Birefringent film, method for manufacturing the same, and method for manufacturing optical film

Abstract

This invention relates to a birefringent film comprising solvent A, solvent B, and a crystalline polymer, wherein the boiling point Bp(SA) (°C) of solvent A and the boiling point Bp(SB) (°C) of solvent B satisfy Bp(SA)-Bp(SB)≥5, and the total content of solvent A and solvent B in the birefringent film is 0.01% by weight or more and 3% by weight or less, and Rth≤-100nm. This invention also relates to a manufacturing method comprising the step of contacting a specific film with a mixed solvent comprising solvent A and solvent B, thereby causing a change in the birefringence of the film along its thickness direction.

Description

Technical Field

[0001] This invention relates to birefringent films that can be usefully used in the manufacture of optical films, methods for manufacturing the same, and methods for manufacturing optical films. Background Technology

[0002] Resin films with specific optical properties have long been used for optical applications. For example, a film with an NZ coefficient satisfying 0 < NZ < 1 is called a three-dimensional retardation film. It is known that when a three-dimensional retardation film is applied to a display device such as a liquid crystal display, it can exhibit the following effect: reducing the coloration of the display surface when viewed from an oblique direction.

[0003] Three-dimensional retardation films have a larger phase difference in the z-axis direction (i.e., the thickness direction) than in the y-axis direction (i.e., the in-plane direction orthogonal to the in-plane slow axis). Therefore, conventional methods for manufacturing retardation films, such as simply stretching a resin with inherently positive birefringence, are not feasible. Consequently, a method has been proposed to combine resins with inherently positive and negative birefringence to manufacture three-dimensional retardation films or similar films (e.g., Patent Documents 1-2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 188205;

[0007] Patent Document 2: International Publication No. 2020 / 137409. Summary of the Invention

[0008] The problem the invention aims to solve

[0009] The previously proposed method for manufacturing a three-dimensional phase difference film that combines resins with inherent positive and negative birefringence has the following problems: it requires a complex stretching process, a post-stretching bonding process, and troublesome positioning.

[0010] Therefore, the object of the present invention is to provide a means for easily manufacturing a three-dimensional retardation film that can exhibit good results.

[0011] Solution for solving the problem

[0012] If a film with a small thickness retardation Rth (especially a film with a negative Rth and a large absolute value) can be easily obtained, then a three-dimensional phase retardation film can be easily fabricated through a simple operation (such as a single uniaxial stretching). Therefore, in order to solve the above-mentioned problems, the inventors have studied films with small Rth that are easy to manufacture.

[0013] In this research, the inventors investigated the following: contacting a resin film containing a crystalline polymer with a solvent to create a solvent-impregnated state, thereby altering the birefringence of the film along its thickness direction and producing a film with a small Rth. However, during the research, a problem arose where a large amount of solvent remained in the film when the solvent was impregnated in the resin. When a large amount of solvent remains, an undesirable phenomenon occurs: in display devices manufactured using this film, the solvent gradually evaporates from the film, causing the film to deteriorate over time during use or adversely affecting other components of the device. Furthermore, the solvent in the film with a large amount of residual solvent evaporates in the next process, necessitating the use of an explosion-proof device in that next process. On the other hand, if high-temperature, long-duration drying is performed during the film manufacturing process to reduce the amount of residual solvent, the quality of the film will be degraded.

[0014] To reduce the amount of residual solvent, solvents with low boiling points are considered. However, according to the inventors' research, solvents that can sufficiently change the birefringence in the thickness direction of crystalline polymers by acting on them are limited to solvents with boiling points higher than the glass transition temperature of the crystalline polymers. To date, no solvent has been found that combines a large birefringence change with high volatility.

[0015] However, the inventors conducted further research and discovered that by combining various specific solvents, a balance could be struck between the high degree of birefringence change and volatility, resulting in the easy fabrication of films that exhibit excellent performance as components for manufacturing three-dimensional retardation films. This invention is based on this insight.

[0016] That is, the present invention includes the following contents.

[0017] [1] A birefringent film comprising solvent A, solvent B, and a crystalline polymer, wherein,

[0018] The boiling point Bp(SA) (°C) of solvent A and the boiling point Bp(SB) (°C) of solvent B satisfy Bp(SA)-Bp(SB)≥5.

[0019] The total content of solvent A and solvent B in the above-mentioned birefringent film is 0.01% by weight or more and 3% by weight or less.

[0020] The above birefringent film satisfies Rth ≤ -100nm.

[0021] [2] The birefringent film according to [1], wherein the birefringent film is a processed product of melt extrusion film.

[0022] [3] The birefringent film according to [1] or [2], wherein the inherent birefringence value of the crystalline polymer is positive.

[0023] [4] The birefringent film according to any one of [1] to [3], wherein the crystalline polymer described above contains an alicyclic structure.

[0024] [5] The birefringent film according to any one of [1] to [4], wherein the crystallinity obtained by X-ray diffraction is 10% or more.

[0025] [6] The birefringent film according to any one of [1] to [5], wherein the boiling point Bp(SA) of the solvent A, the boiling point Bp(SB) of the solvent B, and the glass transition temperature TgP of the polymer satisfy the relationship Bp(SA)≥TgP and Bp(SB)≤TgP.

[0026] [7] A manufacturing method for manufacturing a birefringent film according to any one of [1] to [6], wherein the manufacturing method includes the following steps:

[0027] Step (I) involves melt-extruding a resin (pa) containing a crystalline polymer into a film to obtain a film (pA); and

[0028] In step (II), the above-mentioned film (pA) is brought into contact with a mixed solvent containing solvent A and solvent B, the solvent is impregnated in the above-mentioned resin (pa), and the birefringence of the film (pA) along the thickness direction is changed to form film (qA).

[0029] [8] A method for manufacturing an optical film, comprising the following steps:

[0030] The process of obtaining a birefringent film by the manufacturing method described in [7]; and

[0031] Step (III) involves stretching the birefringent film.

[0032] Invention Effects

[0033] According to the present invention, a method for manufacturing a three-dimensional retardation film that can be easily manufactured and exhibits good effects is provided, a birefringent film that can be usefully used to manufacture the three-dimensional retardation film, and a method for manufacturing the birefringent film that can be easily manufactured. Detailed Implementation

[0034] 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.

[0035] In the following descriptions, unless otherwise specified, the in-plane retardation Re of layered structures such as membranes is represented by Re = (nx - ny) × d. Unless otherwise specified, the thickness retardation Rth of layered structures is represented by Rth = [{(nx + ny) / 2} - nz] × d. Unless otherwise specified, the NZ coefficient of layered structures is represented by (nx - nz) / (nx - ny).

[0036] nx represents the refractive index in the direction perpendicular to the thickness direction of the layered structure (in-plane direction) and providing the maximum refractive index. ny represents the refractive index in the aforementioned in-plane direction of the layered structure and orthogonal to the nx direction. nz represents the refractive index of the layered structure along its thickness direction. d represents the thickness of the layered structure. Unless otherwise specified, the measurement wavelength is 590 nm.

[0037] In the following description, unless otherwise stated, a material with positive intrinsic birefringence is one whose refractive index in the stretching direction is greater than that in the direction perpendicular to it. Conversely, unless otherwise stated, a material with negative intrinsic birefringence is one whose refractive index in the stretching direction is less than that in the direction perpendicular to it. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0038] In the following description, "strip" film refers to a film with a length of 5 times or more, preferably 10 times or more, relative to its width; specifically, it refers to a film with a length sufficient to be rolled up for storage or transport. There is no particular upper limit to the length, but it is typically less than 100,000 times the width.

[0039] Unless otherwise stated, the slow axis of a layered structure is an in-plane slow axis in the following description.

[0040] [Birefringent film]

[0041] The birefringent film of the present invention comprises solvent A, solvent B, and a crystalline polymer. Specifically, the birefringent film of the present invention can be a film composed of a crystalline resin having a crystalline polymer as the main component and also comprising specific amounts of various solvents as described below.

[0042] [Crystallizable polymers]

[0043] "A crystalline polymer" refers to a polymer having a melting point Tm. That is, "a crystalline polymer" means a polymer whose melting point can be observed using a differential scanning calorimeter (DSC). In the following description, a crystalline polymer is sometimes referred to as a "crystalline polymer". Resins containing a crystalline polymer as a main component can exhibit properties based on the crystalline polymer. Such resins are sometimes referred to as crystalline resins. Crystalline resins are preferably thermoplastic resins.

[0044] Crystalline polymers preferably have positive intrinsic birefringence, thus crystalline resins have positive intrinsic birefringence values. By using crystalline resins with positive intrinsic birefringence, it is particularly easy to manufacture birefringent films that satisfy the requirements of the present invention (especially the requirement of Rth ≤ -100 nm), and three-dimensional phase retardation films can be easily manufactured using such birefringent films.

[0045] The crystalline polymer is not particularly limited and can be, for example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene (PE) and polypropylene (PP), but preferably contains an alicyclic structure. By using a crystalline polymer containing an alicyclic structure, the mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and lightweight of the film can be improved. A polymer with an alicyclic structure means a polymer containing an alicyclic structure within its molecule. Such a polymer containing an alicyclic structure can be, for example, a polymer or its hydride that can be obtained by polymerization of a cyclic olefin as a monomer.

[0046] Examples of alicyclic structures include cycloalkane and cycloolefin structures. Among these, cycloalkane structures are preferred from the perspective of easily obtaining phase retardation films with excellent properties such as thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, more preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. By ensuring that the number of carbon atoms contained in one alicyclic structure is within the above range, a high balance can be achieved between mechanical strength, heat resistance, and formability.

[0047] In crystalline polymers containing alicyclic structures, the proportion of alicyclic structural units relative to all structural units is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight or more. By increasing the proportion of alicyclic structural units as described above, heat resistance can be improved. The proportion of alicyclic structural units relative to all structural units can be 100% by weight or less. Furthermore, in crystalline polymers containing alicyclic structures, the remaining portion besides the alicyclic structural units is not particularly limited and can be appropriately selected according to the intended use.

[0048] Examples of crystalline polymers containing an alicyclic structure include polymers (α) to (δ). Among them, polymer (β) is preferred from the perspective of easily obtaining a phase retardation film with excellent heat resistance.

[0049] Polymer (α): Ring-opening polymers with crystalline cyclic olefin monomers.

[0050] Polymer (β): A hydride of a crystalline polymer (α).

[0051] Polymer (γ): Addition polymers of crystalline cyclic olefin monomers.

[0052] Polymer (δ): A hydride of a crystalline polymer (γ).

[0053] Specifically, as a crystalline polymer containing an alicyclic structure, a ring-opening polymer of crystalline dicyclopentadiene and a hydride of a ring-opening polymer of crystalline dicyclopentadiene are more preferred. Among these, hydrides of ring-opening polymers of crystalline dicyclopentadiene are particularly preferred. Here, a ring-opening polymer of dicyclopentadiene refers to a polymer in which the proportion of structural units derived from dicyclopentadiene relative to all structural units is typically 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight.

[0054] The hydrides of dicyclopentadiene ring-opening polymers preferably have a high proportion of syndiotactic binomial units. Specifically, the proportion of syndiotactic binomial units in the hydrides of dicyclopentadiene ring-opening polymers is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high proportion of syndiotactic binomial units indicates high syndiotactic stereoregularity. Therefore, there is a tendency that the higher the proportion of syndiotactic binomial units, the higher the melting point of the hydrides of dicyclopentadiene ring-opening polymers.

[0055] The ratio of the two units can be based on the embodiments described later. 13 To determine this, C-NMR spectroscopy analysis was used.

[0056] The polymers (α) to (δ) described above can be obtained using the manufacturing method disclosed in International Publication No. 2018 / 062067.

[0057] The melting point Tm of the crystalline polymer is preferably 200°C or higher, more preferably 230°C or higher, and most preferably 290°C or lower. By using a crystalline polymer with such a melting point Tm, a birefringent film with an even better balance between formability and heat resistance can be obtained.

[0058] Typically, crystalline polymers possess a glass transition temperature (TgP), therefore, crystalline resins with crystalline polymers as the main component can also exhibit a glass transition temperature based on the glass transition temperature of the crystalline polymer. The TgP of crystalline polymers is typically above 85°C and below 170°C.

[0059] The glass transition temperature (TgP) and melting point (Tm) of a polymer can be determined by the following method. First, the polymer is melted by heating, and then the melted polymer is rapidly cooled with dry ice. Next, the polymer can be used as a test sample, and the glass transition temperature (TgP) and melting point (Tm) of the polymer are determined using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min (heating mode).

[0060] The weight-average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, more preferably 1,000,000 or less, and more preferably 500,000 or less. Crystalline polymers with such a weight-average molecular weight have an excellent balance between processability and heat resistance.

[0061] The molecular weight distribution (Mw / Mn) of the crystalline polymer is preferably 1.0 or more, more preferably 1.5 or more, more preferably 4.0 or less, and more preferably 3.5 or less. Here, Mn represents the number-average molecular weight. Crystalline polymers with such a molecular weight distribution exhibit excellent processability.

[0062] The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer can be determined in polystyrene equivalents by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent.

[0063] The crystallinity of the crystalline polymer contained in the membrane of the present invention is not particularly limited, but is generally above a certain level. When measuring the crystallinity of the resin containing the crystalline polymer, a specific range of crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The upper limit of crystallinity can be 100% or less. Crystallinity can be measured by X-ray diffraction.

[0064] Crystalline polymers can be used alone or in combination of two or more in any ratio.

[0065] The birefringent film of the present invention preferably contains 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of the crystalline polymer is at or above the aforementioned lower limit, the birefringence manifestation and heat resistance of the film can be improved. The upper limit of the proportion of the crystalline polymer can be 99.99% by weight or less.

[0066] [solvent]

[0067] The birefringent film of the present invention can contain solvent A and solvent B as various solvents. These solvents are typically absorbed into the film in step (II) of the manufacturing method of the present invention.

[0068] In step (II), all or part of the solvent absorbed into the membrane can penetrate into the interior of the crystalline polymer. Therefore, even after drying above the solvent's boiling point, it is difficult to easily and completely remove the solvent. Consequently, the birefringent membrane of the present invention typically contains a solvent.

[0069] For solvents A and B, their boiling points have a specific relationship. That is, the boiling point Bp(SA) (°C) of solvent A and the boiling point Bp(SB) (°C) of solvent B satisfy Bp(SA)-Bp(SB)≥5 (°C).

[0070] The temperature of Bp(SA)-Bp(SB) is 5°C or higher, preferably 10°C or higher. According to the inventors' discovery, by using solvents A and B, which have this relationship between Bp(SA) and Bp(SB), it is possible to significantly vary the birefringence of the crystalline polymer along the thickness direction to the extent that it can become a material for forming a three-dimensional retardation film, and it is also easy to remove the solvent from the film by evaporation. The upper limit of Bp(SA)-Bp(SB) is not particularly limited, and can be, for example, 100°C or lower.

[0071] When the birefringent film of the present invention contains a mixture of three or more solvents as a solvent, if two of them are solvent A and solvent B, and the above-mentioned requirements are met, it can become a birefringent film that meets the above-mentioned requirements. In this case, the total proportion of solvent A and solvent B to the total solvent is preferably 50% by weight or more, and more preferably 70% by weight or more.

[0072] The proportions of solvent A and solvent B in the total amount of solvent A and solvent B can be varied by appropriately adjusting their usage in the manufacturing process, so as to achieve the desired magnitude of birefringence change and volatility. Specifically, the weight ratio of solvent A to solvent B is preferably 3:7 to 99:1, and more preferably 4:6 to 9:1.

[0073] The total content of solvent A and solvent B in the birefringent film of the present invention is 3% by weight or less, preferably 2% by weight or less. By keeping the total content of solvent A and solvent B below the above-mentioned upper limit, it is possible to effectively suppress the undesirable phenomenon that the birefringent film deteriorates over time during use or adversely affects other components of the device on which the birefringent film is mounted. On the other hand, when the birefringent film is manufactured in a process including step (II) of the manufacturing method of the present invention, it is possible to leave 0.01% by weight or more of solvent. The lower limit of the proportion of residual solvent can also be 0.1% by weight or more.

[0074] The types, composition, and proportions of solvents in the membrane can be analyzed using appropriate analytical methods. Furthermore, the total solvent content in the membrane can be determined using thermogravimetric analysis.

[0075] The solvent contained in the birefringent film of the present invention can be an organic solvent that does not dissolve crystalline polymers. Preferred organic solvents include, for example, hydrocarbon solvents such as toluene, decahydronaphthalene, hexane, and limonene; ethers such as tetrahydrofuran; ketones such as methyl ethyl ketone; chlorobenzene; and carbon disulfide.

[0076] As particularly preferred examples of specific combinations of solvent A and solvent B, combinations of toluene and methyl ethyl ketone, and toluene and hexane, can be cited. By employing these combinations in the manufacturing process of birefringent films, birefringent films containing them can be manufactured, which can better exhibit the magnitude and volatility of the desired birefringence change, and can be easily manufactured at room temperature.

[0077] In the birefringent film of the present invention, the boiling point Bp(SA) of solvent A, the boiling point Bp(SB) of solvent B, and the glass transition temperature TgP of the crystalline polymer preferably have a specific relationship. Specifically, they preferably satisfy the relationship that Bp(SA) ≥ TgP and Bp(SB) ≤ TgP. Regarding this relationship, the value of Bp(SA) - TgP is preferably 10°C or higher, more preferably 20°C or higher. The value of TgP - Bp(SB) is preferably 5°C or higher, more preferably 10°C or higher. By satisfying this relationship, the magnitude and volatility of the desired birefringence change effect can be better manifested. The upper limit of the value of Bp(SA) - TgP is not particularly limited and can be, for example, 200°C or lower. The upper limit of the value of TgP - Bp(SB) is not particularly limited and can be, for example, 100°C or lower.

[0078] In addition to crystalline polymers and solvents, the birefringent film of the present invention can contain any other components. Examples of such components include: antioxidants such as phenolic antioxidants, phosphorus antioxidants, and sulfur antioxidants; light stabilizers such as hindered amine light stabilizers; waxes such as petroleum-based waxes, Fischer-Tropsch waxes, and polyalkylene waxes; nucleating agents such as sorbitol compounds, metal salts of organophosphates, metal salts of organocarboxylic acids, kaolin, and talc; and diaminostilbene derivatives, coumarin derivatives, and azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, benzimidazole derivatives, and benzothiazole derivatives). Fluorescent whitening agents such as biological (carbazole derivatives, pyridine derivatives, naphthalenecarboxylic acid derivatives, and imidazole derivatives); ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fiber; colorants; flame retardants; flame retardant additives; antistatic agents; plasticizers; near-infrared absorbers; slip agents; fillers; and any polymer other than crystalline polymers such as soft polymers. Any component may be used alone or in combination of two or more in any ratio.

[0079] [Optical Properties]

[0080] In the birefringent film of the present invention, the thickness retardation Rth satisfies Rth ≤ -100 nm. Rth is preferably -150 nm or less, more preferably -200 nm or less. When a film with such a small Rth is used, a three-dimensional retardation film can be easily manufactured by a simple operation (such as a single uniaxial stretching). The lower limit of Rth is not particularly limited and can be, for example, -1000 nm or more.

[0081] The in-plane retardation Re of the birefringent film of the present invention is preferably 0 nm or more, more preferably 1 nm or more, and more preferably 100 nm or less, more preferably 50 nm or less. When Rth satisfies the above conditions and Re is within the above preferred range, the effect of easily manufacturing a three-dimensional retardation film through simple operation can be further improved.

[0082] [Other physical properties]

[0083] The thickness of the birefringent film of the present invention can be appropriately adjusted to achieve the desired optical properties. The thickness of the birefringent film is preferably 10 μm or more, more preferably 15 μm or more, and more preferably 200 μm or less, more preferably 150 μm or less. Optical films used in devices such as display devices generally require a certain thickness to exhibit optical properties, but are also required to be thin due to the need for device miniaturization. The birefringent film of the present invention, by satisfying the requirements of the present invention, can become a component that facilitates the manufacture of an optical film that satisfies the desired optical properties even with a thin thickness.

[0084] In one embodiment, the birefringent film of the present invention can be a processed product of melt-extruded film. Specifically, as described in the manufacturing method of the present invention below, a film is formed by melt-extruded molding of a resin containing a crystalline polymer, and further processing thereof can yield the birefringent film of the present invention.

[0085] [Manufacturing method of birefringent film]

[0086] The birefringent film of the present invention can be manufactured by a manufacturing method comprising the following steps (I) to (II). Hereinafter, the manufacturing method of the birefringent film of the present invention will be described.

[0087] Process (I): A process of melt extruding a resin (pa) containing a crystalline polymer to obtain a film (pA).

[0088] Step (II): The process of contacting the film (pA) with a mixed solvent containing solvent A and solvent B, impregnating the solvent with resin (pa), and causing the birefringence of the film (pA) to change along the thickness direction to form film (qA).

[0089] [Process (I)]

[0090] In step (I), a resin (pa) containing a crystalline polymer is melt-extruded to form a film (pA). Specifically, the crystalline resin (pa) is melt-extruded using an extrusion apparatus equipped with a conventional extrusion die, thereby forming a strip of crystalline resin (pa) film (pA). The film-forming conditions can be appropriately adjusted according to the properties of the crystalline resin (pa). The thickness of the film (pA) formed in step (I) is not particularly limited and can be appropriately adjusted so that the thickness of the birefringent film or optical film as the product is a desired value. The film (pA) can also be an optically anisotropic film, and in particular, even in a state without optical anisotropy, the birefringent film of the present invention can be easily manufactured by supplying it to subsequent steps.

[0091] [Process (II)]

[0092] In step (II), the membrane (pA) is brought into contact with a mixed solvent containing solvent A and solvent B. Examples of the types of solvent A and solvent B, and their combinations, are described above.

[0093] The mixed solvent consists only of solvent A and solvent B, or solvent A and solvent B are the main components. The total proportion of solvent A and solvent B in the mixed solvent is preferably 50% by weight or more, more preferably 70% by weight or more.

[0094] The proportions of solvent A and solvent B in the total amount of solvent A and solvent B can be appropriately adjusted to exhibit the desired large birefringence change and volatility. Specifically, the weight ratio of solvent A to solvent B is preferably 3:7 to 99:1, and more preferably 4:6 to 9:1.

[0095] The contact in step (II) can be achieved through any operation. Examples of contact operations include spraying a mixed solvent onto the surface of the membrane (pA); coating a mixed solvent onto the surface of the membrane (pA); and immersing the membrane (pA) in a mixed solvent. From the viewpoint of facilitating continuous contact, the immersion method is preferred. However, when it is necessary to control the amount of mixed solvent used for contact by means of coating thickness, spraying and coating methods are preferred.

[0096] The temperature of the mixed solvent during contact in step (II) is arbitrary within a range that allows the mixed solvent to maintain a liquid state. Therefore, it can be set within a range above the melting point of the mixed solvent (typically above the melting point of the solvent with the highest melting point among the solvents constituting the mixed solvent) and below its boiling point (typically below the boiling point of the solvent with the lowest boiling point among the solvents constituting the mixed solvent). However, from the viewpoint of ease of operation, it is preferable that the solvents constituting the mixed solvent are a combination of substances that are all liquid at room temperature and exhibit the desired birefringence change at room temperature, and that the operation is performed at room temperature.

[0097] When the membrane (pA) is brought into contact with the mixed solvent by immersion, the contact time is preferably 0.5 seconds or more, more preferably 1.0 seconds or more, particularly preferably 5.0 seconds or more, preferably 120 seconds or less, more preferably 80 seconds or less, and particularly preferably 60 seconds or less.

[0098] When the film (pA) is brought into contact with the mixed solvent through coating with the mixed solvent, the coating thickness, calculated based on the coating area and the supply amount of the mixed solvent, can be appropriately adjusted. The coating thickness is preferably 5 μm or more, more preferably 10 μm or more, and on the other hand, it is preferably 100 μm or less.

[0099] When the contact time or coating thickness is above the aforementioned lower limit, the birefringence of the birefringent film can be effectively adjusted through contact with the mixed solvent. On the other hand, there is a tendency that even if the contact time is longer than the aforementioned upper limit or the coating thickness is thicker than the aforementioned upper limit, the adjustment amount of birefringence will not change significantly. Therefore, when the contact time or coating thickness is below the aforementioned upper limit, productivity can be improved without compromising the quality of the birefringent film.

[0100] The contact with the mixed solvent in step (II) results in a change in the thickness and birefringence of the film (pA) in the thickness direction, thus forming the film (qA). Such a change resulting from contact with the mixed solvent is difficult to achieve by simply stretching a resin used for optical films, a common method for manufacturing chromatic aberration films. Therefore, this change allows for the easy manufacture of the birefringent film of the present invention.

[0101] The result of step (II) is that the obtained film (qA) can be directly used as the birefringent film of the present invention. Alternatively, the obtained film can be further processed in any way to become the birefringent film of the present invention. As an example of any step, a step of removing the solvent adhering to the film can be included. As methods for removing the solvent, examples include drying, wiping, etc.

[0102] Because the film (qA) has undergone process (II), the refractive index in its thickness direction can change significantly from that of the film (pA). For example, the film (pA) is optically isotropic with Rth of 0 nm or close to it. In contrast, through process (II), the film (qA) can be easily obtained as a birefringent film with optical properties of Rth ≤ -100 nm, which is difficult to obtain by simply stretching the resin used to manufacture optical films, which is a common method for manufacturing phase refraction films.

[0103] [Manufacturing methods for optical films]

[0104] The method for manufacturing the optical film of the present invention includes: a step of obtaining a birefringent film by the above-described method for manufacturing a birefringent film of the present invention; and a step (III) of stretching the birefringent film. Specifically, the method for manufacturing the optical film of the present invention can be implemented by obtaining a film (qA) by steps (I) to (II) as described above and further stretching it. Through this stretching, the polymer molecules contained in the film (qA) are oriented in a direction consistent with the stretching direction. Since the film (qA) has undergone step (II), it is possible to easily obtain an optical film with optical properties that are difficult to obtain by simply stretching a resin for optical films, as is the case with conventional methods for manufacturing phase refraction films.

[0105] The stretching in step (III) can be uniaxial stretching or biaxial stretching or more. Furthermore, the stretching can be performed only once or more times. Preferably, it is a single uniaxial stretching or biaxial stretching, wherein the biaxial stretching is performed simultaneously or sequentially once in one direction and once in another direction. Because the film (qA) has undergone step (II), an optical film with optical properties that are difficult to obtain through conventional methods of manufacturing retardation films can be easily obtained through this simple stretching process.

[0106] In uniaxial stretching, the stretching can be either free-end uniaxial stretching or fixed-end uniaxial stretching. Free-end uniaxial stretching of the membrane refers to uniaxial stretching performed in a manner that allows contraction in the in-plane direction orthogonal to the stretching direction. In contrast, fixed-end uniaxial stretching refers to uniaxial stretching performed in a manner that fixes the dimension in the direction orthogonal to the stretching direction, preventing contraction in that direction (i.e., setting the stretching ratio in the direction orthogonal to the stretching direction to 1).

[0107] There are no restrictions on the stretching direction in process (III), and examples include the length direction, the width direction, and the tilt direction. Here, the tilt direction refers to the direction perpendicular to the thickness direction in which the angle with the width direction is neither 0° nor 90° (i.e., the angle with the width direction is greater than 0° and less than 90°).

[0108] In cases where a film with equivalent optical properties is to be manufactured using a method that does not involve step (III), a more complex stretching process and a more complex resin film structure are usually required, which is highly disadvantageous from the viewpoint of manufacturing efficiency. In contrast, in the manufacturing method of the present invention, an optical film can be obtained through a simpler process, which is advantageous from the viewpoint of manufacturing efficiency and product quality.

[0109] The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, more preferably 20.0 times or less, more preferably 10.0 times or less, even more preferably 5.0 times or less, and particularly preferably 2.0 times or less. The specific stretching ratio is preferably set appropriately based on factors such as the optical properties, thickness, and strength of the optical film used in the product. When the stretching ratio is above the aforementioned lower limit, a significant change in birefringence can be achieved through stretching. Furthermore, when the stretching ratio is below the aforementioned upper limit, the direction of the slow axis can be easily controlled, effectively suppressing film breakage.

[0110] The stretching temperature can be specified in accordance with the glass transition temperature (TgP) of the crystalline polymer. The stretching temperature is preferably 5°C or higher (TgP+5°C), more preferably 10°C or higher (TgP+100°C), and more preferably 90°C or lower (TgP+90°C). When the stretching temperature is above the lower limit, the film can be sufficiently softened and stretched uniformly. Furthermore, when the stretching temperature is below the upper limit, film solidification caused by the crystallization of the crystalline polymer can be suppressed, allowing for smooth stretching. Additionally, stretching can result in greater birefringence. Consequently, the haze of the resulting optical film is generally reduced, improving transparency. Moreover, by stretching at this temperature, the crystallinity of the crystalline polymer increases, making it easier to adjust the optical properties of the resulting optical film within the desired range.

[0111] Since birefringence can be changed through process (III), the NZ coefficient can be adjusted. Thus, an optical film with desired optical properties can be obtained through stretching in process (III). The film (sA) obtained as a result of process (III) can be directly used as an optical film for a product. Alternatively, the obtained film can be further processed arbitrarily to become a product. Examples of arbitrarily processed processes include heat treatment while maintaining the stretched dimensions, or a gradual reduction process to shorten the stretched dimensions, to adjust birefringence.

[0112] The optical film obtained by the manufacturing method of the optical film of the present invention has an NZ coefficient NZ(rA) that is less than 1. Specifically, it can satisfy 0 < NZ(rA) < 1. Such a film can be usefully used as a so-called three-dimensional retardation film. NZ(rA) is preferably 0.2 or more, and on the other hand, it is preferably 0.8 or less. By making NZ(rA) within this range, when the optical film is applied to a display device such as a liquid crystal display device, the effect of reducing the coloration of the display surface when viewed from an oblique direction can be particularly well displayed.

[0113] [use]

[0114] The birefringent film of the present invention and the optical film manufactured using the birefringent film of the present invention, after being processed into a desired shape such as a rectangle as needed, can be used as structural elements of optical devices such as display devices. When the birefringent film and the optical film of the present invention are used as structural elements of a display device, the display quality of the image displayed by the display device, such as viewing angle, contrast, and image quality, can be improved.

[0115] [Example]

[0116] The present invention will now be specifically described with reference to the embodiments shown below. However, the present invention is not limited to the embodiments shown below, and can be implemented in any way without departing from the scope of the claims of the present invention and its equivalents.

[0117] Unless otherwise stated, in the following instructions, "%" and "parts" refer to quantities based on weight. Furthermore, unless otherwise stated, the operations described below are performed under normal temperature and pressure conditions.

[0118] [Evaluation Method]

[0119] (Methods for determining the weight-average molecular weight Mw and number-average molecular weight Mn of polymers)

[0120] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polymer were determined using a gel permeation chromatography (GPC) system (Tosoh Corporation, "HCL-8320"), expressed as polystyrene equivalents. An H-type column (Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The measurement temperature was 40°C.

[0121] (Method for determining the hydrogenation rate of polymers)

[0122] The hydrogenation rate of the polymer is determined by the hydrogenation rate of o-dichlorobenzene-d 4 As a solvent, it passes through at 145°C. 1 The measurements were performed using H-NMR.

[0123] [Methods for determining glass transition temperature Tg and melting point Tm]

[0124] The glass transition temperature (Tg) and melting point (Tm) of the polymer were determined as follows. First, the polymer was melted by heating, and then the melted polymer was rapidly cooled with dry ice. Next, using this polymer as the test specimen, the glass transition temperature (Tg) and melting point (Tm) of the polymer were determined using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min (heating mode).

[0125] (Method for determining the ratio of syndiotactic and diunitary units in polymers)

[0126] The ratio of syndio- and diunitary units in the polymer was determined as follows. o-Dichlorobenzene-d 4 As a solvent, the polymer was processed at 200°C using inverse-gated decoupling. 13 C-NMR determination. Based on this... 13 The results of C-NMR determination, with o-dichlorobenzene-d 4 Using a peak of 127.5 ppm as the reference shift, signals from the isomeric binomial group at 43.35 ppm and from the metameric binomial group at 43.43 ppm were identified. Based on the intensity ratio of these signals, the proportion of metameric binomial groups in the polymer was determined.

[0127] (Methods for measuring the optical properties of films, such as retardation Re and Rth)

[0128] The optical properties of the film, such as the in-plane retardation Re and the thickness retardation Rth, were measured using a phase difference meter (AxoScan OPMF-1, manufactured by AXOMETRICS). The measurement wavelength was 590 nm.

[0129] (Methods for measuring membrane thickness)

[0130] The thickness of the membrane was measured using a contact thickness gauge (Mitutoyo Corporation, Code No. 543-390).

[0131] (Method for determining the total content of solvent)

[0132] For the membrane (pA), its weight was determined by thermogravimetric analysis (TGA: under nitrogen atmosphere, heating rate 10℃ / min, 30℃~300℃). The weight W of the membrane (pA) at 30℃ was... O (30℃) minus the weight W of the membrane at 300℃ O (300℃), calculate the weight of the membrane at 300℃ minus ΔW. O The membranes (pA) used in the examples and comparative examples described later are manufactured by melt extrusion and therefore do not contain solvents. As a result, the weight of the membrane (pA) used is reduced by a small amount ΔW. O It is used as a reference in equation (X) described later.

[0133] Furthermore, the membrane of the test object was weighed using thermogravimetric analysis (TGA: under nitrogen atmosphere, heating rate 10°C / min, 30°C–300°C) in the same manner as described above. The weight W of the membrane at 30°C was determined. R (30℃) minus the weight W of the membrane at 300℃ R (300℃), calculate the weight of the membrane at 300℃ minus ΔW. R .

[0134] The following formula (X) is used to reduce the weight of the membrane (pA) at 300°C by ΔW. O The weight of the membrane measured at 300℃ is reduced by ΔW. R Calculate the total solvent content of the membrane.

[0135] Total solvent content (%) = {(ΔW)} R -ΔW o ) / W R (30℃)}×100 (X) [Manufacturing Example 1. Manufacturing of a crystalline resin containing a hydride of a ring-opening polymer of dicyclopentadiene]

[0136] After thoroughly drying the metal pressure reactor, nitrogen replacement was performed. A 70% cyclohexane solution (30 parts of dicyclopentadiene) containing 154.5 parts of cyclohexane, 42.8 parts of dicyclopentadiene (with an endosome content of over 99%), and 1.9 parts of 1-hexene were added to the metal pressure reactor, and the mixture was heated to 53°C.

[0137] A solution was prepared by dissolving 0.014 parts of tungsten tetrachloride benzoimide (tetrahydrofuran) coordination compound in 0.70 parts of toluene. A catalyst solution was prepared by adding 0.061 parts of a 19% diethylethoxide aluminum / n-hexane solution to this solution and stirring for 10 minutes. This catalyst solution was then added to a pressure reactor to initiate a ring-opening polymerization reaction. The reaction was then carried out at 53°C for 4 hours to obtain a solution of the ring-opening polymer of dicyclopentadiene. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained ring-opening polymer of dicyclopentadiene were 8750 and 28100, respectively, resulting in a molecular weight distribution (Mw / Mn) of 3.21.

[0138] To a solution of 200 parts of the obtained dicyclopentadiene ring-opening polymer, 0.037 parts of 1,2-ethylene glycol as a terminator were added, and the mixture was heated to 60°C and stirred for 1 hour to terminate the polymerization reaction. Then, 1 part of a hydrotalcite-like compound (manufactured by Kyowa Chemical Industry Co., Ltd., "Kyoward (registered trademark) 2000") was added, and the mixture was heated to 60°C and stirred for 1 hour. Next, 0.4 parts of a filter aid (manufactured by Showa Chemical Industry Co., Ltd., "Radiolite (registered trademark) #1500") was added, and the adsorbent and solution were separated by filtration using a polypropylene pleated cartridge filter (manufactured by ADVANTEC Toyo Co., Ltd., "TCP-HX").

[0139] 100 parts of cyclohexane and 0.0043 parts of ruthenium hydrochlorocarbonyltris(triphenylphosphine) were added to a solution of 200 parts of filtered dicyclopentadiene ring-opening polymer (polymer amount 30 parts). The mixture was then subjected to a hydrogenation reaction at 6 MPa and 180 °C for 4 hours. This yielded a reaction solution containing a hydride of the dicyclopentadiene ring-opening polymer. In this reaction solution, the hydride precipitates, forming a slurry solution.

[0140] The hydrides contained in the above reaction solution were separated from the solution using a centrifuge. The solution was then dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a crystalline dicyclopentadiene ring-opening polymer hydride. This hydride had a hydrogenation rate of over 99%, a glass transition temperature (TgP) of 93°C, a melting point (Mp) of 262°C, and a binomial proportion of 89%.

[0141] To 100 parts of the obtained dicyclopentadiene ring-opening polymer hydride, 1.1 parts of an antioxidant (tetra[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane, manufactured by BASF Japan, "Irganox (registered trademark) 1010") was mixed and added to a biaxial extruder (product name "TEM-37B", manufactured by Toshiba Machine Co., Ltd.) with four die orifices of 3 mm Φ. After the mixture of the dicyclopentadiene ring-opening polymer hydride and the antioxidant was formed into a strand by hot melt extrusion molding, it was shredded in a wire cutter to obtain granular crystalline resin (PA). The operating conditions of the above-mentioned biaxial extruder are as follows.

[0142] • Set cylinder temperature = 270~280℃

[0143] • Die head set temperature = 250℃

[0144] Screw speed = 145 rpm

[0145] [Example 1]

[0146] (1-1. Process (I): Manufacturing of membrane (pA))

[0147] The crystalline resin (pa) manufactured in Manufacturing Example 1 was formed using a hot melt extrusion film forming machine (Optical Control Systems "Measuring Extruder Type Me-20 / 2800V3") with a T-die, and wound into a roll at a speed of 1.5 m / min to obtain a strip film (pA) with a width of approximately 120 mm (thickness of 50 μm). The operating conditions of the film forming machine described above are as follows.

[0148] • Set cylinder temperature = 280℃~300℃

[0149] • Die head temperature = 270℃

[0150] Screw speed = 30 rpm

[0151] • Casting roll temperature = 80℃

[0152] (1-2. Process (II): Contact between the membrane (pA) and the mixed solvent)

[0153] The film (pA) was cut into 100mm × 100mm pieces to form rectangular films (pA). The optical properties of the film (pA) were measured. The in-plane retardation Re of the film (pA) was 5nm, and the thickness retardation Rth was 6nm. As described above, this resin film was manufactured by hot melt extrusion at high temperature (280℃~300℃), therefore it was assumed that the resin film did not contain solvent, and its solvent content was taken as 0.0%.

[0154] Mixed solvent M1 was prepared by mixing toluene (boiling point Bp(SA) = 110.6℃) and methyl ethyl ketone (boiling point Bp(SB) = 79.6℃) in a 1:1 (weight ratio).

[0155] Fill a flat-bottomed square dish (vat) with mixed solvent M1, and immerse a rectangular film (pA) in it for 5 seconds. Then, remove the film (pA) from the mixed solvent M1, wipe off the solvent on the surface of the film with gauze, and dry it in a drying oven at 90°C for 1 minute to obtain a birefringent film (qA).

[0156] The optical and physical properties of the birefringent film (qA) were evaluated. The birefringent film (qA) has an in-plane retardation Re of 18 nm, a thickness retardation Rth of -292 nm, a thickness of 64 μm, a crystallinity of 13%, and a total solvent content of 2%.

[0157] [Example 2]

[0158] Mixed solvent M2 was prepared by mixing toluene and n-hexane (boiling point Bp(SB) = 68.7℃) in a 1:1 (weight ratio).

[0159] Using mixed solvent M2 instead of mixed solvent M1, a birefringent film (qA) was obtained and evaluated through the same procedures as in Example 1. The birefringent film (qA) had an in-plane retardation Re of 18 nm, a thickness retardation Rth of -354 nm, a thickness of 64 μm, a crystallinity of 14%, and a total solvent content of 1.7%.

[0160] [Comparative Example 1]

[0161] Using toluene instead of the mixed solvent M1, a birefringent film (qA) was obtained and evaluated through the same procedures as in Example 1. The birefringent film (qA) had an in-plane retardation Re of 20 nm, a thickness retardation Rth of -575 nm, a thickness of 64 μm, a crystallinity of 15%, and a total solvent content of 6.2%.

[0162] [Comparative Example 2]

[0163] Using methyl ethyl ketone instead of the mixed solvent M1, a birefringent film (qA) was obtained and evaluated through the same procedures as in Example 1. The birefringent film (qA) had an in-plane retardation Re of 12 nm, a thickness retardation Rth of -17 nm, a thickness of 64 μm, a crystallinity of 3%, and a total solvent content of 0.8%.

[0164] The summary and evaluation results of Examples 1-2 and Comparative Examples 1-2 are shown in Table 1 below.

[0165] [Table 1]

[0166] Table 1

[0167]

[0168] [Example 3]

[0169] A stretching apparatus (manufactured by ETO Corporation, "SDR-562Z") is prepared. This stretching apparatus includes an oven and clamps capable of holding the ends of a rectangular resin film. A total of 24 clamps are provided, with 5 clamps on each side of the resin film and 1 clamp at each vertex of the resin film. The resin film can be stretched by moving these clamps. In addition, two ovens are provided, and the stretching temperature and heat treatment temperature can be set separately. Furthermore, in this stretching apparatus, the movement of the resin film from one oven to another can be performed directly while it is held by the clamps.

[0170] The birefringent film (qA) obtained in Example 1 was installed in a stretching apparatus and preheated to 110°C for 10 seconds. Then, the birefringent film (qA) was stretched at a stretching temperature of 110°C, a longitudinal stretching ratio of 1, a transverse stretching ratio of 1.5, and a stretching speed of 1.5 times / 10 seconds. The "longitudinal stretching ratio" refers to the stretching ratio in the direction aligned with the long side of the strip of raw material film, and the "transverse stretching ratio" refers to the stretching ratio in the direction aligned with the width of the strip of raw material film. Thus, the birefringent film (qA) was stretched to obtain an optical film (rA).

[0171] The optical properties and physical properties of the optical film (rA) were evaluated. The in-plane retardation Re of the optical film (rA) is 347 nm, the thickness retardation Rth is -12 nm, the thickness is 47 μm, and the crystallinity is 18%.

[0172] As can be clearly seen from the results of the examples and comparative examples, the manufacturing method according to the present invention takes into account both the magnitude of the effect of birefringence change and volatility, and as a result, it is possible to easily manufacture a film that exhibits good performance as a component for manufacturing three-dimensional phase difference films.

Claims

1. A birefringent film comprising solvent A, solvent B, and a crystalline polymer, The boiling point Bp(SA) (°C) of solvent A and the boiling point Bp(SB) (°C) of solvent B satisfy Bp(SA)-Bp(SB)≥5. The combined content of solvent A and solvent B in the birefringent film is more than 0.01% by weight and less than 3% by weight. The birefringent film satisfies Rth ≤ -100nm The weight ratio of solvent A to solvent B is 3:7 to 99:

1.

2. The birefringent film according to claim 1, wherein, The birefringent film is a processed product of melt-extruded film.

3. The birefringent film according to claim 1 or 2, wherein, The crystalline polymer has a positive inherent birefringence value.

4. The birefringent film according to claim 1 or 2, wherein, The crystalline polymer contains an alicyclic structure.

5. The birefringent film according to claim 1 or 2, wherein, The crystallinity obtained by X-ray diffraction is above 10%.

6. The birefringent film according to claim 1 or 2, wherein, The boiling point Bp(SA) of solvent A, the boiling point Bp(SB) of solvent B, and the glass transition temperature TgP of the polymer satisfy the relationships Bp(SA)≥TgP and Bp(SB)≤TgP.

7. A manufacturing method for the birefringent film according to any one of claims 1 to 6, the manufacturing method comprising the following steps: Step (I) involves melt-extruding a resin (pa) containing a crystalline polymer into a film to obtain a film (pA); and In step (II), the film (pA) is contacted with a mixed solvent containing solvent A and solvent B in a weight ratio of 3:7 to 99:1, the mixed solvent is impregnated in the resin (pa), and the birefringence of the film (pA) along the thickness direction is changed to form film (qA).

8. A method for manufacturing an optical film, comprising the following steps: The process of obtaining a birefringent film by the manufacturing method according to claim 7; and Step (III) involves stretching the birefringent film.

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