Optical film

Abstract

Provided is an optical film that has excellent wet heat resistance and can be used as a polarizer protection film in an image display device in place of a TAC film without the need to adjust the optical characteristics of other elements. Provided is an optical film that comprises a resin composition that includes a resin (A) that demonstrates positive intrinsic birefringence and a resin (B) that demonstrates negative intrinsic birefringence. The optical film is characterized in that: the resin composition has a glass transition temperature of 110°C–160°C; the resin (A) includes a ringed structural unit (p1) that includes a ring structure on a principal chain and a structural unit (q1) that is derived from an alkyl (meth)acrylate; as measured with light of 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; and when R(45,λ) is the absolute value of the phase difference as measured with light of a wavelength of λ (nm) at an incidence angle of 45 degrees, R(45,400) / R(45,550) is at least 1.05, and R(45,550) / R(45,700) is greater than 1.

Description

Optical Film

[0001] The present disclosure relates to optical films.

[0002] A typical liquid crystal display device includes a liquid crystal cell and two polarizing plates laminated on both sides of the liquid crystal cell. Each of the two polarizing plates includes a polarizer and two polarizer protective films laminated on both sides of the polarizer. Conventionally, triacetyl cellulose film (hereinafter referred to as TAC film) has been used as the polarizer protective film. However, TAC film has a problem of low resistance to moist heat.

[0003] Therefore, (meth)acrylic films, which have better resistance to moist heat than TAC films, have been proposed as polarizer protective films (see, for example, Patent Document 1).

[0004] JP 2015-057664 A

[0005] As described in paragraph 0002 of Patent Document 1, optical films are required to have optical properties that correspond to the optical design of image display devices. In other words, polarizer protective films are required to be compatible with elements (polarizers, liquid crystal cells, etc.) other than the polarizer protective film that constitute the image display device.

[0006] TAC films, which have traditionally been used as polarizer protective films, have a characteristic (normal dispersion) in which the absolute value of the retardation on the short wavelength side, around 400 nm, is larger than the absolute value of the retardation on the long wavelength side, around 700 nm. In particular, when viewed from an oblique angle, a pure black display cannot be achieved, resulting in a strongly bluish display. Therefore, in conventional image display devices, the optical design of the image display device has been designed to avoid a bluish tinge by adjusting elements other than the polarizer protective film, assuming the use of a TAC film as a polarizer protective film.

[0007] In such an image display device, if the polarizer protective film is changed from a TAC film to a (meth)acrylic film that has a small in-plane retardation and a small thickness retardation, the display may appear more yellowish when viewed from an oblique direction because the absolute value of the retardation on the short wavelength side near a wavelength of 400 nm is smaller in the (meth)acrylic film than in the TAC film. In other words, if the polarizer protective film in an image display device is changed from a TAC film to a (meth)acrylic film, it becomes necessary to adjust the optical properties of elements other than the polarizer protective film.

[0008] The present disclosure has been made in light of the above-mentioned circumstances, and its purpose is to provide an optical film that has excellent moisture and heat resistance and does not require adjustment of the optical properties of elements other than the polarizer protective film when used in place of a TAC film in an image display device.

[0009] As a result of extensive investigation, a means for obtaining a (meth)acrylic film having optical properties closer to those of a TAC film than conventional films has been found.

[0010] That is, the present disclosure includes the following configurations: [1] An optical film made of a resin composition containing a resin (A) exhibiting positive intrinsic birefringence and a resin (B) exhibiting negative intrinsic birefringence, wherein the resin composition has a glass transition temperature of 110 to 160°C, the resin (A) contains a cyclic structural unit (p1) having a cyclic structure in the main chain and a structural unit (q1) derived from an alkyl (meth)acrylate, and when measured with light having wavelengths of 400 nm, 550 nm, and 700 nm, the absolute values ​​of the in-plane retardation Re are all 0 to 2 nm, and the absolute values ​​of the thickness direction retardation Rth are all 4 to 20 nm, and when R(45, λ) is the absolute value of the retardation when measured with light having an incident angle of 45 degrees and a wavelength λ (nm), R(45,400) / R(45,550) is 1.05 or more, and R(45,550) / R(45,700) is greater than 1. [2] The optical film according to [1], wherein the resin (A) further contains a structural unit (q2) derived from an aromatic vinyl, and the content of the cyclic 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. [3] The optical film according to [1] or [2], wherein the resin (B) contains a structural unit (r1) derived from acrylonitrile and a structural unit (r2) derived from styrene. [4] The optical film according to [3], wherein the resin composition contains 1 to 5 parts by mass of the resin (B) per 100 parts by mass of the resin (A). [5] The optical film according to any one of [1] to [4], wherein the cyclic structural unit (p1) contains at least one selected from the group consisting of a lactone ring structural unit and a glutarimide structural unit. [6] The resin composition has an absolute stress-optical coefficient of 5×10 －１１ ~20 x 10 －１１ Pa －１The optical film according to any one of [1] to [5], wherein the difference between the absolute value of the in-plane retardation Re and the absolute value of the thickness direction retardation Rth is 3.5 to 18 nm when measured with light having wavelengths of 400 nm, 550 nm, and 700 nm. [8] The optical film according to any one of [1] to [7], wherein R(45,400) / R(45,700) is 1.1 to 1.5. [9] The optical film according to any one of [1] to [8], wherein R(45,400), R(45,550), and R(45,700) are all 0.5 to 10 nm.

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

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

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

[0011] The optical film of the present disclosure is a (meth)acrylic film in which the absolute value of the retardation on the short wavelength side is greater than the absolute value of the retardation on the long wavelength side when measured with light at an incident angle of 45 degrees, and therefore, even when the optical film of the present disclosure is used as a polarizer protective film in place 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. Furthermore, the optical film of the present disclosure has better moist heat resistance than a TAC film.

[0012] The present disclosure provides an optical film made of a resin composition containing a resin (A) that exhibits positive intrinsic birefringence and a resin (B) that exhibits negative intrinsic birefringence.

[0013] [Resin (A)] Resin (A) contains a cyclic structural unit (p1) having a cyclic structure in the main chain and a structural unit (q1) derived from an alkyl (meth)acrylate. In the present disclosure, the term "(meth)acrylic acid" encompasses both methacrylic acid and acrylic acid.

[0014] <Ring structural unit (p1)> The ring structural unit (p1) has the effect of imparting positive intrinsic birefringence to the resin (A). In other words, the ring structural unit (p1) is a structural unit whose slow axis is the stretching direction (which can also be considered the orientation direction). In the resin (A), the content of the ring structural unit (p1) is preferably 15 to 35 mass%, more preferably 18 to 30 mass%. By setting the content of the ring structural unit (p1) within the above range, the optical film is more likely to exhibit desired retardation characteristics. Note that the numerical range indicated by X to Y means not less than X and not more than Y. Furthermore, 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 predetermined range.

[0015] The ring structure constituting the main chain of the ring structural unit (p1) may be any of a 4-membered ring structure, a 5-membered ring structure, a 6-membered ring structure, a 7-membered ring structure, an 8-membered ring structure, etc., and is preferably a 5-membered ring structure or a 6-membered ring structure.

[0016] The ring structure constituting the main chain of the ring structural unit (p1) may be introduced by polymerizing a (meth)acrylic monomer having a ring structure, or may be introduced by polymerizing a (meth)acrylic monomer having a group for forming a ring structure and then chemically reacting the polymerized monomer.

[0017] Specific examples of the ring structural unit (p1) include, but are not limited to, a lactone ring structural unit, a lactam ring structural unit, a succinic anhydride structural unit, a succinimide structural unit, a glutaric anhydride structural unit, and a glutarimide structural unit. The ring structural unit (p1) may contain only one type of these structural units, or may contain two or more types.

[0018] 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, and may be, for example, any of a 4-membered ring to an 8-membered ring. From the viewpoint of enhancing the stability of the ring structure, the lactone ring structure is preferably a 5-membered or 6-membered ring, and more preferably a 6-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, and may be, for example, any of a 4-membered ring to an 8-membered ring. From the viewpoint of enhancing the stability of the ring structure, the lactam ring structure is preferably a 5-membered or 6-membered ring, and more preferably a 5-membered ring.

[0019] The lactone ring structural unit is preferably a structural unit represented by the following formula (1a): The lactam ring structural unit is preferably a structural unit represented by the following formula (1b):

[0020]

[0021] In formula (1a), R １１ and R １２ are each independently, but are not particularly limited to, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R １３ is a hydrogen atom or a methyl group.

[0022] In formula (1b), R １５ and R １６ are each independently, but are not particularly limited to, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R １４ is a hydrogen atom or a methyl group.

[0023] In formula (1a), R １１ and R １２ are preferably each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably each independently a hydrogen atom or a methyl group. １５ and R１６ are preferably each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably each independently a hydrogen atom or a methyl group.

[0024] The structural unit represented by formula (1a) can be formed, for example, by polymerizing a group of monomers containing methyl 2-(hydroxymethyl)acrylate and methyl (meth)acrylate, followed by dealcoholization condensation between the hydroxy group and the ester bond. The structural unit represented by formula (1b) can be formed, for example, by polymerizing a group of monomers containing N-vinylacetamide and methyl (meth)acrylate, followed by dealcoholization condensation between the amide group and the ester bond.

[0025] The ring structural unit (p1) may contain only one type of lactone ring structural unit represented by formula (1a), or may contain two or more types of lactam ring structural unit represented by formula (1b).

[0026] The succinic anhydride structural unit (structural unit derived from a maleic anhydride monomer) is preferably a structural unit represented by the following formula (2a): The succinimide structural unit (structural unit derived from a maleimide monomer) is preferably a structural unit represented by the following formula (2b):

[0027]

[0028] In formula (2a), R ２１ and R ２２ are each independently a hydrogen atom or a methyl group.

[0029] In formula (2b), R ２３ and R ２４ R each independently represents a hydrogen atom or a methyl group. ２５ is not particularly limited, but is, for example, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R ２５is preferably a methyl group, an ethyl group, a cyclohexyl group, a phenyl group, a naphthyl group or a benzyl group, and more preferably a cyclohexyl group or a phenyl group.

[0030] The structural unit represented by formula (2a) can be formed, for example, by polymerizing a group of monomers including a maleic anhydride monomer, and the structural unit represented by formula (2b) can be formed, for example, by polymerizing a group of monomers including a maleimide monomer or an N-substituted maleimide monomer.

[0031] The ring structural unit (p1) may contain only one type of succinic anhydride structural unit represented by formula (2a), or may contain two or more types of succinimide structural units represented by formula (2b).

[0032] The glutaric anhydride structural unit is preferably a structural unit represented by the following formula (3a): The glutarimide structure is preferably a structural unit represented by the following formula (3b):

[0033]

[0034] In formula (3a), R ３１ ~R ３３ each independently represents a hydrogen atom or a methyl group.

[0035] In formula (3b), R ３４ ~R ３６ R each independently represents a hydrogen atom or a methyl group. ３７ is not particularly limited, but is, for example, a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. R ３７ is preferably a hydrogen atom, a methyl group, a cyclohexyl group, a phenyl group or a tolyl group, and more preferably a hydrogen atom or a methyl group.

[0036] The structural unit represented by formula (3a) can be formed, for example, by polymerizing a monomer group containing a (meth)acrylic acid monomer and a methyl (meth)acrylate monomer, followed by dehydration condensation between a carboxy group and an ester bond. The structural unit represented by formula (3b) can be formed, for example, by polymerizing a monomer group containing a methyl (meth)acrylate monomer, followed by imidization between two ester bonds.

[0037] The cyclic structural unit (p1) may contain only one type of glutaric anhydride structural unit represented by formula (3a), or may contain two or more types of glutarimide structural units represented by formula (3b).

[0038] From the viewpoint of stability of the ring structure, the ring structural unit (p1) preferably contains at least one selected from the group consisting of a lactone ring structural unit, a succinimide structural unit, and a glutarimide structural unit, and more preferably contains at least one selected from the group consisting of a lactone ring structural unit and a glutarimide structural unit. From the viewpoint of yellowness when formed into an optical film, the ring structural unit (p1) preferably contains a lactone ring structural unit.

[0039] <Structural Units (q1) and (q2)> Specific examples of the structural unit (q1) are not particularly limited, and include structural units derived from monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, etc. The alkyl group of the alkyl (meth)acrylate is preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, even more preferably an alkyl group having 1 to 3 carbon atoms, particularly preferably an alkyl group having 1 or 2 carbon atoms, and most preferably an alkyl group having 1 carbon atom (methyl group).

[0040] In the resin (A), the content of the structural unit (q1) is preferably 45 to 80% by mass, more preferably 60 to 76% by mass. The structural unit (q1) is a structural unit that has the effect of imparting negative intrinsic birefringence, but by setting the content of the structural unit (q1) within the above range, the resin (A) can be made to exhibit positive intrinsic birefringence, and the optical film can easily exhibit desired retardation characteristics.

[0041] It is preferable that the resin (A) further contains a structural unit (q2) derived from a copolymerizable aromatic vinyl. The structural unit (q2) derived from an aromatic vinyl is a structural unit that has the effect of imparting negative intrinsic birefringence, and by including the structural unit (q2) derived from an aromatic vinyl, the absolute value of the stress-optical coefficient of the resin composition is more likely to fall within the predetermined range described below. Specific examples of the structural unit (q2) are not particularly limited as long as they are structural units derived from a compound in which a vinyl group is bonded to an aromatic ring, and include structural units derived from monomers such as styrene-based monomers such as styrene, vinyltoluene, methoxystyrene, α-methylstyrene, α-hydroxymethylstyrene, and α-hydroxyethylstyrene; polycyclic aromatic hydrocarbon ring vinyls such as 2-vinylnaphthalene; and aromatic heterocyclic vinyls such as N-vinylcarbazole, 2-vinylpyridine, vinylimidazole, and vinylthiophene. Styrenic monomers include not only styrene but also, as described above, styrene derivatives in which an optional substituent is bonded to the polymerizable double-bond carbon or benzene ring of styrene. The substituent is not particularly limited, but examples thereof include an alkyl group, an alkoxy group, a hydroxy group, a halogen group, an amino group, a nitro group, and a sulfo group. The alkyl group and the alkoxy group preferably contain 1 to 4 carbon atoms, and more preferably contain 1 to 2 carbon atoms. The structural unit (q2) is preferably a structural unit derived from styrene.

[0042] When the resin (A) contains the structural unit (q2), the content of the structural unit (q2) in the resin (A) is preferably 0.1 to 20 mass%, more preferably 1 to 10 mass%, and even more preferably 3 to 5 mass%. By setting the content of the structural unit (q2) within the above range, the absolute value of the stress optical coefficient of the resin composition tends to fall within the specified range described below.

[0043] When the resin (A) contains the structural unit (q2), the ratio of the content of the structural unit (q2) to the total content of the structural unit (q1) and the structural unit (q2) in the resin (A) is preferably 0.1 to 31 mass%, more preferably 3 to 20 mass%, and even more preferably 5 to 10 mass%. By keeping the content ratio of the structural unit (q2) within the above range, the absolute value of the stress optical coefficient of the resin composition tends to fall within the specified range described below.

[0044] When the resin (A) contains the structural unit (q1) and the structural unit (q2), it is preferable that the content of the cyclic 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, and it is more preferable that the content of the cyclic structural unit (p1) in the resin (A) is 18 to 30% by mass, the content of the structural unit (q1) is 60 to 76% by mass, and the content of the structural unit (q2) is 3 to 10% by mass. By setting the contents of the structural units in the resin (A) within the above ranges, the glass transition temperature of the resin composition is kept within the desired range, and the optical film is more likely to exhibit the desired retardation characteristics.

[0045] When the resin (A) contains the cyclic structural unit (p1), the structural unit (q1), and the structural unit (q2), the total content of the cyclic structural unit (p1), the structural unit (q1), and the structural unit (q2) in the resin (A) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and most preferably 100% by mass.

[0046] Resin (A) preferably contains only the cyclic structural unit (p1) and the structural unit (q1), or only the cyclic structural unit (p1), the structural unit (q1), and the structural unit (q2). However, as long as the optical properties of the resin composition are not significantly impaired, it may contain a structural unit other than the cyclic structural unit (p1), the structural unit (q1), and the structural unit (q2) (hereinafter referred to as structural unit (s)). Specific examples of structural unit (s) include, but are not limited to, structural units derived from monomers such as benzyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, vinyl chloride, and indene. Even when structural unit (s) is contained, it is preferable that the absolute value of the stress optical coefficient of the resin composition be within a predetermined range described below.

[0047] [Resin (B)] Resin (B) is a resin that exhibits negative intrinsic birefringence, or in other words, a resin whose fast axis is the stretching direction (which can also be referred to as the orientation direction). Resin (B) is not particularly limited as long as it exhibits negative intrinsic birefringence, but is preferably polymethyl methacrylate or a resin containing a structural unit (r1) derived from acrylonitrile and a structural unit (r2) derived from styrene. Examples of resin (B) containing a structural unit (r1) derived from acrylonitrile and a structural unit (r2) derived from styrene include acrylonitrile-styrene copolymers, acrylonitrile-styrene-maleimide copolymers, and acrylonitrile-styrene-maleic anhydride copolymers. Among these, it is preferable to use acrylonitrile-styrene copolymers because they are commercially available and easily available.

[0048] The resin composition preferably contains 1 to 5 parts by mass, and more preferably 1.5 to 4 parts by mass, of resin (B) per 100 parts by mass of resin (A). By setting the content of resin (B) within the above range, the absolute value of the stress optical coefficient of the resin composition tends to fall within the specified range described below.

[0049] <Others> The resins contained in the resin composition used in the present disclosure are preferably only resin (A) and resin (B), but a resin other than resin (A) and resin (B) (hereinafter referred to as resin (C)) may be contained as long as the optical properties of the resin composition are not significantly impaired. Even when resin (C) is contained, it is preferable that the absolute value of the stress optical coefficient of the resin composition be within a predetermined range described below.

[0050] The resin (C) is not particularly limited, but examples thereof include polyester resin, polyolefin resin, polyamide resin, polyimide resin, etc. The content of resin (C) in the resin component contained in the resin composition is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 2% by mass or less, and most preferably 0% by mass.

[0051] The resin composition used in the present disclosure may contain various additives as long as the optical properties of the resin composition are not significantly impaired. Examples of additives include ultraviolet absorbers; antioxidants; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; near-infrared absorbers; flame retardants; antistatic agents; colorants; organic fillers and inorganic fillers; and resin modifiers. The total content of additives in the resin composition is preferably 0 to 5% by mass, and more preferably 0 to 2% by mass.

[0052] <Film Manufacturing Method> The optical film of the present disclosure is preferably manufactured by biaxial stretching to exhibit desired retardation properties. Biaxial stretching can achieve a desired retardation in the thickness direction while bringing the in-plane retardation Re to near zero. For example, a resin composition can be melt-extruded using an extruder to form an unstretched film, which can then be stretched in the machine direction (MD) and then stretched in the transverse direction (TD).

[0053] The stretching ratio in the machine direction is preferably 1.4 to 3.0 times, more preferably 1.7 to 2.5 times. By setting it within this range, it is possible to obtain a desired retardation in the thickness direction while making the in-plane retardation Re close to zero after transverse stretching.

[0054] The stretching temperature in the machine direction is preferably Tg+10° C. to Tg+30° C., more preferably Tg+12° C. to Tg+24° C. By setting the temperature within the above range, it is possible to obtain a desired retardation in the thickness direction, while making the in-plane retardation Re close to zero after transverse stretching.

[0055] The stretching ratio in the transverse direction is preferably 1.8 to 3.2 times, more preferably 2.2 to 2.6 times. By setting it within this range, it is possible to obtain a desired retardation in the thickness direction while making the in-plane retardation Re close to zero.

[0056] The stretching temperature in the transverse direction is preferably Tg+7°C to Tg+27°C, more preferably Tg+10°C to Tg+22°C. By setting the temperature within the above range, it is possible to obtain a desired retardation in the thickness direction while making the in-plane retardation Re close to zero after transverse stretching. In particular, from the viewpoint of preventing the retardation in the thickness direction caused by stretching in the longitudinal direction from becoming small, it is preferable that the stretching temperature in the transverse direction is lower than the stretching temperature in the longitudinal direction.

[0057] Preheating may be carried out before the transverse stretching. When preheating is carried out, the preheating temperature is preferably lower than the stretching temperature in the longitudinal direction.

[0058] When the stretched film is used as an optical film, it may be subjected to heat treatment (annealing) after stretching as necessary to stabilize the optical and mechanical properties of the optical film. When heat treatment is performed, the heat treatment temperature is preferably Tg-10°C to Tg+10°C, and more preferably Tg-5°C to Tg+5°C. By setting the temperature within the above range, it becomes easier to obtain a desired retardation in the thickness direction.

[0059] <Physical Properties of Optical Film and Resin Composition> (Thickness of Optical Film) The thickness of the optical film of the present disclosure is preferably 5 to 50 μm, more preferably 10 to 45 μm, and even more preferably 20 to 40 μm.

[0060] (In-plane retardation Re, thickness direction retardation Rth, retardation measured with light at an incident angle of 45 degrees) The in-plane retardation Re and thickness direction retardation Rth of an optical film can be calculated from the following formulas. Here, nx is the refractive index in the slow axis direction of the optical film in the plane, ny is the refractive index in the fast axis direction of the film in the plane, nz is the refractive index in the thickness direction of the film, and d is the thickness of the film. In-plane retardation Re=(nx-ny)×d Thickness direction retardation Rth=[(nx+ny) / 2-nz]×d

[0061] The in-plane retardation Re, thickness direction retardation Rth, and retardation when measured with light at an incident angle of 45 degrees of the optical film of the present disclosure will be described below. The absolute value of the in-plane retardation Re when measured with light of wavelength λ (nm) is represented as Re(λ), the absolute value of the thickness direction retardation Rth when measured with light of wavelength λ (nm) is represented as Rth(λ), and the absolute value of the retardation when measured with light of wavelength λ (nm) at an incident angle of 45 degrees is represented as R(45, λ).

[0062] The in-plane retardation Re of Re(400), Re(550), and Re(700) is 0 to 2 nm, preferably 0 to 1.5 nm, and more preferably 0 to 1 nm. The difference between the maximum and minimum values ​​of the three values ​​of Re(400), Re(550), and Re(700) is preferably 1 nm or less, more preferably 0.6 nm or less, even more preferably 0.4 nm or less, and particularly preferably 0.1 to 0.2 nm.

[0063] The thickness direction retardation Rth is preferably 4 to 20 nm, more preferably 4.5 to 17 nm, more preferably 5 to 15 nm, and even more preferably 5.5 to 12 nm, for Rth(400), Rth(550), and Rth(700). The difference between the maximum and minimum values ​​of the three values, Rth(400), Rth(550), and Rth(700), is preferably 10 nm or less, more preferably 1 to 7 nm, even more preferably 1.5 to 5.0 nm, and particularly preferably 2.5 to 3.5 nm. The absolute values ​​of the in-plane retardation Re and the thickness direction retardation Rth indicate the ease with which elliptically polarized light is generated (the ease with which light leaks).

[0064] The retardation Rth in the thickness direction is preferably a negative value. In any of the examples described later, the values ​​measured with light having wavelengths of 400 nm, 550 nm, and 700 nm are all negative, but they may be made positive by adjusting the composition of the resin composition or the production conditions of the film.

[0065] The difference between Re(400) and Rth(400), the difference between Re(550) and Rth(550), and the difference between Re(700) and Rth(700) (the difference between the absolute value of the in-plane retardation Re and the absolute value of the retardation Rth in the thickness direction when measured with light having wavelengths of 400 nm, 550 nm, and 700 nm) are each preferably 3.5 to 18 nm, more preferably 4 to 15 nm, and even more preferably 4.5 to 10 nm.

[0066] The retardation values ​​R(45,400), R(45,550), and R(45,700) measured with light at an incident angle of 45 degrees are preferably 0.5 to 10 nm, more preferably 1.0 to 7.0 nm, and even more preferably 2.0 to 5.0 nm. The difference between the maximum and minimum values ​​of the three values ​​R(45,400), R(45,550), and R(45,700) 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 to 1.5 nm.

[0067] The value of R(45,400) / R(45,550) is 1.05 or more, and the value of R(45,550) / R(45,700) is greater than 1. It is preferable that both R(45,400) / R(45,550) and R(45,550) / R(45,700) are 1.05 or more.

[0068] The value of R(45,400) / R(45,550) is preferably 1.05 to 1.3, and more preferably 1.15 to 1.3. The value of R(45,550) / R(45,700) is preferably 1.03 to 1.2, and more preferably 1.05 to 1.15. The value of R(45,400) / R(45,700) is preferably 1.1 to 1.5.

[0069] (Stress-optical coefficient Cr) In the resin composition used in the present disclosure, the absolute value of the stress-optical coefficient Cr is 5×10 －１１ ~20 x 10 －１１ Pa －１ Preferably, it is 7×10 －１１ ~17 x 10 －１１ Pa －１ More preferably, it is 8×10 －１１ ~15 x 10 －１１ Pa －１ When the absolute value of the stress optical coefficient Cr is within the above range, the optical film is likely to exhibit desired flexibility and retardation properties.

[0070] (Glass transition temperature) The resin composition used in the present disclosure has a glass transition temperature of 110 to 160°C. This allows the heat resistance of the resin composition to be improved while ensuring moldability. The resin composition used in the present invention more preferably has a glass transition temperature of 115 to 150°C, and even more preferably has a glass transition temperature of 120 to 140°C.

[0071] The weight-average molecular weight of the resin composition used in the present disclosure is preferably 5,000 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, it becomes easier to improve the molding processability of the resin composition, and the mechanical strength of the obtained optical film can be ensured.

[0072] The number average molecular weight of the resin composition used in the present disclosure is preferably 5,000 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, it becomes easier to improve the moldability of the resin composition, and the mechanical strength of the obtained optical film can be ensured.

[0073] <Applications of Optical Film> The optical film of the present disclosure can be suitably used in image display devices, and can be used, for example, as a polarizer protective film, a retardation film, a transparent conductive film, or a light conversion film. Among these, it is preferable to use the optical film as a polarizer protective film by laminating it on one or both sides of a polarizer. Examples of image display devices include liquid crystal display devices. In the case of liquid crystal display devices, the image display unit can be configured to include the optical film of the present disclosure together with components such as a liquid crystal cell, a polarizing plate, and a backlight. Examples of image display devices other than liquid crystal display devices include electroluminescence (EL) display panels, plasma display panels (PDPs), field emission displays (FEDs), QLEDs, microLEDs, and the like.

[0074] 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 specification of Japanese Patent Application No. 2024-060473, filed on April 3, 2024, are incorporated herein by reference.

[0075] The present disclosure will be described below with reference to examples, but the present disclosure is not limited to these examples. The evaluation methods used in each example, comparative example, and reference example are as follows.

[0076] <Glass transition temperature Tg> The glass transition temperature of the resin compositions obtained in the Production Examples was measured in accordance with the provisions of Japanese Industrial Standards (JIS) K 7121. Using a differential scanning calorimeter (Rigaku Corporation; Thermo plus EVO DSC-8230), approximately 10 mg of a sample was heated from room temperature to 200°C (heating rate 20°C / min) in a nitrogen gas atmosphere, and the glass transition temperature Tg was measured by the starting point method from the DSC curve obtained. α-Alumina was used as a reference.

[0077] <Thickness of Optical Film> The thickness of the optical film was measured using a Digimatic Micrometer (manufactured by Mitutoyo Corporation).

[0078] <Weight-average molecular weight and number-average molecular weight> The weight-average molecular weight and number-average molecular weight of the (meth)acrylic resin composition were determined in terms of polystyrene using gel permeation chromatography (GPC). The equipment and conditions used for the measurement are as follows. Measurement system: GPC system HLC-8220 manufactured by Tosoh Corporation Measurement column configuration: Guard column (TSK Gel guard column Super HZ-L manufactured by Tosoh Corporation) Separation column (TSK Gel Super HZM-M manufactured by Tosoh Corporation), two columns connected in series Reference column configuration: Reference column (TSK Gel Super H-RC manufactured by Tosoh Corporation) Developing solvent: chloroform (special grade manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Developing solvent flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (PS-oligomer kit manufactured by Tosoh Corporation)

[0079] <Stress-optical coefficient Cr> The stress-optical coefficient Cr of the resin composition obtained in the Production Examples was evaluated as follows. A film (unstretched film) having a thickness of 100 μm was obtained from the resin composition by melt extrusion. A measurement sample of 60 mm × 20 mm was cut out from the film. During uniaxial stretching described below, a stress of 1 N / mm ２A weight having a mass such that the following stress was applied to the measurement sample was selected, and the weight was attached to one short side of the measurement sample. Next, the measurement sample was placed in a dryer (manufactured by AS ONE Corporation; DOV-450A) maintained at Tg + 3 ° C of the resin composition. In the dryer, the other short side of the measurement sample was fixed with a chuck, so that the measurement sample was free-end uniaxially stretched in the vertical direction due to the stress generated by the mass of the weight. The distance between the upper end of the part of the measurement sample where the weight was attached and the lower end of the chuck was 40 mm. After leaving it for 30 minutes, the heater of the dryer was turned off, and the temperature inside the dryer was cooled at a rate of approximately 1 ° C / min until the temperature inside the dryer reached Tg - 40 ° C of the resin composition. The measurement sample was removed from the dryer, and the length and thickness of the measurement sample, the in-plane retardation Re for light with a wavelength of 590 nm, and the mass of the weight were measured. The same test was performed four more times while changing the mass of the weight. The measured in-plane retardation Re was divided by the thickness d (nm) of the measurement sample to determine the birefringence Δn (= nx - ny, measurement wavelength 590 nm) of the measurement sample. The birefringence Δn was plotted on the y-axis, and the stress σ (Pa) applied to the measurement sample was plotted on the x-axis. A regression line was calculated using the least squares method based on the results of five tests. The absolute value of the slope was taken as the absolute value of the stress-optical coefficient Cr.

[0080] <In-plane retardation Re, thickness direction retardation Rth, retardation R(45, λ)> A 40 mm × 40 mm measurement sample was cut out from the optical film. Using a polarimeter (Axometrics; AxoScan), the in-plane retardation Re of the cut-out sample was measured at wavelengths of 400 nm, 550 nm, and 700 nm. The thickness direction retardation Rth and the retardation at an incident angle of 45 degrees were also measured at wavelengths of 400 nm, 550 nm, and 700 nm, similarly to the in-plane retardation Re. The retardation at an incident angle of 45 degrees was determined as the retardation when tilted 45 degrees around the optical axis (slow axis). The in-plane retardation Re, thickness direction retardation Rth, and absolute values ​​of the retardation at an incident angle of 45 degrees at wavelengths of 400 nm, 550 nm, and 700 nm are shown in Table 1. In Table 1, the absolute value of the in-plane retardation Re when measured with light of wavelength λ (nm) is represented as Re(λ), the absolute value of the retardation Rth in the thickness direction when measured with light of wavelength λ (nm) is represented as Rth(λ), and the absolute value of the retardation when measured with light of wavelength λ (nm) at an incident angle of 45 degrees is represented as R(45, λ).

[0081] Production Example 1 (Meth)Acrylic Resin Composition (A-1) A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen inlet tube was charged with 83.5 parts by mass of methyl methacrylate, 12.0 parts by mass of methyl 2-(hydroxymethyl)acrylate, and 88.7 parts by mass of toluene, and the temperature was raised to 105°C while nitrogen was passed through. When refluxing began as the temperature increased, 0.535 parts by mass of a toluene solution (manufactured by Arkema Yoshitomi Co., Ltd.; Lupelox (registered trademark) 570T20) containing 20% ​​by mass of t-amylperoxyisononanoate was added. Subsequently, a solution consisting of 4.5 parts by mass of styrene and 0.15 parts by mass of n-dodecyl mercaptan was added dropwise over 2 hours. Additionally, 1.065 parts by mass of a toluene solution (Arkema Yoshitomi Co., Ltd.; Lupelox (registered trademark) 570T20) containing 20% ​​by mass of t-amylperoxyisononanoate was added dropwise over 4 hours. During this dropwise addition, the mixture was refluxed at approximately 105 to 110°C to allow solution polymerization to proceed. After completion of the dropwise addition, the mixture was aged for an additional 2 hours at the same temperature. 0.0312 parts by mass of butyl phosphate (SC Organic Chemicals; Phoslex A-4) was added to the resulting polymerization solution, and a cyclization condensation reaction to form a lactone ring structure was allowed to proceed under reflux at approximately 90 to 110°C for 2 hours. The resulting polymerization solution was passed through a multi-tube heat exchanger heated to 235°C to complete the cyclization condensation reaction. The resulting polymerization solution was introduced into a vented twin-screw extruder (L / D = 52) at a rate of 97.5 parts by mass / hour in terms of resin amount, and devolatilization was performed. The vent-type twin-screw extruder is equipped with one rear vent, four fore 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 leaf disk-type polymer filter (filtration accuracy: 10 μm) is located at the tip. An extrusion die is provided further forward than the polymer filter. The resin discharge surface of the extrusion die has multiple through-holes formed along the circumference and is equipped with an underwater cutter. Devolatilization was performed at a screw speed of 80 rpm, a vacuum of 25 to 800 hPa, and a barrel temperature of 255°C (heated with a 255°C heat transfer medium).In addition, in conjunction with the introduction of the polymerization solution, ion-exchanged water was introduced from upstream of the second and third vents at a rate of 1.5 parts by mass / hour, and from upstream of the fourth vent at a rate of 3 parts by mass / hour. Furthermore, pellets of an acrylonitrile-styrene copolymer (SANREX (registered trademark) 290LF manufactured by Techno UMG Co., Ltd.) (hereinafter referred to as AS resin) were introduced from a side feeder at a rate of 2.5 parts by mass / hour. After devolatilization was completed, the (meth)acrylic resin composition was passed through a polymer filter and then extruded from an extrusion die. The extruded (meth)acrylic resin composition was cut, water-cooled, dehydrated using a centrifugal dryer, and finally cooled in a storage silo. In this way, pellets of a (meth)acrylic resin composition (A-1) containing an AS resin (resin (B)) and a (meth)acrylic resin having a lactone ring structural unit (resin (A)) were obtained. The (meth)acrylic resin composition (A-1) 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.

[0082] Production Example 2 (Meth)acrylic Resin Composition (A-2) Pellets of a (meth)acrylic resin composition (A-2) were obtained in the same manner as in Production Example 1, except that the amount of polymerization solution introduced into the vent-type twin-screw extruder was changed to 98.0 parts by mass / hour, calculated as the resin amount, and the amount of AS resin introduced was changed to 2.0 parts by mass / hour. The glass transition temperature of the (meth)acrylic resin composition (A-2) was 124°C, the weight average molecular weight was 131,000, and the number average molecular weight was 54,000.

[0083] Production Example 3 (Meth)acrylic Resin Composition (A-3) Pellets of a (meth)acrylic resin composition (A-3) were obtained in the same manner as in Production Example 1, except that the amount of polymerization solution introduced into the vent-type twin-screw extruder was changed to 90.0 parts by mass / hour, calculated as the resin amount, and the amount of AS resin introduced was changed to 10.0 parts by mass / hour. The glass transition temperature of the (meth)acrylic resin composition (A-3) was 125°C, the weight average molecular weight was 135,000, and the number average molecular weight was 54,000.

[0084] In the following Examples and Comparative Examples, the pellets of the resin composition obtained in each Production Example were dried in dry air at 60° C. for 24 hours before use.

[0085] Example 1 Optical Film (F-1) The (meth)acrylic resin composition (A-1) was fed to a single-screw extruder (L / D = 52) equipped with a leaf-disc-type polymer filter (filtration accuracy 5 μm) and a T-die at the tip, and melt-molded at a molding temperature of 270°C to produce a raw film (thickness 144 μm). The raw film was directly transported to an oven longitudinal stretching machine and longitudinally stretched, and subsequently transported to a tenter transverse stretching machine and transversely stretched to obtain an optical film (F-1) with a thickness of 40 μm. In the longitudinal stretching, the stretching temperature was Tg of the (meth)acrylic resin composition (A-1) + 16°C, and the stretch ratio was 2.0 times. In the transverse stretching, the stretching temperatures were Tg + 12°C in the preheating zone, Tg + 12°C in the stretching zone, and Tg - 2°C in the heat treatment zone, and the stretch ratio was 2.4 times. After slitting both ends of the optical film (F-1) in the width direction, a polyethylene protective film was laminated thereon to form a film roll.

[0086] Example 2 Optical Film (F-2) An optical film (F-2) having a thickness of 40 μm was obtained in the same manner as in Example 1, except that the (meth)acrylic resin composition (A-2) obtained in Production Example 2 was used.

[0087] Example 3 Optical Film (F-3) An optical film (F-3) having a thickness of 40 μm was obtained in the same manner as in Example 1, except that the temperature for longitudinal stretching was Tg+20° C., and the stretching temperatures for transverse stretching were Tg+18° C. in the preheating zone, Tg+18° C. in the stretching zone, and Tg−2° C. in the heat treatment zone.

[0088] Comparative Example 1 Optical Film (Fc-1) An optical film (Fc-1) having a thickness of 40 μm was obtained in the same manner as in Example 1, except that the (meth)acrylic resin composition (A-3) obtained in Production Example 3 was used, the thickness of the raw film was 160 μm, the stretching temperature for longitudinal stretching was Tg+19° C., the stretching ratio for longitudinal stretching was 1.9 times, the stretching temperatures for transverse stretching were Tg+19° C. in the preheating zone, Tg+19° C. in the stretching zone, and Tg−2° C. in the heat treatment zone, and the stretching ratio for transverse stretching was 2.76 times.

[0089] Reference Example 1 Optical Film (Fr-1) A triacetyl cellulose resin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., intrinsic viscosity [η]: 1.335 dL / g, degree of acetylation: 2.917) was dissolved in a mixed solvent of methylene chloride and methanol (mass ratio 9 / 1) to prepare a dope with a solid content of 20 mass %. A 60 μm-thick optical film (Fr-1) was produced from this dope by a solution casting method. The value of R(45,400) / R(45,550) was 1.12, and the value of R(45,550) / R(45,700) was 1.05.

[0090] Various physical properties of the optical films of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0091]

Claims

1. An optical film made from a resin composition containing a resin (A) that exhibits positive intrinsic birefringence and a resin (B) that exhibits negative intrinsic birefringence, wherein the resin composition has a glass transition temperature of 110 to 160°C, and the resin (A) contains a cyclic structural unit (p1) having a ring structure in the main chain and a structural unit (q1) derived from an alkyl (meth)acrylate, wherein, when measured with light of wavelengths of 400 nm, 550 nm, and 700 nm, the absolute values ​​of the in-plane retardation Re are all 0 to 2 nm and the absolute values ​​of the thickness direction retardation Rth are all 4 to 20 nm, and when the absolute value of the retardation when measured with light of wavelength λ (nm) at an incident angle of 45 degrees is 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.

2. The optical film according to claim 1, wherein the resin (A) further contains a structural unit (q2) derived from an aromatic vinyl, and the content of the cyclic 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.

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

4. The optical film according to claim 3, wherein the resin composition contains 1 to 5 parts by mass of the resin (B) per 100 parts by mass 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 a lactone ring structural unit and a glutarimide structural unit.

6. The absolute value of the stress optical coefficient of the resin composition is 5×10 －１１ ~20 x 10 －１１ Pa －１ 3. The optical film according to claim 1, wherein 7. The optical film according to claim 1 or 2, wherein the difference between the absolute value of the in-plane retardation Re and the absolute value of the thickness direction retardation Rth is 3.5 to 18 nm when measured with light having wavelengths of 400 nm, 550 nm, and 700 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 to 10 nm.

10. The optical film according to claim 1 or 2, which has a thickness of 5 to 50 μm.

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

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