Phase retardation film and manufacturing method

Abstract

A phase retardation film and its manufacturing method are disclosed. The phase retardation film is formed from a resin C comprising a copolymer P, wherein the copolymer P comprises polymeric units A and B. The phase retardation film comprises a phase exhibiting structural birefringence, wherein the phase retardation structure comprises a phase mainly composed of polymeric unit A and a phase mainly composed of polymeric unit B. The phase retardation film has an NZ coefficient greater than 0 and less than 1. Preferably, the phase retardation structure has any one of the following morphologies: layered, columnar, or ellipsoidal, and the interphase distance in the phase retardation structure is less than 200 nm.

Description

Technical Field

[0001] This invention relates to a phase difference film and its manufacturing method. Background Technology

[0002] In display devices such as liquid crystal displays (LCDs), phase retardation films such as λ / 2 waveplates and λ / 4 waveplates are sometimes used to improve display quality. For example, in IPS (In-Plane Switching) LCDs, phase retardation films are sometimes used for purposes such as compensating for viewing angles.

[0003] For retardation films used to compensate viewing angles in IPS liquid crystal displays, their NZ coefficient is required to be greater than 0 and less than 1. Furthermore, the NZ coefficient is preferably 0.5 or a value close to it. To achieve such an NZ coefficient, the three-dimensional refractive indices nx, ny, and nz of the film need to satisfy the relationship nx > nz > ny. Moreover, rather than retardation films that combine multiple resin films to exhibit the desired optical properties, retardation films that exhibit the desired optical properties using only a single resin film are preferred.

[0004] Such phase retardation films are difficult to manufacture. This is because it is impossible to achieve a film that satisfies the nx>nz>ny relationship by simply processing ordinary resin films through conventional methods such as stretching. It is necessary to use some unusual materials and / or methods to control the refractive index.

[0005] As a method for manufacturing a membrane that satisfies the relationship nx>nz>ny, there are known methods including a process of shrinking a resin membrane (Patent Document 1) and a method of combining multiple layers (Patent Document 2).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 5-157911 (corresponding publication: U.S. Patent Application Publication No. 5245456);

[0009] Patent Document 2: International Publication No. 2008 / 146924 (corresponding publication: U.S. Patent Application Publication No. 2010283949). Summary of the Invention

[0010] The problem the invention aims to solve

[0011] The method in Patent Document 1 suffers from high cost and low productivity in the process of shrinking the film. Furthermore, the method in Patent Document 2, due to the combination of multiple layers to reveal the desired optical properties, suffers from structural complexity, resulting in high cost and low productivity.

[0012] Therefore, the object of the present invention is to provide a retardation film and a method for manufacturing the same, which has useful optical properties and can be easily manufactured at low cost.

[0013] Solution for solving the problem

[0014] In order to solve the above problems, the inventors conducted in-depth research and found that the above problems can be solved by using copolymers with specific phase separation structures as the materials constituting the phase difference film.

[0015] That is, the present invention is as follows.

[0016] [1] A phase retardation film is formed from a resin C comprising a copolymer P, wherein the copolymer P comprises polymeric unit A and polymeric unit B.

[0017] The aforementioned phase retardation film comprises a phase-separated structure exhibiting structural birefringence, wherein the phase-separated structure comprises a phase mainly composed of polymer unit A and a phase mainly composed of polymer unit B.

[0018] The aforementioned phase difference film has an NZ coefficient greater than 0 and less than 1.

[0019] [2] According to the phase difference film described in [1], the phase separation structure has any one of the following morphologies: layered, columnar, spherical, or ellipsoidal.

[0020] The interphase distance in the above phase-separated structure is less than 200 nm.

[0021] [3] According to the phase difference film of [1] or [2], wherein the copolymer P is a block copolymer having a block (A) with the polymer unit A as the main component and a block (B) with the polymer unit B as the main component.

[0022] [4] The phase difference film according to any one of [1] to [3], wherein the above-mentioned polymer unit A is a unit represented by general formula (A).

[0023] [Chemical Formula 1]

[0024]

[0025] In the formula R C The radical is selected from phenyl, biphenyl, naphthyl, anthraceneyl, phenanthryl, tetraphenyl, pentaphenyl, and terphenyl.

[0026] R 1 ~R 3 Each is independent and is a group selected from hydrogen atoms and alkyl groups having 1 to 12 carbon atoms.

[0027] [5] The phase difference film according to any one of [1] to [4], wherein the polymer unit B is a unit represented by general formula (B-1), a unit represented by general formula (B-2), or a combination thereof:

[0028] [Chemical Formula 2]

[0029]

[0030] In the formula R 4 ~R 9 Each is independent and is a group selected from hydrogen atoms and alkyl groups having 1 to 6 carbon atoms.

[0031] [6] The phase retardation film according to any one of [1] to [5], wherein the copolymer P comprises a triblock copolymer P',

[0032] The triblock copolymer P' is a (A)-(B)-(A) triblock copolymer having a block (A) with polymer unit A as the main component and a block (B) with polymer unit B as the main component.

[0033] [7] According to the phase difference film of [6], wherein the copolymer P further comprises a diblock copolymer P''.

[0034] The aforementioned diblock copolymer P” is an (A)-(B) diblock copolymer having the aforementioned block (A) and the aforementioned block (B).

[0035] The proportion of the diblock copolymer P” relative to the total of the above triblock copolymer P’ and the above diblock copolymer P” is 5 to 40% by weight.

[0036] [8] The phase difference film according to any one of [1] to [7], wherein the copolymer P has a negative intrinsic birefringence value.

[0037] [9] The phase difference film according to any one of [1] to [8], wherein the polymer unit A has a negative intrinsic birefringence value and the polymer unit B has a positive intrinsic birefringence value.

[0038]

[10] A method for manufacturing a phase retardation film according to any one of [1] to [9], comprising a step of forming a monolayer film of the above-mentioned resin C, and

[0039] The process of performing phase separation of the above-mentioned resin C in the above-mentioned membrane.

[0040]

[11] The method for manufacturing a phase difference film according to

[10] includes a step of applying stress to the film along its thickness direction in the process of separating the resin C phase.

[0041]

[12] The method for manufacturing a phase difference film according to

[10] or

[11] , wherein the step of forming the film includes melting and extruding the copolymer P in a single layer.

[0042]

[13] The method for manufacturing a phase difference film according to any one of

[10] to

[12] further includes a step of stretching the film.

[0043] Invention Effects

[0044] According to the present invention, a retardation film and a method for manufacturing the same are provided, the retardation film having useful optical properties and being easily manufactured at low cost. Detailed Implementation

[0045] The present invention will now be described in detail with respect to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and any modifications and implementations may be made without departing from the scope of the claims of the present invention and its equivalents.

[0046] In the following description, "strip" film refers to a film with a length of 5 times or more relative to its width, preferably 10 times or more, specifically a length sufficient to be rolled up for storage or transport. There is no particular upper limit to the ratio of length to width, for example, it can be less than 100,000 times.

[0047] In the following description, unless otherwise specified, the in-plane retardation Re of the film is represented by Re = (nx - ny) × d. Furthermore, unless otherwise specified, the thickness retardation Rth of the film is represented by Rth = {(nx + xy) / 2 - nz} × d. Furthermore, unless otherwise specified, the NZ coefficient is represented by (nx - nz) / (nx - ny). Here, nx represents the refractive index in the direction perpendicular to the film thickness direction (in-plane direction). ny represents the refractive index in the direction orthogonal to the nx direction among the aforementioned in-plane directions. nz represents the refractive index in the thickness direction. d represents the film thickness. Unless otherwise specified, the measurement wavelength is 540 nm.

[0048] In the following description, unless otherwise specified, “polarizer,” “λ / 2 waveplate,” and “λ / 4 waveplate” include not only rigid components but also flexible components such as resin films.

[0049] In the following description, unless otherwise specified, the slow axis of a membrane refers to the slow axis in the plane of the membrane.

[0050] The sign of the intrinsic birefringence of a resin is defined by the change in the refractive index of the molded article when the resin is stretched. That is, a resin with a positive intrinsic birefringence is one whose refractive index in the stretching direction increases compared to before stretching. Conversely, a resin with a negative intrinsic birefringence is one whose refractive index in the stretching direction decreases compared to before stretching. The intrinsic birefringence value can be calculated based on the dielectric constant distribution.

[0051] Furthermore, a positive intrinsic birefringence value for a specific polymeric unit means that the polymer formed solely from that unit has a positive intrinsic birefringence value, and a negative intrinsic birefringence value for a specific polymeric unit means that the polymer formed solely from that unit has a negative intrinsic birefringence value. Therefore, the sign of the intrinsic birefringence value of a polymeric unit can be easily determined by the following process: preparing a homopolymer formed solely from that polymeric unit, molding the polymer into a molded article of arbitrary shape, stretching the molded article, and measuring its optical properties. Generally, it is known that polymeric units of hydrocarbons such as olefins and dienes often have positive intrinsic birefringence values; on the other hand, it is known that polymers of hydrocarbons with aromatic rings in their side chains, such as styrene and vinylnaphthalene, often have negative intrinsic birefringence values.

[0052] In the following description, blocks in polymers composed of polymeric units generated by the polymerization of a monomer are sometimes referred to by the name of that monomer. For example, blocks composed of polymeric units generated by the polymerization of 2-vinylnaphthalene are sometimes referred to as "2-vinylnaphthalene blocks", and blocks composed of polymeric units generated by the polymerization of isoprene are referred to as "isoprene blocks".

[0053] [1. Phase retardation film]

[0054] The phase difference film of the present invention is formed from resin C.

[0055] [1.1. Resin C]

[0056] Resin C contains a specific copolymer P. Copolymer P comprises polymeric units A and B. Copolymer P is preferably a block copolymer having blocks (A) primarily composed of polymeric unit A and blocks (B) primarily composed of polymeric unit B. Generally, a block copolymer refers to a polymer having a molecular structure with multiple blocks linked together, each block being a chain formed by polymeric units. The specific block copolymer in this invention has specific blocks (A) and blocks (B). In the following description, this specific block copolymer is sometimes simply referred to as a "block copolymer".

[0057] Polymer unit A can be a polymer unit with a negative intrinsic birefringence value. On the other hand, polymer unit B can be a polymer unit with a positive intrinsic birefringence value.

[0058] As an example of a polymer unit A, the unit represented by the following general formula (A) can be cited.

[0059] [Chemical Formula 3]

[0060]

[0061] R C It is a group selected from phenyl, biphenyl, naphthyl, anthraceneyl, phenanthryl, tetraphenyl, pentaphenyl and triphenyl.

[0062] R 1 ~R 3 Each group is independent and is selected from alkyl groups having 1 to 12 hydrogen atoms. Examples of such alkyl groups include methyl, ethyl, propyl, and hexyl. In formula (A), R is preferred. 2 and R 3 It is a hydrogen atom. More preferably, R 2 and R 3 It is a hydrogen atom and R C It is naphthyl, or R 2 and R 3 It is a hydrogen atom and R 1 It is a hydrogen atom. Further optimization of R... 2 and R 3 For hydrogen atoms, R C It is naphthyl and R 1 It is a hydrogen atom.

[0063] Polymer unit A can be obtained by polymerizing the monomer (a) that forms polymer unit A. Examples of monomer (a) include vinylnaphthalene and its derivatives. Examples of vinylnaphthalene include 1-vinylnaphthalene and 2-vinylnaphthalene. Examples of vinylnaphthalene derivatives include α-methyl-1-vinylnaphthalene, α-ethyl-1-vinylnaphthalene, α-propyl-1-vinylnaphthalene, α-hexyl-1-vinylnaphthalene, α-methyl-2-vinylnaphthalene, α-ethyl-2-vinylnaphthalene, α-propyl-2-vinylnaphthalene, and α-hexyl-2-vinylnaphthalene. From the viewpoint of ease of industrial acquisition, 2-vinylnaphthalene is preferred as vinylnaphthalene and its derivatives.

[0064] In polymer P, polymeric unit A can be a single type or a combination of two or more types in any proportion. Therefore, monomer (a) used to form polymeric unit A can be a single type or a combination of two or more types in any proportion.

[0065] As an example of the aggregation unit B, the units represented by the following general formulas (B-1) and / or (B-2) can be cited.

[0066] [Chemical Formula 4]

[0067]

[0068] R 4 ~R 9 Each group is independent and is selected from alkyl groups having 1 to 6 carbon atoms. Examples of such alkyl groups include methyl, ethyl, propyl, and hexyl. 4 ~R 9 Each is independent, preferably a hydrogen atom or a methyl group.

[0069] Polymer unit B can be obtained by polymerizing the monomer (b) that forms polymer unit B to form a polymer unit, and then hydrogenating the polymer unit in the presence of a double bond. Examples of monomer (b) include compounds represented by the following general formula (bm).

[0070] [Chemical Formula 5]

[0071]

[0072] As a preferred example of monomer (b), butadiene (R in formula (bm)) can be cited. 4 ~R 9 (all hydrogen atoms), isoprene (R in formula (bm)) 4 ~R 9 In the middle, R 6 Or R 7 The monomers are methyl group (with the others being hydrogen atoms), 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-hexadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, and 2,4-dimethyl-1,3-pentadiene. From the viewpoint of obtaining resin C with excellent transparency, heat resistance, and processability, butadiene and isoprene are more preferred. As a preferred example of polymer unit B, it can be described as having R in a preferred example of monomer (b). 4 ~R 9 The same group as R 4 ~R 9 Aggregation unit B.

[0073] Polymer P may have only one type of polymeric unit B, or it may combine two or more polymeric units B in any proportion. Therefore, monomer (b) used to form polymeric unit B may be used alone, or it may be used in any proportion of two or more monomers.

[0074] When copolymer P has a block (A), the block (A) can have any polymeric unit other than polymeric unit A. Examples of such arbitrary polymeric units include units formed by polymerization of any monomer capable of copolymerizing with monomer (a) and units formed by hydrogenation of the unit.

[0075] When copolymer P has blocks (B), blocks (B) can have any polymeric unit other than polymeric unit B. Examples of such arbitrary polymeric units include polymeric units formed by polymerization of monomer (b) with residual unhydrogenated double bonds, units formed by polymerization of any monomer capable of copolymerizing with monomer (b), and units formed by hydrogenating such units.

[0076] However, from the viewpoint of showcasing the optical and mechanical properties of resin C, it is preferable that both the proportion of polymeric unit A in block (A) and the proportion of polymeric unit B in block (B) are high. The proportion of polymeric unit A in block (A) is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably, block (A) is formed solely of polymeric unit A. The proportion of polymeric unit B in block (B) is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably, block (B) is formed solely of polymeric unit B.

[0077] Blocks (A) and (B) are preferably immiscible. Their immiscibility allows for the easy acquisition of the phase retardation film of the present invention with a specific NZ coefficient. Whether blocks (A) and (B) are immiscible can be determined based on the compatibility of homopolymers formed from polymeric unit A and homopolymers formed from polymeric unit B, having molecular weights similar to those of the blocks in the block copolymer. The compatibility of these homopolymers can be determined by mixing them to form a mixture and observing whether they separate at the melting temperature.

[0078] The molecular structure of copolymer P is not particularly limited as long as it has polymeric units A and B, and can have any molecular structure. For example, when copolymer P is a block copolymer, it can be a linear block copolymer or a grafted block copolymer.

[0079] Examples of linear block copolymers include diblock copolymers (sometimes referred to as "copolymer P" in this application) consisting of (A)-(B) blocks connected to block (A), triblock copolymers (sometimes referred to as "copolymer P'" in this application) consisting of (A)-(B)-(A) blocks connected in sequence with block (A), block (B), and another block (A), and linear block copolymers consisting of blocks connected to more than these. Examples of blocks consisting of multiple connected blocks include (A)-((B)-(A))n-(B)-(A) and (B)-((A)-(B))n-(A)-(B) (where n is an integer greater than or equal to 1).

[0080] As an example of a grafted block copolymer, a block copolymer consisting of an (A)-g-(B) block having a block (B) attached as a side chain to a block (A) can be cited.

[0081] From the viewpoint of enabling resin C to exhibit the desired optical properties, copolymer P is preferably a block copolymer having a molecular structure in which each molecule has two or more polymer blocks (A) and one or more polymer blocks (B). More preferably, the block copolymer is a triblock copolymer having blocks having (A)-(B)-(A).

[0082] Resin C may contain only one copolymer P, or it may combine two or more copolymers P in any proportion.

[0083] When resin C contains two block copolymers, a preferred example of a combination of these block copolymers is a combination of a diblock copolymer P” having an (A)-(B) block structure and a triblock copolymer P' having an (A)-(B)-(A) block structure. By including copolymer P' and copolymer P” in resin C, resin C with the desired optical and mechanical properties can be easily obtained. More specifically, by including copolymer P' and copolymer P” in resin C, and having units represented by the above general formulas (B-1) and / or (B-2) as polymeric units constituting block (B), the processability of resin C can be improved. As a result, the manufacture of the retardation film of the present invention becomes easier.

[0084] When resin C comprises a combination of copolymer P' and copolymer P'", their ratio can be adjusted to obtain desired optical and mechanical properties. Specifically, relative to the total amount of copolymer P' and copolymer P' in resin C, the proportion of copolymer P' is preferably 5% by weight or more, more preferably 10% by weight or more, further preferably 15% by weight or more, and preferably 40% by weight or less. By keeping the proportion of copolymer P' within the above range, desired optical and mechanical properties can be obtained. In particular, by keeping the proportion of copolymer P' below the above upper limit, good heat resistance of resin C can be achieved.

[0085] In copolymer P, the weight fraction of polymeric unit A can be adjusted to obtain the desired optical properties. The weight fraction of polymeric unit A refers to the weight of polymeric unit A relative to the total weight of polymeric units A and B. When resin C contains multiple copolymers P, the weight fraction of polymeric unit A referred to here means the weight of polymeric unit A relative to the total weight of polymeric units A and B in the total number of included copolymers P. The weight fraction of polymeric unit A in copolymer P is 50% by weight or more, preferably 55% by weight or more, and on the other hand, 90% by weight or less, more preferably 85% by weight or less.

[0086] The molecular weight of copolymer P is not particularly limited and can be suitably adjusted within a range where preferred optical and mechanical properties are obtained. The molecular weight of copolymer P can be, for example, in the range of 100,000 to 400,000. Furthermore, the glass transition temperature (Tg) of copolymer P can be, for example, in the range of 110°C to 150°C.

[0087] Resin C preferably has a negative intrinsic birefringence value. This negative intrinsic birefringence value can be acquired by adjusting the proportion of polymeric units in copolymer P. Specifically, a resin with a negative intrinsic birefringence value can be produced by adjusting the weight fraction of polymeric unit A within a range above the aforementioned lower limit. Because resin C has a negative intrinsic birefringence value, the desired optical properties can be imparted to the retardation film.

[0088] Resin C may be formed solely from copolymer P, or it may contain any component other than copolymer P. Examples of such components include dyes, pigments, antioxidants, and other additives. The proportion of these arbitrary components can be within a range that does not impair the effects of the present invention. Specifically, the proportion of copolymer P in resin C is preferably 98% by weight or more, more preferably 99% by weight or more, and even more preferably resin C is formed solely from copolymer P.

[0089] [1.2. Optical Properties of Phase Reversal Films]

[0090] The phase retardation film of the present invention has an NZ coefficient greater than 0 and less than 1. The NZ coefficient is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, preferably 0.8 or less, more preferably 0.7 or less, and even more preferably 0.6 or less.

[0091] A retardation film with such an NZ coefficient can be easily obtained by using the aforementioned specific resin as resin C as the material and implementing a preferred manufacturing method. A retardation film with such an NZ coefficient is particularly useful for applications such as viewing angle compensation in display devices like IPS liquid crystal displays, but on the other hand, it cannot be obtained solely through conventional processing methods such as stretching. Therefore, the retardation film of the present invention is highly useful in terms of possessing useful optical properties and being easy to manufacture.

[0092] The in-plane retardation Re and thickness direction retardation Rth of the retardation film of the present invention can be adjusted to desired values ​​suitable for the application of the retardation film. For example, when the retardation film of the present invention is used as a λ / 2 waveplate, Re can be in the range of 250 nm to 290 nm. When the retardation film of the present invention is used as a λ / 4 waveplate, Re can be in the range of 120 nm to 160 nm.

[0093] [1.3. Other properties and shapes of retardation films, etc.]

[0094] The retardation film of the present invention comprises a phase-separated structure exhibiting structural birefringence. The phase-separated structure is formed within a layer of resin C constituting the retardation film. The phase-separated structure of resin C refers to the separation of a phase dominated by polymeric unit A and a phase dominated by polymeric unit B within the layer into distinct phases through self-organization of the portions (e.g., blocks (A)) and portions (e.g., blocks (B)) of copolymer P in resin C, respectively. In the following description, these phases are sometimes simply referred to as the "phase of polymeric unit A" and the "phase of polymeric unit B". An orientation layer exhibiting such a phase-separated structure can exhibit structural birefringence even when the structure is sufficiently smaller than the wavelength of light.

[0095] Structural birefringence refers to birefringence that occurs in a structure containing multiple phases with different refractive indices, such that the phases are separated. For example, in a structure where a phase with a refractive index n1 contains a phase with a refractive index n2, the structure can exhibit structural birefringence. Structural birefringence produces birefringence even when the phases are formed through an isotropic medium, which is distinctly different from oriented birefringence produced by molecular orientation based on stretching.

[0096] The magnitude and direction of structural birefringence can be controlled by adjusting the shape, arrangement, and volume fraction of each phase in a phase-separated structure, as well as the difference in refractive index between phases, to exhibit the desired structural birefringence. Detailed information is described, for example, in *Form birefringence of macromolecules* (WLBragg et al., 1953).

[0097] The greater the refractive index difference between the phase mainly composed of polymer unit A and the phase mainly composed of polymer unit B, the more efficiently the structural birefringence can be manifested. The refractive index difference between the two is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more.

[0098] The content ratio of polymeric unit A in the phase mainly composed of polymeric unit A and the content ratio of polymeric unit B in the phase mainly composed of polymeric unit B can be adjusted by appropriately adjusting the materials used to manufacture polymer P and the manufacturing operation. From the perspective of effect, a higher content ratio is preferred. The content ratio of polymeric unit A in the phase mainly composed of polymeric unit A is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably 100% by weight. The content ratio of polymeric unit B in the phase mainly composed of polymeric unit B is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably 100% by weight.

[0099] By controlling the shape and arrangement of the phase separation structure, the phase retardation film of the present invention can be endowed with negative C-plate birefringence. For example, when the layers constituting the film exhibit a layered phase separation structure, and the average stacking direction of the layers (the direction perpendicular to the layers constituting the film) is close to the normal direction of the film, the layers can exhibit negative C-plate birefringence. When the layers exhibit a columnar phase separation structure or an ellipsoidal phase separation structure, for example, if the major axis of the column or ellipsoid is in the in-plane direction and the direction of the major axis in the in-plane is random, the layers can exhibit a negative C-plate structural birefringence.

[0100] By combining this structural birefringence with the molecular orientation birefringence generated by the orientation of the resin C, a phase retardation film with a specific range of NZ coefficients that cannot be easily manufactured by conventional methods can be readily obtained.

[0101] Specific examples of phase-separated structures include layered, ellipsoidal, and columnar structures. In any of these cases, a preferred effect is achieved when a structure exhibiting negative C-plate-like birefringence is formed. That is, a structure exhibiting birefringence where the refractive index in the thickness direction is less than the average refractive index in the in-plane direction is preferred. Which of these phase-separated structures is exhibited is influenced by various factors. One major factor affecting the structure's appearance is the volume ratio of the phase primarily composed of polymeric unit A to the phase primarily composed of polymeric unit B. This volume ratio can be adjusted by varying the proportions of blocks (A) and (B) in the block copolymer.

[0102] In a phase-separated structure, the size of the structure can be appropriately adjusted within the range where the phase retardation film can provide the desired optical properties. For example, the interphase distance is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. The size of each phase after phase separation is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less. The interphase distance, in the case of layered phase separation, refers to the spacing between layers (i.e., the spacing between the layer repeating units of the layer), and in the case of columnar phase-separated structures, it refers to the spacing between columns. The size of the phases after phase separation refers to the thickness of the layers in the case of layered phase separation, and to the column radius in the case of columnar phase separation. The interphase distance can be a value obtained by fitting a scattering image obtained by small-angle X-ray scattering measurement to a theoretical curve.

[0103] By ensuring that the interphase distance and the size of the separated phase are sufficiently short compared to visible light, structural birefringence becomes apparent, and film coloration and reduced light transmittance are suppressed. There is no particular limitation on the lower limit of the interphase distance; for example, it can be set to 10 nm or more. Similarly, there is no particular limitation on the lower limit of the size of the separated phase; for example, it can be set to 10 nm or more. The interphase distance can be adjusted by modifying the molecular structure of copolymer P. For example, a block copolymer can be used as copolymer P, and factors such as the lengths of blocks (A) and (B) can be adjusted accordingly.

[0104] The thickness of the retardation film of the present invention can be appropriately adjusted within a range that yields the desired optical and mechanical properties. Specifically, it is preferably 10 μm or more, more preferably 15 μm or more, more preferably 100 μm or less, and more preferably 90 μm or less.

[0105] [2. Manufacturing method]

[0106] The phase retardation film of the present invention can be manufactured by a manufacturing method comprising a step of forming a monolayer film of resin C and a step of separating the resin C phase in the film. This manufacturing method will be described below as the manufacturing method of the present invention.

[0107] Examples of specific film-forming methods for the process of forming a film from resin C include solution casting, melt extrusion, calendering, and compression molding. Melt extrusion is particularly preferred for the efficient production of large quantities of phase difference films. Melt extrusion involves feeding molten resin C to a die such as a T-die using an extruder such as a biaxial extruder, and extruding the resin C from the die.

[0108] The process of separating the resin C phase in the membrane can be performed after the membrane formation process or simultaneously with the membrane formation process.

[0109] The phase separation process can be performed, for example, by slowly cooling molten resin C. Specifically, as a film-forming process, in the case of melt extrusion and other methods, the molten resin can be formed and then cooled under slow cooling conditions. The specific mechanism is still unclear, but by performing this slow cooling, a phase-separated structure of resin C exhibiting a negative C-plate-like birefringence can be easily formed, and a phase-reflection film with the desired optical properties can be easily obtained. For example, in melt extrusion film formation using an extruder and die, after the resin is extruded from the die, the process of pressing the resin onto a cooling roller can be achieved by setting the die temperature and cooling roller temperature to a slow cooling condition. Although the cooling conditions are also affected by factors other than the die temperature and cooling roller temperature, a slower cooling condition than usual can be achieved by adjusting the die temperature and cooling roller temperature. The cooling conditions can be set relative to the glass transition temperature Tg of the resin C. More specifically, it is preferable to use a die head temperature of (Tg+100)℃~(Tg+150)℃ and a cooling roller temperature of (Tg-50)℃~(Tg+50)℃.

[0110] In addition to the aforementioned gradual cooling process, a pressing process can be performed on the film as part of the phase separation process, or the pressing process can be performed instead. By applying pressure to the resin C film, a phase-separated structure exhibiting a negative C plate-like structure with birefringence can be easily formed, and a phase retardation film with the desired optical properties can be easily obtained.

[0111] Specifically, the pressurization process can be performed by applying pressure along the thickness direction to a sheet of resin C. For this operation, a pressurizing device such as a metal mold can be used to apply pressure to the surface of the membrane. When the resin C membrane is formed by compression molding, the pressurization process can be performed as part of the molding process, either simultaneously with molding or after molding. The temperature of the resin C during pressurization can be set to (Tg+10)℃ to (Tg+150)℃. The pressurization pressure is preferably 1 MPa or more, more preferably 5 MPa or more, even more preferably 10 MPa or more, preferably 50 MPa or less, more preferably 45 MPa or less, even more preferably 40 MPa or less. The pressurization time is preferably 10 seconds or more, more preferably 20 seconds or more, even more preferably 30 seconds or more, preferably 180 seconds or less, more preferably 150 seconds or less, even more preferably 120 seconds or less. By keeping the pressurization conditions within the above ranges, a membrane with uniform thickness and phase separation structure can be obtained.

[0112] The pressurization process can also be performed using an apparatus that continuously applies pressure to a strip of resin C. Such an operation can be performed using pressurizing devices such as pressure rollers. In the case of forming a film of resin C by melt extrusion, the pressurization process can be performed by passing the resin C extruded from the die between two pressure rollers, thereby applying pressure to the resin C. The linear pressure during pressurization is preferably 10 N / cm or more, more preferably 50 N / cm or more, further preferably 100 N / cm or more, preferably 500 N / cm or less, more preferably 450 N / cm or less, and even more preferably 400 N / cm or less. The temperature of the resin C during pressurization can be from (Tg+10) °C to (Tg+150) °C. By keeping the pressurization conditions within the above range, a film with uniform thickness and phase separation structure can be obtained.

[0113] A membrane of resin C with a phase separation structure can typically be further fed into a stretching process to impart the desired phase difference, thereby obtaining the phase difference membrane of the present invention. The stretching process can be performed on a production line connected to the manufacturing line that forms the membrane of resin C. Alternatively, the manufactured membrane of resin C can be temporarily wound into a roll, and then the roll can be unwound and fed into the stretching process. The stretching process is typically performed using a flat method, where the membrane is stretched along its in-plane direction. Examples of flat stretching include uniaxial stretching and biaxial stretching. Uniaxial stretching involves stretching the membrane along one direction within its plane; examples include free-width uniaxial stretching and fixed-width uniaxial stretching. Biaxial stretching involves stretching the membrane along two directions within its plane. Examples of biaxial stretching include successive biaxial stretching and simultaneous biaxial stretching. The stretching in each direction can be either free-width stretching or fixed-width stretching. As more specific examples of the successive biaxial stretching method, full-expansion and roll-expansion methods can be cited. The stretching method used in the stretching step of the manufacturing method of the present invention can be any of these methods, and a suitable method can be selected to obtain the desired phase difference film.

[0114] The stretching temperature in the stretching process is preferably (Tg-5)℃ or higher, more preferably (Tg+5)℃ or higher, even more preferably (Tg+15)℃ or higher, preferably (Tg+50)℃ or lower, and more preferably (Tg+40)℃ or lower. By setting the stretching temperature below the upper limit, process instability caused by film softening can be prevented. On the other hand, by setting the stretching temperature above the lower limit, cracking and whitening during stretching can be prevented.

[0115] Confirming the actual occurrence of structural birefringence can be done by measuring the optical properties of the unstretched film. Unstretched films formed using conventional methods such as extrusion, pressing, and solvent casting typically have random molecular orientations, resulting in Re and Rth values ​​close to zero. However, unstretched films exhibiting structural birefringence show higher Re and Rth values ​​than those observed in typical unstretched films formed using conventional methods. Therefore, measuring these values ​​confirms the presence of structural birefringence. Furthermore, simultaneous structural observation using electron microscopy and small-angle X-ray scattering provides even more definitive confirmation of the presence of structural birefringence.

[0116] In the method for manufacturing the phase retardation film of the present invention, a heat treatment step can be performed as an arbitrary step. The heat treatment step can be performed at any stage of the manufacturing method. However, the heat treatment step is preferably performed between the step of forming the film of resin C and the stretching step. When heat treatment is performed after the stretching step, the phase difference generated by stretching decreases due to relaxation, so it is necessary to limit the heat treatment conditions to a range that can suppress the decrease in phase difference.

[0117] The heat treatment process can be performed by keeping the resin C film heated using a float glass oven or needle diffuser. This heat treatment promotes the formation of phase-separated structures. The heat treatment temperature is preferably above Tg℃, more preferably above (Tg+20)℃, even more preferably above (Tg+25)℃, preferably below (Tg+50)℃, and more preferably below (Tg+40)℃. By keeping the heat treatment temperature within the above range, the formation of phase-separated structures can be easily promoted. Furthermore, by keeping the heat treatment temperature below the above upper limit, film softening can be suppressed, and a phase-separation film with uniform film thickness and optical properties can be easily manufactured. The heat treatment process can be performed on the resin C film without substantial stretching. "Without substantial stretching" means that the stretching ratio of the film in any direction is generally less than 1.1 times, preferably less than 1.01 times.

[0118] [3. Applications]

[0119] The phase retardation film of this invention can be used as a structural element in display devices such as liquid crystal displays and organic electroluminescent displays. For example, in display devices, it can be used as an optical element such as a λ / 2 waveplate or a λ / 4 waveplate. Such an optical element can be installed in a display device as a component with functions such as viewing angle compensation and anti-reflection.

[0120] Example

[0121] The present invention will now be specifically described with reference to the embodiments shown. However, the present invention is not limited to the following embodiments, and may be implemented in any way without departing from the scope of the claims of the present invention and its equivalents.

[0122] In the following instructions, unless otherwise specified, "%" and "parts" refer to quantities based on weight. Unless otherwise specified, the following operations shall be performed at normal temperature and pressure in an atmospheric environment.

[0123] [Evaluation Method]

[0124] (Re and NZ coefficients of the phase retardation film)

[0125] Using AXOSCAN manufactured by AXOMETRICS, the Re and NZ coefficients at a wavelength of 540nm were determined.

[0126] (Phase-separated structure)

[0127] The obtained membrane was cut into 2mm × 4mm pieces, and 30 pieces were overlapped along the thickness direction. These were then fixed onto a folding device, and a small-angle X-ray scattering (SAXS) instrument (Aichi SR, Beamline 8S3) was used with a lens length of 4m and an X-ray energy of 8.2 keV. The measurement range was approximately 0.06–3 nm. -1 Scattering images were obtained under the condition of 60 seconds of exposure time per sample. The obtained scattering images were fitted with theoretical curves to calculate the phase separation structure and interphase distance.

[0128] The X-ray irradiation surface is set as the cross-section of the film, and the integration range is set to 20° for both the thickness direction and the direction perpendicular to the thickness direction. The interphase distance is calculated based on the data obtained from the respective integrations, and the average value of the interphase distance in the thickness direction and the direction perpendicular to the thickness direction is taken as the measured value.

[0129] (Processability)

[0130] The phase retardation film was cut to obtain a strip-shaped specimen. The specimen was cut with its length direction perpendicular to the tensile direction. The specimen width was set to 10 mm. A tensile test was performed on the specimen. The number of tensile test samples was set to 20. The tensile test conditions were set as follows: initial clamp spacing of 100 mm and test speed of 100 mm / min. Whether or not fracture occurred before reaching the yield point was observed, and the evaluation was based on the following evaluation criteria.

[0131] A…less than 10% of the specimens fractured before reaching the yield point.

[0132] B…more than 10% but less than 30% of the specimens fractured before reaching the yield point.

[0133] C…more than 30% but less than 50% of the specimens fractured before reaching the yield point.

[0134] D… More than 50% of the specimens fractured before reaching the yield point.

[0135] (Display characteristics: λ / 2 waveplate)

[0136] As a polarizer, a long strip polarizer (manufactured by Sanritz, trade name "HLC2-5618S", thickness 180 μm) with the transmission axis in the width direction was prepared. The protective film on one surface of the polarizer was removed, and the retardation film obtained in Examples 1-11 and the Comparative Example was laminated onto that surface. Lamination was performed with the slow axis direction of the phase difference aligned with the transmission axis direction of the polarizer. Through this operation, a polarizer having the retardation film of the Example or Comparative Example as one of the double-sided protective films was obtained.

[0137] By replacing the polarizer originally present on the viewable side of a commercially available IPS liquid crystal display device (LG Electronics, 23MP47HQ) with the obtained polarizer, a liquid crystal display device having the retardation film obtained through the embodiments and comparative examples was obtained. During replacement, the polarizer was configured such that the side having the retardation film obtained through the embodiments and comparative examples was the liquid crystal cell side. Furthermore, the transmission axis of the polarizer was in the same direction as the polarizer in the polarizer originally present in the IPS liquid crystal display device.

[0138] The display status of the liquid crystal display device is observed at various azimuth angles along the direction of tilt relative to the display surface (45° relative to the normal direction). A case where the contrast is higher in all directions compared to before replacement is rated as "good", and a case where the contrast is the same or worse in one or more azimuth angles compared to before replacement is rated as "poor".

[0139] (Display characteristics: λ / 4 waveplate)

[0140] As a polarizer, a long strip polarizer (manufactured by Sanritz, trade name "HLC2-5618S", thickness 180 μm) with the transmission axis in the width direction was prepared. The protective film on one surface of the polarizer was removed, and the retardation film obtained in Example 12 was laminated onto that surface. The lamination was performed at a 45° angle between the slow axis of the phase difference and the transmission axis of the polarizer. Through this operation, a polarizer having the retardation film of the example as one of the double-sided protective films was obtained.

[0141] By replacing the polarizer originally present on the viewable side of a commercially available organic EL display device (LG Electronics, OLED55EG9600) with the obtained polarizer, an organic EL display device having the retardation film obtained in the embodiment was obtained. During the replacement, the polarizer was configured such that one side of the retardation film obtained in the embodiment was on the organic EL cell side. Furthermore, the transmission axis of the polarizer was in the same direction as the polarizer in the polarizer originally present in the organic EL display device.

[0142] The display status of the organic EL display device is observed at various azimuth angles along the direction of tilt relative to the display surface (45° relative to the normal direction). A case where reflectivity is suppressed in all directions compared to before replacement is rated as "good", and a case where reflectivity is equal to or better in one or more azimuth angles compared to before replacement is rated as "poor".

[0143] [Example 1]

[0144] (1-1. Triblock copolymer)

[0145] In a dry and nitrogen-replaced pressure-resistant reactor, 500 ml of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were added, followed by the addition of 14 g of 2-vinylnaphthalene as polymerization unit A. The reactor was then reacted at 25 °C for 1 hour to carry out the first stage of polymerization.

[0146] After the first stage of polymerization was terminated, 7 g of isoprene as polymerization unit B was added, and the mixture was further reacted at 25°C for 1 hour to carry out the second stage of polymerization. As a result, a diblock copolymer with a (2-vinylnaphthalene block)-(isoprene block) block structure was obtained in the reaction mixture. Then, 14 g of 2-vinylnaphthalene as polymerization unit A was further added to the reaction mixture, and the mixture was reacted at 25°C for 1 hour to carry out the third stage of polymerization. As a result, a triblock copolymer with a (2-vinylnaphthalene block)-(isoprene block)-(2-vinylnaphthalene block) block structure was obtained in the reaction mixture. The reaction mixture was injected into a large amount of 2-propanol to precipitate and separate the triblock copolymer.

[0147] The obtained triblock copolymer was dissolved in 700 ml of p-xylene to prepare a solution. 7.6 g of p-toluenesulfonic acid hydrazide was added to the solution, and the reaction was carried out at 130 °C for 8 hours. This reaction hydrogenated the double bonds of the isoprene units. After hydrogenation, the reaction solution was injected into a large amount of 2-propanol to obtain 32 g of the blocky product (A)-(B)-(A) triblock copolymer.

[0148] The triblock copolymer was obtained by NMR analysis. The results showed that the weight ratio of 2-vinylnaphthalene units to hydrogenated isoprene units in the triblock copolymer was 80:20, therefore the weight fraction of block (A) was 80%. Furthermore, the hydrogenation rate of the triblock copolymer was 99%. The weight-average molecular weight of the triblock copolymer, determined by GPC, was 250,000. The glass transition temperature of the triblock copolymer, determined by TMA, was 135 °C.

[0149] (1-2. Membrane before stretching)

[0150] The triblock copolymer obtained through (1-1) was used as resin C. Resin C was pulverized to form a powder. The resulting powder was sandwiched between a pair of polyimide films (each 100 μm thick) to form a laminate, which was then pressurized. Pressurization was performed using an electrothermal pressurization device. The pressurization conditions were: temperature 290 °C, pressure 40 MPa, and pressurization time 5 minutes. After pressurization, depressurization was performed, and the film was cooled to room temperature in air to remove the polyimide films. Through this operation, a pre-stretch membrane 1 with a thickness of 75 μm was produced.

[0151] X-rays were irradiated onto the cross-section of the unstretched membrane 1, and observed using small-angle scattering. A layer structure with an interphase spacing of 40 nm and a thickness of 20 nm was observed.

[0152] Furthermore, sections with cross-sections parallel to the thickness direction were prepared and observed using TEM, confirming a layered phase-separated structure.

[0153] The Re and Rth of the membrane 1 before stretching were measured, and the results were Re = 15 nm and Rth = 90 nm, confirming that the properties close to those of a negative C plate were obtained through structural birefringence.

[0154] (1-3. Phase retardation film)

[0155] Cut the membrane 1 obtained before stretching through (1-2) to make a rectangular membrane of size 80mm×80mm.

[0156] A rectangular film was subjected to free-width uniaxial stretching. The stretching was performed using a batch stretching apparatus manufactured by Toyo Seiki Co., Ltd. The stretching conditions were set as follows: stretching temperature 145°C, stretching ratio 1.5, and stretching speed 33% per minute. As a result, a phase reversal film with a thickness of 60 μm was obtained.

[0157] The obtained phase difference film was evaluated for its Re and NZ coefficients, processability, and display characteristics.

[0158] [Examples 2-3]

[0159] The stretching conditions in (1-3) were changed as shown in Table 1. Otherwise, the phase difference film was obtained and evaluated by the same operation as in Example 1.

[0160] [Examples 4-7]

[0161] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedures as in Example 1.

[0162] • The amounts of 2-vinylnaphthalene and isoprene added in the polymerization reaction of (1-1) were changed. However, the amounts added needed to be distributed in such a way that the amount of 2-vinylnaphthalene added in the first stage of polymerization was equal to the amount of 2-vinylnaphthalene added in the third stage of polymerization. In addition, the total amount of 2-vinylnaphthalene and isoprene added was 35 g, the same as in Example 1. The weight fraction of block (A) in the obtained triblock copolymer and the glass transition temperature of resin C are shown in Table 1. Furthermore, in both examples, a layered structure resulting from phase separation was observed by X-ray observation and TEM observation in (1-2).

[0163] • Modify the stretching conditions in (1-3) as shown in Table 1.

[0164] [Examples 8-10]

[0165] (8-1. Diblock copolymer)

[0166] In a dry and nitrogen-replaced pressure-resistant reactor, 500 ml of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were added, followed by the addition of 14 g of 2-vinylnaphthalene as polymerization unit A. The reactor was then reacted at 25 °C for 1 hour to carry out the first stage of polymerization.

[0167] After the first stage of polymerization was terminated, 7 g of isoprene as polymerization unit B was added, and the mixture was further reacted at 25°C for 1 hour to carry out the second stage of polymerization. As a result, a diblock copolymer with (2-vinylnaphthalene block)-(isoprene block) segments was obtained in the reaction mixture. The reaction mixture was injected into a large amount of 2-propanol to precipitate the diblock copolymer for separation.

[0168] The obtained diblock copolymer was dissolved in 700 ml of p-xylene to prepare a solution. 7.6 g of p-toluenesulfonic acid hydrazine was added to the solution, and the reaction was carried out at 130 °C for 8 hours. This reaction hydrogenated the double bonds of the isoprene units. After hydrogenation, the reaction solution was injected into a large amount of 2-propanol to obtain 18 g of the blocky product (A)-(B) diblock copolymer.

[0169] The diblock copolymer was obtained by NMR analysis. The results showed that the weight ratio of 2-vinylnaphthalene units to hydrogenated isoprene units in the diblock copolymer was 67:33, therefore the weight fraction of block (A) was 67%. Furthermore, the hydrogenation rate of the diblock copolymer was 99%. The weight-average molecular weight of the diblock copolymer, determined by GPC, was 150,000. The glass transition temperature of the diblock copolymer, determined by TMA, was 120 °C.

[0170] (8-2. Copolymer Mixture)

[0171] The triblock copolymer obtained in (1-1) of Example 1 and the diblock copolymer obtained in (8-1) were mixed in the proportions shown in Table 1 to obtain a copolymer mixture, which was used as resin C in the following operations. The glass transition temperatures of resin C are shown in Table 1.

[0172] (8-3. Phase retardation film)

[0173] Except for the changes described below, a phase difference film was obtained and evaluated by the same operation as in Example 1 (1-2) to (1-3).

[0174] • Resin C was used instead of the triblock copolymer obtained by (1-1), and the copolymer mixture obtained by (8-2) was used. Through X-ray observation and TEM observation in (1-2), it was confirmed that Examples 8-9 were layered and Example 10 was a columnar phase-separated structure with a column diameter of 15 nm and an interphase distance of 50 nm.

[0175] • Modify the stretching conditions in (1-3) as shown in Table 1.

[0176] [Example 11]

[0177] In step (1-2), the amount of resin C powder added between the pair of polyimide films was reduced. Otherwise, a phase difference film was obtained and evaluated by the same operation as in Example 1. As a result of reducing the amount of resin C powder, the thickness of the film before stretching became 38 μm.

[0178] [Comparative Example 1]

[0179] (C1-1. Polymer)

[0180] In a dry, nitrogen-purified pressure reactor, 500 ml of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were added, followed by the addition of 14 g of 2-vinylnaphthalene as polymerization unit A. The reaction was carried out at 25 °C for 2 hours to induce polymerization. The resulting polymer was then obtained in the reaction mixture. The reaction mixture was injected into a large volume of 2-propanol to precipitate the polymer, which was then separated.

[0181] The polymer was obtained by NMR analysis. The results showed that the polymer consisted only of 2-vinylnaphthalene units, therefore the weight fraction of block (A) was 100%. The weight-average molecular weight of the polymer, determined by GPC, was 250,000. The glass transition temperature of the polymer, determined by TMA, was 143 °C.

[0182] (C1-2. Phase retardation film)

[0183] Except for the changes described below, a phase difference film was obtained and evaluated by operating in the same manner as in Example 1 (1-2) to (1-3).

[0184] Instead of the triblock copolymer obtained in (1-1), the polymer obtained in (C1-1) was used as resin C. No phase separation structure was observed by TEM observation of (1-2).

[0185] • Modify the stretching conditions in (1-3) as shown in Table 1.

[0186] The refractive index of the obtained phase retardation film is nx = nz > ny, therefore the obtained phase retardation film is a negative A plate.

[0187] [Comparative Examples 2-3]

[0188] Except for the changes described below, a phase difference film was obtained and evaluated through the same operation as in Example 1.

[0189] • The amounts of 2-vinylnaphthalene and isoprene added in the polymerization reaction of (1-1) were changed. However, it was necessary to ensure that the amount of 2-vinylnaphthalene added in the first stage of polymerization was equal to the amount of 2-vinylnaphthalene added in the third stage of polymerization. Furthermore, the total amount of 2-vinylnaphthalene and isoprene added was the same as in Example 1, which was 35 g. The weight fraction of block (A) in the obtained triblock copolymer and the glass transition temperature of resin C are shown in Table 1. The weight-average molecular weight of the triblock copolymers of Comparative Examples 2 and 3, as determined by GPC, was 250,000.

[0190] • Modify the stretching conditions in (1-3) as shown in Table 1.

[0191] The refractive index of the phase retardation film obtained in Comparative Example 2 is nx = nz > ny, therefore the obtained phase retardation film is a negative A plate.

[0192] The membrane obtained in Comparative Example 3 before stretching was severely turbid and could not be used as a phase retardation membrane.

[0193] [Comparative Example 4]

[0194] (C4-1. Random copolymer)

[0195] In a dry, nitrogen-purified pressure reactor, 500 ml of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were added, followed by the addition of a mixture of 28 g of 2-vinylnaphthalene and 7 g of isoprene. The polymerization reaction was carried out at 25 °C for 1 hour. The resulting polymer solution was injected into a large amount of 2-isopropanol to precipitate it, yielding a random copolymer.

[0196] The obtained random copolymer was dissolved in 700 ml of p-xylene, and 7.6 g of p-toluenesulfonyl hydrazine was added. The mixture was then subjected to a hydrogenation reaction at 130 °C for 8 hours. After the reaction, the reaction solution was injected into a large amount of 2-propanol to obtain 30 g of a blocky random copolymer with hydrogenated olefinic sites of isoprene (hydrogenation rate: 99%). According to NMR determination, the 2-vinylnaphthalene unit / hydrogenated isoprene unit ratio of the obtained copolymer was 67:33 wt%, and the weight-average molecular weight determined by GPC was 250,000.

[0197] In addition, the glass transition temperature was determined using TMA, and the result showed that the glass transition temperature was 100℃.

[0198] (C4-2. Phase retardation film)

[0199] Except for the changes described below, a phase difference film was obtained and evaluated by operating in the same manner as in Example 1 (1-2) to (1-3).

[0200] Instead of the triblock copolymer obtained in (1-1), the random copolymer obtained in (C4-1) was used as resin C. No phase separation structure was observed by TEM observation of (1-2).

[0201] [Example 12]

[0202] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedure as in Example 1.

[0203] • In step (1-1), the monomers used in the first and third stage polymerization reactions are changed to a mixture of 2-vinylnaphthalene and 1-vinylnaphthalene in a weight ratio of 1:1. Furthermore, the amounts of the mixture of 1-vinylnaphthalene and 2-vinylnaphthalene used in the first stage polymerization reaction, the isoprene used in the second stage polymerization reaction, and the mixture of 1-vinylnaphthalene and 2-vinylnaphthalene used in the third stage polymerization reaction are 9 g, 6 g, and 9 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0204] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 90,000, the weight-average molecular weight (Mw) was 100,000, and the molecular weight distribution was 1.11. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1 ¹H-NMR analysis confirmed that the microstructure of the isoprene block copolymer consisted of 92% poly(1,4-isoprene), and 8% poly(1,2-isoprene) and poly(3,4-isoprene). GPC analysis of the hydrogenated block copolymer confirmed a number-average molecular weight (Mn) of 101,000, a weight-average molecular weight (Mw) of 108,000, and a molecular weight distribution of 1.07. TMA analysis determined the glass transition temperature of the hydrogenated triblock copolymer to be 142 °C.

[0205] [Example 13]

[0206] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedures as in Example 1.

[0207] • In step (1-1), the monomer used for the first and third stage polymerization reactions is changed to 1-vinylnaphthalene. Furthermore, the amounts of 1-vinylnaphthalene used for the first stage polymerization reaction, isoprene used for the second stage polymerization reaction, and 1-vinylnaphthalene used for the third stage polymerization reaction are 9 g, 6 g, and 9 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0208] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 89,000, the weight-average molecular weight (Mw) was 100,000, and the molecular weight distribution was 1.12. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1 ¹H-NMR analysis confirmed that the microstructure of the isoprene block copolymer consisted of 93% poly(1,4-isoprene), and 7% poly(1,2-isoprene) and poly(3,4-isoprene). GPC analysis of the hydrogenated block copolymer confirmed a number-average molecular weight (Mn) of 107,000, a weight-average molecular weight (Mw) of 114,000, and a molecular weight distribution of 1.07. TMA analysis determined the glass transition temperature of the hydrogenated triblock copolymer to be 142 °C.

[0209] [Example 14]

[0210] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedures as in Example 1.

[0211] • In step (1-1), the monomer used in the first and third stage polymerization reactions is changed to styrene. Furthermore, the amounts of styrene used in the first stage polymerization reaction, isoprene used in the second stage polymerization reaction, and styrene used in the third stage polymerization reaction are 9 g, 6 g, and 9 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0212] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 92,000, the weight-average molecular weight (Mw) was 96,000, and the molecular weight distribution was 1.05. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1¹H-NMR analysis confirmed that the microstructure of the isoprene block copolymer consisted of 92% poly(1,4-isoprene), and 8% poly(1,2-isoprene) and poly(3,4-isoprene). GPC analysis of the hydrogenated block copolymer confirmed a number-average molecular weight (Mn) of 92,000, a weight-average molecular weight (Mw) of 96,000, and a molecular weight distribution of 1.05. TMA analysis determined the glass transition temperature of the hydrogenated triblock copolymer to be 95 °C.

[0213] [Example 15]

[0214] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedures as in Example 1.

[0215] • In step (1-1), the monomer used for the second-stage polymerization reaction is changed to butadiene. Furthermore, the amounts of 2-vinylnaphthalene used for the first-stage polymerization reaction, butadiene used for the second-stage polymerization reaction, and 2-vinylnaphthalene used for the third-stage polymerization reaction are 8 g, 8 g, and 8 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0216] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 95,000, the weight-average molecular weight (Mw) was 104,000, and the molecular weight distribution was 1.10. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1 ¹H-NMR analysis confirmed that the microstructure of the butadiene block copolymer consisted of 90% poly(1,4-butadiene) and 10% poly(1,2-butadiene). The glass transition temperature of the hydrogenated triblock copolymer, determined by TMA, was 140 °C.

[0217] [Example 16]

[0218] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedure as in Example 1.

[0219] • In step (1-1), the monomers used in the first and third stage polymerization reactions are changed to a mixture of 2-vinylnaphthalene and 1-vinylnaphthalene in a weight ratio of 1:1. Furthermore, the monomer used in the second stage polymerization reaction is changed to butadiene. The amounts of the mixture of 1-vinylnaphthalene and 2-vinylnaphthalene used in the first stage polymerization reaction, the butadiene used in the second stage polymerization reaction, and the mixture of 1-vinylnaphthalene and 2-vinylnaphthalene used in the third stage polymerization reaction are 8 g, 8 g, and 8 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0220] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 94,000, the weight-average molecular weight (Mw) was 104,000, and the molecular weight distribution was 1.10. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1 ¹H-NMR analysis confirmed that the microstructure of the butadiene block copolymer consisted of 89% poly(1,4-butadiene) and 11% poly(1,2-butadiene). The glass transition temperature of the hydrogenated triblock copolymer, determined by TMA, was 140 °C.

[0221] [Example 17]

[0222] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedures as in Example 1.

[0223] • In step (1-1), the monomer used in the first and third stage polymerization reactions is changed to 1-vinylnaphthalene. Furthermore, the monomer used in the second stage polymerization reaction is changed to butadiene. The amounts of 1-vinylnaphthalene used in the first stage polymerization reaction, butadiene used in the second stage polymerization reaction, and 1-vinylnaphthalene used in the third stage polymerization reaction are 8 g, 8 g, and 8 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0224] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 94,000, the weight-average molecular weight (Mw) was 104,000, and the molecular weight distribution was 1.10. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1 ¹H-NMR analysis confirmed that the microstructure of the butadiene block copolymer consisted of 89% poly(1,4-butadiene) and 11% poly(1,2-butadiene). The glass transition temperature of the hydrogenated triblock copolymer, determined by TMA, was 140 °C.

[0225] [Example 18]

[0226] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedures as in Example 1.

[0227] • In step (1-1), the monomer used in the first and third stage polymerization reactions is changed to styrene. Furthermore, the monomer used in the second stage polymerization reaction is changed to butadiene. The amounts of styrene used in the first stage polymerization reaction, butadiene used in the second stage polymerization reaction, and styrene used in the third stage polymerization reaction are 8 g, 8 g, and 8 g, respectively. The weight fraction of block (A) in the resulting triblock copolymer and the glass transition temperature of resin C are shown in Table 1.

[0228] GPC analysis confirmed that the number-average molecular weight (Mn) of the unhydrogenated triblock copolymer was 91,000, the weight-average molecular weight (Mw) was 101,000, and the molecular weight distribution was 1.11. Furthermore, based on the second-stage polymerization of the diblock copolymer... 1 ¹H-NMR analysis confirmed that the microstructure of the butadiene block copolymer consisted of 90% poly(1,4-butadiene) and 10% poly(1,2-butadiene). The glass transition temperature of the hydrogenated triblock copolymer, determined by TMA, was 95 °C.

[0229] The results of the examples and comparative examples are summarized in Table 1.

[0230] [Table 1]

[0231] Table 1

[0232]

[0233] Based on the results shown in Table 1, it is evident that, in the examples, retardation films with a desired NZ coefficient close to 0.5, excellent processability, and display properties can be readily obtained. In particular, in Examples 8-10, where resin C further comprises a specific proportion of (A)-(B) diblock copolymer P” as a block copolymer, the processability is particularly excellent.

Claims

1. A method for producing a phase difference film, the phase difference film being formed of a resin C containing a copolymer P, the copolymer P containing a polymerization unit A and a polymerization unit B, the copolymer P having a negative intrinsic birefringence value, the phase difference film containing a phase separation structure exhibiting structural birefringence, the phase separation structure containing a phase mainly composed of the polymerization unit A and a phase mainly composed of the polymerization unit B, the phase difference film having an NZ factor greater than 0 and less than 1, the phase separation structure having any one of a lamellar shape, a columnar shape, and an ellipsoidal shape, an interphase distance in the phase separation structure being 200 nm or less, an in-plane retardation Re of the phase difference film being in a range of 120 nm to 160 nm or 250 nm to 290 nm, the method comprising: a step of forming a single layer film of the resin C by melt extrusion, a step of causing the resin C to undergo phase separation in the film, and a step of stretching the film to impart molecular orientation birefringence, the step of causing the resin C to undergo phase separation including a step of applying stress in a thickness direction of the film by applying pressure in the thickness direction of the film. The copolymer P is a block copolymer having a block A mainly composed of the polymerization unit A and a block B mainly composed of the polymerization unit B. The polymerization unit A is a unit represented by general formula (A), The polymerization unit B is a unit represented by general formula (B-1), a unit represented by general formula (B-2), or a combination thereof, The copolymer P contains a triblock copolymer P', The triblock copolymer P' is an A-B-A triblock copolymer having a block A mainly composed of the polymerization unit A and a block B mainly composed of the polymerization unit B. The copolymer P further contains a diblock copolymer P", The diblock copolymer P" is an A-B diblock copolymer having the block A and the block B, The proportion of the diblock copolymer P" is 5 to 40% by weight relative to the total of the triblock copolymer P' and the diblock copolymer P". The polymerization unit A has a negative intrinsic birefringence value, and the polymerization unit B has a positive intrinsic birefringence value. ​ ​ 2. The method for producing a phase difference film according to claim 1, wherein ​ 3. The method for producing a phase difference film according to claim 1 or 2, wherein ​ In the formula R C The radical is selected from phenyl, biphenyl, naphthyl, anthraceneyl, phenanthryl, tetraphenyl, pentaphenyl, and terphenyl. R 1 ~R 3 each independently is a group selected from a hydrogen atom and an alkyl group having 1 to 12 carbon atoms.

4. The method for producing a phase difference film according to claim 1 or 2, wherein ​ wherein R 4 ~R 9 each independently is a group selected from a hydrogen atom and an alkyl group having 1 to 6 carbon atoms.

5. The method for producing a phase difference film according to claim 1 or 2, wherein ​ ​ 6. The method for producing a phase difference film according to claim 5, wherein ​ ​ ​ 7. The method for producing a phase difference film according to claim 1 or 2, wherein ​

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