JP7585604B2 - Resin composition and optical film using same - Google Patents

Description

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

In recent years, there has been a growing demand for display performance and durability in various displays, and it has become an issue to improve response speed and compensate for a wider range of viewing angles, such as contrast and color balance when the displayed image is observed from an oblique direction. To solve these issues, display elements of the VA (Vertical Alignment) type, OCB (Optical Compensated Bend) type, and IPS (In-Plane Switching) type have been developed, and optical compensation film materials with various retardation expression properties according to each liquid crystal type are required.

Conventional optical compensation films include stretched films of cellulose resins, polycarbonates, cyclic polyolefins, etc. In particular, stretched films made of cellulose resins such as cellulose acylate are widely used as optical compensation films for liquid crystal display devices due to their transparency, toughness, moisture permeability (necessary for processing), and low wavelength dispersion.

However, optical compensation films made of cellulose-based resins have some problems. For example, cellulose-based resin films are processed into optical compensation films with retardation values suited to various displays by adjusting the stretching conditions, but the three-dimensional refractive index of the film obtained by uniaxial or biaxial stretching of cellulose-based resin films is ny≧nx>nz. In order to manufacture optical compensation films with other three-dimensional refractive indexes, such as ny>nz>nx or ny=nz>nx, a special stretching method is required, such as bonding a heat-shrinkable film to one or both sides of the film and subjecting the laminate to a heat stretching treatment to apply a shrinking force in the thickness direction of the polymer film, and it is also difficult to control the refractive index (retardation value) (see, for example, Patent Documents 1 to 3). Here, nx represents the refractive index in the fast axis direction (the direction with the smallest refractive index) in the film plane, ny represents the refractive index in the slow axis direction (the direction with the largest refractive index) in the film plane, and nz represents the refractive index outside the film plane (thickness direction).

Furthermore, cellulose-based resin films are generally produced by a solvent casting method, but cellulose-based resin films formed by the casting method have an out-of-plane retardation (Rth) of about 40 nm in the film thickness direction, which causes problems such as color shifts in IPS mode liquid crystal displays, etc. Here, the out-of-plane retardation (Rth) is a retardation value expressed by the following formula.
Rth=[(nx+ny)/2-nz]×d
(In the formula, 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 refractive index outside the film plane, and d represents the film thickness.)
Further, 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 resin is nz>ny>nx, and in order to obtain an optical compensation film that exhibits the above three-dimensional refractive index, lamination with other optical compensation films, etc. is necessary.

In response to this, resin compositions and optical compensation films using the same have been proposed as optical compensation films that exhibit the above three-dimensional refractive index (see, for example, Patent Documents 5 to 7). Although Patent Documents 5 to 7 have excellent performance as optical compensation films, there is a demand for optical compensation films that exhibit the desired Re with thinner films.

Here, optical compensation films are generally used as anti-reflection layers for reflective liquid crystal displays, touch panels, and organic electroluminescence (EL) displays, and in these applications, optical compensation films with larger retardation (hereinafter referred to as "reverse wavelength dispersion films") are required, particularly in the longer wavelength range. For example, when a reverse wavelength dispersion film is used as an optical compensation film for an organic EL circular polarizer, the phase difference is preferably about 1/4 of the measured wavelength λ, and the ratio of the retardation at 450 nm to the retardation at 550 nm, Re(450)/Re(550), varies depending on the display configuration, but is generally preferably about 0.80 to 0.86. In addition, in consideration of the trend toward thinner display devices, the reverse wavelength dispersion films used are also required to be thin. Various optical compensation films have been developed to meet the above-mentioned required characteristics.

Retardation films containing cellulose resins and fumaric acid ester polymers have been proposed as retardation films (optical compensation films) that exhibit the above three-dimensional refractive index and are used as reverse wavelength dispersion films (see, for example, Patent Documents 8 and 9). However, the retardation films described in Patent Documents 8 and 9 have issues with durability in high-temperature environments due to embrittlement and coloring caused by decomposition of ethyl cellulose, and coloring of ester resins that have many aromatic groups or polycyclic aromatic groups and exhibit negative birefringence, and there is a demand for optical compensation films that are more stable at high temperatures.

Patent No. 2818983 Japanese Patent Application Publication No. 5-297223 Japanese Patent Application Publication No. 5-323120 JP 2008-64817 A JP 2013-28741 A JP 2014-125609 A JP 2014-125610 A JP 2015-157928 A JP 2019-19303 A

The present invention was made in consideration of the above problems, and its purpose is to provide an optical film that uses a resin composition that has excellent retardation properties and wavelength dispersion properties and is highly stable at high temperatures.

As a result of intensive research into solving the above problems, the inventors discovered that a resin composition containing a specific antioxidant and an optical film using the same could solve the above problems, and thus completed the present invention.

That is, the present invention relates to a cellulose resin (A) represented by the following general formula (1) in an amount of 50% by weight or more and 98.99% by weight or less:
A cinnamic acid ester copolymer (B) containing a cinnamic acid ester residue unit represented by the following general formula (2) and a residue unit represented by the following general formula (3) in an amount of 1% by weight or more and 49.99% by weight or less:
The present invention relates to a resin composition containing 0.01% by weight or more and 5.0% by weight or less of an antioxidant (C) having a molecular weight of 350 or more.

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

(In the formula, R ₄ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R ₅ to R ₉ represent a hydrogen atom, 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 thiol group, an amide group, an amino group, a hydroxyl group, an alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms; and Y 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 thiol group, an amide group, or an ester group.)

(In the formula, R ₁₀ represents a 5-membered or 6-membered heterocyclic residue containing one or more nitrogen or oxygen atoms as heteroatoms (the 5-membered or 6-membered heterocyclic residue may form a condensed ring structure with another ring structure).)

The contents of the present invention are explained in detail below.

The resin composition of the present invention comprises 50% by weight or more and 98.99% by weight or less of the cellulose resin (A) represented by the general formula (1),
a cinnamate ester copolymer (B) containing a cinnamate ester residue unit represented by the general formula (2) and a residue unit represented by the general formula (3) in an amount of 1% by weight or more and 49.99% by weight or less;
The resin composition contains 0.01% by weight or more and 5.0% by weight or less of an antioxidant (C) having a molecular weight of 350 or more.

The cellulose resin (A) 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 a hydrogen atom or a substituent having 1 to 12 carbon atoms.)

Examples of cellulose resins include cellulose and/or cellulose derivatives. Examples of cellulose derivatives include cellulose ethers in which at least a portion of the hydroxyl groups in cellulose are etherified, and cellulose ether esters in which at least a portion of the hydroxyl groups are esterified. The resin composition of the present invention may contain one or more of these cellulose resins.

In the present invention, the degree of substitution (hereinafter referred to as "DS") of the cellulose resin is preferably 1.5 to 2.95, more preferably 1.8 to 2.8. This makes the resin composition of the present invention more excellent in terms of its solubility, compatibility, and stretchability. Here, DS can be defined as the ratio of hydroxyl groups of cellulose in a cellulose derivative to which they are substituted, and DS = 3 when 100% is substituted. The DS can be measured from the gas chromatography peak area after the elimination of the substituents after the reaction of cellulose to a derivative, as described in the 17th Revised Japanese Pharmacopoeia. When there are two or more types of substituents, the degree of substitution is expressed separately for each type. When ethyl cellulose is used, DS is the degree of substitution of the ethyl group.

Since the cellulose resin has excellent mechanical properties and excellent moldability during film formation, it has a number average molecular weight (Mn) of 1×10 ³ to 1×10 ⁶ , and more preferably 5×10 ³ to 2×10 ⁵ , calculated as standard polystyrene, obtained from an elution curve measured by gel permeation chromatography (GPC).

The cellulose resin is preferably a cellulose ether. This provides better compatibility with the cinnamate ester copolymer (B), and the resulting composition has a larger in-plane retardation Re and is excellent in stretchability.

Cellulose ether is a polymer in which β-glucose units are polymerized in a linear chain, and some or all of the hydroxyl groups at the 2nd, 3rd, and 6th positions of the glucose units are etherified.

In the cellulose ether of formula (1), R ₁ to R ₃ each independently represent a hydrogen atom or a substituent having 1 to 12 carbon atoms. From the viewpoint of solubility and compatibility, R ₁ to R ₃ are preferably 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, a t-butyl group, a cyclohexyl group, a phenonyl group, a benzyl group, and a naphthyl group. Among these, from the viewpoint of solubility and compatibility, an alkyl group having 1 to 5 carbon atoms, that is, a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group, are preferred.

The hydroxyl groups of the cellulose ether used in the present invention may be substituted with one type of ether group, or may be substituted with two or more types of ether groups, such as ethyl methyl cellulose. In addition to the ether groups, they may also be substituted with ester groups.

Examples of cellulose ethers include alkyl celluloses such as methyl cellulose, ethyl cellulose, and propyl cellulose; hydroxyalkyl celluloses such as hydroxyethyl cellulose and hydroxypropyl cellulose; aralkyl celluloses such as benzyl cellulose and trityl cellulose; cyanoalkyl celluloses such as cyanoethyl cellulose; carboxyalkyl celluloses such as carboxymethyl cellulose and carboxyethyl cellulose; carboxyalkyl alkyl celluloses such as carboxymethyl methyl cellulose and carboxymethyl ethyl cellulose; and aminoalkyl celluloses such as aminoethyl cellulose. The cellulose ether is preferably at least one member of the group consisting of methyl cellulose, ethyl cellulose, and propyl cellulose. This provides better compatibility with the cinnamic acid ester copolymer.

Cellulose ethers are generally synthesized by alkaline decomposition of cellulose pulp obtained from wood or cotton, and etherification of the alkaline decomposed cellulose pulp. Examples of the alkali that can be used include hydroxides of alkali metals such as lithium, potassium, and sodium, and ammonia. The alkali is generally used as an aqueous solution. The alkaline decomposed cellulose pulp is then etherified by contacting it with an etherification agent. Examples of the etherification 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; and alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide. The desired etherification agent can be used depending on the type of cellulose derivative to be produced, and the etherification agents can be used alone or in combination.

For example, when etherifying cellulose resin, an example method is to carry out an etherification reaction with a chloride or the like after alkali treatment.

If necessary, after etherification, depolymerization may be performed with hydrogen chloride, hydrogen bromide, hydrochloric acid, sulfuric acid, etc. to adjust the viscosity.

The resin composition of the present invention contains a cinnamate ester copolymer (B) containing a cinnamate ester residue unit represented by the following general formula (2) and a residue unit represented by the following general formula (3):

(In the formula, R ₄ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R ₅ to R ₉ represent a hydrogen atom, 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 thiol group, an amido group, an amino group, a hydroxyl group, an alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms; and Y 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, or a thiol group.)

(In the formula, R ₁₀ represents a 5-membered or 6-membered heterocyclic residue containing one or more nitrogen or oxygen atoms as heteroatoms (the 5-membered or 6-membered heterocyclic residue may form a condensed ring structure with another ring structure).)

The cinnamate ester copolymer (B) exhibits negative birefringence. This is due to the inclusion of residue units represented by the general formula (2) and the general formula (3).

Here, the positive and negative birefringence are defined as follows.
Negative birefringence is when the stretching direction is the fast axis direction, and positive birefringence is when the perpendicular direction to the stretching direction is the fast axis direction. In other words, a resin that exhibits positive birefringence when uniaxially stretched has a small refractive index in the direction perpendicular to the stretching axis (fast axis: perpendicular to the stretching direction), and a resin that exhibits negative birefringence when uniaxially stretched has a small refractive index in the direction of the stretching axis (fast axis: stretching direction). The high expression of negative birefringence in the cinnamate ester copolymer (B) allows the optical compensation film to be made thinner.

_R4 in the general formula (2) represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, an s-butyl group, a t-butyl group, and an ethylhexyl group.
_R5 to _R9 in general formula (2) each represent a hydrogen atom, 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 thiol group, an amino group, a hydroxyl group, an alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms.
Y in the general formula (2) 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, or a thiol group.

Specific examples of the residue unit represented by the general formula (2) include α-cyano-hydroxycinnamic acid ester residue units such as α-cyano-4-hydroxycinnamic acid methyl residue unit, α-cyano-2-hydroxycinnamic acid ethyl residue unit, α-cyano-3-hydroxycinnamic acid ethyl residue unit, α-cyano-4-hydroxycinnamic acid ethyl residue unit, and α-cyano-2,4-dihydroxycinnamic acid methyl residue unit; α-cyano-4-carboxycinnamic acid ester residue units such as α-cyano-4-carboxycinnamic acid methyl residue unit, α-cyano-4-carboxycinnamic acid ethyl residue unit, α-cyano-2,3-dicarboxycinnamic acid methyl residue unit, and α-cyano-2,3-dicarboxycinnamic acid ethyl residue unit; α-cyano-2-carboxy-3-hydroxycinnamic acid methyl residue unit, and α-cyano-2-carboxy-3-hydroxycinnamic acid ethyl residue unit; Acid ester residue units; hydroxybenzylidene malonate diester residue units such as dimethyl hydroxybenzylidene malonate residue units, diethyl hydroxybenzylidene malonate residue units, di-n-propyl hydroxybenzylidene malonate residue units, and diisopropyl hydroxybenzylidene malonate residue units; carboxybenzylidene malonate diester residue units such as dimethyl carboxybenzylidene malonate residue units, diethyl carboxybenzylidene malonate residue units, di-n-propyl carboxybenzylidene malonate residue units, and diisopropyl carboxybenzylidene malonate residue units; are preferred, and α-cyano-hydroxycinnamic acid ester residue units; α-cyano-carboxycinnamic acid ester residue units; carboxybenzal malononitrile residue units, hydroxybenzylidene malonate diester residue units, and carboxybenzylidene malonate diester residue units are even more preferred.

In the cinnamic acid ester copolymer (B), the residue unit represented by the general formula (2) may contain one type of the residue unit in the above examples, or may contain two or more types.

In general formula (3), _R10 represents a 5-membered or 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as heteroatoms (the 5-membered or 6-membered heterocyclic residue may form a condensed ring structure with another ring structure).

Specific examples of the residue unit represented by general formula (3) include 1-vinylpyrrole residue unit, 2-vinylpyrrole residue unit, 1-vinylindole residue unit, 9-vinylcarbazole residue unit, 2-vinylquinoline residue unit, 4-vinylquinoline residue unit, N-vinylphthalimide residue unit, N-vinylsuccinimide residue unit, 2-vinylfuran residue unit, 2-vinylbenzofuran residue unit, styrene residue unit, and 2-vinylnaphthalene residue unit, and more preferably 9-vinylcarbazole residue unit and N-vinylphthalimide residue unit.

In the cinnamate ester copolymer (B), the monomer component related to the cinnamate ester residue unit of the general formula (2) preferably comprises 21 mol% or more and 50 mol% or less relative to 100 mol% of the total of all monomer components.

In addition to the general formulas (2) and (3), the cinnamic acid ester copolymer (B) preferably has a residue unit represented by the following formula (4):

(Here, R ₁₁ and R ₁₂ each independently represent a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.)

In the residue unit represented by formula (4), R ₁₁ and R ₁₂ each independently represent a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.

Examples of the linear alkyl group having 1 to 12 carbon atoms for R ₁₁ and R ₁₂ include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, and an n-hexyl group.
Examples of the branched alkyl group having 1 to 12 carbon atoms for R ₁₁ and R ₁₂ include an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.
Examples of the cyclic alkyl group having 3 to 6 carbon atoms for R ₁₁ and R ₁₂ include a cyclopropyl group, a cyclobutyl group, and a cyclohexyl group.

As R ₁₁ and R ₁₂ in general formula (4), a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a sec-pentyl group, a 3-pentyl group, a neopentyl group, a hexyl group, an isohexyl group, or a neohexyl group is preferable, since the ratio Re(450)/Re(550) of the in-plane retardation (Re) at a light wavelength of 450 nm to the in-plane retardation (Re) at a light wavelength of 550 nm is good, and a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, or an isobutyl group is more preferable.

The residue unit represented by the general formula (4) is preferably an acrylic resin residue unit. Specific examples of the acrylic resin residue unit represented by the general formula (4) include an acrylic acid residue unit, a methacrylic acid residue unit, a 2-ethylacrylic acid residue unit, a 2-propylacrylic acid residue unit, a 2-isopropylacrylic acid residue unit, a 2-pentylacrylic acid residue unit, a 2-hexylacrylic acid residue unit, a methyl acrylate residue unit, an ethyl acrylate residue unit, an n-propyl acrylate residue unit, an isopropyl acrylate residue unit, an n-butyl acrylate residue unit, an isobutyl acrylate residue unit, a sec-butyl acrylate residue unit, an n-pentyl acrylate residue unit, an isopentyl acrylate residue unit, a sec-pentyl acrylate residue unit, a 3-pentyl acrylate residue unit, a neopentyl acrylate residue unit, an n-hexyl acrylate residue unit, an isohexyl acrylate residue unit, a neohexyl acrylate residue unit, a methyl methacrylate residue unit, Examples of the methacrylate residue unit include ethyl methacrylate residue unit, n-propyl methacrylate residue unit, isopropyl methacrylate residue unit, n-butyl methacrylate residue unit, isobutyl methacrylate residue unit, sec-butyl methacrylate residue unit, n-pentyl methacrylate residue unit, isopentyl methacrylate residue unit, sec-pentyl methacrylate residue unit, 3-pentyl methacrylate residue unit, neopentyl methacrylate residue unit, n-hexyl methacrylate residue unit, isohexyl methacrylate residue unit, neohexyl methacrylate residue unit, methyl 2-ethylacrylate residue unit, ethyl 2-ethylacrylate residue unit, n-propyl 2-ethylacrylate residue unit, isopropyl 2-ethylacrylate residue unit, n-butyl 2-ethylacrylate residue unit, isobutyl 2-ethylacrylate residue unit, and sec-butyl 2-ethylacrylate residue unit.

Among these, the ratio Re(450)/Re(550) of the in-plane retardation (Re) at a light wavelength of 450 nm to the in-plane retardation (Re) at a light wavelength of 550 nm is favorable, and therefore, methyl acrylate residue units, ethyl acrylate residue units, n-propyl acrylate residue units, isopropyl acrylate residue units, n-butyl acrylate residue units, isobutyl acrylate residue units, sec-butyl acrylate residue units, methyl methacrylate residue units, ethyl methacrylate residue units, n-propyl methacrylate residue units, isopropyl methacrylate residue units, n-butyl methacrylate residue units, methacrylate isobutyl methacrylate residue unit, sec-butyl methacrylate residue unit, methyl methacrylate residue unit, ethyl methacrylate residue unit, n-propyl methacrylate residue unit, isopropyl methacrylate residue unit, n-butyl methacrylate residue unit, isobutyl methacrylate residue unit, and sec-butyl methacrylate residue unit are preferred, and methyl methacrylate residue unit, ethyl methacrylate residue unit, n-propyl methacrylate residue unit, isopropyl methacrylate residue unit, n-butyl methacrylate residue unit, isobutyl methacrylate residue unit, and sec-butyl methacrylate residue unit are more preferred.

The cinnamic acid ester copolymer (B) preferably contains a cinnamic acid ester residue unit represented by the general formula (2), a residue unit represented by the general formula (3), and a residue unit represented by the general formula (4). The cinnamic acid ester copolymer (B) exhibits good compatibility and is more suitable for facilitating the formation of a composite with a different polymer, and is therefore preferably an α-cyano-2-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, an α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, an α-cyano-2-hydroxycinnamic acid ester-1-vinylindole-acrylic acid ester copolymer, an α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid ester copolymer, an α-cyano-3-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, an α-cyano-3-hydroxycinnamic acid ester-3-vinylnaphthalene ... Hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-1-vinylindole-acrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid ester copolymer, 4-hydroxy-α-cyanocinnamic acid ester-styrene-acrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester-1-vinylindole-acrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester-9-vinyl α-cyano-3-hydroxycinnamic acid ester-styrene-methacrylic acid ester copolymer, 2-hydroxy-α-cyanocinnamic acid ester-2-vinylnaphthalene-methacrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-1-vinylindole-methacrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole-methacrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-styrene-methacrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-2-vinylnaphthalene-methacrylic acid ester Copolymers, α-cyano-3-hydroxycinnamic acid ester-1-vinyl indole-methacrylic acid ester copolymers, α-cyano-3-hydroxycinnamic acid ester-9-vinyl carbazole-methacrylic acid ester copolymers, α-cyano-4-hydroxycinnamic acid ester-styrene-methacrylic acid ester copolymers, α-cyano-4-hydroxycinnamic acid ester-2-vinyl naphthalene-methacrylic acid ester copolymers, α-cyano-4-hydroxycinnamic acid ester-1-vinyl indole-methacrylic acid ester copolymers, and α-cyano-4-hydroxycinnamic acid ester-9-vinyl carbazole-methacrylic acid ester copolymers are preferred.

The cinnamate ester copolymer (B) is characterized by having a high retardation even in a thin film because it contains a residue unit represented by general formula (2), a residue unit represented by general formula (3), and a residue unit represented by general formula (4).

In the cinnamate ester copolymer (B), the monomer component related to the cinnamate ester residue unit of the general formula (2) preferably comprises 21 mol% or more and 50 mol% or less relative to the total of 100 mol% of all monomer components. The residue unit represented by the general formula (3) preferably comprises 21 mol% or more and 65 mol% or less relative to the total of 100 mol% of all monomer components.

When the cinnamic acid ester copolymer (B) contains residue units of formula (2) and formula (3), the monomer component of formula (2) is preferably contained in an amount of 21 mol% to 70 mol%, and more preferably 35 mol% to 60 mol%, relative to 100 mol% of the total of formula (2) and formula (3).

When the cinnamic acid ester copolymer (B) contains the residue units of formula (2), formula (3) and formula (4), the content of each residue unit component is preferably from 21 mol% to 49 mol% (2), from 35 mol% to 60 mol% (3), and from 1 mol% to 30 mol% (4). This provides better retardation properties when the resin composition of the present invention is used as a film.

Here, the composition ratio of the copolymer (B) can be measured by ¹ H-NMR.

The cinnamic acid ester copolymer (B) may contain monomer residue units other than those of the general formulae (2) to (4). Examples of such monomer residue units include styrene residues such as styrene residues and α-methylstyrene residues; acrylic acid residues; acrylic acid ester residues; methacrylic acid residues; methacrylic acid ester residues; vinyl ester residues such as vinyl acetate residues and vinyl propionate residues; vinyl ether residues such as methyl vinyl ether residues, ethyl vinyl ether residues and butyl vinyl ether residues; N-substituted maleimide residues such as N-methylmaleimide residues, N-cyclohexylmaleimide residues and N-phenylmaleimide residues; acrylonitrile residues; methacrylonitrile residues; cinnamic acid residues; fumaric acid ester residues; fumaric acid residues; olefin residues such as ethylene residues and propylene residues.

The cinnamic acid ester copolymer (B) has particularly excellent mechanical properties and excellent moldability during film formation, and therefore has a number average molecular weight (Mn) of preferably 1×10 ³ to 5×10 ⁶ , more preferably 5×10 ³ to 3×10 ⁵ , calculated as standard polystyrene, obtained from an elution curve measured by gel permeation chromatography (GPC).

The cinnamic acid ester copolymer (B) may be produced by any method as long as the copolymer is obtained, and can be produced by radical polymerization.

As a radical polymerization method, for example, any of the following methods can be used: bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, emulsion polymerization, etc.

The antioxidant (C) contained in the resin composition of the present invention has a molecular weight of 350 or more. Preferably, the molecular weight of the antioxidant is 500 or more.

Here, whether the resin composition of the present invention contains an antioxidant can be determined, for example, by measuring the UV-visible absorption spectrum of the resin composition.

The antioxidant (C) functions as a radical scavenger, a peroxide decomposer, and a radical chain initiation inhibitor. These can be used alone or in a mixture of two or more. Examples of radical scavengers include phenol-based antioxidants, amine-based antioxidants, and hindered amine-based stabilizers. Examples of peroxide decomposers include phosphorus-based antioxidants and sulfur-based antioxidants. Examples of radical chain initiation inhibitors include metal deactivators, ultraviolet absorbers, and quenchers. Among these, phenol-based antioxidants and the combination of phenol-based antioxidants with phosphate esters are particularly preferred because they are less coloring and have a large antioxidant effect even in small amounts.

In the present invention, the phenolic antioxidant is a compound having a phenol group and a molecular weight of 350 or more, such as a hindered phenolic antioxidant, a semi-hindered antioxidant, and a less hindered antioxidant. Examples of the hindered phenolic antioxidant include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 1,3,5-tris[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, which are commercially available. Examples of semi-hindered antioxidants include bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, etc. Examples of unhindered phenols include 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, etc. Among these, bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylene bis(oxyethylene)], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate, and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are preferred because they are less likely to be colored and have a large antioxidant effect even in small amounts.

In the present invention, the phosphorus-based antioxidant is not particularly limited as long as it is a compound having a phosphite ester group and a molecular weight of 350 or more, and examples thereof include tris(2,4-di-tert-butylphenyl) phosphite, 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 2,2'-methylenebis(4,6-di-tert-butyl-phenyl)-2-ethylhexyl phosphite, and tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl diphosphonite. Among these, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, tris(2,4-di-tert-butylphenyl) phosphite, and tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyl diphosphonite are particularly preferred, as they are relatively less prone to hydrolysis.

In the present invention, the hindered amine stabilizer is not particularly limited as long as it is a compound having a molecular weight of 350 or more and has a 2,2,6,6-tetramethylpiperidine structure, and examples thereof include bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, 1-methyl 10-(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, dimethyl succinate/1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine polymer, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, [6-[(1,1,3,3-tetramethylbutoxy) 2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl(2,2,6,6-tetramethyl-4-piperidinyl)imino] polymer, bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate, 1,2,3,4-butanetetracarboxylic acid tetrakis(1,2,2,6,6-pentamethylpiperidin-4-yl), 1,2,3,4-butanetetracarboxylic acid tetrakis(2,2,6,6-tetramethylpiperidin-4-yl), and the like. Among the hindered amine stabilizers, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate and bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl) carbonate are preferred due to their low compatibility and coloring.

In the present invention, the sulfur-based antioxidant is not particularly limited as long as it is a compound having a thioether group and a molecular weight of 350 or more, and examples thereof include 2,2-bis[[3-(dodecylthio)propionic acid]-1,3-propanediyl, ditridecyl 3,3'-thiobispropionate, and distearyl thiodipropionate.

In the present invention, the amine-based antioxidant is not particularly limited as long as it is a compound having an aromatic amine or hydroxylamine structure and a molecular weight of 350 or more, and examples of such an antioxidant include bis(octadecyl)hydroxylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and di(4-octylphenyl)amine.

In the present invention, the ultraviolet absorber is not particularly limited as long as it is a compound having a molecular weight of 350 or more and has a benzotriazole structure, triazine structure, benzophenone structure, cyanoacrylate structure, or salicylate structure, and examples thereof include 2,2'-methylenebis[6-(benzotriazol-2-yl)-4-tert-octylphenol], 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyloxy)phenol, and 2-bis{[(2-cyano-3,3-diphenylacryloyl)oxy]methyl}propane-1,3-diyl-bis(2-cyano-3,3-diphenylacrylate).

In the present invention, the metal deactivator is not particularly limited as long as it is a compound with a molecular weight of 350 or more that chelates and detoxifies metal ions, such as oxalic acid derivatives, salicylic acid derivatives, and hydrazide derivatives.

In the present invention, the quencher is not particularly limited as long as it is a compound having a chelate structure such as Ni and a molecular weight of 350 or more.

The resin composition of the present invention contains 50% by weight or more and 98.99% by weight or less of cellulose resin (A) represented by general formula (1), 1% by weight or more and 49.99% by weight or less of cinnamic acid ester resin copolymer (B) containing cinnamic acid ester residue units represented by general formula (2) and residue units represented by general formula (3), and 0.01% by weight or more and 5.0% by weight or less of antioxidant (C) having a molecular weight of 350 or more. If the content of (C) is less than 0.01% by weight, the antioxidant effect is small, and if it is more than 5.0% by weight, it causes bleeding and blooming, and a decrease in the stability of the optical properties of the film. More preferably, it contains 50% by weight or more and 98.98% by weight or less of (A), 1% by weight or more and 49.98% by weight or less of (B), and 0.04% by weight or more and 1.0% by weight or less of antioxidant (C) having a molecular weight of 350 or more. Here, the composition ratio is 100% by weight of the total amount of (A) to (C).

The resin composition of the present invention may contain additives other than (A) to (C). In that case, the weight ratio of the additive may be expressed as a value relative to the total amount of (A) to (C) being 100% by weight or 100 parts by weight.

The cellulose resin (A), cinnamic acid ester copolymer (B) and antioxidant (C) can be blended by melt blending, solution blending or the like. The melt blending method is a method of manufacturing by melting the resin and antioxidant by heating and kneading them. The solution blending method is a method of dissolving the resin and antioxidant in a solvent and blending them. The solvent used for solution blending may be any solvent that can dissolve the resin, antioxidant, etc., but the boiling point of the solvent is preferably 200°C or less, more preferably 170°C or less, so that residual solvent is less likely to remain in the film formation process.

Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and dichlorobenzene; phenols such as phenol and chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, mesitylene, and dimethoxybenzene; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexane, and the like. These include ketone solvents such as xanone, cyclopentanone, 2-pyrrolidone, and N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; alcohol solvents such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-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; and carbon disulfide, ethyl cellosolve, and butyl cellosolve, used alone or in mixture.

Any method may be used as a method for producing a film using the resin composition of the present invention, but it is preferable to produce the film by a solution casting method. Here, the solution casting method is a method in which a resin solution (generally called a dope) is cast onto a support substrate, and then the solvent is evaporated by heating to obtain a film. The coating method is not particularly limited, and a normal method can be used. For example, the T-die method, doctor blade method, bar coater method, slot die method, lip coater method, reverse gravure coat method, microgravure method, spin coat method, brush coating method, roll coat method, flexographic printing method, etc. are included. In addition, the support substrate to be used is not particularly limited, and examples thereof include polymer substrates made of polyester, polycarbonate, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polysulfone, polyether sulfone, epoxy resin, etc., glass substrates such as glass plates and quartz substrates, metal substrates such as aluminum, stainless steel, and ferrotype, and inorganic substrates such as ceramic substrates. The substrate is preferably a polymer substrate or a metal substrate.

The film of the present invention has excellent transparency and can be suitably used as an optical film.

The viscosity of the resin solution when manufacturing 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. There are no particular limitations on the viscosity of the resin solution, but in order to facilitate easier film coating, it is preferably 100 to 30,000 cps, more preferably 300 to 20,000 cps, and particularly preferably 500 to 15,000 cps.

There are no particular limitations on the drying method used in the drying process of the coating solution, and any conventional heating means can be used. Examples include a hot air blower, a heating roll, and a far-infrared heater.

In the method for producing a film using the resin composition of the present invention, the drying temperature may be in a single stage, or in order to maintain the appearance and shorten the drying time, multi-stage drying may be used, in which the first stage is dried at a low temperature and the second and subsequent stages are dried at a high temperature.

In the present invention, the concentrations of the cellulose resin (A), the cinnamic acid ester copolymer (B) and the antioxidant (C) in the dope are not particularly limited as long as dissolution and film formation are possible. The method of dissolving the cellulose resin (A), the cinnamic acid ester copolymer (B) and the antioxidant (C) may be carried out so that the desired concentration is reached at the dissolution stage, or a low-concentration solution may be prepared in advance and then adjusted to a desired high-concentration solution in a concentration process. Furthermore, a high-concentration resin solution of the cellulose resin (A) and the cinnamic acid ester copolymer (B) may be prepared in advance, and then an antioxidant and various additives may be added to prepare a resin solution of a desired low concentration.

The optical film of the present invention has excellent retardation characteristics and can therefore 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. As a method for stretching the optical compensation film, a longitudinal uniaxial stretching method using roll stretching, a transverse uniaxial stretching method or an oblique stretching method using tenter stretching, or an unbalanced sequential biaxial stretching method or an unbalanced simultaneous biaxial stretching method that combines these methods can be used.

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

In addition, the thickness of the optical compensation film after stretching is preferably 5 to 100 μm, and more preferably 5 to 60 μm, in order to reduce the thickness of the image display device.

The stretching temperature is not particularly limited, but is preferably 50 to 200°C, more preferably 100 to 200°C, since good retardation properties are obtained. The stretching ratio is not particularly limited, but is preferably 1.05 to 4.0 times, more preferably 1.1 to 3.5 times, since good retardation properties are obtained. The retardation can be controlled by the stretching temperature and stretching ratio.

In the optical compensation film using the resin composition of the present invention, the retardation can be adjusted by the content of cellulose resin (A), the DS of the cellulose resin (A) contained, the substitution degree distribution at the 2nd, 3rd, and 6th positions of the substituent, and the stretching ratio.

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

The phase difference characteristics of the optical compensation film using the resin composition of the present invention vary depending on the intended optical compensation film, and examples thereof include those in which the retardation (Re) shown in the following formula (5) is preferably 50 to 300 nm, more preferably 100 to 300 nm, and particularly preferably 120 to 280 nm, and the Nz coefficient shown in the following formula (6) is preferably 0.3 to 1.0, and more preferably 0.4 to 0.8. The phase difference characteristics are measured using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments Co., Ltd., product name KOBRA-21ADH) at a measurement wavelength of 589 nm.

These films have retardation properties that are difficult to achieve with conventional optical compensation films made of cellulose-based resins.
Re=(ny-nx)×d (5)
Nz=(ny-nz)/(ny-nx) (6)
Rth=[(nx+ny)/2-nz]×d (7)
(In the formula, 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 refractive index outside the film plane, and d represents the film thickness.)

The retardation properties of the optical film of the present invention are suitable for use as a retardation film for circular polarizers and IPS liquid crystals, so the retardation (Re) at a measurement wavelength of 589 nm is preferably 30 nm or more and 300 nm or less, more preferably 65 nm or more and 300 nm or less, and even more preferably 130 nm or more and 300 nm or less.

The retardation properties of the optical film of the present invention are suitable for use as a retardation film for circular polarizers and IPS liquid crystals, so the Nz coefficient at a measurement wavelength of 589 nm is preferably 0.3 to 1.5, more preferably 0.4 to 1.1.

The wavelength dispersion characteristics of the optical film of the present invention are preferably 0.60<Re(450)/Re(550)<1.05, more preferably 0.70<Re(450)/Re(550)<1.02, and particularly preferably 0.75<Re(450)/Re(550)<1.00, in order to suppress color shift.

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

It is generally difficult for optical compensation films using cellulose-based resins to simultaneously satisfy these retardation characteristics and wavelength dispersion characteristics, but the optical compensation film of the present invention satisfies both of these characteristics simultaneously.

From the viewpoints of film handling and suitability for thinning optical components, 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, particularly preferably 20 to 80 μm, and most preferably 10 to 60 μm.

In order to avoid changes in color tone when used in an image display device, the optical compensation film using the resin composition of the present invention has a YI of preferably 1.7 or less, more preferably 1.5 or less, and even more preferably 1.0 or less when made into a film. Here, the YI was measured in accordance with JIS-K 7373 using a halogen lamp with a C light source as the light source and with a field of view of 2°. The thickness of the film made of the resin composition was measured at 30 μm.

In order to avoid color tone changes in the screen display device in a high-temperature environment and to maintain the color tone, it is further preferable that the optical compensation film using the resin composition of the present invention has a YI of 1.5 or less after 500 hours in an 85°C environment.

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 transmittance of 85% or more, and more preferably 90% or more when made into a film. Here, the light transmittance represents the total light transmittance, and is measured in accordance with JIS K 7361-1 (1997 edition) using a white light source at wavelengths of 380 nm to 780 nm. The thickness of the film made of the resin composition was measured at 30 μm.

The optical compensation film using the resin composition of the present invention preferably has a haze of 3.0% or less, more preferably 1.5% or less. By controlling the haze within the above range, a high-contrast image can be obtained when the film is incorporated into a display device as a retardation film. The haze used here is a value measured using a white light source at wavelengths of 380 nm to 780 nm in accordance with JIS-K 7136 (2000 edition). The film made of the resin composition was measured at a thickness of 30 μm.

In order to avoid a decrease in the amount of light of a screen display device in a high-temperature environment and to maintain a high-contrast image, the optical compensation film using the resin composition of the present invention has a haze of 3% or less after 500 hours in an 85°C environment and a transmittance of preferably 85% or more, and more preferably 90%.

The optical compensation film using the resin composition of the present invention preferably has a change in yellowness index YI of less than 1.0 after high-temperature treatment for 500 hours in an 85°C environment. Here, the change in yellowness index YI can be expressed as (YI after high-temperature treatment) - (YI before high-temperature treatment).

The optical compensation film using the resin composition of the present invention preferably has a haze change of less than 2.0% after high-temperature treatment for 500 hours in an 85°C environment. Here, the haze change can be expressed as (haze after high-temperature treatment) - (haze before high-temperature treatment).

The optical compensation film using the resin composition of the present invention can be laminated with a film containing other resins as necessary. Examples of other resins include polyethersulfone, polyarylate, polyethylene terephthalate, polynaphthalene terephthalate, polycarbonate, cyclic polyolefin, maleimide resin, fluorine resin, polyimide, etc. It is also possible to laminate a liquid crystal layer, a hard coat layer, a gas barrier layer, or a layer with a controlled refractive index (low reflection layer).

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

The resin composition of the present invention and the film using the same have excellent retardation properties and wavelength dispersion, and therefore can be suitably used in polarizing plates, liquid crystal displays, organic EL displays, etc., and can exhibit excellent display performance and high stability under high temperature and high humidity conditions.

The present invention will be described below 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.
<Measurement of Phase Difference Characteristics>
The retardation properties (Re and Nz coefficients) of the retardation film were measured using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, trade name KOBRA-21ADH) with light having a wavelength of 589 nm.
<Measurement of total light transmittance and haze>
The total light transmittance and haze of the prepared film were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name: NDH5000, light source: white LED (5V3W, wavelength range 380 nm to 780 nm, total light transmittance and haze values are the sum values within this range)) in accordance with JIS K 7361-1 (1997 edition) for the measurement of total light transmittance and JIS-K 7136 (2000 edition) for the measurement of haze.
<Measurement of Yellowness Index YI>
The yellowness index YI of the prepared film was measured in accordance with JIS-K 7373 using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., trade name: SD-5000, light source: C light source halogen lamp (12V50W), field of view: 2°).
<Heat resistance test>
The heat resistance was measured by examining the haze, total light transmittance, YI, and molecular weight change after 500 hours in a high-temperature environment of 85° C. using a gear oven (manufactured by Toyo Seiki Seisakusho, product name: STD60P) (replacement rate 3 times/min).
The change in molecular weight was measured by gel permeation chromatography (GPC) on the film before and after exposure to a high temperature environment, and the difference in the weight average molecular weight calculated as standard polystyrene was used as the rate of change. Here, the weight average molecular weight was measured by GPC on the composition itself, not on the individual components contained in the film, and the measurement data obtained was used.
<Phase difference and wavelength dispersion>
The retardation and wavelength dispersion were measured for the stretched optical compensation film using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, product name KOBRA-21ADH, light source: halogen lamp (12V100W)) at measurement wavelengths of 550 nm and 450 nm, measuring R450/R550 .

Synthesis Example 1 (Synthesis of cinnamic acid ester copolymer (B-1) (9-vinylcarbazole/ 4-hydroxy- α-isobutyl cyanocinnamate/isobutyl acrylate))
A 50 mL glass ampoule was charged with 5.0 g ( 0.026 mol ) of 9-vinylcarbazole, 3.2 g (0.013 mol) of isobutyl 4-hydroxy-α-cyanocinnamate, 1.7 g (0.013 mol) of isobutyl acrylate, 0.093 g (0.00022 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane as a polymerization initiator, and 24.6 g of ethyl cellosolve, and the ampoule was sealed under reduced pressure after repeated nitrogen replacement and depressurization. The ampoule was placed in a thermostatic chamber at 47°C and held for 24 hours to carry out radical polymerization. After the polymerization reaction was completed, the polymer was removed from the ampoule, 41 g of tetrahydrofuran was added, and the polymer solution was dropped into 330 g of a methanol/water mixed solvent (weight ratio 80/20) to precipitate, filtered, and the filtrate was washed five times with 45 g of a methanol/water mixed solvent (weight ratio 90/10) and filtered. The resin obtained was vacuum dried at 80° C. for 10 hours to obtain 9.2 g of a cinnamic acid ester copolymer (B-1) exhibiting negative birefringence (yield: 94%). The number average molecular weight of the obtained B-1 was 77,000, and the ratio of the residue units was 50 mol % of 9-vinylcarbazole residue units, 25 mol % of 4-hydroxy-α-cyanocinnamate isobutyl residue units, and 25 mol % of isobutyl acrylate residue units.

Synthesis Example 2 (Synthesis of cinnamic acid ester copolymer (B-2) (4-hydroxy-α-ethyl cyanocinnamate/9-vinylcarbazole copolymer)
5.0 g of ethyl 4-hydroxy-α-cyanocinnamate, 4.4 g of 9-vinylcarbazole, 0.17 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane as a polymerization initiator, and 8.5 g of tetrahydrofuran were placed in a 50 mL glass ampoule, and after repeated nitrogen replacement and depressurization, the ampoule was sealed under reduced pressure. The ampoule was placed in a thermostatic chamber at 62°C and held for 48 hours to carry out radical polymerization. After the polymerization reaction was completed, the polymer was removed from the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was dropped into 500 mL of methanol to precipitate, and then vacuum dried at 60°C for 10 hours to obtain 7.7 g of cinnamic acid ester copolymer (B-2) exhibiting negative birefringence (yield: 82%). The number average molecular weight of the obtained B-2 was 22,000, and the ratio of the residue units was 58 mol % of 9-vinylcarbazole residue units and 42 mol % of ethyl 4-hydroxy-α-cyanocinnamate residue units.

Example 1
As the cellulose resin (A), 31.15 g of ethyl cellulose (ETHOCEL standard 100, manufactured by Dow Chemical Company, number average molecular weight Mn = 58,000, weight average molecular weight Mw = 180,000, Mw / Mn = 3.2, total substitution degree DS = 2.51), 8.75 g of the cinnamic acid ester resin (B-1) obtained in Synthesis Example 1, and 0.10 g of a semi-hindered phenol-based antioxidant Irganox 245 (manufactured by BASF, compound name: bis [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionic acid] [ethylene bis (oxyethylene)], Fw: 587) were dissolved in a toluene / ethyl acetate = 8 / 2 (weight ratio) solution to prepare a 15 wt% resin solution. The solution was cast onto a polyethylene terephthalate film using a coater, and after drying at 40°C for 6 minutes and then drying in two stages at 155°C for 5 minutes, a film (resin composition) with a width of 150 mm and a thickness of 39 μm was obtained (cellulose resin: 77.87% by weight, cinnamic acid ester copolymer (B-1): 21.88% by weight, semi-hindered phenol-based antioxidant: 0.25% by weight). The obtained film was cut into a 50 mm square, and then uniaxially stretched 2.0 times at 155°C (thickness after stretching: 30 μm) to obtain an optical compensation film. The obtained film had a total light transmittance of 93%, a haze of 0.4%, and a YI of 0.5, and after a heat resistance test, the total light transmittance was 93%, the haze was 0.5%, and the YI was 0.9.
The total light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and heat resistance of the obtained optical compensation film were measured. The results are shown in Table 1.

The resulting optical compensation film had high total light transmittance, low haze and YI, and high heat resistance.

Example 2
31.15 g of the ethyl cellulose used in Example 1, 8.75 g of the cinnamic acid ester copolymer (B-2) exhibiting negative birefringence obtained in Synthesis Example 2, and two kinds of antioxidants, namely, 0.05 g of a semi-hindered phenol-based antioxidant Irganox 245 (manufactured by BASF, Fw: 587) and 0.05 g of a phosphite- based antioxidant Adeka STAB PEP-36 (manufactured by ADEKA, compound name: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, Fw: 633), were dissolved in a toluene/ethyl acetate=8/2 (weight ratio) solution to prepare a 15 wt % resin solution. The solution was cast onto a polyethylene terephthalate film using a coater, and after drying at 40° C. for 6 minutes, it was dried in two stages at 155° C. for 5 minutes, and a film (resin composition) with a width of 150 mm and a thickness of 39 μm was obtained (cellulose resin : 77.88% by weight, cinnamic acid ester copolymer (B-2): 21.88% by weight, semi-hindered phenol-based antioxidant: 0.12% by weight, phosphite -based antioxidant: 0.12% by weight). The obtained film was cut into a 50 mm square, and then uniaxially stretched 2.0 times at 157° C. (thickness after stretching: 30 μm) to obtain an optical compensation film. The obtained film had a total light transmittance of 92%, a haze of 0.6%, and a YI of 0.5, and after a heat resistance test, the total light transmittance was 92%, the haze was 0.6%, and the YI was 0.9.
The total light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and heat resistance of the obtained optical compensation film were measured. The results are shown in Table 1.
The optical compensation film thus obtained had a high total light transmittance, low haze and YI, and high heat resistance.

Example 3
31.10 g of the ethyl cellulose used in Example 1, 8.70 g of the cinnamic acid ester copolymer (B-1) used in Example 1, and 0.20 g of the semi-hindered phenol-based antioxidant Irganox 245 (manufactured by BASF, Fw: 587) were dissolved in a toluene/ethyl acetate = 8/2 (weight ratio) solution to obtain a 15 wt% resin solution. The solution was cast onto a polyethylene terephthalate film by a coater, and after drying at a drying temperature of 40 ° C. for 6 minutes and then at 155 ° C. for 5 minutes in two stages, a film (resin composition) with a width of 150 mm and a thickness of 39 μm was obtained (cellulose-based resin: 77.75 wt%, cinnamic acid ester copolymer (B-1): 21.75 wt%, semi-hindered phenol-based antioxidant: 0.50 wt%). The obtained film was cut into a 50 mm square and then uniaxially stretched 2.0 times at 152° C. (thickness after stretching: 30 μm) to obtain an optical compensation film.
The obtained film had a total light transmittance of 93%, a haze of 0.4% and a YI of 0.5, and after a heat resistance test, the total light transmittance was 93%, the haze was 0.5% and the YI was 0.8.
The total light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and heat resistance of the obtained optical compensation film were measured. The results are shown in Table 1.
The optical compensation film thus obtained had a high total light transmittance, low haze and YI, and high heat resistance.

Example 4
31.18 g of the ethyl cellulose used in Example 1, 8.78 g of the cinnamic acid ester copolymer (B-1) used in Example 1, and 0.04 g of the semi-hindered phenol-based antioxidant Irganox 245 (manufactured by BASF, Fw: 587) were dissolved in a toluene/ethyl acetate = 8/2 (weight ratio) solution to obtain a 15 wt% resin solution. The solution was cast onto a polyethylene terephthalate film by a coater, and after drying at a drying temperature of 40 ° C. for 6 minutes and then at 155 ° C. for 5 minutes in two stages, a film (resin composition) with a width of 150 mm and a thickness of 39 μm was obtained (cellulose-based resin: 77.95 wt%, cinnamic acid ester copolymer (B-1): 21.95 wt%, semi-hindered phenol-based antioxidant: 0.10 wt%). The obtained film was cut into a 50 mm square and then uniaxially stretched 2.0 times at 155° C. (thickness after stretching: 30 μm) to obtain an optical compensation film.
The obtained film had a total light transmittance of 93%, a haze of 0.4% and a YI of 0.5, and after a heat resistance test, the total light transmittance was 93%, the haze was 0.5% and the YI was 0.9.
The total light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and heat resistance of the obtained optical compensation film were measured. The results are shown in Table 1.
The optical compensation film thus obtained had a high total light transmittance, low haze and YI, and high heat resistance.

Example 5
31.18 g of the ethyl cellulose used in Example 1, 8.78 g of the cinnamic acid ester copolymer (B-1) used in Example 1, and 0.04 g of a sulfur-based antioxidant, ADK STAB AO-412S (manufactured by ADEKA Corporation, compound name: bis[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropyloxy]methyl] -1,3 -propanediyl, Fw: 1162), were dissolved in a toluene/ethyl acetate=8/2 (weight ratio) solution to prepare a 15 wt % resin solution. The solution was cast onto a polyethylene terephthalate film using a coater, and then dried in two stages at 40°C for 5 minutes and then 155°C for 6 minutes, to obtain a film (resin composition) with a width of 150 mm and a thickness of 39 μm (cellulose resin: 77.95% by weight, cinnamic acid ester copolymer (B-1): 21.95% by weight, sulfur-based antioxidant: 0.10% by weight). The obtained film was cut into a 50 mm square, and then uniaxially stretched 2.0 times at 155°C (thickness after stretching: 30 μm) to obtain an optical compensation film.
The obtained film had a total light transmittance of 93%, a haze of 0.4% and a YI of 0.5, and after a heat resistance test, the total light transmittance was 93%, the haze was 0.5% and the YI was 1.2.
The total light transmittance, haze, retardation characteristics, wavelength dispersion characteristics, and heat resistance of the obtained optical compensation film were measured. The results are shown in Table 1.
The optical compensation film thus obtained had a high total light transmittance, low haze and YI, and high heat resistance.

Comparative Example 1
An optical compensation film was obtained under the same conditions as in Example 1, except that no antioxidant was used. The obtained film had a total light transmittance of 93%, a haze of 0.4%, and a YI of 0.5. After the heat resistance test, the total light transmittance was 93%, the haze was 0.4%, and the YI was 1.8. The results are shown in Table 2.
The optical compensation film thus obtained had a high YI and low heat resistance.

Comparative Example 2
An optical compensation film was obtained under the same conditions as in Example 1, except that the film contained 10% by weight of the semi-hindered phenol-based antioxidant Irganox 245. The obtained film had a total light transmittance of 91%, a haze of 1.3%, and a YI of 0.6%, and after a heat resistance test, the total light transmittance was 89% and the haze was 3.5%. The results are shown in Table 2.
The obtained optical compensation film had high haze and low heat resistance.

Comparative Example 3
An optical compensation film was obtained under the same conditions as in Example 1, except that a low molecular weight semi-hindered phenol-based antioxidant Sumilizer MDP-S (manufactured by Sumitomo Chemical, chemical name: 2,2'-methylenebis(6-tert-butyl-p-cresol), Fw: 341) was used instead of the semi-hindered phenol-based antioxidant Irganox 245 (manufactured by BASF, Fw: 587). The obtained film had a total light transmittance of 92%, a haze of 0.5%, and a YI of 0.5, and after a heat resistance test, the total light transmittance was 92%, the haze was 0.8%, and the YI was 1.6. The results are shown in Table 2.
The optical compensation film thus obtained had a high YI and low heat resistance.

Claims (12)

A cellulose resin (A) having a cellulose residue unit represented by the following general formula (1) of 50% by weight or more and 98.98% by weight or less,
A resin composition comprising: 1% by weight or more and 49.98% by weight or less of a cinnamic acid ester copolymer (B) containing a cinnamic acid ester residue unit represented by the following general formula (2) and a residue unit represented by the following general formula (3); and 0.01% by weight or more and 1.0% by weight or less of an antioxidant (C) having a molecular weight of 350 or more and being at least one member selected from the group consisting of phenol-based antioxidants and sulfur-based antioxidants.
(In the formula, R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom or a substituent having 1 to 12 carbon atoms.)
(In the formula, R ₄ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R ₅ to R ₉ represent a hydrogen atom, 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 thiol group, an amido group, an amino group, a hydroxyl group, an alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms; and Y 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, or a thiol group.)
(In the formula, R ₁₀ represents a 5-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as heteroatoms, or a 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as heteroatoms (the 5-membered heterocyclic residue and the 6-membered heterocyclic residue may form a condensed ring structure with another ring structure).) The resin composition according to claim 1, wherein the cinnamic acid ester copolymer (B) contains a residue unit represented by the general formula (2) and a residue unit represented by the general formula (3), and further contains a residue unit represented by the following general formula (4).
(Here, R ₁₁ and R ₁₂ each independently represent a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.) The resin composition according to claim 1 or 2, wherein in the cinnamate ester copolymer (B), the ratio of the monomer component related to the cinnamate ester residue unit of the general formula (2) is 21 mol% or more and 50 mol% or less with respect to 100 mol% of the total of all monomer components. A film comprising the resin composition according to any one of claims 1 to 3. The film according to claim 4, wherein the retardation (Re) represented by the following formula (5) is 30 nm or more and 300 nm or less, the Nz coefficient represented by the following formula (6) is 0.3 or more and 1.5 or less, and the ratio Re(450)/Re(550) of the retardation at 450 nm (Re(450)) to the retardation at 550 nm (Re(550)) is more than 0.60 and less than 1.05.
Re=(ny-nx)×d (5)
Nz=(ny-nz)/(ny-nx) (6)
(In the formula, 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 refractive index outside the film plane, and d represents the film thickness.) The film according to claim 4 or 5, which has a thickness of 30 μm and a total light transmittance of 85% or more at measurement wavelengths of 500 nm to 650 nm. The film described in any one of claims 4 to 6, having a yellowness index YI of 1.7 or less. A film according to any one of claims 4 to 7, having a thickness of 30 μm and a haze of 3.0% or less at measurement wavelengths of 500 nm to 650 nm. The film described in any one of claims 4 to 8 has a YI of 1.7 or less after 500 hours in an 85°C environment. The film described in any one of claims 4 to 9, in which the change in yellowness index YI after high-temperature treatment for 500 hours in an 85°C environment is less than 1.0. A film according to any one of claims 4 to 10, in which the change in haze after high-temperature treatment for 500 hours in an 85°C environment is less than 2.0%. A polarizing plate using the film according to claim 4 .