Epocross WS-500, Epocross WS-700, Epocross RPS-1005, and the like. (manufactured by Nippon Shokubai Co., Ltd.).

The melamine group-containing compound used in the present invention is not particularly limited as long as it has a melamine group as a functional group in the compound. For example, melamine; melamine derivatives; compounds obtained by reacting methylolated melamine with a lower alcohol to partially or completely etherify, and mixtures thereof.

The melamine group-containing compound may be a monomer, a condensate composed of a dimer or higher polymer, or a mixture thereof. Examples of specific melamine group-containing compounds include imino group-type methylated melamine resins, methylol group-type melamine resins, methylol group-type methylated melamine resins, and completely alkyl-type methylated melamine resins.

The resin composition of the present invention and the film using the same may contain other polymers, surfactants, polymer electrolytes, conductive complexes, pigments, dyes, antistatic agents, anti-blocking agents within the scope of the invention. , a lubricant, and the like.

The resin composition of the present invention and the film using it 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 vitamins. Examples include E-based antioxidants and other antioxidants, and these antioxidants may be used alone or in combination of two or more.

The resin composition of the present invention and a film using the same may contain a hindered amine light stabilizer or an ultraviolet absorber to enhance weather resistance. Examples of ultraviolet absorbers include benzotriazole, benzophenone, triazine, and benzoate absorbers.

As a method for blending the cellulose resin, the ester resin exhibiting negative birefringence, and the hydroxyl group-reactive cross-linking agent, methods such as melt blending and solution blending can be used. The melt blending method is a method of producing by melting and kneading a resin and a hydroxy group-reactive cross-linking agent by heating. The solution blending method is a method of dissolving a resin and a hydroxyl group-reactive cross-linking agent in a solvent and blending them. The solution blending method is preferable because non-uniform cross-linking due to cross-linking during blending can be suppressed. As the solvent used for solution blending, any solvent can be used as long as it can dissolve the resin, cross-linking agent, etc., but the boiling point of the solvent is 200° C. or less so that residual solvent is less likely to remain in the film forming process. is preferred, and 170°C or lower is more preferred.

Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichlorethylene, tetrachlorethylene, chlorobenzene, and orthodichlorobenzene; phenols such as phenol and valachlorophenol; benzene, toluene, aromatic hydrocarbons such as xylene, methoxybenzene, mesitylene and 1,2-dimethoxybenzene; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone and N-methyl-2-pyrrolidone Ester-based solvents such as ethyl acetate and butyl acetate; t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2, alcohol solvents such as 4-pentanediol; amide solvents such as dimethylformamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile; ether solvents such as diethyl ether, dibutyl ether and tetrahydrofuran; Solvents such as carbon, ethyl cellosolve, butyl cellosolve, etc. may be used alone or in combination.

Any method may be used as a method for producing a film using the resin composition of the present invention, but production by a solution casting method is preferred. Here, the solution casting method is a method of casting a resin solution (generally referred to as a dope) on a support substrate and then heating to evaporate the solvent to obtain a film. A coating method is not particularly limited, and a usual method can be adopted. For example, T-die method, doctor blade method, bar coater method, slot die method, lip coater method, reverse gravure coating method, micro gravure method, spin coating method, brush coating method, roll coating method, flexographic printing method, and the like. The supporting substrate used is not particularly limited, but examples include polyester, polycarbonate, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polysulfone, poly Polymer substrates such as ethersulfone and epoxy resins, glass substrates such as glass plates and quartz substrates, metal substrates such as aluminum, stainless steel and ferrotype substrates, inorganic substrates such as ceramic substrates, and the like can be used. The base material is preferably a polymer base material or a metal base material.

Since the film of the present invention is excellent in transparency, it can be suitably used as an optical film.

The viscosity of the resin solution when producing an optical film using the resin composition of the present invention can be adjusted by the molecular weight and concentration of each component and the type of solvent. Although the viscosity of the resin solution is not particularly limited, it is preferably 100 to 30,000 cps, more preferably 300 to 20,000 cps, particularly preferably 500 to 10,000 cps, in order to facilitate film coating.

In the present invention, the cellulose-based resin is crosslinked during casting film formation. That is, a hydroxyl-reactive cross-linking agent is added to the dope, cast to form a film, and the reaction is accelerated by heating, drying, and the like.

In the drying step of the coating solution, the drying method is not particularly limited, and ordinary heating means can be employed. Examples include hot air blowers, heating rolls, and far infrared heaters.

In the method for producing a film using the resin composition of the present invention, the drying temperature may be only one step, and in order to maintain the appearance and shorten the drying time, the first step is dried at a low temperature, and the second step and later. Multi-stage drying such as drying at high temperatures may also be used. In order to promote the cross-linking reaction, it is preferable to include a drying step with a drying temperature range of 80°C to 200°C.

In the present invention, the concentrations of the cellulose-based resin, the ester-based resin exhibiting negative birefringence, and the hydroxyl group-reactive cross-linking agent are not particularly limited as long as dissolution and film formation are possible. The method of dissolving the cellulose-based resin, the ester-based resin exhibiting negative birefringence, and the hydroxy group-reactive cross-linking agent may be carried out so that the concentration reaches a predetermined level at the stage of dissolution, or a low concentration may be obtained in advance. After being prepared as a solution, it may be adjusted to a predetermined high-concentration solution in a concentration step. Furthermore, after preparing a high-concentration resin solution of a cellulose resin and an ester-based resin exhibiting negative birefringence in advance, a hydroxy group-reactive cross-linking agent and various additives are added to obtain a predetermined low-concentration resin solution. may be

Since the optical film of the present invention is excellent in retardation properties, it can be suitably used as an optical compensation film.

The method for producing an optical compensation film using the resin composition of the present invention is not particularly limited as a method for expressing retardation. Uniaxial stretching or unbalanced biaxial stretching is preferred. Methods for stretching the optical compensation film include vertical uniaxial stretching by roll stretching, horizontal uniaxial stretching by tenter stretching, oblique stretching, and unbalanced successive biaxial stretching and unbalanced simultaneous biaxial stretching by combining these methods. can be used.

The thickness of the unstretched film before stretching is preferably 5 to 200 μm, more preferably 5 to 150 μm, particularly preferably 5 to 100 μm, from the viewpoints of ease of stretching and suitability for thinning of optical members. .

The thickness of the optical compensation film after stretching is preferably 5 to 100 μm, more preferably 5 to 60 μm, in order to make the image display device thinner.

The stretching temperature is not particularly limited, but is preferably 50 to 200° C., more preferably 100 to 200° C., since good retardation properties can be obtained. The stretching ratio for uniaxial stretching is not particularly limited, but it is preferably 1.05 to 4.0 times, more preferably 1.1 to 3.5 times, because good retardation properties can be obtained. The stretching ratio of the unbalanced biaxial stretching is not particularly limited, but is preferably 1.05 to 4.0 times, more preferably 1.1 to 3.5 times in the longitudinal direction because of excellent optical properties. Retardation can be controlled by stretching temperature and stretching ratio.

In the optical compensation film using the resin composition of the present invention, the content of the cellulose resin, the total degree of substitution of the cellulose resin contained, the degree of substitution distribution at the 2-, 3-, and 6-positions of the substituents, and the draw ratio You can adjust the retardation by

A film using the resin composition of the present invention is suitable for use as an optical compensation film, and the optical compensation film is characterized by having excellent retardation properties and excellent wavelength dispersion properties.

The retardation characteristics of the optical compensation film using the resin composition of the present invention differ depending on the intended optical compensation film. For example, 1) the retardation (Re) represented by the following formula (1) is preferably 50 to 300 nm, more preferably 100 to 300 nm, particularly preferably 120 to 280 nm, and the Nz coefficient represented by the following formula (2) is preferably 0.3 to 1.0, more preferably 0.3 to 1.0. 4 to 0.8, and the like. The retardation characteristics at this time are measured using a fully automatic birefringence meter (trade name: KOBRA-21ADH, manufactured by Oji Scientific Instruments Co., Ltd.) under the condition of a measurement wavelength of 589 nm.

These have retardation properties that are difficult to develop with conventional optical compensation films made of cellulose-based resins.

Re=(ny−nx)×d (1)
Nz=(ny−nz)/(ny−nx) (2)
Rth=[(nx+ny)/2−nz]×d (3)
(Wherein, nx represents the refractive index in the fast axis direction in the film plane, ny represents the refractive index in the slow axis direction in the film plane, nz represents the out-of-plane refractive index of the film, and d represents the film thickness.)
The wavelength dispersion characteristic of the optical film of the present invention is preferably 0.60<Re(450)/Re(550)<1.05, more preferably 0.70<Re(450 )/Re(550)<1.02, particularly preferably 0.75<Re(450)/Re(550)<1.00.

When the cellulose-based resin of the present invention is used alone, an optical film with low wavelength dispersion can be provided. A resin composition obtained by blending this film with an ester resin exhibiting negative birefringence in the stretching direction can generally provide an optical film exhibiting reverse wavelength dispersion.

It is generally difficult for an optical compensation film using a cellulose-based resin to simultaneously satisfy these retardation characteristics and wavelength dispersion characteristics, but the optical compensation film according to the present invention satisfies these characteristics at the same time. It is something to do.

The optical compensation film using the resin composition of the present invention preferably has a thickness of 5 to 200 μm, more preferably 10 to 100 μm, from the viewpoint of film handling property and suitability for thinning of optical members. 20-80 μm is particularly preferred, and 10-60 μm is most preferred.

The optical compensation film using the resin composition of the present invention preferably has a transmittance of 85% or more, more preferably 90% or more when formed into a film, in order to avoid a decrease in the amount of light in an image display device.

The optical compensation film using the resin composition of the present invention preferably has a haze of 3% or less, more preferably 1.5% or less. By controlling the haze within the above range, a high-contrast image can be obtained when incorporated as a retardation film into a display device.

The optical compensation film using the resin composition of the present invention avoids a decrease in the light amount of the screen display device in a high-temperature and high-humidity environment and maintains a high-contrast image. It preferably has a haze of 3% or less and a transmittance of 85% or more, more preferably 90%.

The optical compensation film using the resin composition of the present invention can be laminated with a film containing other resins, if necessary. Other resins include, for example, polyether sulfone, polyarylate, polyethylene terephthalate, polynaphthalene terephthalate, polycarbonate, cyclic polyolefin, maleimide-based resin, fluorine-based resin, and polyimide. It is also possible to laminate a liquid crystal layer, a hard coat layer, a gas barrier layer, and a layer with a controlled refractive index (low reflection layer).

The optical compensation film using the resin composition of the present invention is suitably used in polarizing plates used for applications such as liquid crystal display devices and organic EL display devices. Moreover, the polarizing plate is preferably used as an image display device.

The resin composition of the present invention and a film using the same can be suitably used for polarizing plates, liquid crystal display devices, organic EL display devices, etc., and exhibits excellent display performance and high stability under high temperature and high humidity. be able to.

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

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

<Measurement of retardation characteristics>
Retardation characteristics of the retardation film were measured using light with a wavelength of 589 nm using an automatic sample tilt type birefringence meter (manufactured by Oji Scientific Instruments, trade name: KOBRA-WR).
<Measurement of light transmittance and haze of retardation film>
The light transmittance and haze of the prepared film were measured using a haze meter (manufactured by Nippon Denshoku Industries, trade name: NDH2000). Each was measured according to JIS-K 7136 (2000 edition).
<Moisture and heat resistance test>
A constant temperature and humidity chamber (manufactured by Yamato Scientific Co., Ltd., product name: IG400) is used in a high temperature and high humidity environment of 65 ° C. relative humidity of 90%, and the total light transmittance and haze after 120 hours are examined (hereinafter referred to as "moisture resistance We measured the resistance to moisture and heat by “heat test”).

Synthesis Example 1 (Synthesis of ester-based resin (1) (diisopropyl fumarate/monoethyl fumarate-based resin) exhibiting negative birefringence)
42 g of diisopropyl fumarate, 7.7 g of monoethyl fumarate, and 0.66 g of tert-butyl peroxypivalate, which is a polymerization initiator, were placed in a glass ampoule with a capacity of 75 mL. did. This ampoule was placed in a constant temperature bath at 55° C. and held for 24 hours to effect 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 dropped into 4 L of hexane for precipitation, and then vacuum-dried at 80° C. for 10 hours to obtain 27 g of an ester resin (1) exhibiting negative birefringence. The resulting ester resin (1) exhibiting negative birefringence had a number average molecular weight of 53,000, diisopropyl fumarate residue units of 82 mol %, and monoethyl fumarate residue units of 18 mol %.

Synthesis Example 2 (Synthesis of ester resin (2) (monoethyl fumarate/diisopropyl fumarate/n-propyl 4-methoxycinnamate resin) exhibiting negative birefringence)
600 g of distilled water, 3.4 g of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., trade name Metolose 60SH-50) as a dispersing agent, and diisopropyl fumarate were placed in a 1-liter reactor equipped with a stirrer, condenser, nitrogen inlet tube and thermometer. 212.3 g, monoethyl fumarate 52.9 g, n-propyl 4-methoxycinnamate 134.7 g and oil-soluble radical initiator 2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy ) 20.3 g of hexane (T ₁₀ =66° C.) was added, and after nitrogen bubbling was performed for 1 hour, the temperature was started to rise while stirring at 400 rpm. was maintained at 73° C. for 48 hours to carry out radical suspension polymerization. After completion of the polymerization reaction, the contents were recovered from the reactor, the polymer was separated by filtration, washed 6 times with 2000 g of distilled water, and washed with 2000 g of a methanol/water mixed solvent (weight ratio 80/20). It was washed twice and vacuum-dried at 80° C. for 12 hours to obtain 282 g (70% yield) of an ester resin (2) exhibiting negative birefringence. The resulting ester resin (2) exhibiting negative birefringence had a number average molecular weight of 41,000, diisopropyl fumarate residue units of 56 mol%, monoethyl fumarate residue units of 14 mol%, and 4-methoxy cinnamon. It was 30 mol % of n-propyl acid.

Example 1
Ethyl cellulose (ETHOCEL standard 300 manufactured by Dow Chemical Co., molecular weight Mn = 85,000, molecular weight Mw = 263,000, Mw/Mn = 3.1, total degree of substitution DS = 2.51) as a cellulose-based resin Toluene/ethyl acetate = 8/2 (weight ratio) solution to obtain a 15% by weight resin solution, poured onto a polyethylene terephthalate film by a coater, dried at a drying temperature of 40°C and then at 155°C in two steps, and then a film of 150 mm in width. (Resin composition) was obtained (cellulose resin: 59.88% by weight, ester resin exhibiting negative birefringence: 39.87% by weight, hydroxy group-reactive cross-linking agent: 0.25% by weight). The resulting film had a light transmittance of 92% and a haze of 0.7%, and after the wet heat resistance test, had a light transmittance of 91% and a haze of 1.5%.

Moreover, after cutting the obtained film into a 50 mm square, it was uniaxially stretched 2.0 times at 140° C. (thickness after stretching: 30 μm) to obtain a film.

The light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and moist heat resistance of the obtained film were measured. Table 1 shows the results.

The obtained film had a high light transmittance, a low haze, and a high resistance to moist heat.

Example 2
24.98 g of ethyl cellulose used in Example 1, 14.82 g of ester resin (2) exhibiting negative birefringence obtained in Synthesis Example 2, and 0.2 g of carbodiimide-based cross-linking agent Carbodilite V-05 (manufactured by Nisshinbo) was dissolved in a toluene/ethyl acetate = 8/2 (weight ratio) solution to obtain a 15% by weight resin solution, which was poured onto a polyethylene terephthalate film using a coater, dried at a temperature of 40°C and then dried at 155°C in two stages. After that, a film (resin composition) having a width of 150 mm was obtained (cellulose resin: 62.5% by weight, ester resin exhibiting negative birefringence: 37.0% by weight, hydroxy group-reactive cross-linking agent: 0.5% by weight). The resulting film had a light transmittance of 92% and a haze of 0.8%, and a light transmittance of 90% and a haze of 2.1% after the moisture and heat resistance test.
Also, after cutting the obtained film into a 50 mm square, it was uniaxially stretched 2.0 times at 140° C. (thickness after stretching: 30 μm) to obtain an optical compensation film.

The obtained optical compensation film was measured for light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and moist heat resistance. The results are also shown in Table 1.

The obtained optical compensation film had a high light transmittance, a low haze, and a high resistance to moist heat.

Example 3
24.98 g of the ethyl cellulose used in Example 1, 14.92 g of the ester resin (2) exhibiting negative birefringence obtained in Synthesis Example 2, and 0.1 g of the blocked isocyanate cross-linking agent BI7951 (manufactured by BAXENDENE) were combined. It was dissolved in a toluene/ethyl acetate = 8/2 (weight ratio) solution to obtain a 15% by weight resin solution, which was poured onto a polyethylene terephthalate film using a coater, dried at a temperature of 40°C and then dried at 155°C in two steps. , a film (resin composition) having a width of 150 mm was obtained (cellulose-based resin: 62.45% by weight, ester-based resin exhibiting negative birefringence: 37.3% by weight, hydroxy group-reactive cross-linking agent: 0.5% by weight). 25% by weight). The resulting film had a light transmittance of 92% and a haze of 0.8%, and after the wet heat resistance test, had a light transmittance of 90% and a haze of 1.7%.
Also, after cutting the obtained film into a 50 mm square, it was uniaxially stretched 2.0 times at 140° C. (thickness after stretching: 30 μm) to obtain an optical compensation film.

The obtained optical compensation film was measured for light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and moist heat resistance. The results are also shown in Table 1.

The obtained optical compensation film had a high light transmittance, a low haze, and a high moist heat resistance.

Comparative example 1
22.0 g of ethyl cellulose used in Example 1 as the cellulose resin, 14.0 g of the ester resin (1) exhibiting negative birefringence obtained in Synthesis Example 1, and a blocked isocyanate cross-linking agent BI7951 (manufactured by BAXENDENE) ) was dissolved in a toluene/ethyl acetate = 8/2 (weight ratio) solution to obtain a 15% by weight resin solution, which was poured onto a polyethylene terephthalate film by a coater, dried at a temperature of 40°C and then heated to 155°C. After drying in two steps, a film (resin composition) having a width of 150 mm was obtained (cellulose resin: 55% by weight, ester resin exhibiting negative birefringence: 35% by weight, hydroxy group-reactive cross-linking agent: 10% by weight). The light transmittance, haze and moist heat resistance of the obtained film were measured. Table 2 shows the results.

The resulting film had a light transmittance of 82%, a haze of 4.2%, and a light transmittance of 85% and a haze of 5.8% after the heat and humidity resistance test, showing poor heat and humidity resistance.

Comparative example 2
24.0 g of the ethyl cellulose used in Example 1 and 16.0 g of the ester resin (1) exhibiting negative birefringence obtained in Synthesis Example 1 were added to a toluene/ethyl acetate = 8/2 (weight ratio) solution. It was dissolved to form a 15% by weight resin solution, which was poured onto a polyethylene terephthalate film using a coater, dried at a drying temperature of 40° C. and then dried at 155° C. in two steps to obtain a film (resin composition) with a width of 150 mm ( Cellulose-based resin: 60% by weight, Ester-based resin exhibiting negative birefringence: 40% by weight).

The light transmittance, haze and moist heat resistance of the obtained film were measured. Table 2 shows the results.

The resulting film had a light transmittance of 92%, a haze of 0.7%, and a light transmittance of 88% and a haze of 3.3% after the heat and humidity resistance test, showing poor heat and humidity resistance.

Claims (5)

Cellulose-based resin having a substitution degree of 1.5 to 2.95 represented by the following general formula (1) and 50 to 98.99% by weight, and a negative birefringence represented by the following general formula (2) 1 to 49.99% by weight of an ester resin containing a cinnamic ester residue unit and/or a fumarate ester residue unit represented by the following general formula (3), an isocyanate group, a carbodiimide group, a vinyl sulfone group, 0.01 to 5% by weight of a hydroxy group-reactive cross-linking agent having at least one group selected from an epoxy group, an oxazoline group, a melamine group, a dialdehyde group, and an ethyleneimine group. .

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

(In the formula, R ₄ represents an alkyl group having 1 to 12 carbon atoms. X and Y are each independently hydrogen, 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, a hydroxyl group, or 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.) A film using the resin composition according to claim 1 . 3. The film according to claim 2 , having a haze of 3% or less and a total light transmittance of 85% or more after 120 hours in an environment of 65° C. and 90% relative humidity. Using the film according to claim 2 or claim 3 , the retardation (Re) represented by the following formula (1) is 30 to 300 nm, and the Nz coefficient represented by the following formula (2) is 0 .3 to 1.0, and the ratio Re(450)/Re(550) of the retardation at 450 nm and the retardation at 550 nm is 0.60<Re(450)/Re(550) )<1.05.
Re=(ny−nx)×d (1)
Nz=(ny−nz)/(ny−nx) (2)
(Wherein, nx represents the refractive index in the fast axis direction in the film plane, ny represents the refractive index in the slow axis direction in the film plane, nz represents the out-of-plane refractive index of the film, and d represents the film thickness.) A polarizing plate using the optical film according to claim 4 .