Phase retardation film and manufacturing method

Abstract

A phase retardation film and a method thereof are disclosed. The phase retardation film is substantially formed from only one copolymer P comprising polymeric unit A and polymeric unit B, exhibiting a phase-separated structure with structural birefringence and having an NZ coefficient greater than 0 and less than 1. Preferably, the phase-separated structure comprises a phase with polymeric unit A as the main component and a phase with polymeric unit B as the main component. The phase-separated structure has any of the following morphologies: sheet-like, columnar, or spherical. The interphase distance in the phase-separated 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, phase retardation films such as λ / 2 waveplates and λ / 4 waveplates are sometimes provided to improve display quality. For example, in IPS (In-Plane Switching) liquid crystal displays, phase retardation films are sometimes provided for purposes such as viewing angle compensation.

[0003] For retardation films used for viewing angle compensation in IPS liquid crystal display devices, their NZ coefficient is required to be greater than 0 and less than 1. Furthermore, an NZ coefficient of 0.5 or a value close to it is preferred. 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] Fabricating such a phase retardation film is difficult. This is because films that satisfy the nx>nz>ny relationship cannot be achieved by simply processing ordinary resin films using conventional methods such as stretching; it requires the use of materials and / or methods different from the usual ones 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 is complex in construction due to the combination of multiple layers to achieve the desired optical properties, resulting in high cost and low productivity.

[0012] Therefore, the object of the present invention is to provide a phase retardation film with useful optical properties that can be easily manufactured at low cost and a method thereof.

[0013] Solution for solving the problem

[0014] In order to solve the above problems, the inventors conducted research and found that the above problems can be solved by making the material constituting the phase difference film a material that is essentially formed only by copolymers exhibiting a specific phase separation structure.

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

[0016] [1] A phase retardation film, which is essentially formed only of one copolymer P comprising polymeric unit A and polymeric unit B,

[0017] It exhibits a phase-separated structure with visible structural birefringence.

[0018] It has an NZ coefficient greater than 0 and less than 1.

[0019] [2] According to the phase difference film described in [1], wherein the phase separation structure comprises a phase in which the polymerization unit A is the main component and a phase in which the polymerization unit B is the main component.

[0020] The aforementioned phase separation structures can have any of the following morphologies: plate-like, columnar, or spherical.

[0021] The interphase distance in the above phase-separated structure is less than 200 nm.

[0022] [3] According to the phase difference film of [1] or [2], wherein the copolymer P is a block copolymer having a block (A) having the polymeric unit A as the main component and a block (B) having the polymeric unit B as the main component.

[0023] [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),

[0024] [Chemical Formula 1]

[0025]

[0026] In the formula, R c The group is selected from phenyl, biphenyl, naphthyl, anthracene, phenanthryl, tetraphenyl, pentaphenyl, and terphenyl.

[0027] R 1 ~R 3 Each group is independently selected from hydrogen atoms and alkyl groups having 1 to 12 carbon atoms.

[0028] [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.

[0029] [Chemical Formula 2]

[0030]

[0031] In the formula, R 4 ~R 9 Each group is independently selected from hydrogen atoms and alkyl groups having 1 to 6 carbon atoms.

[0032] [6] The phase difference film according to any one of [1] to [5], wherein the copolymer P is an (A)-(B)-(A) triblock copolymer P' having a block (A) with the polymeric unit A as the main component and a block (B) with the polymeric unit B as the main component.

[0033] [7] The phase difference film according to any one of [1] to [6], wherein the copolymer P has a negative intrinsic birefringence value.

[0034] [8] The phase difference film according to any one of [1] to [7], wherein the polymer unit A has a negative intrinsic birefringence value and the polymer unit B has a positive intrinsic birefringence value.

[0035] [9] A method for manufacturing a phase retardation film according to any one of [1] to [8], comprising the following steps:

[0036] The process of forming a monolayer film of resin C, wherein resin C is substantially formed solely from the copolymer P, and

[0037] The process of separating the above-mentioned resin C phase in the above-mentioned membrane.

[0038]

[10] The method for manufacturing a phase difference film according to [9] includes a step of applying stress to the film along its thickness direction in the step of separating the resin C phase.

[0039]

[11] The method for manufacturing a phase difference film according to [9] or

[10] , wherein the step of forming the film includes a step of melt-extruding the copolymer P in a single layer.

[0040]

[12] The method for manufacturing a phase difference film according to any one of [9] to

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

[0041] Invention Effects

[0042] According to the present invention, a phase retardation film having useful optical properties and a method thereof that can be easily manufactured at low cost is provided. Detailed Implementation

[0043] The present invention will now be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented in any way without departing from the scope of the claims of the present invention and its equivalents.

[0044] 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, and it can be, for example, up to 100,000 times.

[0045] 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 + ny) / 2 - nz} × d. Furthermore, unless otherwise specified, the NZ coefficient is represented by (nx - nz) / (nx - ny). Here, nx represents the refractive index of the direction perpendicular to the thickness direction (in-plane direction) that imparts the highest refractive index. ny represents the refractive index of 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.

[0046] 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.

[0047] In the following description, unless otherwise specified, the slow axis of a membrane refers to the slow axis in the plane of the membrane.

[0048] The sign of the intrinsic birefringence of a resin is defined by the change in the refractive index of the molded article when it is stretched. That is, a resin with a positive intrinsic birefringence is one whose refractive index in the stretching direction is greater than before stretching. Conversely, a resin with a negative intrinsic birefringence is one whose refractive index in the stretching direction is less than before stretching. The intrinsic birefringence can be calculated from the dielectric constant distribution.

[0049] 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 preparing a homopolymer formed solely from that polymeric unit, molding the polymer into an arbitrary shape, stretching the molded article, and measuring its optical properties. Generally, it is known that polymeric units of hydrocarbons such as alkenes and dienes mostly 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, mostly have negative intrinsic birefringence values.

[0050] In the following description, there are cases where blocks in a polymer composed of polymeric units produced by the polymerization of a monomer are represented using the name of that monomer. For example, blocks composed of polymeric units produced by the polymerization of 2-vinylnaphthalene are represented as "2-vinylnaphthalene blocks", and blocks composed of polymeric units produced by the polymerization of isoprene are represented as "isoprene blocks".

[0051] [1. Phase retardation film]

[0052] The phase retardation film of the present invention is substantially formed from only one specific copolymer P, and is typically composed of a resin substantially formed from only one specific copolymer P. In the following description, for ease of explanation, this resin is sometimes referred to as "resin C".

[0053] [1.1. Resin C]

[0054] The copolymer P constituting resin C comprises polymeric units A and B. Copolymer P is preferably a block copolymer having blocks (A) with polymeric unit A as the main component and blocks (B) with polymeric unit B as the main component. Generally, a block copolymer is a polymer having a molecular structure composed of multiple linked blocks, 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 may be simply referred to as a "block copolymer".

[0055] 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.

[0056] As an example of a polymer unit A, a unit represented by the following general formula (A) can be cited.

[0057] [Chemical Formula 3]

[0058]

[0059] R c It is a group selected from phenyl, biphenyl, naphthyl, anthracene, phenanthryl, tetraphenyl, pentaphenyl and terphenyl.

[0060] R 1 ~R 3 Each group is independently 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 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 It is a hydrogen atom, and R c It is naphthyl, and R 1 It is a hydrogen atom.

[0061] 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.

[0062] In copolymer 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.

[0063] As an example of the aggregation unit B, the unit represented by the following general formulas (B-1) and / or (B-2) can be cited.

[0064] [Chemical Formula 4]

[0065]

[0066] R 4 ~R 9Each group is independently selected from alkyl groups having 1 to 6 carbon atoms. Examples of such alkyl groups include methyl, ethyl, propyl, and hexyl. R is preferred. 4 ~R 9 Each can be a hydrogen atom or a methyl group independently.

[0067] Polymer unit B can be obtained by polymerizing the monomer (b) that forms polymer unit B to form a polymer unit, and further hydrogenating the polymer unit in the presence of a double bond. Examples of monomer (b) include compounds represented by the following general formula (bm).

[0068] [Chemical Formula 5]

[0069]

[0070] 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 Among them R 6 or R 7 The monomers are methyl (with other atoms being hydrogen), 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, R is a preferred example of monomer (b). 4 ~R 9 The same group as R 4 ~R 9 Aggregation units.

[0071] In copolymer P, polymeric unit B can be a single type or a combination of two or more types in any proportion. Therefore, monomer (b) used to form polymeric unit B can be a single type or a combination of two or more types in any proportion.

[0072] 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 that can copolymerize with monomer (a) and units formed by hydrogenation of such units.

[0073] When copolymer P has blocks (B), blocks (B) can have any polymeric units other than polymeric unit B. Examples of such arbitrary polymeric units include: polymeric units formed by polymerization of monomer (b) that have residual unhydrogenated double bonds, units formed by polymerization of any monomer that can copolymerize with monomer (b), and units formed by hydrogenating such units.

[0074] From the viewpoint of revealing 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.

[0075] Preferably, blocks (A) and (B) are immiscible. Because they are immiscible, the phase difference film of the present invention with a specific NZ coefficient can be readily obtained. Whether blocks (A) and (B) are immiscible can be determined based on whether a homopolymer formed from polymeric unit A and a homopolymer formed from polymeric unit B, having molecular weights similar to the sizes of their blocks in the block copolymer, are miscible.

[0076] 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.

[0077] Examples of linear block copolymers include: diblock copolymers consisting of blocks (A)-(B) linked together (A) and (B) (in this application, this may be referred to as "polymer P"); triblock copolymers consisting of blocks (A), (B), and another block (A) linked sequentially (A)-(B)-(A) (in this application, this may be referred to as "polymer P'"); and linear block copolymers consisting of blocks linked together with more blocks. Examples of block copolymers consisting of multiple linked blocks include (A)-((B)-(A)). n -(B)-(A) and (B)-((A)-(B)) n The structure consists of segments -(A)-(B) (where n is an integer greater than or equal to 1).

[0078] As an example of grafted block copolymers, a block copolymer consisting of blocks having (A)-g-(B) as side chains attached to block (A) can be cited.

[0079] From the viewpoint of enabling resin C to exhibit the desired optical properties, copolymer P is preferably a block copolymer having a molecular structure of two or more polymer blocks (A) and one or more polymer blocks (B) per molecule. More preferably, the block copolymer is a triblock copolymer having blocks of (A)-(B)-(A).

[0080] In copolymer P, the weight fraction of polymeric unit A can be adjusted in a manner that reveals 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 unit A and polymeric unit B. When resin C contains multiple copolymers P, the weight fraction of polymeric unit A referred to here is the weight of polymeric unit A relative to the total weight of polymeric unit A and polymeric unit 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, it is 90% by weight or less, preferably 85% by weight or less.

[0081] The molecular weight of copolymer P is not particularly limited and can be appropriately adjusted within a range to obtain preferred optical and mechanical properties. 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.

[0082] The phrase "substantially composed solely of" copolymer P refers not only to the case where resin C is composed solely of copolymer P, but also to the case where resin C contains, in addition to copolymer P, a compounding agent that does not impede the manifestation of the structural birefringence of resin C. Examples of compounding agents include dyes, pigments, antioxidants, and other additives. The proportion of such compounding agents 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 composed solely of copolymer P.

[0083] The resin C is substantially formed from "only one" copolymer P, meaning that the copolymer P constituting the resin C has a common polymeric unit A and polymeric unit B. In the case of a block copolymer, it is particularly preferred that the resin C is substantially formed from a copolymer P consisting of only one type of block. More specifically, it is preferred that the resin C is substantially formed from a triblock copolymer P' consisting of a (A)-(B)-(A) block. By adopting such a configuration, a phase retardation film that is easier to manufacture and can easily achieve the desired optical properties in a thin layer can be provided compared to prior art phase retardation films (phase retardation films having multiple layers, each layer formed from a different resin; for example, the phase retardation film described in Patent Document 2).

[0084] Preferred resin C 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, by adjusting the weight fraction of polymeric unit A within a range above and below the aforementioned lower limit, a resin with a negative intrinsic birefringence value can be obtained. By having resin C with a negative intrinsic birefringence value, the desired optical properties of the retardation film can be imparted.

[0085] [1.2. Optical Properties of Phase Reversal Films]

[0086] 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.

[0087] A retardation film with such an NZ coefficient can be easily obtained by using the specific resin described above as resin C and performing 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, and it is something that cannot be obtained by conventional processing methods such as stretching. Therefore, the retardation film of the present invention is highly useful in terms of having useful optical properties and being easy to manufacture.

[0088] The in-plane delay Re and thickness direction delay Rth of the retardation film of the present invention can be adjusted to desired values ​​corresponding to 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.

[0089] [1.3. Other properties and shapes of retardation films, etc.]

[0090] The retardation film of the present invention comprises a phase-separated structure exhibiting structural birefringence. The phase-separated structure can be formed within a layer of resin C constituting the retardation film. A phase-separated structure refers to the separation of multiple phases into distinguishable states within a film layer through self-organization of the materials constituting the retardation film. The phase-separated structure can be formed by the separation of a phase with polymeric unit A as the main component and a phase with polymeric unit B as the main component, caused by the self-organization of portions of copolymer P in resin C composed of polymeric unit A (e.g., block (A)) and portions composed of polymeric unit B (e.g., block (B)). In the following description, these phases are sometimes referred to simply as the "phase of polymeric unit A" and the "phase of polymeric unit B". A layer exhibiting such a phase-separated structure can exhibit structural birefringence when the structure is sufficiently small compared to the wavelength of light.

[0091] Structural birefringence refers to birefringence that occurs in structures containing multiple phases with different refractive indices, such as phase-separated structures. For example, in a structure where a phase with a refractive index n1 contains a phase with a different refractive index n2, structural birefringence can be observed. Structural birefringence is distinctly different from oriented birefringence caused by molecular orientation due to stretching in that it occurs even when the phases are formed by isotropic media.

[0092] The magnitude and orientation of structural birefringence can be controlled by adjusting the shape, arrangement, and volume fraction of each phase exhibiting a phase-separated structure, as well as the difference in refractive index between phases, in order to manifest the desired structural birefringence. Specific details are described, for example, in *Form birefringence of macromolecules* (WLBragg et al., 1953).

[0093] The greater the refractive index difference between the phase with polymer unit A as the main component and the phase with polymer unit B as the main component, the more efficiently and well 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.

[0094] The proportions of polymeric unit A in the phase where polymeric unit A is the main component and the proportions of polymeric unit B in the phase where polymeric unit B is the main component can be adjusted by appropriately adjusting the materials used to manufacture copolymer P and the manufacturing operation. For optimal effect, a higher proportion is preferred. The proportion of polymeric unit A in the phase where polymeric unit A is the main component is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably 100% by weight. The proportion of polymeric unit B in the phase where polymeric unit B is the main component is preferably 50% by weight or more, more preferably 75% by weight or more, and even more preferably 100% by weight.

[0095] By controlling the shape and arrangement of the phase separation structure, the phase retardation film of the present invention can be endowed with birefringence similar to that of a negative C-plate. For example, when the layers constituting the film have a sheet-like phase separation structure, and the average direction of the stacking of the sheets (the direction perpendicular to the layers constituting the sheets) is close to the normal direction of the film, the layers can exhibit birefringence similar to that of a negative C-plate. When the layers have a columnar phase separation structure or a spherical phase separation structure, if, for example, the major axis of the column or ellipsoid is in the in-plane direction and the orientation of the major axis is random in the in-plane, the layers can exhibit structural birefringence similar to that of a negative C-plate.

[0096] By combining such structural birefringence with molecular orientation birefringence resulting from the orientation of the molecules constituting resin C, it is possible to readily obtain a phase retardation film with a specific range of NZ coefficients that cannot be easily manufactured by conventional means.

[0097] Specific examples of phase-separated structures include sheet structures, spherical structures, and columnar structures. In any case, a preferred effect is achieved as long as the structure exhibits structural birefringence similar to that of a negative C-plate. That is, a structure exhibiting structural birefringence where the refractive index in the thickness direction is smaller than the average refractive index in the in-plane direction is preferred. Which of these phase-separated structures exhibits is influenced by various factors. One of the main factors affecting the structure's appearance is the volume ratio of the phase with polymer unit A as the main component to the phase with polymer unit B as the main component. This volume ratio can be adjusted by varying the proportions of blocks (A) and (B) in the block copolymer.

[0098] In a phase-separated structure, the size of the structure can be appropriately adjusted within the range that the phase retardation film can provide the desired optical properties. For example, regarding the interphase distance, it 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 100 nm or less, preferably 80 nm or less, and even more preferably 60 nm or less. The interphase distance, for example, in the case of sheet-like phase separation, refers to the spacing between sheets (i.e., the spacing between repeating units of the sheet layer), and in the case of columnar phase-separated structures, refers to the spacing between columns. Regarding the size of the phase after phase separation, in the case of sheet-like phase separation, it refers to the thickness of the sheet, and in the case of columnar phase separation, it refers to the radius of the column. The interphase distance can be a value obtained by fitting a scattering pattern obtained from small-angle X-ray scattering measurements to a theoretical curve.

[0099] By ensuring that the interphase spacing and the size of the phase-separated phases are sufficiently small compared to visible light, structural birefringence is achieved, and film coloration and a decrease in transmittance are suppressed. The lower limit of the interphase spacing is not particularly limited and can be, for example, 10 nm or more. The lower limit of the size of the phase-separated phases is also not particularly limited and can be, for example, 10 nm or more. The interphase spacing can be adjusted by regulating the molecular structure of copolymer P. This can be achieved, for example, by using a block copolymer as copolymer P and appropriately adjusting factors such as the lengths of blocks (A) and (B).

[0100] The thickness of the retardation film of the present invention can be appropriately adjusted within a range that yields desired optical and mechanical properties. Specifically, it is preferably 15 μm or more, more preferably 20 μm or more, more preferably 100 μm or less, and more preferably 90 μm or less.

[0101] [2. Manufacturing method]

[0102] The phase retardation film of the present invention can be manufactured by a manufacturing method comprising the following steps: a step of forming a monolayer 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.

[0103] Examples of specific film-forming methods for the process of forming a film of resin C include solution casting, melt extrusion, calendering, and compression molding. Melt extrusion is particularly preferred for efficiently producing large quantities of phase difference films. Melt extrusion can be performed by 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.

[0104] 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.

[0105] The phase separation process can be performed, for example, by slowly cooling molten resin C. Specifically, in the process of forming a film, when using melt extrusion and other methods, the following operation can be performed: molten resin is molded and then cooled under slow cooling conditions. Although the specific mechanism is unclear, by performing this slow cooling, a phase-separated structure of resin C exhibiting structural birefringence, such as that of a negative C-plate, can be easily formed, and a phase retardation film with desired optical properties can be easily obtained. For example, in the typical melt extrusion process for forming a film using an extruder and a die, after the resin is extruded from the die, a process of casting the resin onto a cooling roller is performed. As a result, slow cooling can be achieved by setting the die temperature and cooling roller temperature in a manner that results in slow cooling conditions. Although the cooling conditions are also affected by factors other than the die temperature and cooling roller temperature, slower cooling conditions 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 resin C. More specifically, it is preferred to use a die head temperature of (Tg+100)℃~(Tg+150)℃ and a cooling roller temperature of (Tg-50)℃~(Tg+50)℃.

[0106] As a phase separation process, in addition to or instead of the slow cooling described above, a process of pressurizing the film can also be performed. By applying pressure to the film of resin C, a phase separation structure exhibiting structural birefringence, similar to a negative C plate, can be easily formed, and a phase retardation film with desired optical properties can be easily obtained.

[0107] Specifically, the pressurization process can be performed by applying pressure to a sheet of resin C in its thickness direction. In such an operation, a pressurizing device such as a 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 simultaneously with molding as part of the molding process, or it can be performed after molding. The temperature of the resin C during pressurization can be (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, and 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, and even more preferably 120 seconds or less. By setting the pressurization conditions within the above ranges, a membrane with uniform thickness and phase separation structure can be obtained.

[0108] The pressurization process can also be performed using a device that continuously applies pressure to a strip of resin C. In such an operation, pressure rollers or similar pressurizing devices can be used. When 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, through which pressure is applied to the resin C. The linear pressure during pressurization is preferably 10 N / cm or more, more preferably 50 N / cm or more, even more 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 (Tg+10)℃ to (Tg+150)℃. By setting the pressurization conditions within the above range, a film with uniform thickness and phase separation structure can be obtained.

[0109] A membrane of resin C with a phase separation structure is typically further fed to 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 continuously connected to the production line where the resin C membrane is formed. Alternatively, the manufactured resin C membrane can be temporarily wound into a roll, then unwound from the roll and fed to the stretching process. The stretching process is typically performed by planar stretching, where the membrane is stretched in its in-plane direction. Examples of planar stretching include uniaxial stretching and biaxial stretching. Uniaxial stretching involves stretching the membrane in one direction within its plane; examples include free-width uniaxial stretching and fixed-width uniaxial stretching. Biaxial stretching involves stretching the membrane in two directions within its plane. Examples of biaxial stretching include sequential biaxial stretching and simultaneous biaxial stretching. Stretching in each direction can be free-width stretching or fixed-width stretching. More specific examples of sequential biaxial stretching include full-width tenter frame and roll tenter frame methods. The stretching method used in the manufacturing method of the present invention can be any of these methods, or a method adapted to obtaining the desired phase difference film can be selected.

[0110] The stretching temperature in the stretching process is preferably (Tg-5)°C or higher, more preferably (Tg+5)°C or higher, even more preferably (Tg+15)°C or higher, more preferably (Tg+50)°C or lower, and even more preferably (Tg+40)°C or lower. By keeping the stretching temperature below the upper limit, process instability caused by film softening can be prevented. On the other hand, by keeping the stretching temperature above the lower limit, breakage and whitening during stretching can be prevented.

[0111] The presence of structural birefringence can be confirmed by measuring the optical properties of the unstretched film. Since unstretched films prepared using conventional methods such as extrusion, pressing, and solvent casting typically have random molecular orientations, Re and Rth are almost zero. On the other hand, unstretched films exhibiting structural birefringence show significantly larger Re and Rth values ​​than those observed in ordinary unstretched films prepared using conventional methods. Therefore, the presence of structural birefringence can be confirmed by measuring these values. However, a more reliable confirmation of structural birefringence can be achieved by simultaneously performing structural observations using electron microscopy and small-angle X-ray scattering.

[0112] In the method for manufacturing the phase retardation film of the present invention, the heat treatment step can be performed as any step. The heat treatment step can be performed at any stage of the manufacturing method. However, it is preferable that the heat treatment step is 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 such a decrease in phase difference.

[0113] The heat treatment process can be performed by heating the resin C film using a floating oven or a pin tenter frame. This heat treatment promotes the formation of phase separation structures. The heat treatment temperature is preferably above Tg, more preferably above (Tg+20)°C, even more preferably above (Tg+25)°C, preferably below (Tg+50)°C, and more preferably below (Tg+40)°C. By keeping the heat treatment temperature within the above range, the formation of phase separation 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 retardation film with uniform film thickness and optical properties can be easily manufactured. The heat treatment process can be performed in a state where the resin C film is not substantially stretched. "Not substantially stretched" means that the stretch ratio of the film in any direction is less than 1.1 times, preferably less than 1.01 times.

[0114] [3. Applications]

[0115] The phase retardation film of this invention can be used as a component of 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 provided in a display device as a component with functions such as viewing angle compensation and anti-reflection.

[0116] Example

[0117] The present invention will now be specifically described with reference to the embodiments shown below. However, the present invention is not limited to the following embodiments, and can be implemented in any way without departing from the scope of the claims of the present invention and its equivalents.

[0118] Unless otherwise stated, in the following instructions, "%" and "parts" refer to quantities based on weight. Unless otherwise stated, the following operations are performed at normal temperature and pressure in an atmospheric environment.

[0119] [Evaluation Method]

[0120] (Re and NZ coefficients of the phase retardation film)

[0121] Using AXOSCAN manufactured by AXOMETRICS, the Re and NZ coefficients at a wavelength of 540nm were determined.

[0122] (Phase-separated structure)

[0123] The obtained membrane was cut into 2mm × 4mm pieces, and 30 pieces were overlapped in the thickness direction and fixed in a folder. A small-angle X-ray scattering (SAXS) instrument (AICHI SR, BEAMLINE8S3) was used with a camera length of 4m, X-ray energy of 8.2keV, and a measurement range of approximately 0.06–3nm. -1 Scattering patterns were obtained under the condition of an exposure time of 60 seconds per sample. The obtained scattering patterns were then fitted with theoretical curves to calculate the phase separation structure and interphase distance.

[0124] The X-ray irradiation surface is the film cross-section, and the integration range is 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 integration, 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.

[0125] (Processability)

[0126] The phase retardation film was cut to obtain a strip-shaped specimen. The specimen was cut with its long side perpendicular to the tensile direction. The specimen width was 10 mm. A tensile test was performed on the specimen. The number of tensile tests was 20. The tensile test conditions were an initial clamp spacing of 100 mm and a test speed of 100 mm / min. The presence or absence of fracture up to the yield point was observed, and the specimen was evaluated based on the following evaluation criteria.

[0127] A: Less than 10% of the specimens fractured before reaching the yield point.

[0128] B: More than 10% but less than 30% of the specimen breaks before reaching the yield point.

[0129] C: More than 30% but less than 50% of the specimen breaks before reaching the yield point.

[0130] D: More than 50% of the specimen breaks before reaching the yield point.

[0131] (Display characteristics: λ / 2 waveplate)

[0132] 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 side of the polarizer was removed, and the retardation film obtained in Examples 1-11 and the Comparative Examples was laminated onto that side. Lamination was performed such that the slow axis direction of the retardation film was aligned with the transmission axis direction of the polarizer. Through this operation, a polarizer was obtained having the retardation film of the Examples or Comparative Examples as one of the two protective films.

[0133] The obtained polarizer was replaced with the polarizer originally present on the viewing side of a commercially available IPS liquid crystal display device (LG Electronics, 23MP47HQ) to obtain a liquid crystal display device having the retardation film obtained in the embodiments and comparative examples. During the replacement, the polarizer was configured such that the side having the retardation film obtained in the embodiments and comparative examples became the liquid crystal cell side. Furthermore, the transmission axis of the polarizer was set to the same direction as the polarizer in the polarizer originally present in the IPS liquid crystal display device.

[0134] The display status of the liquid crystal display device is observed from various azimuth angles relative to the tilt direction of the display surface (45° relative to the normal direction). If the contrast ratio is improved throughout the entire field of view compared to before replacement, it is rated as "good"; if the contrast ratio is the same or worse in more than one position compared to before replacement, it is rated as "poor".

[0135] (Display characteristics: λ / 4 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 is prepared. The protective film on one side of the polarizer is removed, and the retardation film obtained in Example 12 is bonded to that side. Bonding is performed at a 45° angle between the slow axis direction of the retardation film and the transmission axis direction of the polarizer. Through this operation, a circular polarizer having the retardation film of the example as one of the two protective films is obtained.

[0137] The obtained circular polarizer was replaced with the circular polarizer originally present on the viewing side of a commercially available organic EL display device (LG Electronics, OLED55B6P) to obtain an organic EL display device having the retardation film obtained in the embodiment. During replacement, the circular polarizer was configured such that the side having the retardation film obtained in the embodiment became the organic EL cell side. Furthermore, the transmission axis of the polarizer was set to the same direction as the polarizer in the circular polarizer originally present in the organic EL display device.

[0138] The display status of the organic EL display device was observed at various azimuth angles relative to the tilt direction of the display surface (45° relative to the normal direction). Compared with the original device, the device was rated as "good" if reflectivity was suppressed in all directions. Compared with the original device, the device was rated as "poor" if reflectivity was equal or better in more than one azimuth.

[0139] [Example 1]

[0140] (1-1. Triblock copolymer)

[0141] In a pressure-resistant reactor that has been dried and purged with nitrogen, 500 ml of toluene was added as a solvent and 0.29 mmol of n-butyllithium was added as a polymerization catalyst. Then, 14 g of 2-vinylnaphthalene was added as polymerization unit A, and the reaction was carried out at 25 °C for 1 hour to carry out the first stage of polymerization.

[0142] After the first stage of polymerization, 7g of isoprene was added as polymerization unit B, and the reaction was further carried out at 25°C for 1 hour to conduct the second stage of polymerization. The result was a diblock copolymer in the reaction mixture consisting of (2-vinylnaphthalene)-(isoprene) blocks. Subsequently, 14g of 2-vinylnaphthalene was added to the reaction mixture as polymerization unit A, and the reaction was carried out at 25°C for 1 hour to conduct the third stage of polymerization. The result was a triblock copolymer in the reaction mixture consisting of (2-vinylnaphthalene)-(isoprene)-(2-vinylnaphthalene) blocks. The reaction mixture was injected into a large amount of 2-propanol to precipitate the triblock copolymer, which was then separated and removed.

[0143] The obtained triblock copolymer was dissolved in 700 ml of p-xylene to prepare a solution. 7.6 g of p-toluenesulfonyl hydrazine was added to the solution, and the reaction was carried out at 130 °C for 8 hours. Hydrogen was added to the double bonds of the isoprene units via this reaction. After hydrogenation, the reaction solution was injected into a large amount of 2-propanol to obtain 32 g of the (A)-(B)-(A) triblock copolymer as a bulk product.

[0144] The triblock copolymer was analyzed by NMR. 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.

[0145] (1-2. Pre-stretch membrane)

[0146] The triblock copolymer obtained in (1-1) was used as resin C. Resin C was pulverized into powder using a pulverizer. 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, the pressure was released, and the laminate was cooled to room temperature in air to remove the polyimide films. Through this operation, a pre-stretch film 1 with a thickness of 75 μm was produced.

[0147] X-rays were incident on the cross section of the pre-stretched membrane 1 and observed using small-angle scattering. The results showed a sheet-like structure with an interphase distance of 40 nm and a thickness of 20 nm.

[0148] Furthermore, slices with cross-sections parallel to the thickness direction were prepared and observed using TEM, confirming the sheet-like phase-separated structure.

[0149] The Re and Rth of the obtained pre-stretch membrane 1 were measured, and the results showed that Re = 15 nm and Rth = 90 nm, confirming that the properties obtained through structural birefringence are close to those of the negative C plate.

[0150] (1-3. Phase retardation film)

[0151] Cut the pre-stretched membrane 1 obtained in (1-2) to form a rectangular membrane with a size of 80mm×80mm.

[0152] A rectangular film was subjected to free-width uniaxial stretching. The stretching was performed using an intermittent stretching apparatus manufactured by Toyo Seiki Co., Ltd. The stretching conditions were: stretching temperature 145°C, stretching ratio 1.5 times, and stretching speed 33% per minute. The result was a retardation film with a thickness of 60 μm.

[0153] The Re and NZ coefficients, processability, and display characteristics of the obtained phase difference film were evaluated.

[0154] [Examples 2-3]

[0155] The stretching conditions in (1-3) were changed to those shown in Table 1. Otherwise, the phase difference film was obtained and evaluated by the same operation as in Example 1.

[0156] [Examples 4-7]

[0157] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedure as in Example 1.

[0158] • The amounts of 2-vinylnaphthalene and isoprene added in the polymerization reaction of (1-1) were changed. Specifically, the amounts of 2-vinylnaphthalene added in the first stage of polymerization were equal to the amounts added in the third stage of polymerization. Furthermore, 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 X-ray and TEM observations of (1-2), a lamellar structure resulting from phase separation was observed in either example.

[0159] The stretching conditions in (1-3) are changed as shown in Table 1.

[0160] [Example 8]

[0161] In steps (1-2), the amount of resin C powder added between the pair of polyimide films was reduced. Otherwise, the phase difference film was obtained and evaluated by the same procedure as in Example 1. The result of reducing the amount of resin C powder was that the thickness of the film before stretching became 38 μm.

[0162] [Comparative Example 1]

[0163] (C1-1. Polymer)

[0164] In a dry, nitrogen-purified pressure reactor, 500 ml of toluene was added as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst. Then, 14 g of 2-vinylnaphthalene was added as polymerization unit A, and the reaction was carried out at 25°C for 2 hours. The resulting polymer was obtained in the reaction mixture. The reaction mixture was then injected into a large amount of 2-propanol to precipitate the polymer, which was then separated and removed.

[0165] The polymer was analyzed by NMR. The results showed that the polymer consisted solely 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.

[0166] (C1-2. Phase retardation film)

[0167] 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).

[0168] • The polymer obtained in (C1-1) was used instead of the triblock copolymer obtained in (1-1) as resin C. In the TEM observation of (1-2), no structure resulting from phase separation was observed.

[0169] The stretching conditions in (1-3) are changed as shown in Table 1.

[0170] The refractive index of the obtained phase retardation film is nx = nz > ny, therefore, the obtained phase retardation film is a negative A plate.

[0171] [Comparative Examples 2-3]

[0172] Except for the changes described below, a phase difference film was obtained and evaluated using the same procedure as in Example 1.

[0173] • The amounts of 2-vinylnaphthalene and isoprene added in the polymerization reaction of (1-1) were changed. Specifically, the amount of 2-vinylnaphthalene added in the first stage of the polymerization reaction was equal to the amount added in the third stage. Furthermore, 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. The weight-average molecular weight of the triblock copolymer, determined by GPC, was 250,000 in both Comparative Examples 2 and 3.

[0174] The stretching conditions in (1-3) are changed as shown in Table 1.

[0175] In Comparative Example 2, the refractive index of the phase retardation film obtained is nx = nz > ny. Therefore, the obtained phase retardation film is a negative A plate.

[0176] The pre-stretch film obtained in Comparative Example 3 was severely turbid and could not be used as a phase retardation film.

[0177] [Comparative Example 4]

[0178] (C4-1. Random copolymer)

[0179] In a dry, nitrogen-purified pressure reactor, 500 ml of toluene was added as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst. Then, a mixture of 28 g of 2-vinylnaphthalene and 7 g of isoprene was added, and the polymerization reaction was carried out at 25 °C for 1 hour. The resulting polymer solution was injected into a large amount of 2-propanol to precipitate it, yielding a random copolymer.

[0180] The obtained 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 (hydrogenation rate: 99%) containing hydrogenated olefinic portions of isoprene. NMR analysis showed that 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.

[0181] In addition, the glass transition point was determined using TMA, and the result was a glass transition point of 100℃.

[0182] (C4-2. Phase retardation film)

[0183] 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).

[0184] • The random copolymer obtained in (C4-1) was used instead of the triblock copolymer obtained in (1-1) as resin C. In the TEM observation of (1-2), no structure resulting from phase separation was observed.

[0185] The results of the examples and comparative examples are summarized in Table 1.

[0186] [Table 1]

[0187] Table 1

[0188]

[0189] As can be clearly seen from the results shown in Table 1, a phase retardation film with an expected NZ coefficient close to 0.5 and excellent performance can be easily obtained in the embodiments.

Claims

1. A phase retardation film, substantially formed solely of a copolymer P containing polymeric units A and B and having a negative intrinsic birefringence. It exhibits a phase-separated structure with structural birefringence and a molecular orientation with molecular orientation birefringence. It has an NZ coefficient that is greater than 0 and less than 1. The in-plane delay Re is in the range of 120nm~160nm or 250nm~290nm. The aggregation unit A is a unit represented by the general formula (A). In the formula, R c The group is selected from phenyl, biphenyl, naphthyl, anthracene, phenanthryl, tetraphenyl, pentaphenyl, and terphenyl. R 1 ~R 3 Each group is independently selected from hydrogen atoms and alkyl groups having 1 to 12 carbon atoms. The phase-separated structure comprises a phase in which polymerization unit A is the principal component and a phase in which polymerization unit B is the principal component. The phase separation structure can have any of the following shapes: plate-like, columnar, or spherical. The interphase distance in the phase-separated structure is less than 200 nm. The size of each phase after phase separation is greater than 10 nm and less than 100 nm.

2. The phase retardation film according to claim 1, wherein, The copolymer P is a block copolymer having block A, which has polymeric unit A as the main component, and block B, which has polymeric unit B as the main component.

3. The phase retardation film according to claim 1 or 2, 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. In the formula, R 4 ~R 9 Each group is independently selected from hydrogen atoms and alkyl groups having 1 to 6 carbon atoms.

4. The phase retardation film according to claim 1 or 2, wherein, The copolymer P is an ABA triblock copolymer P' having block A, which has polymeric unit A as the main component, and block B, which has polymeric unit B as the main component.

5. The phase retardation film according to claim 1 or 2, wherein, The polymer unit A has a negative intrinsic birefringence value, and the polymer unit B has a positive intrinsic birefringence value.

6. A method for manufacturing a phase retardation film according to any one of claims 1 to 5, comprising the following steps: The process of forming a monolayer film of resin C, wherein resin C is substantially formed solely from the copolymer P, and The process of separating the resin C phase in the membrane.

7. The method for manufacturing a phase retardation film according to claim 6, wherein, The process of separating the resin C phase includes the process of applying stress to the membrane along its thickness direction.

8. The method for manufacturing a phase retardation film according to claim 6 or 7, wherein, The process of forming the film includes the step of melt-extruding the copolymer P in a single layer.

9. The method for manufacturing a phase retardation film according to claim 6 or 7, wherein, It further includes a step of stretching the membrane.

Images