Phase difference film and method for manufacturing a phase difference film

Abstract

To provide a retardation film that has high birefringence and indicates reverse wavelength dispersion characteristics.SOLUTION: A retardation film is a stretched film of a resin film including a resin component including a cellulose resin having a specific constitutional unit in an amount of 30 weight% to 99 weight% and an ester resin having a specific constitutional unit in an amount of 1 weight% to 70 weight%, and an acrylic plasticizer having a glass-transition temperature of 50°C or more.SELECTED DRAWING: None

Description

[[Technical Field]]

[0001] The present invention relates to a retardation film and a method for producing the retardation film. [[Background Art]]

[0002] In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices) have been rapidly spreading. It is known that in organic EL display devices, arranging a circularly polarizing plate including a λ / 4 plate on the viewing side of an organic EL cell can prevent problems such as external light reflection and background reflection (see, for example, Patent Documents 1 and 2).

[0003] Regarding the λ / 4 plate used for the above circularly polarizing plate, from the viewpoint of realizing excellent antireflection properties over a wide wavelength range, there is a demand for a retardation film that exhibits so-called reverse wavelength dispersion characteristics, in which the in-plane retardation increases as the wavelength becomes longer. In response to such a demand, a retardation film containing a cellulose resin exhibiting positive birefringence and an ester resin exhibiting negative birefringence and exhibiting reverse wavelength dispersion characteristics has been proposed (Patent Document 3). [[Prior Art Literature]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2002-311239 [[Patent Document 2]] Japanese Unexamined Patent Application Publication No. 2002-372622 [[Patent Document 3]] Japanese Unexamined Patent Application Publication No. 2021-140095 [[Summary of the Invention]] [[Problems to be Solved by the Invention]]

[0005] In the production of the retardation film exhibiting reverse wavelength dispersion characteristics disclosed in Patent Document 3, there is a problem in stably stretching a raw film at a high stretching ratio.

[0006] The present invention was made to solve the above problems, and its main objective is to provide a phase difference film that has high birefringence and exhibits inverse wavelength dispersion characteristics. [Means for solving the problem]

[0007] According to one aspect of the present invention, a phase difference film is provided, which is a stretched resin film comprising a resin component containing 30% to 99% by weight of a cellulose resin having the constituent units shown in formula (1) below, 1% to 70% by weight of an ester resin having the constituent units shown in formula (2), formula (3), and formula (4) below, and an acrylic plasticizer having a glass transition temperature of 50°C or higher. [ka] (In formula (1), R1 to R3 each independently represent a hydrogen atom or a substituent having 1 to 12 carbon atoms.) [ka] (In formula (2), R4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R 5a R represents one selected from an alkyl group having 1 to 12 carbon atoms, 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; R 5b R6 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R6 represents one selected from 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 alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms;) [ka] (In formula (3), R7 represents a five-membered heterocyclic residue or a six-membered heterocyclic residue containing one or more nitrogen or oxygen atoms as heteroatoms (the five-membered heterocyclic residue and the six-membered heterocyclic residue may form a fused ring structure with other cyclic structures).) [ka] (In formula (4), R8 and R9 each independently represent one selected from 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 one embodiment, the birefringence Δn(590) of the phase difference film at a measurement wavelength of 590 nm, the in-plane phase difference Re(450) at a measurement wavelength of 450 nm, and the in-plane phase difference Re(550) at a measurement wavelength of 550 nm satisfy the following equation (a). Δn(590)≧0.0140×(Re(450) / Re(550))-0.0092···(a) In one embodiment, the content of the acrylic plasticizer is 1 to 30 parts by weight per 100 parts by weight of the resin component. In one embodiment, the acrylic plasticizer comprises a copolymer of monomer components including a (meth)acrylic acid ester and a styrene monomer. In one embodiment, the number of MIT cycles in a direction perpendicular to the stretching direction of the stretched film is 400 or more. According to another aspect of the present invention, a method for producing a phase difference film is provided, comprising stretching a resin film comprising a resin component containing 30% to 99% by weight of a cellulose resin having the constituent units shown in formula (1) and 1% to 70% by weight of an ester resin having the constituent units shown in formula (2), formula (3), and formula (4), and an acrylic plasticizer having a glass transition temperature of 50°C or higher, at a stretching ratio of 2.2 times or more in a temperature range of Tg1-20°C to Tg1+50°C with respect to the glass transition temperature (Tg1) of the resin having the lowest glass transition temperature among the oriented resins in the resin component. [Effects of the Invention]

[0008] According to embodiments of the present invention, a resin film containing a predetermined cellulose-based resin and a predetermined ester-based resin in predetermined proportions, and an acrylic plasticizer having a glass transition temperature (Tg) of 50°C or lower, is used as the base film. Because the resin film contains an acrylic plasticizer, it can be stably stretched at a high stretching ratio, thereby enabling the stable production of a phase difference film exhibiting high birefringence and inverse wavelength dispersion characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] This graph shows the relationship between birefringence and wavelength dispersion of the phase difference films obtained in the examples and comparative examples. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In this specification, the "~" symbol indicating a numerical range includes its upper and lower limits. In this specification, "weight" is synonymous with "mass" in the SI system, meaning weight.

[0011] (Definitions of terms and symbols) The definitions of terms and symbols used in this specification are as follows: (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the refractive index is maximum in the plane (i.e., the slow phase axis direction), "ny" is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., the fast phase axis direction), and "nz" is the refractive index in the thickness direction. (2) Birefringence (Δn(λ)) "Δn(λ)" is the in-plane birefringence measured with light of wavelength λnm at 23℃. The in-plane birefringence (Δn) can be calculated from the formula: Δn = nx - ny. (3) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be calculated using the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (4) Phase difference in the thickness direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be calculated using the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (5) Nz coefficient The Nz coefficient is calculated using the formula Nz = Rth / Re. (6)Angle In this specification, when an angle is referred to, it includes both clockwise and counterclockwise directions with respect to the reference direction. Therefore, for example, "45°" means 45° in either a clockwise or counterclockwise direction. (7) In this specification, “(meth)acrylic” means “methacrylic and / or acrylic.”

[0012] A. Phase difference film The phase difference film according to an embodiment of the present invention is a stretched film obtained by stretching a resin film comprising a resin component containing 30% to 99% by weight of a cellulose resin having the constituent units shown in formula (1), 1% to 70% by weight of an ester resin having the constituent units shown in formula (2), formula (3), and formula (4), and an acrylic plasticizer having a glass transition temperature (Tg) of 50°C or higher. The resin film to be stretched may further contain any appropriate additive components depending on the purpose. The method for stretching the resin film, i.e., the method for manufacturing the phase difference film, will be described in detail in Section B.

[0013] Phase difference films typically exhibit refractive index characteristics where nx > ny ≥ nz. "ny = nz" includes not only cases where ny and nz are completely identical, but also cases where ny and nz are substantially identical. Phase difference films with refractive index characteristics nx > ny = nz are sometimes referred to as "positive A plates," etc. Phase difference films with refractive index characteristics nx > ny > nz are sometimes referred to as "negative B plates," etc.

[0014] The birefringence (Δn(590)) of the phase difference film at a measurement wavelength of 590 nm is preferably 0.0031 or higher, more preferably 0.0035 or higher. The Δn(590) of the phase difference film may be, for example, 0.01 or lower.

[0015] The in-plane phase difference of the phase difference film can be any appropriate value depending on the application. In one embodiment, the phase difference film can function as a λ / 4 plate. In this case, the Re(550) of the phase difference film is, for example, 90 nm to 200 nm, preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and even more preferably 130 nm to 160 nm.

[0016] The Nz coefficient of the phase difference film is preferably 0.9 to 3, more preferably 0.9 to 2.5, even more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying this relationship, when used as a circular polarizer in an image display device in combination with a polarizer, an extremely excellent reflective hue can be achieved.

[0017] Typically, the retardation film exhibits reverse dispersion wavelength characteristics where the in-plane retardation increases in accordance with the wavelength of measurement light. The retardation film typically satisfies the relationship Re(450) / Re(550) < 1, for example, satisfies the relationship Re(450) / Re(550) < 0.95, more preferably satisfies the relationship Re(450) / Re(550) < 0.93, still more preferably satisfies the relationship Re(450) / Re(550) < 0.90, even more preferably satisfies the relationship Re(450) / Re(550) < 0.88, even still more preferably satisfies the relationship 0.80 < Re(450) / Re(550) < 0.87. When such a retardation film that satisfies the above relationship is combined with a polarizer to form a circularly polarizing plate for use in an image display device, extremely excellent antireflection properties can be achieved.

[0018] Preferably, for the retardation film, Δn(590), Re(450), and Re(550) satisfy the following formula (a). A retardation film satisfying formula (a) can achieve both high birefringence (Δn) and reverse wavelength dispersion characteristics. Δn(590)≧0.0140×(Re(450) / Re(550))-0.0092···(a)

[0019] In one embodiment, a nanophase separation structure is formed in the retardation film. As will be described later in detail, the cellulose-based resin has a relatively low glass transition temperature (Tg), and the ester-based resin has a relatively high Tg. By using a resin film containing such resins, the retardation film can be imparted with both the residual stress reduction effect provided by the cellulose-based resin and the shrinkage reduction effect provided by the ester-based resin in a well-balanced manner. In addition, the formation of the nanophase separation structure can suppress abrupt shrinkage of the retardation film under high temperature and high humidity environments (e.g., 110°C and 85% RH (relative humidity)), and as a result, cracking of the retardation film can be suppressed. Furthermore, when a nanophase separation structure is formed in the retardation film, the function as a reverse dispersion retardation film can be stably ensured.

[0020] In this specification, "nanophase separation structure" refers to a structure in which two components with different electron densities are phase-separated by domain sizes on the nano-order (typically at the level of several tens of nanometers). Cellulose resins and ester resins may have a sea-island structure or a co-continuous structure. Examples of means for confirming the nanophase separation structure include transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS), with TEM observation of a cross-section of a phase-contrast film being preferred. TEM observation will be described in detail in the examples. When a nanophase separation structure is formed on a phase-contrast film, two types of domains with different electron densities can be confirmed by TEM observation of a cross-section of the phase-contrast film, and it can be confirmed that the size (maximum length) of all domains is less than 100 nm.

[0021] The phase difference film exhibits excellent flexibility in the stretching direction and in directions perpendicular to the stretching direction. For example, the phase difference film exhibits significantly superior flexibility in the direction perpendicular to the stretching direction compared to conventional phase difference films composed of polycarbonate resin films, liquid crystal polymer films, etc. The reason why the phase difference film has such excellent flexibility is not clear, but it is presumed to be due to one or more of the following components of the phase difference film, namely, the inclusion of the above-mentioned cellulose resin and the above-mentioned ester resin in predetermined proportions, the inclusion of an acrylic plasticizer, and the formation of a nanophase separation structure.

[0022] The number of MIT cycles for the phase difference film in the stretching direction is, for example, 800 or more, preferably 1000 or more, more preferably 1500 or more, and for example, 2500 or less. The number of MIT cycles can be measured in accordance with JIS P 8115 (the same applies hereinafter). The number of MIT cycles of the phase difference film in the direction perpendicular to the stretching direction is, for example, 400 or more, preferably 500 or more, more preferably 600 or more, even more preferably 1000 or more, and particularly preferably 1300 or more, and for example, 2000 or less.

[0023] The thickness of the phase difference film is, for example, 10 μm to 80 μm, preferably 10 μm to 60 μm, and more preferably 10 μm to 30 μm. The phase difference film obtained by the manufacturing method of the embodiment of the present invention has high in-plane birefringence, and therefore can have a practically sufficient in-plane phase difference with a small thickness.

[0024] The phase difference film may be in the form of a single sheet or in the form of a long strip. The phase difference film is preferably in the form of a long strip. In this specification, "long strip" means an elongated shape in which the length is sufficiently longer than the width, and for example, includes an elongated shape in which the length is 10 times or more, preferably 20 times or more, than the width. The long strip of phase difference film can be wound into a roll.

[0025] A-1. Resin components The resin component comprises 30% to 99% by weight of a cellulose resin having the structural units shown in formula (1), and 1% to 70% by weight of an ester resin having the structural units shown in formula (2), formula (3), and formula (4). Due to having such structural units, the cellulose resin exhibits positive birefringence, and the ester resin exhibits negative birefringence. By using a resin component containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence in predetermined proportions, a phase difference film with excellent optical properties can be obtained.

[0026] Here, "exhibiting positive birefringence" means that when a polymer is oriented by stretching or other means, the refractive index in the direction perpendicular to the stretching direction becomes relatively smaller. In other words, it means that the refractive index in the stretching direction becomes larger. "Exhibiting negative birefringence" means that when a polymer is oriented by stretching or other means, the refractive index in the stretching direction becomes relatively smaller. In other words, it means that the refractive index in the direction perpendicular to the stretching direction becomes larger.

[0027] The resin component may further contain any other suitable thermoplastic resin (excluding those corresponding to the acrylic plasticizers described in Section A-2) insofar as the effects of the present invention are obtained. The total content ratio of the cellulose resin and the ester resin in the resin component is preferably 95% to 100% by weight, for example, 100% by weight.

[0028] A-1-1. Cellulose resin The cellulose resin used in the phase difference film according to the embodiment of the present invention is typically a polymer in which β-glucose units are polymerized in a linear manner, and has the constituent units shown in the following formula (1). [ka] (In formula (1), each of R1 to R3 represents a hydrogen atom or a substituent having 1 to 12 carbon atoms).

[0029] Examples of substituents having 1 to 12 carbon atoms represented by R1 to R3 in formula (1) above include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decanyl, dodecanyl, isobutyl, and t-butyl groups; cycloalkyl groups such as cyclohexyl groups; aryl groups such as phenyl and naphthyl groups; aralkyl groups such as benzyl groups; acyl groups such as acetyl and propionyl groups; cyanoalkyl groups such as cyanoethyl groups; aminoalkyl groups such as aminoethyl groups; and hydroxyalkyl groups such as 2-hydroxyethyl and 3-hydroxypropyl groups. In equation (1) above, R1 to R3 may be the same or different from each other. Preferably, R1 to R3 in formula (1) above are a hydrogen atom and an alkyl group having 1 to 12 carbon atoms, more preferably a hydrogen atom and an alkyl group having 1 to 4 carbon atoms, and even more preferably a hydrogen atom and an ethyl group.

[0030] The degree of substitution (hereinafter referred to as DS) of cellulose resins is typically between 1.5 and 2.95, preferably between 1.8 and 2.8. DS represents the percentage of hydroxyl groups substituted in the cellulose resin, with DS being 3 when 100% substitution occurs. DS can be calculated from the peak area of ​​gas chromatography, as described in the 17th edition of the Japanese Pharmacopoeia.

[0031] The number-average molecular weight (Mn) of cellulose resins, in terms of standard polystyrene equivalents, is, for example, 1 × 10⁻⁶. 3 The above 1 x 10 6 Preferably, 5 × 10 3 The above 2 x 10 5 The following applies: The manganese content (Mn) of cellulose-based resins can be calculated from the elution curve measured by gel permeation chromatography (GPC). If the Mn content of the cellulose-based resin is within the above range, the mechanical properties and / or moldability of the resin film can be improved.

[0032] The glass transition temperature (Tg) of cellulose-based resins is, for example, 140°C or lower, preferably 135°C or lower, and for example, 120°C or higher, preferably 125°C or higher. The glass transition temperature (Tg) of cellulose-based resins can be measured by a thermal analyzer such as a DSC (Differential Scanning Calorimetry).

[0033] Specific examples of cellulosic resins include alkylcellulose such as methylcellulose, ethylcellulose, and propylcellulose; hydroxyalkylcellulose such as hydroxyethylcellulose and hydroxypropylcellulose; aralkylcellulose such as benzylcellulose; cyanoalkylcellulose such as cyanoethylcellulose; carboxyalkylcellulose such as carboxymethylcellulose and carboxyethylcellulose; carboxyalkylalkylcellulose such as carboxymethylmethylcellulose and carboxymethylethylcellulose; and aminoalkylcellulose such as aminoethylcellulose. Cellulosic resins can be used alone or in combination. Among cellulosic resins, alkylcellulose is preferred, and ethylcellulose is more preferred.

[0034] The content of the above-mentioned cellulose-based resin in the resin component is typically 30% to 99% by weight, preferably 30% to 90% by weight, and more preferably 40% to 80% by weight. If the content of the cellulose-based resin is less than 30% by weight or more than 99% by weight, it is difficult to control the phase difference.

[0035] In one embodiment, the content of cellulose resin in the resin component is typically more than 50% by weight, preferably 60% by weight or more, and more preferably 70% by weight or more, when the total sum of cellulose resin and ester resin is taken as 100% by weight. As long as the content of cellulose resin is above the lower limit, the cellulose resin and ester resin can stably form a nanophase separation structure. The upper limit of the content of cellulose resin is typically 99% by weight or less, and preferably 90% by weight or less, when the total sum of cellulose resin and ester resin is taken as 100% by weight.

[0036] A-1-2. Ester resins The ester resin used in the phase difference film according to the embodiment of the present invention typically has the constituent units shown in formula (2), formula (3), and formula (4) below. [ka] (In formula (2), R4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R 5a R represents one selected from an alkyl group having 1 to 12 carbon atoms, 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; R 5brepresents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R6 represents one selected from 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 hydroxy group, an alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms.) Chemical Formula (In formula (3), R7 represents a 5-membered heterocyclic residue or a 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as heteroatoms (said 5-membered heterocyclic residue and said 6-membered heterocyclic residue may form a fused ring structure with another cyclic structure).) Chemical Formula (In formula (4), R8 and R9 each independently represent one selected from 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.)

[0037] Since the ester resin contains the residue units represented by formulas (2) to (4), it has high negative birefringence developability, and can exhibit high retardation even with a small thickness, thereby contributing to thinning of the retardation film.

[0038] The structural unit represented by formula (2) is a cinnamic acid ester residue unit. Examples of the alkyl group having 1 to 12 carbon atoms represented by R4 in formula (2) 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, an isobutyl group, and an ethylhexyl group. Among R4 in formula (2), an alkyl group having 1 to 4 carbon atoms is preferred, and an ethyl group and an isobutyl group are more preferred. R in the above formula (2) 5a , an alkyl group having 1 to 12 carbon atoms and a cyano group are preferred; an alkyl group having 1 to 4 carbon atoms and a cyano group are more preferred; and a cyano group is even more preferred. R in equation (2) above 5b Among these, hydrogen atoms and alkyl groups having 1 to 4 carbon atoms are preferred. In formula (2) above, R6 may be bonded to the benzene ring as a single entity or as two or more entities. Among the R6 groups in formula (2) above, carboxylic acid groups and hydroxyl groups are preferred.

[0039] Specific examples of the constituent units (cinnamic acid ester residue units) shown in formula (2) above include α-cyano-4-hydroxycinnamate methyl residue unit, α-cyano-2-hydroxycinnamate ethyl residue unit, α-cyano-3-hydroxycinnamate ethyl residue unit, α-cyano-4-hydroxycinnamate ethyl residue unit, α-cyano-4-hydroxycinnamate n-propyl residue unit, α-cyano-4-hydroxycinnamate isopropyl residue unit, α-cyano-4-hydroxycinnamate n-butyl residue unit, and α-cyano-4-hydroxycinnamate α-cyano-hydroxycinnamic acid ester residue units such as isobutyl hydroxycinnamate residue units, α-cyano-4-hydroxycinnamate s-butyl residue units, and α-cyano-2,4-dihydroxycinnamate methyl residue units; α-cyano-carboxycinnamic acid ester residue units such as α-cyano-4-carboxycinnamate methyl residue units, α-cyano-4-carboxycinnamate ethyl residue units, α-cyano-2,3-dicarboxycinnamate methyl residue units, and α-cyano-2,3-dicarboxycinnamate ethyl residue units; α-Cyano-2-carboxy-3-hydroxycinnamate methyl residue unit, α-Cyano-2-carboxy-3-hydroxycinnamate ethyl residue unit, and other α-Cyano-2-carboxy-3-hydroxycinnamate ethyl residue unit; 3-alkyl-3-(hydroxyphenyl)-propa-2-enoate methyl residue unit, 3-ethyl-3-(hydroxyphenyl)-propa-2-enoate ethyl residue unit, and other 3-alkyl-3-(hydroxyphenyl)-propa-2-enoate ethyl residue unit; 3-methyl-3-(carboxyphenyl 3-alkyl-3-(carboxyphenyl)-propa-2-enoic acid ester residue units such as methyl methyl residue units and ethyl ethyl ethyl 3-ethyl-3-(carboxyphenyl)-propa-2-enoic acid residue units; 2-cyano-3-alkyl-3-(hydroxyphenyl)-propa-2-enoic acid ester residue units such as methyl methyl 2-cyano-3-methyl-3-(hydroxyphenyl)-propa-2-enoic acid residue units and ethyl ethyl 2-cyano-3-ethyl-3-(hydroxyphenyl)-propa-2-enoic acid residue units;Examples include 2-cyano-3-alkyl-3-(carboxyphenyl)-propa-2-enoic acid ester residue units such as 2-cyano-3-methyl-3-(carboxyphenyl)-propa-2-enoic acid methyl residue units and 2-cyano-3-ethyl-3-(carboxyphenyl)-propa-2-enoic acid ethyl residue units.

[0040] The ester resin may contain only one of the constituent units shown in formula (2) above, or it may contain two or more. Among the constituent units shown in formula (2) above, preferred examples include α-cyano-hydroxycinnamic acid ester residue units, α-cyano-carboxycinnamic acid ester residue units, 3-alkyl-3-(hydroxyphenyl)-propa-2-enoic acid ester residue units, and 3-alkyl-3-(carboxyphenyl)-propa-2-enoic acid ester residue units.

[0041] Specific examples of the ring structure represented by R7 in formula (3) above include 1-vinylpyrrole residue units, 2-vinylpyrrole residue units, 1-vinylindole residue units, 9-vinylcarbazole residue units, 2-vinylquinoline residue units, 4-vinylquinoline residue units, N-vinylphthalimide residue units, N-vinylsuccinimide residue units, 2-vinylfuran residue units, and 2-vinylbenzofuran residue units, with 9-vinylcarbazole residue units and N-vinylphthalimide residue units being preferred.

[0042] The ester resin may contain only one of the constituent units shown in formula (3) above, or it may contain two or more of them.

[0043] In formula (4) above, examples of linear alkyl groups having 1 to 12 carbon atoms represented by R8 and R9 include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, and the like. In formula (4) above, examples of branched alkyl groups having 3 to 12 carbon atoms represented by R8 and R9 include isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, etc. In formula (4) above, examples of cyclic alkyl groups having 3 to 6 carbon atoms represented by R8 and R9 include cyclopropyl group, cyclobutyl group, and cyclohexyl group. In equation (4) above, R8 and R9 may be the same or different from each other. In formula (4) above, R8 is preferably a hydrogen atom and a linear alkyl group having 1 to 12 carbon atoms, and more preferably a hydrogen atom and a methyl group. In formula (4) above, R9 is preferably a branched alkyl group having 3 to 12 carbon atoms, and more preferably a branched alkyl group having 3 to 8 carbon atoms.

[0044] The constituent units shown in formula (4) above are typically acrylic resin residue units. Specific examples of the constituent units shown in formula (4) above include acrylic acid residue units, methacrylic acid residue units, 2-ethyl acrylic acid residue units, 2-propyl acrylic acid residue units, 2-isopropyl acrylic acid residue units, 2-pentyl acrylic acid residue units, 2-hexyl acrylic acid residue units, 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, n-pentyl acrylate residue units, isopentyl acrylate residue units, sec-pentyl acrylate residue units, 3-pentyl acrylate residue units, neopentyl acrylate residue units, n-hexyl acrylate residue units, isohexyl acrylate residue units, neohexyl acrylate residue units, methyl methacrylate residue units, ethyl methacrylate residue units, and methacrylate residue units. Examples include n-propyl methacrylate residue units, isopropyl methacrylate residue units, n-butyl methacrylate residue units, isobutyl methacrylate residue units, sec-butyl methacrylate residue units, n-pentyl methacrylate residue units, isopentyl methacrylate residue units, sec-pentyl methacrylate residue units, 3-pentyl methacrylate residue units, neopentyl methacrylate residue units, n-hexyl methacrylate residue units, isohexyl methacrylate residue units, neohexyl methacrylate residue units, methyl 2-ethylacrylate residue units, ethyl 2-ethylacrylate residue units, n-propyl 2-ethylacrylate residue units, isopropyl 2-ethylacrylate residue units, n-butyl 2-ethylacrylate residue units, isobutyl 2-ethylacrylate residue units, sec-butyl 2-ethylacrylate residue units, and the like, with isobutyl acrylate residue units being preferred.

[0045] The ester resin may contain only one of the constituent units shown in formula (4) above, or it may contain two or more of them.

[0046] In ester resins, the preferred content of each constituent unit is such that, relative to 100 mol% of all constituent units, the content of the constituent unit shown in formula (2) is 21 mol% to 49 mol%, the content of the constituent unit shown in formula (3) is 35 mol% to 60 mol%, and the content of the constituent unit shown in formula (4) is 1 mol% to 30 mol%. This allows for the production of a phase difference film with superior phase difference characteristics. The composition ratio of the ester resin can be measured by 1H-NMR.

[0047] Ester resins may contain monomer residue units other than those of formulas (2) to (4) above. Examples of such monomer residue units include styrene residues such as styrene residues and α-methylstyrene residues; vinylnaphthalene 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; fumarate ester residues; fumarate residues; and olefin residues such as ethylene residues and propylene residues.

[0048] The number-average molecular weight (Mn) of ester resins on a standard polystyrene basis is, for example, 1 × 10⁻⁶. 3 The above 5 x 10 6 The following is preferable: 5 × 10 3 The above 3 x 10 5 The following applies: The manganese (Mn) content of ester resins can be calculated from the elution curve measured by gel permeation chromatography (GPC). If the Mn content of the ester resin falls within the above range, the mechanical properties and / or moldability of the resin film can be improved.

[0049] The glass transition temperature (Tg) of ester resins is, for example, 220°C or lower, preferably 210°C or lower, and for example, 180°C or higher, preferably 190°C or higher. The glass transition temperature (Tg) of ester resins can be measured by a thermal analyzer such as a DSC (Differential Scanning Calorimetry).

[0050] Specific examples of the above ester resins include α-cyano-2-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-1-vinylindole-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, and α-cyano-hydroxycinnamic acid ester copolymer. Ano-3-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid copolymer, α-cyano-3-hydroxycinnamic acid ester-1-vinylindole-acrylic acid copolymer, α-cyano-3-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid copolymer, α-cyano-4-hydroxycinnamic acid ester-styrene-acrylic acid copolymer, α-cyano-4-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid copolymer, α-cyano-4-hydroxycinnamic acid ester Tel-1-vinylindole-acrylic acid copolymer, α-cyano-4-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-styrene-methacrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene-methacrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-1-vinylindole-methacrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole α-Methacrylic acid copolymer, α-Cyano-3-Hydroxycinnamic acid ester-styrene-methacrylic acid copolymer, α-Cyano-3-Hydroxycinnamic acid ester-2-Vinylnaphthalene-methacrylic acid copolymer, α-Cyano-3-Hydroxycinnamic acid ester-1-Vinylindole-methacrylic acid copolymer, α-Cyano-3-Hydroxycinnamic acid ester-9-Vinylcarbazole-methacrylic acid copolymer, α-Cyano-4-Hydroxycinnamic acid ester-styrene-methacrylic acid copolymer,Examples include α-cyano-4-hydroxycinnamic acid ester-2-vinylnaphthalene-methacrylate copolymer, α-cyano-4-hydroxycinnamic acid ester-1-vinylindole-methacrylate copolymer, and α-cyano-4-hydroxycinnamic acid ester-9-vinylcarbazole-methacrylate copolymer.

[0051] The content of the ester resin in the resin component is typically 1% to 70% by weight, preferably 10% to 70% by weight, and more preferably 20% to 60% by weight. If the content of the ester resin is less than 1% by weight or more than 70% by weight, it is difficult to control the phase difference.

[0052] A-2. Acrylic plasticizers As the acrylic plasticizer, an acrylic polymer with a Tg of 50°C or higher can be used. Such an acrylic plasticizer has excellent compatibility with the above-mentioned resin components and can improve the stretchability without significantly lowering the Tg of the resin film. The upper limit of the Tg of the acrylic plasticizer is not limited as long as the effects of the present invention are obtained.

[0053] The weight-average molecular weight (Mw) of acrylic plasticizers, on a standard polystyrene basis, is, for example, 1,000 to 100,000, preferably 1,000 to 50,000, and more preferably 1,000 to 20,000. The Mw of acrylic plasticizers can be calculated from the elution curve measured by gel permeation chromatography (GPC). When the weight-average molecular weight is within the above range, the plasticizer can suitably exhibit its effect while avoiding problems such as bleed-out and decreased stability.

[0054] The monomer components constituting the above acrylic polymer include (meth)acrylic acid esters and may further include any suitable copolymerizable monomers that can copolymerize with (meth)acrylic acid esters, depending on the purpose.

[0055] Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, phenyl (meth)acrylate, toluyl (meth)acrylate, benzyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. Examples include ropil, stearyl (meth)acrylate, glycidyl (meth)acrylate, 2-aminoethyl (meth)acrylate, γ-(methacryloyloxypropyl)trimethoxysilane, ethylene oxide adducts of (meth)acrylic acid, trifluoromethylmethyl (meth)acrylate, 2-trifluoromethylethyl (meth)acrylate, 2-perfluoroethylethyl (meth)acrylate, 2-perfluoroethyl-2-perfluorobutylethyl (meth)acrylate, 2-perfluoroethyl (meth)acrylate, perfluoromethyl (meth)acrylate, diperfluoromethylmethyl (meth)acrylate, 2-perfluoromethyl-2-perfluoroethylmethyl (meth)acrylate, 2-perfluorohexylethyl (meth)acrylate, 2-perfluorodecylethyl (meth)acrylate, and 2-perfluorohexadecylethyl (meth)acrylate. The (meth)acrylic acid ester may have functional groups such as hydroxyl groups, carboxyl groups, and epoxy groups. (Meth)acrylic acid esters may be used individually or in combination of two or more types.

[0056] Examples of copolymer monomers include styrene monomers such as styrene, α-methylstyrene, alkylated α-methylstyrene, ethylstyrene, isobutylstyrene, t-butylstyrene, chlorostyrene, bromostyrene, and vinyltoluene; vinyl carboxylic acid monomers such as (meth)acrylic acid, fumaric acid, and maleic acid, or their acid anhydride monomers; vinyl cyanide monomers such as (meth)acrylonitrile; halogenated vinyl monomers such as vinyl chloride, vinyl bromide, and chloroprene; alkenes such as vinyl acetate, ethylene, propylene, butylene, butadiene, and isobutylene; halogenated alkenes; and polyfunctional monomers such as allyl methacrylate, diallyl phthalate, triallyl cyanurate, monoethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, divinylbenzene, and glycidyl methacrylate. Copolymer monomers may be used individually or in combination of two or more.

[0057] In one embodiment, the acrylic plasticizer is a copolymer (acrylic-styrene polymer) of monomer components including a (meth)acrylic acid ester and a styrene monomer. The acrylic-styrene polymer has excellent compatibility with the above resin components and tends to exhibit a high Tg.

[0058] Examples of acrylic plasticizers that can be used include UH-2170 (Tg=60℃), UC-3000 (Tg=65℃), UC-3080 (Tg=133℃), UF-5041 (Tg=77℃), UG-4035 (Tg=52℃), UG-4040 (Tg=63℃), and UG-4070 (Tg=58℃), all manufactured by Toagosei Co., Ltd.

[0059] The amount of acrylic plasticizer blended in the resin film (resulting in a phase difference film) is, for example, 1 to 30 parts by weight, preferably 1 to 20 parts by weight, and more preferably 1 to 10 parts by weight, per 100 parts by weight of the resin component. If the blending amount is less than the above range, the effect of improving stretchability may be insufficient. Conversely, if the blending amount is more than the above range, concerns may arise regarding bleed-out and clouding of the film.

[0060] A-3.Additional ingredients Additives can be appropriately selected depending on the purpose. Specific examples of additives include antioxidants such as hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, amine antioxidants, hydroxylamine antioxidants, vitamin E antioxidants, and other antioxidants; hindered amine light stabilizers; UV absorbers such as benzotriazole, benzophenone, triazine, and benzoate; surfactants; polymer electrolytes; conductive complexes; pigments; dyes; antistatic agents; antiblocking agents; and lubricants.

[0061] The content of each additive component in the resin film (and consequently the phase difference film) is, for example, 0.01 to 10 parts by weight, preferably 0.1 to 10 parts by weight, per 100 parts by weight of the resin component.

[0062] A-4. Applications of phase difference film The above-mentioned phase difference film can be applied to image display devices. Typical examples of image display devices include liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays).

[0063] When used in organic EL display devices, the phase difference film, with a value of λ / 4, can form a circular polarizer together with the polarizer and be positioned on the viewing side of the organic EL element to exhibit an anti-reflective function. In a circular polarizer, the phase difference film is positioned such that its slow axis direction is at an angle of, for example, 40° to 50°, preferably 42° to 48°, and more preferably about 45° with respect to the absorption axis direction of the polarizer. A circular polarizer having such a configuration can exhibit very excellent circular polarization characteristics (and consequently, very excellent anti-reflective characteristics).

[0064] The polarizer is typically composed of a polyvinyl alcohol-based resin film containing a dichroic substance (e.g., iodine). The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The transmittance of the polarizer is, for example, 41.0% or more, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0065] The thickness of the polarizer is, for example, 30 μm or less, preferably 15 μm or less, more preferably 1 μm to 12 μm, even more preferably 2 μm to 10 μm, and even more preferably 2 μm to 8 μm.

[0066] B. Method for manufacturing phase difference film Another aspect of the present invention provides a method for manufacturing a phase difference film. The method for manufacturing a phase difference film according to an embodiment of the present invention includes stretching a resin film comprising a resin component containing 30% to 99% by weight of a cellulose resin having the constituent units shown in formula (1) and 1% to 70% by weight of an ester resin having the constituent units shown in formula (2), formula (3), and formula (4), and an acrylic plasticizer having a Tg of 50°C or higher. The resin film can be obtained by forming a resin composition containing the above resin component and the acrylic plasticizer, and optionally further containing additive components, into a film. According to the method for manufacturing a phase difference film according to an embodiment of the present invention, the phase difference film described in section A can be suitably obtained.

[0067] In one embodiment, a method for manufacturing a phase difference film includes the steps of: preparing a resin solution by dissolving the resin component and acrylic plasticizer described in Section A in a solvent; coating the resin solution onto a substrate; heating the coating on the substrate to prepare a resin film; and stretching the resin film. The method for manufacturing a phase difference film may optionally further include a step of heat-shrinking the resin film in the stretching direction after the stretching step.

[0068] First, the resin component, the acrylic plasticizer, and any optional additives are dissolved in the solvent in the proportions described in Section A. Examples of solvents 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; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, cyclopentanone (CPN), 2-pyrrolidone, and N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; butanol, t-butyl alcohol, glycerin, and ethyl acetate. Examples of solvents include alcohol-based solvents such as ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol; amide-based solvents such as dimethylformamide and dimethylacetamide; nitrile-based solvents such as acetonitrile and butyronitrile; ether-based solvents such as 1,3-dioxolane, cyclopentyl methyl ether (CPME), propylene glycol methyl ether acetate (PGMEA), diethyl ether, dibutyl ether, and tetrahydrofuran; carbon disulfide, ethyl cellosolve, butyl cellosolve, and mixtures thereof.

[0069] Among the solvents, mixed solvents are preferred. Examples of mixed solvent combinations include ester solvent / aromatic hydrocarbons, ether solvent / aromatic hydrocarbons, ester solvent / ether solvent, ester solvent / alcohol solvent, ester solvent / ketone solvent, two types of ether solvents, and two types of ester solvents.

[0070] Hansen solubility parameter distance (hereinafter referred to as HSP distance) between cellulose resins and solvents. *セルロース系 It may be referred to as the HSP distance.) is, for example, 12.00 or less, preferably 11.30 or less, and more preferably 11.20 or less. *セルロース系If the above upper limit is below, the stretch orientation of the phase difference film can be improved. HSP distance *セルロース系 This can be calculated, for example, by the following formula (I). Note that HSP distance *セルロース系 The lower limit is typically 6.0 or higher. Equation (I): HSP distance *セルロース系 =[4(δ d2 -δ d1 ) 2 +( δ p2 -δ p1 ) 2 +( δ h2 -δ h1 ) 2 ] 0.5 (In formula (I), δ d1 This represents the intermolecular dispersion force energy of the solvent; δ d2 This represents the intermolecular dispersion force energy of cellulose resins; δ p1 This represents the dipole interaction energy between molecules in the solvent; δ p2 This represents the intermolecular dipole interaction energy of cellulose-based resins; δ h1 δ represents the hydrogen bond energy between molecules in the solvent; h2 This indicates the hydrogen bond energy between molecules in cellulose-based resins.

[0071] The HSP distance between the ester resin and the solvent (hereinafter referred to as HSP distance) *エステル系 It may be referred to as ) is, for example, 6.5 or less, preferably 6.0 or less, and for example, 2.0 or more. HSP distance *エステル系 This can be calculated, for example, by the following formula (II). Formula (II): HSP distance *エステル系 =[4(δ d3 -δ d1 ) 2 +( δ p3 -δ p1 ) 2 +( δ h3 -δ h1 ) 2 ] 0.5 (In formula (II), δ d3This represents the intermolecular dispersion force energy of ester resins; δ p3 This indicates the intermolecular dipole interaction energy of ester resins; δ h3 This indicates the intermolecular hydrogen bond energy of ester resins; δ d1 , δ p1 and δ h1 Each of these represents the intermolecular energy of the solvent, similar to that in equation (I) above.

[0072] (HSP distance *セルロース系 -HSP distance *エステル系 ) 2 For example, it is 60 or less, preferably 55 or less, more preferably 50 or less, even more preferably 45 or less, and especially preferably 30 or less. (HSP distance) *セルロース系 -HSP distance *エステル系 ) 2 If the above upper limit is below this value, the inverse dispersion of the phase difference film can be stably ensured. (HSP distance) *セルロース系 -HSP distance *エステル系 ) 2 The lower limit is, for example, 10 or more.

[0073] More preferably, the mixed solvent is an ester solvent / aromatic hydrocarbon, even more preferably ethyl acetate / toluene, and particularly preferably 60% by mass of ethyl acetate / 40% by mass of toluene. When the solvent is such a mixed solvent, the cellulose resin and the ester resin can form a nanophase separation structure more stably in the resin film (and consequently, the phase difference film).

[0074] The solid content concentration in the resin solution is, for example, 1% by mass or more, preferably 5% by mass or more, and for example, 30% by mass or less, preferably 20% by mass or less.

[0075] Preferably, the resin solution is stirred for a predetermined time, then allowed to stand to remove bubbles. The stirring time is, for example, 5 minutes or more, preferably 10 minutes or more, and for example, 3 hours or less, preferably 1 hour or less. The defoaming time (standing time) is, for example, 30 minutes or more, preferably 1 hour or more, and for example, 5 hours or less, preferably 3 hours or less.

[0076] Next, the resin solution is applied to the substrate (typically a resin film). Any suitable method can be used for the application. An applicator can be used as an application method. This forms a coating film of the resin solution on the substrate.

[0077] The thickness of the coating film is, for example, 30 μm to 500 μm, preferably 50 μm to 300 μm, and more preferably 70 μm to 200 μm.

[0078] Next, the coating on the substrate is heated to prepare a resin film. The heating temperature is, for example, 35°C to 165°C, and the heating time is 1 minute to 100 minutes. More specifically, such a heating process includes a primary heating process (drying process) heated at 165°C or lower, and a secondary heating process (annealing process) heated at 110°C or higher.

[0079] The drying process may be carried out in one stage or in multiple stages. Preferably, the drying process is carried out in multiple stages. When the drying process is carried out in multiple stages, the heating temperature for the first drying stage is set to, for example, 35°C to 65°C, preferably 45°C to 65°C, and the heating time for the first drying stage is set to, for example, 1 minute to 30 minutes, preferably 1 minute to 8 minutes. Thereafter, for each additional drying stage, the heating temperature is increased by, for example, 10°C to 130°C, preferably 10°C to 40°C. The heating time for each stage from the second stage onward is typically shorter than the heating time for the first drying stage, preferably 20 seconds to 20 minutes, more preferably 30 seconds to 5 minutes. The number of drying stages is preferably 2 to 4, more preferably 3 or fewer. The maximum temperature in the drying process is, for example, 165°C or less, preferably less than 130°C, more preferably less than 120°C, and even more preferably 115°C or less.

[0080] Subsequently, if necessary, the coating film heated in the drying step is cooled to, for example, 30°C or lower, preferably room temperature (23°C). Cooling the coating film after drying allows the nanophase separation structure formed in the drying step to be fixed, and the nanophase separation structure can be maintained without changing it in the subsequent annealing step. Next, the coating film is heated in the annealing step. The heating temperature in the annealing step is typically higher than the maximum temperature in the drying step. The heating temperature in the annealing step is, for example, 110°C or higher, preferably 120°C or higher, more preferably 130°C or higher, and for example, 180°C or lower, preferably 165°C or lower, more preferably 150°C or lower, and even more preferably 140°C or lower. The heating time in the annealing step is, for example, 1 minute or more, preferably 5 minutes or more, even more preferably 15 minutes or more, and for example, 60 minutes or less, preferably 45 minutes or less.

[0081] This forms a resin film on the substrate. Next, the resin film is peeled off the substrate.

[0082] The thickness of the resin film is, for example, 70 μm to 200 μm, preferably 70 μm to 150 μm.

[0083] Next, the resin film is stretched. In one embodiment, the resin film is stretched in the width direction perpendicular to the transport direction while being transported in the longitudinal direction (lateral stretching at the fixed end).

[0084] The stretching ratio is preferably 2.2 times or more, more preferably 2.3 times to 8.0 times, and even more preferably 2.5 times to 5.0 times. The resin film containing the resin component and acrylic plasticizer described in Section A has excellent stretchability, and therefore a high stretching ratio can be applied.

[0085] The stretching speed is, for example, 1 mm / second or more, preferably 2 mm / second or more, and for example, 200 mm / second or less, preferably 100 mm / second or less.

[0086] The stretching temperature can vary depending on the desired in-plane phase difference and thickness of the phase difference film, the type of resin used, the thickness of the resin film, the stretching ratio, etc. The stretching temperature fluctuates in relation to the Tg of the materials contained in the resin film, and is, for example, Tg1-20°C to Tg1+50°C, preferably Tg1-20°C to Tg1+40°C, and more preferably Tg1-10°C to Tg1+40°C, relative to the glass transition temperature (Tg1) of the resin with the lowest Tg among the oriented resins in the resin component. If the stretching temperature is within this range, the film can be stretched stably. Tg1 is, for example, the Tg of a cellulose-based resin.

[0087] The resin film is preferably preheated before stretching. The preheating temperature is set with respect to Tg1, similar to the stretching temperature. The preheating temperature is, for example, Tg1-20°C or higher, preferably Tg1-10°C or higher, and for example, Tg1+50°C or lower, preferably Tg1+40°C or lower. Typically, the preheating temperature is higher than the stretching temperature, preferably 5°C or higher than the stretching temperature.

[0088] If necessary, the process may include a step of heat-shrinking the stretched resin film in the stretching direction. The heat shrinkage temperature is set with respect to Tg1, similar to the preheating and stretching temperatures, and is, for example, Tg1-20°C or higher, preferably Tg1-15°C or higher, and for example, Tg1+45°C or lower, preferably Tg1+35°C or lower. The heat shrinkage temperature is more preferably below the stretching temperature. The shrinkage rate is typically 1% to 5%. [Examples]

[0089] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight. (1) Thickness The measurement was performed using a dial gauge (PEACOCK Corporation, product name "DG-205 type pds-2"). (2) In-plane phase difference (Re(λ)) The in-plane phase difference at the measurement wavelength λnm was automatically measured using Axoscan (manufactured by Axometrics). The measurement temperature was 23°C. (3) Birefringence (Δn(λ)) Δn(590) was calculated by dividing the in-plane phase difference at a wavelength of 590 nm of the measurement sample measured in (2) above by the thickness of the measurement sample. (4) Glass transition temperature (Tg) The glass transition temperatures of resins and films were measured using a differential scanning calorimeter "DSC6220" manufactured by SII Nanotechnology Co., Ltd. Approximately 10 mg of resin sample was placed in an aluminum pan manufactured by the same company, sealed, and heated from 30°C to 200°C at a heating rate of 20°C / min under a nitrogen flow of 50 mL / min. After holding the temperature for 3 minutes, it was cooled to 30°C at a rate of 20°C / min. It was held at 30°C for 3 minutes and then heated again to 250°C at a rate of 20°C / min. From the DSC data obtained from the second heating, the extrapolated glass transition onset temperature was determined, which is the temperature at the intersection of a straight line extending the baseline on the low-temperature side to the high-temperature side and a tangent line drawn at the point where the slope of the curve of the step-like change portion of the glass transition is maximum, and this was defined as the glass transition temperature (Tg). (4) MIT exam The MIT test was conducted in accordance with JIS P 8115. Specifically, the phase difference film was cut to a length of 15 cm and a width of 1.5 cm so that the stretching direction was the width direction (TD direction) and the direction perpendicular to the stretching direction was the longitudinal direction (MD direction), and these were used as test samples. The test samples were mounted on an MIT folding fatigue tester, model BE-202 (manufactured by Tester Sangyo Co., Ltd.) (load 1.0 kgf, clamp radius: 0.38 mm), and repeated bending was performed in the longitudinal direction (MD direction) at a test speed of 90 cpm and a bending angle of 90° (the direction of stretching of the bending line was the TD direction). The number of bending cycles at which the test sample broke was defined as the MIT cycle.

[0090] [Synthesis Example 1] Synthesis of cinnamic acid ester copolymer (9-vinylcarbazole / α-cyano-4-hydroxycinnamate isobutyl / acrylate isobutyl) 12.20 g of 9-vinylcarbazole, 7.74 g of isobutyl α-cyano-4-hydroxycinnamate, 4.05 g of isobutyl acrylate, and 0.453 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane and 36.00 g of methyl ethyl ketone, which are polymerization initiators, were placed in a 50 mL glass ampoule. After repeated nitrogen purging and pressure release, the ampoule was sealed under reduced pressure. Radical polymerization was carried out by placing this ampoule in a 54°C constant temperature bath and maintaining it for 24 hours. After the polymerization reaction was complete, the polymer was removed from the ampoule, 100 g of tetrahydrofuran was added, and this polymer solution was added dropwise to 800 g of methanol / water mixed solvent (weight ratio 80 / 20) to precipitate. After filtration, the filtrate was washed five times with 110 g of methanol / water mixed solvent (weight ratio 90 / 10) and filtered again. The obtained resin was vacuum-dried at 80°C for 10 hours to yield 22.3 g of a cinnamic acid ester copolymer exhibiting negative birefringence. The number-average molecular weight of the obtained cinnamic acid ester copolymer was 50,000, and the ratio of residue units was 50 mol% 9-vinylcarbazole residue units, 25 mol% α-cyano-4-hydroxycinnamate isobutyl residue units, and 25 mol% isobutyl acrylate residue units. The Tg of the cinnamic acid ester copolymer was approximately 198°C.

[0091] As described below, in the examples and comparative examples, a resin film was prepared and stretched to obtain a phase difference film. The stretching ratio used when preparing the phase difference film was determined by first testing the resin film at various stretching ratios, and the stretching ratio used was the one that allowed the film to be stretched without breakage in more than two-thirds of cases.

[0092] [Example 1] 80 g of ethylcellulose (Dow Chemical Company, Ethocel Standard 100, number average molecular weight Mn=58,000, weight average molecular weight Mw=180,000, Mw / Mn=3.2, degree of total substitution DS=2.51, Tg=approx. 130°C), 20 g of the cinnamic acid ester copolymer obtained in Synthesis Example 1, and 5 g of acrylic plasticizer (acrylic-styrene polymer, Toagosei Co., Ltd., "UG-4070", Tg=58°C, Mw=9,700) (5 parts per 100 parts of resin component) were dissolved in a mixed solvent of ethyl acetate / toluene = 60 / 40 (mass ratio) to obtain a resin solution with a solid content of 16% by mass. Next, the resin solution was stirred in a disperser mixer for 30 minutes, and then allowed to stand for 2 hours to remove air bubbles. The degassed resin solution was then coated onto a polyethylene terephthalate (PET) film (Toyobo Co., Ltd., Cosmoshine A4610) using an applicator. Next, the coating was dried in an oven under three conditions: 65°C / 6 minutes, 85°C / 1 minute, and 110°C / 2 minutes, and then allowed to stand at room temperature (23°C) for 60 minutes. After that, the dried coating was annealed again in an oven at 130°C / 60 minutes and peeled off from the PET film to obtain a resin film with a thickness of 110 μm. The Tg of the obtained resin film was measured and found to be 125.8°C. Next, the resin film was preheated at 165°C for 1 minute, and then stretched 2.8 times at a fixed end transversely at a stretching temperature of 155°C and a stretching speed of 2 mm / second. After that, the stretched resin film was shrunk by 2% in the width direction at a shrinking temperature of 155°C to obtain a phase difference film (thickness 39 μm).

[0093] The refractive index characteristics of the above-mentioned phase difference film showed nx>ny>nz. Furthermore, a sample was taken from near the center of the phase difference film in the thickness direction (specifically, a region within ±20% of the center of the phase difference film in the thickness direction, when the thickness of the phase difference film is set to 100%), and the cross-section of the phase difference film was observed by TEM (HT7820, Hitachi) using an ultrathin sectioning method including heavy metal staining (cross-sectional TEM observation). It was confirmed that a nanophase separation structure was formed in which the size (maximum length) of all domains was less than 100 nm. In addition, when the above-mentioned phase difference film was subjected to MIT testing, the number of MIT cycles in the MD direction exceeded 400.

[0094] [Example 2] A phase difference film (thickness 48 μm) was obtained in the same manner as in Example 1, except that the amount of acrylic plasticizer (Toagosei Co., Ltd., "UG-4070", Tg=58℃, Mw=9,700) added was 2 parts per 100 parts of resin component, and the stretching ratio was 2.3 times. The refractive index characteristics of the obtained phase difference film showed nx>ny>nz. Furthermore, when the central part of the phase difference film in the thickness direction was sampled and observed cross-sectionally with TEM in the same manner as above, it was confirmed that a nanophase separation structure was formed in which the size (maximum length) of all domains was less than 100 nm. In addition, when the above phase difference film was subjected to MIT testing, the number of MIT cycles in the MD direction exceeded 400.

[0095] [Comparative Example 1] A phase difference film (thickness 55 μm) was obtained in the same manner as in Example 1, except that an acrylic plasticizer was not added to the resin solution and the stretching ratio was set to 2.0 times.

[0096] [Comparative Example 2] A phase difference film (thickness 55 μm) was obtained in the same manner as in Example 1, except that an all-acrylic polymer (Toagosei Co., Ltd., "UG-4010", Tg=-57℃, Mw=2,900) was used as the acrylic plasticizer, the stretching temperature was set to 150℃, and the stretching ratio was set to 2.0 times.

[0097] The birefringence and in-plane phase difference of the phase difference films obtained in the examples and comparative examples were measured. The results are shown in Table 1. Figure 1 shows the relationship between the birefringence and wavelength dispersion of each phase difference film. [Table 1]

[0098] As shown in Table 1, the phase difference film of the example, which was made using a resin film containing an acrylic plasticizer with a Tg of 50°C or higher, could be stretched to a higher stretching ratio than the phase difference film of the comparative example and showed a higher Δn. Furthermore, as shown in Figure 1, the phase difference film of the example satisfies equation (a), indicating that it is possible to achieve both high birefringence (Δn) and inverse wavelength dispersion characteristics. [Industrial applicability]

[0099] The phase difference film of the present invention can be suitably used in image display devices such as liquid crystal displays and EL displays.

Claims

1. A stretched resin film comprising: a resin component comprising 30% to 99% by weight of a cellulose resin having the structural units shown in formula (1) below; 1% to 70% by weight of an ester resin having the structural units shown in formula (2), formula (3), and formula (4) below; and an acrylic-styrene polymer copolymer comprising a monomer component containing (meth)acrylic acid ester and styrene monomer, wherein the glass transition temperature is 50°C or higher; and a phase difference film: 【Chemistry 1】 (In formula (1), R １ ~R ３ Each of these independently represents a hydrogen atom or a substituent with 1 to 12 carbon atoms. 【Chemistry 2】 (In formula (2), R ４ R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; ５ａ R represents one selected from an alkyl group having 1 to 12 carbon atoms, 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; R ５ｂ R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; ６ This represents one selected from 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 alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms. 【Transformation 3】 (In formula (3), R ７ This represents a five-membered heterocyclic residue or a six-membered heterocyclic residue containing one or more nitrogen or oxygen atoms as heteroatoms (the five-membered heterocyclic residue and the six-membered heterocyclic residue may form a fused ring structure with other cyclic structures);) 【Chemistry 4】 (In formula (4), R ８ and R ９ each independently represent one selected from the group consisting of a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, and a cyclic alkyl group having 3 to 6 carbon atoms).

2. The phase difference film according to claim 1, wherein the birefringence Δn(590) at a measurement wavelength of 590 nm, the in-plane phase difference Re(450) at a measurement wavelength of 450 nm, and the in-plane phase difference Re(550) at a measurement wavelength of 550 nm satisfy the following formula (a). Δn(590)≧0.0140×(Re(450) / Re(550))−0.0092...(a)

3. The phase difference film according to claim 1 or 2, wherein the content of the acrylic-styrene polymer is 1 to 30 parts by weight per 100 parts by weight of the resin component.

4. The phase difference film according to claim 1 or 2, wherein the number of MIT cycles in a direction perpendicular to the stretching direction of the stretched film is 400 or more.

5. A method for producing a phase difference film, comprising stretching a resin film containing a resin component comprising 30% to 99% by weight of a cellulose resin having the structural units shown in formula (1) below, and 1% to 70% by weight of an ester resin having the structural units shown in formula (2), formula (3), and formula (4) below, and an acrylic-styrene polymer which is a copolymer of a (meth)acrylic acid ester and a monomer component having a glass transition temperature of 50°C or higher, at a stretching ratio of 2.2 times or more in the temperature range of Tg1-20°C to Tg1+50°C with respect to the glass transition temperature (Tg1) of the resin having the lowest glass transition temperature among the oriented resins in the resin component: 【Transformation 5】 (In formula (1), R １ ~R ３ Each of these independently represents a hydrogen atom or a substituent with 1 to 12 carbon atoms. 【Transformation 6】 (In formula (2), R ４ R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; ５ａ R represents one selected from an alkyl group having 1 to 12 carbon atoms, 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; R ５ｂ R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; ６ This represents one selected from 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 alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms. 【Transformation 7】 (In formula (3), R ７ This represents a five-membered heterocyclic residue or a six-membered heterocyclic residue containing one or more nitrogen or oxygen atoms as heteroatoms (the five-membered heterocyclic residue and the six-membered heterocyclic residue may form a fused ring structure with other cyclic structures);) 【Transformation 8】 (In formula (4), R ８ and R ９ Each of these independently represents 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.

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