Optical film

Abstract

The present invention provides an optical film that, even when replaced with a TAC film in an image display device, does not require adjustment of the optical properties of elements other than the polarizer protective film, and has excellent resistance to damp heat. The optical film of the present invention is composed of a resin composition comprising a resin (A) exhibiting positive intrinsic birefringence and a resin (B) exhibiting negative intrinsic birefringence. The optical film is characterized in that the glass transition temperature of the resin composition is 110 to 160°C, and the resin (A) comprises a ring structural unit (p1) having a ring structure in the main chain and a structural unit (q1) derived from (meth)acrylate. When measured with light at wavelengths of 400 nm, 550 nm, and 700 nm, the absolute value of the in-plane phase difference Re is 0 to 2 nm, and the absolute value of the phase difference Rth in the thickness direction is 4 to 20 nm. When the absolute value of the phase difference is set as R(45,λ) when measured with light at an incident angle of 45 degrees and a wavelength of λ (nm), R(45,400) / R(45,550) is 1.05 or more, and R(45,550) / R(45,700) is greater than 1.

Description

Technical Field

[0001] This disclosure relates to an optical film. Background Technology

[0002] A typical liquid crystal display device includes a liquid crystal cell and two polarizing plates stacked on both sides of the liquid crystal cell. Each polarizing plate has a polarizer and two protective films stacked on both sides of the polarizer. Triacetyl cellulose film (hereinafter referred to as TAC film) has traditionally been used as the protective film for the polarizer. However, TAC film suffers from low resistance to damp heat.

[0003] Therefore, as a protective film for polarizers, (meth)acrylic films with superior resistance to damp heat compared to TAC films have been proposed (e.g., Patent Document 1).

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2015-057664 Summary of the Invention The problem that the invention aims to solve As described in paragraph 0002 of Patent Document 1, the optical film is required to have optical characteristics that correspond to the optical design of the image display device. In other words, the polarizer protective film is required to be compatible with elements other than the polarizer protective film constituting the image display device (polarizer, liquid crystal cell, etc.).

[0005] TAC film, traditionally used as a protective film for polarizers, exhibits a characteristic where the absolute value of the phase difference on the shorter wavelength side (around 400 nm) is greater than the absolute value of the phase difference on the longer wavelength side (around 700 nm) (paradispersion). Particularly when viewed from an angle, it cannot display pure black, instead exhibiting a noticeable bluish tint. Therefore, in conventional image display devices, the idea was to use TAC film as a protective film for polarizers, adjusting elements outside the protective film to achieve a balanced optical design that avoids the presence of blue.

[0006] In such an image display device, if the polarizer protective film is changed from a TAC film to a (meth)acrylic film with small in-plane and thickness-direction phase differences, the absolute value of the phase difference on the short wavelength side near 400nm is smaller than that of the TAC film. Therefore, it is conceivable that a noticeable yellowish tint will be observed when viewed from an angle. In other words, in an image display device, if the polarizer protective film is changed from a TAC film to a (meth)acrylic film, it is necessary to adjust the optical properties of elements other than the polarizer protective film.

[0007] This disclosure was made with regard to the above-mentioned situation, and its purpose is to provide an optical film that, even if replaced with a TAC film in an image display device, does not require adjustment of the optical properties of elements other than the polarizer protective film, and has excellent resistance to damp heat.

[0008] Methods for solving problems The result of dedicated research was the discovery of a method to obtain (meth)acrylic acid films with optical properties that are close to those of TAC films compared to previous methods.

[0009] That is, this disclosure includes the following structure.

[0010] [1] An optical film comprising a resin composition comprising a resin (A) exhibiting positive intrinsic birefringence and a resin (B) exhibiting negative intrinsic birefringence, wherein the optical film is characterized in that the glass transition temperature of the resin composition is 110 to 160°C, wherein the resin (A) comprises a ring structural unit (p1) having a ring structure in the main chain and a structural unit (q1) derived from (meth)acrylate, wherein when measured with light of wavelengths of 400 nm, 550 nm and 700 nm, the absolute value of the in-plane phase difference Re is 0 to 2 nm, the absolute value of the phase difference Rth in the thickness direction is 4 to 20 nm, and when the absolute value of the phase difference when measured with light of incident angle of 45 degrees and wavelength λ (nm) is set as R(45,λ), R(45,400) / R(45,550) is 1.05 or more, and R(45,550) / R(45,700) is greater than 1.

[0011] [2] According to the optical film described in [1] above, wherein the resin (A) further comprises a structural unit (q2) derived from aromatic vinyl groups, wherein the content of the ring structural unit (p1) in the resin (A) is 15 to 35% by mass, the content of the structural unit (q1) is 45 to 80% by mass, and the content of the structural unit (q2) is 0.1 to 20% by mass.

[0012] [3] According to the optical film described in [1] or [2] above, wherein the resin (B) comprises structural units (r1) derived from acrylonitrile and structural units (r2) derived from styrene.

[0013] [4] The optical film according to [3] above, wherein the resin composition contains 1 to 5 parts by weight of the resin (B) relative to 100 parts by weight of the resin (A).

[0014] [5] The optical film according to any one of [1] to [4] above, wherein the ring structural unit (p1) comprises at least one selected from the group consisting of lactone ring structural units and glutarimide structural units.

[0015] [6] The optical film according to any one of [1] to [5] above, wherein the absolute value of the stress optical coefficient of the resin composition is 5 × 10⁻⁶. -11 ~20×10 -11 Pa -1 .

[0016] [7] The optical film according to any one of [1] to [6] above, wherein when measured with light of wavelengths of 400 nm, 550 nm and 700 nm, the difference between the absolute value of the in-plane phase difference Re and the absolute value of the phase difference Rth in the thickness direction is 3.5 to 18 nm.

[0017] [8] The optical film according to any one of [1] to [7] above, wherein R(45,400) / R(45,700) is 1.1 to 1.5.

[0018] [9] The optical film according to any one of [1] to [8] above, wherein R (45,400), R (45,550) and R (45,700) are all 0.5 to 10 nm.

[0019]

[10] The optical film according to any one of [1] to [9] above, wherein the thickness of the optical film is 5 to 50 μm.

[0020]

[11] The optical film according to any one of [1] to

[10] above, wherein the optical film is a polarizer protective film.

[0021] Invention Effects Since the optical film of this disclosure is a (meth)acrylic acid film with a larger absolute value of phase difference on the short wavelength side than on the long wavelength side when measured with light at an incident angle of 45 degrees, even if the optical film of this disclosure is used as a polarizer protective film instead of a TAC film in an image display device, there is no need to significantly change the optical properties of elements other than the polarizer protective film. In addition, the optical film of this disclosure has superior resistance to damp heat compared to a TAC film. Detailed Implementation

[0022] This disclosure relates to an optical film comprising a resin composition including a resin (A) exhibiting positive intrinsic birefringence and a resin (B) exhibiting negative intrinsic birefringence.

[0023] [Resin (A)] The resin (A) comprises a cyclic structural unit (p1) having a ring structure in the main chain and a structural unit (q1) derived from an alkyl ester of (meth)acrylate. Furthermore, in this disclosure, (meth)acrylate refers to a term encompassing both methacrylic acid and acrylic acid.

[0024] <Ring Structure Unit (p1)> The ring structural unit (p1) imparts positive intrinsic birefringence to the resin (A). In other words, the ring structural unit (p1) refers to a structural unit whose tensile direction (or orientation direction) is the slow axis. In the resin (A), the content of the ring structural unit (p1) is preferably 15–35% by mass, more preferably 18–30% by mass. By setting the content of the ring structural unit (p1) within the above range, it is easy to make the optical film exhibit the desired phase difference characteristics. Furthermore, the numerical range expressed as X to Y refers to X or more and Y or less. Additionally, by setting the content of the ring structural unit (p1) within the above range, the glass transition temperature of the resin composition can be set within a specified range.

[0025] The ring structure of the main chain constituting the ring structure unit (p1) can be any one of the following: four-membered ring structure, five-membered ring structure, six-membered ring structure, seven-membered ring structure, eight-membered ring structure, etc., preferably a five-membered ring structure or a six-membered ring structure.

[0026] The ring structure that constitutes the main chain of the ring structural unit (p1) can be introduced either by polymerizing (meth)acrylic monomers with ring structures, or by chemically reacting (meth)acrylic monomers with groups for forming ring structures after polymerization.

[0027] There are no particular limitations on the specific examples of the ring structural unit (p1). Examples include: lactone ring structural unit, lactam ring structural unit, succinic anhydride structural unit, succinimide structural unit, glutaric anhydride structural unit, and glutarimide structural unit. The ring structural unit (p1) may contain only one of these structural units or may contain two or more of them.

[0028] The lactone ring structural unit has a lactone ring structure in the main chain. The number of ring members in the lactone ring structure is not particularly limited; for example, any ring from four to eight members is acceptable. From the viewpoint of improving the stability of the ring structure, the lactone ring structure is preferably a five-membered or six-membered ring, more preferably a six-membered ring. The lactam ring structural unit has a lactam ring structure in the main chain. The number of ring members in the lactam ring structure is not particularly limited; for example, any ring from four to eight members is acceptable. From the viewpoint of improving the stability of the ring structure, the lactam ring structure is preferably a five-membered or six-membered ring, more preferably a five-membered ring.

[0029] The lactone ring structural unit is preferably the structural unit shown in formula (1a). The lactam ring structural unit is preferably the structural unit shown in formula (1b).

[0030] [Chemical Formula 1]

[0031] In equation (1a), R 11 and R 12Each group is independent and not particularly limited; for example, it can be a hydrocarbon group with 1 to 20 carbon atoms or a hydrogen atom. This hydrocarbon group can be linear, branched, or cyclic. It can also be an aliphatic or aromatic hydrocarbon group. R 13 It is a hydrogen atom or a methyl group.

[0032] In equation (1b), R 15 and R 16 Each group is independent and not particularly limited; for example, it can be a hydrocarbon group with 1 to 20 carbon atoms or a hydrogen atom. This hydrocarbon group can be linear, branched, or cyclic. It can also be an aliphatic or aromatic hydrocarbon group. R 14 It is a hydrogen atom or a methyl group.

[0033] In equation (1a), R 11 and R 12 Preferably, each is an alkyl group having 1 to 6 carbon atoms, and more preferably, each is an alkyl group having 1 to 6 carbon atoms. In formula (1b), R 15 and R 16 Preferably, each is an alkyl group having 1 to 6 carbon atoms, and more preferably, each is an alkyl group having 1 to 6 carbon atoms.

[0034] The structural unit shown in Formula (1a) can be formed, for example, by a dealcoholization condensation between the hydroxyl group and the ester bond after polymerization of a monomer group containing methyl 2-(hydroxymethyl)acrylate and methyl (meth)acrylate. The structural unit shown in Formula (1b) can be formed, for example, by a dealcoholization condensation between the amide group and the ester bond after polymerization of a monomer group containing N-vinylacetamide and methyl (meth)acrylate.

[0035] The ring structural unit (p1) may contain only one type of lactone ring structural unit shown in formula (1a), or it may contain two or more types. The ring structural unit (p1) may contain only one type of lactam ring structural unit shown in formula (1b), or it may contain two or more types.

[0036] The succinic anhydride structural unit (derived from the maleic anhydride monomer) is preferably the structural unit shown in formula (2a). The succinimide structural unit (derived from the maleimide monomer) is preferably the structural unit shown in formula (2b).

[0037] [Chemical Formula 2]

[0038] In equation (2a), R 21 and R 22 Each can be a hydrogen atom or a methyl group, independently.

[0039] In equation (2b), R23 and R 24 Each can be used independently to represent a hydrogen atom or a methyl group. R 25 There are no particular limitations; for example, it can be a hydrocarbon group with 1 to 20 hydrogen atoms or carbon atoms. This hydrocarbon group can be linear, branched, or cyclic. It can also be an aliphatic or aromatic hydrocarbon group. R 25 Preferably, it is methyl, ethyl, cyclohexyl, phenyl, naphthyl, or benzyl, more preferably cyclohexyl or phenyl.

[0040] The structural unit shown in formula (2a) can be formed, for example, by polymerizing a monomer group containing a maleic anhydride monomer. The structural unit shown in formula (2b) can be formed, for example, by polymerizing a monomer group containing a maleimide monomer or an N-substituted maleimide monomer.

[0041] The ring structural unit (p1) may contain only one or more of the succinic anhydride structural units shown in formula (2a). The ring structural unit (p1) may contain only one or more of the succinimide structural units shown in formula (2b).

[0042] The glutaric anhydride structural unit is preferably the structural unit shown in formula (3a). The glutarimide structure is preferably the structural unit shown in formula (3b).

[0043] [Chemical Formula 3]

[0044] In equation (3a), R 31 ~R 33 Each can be used to represent a hydrogen atom or a methyl group independently.

[0045] In equation (3b), R 34 ~R 36 Each can be used independently to represent a hydrogen atom or a methyl group. R 37 There are no particular limitations; for example, it can be a hydrocarbon group with 1 to 20 hydrogen atoms or carbon atoms. This hydrocarbon group can be linear, branched, or cyclic. It can also be an aliphatic or aromatic hydrocarbon group. R 37 Preferably, it is a hydrogen atom, methyl, cyclohexyl, phenyl or tolyl, more preferably a hydrogen atom or methyl.

[0046] The structural unit shown in formula (3a) can be formed, for example, by dehydration condensation between the carboxyl group and the ester bond after polymerization of a monomer group containing (meth)acrylic acid monomer and (meth)methyl acrylate monomer. The structural unit shown in formula (3b) can be formed, for example, by imidization between two ester bonds after polymerization of a monomer group containing (meth)methyl acrylate monomer.

[0047] The ring structural unit (p1) may contain only one or more of the glutaric anhydride structural units shown in formula (3a). The ring structural unit (p1) may contain only one or more of the glutarimide structural units shown in formula (3b).

[0048] From the viewpoint of the stability of the ring structure, the ring structural unit (p1) preferably comprises at least one selected from the group consisting of lactone ring structural units, succinimide structural units, and glutarimide structural units, and more preferably comprises at least one selected from the group consisting of lactone ring structural units and glutarimide structural units. From the viewpoint of the yellowness when forming an optical film, the ring structural unit (p1) preferably comprises a lactone ring structural unit.

[0049] <Structural units (q1) and (q2)> Specific examples of structural unit (q1) are not particularly limited, and examples include structural units derived from monomers such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and isopropyl methacrylate. The alkyl group of the alkyl methacrylate is preferably an alkyl group with 1 to 5 carbon atoms, more preferably an alkyl group with 1 to 4 carbon atoms, further preferably an alkyl group with 1 to 3 carbon atoms, particularly preferably an alkyl group with 1 to 2 carbon atoms, and most preferably an alkyl group with 1 carbon atom (methyl).

[0050] In resin (A), the content of structural unit (q1) is preferably 45 to 80% by mass, more preferably 60 to 76% by mass. Structural unit (q1) is a structural unit that imparts negative intrinsic birefringence, but by setting the content of structural unit (q1) within the above range, resin (A) can be made to exhibit positive intrinsic birefringence, and the optical film can easily exhibit the desired phase difference characteristics.

[0051] The resin (A) preferably further comprises a structural unit (q2) derived from an aromatic vinyl group capable of copolymerization. The structural unit (q2) derived from the aromatic vinyl group is a structural unit that imparts negative intrinsic birefringence, but by including the structural unit (q2) derived from the aromatic vinyl group, it is easier to make the absolute value of the stress optical coefficient of the resin composition fall within the specified range described later. Specific examples of the structural unit (q2) are not particularly limited as long as they are derived from compounds in which a vinyl group is bonded to an aromatic ring. Examples include structural units derived from monomers such as styrene, vinyltoluene, methoxystyrene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, etc.; polycyclic aromatic hydrocarbon cyclic vinyl groups such as 2-vinylnaphthalene; and aromatic heterocyclic vinyl groups such as N-vinylcarbazole, 2-vinylpyridine, vinylimidazole, vinylthiophene, etc. The styrene-based monomers include not only styrene but also styrene derivatives as described above in which any substituent is bonded to the polymerizable double carbon or benzene ring of styrene. The substituents are not particularly limited, and examples include alkyl, alkoxy, hydroxy, halogen, amino, nitro, and sulfonyl groups. In alkyl and alkoxy groups, the number of carbon atoms contained is preferably 1 to 4, and more preferably 1 to 2. The structural unit (q2) is preferably a structural unit derived from styrene.

[0052] When the resin (A) contains structural unit (q2), the content of structural unit (q2) in the resin (A) is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 3 to 5% by mass. By setting the content of structural unit (q2) within the above range, it is easy to make the absolute value of the stress optical coefficient of the resin composition within the specified range described later.

[0053] When resin (A) contains structural unit (q2), the ratio of the content of structural unit (q2) in resin (A) to the total content of structural units (q1) and (q2) is preferably 0.1 to 31% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 10% by mass. By setting the ratio of the content of structural unit (q2) within the above range, it is easy to make the absolute value of the stress optical coefficient of the resin composition within the specified range described later.

[0054] When resin (A) comprises structural units (q1) and structural units (q2), it is preferable that the content of ring structural units (p1) in resin (A) is 15-35% by mass, the content of structural units (q1) is 45-80% by mass, and the content of structural units (q2) is 0.1-20% by mass. More preferably, the content of ring structural units (p1) in resin (A) is 18-30% by mass, the content of structural units (q1) is 60-76% by mass, and the content of structural units (q2) is 3-10% by mass. By preparing resin (A) with the content of each structural unit within the above-mentioned range, the glass transition temperature of the resin composition can be kept within the desired range, and the optical film can easily exhibit the desired phase difference characteristics.

[0055] When the resin (A) contains ring structural unit (p1), structural unit (q1) and structural unit (q2), the total content of the ring structural unit (p1), structural unit (q1) and structural unit (q2) in the resin (A) is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, particularly preferably 98% by mass or more, and most preferably 100% by mass.

[0056] Resin (A) is preferably composed only of ring structural units (p1) and structural units (q1), or only of ring structural units (p1), structural units (q1), and structural units (q2). However, it may also contain structural units other than ring structural units (p1), structural units (q1), and structural units (q2) (hereinafter referred to as structural units (s)) as long as they are within a range that will not significantly impair the optical properties of the resin composition. Specific examples of structural units (s) are not particularly limited, and examples include structural units derived from monomers such as benzyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, vinyl chloride, and indene. Even when structural units (s) are included, it is preferable that the absolute value of the stress optical coefficient of the resin composition is within the range specified later.

[0057] [Resin (B)] Resin (B) is a resin exhibiting negative intrinsic birefringence; in other words, it refers to a resin whose tensile direction (or orientation direction) is the fast axis. There is no particular limitation on the type of resin (B) as long as it exhibits negative intrinsic birefringence, but a resin containing structural units (r1) derived from polymethyl methacrylate or acrylonitrile and structural units (r2) derived from styrene is preferred. Examples of resins (B) containing structural units (r1) derived from acrylonitrile and structural units (r2) derived from styrene include acrylonitrile-styrene copolymers, acrylonitrile-styrene-maleimide copolymers, and acrylonitrile-styrene-maleic anhydride copolymers. From the viewpoint that it is commercially available and readily available, acrylonitrile-styrene copolymers are preferred.

[0058] In the resin composition, 1 to 5 parts by mass of resin (B) are preferably included relative to 100 parts by mass of resin (A), and more preferably 1.5 to 4 parts by mass of resin (B). By setting the content of resin (B) within the above range, it is easy to make the absolute value of the stress optical coefficient of the resin composition within the specified range described later.

[0059] <Other> The resin composition used in this disclosure preferably contains only resin (A) and resin (B), but may also contain resins other than resin (A) and resin (B) (hereinafter referred to as resin (C)) as long as it is within a range that will not significantly impair the optical properties of the resin composition. Even when resin (C) is included, it is preferable that the absolute value of the stress optical coefficient of the resin composition is within the range specified later.

[0060] The resin (C) is not particularly limited, and examples include polyester resin, polyolefin resin, polyamide resin, and polyimide resin. The content of resin (C) in the resin component of the resin composition is preferably 20% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, particularly preferably 2% by mass or less, and most preferably 0% by mass.

[0061] The resin composition used in this disclosure may contain various additives, provided that they are within a range that will not significantly impair the optical properties of the resin composition. Examples of additives include: ultraviolet absorbers; antioxidants; light stabilizers, weather stabilizers, heat stabilizers, and other stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants; antistatic agents; colorants; organic fillers; inorganic fillers; and resin modifiers. The total content of additives in the resin composition is preferably 0 to 5% by mass, more preferably 0 to 2% by mass.

[0062] <Membrane Manufacturing Methods> To exhibit the desired phase difference characteristics, biaxial stretching is preferably performed to manufacture the optical film of this disclosure. By performing biaxial stretching, a desired phase difference can be achieved in the thickness direction, and the in-plane phase difference Re can be made to be near zero. For example, this can be achieved by melt-extruding a resin composition using an extruder to form an unstretched film, and then stretching the unstretched film longitudinally (MD) and then transversely (TD).

[0063] The longitudinal stretching ratio is preferably 1.4 to 3.0 times, more preferably 1.7 to 2.5 times. By setting it within the above range, a desired phase difference can be achieved in the thickness direction, and the in-plane phase difference Re can be made close to zero after transverse stretching.

[0064] The longitudinal stretching temperature is preferably Tg+10℃~Tg+30℃, more preferably Tg+12℃~Tg+24℃. By setting it within the above range, a desired phase difference can be achieved in the thickness direction, and the in-plane phase difference Re can be made close to zero after transverse stretching.

[0065] The transverse stretching ratio is preferably 1.8 to 3.2 times, more preferably 2.2 to 2.6 times. By setting it within the above range, a desired phase difference can be achieved in the thickness direction, and the in-plane phase difference Re can be made close to zero.

[0066] The transverse stretching temperature is preferably Tg+7℃ to Tg+27℃, more preferably Tg+10℃ to Tg+22℃. By setting it within the above range, a desired phase difference in the thickness direction can be achieved, and the in-plane phase difference Re can be made close to zero after transverse stretching. In particular, from the viewpoint of avoiding a decrease in the phase difference in the thickness direction caused by longitudinal stretching, the transverse stretching temperature is preferably lower than the longitudinal stretching temperature.

[0067] Preheating can also be applied before transverse stretching. When preheating is applied, the preheating temperature is preferably lower than the stretching temperature for longitudinal stretching.

[0068] When a stretched film is used as an optical film, heat treatment (annealing) may be performed after stretching as needed to stabilize the optical and mechanical properties of the film. When performing heat treatment, the preferred heat treatment temperature is Tg-10℃ to Tg+10℃, more preferably Tg-5℃ to Tg+5℃. By setting the temperature within the above range, it is easy to achieve a desired phase difference in the thickness direction.

[0069] <Physical Properties of Optical Films and Resin Compositions> (Thickness of the optical film) The thickness of the optical film disclosed herein is preferably 5 to 50 μm, more preferably 10 to 45 μm, and even more preferably 20 to 40 μm.

[0070] (In-plane phase difference Re, thickness-direction phase difference Rth, phase difference when measured with light at an incident angle of 45 degrees) The in-plane phase difference Re and the thickness-direction phase difference Rth of the optical film can be calculated using the following formula. Furthermore, let nx be the in-plane refractive index along the slow axis, ny be the in-plane refractive index along the fast axis, nz be the thickness of the film, and d be the thickness of the film.

[0071] In-plane phase difference Re = (nx - ny) × d Phase difference in the thickness direction Rth = [(nx + ny) / 2 - nz] × d The following describes the in-plane phase difference Re, the thickness-direction phase difference Rth, and the phase difference when measured with light at an incident angle of 45 degrees. Furthermore, the absolute value of the in-plane phase difference Re when measured with light of wavelength λ (nm) is denoted as Re(λ), the absolute value of the thickness-direction phase difference Rth when measured with light of wavelength λ (nm) is denoted as Rth(λ), and the absolute value of the phase difference when measured with light of incident angle 45 degrees and wavelength λ (nm) is denoted as R(45,λ).

[0072] Regarding the in-plane phase difference Re, Re(400), Re(550), and Re(700) are all 0–2 nm, preferably 0–1.5 nm, and more preferably 0–1 nm. Among the three values ​​of Re(400), Re(550), and Re(700), the difference between the maximum and minimum values ​​is preferably less than 1 nm, more preferably less than 0.6 nm, further preferably less than 0.4 nm, and particularly preferably 0.1–0.2 nm.

[0073] Regarding the phase difference Rth in the thickness direction, Rth(400), Rth(550), and Rth(700) are all 4–20 nm, preferably 4.5–17 nm, more preferably 5–15 nm, and even more preferably 5.5–12 nm. Among the three values ​​of Rth(400), Rth(550), and Rth(700), the difference between the maximum and minimum values ​​is preferably less than 10 nm, more preferably 1–7 nm, even more preferably 1.5–5.0 nm, and particularly preferably 2.5–3.5 nm. Furthermore, the absolute values ​​of the in-plane phase difference Re and the phase difference Rth in the thickness direction refer to the ease of generating elliptically polarized light (the ease of light leakage).

[0074] The phase difference Rth in the thickness direction is preferably negative. In any of the embodiments described below, the values ​​measured with light at wavelengths of 400 nm, 550 nm, and 700 nm are also all negative, but they can also be set to positive values ​​by adjusting the composition of the resin composition and the manufacturing conditions of the film.

[0075] The differences between Re(400) and Rth(400), Re(550) and Rth(550), and Re(700) and Rth(700) (the differences between the absolute values ​​of the in-plane phase difference Re and the absolute values ​​of the phase difference Rth in the thickness direction when measured with light of wavelengths of 400nm, 550nm, and 700nm) are preferably 3.5 to 18nm, more preferably 4 to 15nm, and even more preferably 4.5 to 10nm.

[0076] Regarding the phase difference measured with light at an incident angle of 45 degrees, R(45,400), R(45,550), and R(45,700) are preferably 0.5–10 nm, more preferably 1.0–7.0 nm, and even more preferably 2.0–5.0 nm. Among the three values ​​of R(45,400), R(45,550), and R(45,700), the difference between the maximum and minimum values ​​is preferably 5 nm or less, more preferably 3 nm or less, even more preferably 2.5 nm or less, and particularly preferably 0.2–1.5 nm.

[0077] The value of R(45,400) / R(45,550) is 1.05 or higher, and the value of R(45,550) / R(45,700) is greater than 1. Both R(45,400) / R(45,550) and R(45,550) / R(45,700) are preferably 1.05 or higher.

[0078] The value of R(45,400) / R(45,550) is preferably 1.05 to 1.3, more preferably 1.15 to 1.3.

[0079] The value of R(45,550) / R(45,700) is preferably 1.03 to 1.2, more preferably 1.05 to 1.15.

[0080] The value of R(45,400) / R(45,700) is preferably 1.1 to 1.5.

[0081] (Stress optical coefficient Cr) In the resin composition used in this disclosure, the absolute value of the stress optical coefficient Cr is preferably 5 × 10⁻⁶. -11 ~20×10 -11 Pa -1 More preferably 7×10 -11 ~17×10 -11 Pa -1 Further preferred is 8×10 -11 ~15×10 -11 Pa -1 If the absolute value of the stress optical coefficient Cr is within the above range, the optical film is likely to exhibit the desired flexibility and phase difference characteristics.

[0082] (Glass transition temperature) The resin composition used in this disclosure has a glass transition temperature of 110–160°C. This ensures processability and improves the heat resistance of the resin composition. More preferably, the resin composition used in this invention has a glass transition temperature of 115–150°C, and even more preferably, it has a glass transition temperature of 120–140°C.

[0083] The weight-average molecular weight of the resin composition used in this disclosure is preferably 0.5 million to 350,000, more preferably 10,000 to 300,000, even more preferably 30,000 to 250,000, and particularly preferably 50,000 to 200,000. By setting the weight-average molecular weight of the resin composition within the above range, the molding processability of the resin composition can be easily improved, and the mechanical strength of the obtained optical film can be ensured.

[0084] The number-average molecular weight of the resin composition used in this disclosure is preferably 0.5 million to 250,000, more preferably 10,000 to 200,000, even more preferably 20,000 to 150,000, and particularly preferably 30,000 to 100,000. By setting the number-average molecular weight of the resin composition within the above range, the molding and processability of the resin composition can be easily improved, and the mechanical strength of the obtained optical film can be ensured.

[0085] <Applications of Optical Films> The optical film disclosed herein can be suitably used in image display devices, for example, as a polarizer protective film, a phase retardation film, a transparent conductive film, or a light conversion film. Preferably, it is laminated on one or both sides of a polarizer and used as a polarizer protective film. Examples of image display devices include liquid crystal displays. In the case of a liquid crystal display device, the image display unit can be configured to include liquid crystal cells, a polarizer, a backlight, and the optical film of this disclosure. Examples of image display devices other than liquid crystal displays include electroluminescent (EL) display panels, plasma display panels (PDP), field emission displays (FED), QLEDs (quantum dot light-emitting diodes), and micro LEDs (micro light-emitting diodes).

[0086] This application claims the benefit of priority based on Japanese Patent Application No. 2024-060473, filed on April 3, 2024. The entire contents of the description of Japanese Patent Application No. 2024-060473, filed on April 3, 2024, are incorporated herein by reference.

[0087] Example The present disclosure will now be described through examples, but the present disclosure is not limited to these examples. Furthermore, the evaluation methods used in the various examples, comparative examples, and reference examples are as follows.

[0088] <Glass transition temperature Tg> The glass transition temperature of the resin composition obtained in the manufacturing example was measured according to the Japanese Industrial Standard (JIS) K 7121. Using a differential scanning calorimeter (Rigaku Corporation; Thermo plus EVO DSC-8230), approximately 10 mg of sample was heated from room temperature to 200°C (heating rate of 20°C / min) under a nitrogen atmosphere, and the temperature was measured using the starting point method based on the obtained DSC curve. α-alumina was used as a reference.

[0089] <Thickness of optical film> The thickness of the optical film was measured using a digital micrometer (manufactured by Mitutoyo).

[0090] <Weight-average molecular weight and number-average molecular weight> The weight-average molecular weight and number-average molecular weight of the (meth)acrylic resin compositions were determined by gel permeation chromatography (GPC) using polystyrene conversion. The apparatus and measurement conditions used for the measurements are described below.

[0091] Measurement System: Tosoh GPC System HLC-8220 Measuring the side column structure: Protective column (manufactured by Tosoh, TSK Gel guardcolumn SuperHZ-L) Separation column (manufactured by Tosoh, TSK Gel Super HZM-M), two connected in series Reference side column structure: Reference column (manufactured by Tosoh, TSK gel SuperH-RC) Developing solvent: Chloroform (manufactured by Fujifilm and Kazuko Pure Chemical Industries, premium grade) Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit) <Stress optical coefficient Cr> The stress optical coefficient Cr of the resin composition obtained in the manufacturing example was evaluated as follows: A 100 μm thick film (unstretched film) was obtained from the resin composition by melt extrusion. A 60 mm × 20 mm measurement specimen was cut from the film. A sample was selected that would apply 1 N / mm² to the measurement specimen during uniaxial stretching, as described later. 2 The following stress is applied to a weight of the same mass, which is then mounted on one of the shorter sides of the measuring specimen.

[0092] Next, the test specimen was placed in a dryer (manufactured by Azov Corporation; DOV-450A) maintained at Tg+3°C for the resin composition. Inside the dryer, the other short side of the test specimen was fixed using a chuck, and the stress generated by the mass of the weight caused uniaxial tension at the free end of the test specimen in the vertical direction. The distance between the upper end of the portion of the test specimen with the weight and the lower end of the chuck was 40 mm.

[0093] After 30 minutes, the dryer heater was turned off, and the temperature inside the dryer was cooled to Tg-40°C of the resin composition at a rate of approximately 1°C / min. The measurement sample was removed from the dryer, and its length and thickness, in-plane phase difference Re relative to a wavelength of 590 nm, and the mass of the weight were measured. The same test was repeated four more times while varying the mass of the weight.

[0094] The birefringence Δn (=nx-ny, measurement wavelength 590nm) of the measured specimen is obtained by dividing the measured in-plane phase difference Re by the specimen thickness d (nm). Using the birefringence Δn as the y-axis and the applied stress σ (Pa) as the x-axis, a regression line is obtained using the least squares method based on the results of five experiments. The absolute value of its slope is taken as the absolute value of the stress optical coefficient Cr.

[0095] <In-plane phase difference Re, thickness direction phase difference Rth, phase difference R(45,λ)> A 40mm × 40mm measurement sample was cut from the optical film. The in-plane phase difference Re of the cut sample at wavelengths of 400nm, 550nm, and 700nm was determined using a polarimeter (manufactured by Axometrics; AxoScan). The phase difference Rth along the thickness direction and the phase difference at an incident angle of 45 degrees were also determined similarly at wavelengths of 400nm, 550nm, and 700nm. Furthermore, the phase difference at an incident angle of 45 degrees is the phase difference when tilted 45 degrees around the optical axis (slow axis).

[0096] Table 1 shows the absolute values ​​of the in-plane phase difference Re, the thickness-direction phase difference Rth, and the phase difference at an incident angle of 45 degrees for wavelengths of 400 nm, 550 nm, and 700 nm. Furthermore, in Table 1, the absolute value of the in-plane phase difference Re when measured with light of wavelength λ (nm) is denoted as Re(λ), the absolute value of the thickness-direction phase difference Rth when measured with light of wavelength λ (nm) is denoted as Rth(λ), and the absolute value of the phase difference when measured with light of wavelength λ (nm) at an incident angle of 45 degrees is denoted as R(45,λ).

[0097] <Manufacturing Example 1: (Meth)Acrylic Resin Composition (A-1)> In a reaction vessel equipped with a stirrer, temperature sensor, cooling pipe, and nitrogen inlet pipe, 83.5 parts by weight of methyl methacrylate, 12.0 parts by weight of methyl 2-(hydroxymethyl)acrylate, and 88.7 parts by weight of toluene were added. While purging with nitrogen, the temperature was raised to 105°C. At the start of reflux accompanying the temperature rise, 0.535 parts by weight of a toluene solution (manufactured by Arkema Gefon; Lupelox 570T20) with a concentration of 20% by weight of tert-amyl peroxide was added. Next, a solution consisting of 4.5 parts by weight of styrene and 0.15 parts by weight of n-dodecyl mercaptan was added dropwise over 2 hours. Then, 1.065 parts by weight of a toluene solution (manufactured by Arkema Gefon; Lupelox 570T20) with a concentration of 20% by weight of tert-amyl peroxide was added dropwise over 4 hours. During the addition of these solutions, the mixture was refluxed at approximately 105–110°C and solution polymerization was carried out. After the addition was completed, a further curing process was performed at the same temperature for 2 hours.

[0098] 0.0312 parts by mass of butyl phosphate (manufactured by SC Organic Chemicals; Phoslex A-4) were added to the resulting polymerization solution, and the reaction was carried out under reflux at approximately 90–110 °C for 2 hours for a cyclization condensation reaction to form a lactone ring structure. The resulting polymerization solution was then passed through a multi-tube heat exchanger heated to 235 °C to complete the cyclization condensation reaction.

[0099] For a twin-screw extruder (L / D=52), the obtained polymerization solution was introduced at a rate of 97.5 parts by mass / hour based on resin content calculation, and devolatilization was performed. Furthermore, the twin-screw extruder has one rear vent, four front vents (referred to as the first, second, third, and fourth vents from the upstream side), and a side feeder located between the third and fourth vents. A vane-type polymer filter (10 μm filtration accuracy) is installed at the front end. An extrusion die is positioned further forward than the polymer filter, and multiple through holes are formed along the circumference of the resin discharge surface of the extrusion die, and an underwater cutting device is installed.

[0100] Deviation is carried out under the following conditions: screw speed 80 rpm, pressure reduction 25–800 hPa, and drum temperature 255°C (heated by a 255°C hot medium). Additionally, in accordance with the introduction of the polymerization solution, ion-exchanged water is introduced upstream of the second and third vents at a rate of 1.5 parts by mass / hour, and upstream of the fourth vent at a rate of 3 parts by mass / hour. Furthermore, acrylonitrile-styrene copolymer (SANREX 290LF, manufactured by Techno UMG) granules (hereinafter referred to as AS resin) are introduced from the side feeder at a rate of 2.5 parts by mass / hour.

[0101] After devolatilization, the (meth)acrylic resin composition is passed through a polymer filter and then extruded from an extrusion die. The extruded (meth)acrylic resin composition is cut and water-cooled, dehydrated using a centrifugal dryer, and finally cooled in a storage silo. This yields granules of a (meth)acrylic resin composition (A-1) containing AS resin (resin (B)) and a (meth)acrylic resin with an lactone ring structure (resin (A)). The (meth)acrylic resin composition (A-1) has a glass transition temperature of 124°C, a weight-average molecular weight of 131,000, and a number-average molecular weight of 54,000.

[0102] <Manufacturing Example 2: (Meth)Acrylic Resin Composition (A-2)> Except for the introduction of the twin-screw extruder, changing the amount of polymerization solution input (converted to resin amount) to 98.0 parts by mass / hour, and changing the amount of AS resin input to 2.0 parts by mass / hour, the operation was the same as in Manufacturing Example 1, and granules of the (meth)acrylic resin composition (A-2) were obtained. The (meth)acrylic resin composition (A-2) had a glass transition temperature of 124°C, a weight-average molecular weight of 131,000, and a number-average molecular weight of 54,000.

[0103] <Manufacturing Example 3: (Meth)Acrylic Resin Composition (A-3)> Except for the introduction of the twin-screw extruder, changing the amount of polymerization solution input to 90.0 parts by mass / hour and the amount of AS resin input to 10.0 parts by mass / hour, the operation was the same as in Manufacturing Example 1 to obtain granules of the (meth)acrylic resin composition (A-3). The (meth)acrylic resin composition (A-3) has a glass transition temperature of 125°C, a weight-average molecular weight of 135,000, and a number-average molecular weight of 54,000.

[0104] Furthermore, in the following examples and comparative examples, the resin compositions obtained in each manufacturing example were used after being dried in dry air at 60°C for 24 hours.

[0105] <Example 1: Optical Film (F-1)> A (meth)acrylic resin composition (A-1) was fed into a single-shaft extruder (L / D=52) equipped with a disc-type polymer filter (filtration accuracy 5 μm) at the front end and a T-die. The mixture was melt-molded at a molding temperature of 270°C to produce a raw material film (144 μm thick). The raw material film was then directly fed into an oven longitudinal stretching machine for longitudinal stretching, and subsequently fed into a tenter frame transverse stretching machine for transverse stretching to obtain an optical film (F-1) with a thickness of 40 μm.

[0106] Furthermore, in the longitudinal stretching, the stretching temperature was set to Tg+16°C of the (meth)acrylic resin composition (A-1), and the stretching ratio was set to 2.0 times. In the transverse stretching, the stretching temperature was set to Tg+12°C in the preheating zone, Tg+12°C in the stretching zone, and Tg-2°C in the heat treatment zone, with a stretching ratio of 2.4 times.

[0107] After slits are formed at both ends of the optical film (F-1) in the width direction, a protective film made of polyethylene is laminated and a film roll is made.

[0108] <Example 2: Optical Film (F-2)> Except for using the (meth)acrylic resin composition (A-2) obtained in Manufacturing Example 2, the operation was the same as in Example 1 to obtain an optical film (F-2) with a thickness of 40 μm.

[0109] <Example 3: Optical Film (F-3)> Except for setting the longitudinal stretching temperature to Tg+20℃, the transverse stretching temperature to Tg+18℃ in the preheating zone, Tg+18℃ in the stretching zone, and Tg-2℃ in the heat treatment zone, the operation was the same as in Example 1, and an optical film (F-3) with a thickness of 40 μm was obtained.

[0110] <Comparative Example 1: Optical Film (Fc-1)> Except for using the (meth)acrylic resin composition (A-3) obtained in Manufacturing Example 3, setting the thickness of the raw material film to 160 μm, setting the longitudinal stretching temperature to Tg+19°C, setting the longitudinal stretching ratio to 1.9 times, setting the transverse stretching temperature to Tg+19°C in the preheating zone, Tg+19°C in the stretching zone, and Tg-2°C in the heat treatment zone, and setting the transverse stretching ratio to 2.76 times, the rest of the operation was the same as in Example 1, and an optical film (Fc-1) with a thickness of 40 μm was obtained.

[0111] <Reference Example 1: Optical Film (Fr-1)> Triacetyl cellulose resin (manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd., limiting viscosity [η]: 1.335 dL / g, degree of acetylation: 2.917) was dissolved in a dichloromethane / methanol (9 / 1 mass ratio) mixture to prepare a paste with a solid content of 20% by mass. An optical film (Fr-1) with a thickness of 60 μm was fabricated from this paste using a solution casting method. The values ​​of R(45,400) / R(45,550) were 1.12 and R(45,550) / R(45,700) were 1.05.

[0112] Table 1 shows the various physical properties of the optical films of Examples 1-3 and Comparative Example 1.

[0113]

Claims

1. An optical film comprising a resin composition including a resin (A) exhibiting positive intrinsic birefringence and a resin (B) exhibiting negative intrinsic birefringence, characterized in that, The glass transition temperature of the resin composition is 110–160°C. The resin (A) comprises a ring structural unit (p1) with a ring structure in the main chain and a structural unit (q1) derived from alkyl methacrylates. When measured with light at wavelengths of 400 nm, 550 nm, and 700 nm, the absolute values ​​of the in-plane phase difference Re are all 0–2 nm, and the absolute values ​​of the phase difference Rth in the thickness direction are all 4–20 nm. When the absolute value of the phase difference when measuring light with an incident angle of 45 degrees and a wavelength of λ (nm) is set as R(45,λ), R(45,400) / R(45,550) is greater than 1.05 and R(45,550) / R(45,700) is greater than 1.

2. The optical film according to claim 1, wherein, The resin (A) also contains structural units (q2) derived from aromatic vinyl groups. In the resin (A), the content of the ring structural unit (p1) is 15-35% by mass, the content of the structural unit (q1) is 45-80% by mass, and the content of the structural unit (q2) is 0.1-20% by mass.

3. The optical film according to claim 1 or 2, wherein, The resin (B) comprises structural units (r1) derived from acrylonitrile and structural units (r2) derived from styrene.

4. The optical film according to claim 3, wherein, In the resin composition, 1 to 5 parts by weight of the resin (B) are included relative to 100 parts by weight of the resin (A).

5. The optical film according to claim 1 or 2, wherein, The ring structural unit (p1) comprises at least one selected from the group consisting of lactone ring structural units and glutarimide structural units.

6. The optical film according to claim 1 or 2, wherein, The absolute value of the stress optical coefficient of the resin composition is 5 × 10⁻⁶. -11 ~20×10 -11 Pa -1 .

7. The optical film according to claim 1 or 2, wherein, When measured with light at wavelengths of 400 nm, 550 nm, and 700 nm, the difference between the absolute value of the in-plane phase difference Re and the absolute value of the phase difference Rth in the thickness direction is 3.5–18 nm.

8. The optical film according to claim 1 or 2, wherein, R(45,400) / R(45,700) is 1.1 to 1.

5.

9. The optical film according to claim 1 or 2, wherein, R(45,400), R(45,550) and R(45,700) are all 0.5–10 nm.

10. The optical film according to claim 1 or 2, wherein, The thickness of the optical film is 5–50 μm.

11. The optical film according to claim 1 or 2, wherein, The optical film is a polarizer protective film.

Images