Resin film, phase difference film, laminated phase difference film, method for manufacturing a resin film, and method for manufacturing a phase difference film

Abstract

To provide a resin film and a method for manufacturing the same that can be suitably used in producing a phase difference film containing a fumarate ester resin that has a large phase difference value but a small degree of polarization depolarization, a phase difference film using the resin film and a method for manufacturing the same, and a laminated phase difference film comprising such a phase difference film. [Solution] The resin film according to the embodiment of the present invention contains a fumarate ester resin, has a thickness of 20 μm or more, and a cross-sectional area of ​​1 μm. 2 The number of voids per unit is 3.0 or less.

Description

[Technical Field]

[0001] The present invention relates to a resin film, a phase difference film, a laminated phase difference film, a method for manufacturing a resin film, and a method for manufacturing a phase difference film. [Background technology]

[0002] In recent years, with the spread of thin-screen displays, image display devices equipped with organic EL panels (organic EL display devices) have been proposed. Organic EL panels have a highly reflective metal layer, which can easily cause problems such as reflection of ambient light and background reflections. It is known that these problems can be prevented by providing a phase difference film. In the manufacture of this phase difference film, typically, a resin film is formed by coating it with a resin solution, and the resulting resin film is stretched to obtain the phase difference film (see Patent Document 1).

[0003] However, while there is a demand for improved phase difference values ​​in phase difference films containing fumarate ester resins, increasing the thickness of the phase difference film to increase its phase difference value presents a problem: when the coated resin solution is dried, many air bubbles are generated, causing the resulting resin film to lose its polarization. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-180140 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention has been made to solve the above problems, and its main objective is to provide a resin film and a method for manufacturing the same that can be suitably used in producing a phase difference film containing a fumarate ester resin in which the phase difference value is large but the degree of polarization depolarization is small, a phase difference film using the resin film and a method for manufacturing the same, and a laminated phase difference film comprising such a phase difference film. [Means for solving the problem]

[0006] [1] The resin film according to the embodiment of the present invention contains a fumarate ester resin, has a thickness of 20 μm or more, and a cross-section of 1 μm 2 The number of voids per unit is 3.0 or less. [2] One embodiment is the resin film described in item [1] above, wherein Re(550) is -2.0 nm to 2.0 nm and Rth(550) is -140 nm to -85 nm: where Re(550) represents the in-plane phase difference measured with light of wavelength 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of wavelength 550 nm at 23°C. [3] Another aspect of the present invention provides a phase difference film comprising a fumarate ester resin, exhibiting refractive index characteristics of nz>nx>ny, having a thickness of 20 μm or more, and a cross-section of 1 μm. 2 The number of voids per unit is 3.0 or less. [4] One embodiment is the phase difference film described in item [3] above, wherein Re(550) is 20 nm to 50 nm and Rth(550) is -120 nm to -70 nm: where Re(550) represents the in-plane phase difference measured with light of wavelength 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of wavelength 550 nm at 23°C. [5] A laminated phase difference film according to yet another aspect of the present invention has a first phase difference layer, a second phase difference layer and an adhesive layer in this order, wherein the first phase difference layer exhibits a refractive index characteristic nx>ny>nz, and the second phase difference layer is the phase difference film described in item [3] or [4] above. [6] A method for producing a resin film according to yet another aspect of the present invention comprises a coating step of applying a resin solution containing a solvent and a fumarate ester resin onto a substrate to form a coated film, a first drying step of drying the coated film at 40°C to 70°C, and a second drying step of drying the coated film after the first drying step at 110°C to 150°C, wherein the solvent comprises a low-boiling-point solvent with a boiling point of 85°C or less and a high-boiling-point solvent with a boiling point of 110°C or more, the solvent contains 30% by weight or less of the high-boiling-point solvent, the solid content concentration in the resin solution is 15% by weight or more, and the thickness of the resulting resin film is 20 μm or more. [7] A further aspect of the present invention provides a method for manufacturing a phase difference film, further comprising a stretching step of stretching a resin film manufactured by the resin film manufacturing method described in item [6] above, wherein the thickness of the resulting phase difference film is 20 μm or more. [8] One embodiment is the manufacturing method described in item [6] or [7] above, wherein the resin film has a Re(550) of -2.0 nm to 2.0 nm and a Rth(550) of -140 nm to -85 nm: where Re(550) represents the in-plane phase difference measured with light of a wavelength of 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of a wavelength of 550 nm at 23°C. [9] One embodiment is a manufacturing method according to any of the above items [6] to [8], wherein the viscosity of the resin solution is 1.8 Pa·s to 4.5 Pa·s.

[10] One embodiment is a manufacturing method according to any one of the above items [6] to [9], wherein the resin solution contains 21% by weight or less of the fumarate ester resin.

[11] One embodiment is the manufacturing method described in item [7] above, wherein the phase difference film has a Re(550) of 20 nm to 50 nm and a Rth(550) of -120 nm to -70 nm: where Re(550) represents the in-plane phase difference measured with light of a wavelength of 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of a wavelength of 550 nm at 23°C. [Effects of the Invention]

[0007] According to an embodiment of the present invention, there can be provided a resin film containing a fumarate ester resin, which is suitably used for producing a retardation film capable of reducing the depolarization degree even though the retardation value is large, and a method for producing the same. According to the present invention, there can be further provided a retardation film using said resin film, a method for producing the same, and a laminated retardation film comprising such a retardation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view of a laminated retardation film according to one embodiment of the present invention. [Figure 2] FIG. 2 is an SEM image on the Air side of a cross-section in the thickness direction of the resin film of Example 1. [Figure 3] FIG. 3 is an SEM image on the substrate side of a cross-section in the thickness direction of the resin film of Example 1. [Figure 4] FIG. 4 is an SEM image on the Air side of a cross-section in the thickness direction of the resin film of Comparative Example 1. [Figure 5] FIG. 5 is an SEM image on the substrate side of a cross-section in the thickness direction of the resin film of Comparative Example 1. [Figure 6] FIG. 6 is an SEM image on the Air side of a cross-section in the thickness direction of the resin film of Comparative Example 2. [Figure 7] FIG. 7 is an SEM image on the substrate side of a cross-section in the thickness direction of the resin film of Comparative Example 2. DESCRIPTION OF EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. For clearer explanation, the drawings may schematically represent the width, thickness, shape and the like of each part compared to the actual embodiments, but this is merely an example and does not limit the interpretation of the present invention.

[0010] (Definition of Terms and Symbols) Definitions of terms and symbols used in the present specification are as follows. (1) Refractive indices (nx, ny, nz) "nx" represents the refractive index in the direction where the in-plane refractive index is maximized (i.e., the slow axis direction), "ny" represents the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" represents the refractive index in the thickness direction. (2) In-plane retardation (Re) "Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Thickness direction retardation (Rth) "Rth(λ)" is the thickness direction retardation measured with light having a wavelength of λ nm at 23°C. For example, "Rth(550)" is the thickness direction retardation measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is obtained by the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (4) Angle When an angle is mentioned in the present specification, unless otherwise specifically stated, the angle includes both clockwise and counterclockwise directions relative to the reference direction. Therefore, for example, "45°" means ±45°.

[0011] A. Resin Film The resin film according to an embodiment of the present invention contains a fumarate ester-based resin, has a thickness of 20 µm or more, and has a cross-section in the thickness direction of 1 µm 2 has 3.0 or less voids per The present inventors have found that the depolarization degree of a resin film correlates with the amount of generated bubbles, and that adjusting the number of voids, which are traces of bubble generation, to a specific ratio can reduce the depolarization degree of the resin film, thereby completing the present invention. According to one embodiment of the present invention, in a cross-section of a resin film containing a fumarate ester-based resin, per 1 µm 2By setting the number of voids per unit to 3.0 or less, the resin film and the phase difference film obtained from the resin film may exhibit a low degree of polarization depolarization despite a large phase difference value.

[0012] In one embodiment, the in-plane phase difference Re(550) in the resin film is preferably -2.0 nm to 2.0 nm, more preferably -1.0 nm to 1.0 nm, even more preferably -0.5 nm to 0.5 nm, and particularly preferably 0 nm. If the in-plane phase difference Re(550) in the resin film is within this range, the viewing angle characteristics can be improved when the resin film is used in combination with a polarizer in an image display device. Furthermore, the phase difference Rth(550) in the thickness direction of the resin film is preferably -140 nm to -80 nm, more preferably -130 nm to -85 nm. If the phase difference Rth(550) in the thickness direction of the resin film is within this range, the viewing angle characteristics can be improved when the resin film is used in combination with a polarizer in an image display device. Thus, the resin film can be a positive C plate (a phase difference film exhibiting refractive index characteristics of nz>nx=ny). However, in this specification, for convenience, it is referred to as a resin film to distinguish it from the positive B plate described later.

[0013] B. Method for manufacturing resin film The resin films described above are typically manufactured by the following manufacturing method. A method for manufacturing a resin film according to one embodiment includes the steps of: applying a resin solution containing a solvent and a fumarate ester resin onto a substrate to form a coated film (coating step); drying the coated film (first drying step); and drying the coated film after the first drying step (second drying step).

[0014] B-1.Coating process In the coating process, a resin solution containing a solvent and a fumarate ester resin is applied to the substrate to form a coating film.

[0015] Any suitable substrate can be used as the base material. Examples of substrates include polymer substrates, glass substrates, metal substrates, and inorganic substrates. Examples of polymer substrates include polyethylene terephthalate (PET), polyester, polycarbonate, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, triacetylcellulose, polyvinyl alcohol, polyimide, polyarylate, polysulfone, polyethersulfone, and epoxy resins. Examples of glass substrates include glass plates and quartz substrates. Examples of metal substrates include aluminum, stainless steel, and ferrotype. Examples of inorganic substrates include ceramic substrates. Preferably, the base material is a polymer substrate or a metal substrate, and more preferably polyethylene terephthalate.

[0016] The solvent typically includes a low-boiling point solvent and a high-boiling point solvent, preferably containing 95% or more of the low-boiling point solvent and the high-boiling point solvent based on the total weight of the solvent. By including both a low-boiling point solvent and a high-boiling point solvent in the solvent, it is possible to achieve both improved phase difference characteristics and suppression of polarization depolarization in the resulting resin film and phase difference film.

[0017] The boiling point of the low-boiling solvent is typically 85°C or lower, preferably 55°C to 85°C, and more preferably 75°C to 85°C. If the boiling point of the low-boiling solvent is within this range, the depolarization of the resulting resin film and phase difference film can be suppressed.

[0018] Examples of low-boiling point solvents include ester solvents such as ethyl acetate; ketone solvents such as acetone and methyl ethyl ketone (MEK); alcohol solvents such as 2-propanol; nitrile solvents such as acetonitrile; and mixtures thereof. Preferably, the low-boiling point solvent is an ester solvent or a ketone solvent, more preferably ethyl acetate or methyl ethyl ketone, and even more preferably methyl ethyl ketone. Such low-boiling point solvents can suppress the depolarization of the resulting resin film and phase difference film.

[0019] The boiling point of the high-boiling point solvent is typically 110°C or higher, preferably 110°C to 140°C, more preferably 115°C to 130°C, and even more preferably 115°C to 120°C. If the boiling point of the high-boiling point solvent is within this range, the phase difference characteristics of the resulting resin film and phase difference film can be improved.

[0020] Examples of high-boiling point solvents include ester solvents such as butyl acetate and isobutyl acetate; ketone solvents such as methyl isobutyl ketone (MIBK); alcohol solvents such as 1-butanol; and mixtures thereof. Preferably, the high-boiling point solvent is a ketone solvent, and more preferably, methyl isobutyl ketone. Such high-boiling point solvents can improve the phase difference properties of the resulting resin film and phase difference film.

[0021] Examples of combinations of low-boiling point solvents and high-boiling point solvents include the combination of the low-boiling point solvent and the high-boiling point solvent described above. Preferably, the low-boiling point solvent is an ester-based solvent or a ketone-based solvent, and the high-boiling point solvent is a ketone-based solvent. More preferably, the combination is ethyl acetate and methyl isobutyl ketone, or methyl ethyl ketone and methyl isobutyl ketone. Even more preferably, the combination is methyl ethyl ketone and methyl isobutyl ketone. Such combinations of low-boiling point solvents and high-boiling point solvents can achieve an even higher level of both improved phase difference characteristics and suppression of polarization depolarization in the resulting resin film and phase difference film.

[0022] The solvent typically contains 30% by weight or less of a high-boiling point solvent, preferably 25% by weight or less, and more preferably 20% by weight or less. Furthermore, the solvent contains, for example, 5% by weight or more of a high-boiling point solvent, more preferably 10% by weight or more. If the high-boiling point solvent content of the solvent is below this upper limit, the degree of depolarization of the resulting resin film and phase difference film can be reduced. If the high-boiling point solvent content of the solvent is above this lower limit, the phase difference value of the resulting resin film and phase difference film can be increased.

[0023] The solvent contains, for example, 70% by weight or more of a low-boiling point solvent, preferably 75% by weight or more, and more preferably 80% by weight or more. Alternatively, the solvent may contain, for example, 95% by weight or less of a low-boiling point solvent, preferably 90% by weight or less. If the low-boiling point solvent content of the solvent is above this lower limit, the degree of depolarization of the resulting resin film and phase difference film may be reduced, and if the low-boiling point solvent content of the solvent is below this upper limit, the phase difference value of the resulting resin film and phase difference film may be increased.

[0024] The weight ratio of low-boiling solvent to high-boiling solvent in the solvent (low-boiling solvent / high-boiling solvent) is, for example, 7 / 3 to 19 / 1, preferably 4 / 1 to 10 / 1. If the weight ratio of low-boiling solvent to high-boiling solvent in the solvent is above this lower limit, the degree of depolarization of the resulting resin film and phase difference film can be reduced, and if the weight ratio of low-boiling solvent to high-boiling solvent in the solvent is below this upper limit, the phase difference value of the resulting resin film and phase difference film can be increased.

[0025] Examples of fumarate ester resins include polymers containing monomeric structural units of fumarate diesters. Examples of monomers that form the monomer constituent units of fumarate diesters include fumarate diesters. Examples of fumarate diesters include dimethyl fumarate, diethyl fumarate, dipropyl fumarate, diisopropyl fumarate, di-n-butyl fumarate, di-s-butyl fumarate, di-t-butyl fumarate, di-n-pentyl fumarate, diisopentyl fumarate, di-s-pentyl fumarate, di-t-pentyl fumarate, di-n-hexyl fumarate, diisohexyl fumarate, di-s-hexyl fumarate, di-t-hexyl fumarate, dicyclopropyl fumarate, dicyclopentyl fumarate, dicyclohexyl fumarate, and combinations thereof. Preferably, the fumarate diesters are diethyl fumarate, diisopropyl fumarate, or a combination of diethyl fumarate and diisopropyl fumarate, and more preferably a combination of diethyl fumarate and diisopropyl fumarate. The molar ratio of diethyl fumarate to diisopropyl fumarate (diethyl fumarate / diisopropyl fumarate) is, for example, 3 / 7 to 1 / 19, preferably 2 / 8 to 1 / 9. When the molar ratio of diethyl fumarate to diisopropyl fumarate is within this range, resin films and phase difference films with excellent heat resistance and mechanical properties can be obtained.

[0026] Furthermore, the monomers that form the monomer constituent units of fumarate ester resins may also include monomers copolymerizable with fumarate diesters. Examples of such monomers include styrenes such as styrene and α-methylstyrene; acrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 3-ethyl-3-oxetanylmethyl acrylate, and tetrahydrofurfuryl acrylate; methacrylic acid; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 3-ethyl-3-oxetanylmethyl methacrylate, and tetrahydrofurfuryl methacrylate; vinyl esters such as vinyl acetate and vinyl propionate; acrylonitrile; methacrylonitrile; and olefins such as ethylene and propylene. Preferably, monomers copolymerizable with fumarate diesters are 3-ethyl-3-oxetanylmethyl acrylate and 3-ethyl-3-oxetanylmethyl methacrylate, and more preferably 3-ethyl-3-oxetanylmethyl acrylate. Monomers copolymerizable with fumarate diesters may be used individually or in combination of two or more.

[0027] The monomer constituent units of fumarate diesters contained in the fumarate ester resin are, for example, 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more. If the monomer constituent units of fumarate diesters contained in the fumarate ester resin are within this range, resin films and phase difference films with excellent heat resistance and mechanical properties can be obtained.

[0028] The number-average molecular weight (Mn) of fumarate ester resins is, for example, 1 × 10⁻⁶. 3 The above is preferable to 2 × 10 4 ~3×10 5 Therefore, if the number-average molecular weight is within the above range, a resin film with excellent mechanical properties and excellent moldability during film formation can be obtained. Note that the number-average molecular weight is the standard polystyrene equivalent value obtained by gel permeation chromatography (hereinafter referred to as GPC).

[0029] Any suitable method can be used to produce the fumarate ester resin, as long as the above-mentioned fumarate ester resin can be obtained. A typical production method is radical polymerization.

[0030] Any suitable method can be employed for radical polymerization. Specific examples include bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, and emulsion polymerization.

[0031] Examples of polymerization initiators in radical polymerization include organic peroxides and azo polymerization initiators. Examples of organic peroxides include benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butyl peroxypivalate. Examples of azo polymerization initiators include 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis(cyclohexane-1-carbonitride).

[0032] Suitable solvents for radical polymerization include, for example, aromatic solvents such as benzene, toluene, and xylene; alcoholic solvents such as methanol, ethanol, propyl alcohol, and butyl alcohol; cyclohexane; dioxane; tetrahydrofuran (THF); acetone; methyl ethyl ketone; dimethylformamide; isopropyl acetate; and water. Mixtures of these solvents may also be used as the solvent for radical polymerization.

[0033] The polymerization temperature during radical polymerization can be appropriately set according to the decomposition temperature of the polymerization initiator, for example, in the range of 40 to 150°C.

[0034] The above resin solution is typically prepared by adding a fumarate ester resin to a solvent, stirring for a predetermined time, and then allowing it to stand to degas. The stirring time is, for example, 5 minutes to 3 hours, preferably 10 minutes to 1 hour. The degassing time (standing time) is, for example, 24 to 72 hours, preferably 36 to 60 hours.

[0035] The solid content concentration in the resin solution is typically 15% by weight or more, preferably 17% by weight or more, and more preferably 19% by weight or more. Furthermore, the solid content concentration in the resin solution is preferably 22% by weight or less, and more preferably 21% by weight or less. If the solid content concentration in the resin solution is above this lower limit, the degree of polarization depolarization of the resulting resin film and phase difference film can be reduced, and if it is below this upper limit, coating unevenness on the surface of the resulting resin film and phase difference film can be reduced. The solid content concentration in the resin solution is measured by a drying method. The main component of the solid content in the above resin solution is a fumarate ester resin, and the fumarate ester resin is present in the solid content of the resin solution at, for example, 95% by weight or more.

[0036] The viscosity of the resin solution is preferably 1.8 Pa·s to 4.5 Pa·s, more preferably 1.8 Pa·s to 4.0 Pa·s, even more preferably 2.0 Pa·s to 4.0 Pa·s, particularly preferably 2.5 Pa·s to 3.5 Pa·s, and especially preferably 2.8 Pa·s to 3.3 Pa·s. If the viscosity of the resin solution is above this lower limit, the degree of depolarization of the resulting resin film and phase difference film can be reduced, and if it is below this upper limit, coating unevenness on the surface of the resulting resin film and phase difference film can be reduced. The viscosity of the resin solution is measured using a B-type viscometer in accordance with JIS Z 8803:2011, under conditions of temperature: 25°C and angular velocity: 75.4 rad / s.

[0037] Any suitable additives may be added to the resin solution. 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; plasticizers (e.g., alfons); polymer electrolytes; conductive complexes; pigments; dyes; antistatic agents; antiblocking agents; and lubricants. The type, number, combination, and amount of additives can be appropriately determined depending on the purpose.

[0038] Any suitable coating method can be adopted. Examples of coating methods include those using an applicator, doctor blade, bar coater, slip coater, gravure coater, spin coater, or roll coater. The coating method can be appropriately determined depending on the composition and type of resin solution used, the desired properties of the resin film, and other factors.

[0039] By applying the resin solution to the substrate in this manner, a coating film is formed. The coating film can be any appropriate thickness (before drying) depending on the desired thickness of the resin film.

[0040] B-2. First drying process and second drying process Next, the coating film on the substrate is dried to obtain a resin film. The method for drying the coating film includes a first drying step and a second drying step, in which the coating film on the substrate is dried in the first drying step, and then the coating film is further dried in the second drying step.

[0041] The drying temperature of the first drying step (first drying temperature) is, for example, 40°C to 70°C, preferably 45°C to 65°C, and more preferably 50°C to 60°C. If the first drying temperature is within the above range, the depolarization of the resulting resin film and phase difference film can be suppressed. The first drying step may be carried out in one step or in multiple steps. The drying temperature in the second drying step (second drying temperature) is, for example, 110°C to 150°C, preferably 130°C to 145°C. If the second drying temperature is within the above range, the phase difference characteristics of the resulting resin film and phase difference film can be improved. The second drying step may be carried out in one step or in multiple steps. The drying times in the first and second drying steps can be any appropriate drying time. Specifically, in the first drying step, the drying time is adjusted so that the thickness of the coating film after the first drying step is, for example, 1.5 to 2.0 times the thickness of the coating film after the second drying step. In the second drying step, the drying time is adjusted so that drying continues until no further change in the thickness of the coating film due to drying is observed (for example, the change in the thickness of the coating film becomes 1% / second or less). Note that the drying time will vary depending on the drying temperature, the type of solvent, etc.

[0042] Subsequently, the coating film heated in the first and second drying steps is cooled and / or annealed as needed. The cooling temperature is, for example, 30°C or lower, preferably room temperature (23°C). In the annealing step, the coating film is heated. The heating temperature in the annealing step is preferably higher than the maximum temperature in the drying step. The heating temperature in the annealing step is, for example, 115°C to 180°C, preferably 120°C to 150°C, and more preferably 130°C to 140°C. The heating time in the annealing step is, for example, 1 minute to 60 minutes, preferably 15 minutes to 45 minutes.

[0043] As described above, a resin film is manufactured. A resin film containing a fumarate ester resin manufactured by the above manufacturing method may have a large phase difference value but a small degree of depolarization, and such a phase difference film can be manufactured.

[0044] The resin film preferably contains 70% by weight or more of a fumarate ester resin, more preferably 90% by weight or more of a fumarate ester resin, and even more preferably 95% by weight or more of a fumarate ester resin. If the fumarate ester resin content of the resin film is within the above range, the phase difference characteristics of the resin film and the resulting phase difference film can be improved.

[0045] The thickness of the resin film is typically 20 μm or more, preferably 21 μm or more. Furthermore, the thickness of the resin film is preferably less than 24 μm, more preferably 23 μm or less. If the thickness of the resin film is above this lower limit, the phase difference in the thickness direction can be sufficiently large, and if the thickness of the resin film is below this upper limit, the degree of polarization depolarization of the resin film and the resulting phase difference film can be reduced.

[0046] Cross-section of the resin film in the thickness direction, 1 μm 2The number of voids per is typically 3.0 or less, preferably 2.5 or less, more preferably 1.6 or less, still more preferably 1.3 or less, and particularly preferably 1.2 or less. Further, a 1 μm cross-section in the thickness direction of the resin film 2 The number of voids per is, for example, 0.1 or more, and preferably 0.5 or more. A 1 μm cross-section in the thickness direction of the resin film 2 When the number of voids per falls within the above range, the depolarization degree of the resin film and the obtained retardation film can be reduced. A 1 μm cross-section in the thickness direction of the resin film 2 The number of voids per is obtained by analyzing an image acquired with a scanning electron microscope (SEM).

[0047] The depolarization degree of the resin film is, for example, 0.008 or less, preferably 0.006 or less, and more preferably 0.005 or less. Further, the depolarization degree of the resin film is, for example, 0.001 or more, and preferably 0.002 or more. When the depolarization degree of the resin film falls within the above range, light leakage from the resin film and the obtained retardation film can be suppressed. Note that the depolarization degree of a resin film refers to the difference in polarization degree depending on the presence or absence of the resin film (polarization degree difference of the resin film). The method for measuring the polarization degree difference of the resin film is as follows. Specifically, the value is obtained by measuring the luminosity-corrected polarization degree (Py) using a spectrophotometer (product name "V-7100", manufactured by JASCO Corporation). More specifically, the luminosity-corrected polarization degree is measured in a state where the resin film is laminated on a polarizing plate that has a luminosity-corrected polarization degree of 99.996 when measured as a single polarizing plate, and the difference between the obtained luminosity-corrected polarization degree and 99.996 (the luminosity-corrected polarization degree of the single polarizing plate) is taken as the polarization degree difference of the resin film (the depolarization degree of the resin film). When measuring the polarizing plate laminated with the resin film, the resin film layer is placed between the polarizing plate and the analyzer. The resin film may exhibit normal wavelength dispersion characteristics, reverse wavelength dispersion characteristics, or flat wavelength dispersion characteristics with respect to the retardation in the thickness direction.

[0048] C. Method for producing retardation film The resin films described in sections A and B above can be suitably used in methods for manufacturing phase difference films. The method for manufacturing a phase difference film includes a step of stretching the resin film manufactured by the method for manufacturing a resin film described in section B (stretching step). The resin film may be applied to the method for manufacturing a phase difference film after being peeled from the substrate, or it may be applied to the method for manufacturing a phase difference film while supported on the substrate.

[0049] In the stretching process, any suitable stretching method can be used to stretch the resin film. Various stretching methods, such as free-end stretching, fixed-end stretching, free-end shrinking, and fixed-end shrinking, can be used individually, simultaneously, or sequentially. The stretching direction can also be in various directions and dimensions, such as the length direction, width direction, thickness direction, and diagonal direction.

[0050] Specific examples of stretching methods include fixed-end uniaxial stretching, free-end uniaxial stretching, and oblique stretching. Fixed-end uniaxial stretching can be performed, for example, by using a tenter-type stretching device to transport a long resin film in the longitudinal direction while stretching it in a direction perpendicular to the longitudinal direction (width direction). Free-end uniaxial stretching can be performed, for example, by passing a long resin film between rolls with different peripheral speeds and stretching it in the longitudinal direction. Oblique stretching can be performed, for example, by continuously stretching a long resin film obliquely in a direction at an angle θ with respect to the longitudinal direction. By employing oblique stretching, a long phase difference film having an orientation angle of angle θ with respect to the longitudinal direction of the film (a slow axis in the direction of angle θ) can be obtained. Among such stretching methods, free-end uniaxial stretching is preferred. The resin film may be stretched in one step or in two or more steps. Preferably, it is stretched in one step.

[0051] The stretching temperature is set by focusing on the Tg:(Tg1) of the resin film. The stretching temperature is, for example, (Tg1)-20℃ to (Tg1)+50℃, and preferably (Tg1)-10℃ to (Tg1)+40℃. The stretching speed is, for example, 0.01% / sec to 1.00% / sec, preferably 0.05% / sec to 0.50% / sec, relative to the length of the resin film in the stretching direction before stretching. The stretching ratio (the product of the stretching ratio of the first stretching step and the stretching ratio of the second stretching step when the resin film is stretched in two steps) is adjusted according to the desired in-plane phase difference value Re. The stretching ratio is, for example, 1.04 to 1.10 times.

[0052] The method for manufacturing a phase difference film may further include, if necessary, a step of thermally shrinking the resin film in the stretching direction after the stretching step (thermal shrinking step). The thermal shrinkage temperature is set with respect to (Tg1) in the same way as the stretching temperature, for example, between (Tg1)-20°C and (Tg1)+45°C, preferably between (Tg1)-15°C and (Tg1)+35°C. The thermal shrinkage temperature is more preferably below the stretching temperature. The shrinkage rate is, for example, 1% to 5%.

[0053] A phase difference film is manufactured as described above. A phase difference film containing a fumarate ester resin manufactured by the above method may have a large phase difference value but a small degree of depolarization. The following describes phase difference films.

[0054] D. Phase difference film The phase difference film typically contains a fumarate ester resin, preferably 70% by weight or more of the fumarate ester resin, more preferably 90% by weight or more of the fumarate ester resin, and even more preferably 95% by weight or more of the fumarate ester resin. If the fumarate ester resin content of the phase difference film is within the above range, the phase difference characteristics of the phase difference film can be improved.

[0055] The thickness of the phase difference film is typically 20 μm or more, preferably 21 μm or more. Furthermore, the thickness of the phase difference film is preferably less than 24 μm, more preferably 23 μm or less. If the thickness of the phase difference film is above this lower limit, the phase difference in the thickness direction can be sufficiently large, and if the thickness of the phase difference film is below this upper limit, the degree of polarization depolarization of the phase difference film can be reduced.

[0056] Cross-section of the phase difference film in the thickness direction, 1 μm 2 The number of voids per unit area is typically 3.0 or less, preferably 2.5 or less, more preferably 1.6 or less, even more preferably 1.3 or less, and particularly preferably 1.2 or less. Furthermore, the cross-section of the phase difference film in the thickness direction is 1 μm. 2 The number of voids per unit area is, for example, 0.1 or more, preferably 0.5 or more. Cross-section of the phase difference film in the thickness direction: 1 μm 2 If the number of voids per unit area is within the above range, the degree of polarization depolarization of the phase difference film can be reduced. Cross-section of the phase difference film in the thickness direction: 1 μm 2 The number of voids per unit area is obtained by analyzing images acquired using a scanning electron microscope (SEM).

[0057] Phase difference films typically exhibit refractive index characteristics of nz > nx > ny. Phase difference films with refractive index characteristics of nz > nx > ny are sometimes referred to as "positive B plates."

[0058] The in-plane phase difference Re(550) in the phase difference film is, for example, 20 nm to 50 nm, preferably 25 nm to 45 nm, and more preferably 30 nm to 40 nm. If the in-plane phase difference Re(550) in the phase difference film is within this range, the viewing angle characteristics when the phase difference film is used in combination with a polarizer in an image display device can be improved. Furthermore, the phase difference Rth(550) in the thickness direction is, for example, -120 nm to -70 nm, preferably -110 nm to -75 nm, and more preferably -100 nm to -80 nm. If the phase difference Rth(550) in the thickness direction in the phase difference film is within this range, the viewing angle characteristics when the phase difference film is used in combination with a polarizer in an image display device can be improved.

[0059] The degree of depolarization of the phase difference film is, for example, 0.008 or less, preferably 0.006 or less, and more preferably 0.005 or less. Furthermore, the degree of depolarization of the phase difference film is, for example, 0.001 or more. If the degree of depolarization of the phase difference film is within this range, light leakage from the phase difference film can be suppressed. Note that the degree of depolarization of the phase difference film refers to the difference in polarization degree with and without the phase difference film (the difference in polarization degree of the phase difference film). The method for measuring the difference in polarization degree of the phase difference film is as follows. Specifically, it is determined by measuring the luminous efficiency-corrected polarization degree (Py) using a spectrophotometer (product name "V-7100", manufactured by JASCO Corporation). More precisely, the luminous efficiency-corrected polarization degree is measured when a phase difference film is laminated onto a polarizer whose luminous efficiency-corrected polarization degree alone is 99.996. The difference between the obtained luminous efficiency-corrected polarization degree and 99.996 (luminous efficiency-corrected polarization degree of the polarizer alone) is taken as the polarization degree difference of the phase difference film (depolarization degree of the phase difference film). When measuring a polarizer with a phase difference film laminated onto it, the phase difference film layer is positioned between the polarizer and the analyzer so that the angle between the absorption axis of the polarizer and the slow axis of the phase difference film is 90°. The phase difference film may exhibit positive wavelength dispersion characteristics, inverse wavelength dispersion characteristics, or flat wavelength dispersion characteristics with respect to the in-plane phase difference and the phase difference in the thickness direction.

[0060] The phase difference film may be in the form of a long strip or a single sheet. 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.

[0061] E. Laminated phase difference film The phase difference film may constitute a laminated phase difference film. Figure 1 is a schematic cross-sectional view of a laminated phase difference film according to one embodiment of the present invention. The laminated phase difference film 1 shown in the illustration has a first phase difference layer 10, a second phase difference layer 20, and an adhesive layer 30 in this order.

[0062] The first phase difference layer 10 typically exhibits a refractive index characteristic of nx>ny>nz. A phase difference film with a refractive index characteristic of nx>ny>nz is sometimes referred to as a "negative B plate." The first phase difference layer 10 can be made of any suitable material, as long as it exhibits the above-mentioned refractive index characteristics. The first phase difference layer 10 is composed of, for example, a phase difference film (a stretched polymer film). Any suitable resin can be used as the resin that forms the polymer film. Specific examples include resins that constitute positive birefringence films, such as cyclic olefin resins (e.g., norbornene resins), polycarbonate resins, cellulose resins, polyvinyl alcohol resins, and polysulfone resins. The thickness of the first phase difference layer 10 is, for example, 10 μm to 30 μm, preferably 15 μm to 20 μm.

[0063] The second phase difference layer 20 is typically composed of the phase difference film described in section D above. The thickness of the second phase difference layer 20 is, for example, 20 μm or more, preferably 21 μm or more. Alternatively, the thickness of the second phase difference layer 20 is, for example, less than 24 μm, preferably 23 μm or less.

[0064] The adhesive layer 30 is composed of any suitable adhesive. The adhesive constituting the adhesive layer 30 typically contains a (meth)acrylic polymer, a urethane polymer, a silicone polymer, or a rubber polymer as a base polymer. Preferably, the adhesive is a (meth)acrylic adhesive containing a (meth)acrylic polymer as the main component. The thickness of the adhesive layer 30 is, for example, 5 μm to 30 μm, and preferably 10 μm to 20 μm. [Examples]

[0065] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement and evaluation methods for each characteristic are as follows.

[0066] (1) Measurement of the number-average molecular weight (Mn) of the resin The number-average molecular weight (Mn) of the resins in the examples and comparative examples was calculated from the elution curves measured by gel permeation chromatography (GPC) using a calibration curve prepared with standard polystyrene.

[0067] (2) Measurement of solid content concentration The method was determined by drying. Specifically, the resin solution was placed in a container, the mass of the container containing the resin solution was measured, the resin solution in the container was heated or vacuum-dried to evaporate the solvent in the resin solution, and the mass of the remaining solid material was measured. The solid content concentration of the resin solutions in the examples and comparative examples was then calculated using the following formula. Solid content concentration (%) = {Mass of solid material (g) / Mass of container with resin solution (g)} × 100

[0068] (3) Measurement of viscosity Using a rotational viscometer (product name "BII type viscometer (Type B viscometer: single cylindrical rotational viscometer)", manufactured by Toki Sangyo Co., Ltd.), the viscosity of the resin solutions of the examples and comparative examples was measured in accordance with JIS Z 8803:2011, under conditions of temperature: 25°C and angular velocity: 75.4 rad / s.

[0069] (4) Measurement of thickness The thickness of the resin films and phase difference films obtained in the examples and comparative examples was measured using a reflectance spectrophotometer (product name "MCPD," manufactured by Otsuka Electronics Co., Ltd.).

[0070] (5) Measurement of phase difference The phase difference values ​​(Re(λ), Rth(λ)) of the resin films and phase difference films obtained in the examples and comparative examples were automatically measured using an Axoscan device manufactured by Axometrics. The measurement wavelength was 550 nm and the measurement temperature was 23°C.

[0071] (6) Detection of voids The resin film and phase difference film obtained in the examples and comparative examples were cut along the thickness direction, and panoramic observation was performed using a scanning electron microscope (SEM) (product name "Regulus8230", Hitachi High-Tech Corporation) to capture images of the entire cross-sectional area in the thickness direction of the resin film and phase difference film, and these images were analyzed. The conditions for imaging were set to magnification of 10,000x, acceleration voltage of 2.0kV, beam current of 10μA, and resolution of 1280×960 (1 pixel=1). The overlap rate for generating a panoramic image was set to 20%, and the imaging area was divided into multiple sections, with SEM images being captured for each section. The multiple obtained images were aligned using image processing software (product name "Regulus", Hitachi High-Tech Corporation), the brightness and contrast were adjusted in auto mode, and images for analysis were extracted. From the images for analysis, a width of 4μm and the total thickness were extracted and image analysis was performed. Image analysis was performed using the OpenCV module (4.6.0) in a Python 3.9 programming environment. First, noise was removed from the cross-sectional SEM images by adaptive thresholding (cv2.adaptiveThreshold, calculation condition: Gaussian distribution) and smoothing (CV2.blur, kernel size=(5,5)). Next, a brightness distribution histogram of the denoised image was created, and the brightness in the lower 1% or less was used as the threshold for void detection. The location of the voids was detected by shape detection (cv2.findContours, calculation condition: cv2.RETR_EXTERNAL). After these processes, a plot of the change in the number of voids in the thickness direction was obtained. From these results, the 1 μm thickness of the resin film and phase difference film was determined. 2 The number of voids per unit area (number of voids detected) was calculated.

[0072] (7) Method for calculating the degree of polarization reduction The luminous efficiency-corrected polarization degree (Py) was determined by measuring it using a spectrophotometer (product name "V-7100", manufactured by JASCO Corporation). Specifically, the luminous efficiency-corrected polarization degree was measured when a resin film or phase difference film was laminated onto a polarizer whose luminous efficiency-corrected polarization degree alone was 99.996. The difference between the obtained luminous efficiency-corrected polarization degree and 99.996 (luminous efficiency-corrected polarization degree of the polarizer alone) was defined as the polarization degree difference of the resin film or phase difference film (depolarization degree of the resin film or phase difference film). When measuring the polarizer with the resin film or phase difference film laminated onto it, the phase difference film layer was positioned between the polarizer and the analyzer. In the case of a phase difference film, the phase difference film was laminated so that the angle between the absorption axis of the polarizer and the slow axis of the phase difference film was 90°.

[0073] (8) Evaluation of uneven coating The resin films and phase difference films obtained in the examples and comparative examples were placed under fluorescent light, and interference fringes were visually observed. Coating unevenness was evaluated based on the following criteria. Interference fringes appear on the resin films and phase difference films when there is coating unevenness (i.e., when the thickness of the resin films and phase difference films is uneven). "○": No interference fringes were observed. "△": Interference fringes were observed, but they did not pose any practical problems. "×": Interference fringes were clearly visible, making it unacceptable in practical use.

[0074] <Manufacturing Example 1> [Synthesis of fumarate ester resins] 58.76 g of diisopropyl fumarate, 12.04 g of diethyl fumarate, and 0.39 g of t-butyl peroxypivalate (a polymerization initiator) were placed in a 75 mL glass ampoule. After purging with nitrogen, the ampoule was sealed under reduced pressure. Radical polymerization was carried out by holding this ampoule at 50°C for 24 hours. After cooling to room temperature, the resulting polymer was dissolved in tetrahydrofuran. A white powder polymer was obtained by adding the resulting polymer solution to excess methanol. The obtained polymer was washed three times with methanol and dried under reduced pressure at 80°C to obtain a fumarate ester resin. The number-average molecular weight of the obtained fumarate ester resin was 240,000.

[0075] <Example 1> [Preparation of resin solution] 50 g of the fumarate ester resin obtained in Production Example 1 was dissolved in a mixed solvent of ethyl acetate (boiling point: 77°C) / methyl isobutyl ketone (boiling point: 116°C) = 75:25 (weight ratio). Then, 2 g of a plasticizer (product name "Alfon" (acrylic polymer), manufactured by Toagosei Co., Ltd.) was added to the resulting solution. Next, the resin solution was stirred with a disperser mixer for 60 minutes, and then allowed to stand for 48 hours to degas, yielding a resin solution with a solid content of 18% by weight and a viscosity of 2.6 Pa·s. [Coating Process] Next, the degassed resin solution was applied to a substrate (a 50 μm thick polyethylene terephthalate (PET) film, product name "RS11", manufactured by Toray Industries, Inc.) using an applicator to form a coating film. [First drying process and second drying process] Next, the substrate (sample) on which the coating film was formed was dried at 55°C using a forced-air oven (ESPEC "SPH-202") (first drying step). Then, the sample after the first drying step was dried at 135°C using a forced-air oven (ESPEC "SPH-202") (second drying step) to obtain a resin film with the substrate attached. After that, the substrate was peeled off to obtain the resin film. In the first drying step, the drying time was adjusted so that the thickness of the coating film after the first drying step was approximately twice the thickness of the coating film after the second drying step. In the second drying step, the drying time was adjusted so that drying continued until no change in the thickness of the coating film due to drying was observed (the change in the thickness of the coating film was 1% / second or less). The resulting resin film was a positive C plate with refractive index characteristics of nz > nx = ny. The resin film had a thickness of 21 μm, Re(550) = 0 nm, Rth(550) = -95 nm, and 1 μm. 2 The number of voids per unit area was 1.52, the depolarization degree was 0.006, and no coating unevenness was observed. Table 1 shows the formulation and properties of the resin solution, as well as the numerical values ​​and evaluation results of the properties of the resin film. Figures 2 and 3 show SEM images of the cross-section (Air side and substrate side) in the thickness direction of the obtained resin film. In the thickness direction of the substrate-attached resin film, the side of the resin film on which the substrate is laminated is referred to as the substrate side, and the side opposite to the side on which the substrate is laminated is referred to as the Air side.

[0076] <Examples 2-5 and Comparative Examples 1-3> Resin solutions were prepared using the solvent types and parts by weight of the solvents listed in Table 1, in the same manner as in Example 1, to obtain resin films. The formulations and properties (solid content concentration, viscosity) of the solutions, as well as the numerical values ​​and evaluation results of the properties of the resin films, are shown in Table 1. SEM images of the cross-sections (Air side and substrate side) in the thickness direction of the resin films of Comparative Example 1 and Comparative Example 2 are shown in Figures 4 to 7.

[0077] [Table 1]

[0078] <Example 6> [Stretching process] The resin film with the substrate from Example 1 was uniaxially stretched at its free end under the conditions of a stretching temperature of 210°C and a stretching speed of 0.1% / second relative to the length of the resin film in the stretching direction before stretching. After this, the substrate was peeled off to obtain a phase difference film. The stretching ratio was 1.06 times. The resulting phase difference film was a film (positive B plate) with refractive index characteristics nz>nx>ny. The phase difference film had a thickness of 21 μm, Re(550)=33 nm, Rth(550)=-80 nm, and 1 μm. 2 The void count was 1.52 per unit area, the depolarization degree was 0.006, and no coating inconsistencies were observed. Table 2 shows the formulation and properties of the coating solution, as well as the numerical values ​​and evaluation results of the properties of the phase difference film.

[0079] <Examples 7-10 and Comparative Examples 4-6> Phase difference films were obtained in the same manner as in Example 6 using the resin films with substrates from Examples 2-5 and Comparative Examples 1-3. The formulations and properties of the resin solutions, as well as the numerical values ​​and evaluation results of the properties of the phase difference films, are shown in Table 2. The stretching ratio of Comparative Example 4 was 1.04 times, and the stretching ratios of Examples 7-10 and Comparative Examples 5-6 were 1.06 times.

[0080] [Table 2]

[0081] [evaluation] As is clear from Tables 1 and 2, when the film thickness was sufficiently large, such as 20 μm or more, the phase difference value in the thickness direction of the resin film and phase difference film became sufficiently large. Furthermore, although increasing the film thickness increased the number of detected voids, reducing the number of voids also reduced the degree of polarization depolarization, indicating that resin films and phase difference films with suppressed light leakage were obtained. [Industrial applicability]

[0082] The resin film obtained by the resin film manufacturing method according to the embodiment of the present invention is suitably used in the manufacture of a phase difference film, and the phase difference film obtained by the phase difference film manufacturing method according to the embodiment of the present invention, and the laminated phase difference film comprising the phase difference film, can be suitably used in image display devices such as liquid crystal display devices and EL display devices, and in particular in organic EL display devices. [Explanation of symbols]

[0083] 1. Laminated phase difference film 10 First phase difference layer 20 Second Phase Difference Layer 30 Adhesive layer

Claims

1. Contains fumarate ester resin, The thickness is 20 μm or more. Cross section 1μm ２ A resin film with 3.0 or fewer voids per unit area.

2. The resin film according to claim 1, wherein Re(550) is -2.0 nm to 2.0 nm and Rth(550) is -140 nm to -85 nm: Here, Re(550) represents the in-plane phase difference measured with light of a wavelength of 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of a wavelength of 550 nm at 23°C.

3. Contains fumarate ester resin, It shows refractive index characteristics where nz > NX > ny. The thickness is 20 μm or more. Cross section 1μm ２ A phase difference film with 3.0 or fewer voids per unit area.

4. The phase difference film according to claim 3, wherein Re(550) is 20 nm to 50 nm and Rth(550) is -120 nm to -70 nm: Here, Re(550) represents the in-plane phase difference measured with light of a wavelength of 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of a wavelength of 550 nm at 23°C.

5. It has a first phase difference layer, a second phase difference layer, and an adhesive layer in this order. The first phase difference layer exhibits refractive index characteristics nx > ny > nz, The second phase difference layer is the phase difference film according to claim 3 or 4. Laminated phase difference film.

6. A method for manufacturing a resin film, The process includes a coating step of applying a resin solution containing a solvent and a fumarate ester resin onto a substrate to form a coating film, a first drying step of drying the coating film at 40°C to 70°C, and a second drying step of drying the coating film after the first drying step at 110°C to 150°C. The solvent comprises a low-boiling-point solvent with a boiling point of 85°C or lower and a high-boiling-point solvent with a boiling point of 110°C or higher. The solvent contains 30% by weight or less of the high-boiling point solvent. The solid content concentration in the resin solution is 15% by weight or more. The thickness of the resulting resin film is 20 μm or more. A method for manufacturing resin films.

7. A method for manufacturing a phase difference film, The method further includes a stretching step of stretching the resin film produced by the resin film manufacturing method described in claim 6, The thickness of the resulting phase difference film is 20 μm or more. A method for manufacturing a phase difference film.

8. The manufacturing method according to claim 6 or 7, wherein the Re(550) of the resin film is -2.0 nm to 2.0 nm and the Rth(550) is -140 nm to -85 nm: Here, Re(550) represents the in-plane phase difference measured with light of a wavelength of 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of a wavelength of 550 nm at 23°C.

9. The manufacturing method according to claim 6 or 7, wherein the viscosity of the resin solution is 1.8 Pa·s to 4.5 Pa·s.

10. The manufacturing method according to claim 6 or 7, wherein the resin solution contains 21% by weight or less of the fumarate ester resin.

11. The manufacturing method according to claim 7, wherein the Re(550) of the phase difference film is 20 nm to 50 nm and the Rth(550) is -120 nm to -70 nm: Here, Re(550) represents the in-plane phase difference measured with light of a wavelength of 550 nm at 23°C, and Rth(550) represents the phase difference in the thickness direction measured with light of a wavelength of 550 nm at 23°C.

Images