Phase difference film

Abstract

To provide a retardation film with an NZ coefficient less than 1.0 and a low haze.SOLUTION: A retardation film formed of a resin containing a crystalline polymer is provided. The crystalline polymer contains an alicyclic structure, and has an NZ coefficient of less than 1.0, a haze of less than 1.0%, and either an in-plane birefringence Re / d of 1.0×10-3 or greater, or an absolute value |Rth / d| of a thickness-direction birefringence of 1.0×10-3 or greater.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a phase difference film and a method for manufacturing the same. [Background technology]

[0002] Conventional technologies for manufacturing films using resins have been proposed (Patent Documents 1-3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 02-64141 [Patent Document 2] Japanese Patent Publication No. 2016-26909 [Patent Document 3] International Publication No. 2017 / 065222 [Overview of the project] [Problems that the invention aims to solve]

[0004] One type of film manufactured using resin is a phase difference film. Since phase difference films have retardation in at least one of the in-plane direction and the thickness direction, they are generally required to have large birefringence in at least one of the in-plane direction and the thickness direction.

[0005] The balance between birefringence in the in-plane direction and birefringence in the thickness direction can be expressed by the NZ coefficient. For example, if a phase difference film with an NZ coefficient of less than 1.0 is obtained, it becomes possible to improve the display quality of a display device, such as the viewing angle, contrast, and image quality, using that phase difference film.

[0006] A method for producing a retardation film with an NZ coefficient of less than 1.0 has been conventionally known. However, with the conventional production methods, it has been impossible to easily produce a retardation film with an NZ coefficient of less than 1.0. For example, with the conventional production methods, it has been necessary to combine stretching and shrinking of the film, or to use a film having a plurality of layers with precisely adjusted thicknesses. Therefore, since the number of control items and the number of steps increase, the production method has tended to become complicated.

[0007] In addition, since a retardation film is a type of optical film, it is usually required to have a small haze. However, among retardation films with an NZ coefficient of less than 1.0, those with particularly small haze have been difficult to produce by conventional techniques. Therefore, there has been a demand for a technique for realizing a retardation film with an NZ coefficient of less than 1.0 and a small haze, regardless of whether the production method is simple.

[0008] The present invention was devised in view of the above problems, and an object thereof is to provide a retardation film having an NZ coefficient of less than 1.0 and a small haze; and a production method capable of easily producing a retardation film having an NZ coefficient of less than 1.0.

Means for Solving the Problems

[0009] The present inventor diligently studied to solve the above problems. As a result, the present inventor found that, according to a method including a first step of preparing an optically isotropic resin film formed of a resin containing a crystalline polymer, and a second step of bringing this resin film into contact with an organic solvent to change the birefringence in the thickness direction, a retardation film with an NZ coefficient of less than 1.0 can be easily produced. Furthermore, the present inventor found that, according to this production method, a retardation film with an NZ coefficient of less than 1.0 and a small haze can be realized. Based on these findings, the present inventor completed the present invention. That is, the present invention includes the following.

[0010] 〔1〕 Formed of a resin containing a crystalline polymer, The NZ coefficient is less than 1.0, and Phase contrast film with haze of less than 1.0%. [2] The phase difference film according to [1], wherein the NZ coefficient of the phase difference film is greater than 0.0 and less than 1.0. [3] The phase difference film according to [1] or [2], wherein the phase difference film contains an organic solvent. [4] The phase difference film according to [3], wherein the organic solvent is a hydrocarbon solvent. [5] The phase difference film according to any one of [1] to [4], wherein the crystalline polymer contains an alicyclic structure. [6] The phase difference film according to any one of [1] to [5], wherein the crystalline polymer is a hydride of a ring-opening polymer of dicyclopentadiene. [7] A first step of preparing an optically isotropic resin film formed from a resin containing a crystalline polymer, A method for manufacturing a phase difference film, comprising a second step of contacting the resin film with an organic solvent to change its birefringence in the thickness direction. [8] A method for manufacturing a phase difference film according to [7], comprising a third step of stretching the resin film after the second step. [9] The method for producing a phase difference film according to [7] or [8], wherein the organic solvent is a hydrocarbon solvent.

[10] A method for producing a phase difference film according to any one of [7] to [9], wherein the crystalline polymer contains an alicyclic structure.

[11] The method for producing a phase difference film according to any one of [7] to

[10] , wherein the crystalline polymer is a hydride of a ring-opening polymer of dicyclopentadiene. [Effects of the Invention]

[0011] The present invention provides a phase difference film having an NZ coefficient of less than 1.0 and low haze, as well as a manufacturing method for easily producing a phase difference film having an NZ coefficient of less than 1.0. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be modified and implemented as appropriate without departing from the scope of the claims and equivalents of the present invention.

[0013] In the following explanation, the in-plane retardation Re of the film is given by the value Re = (nx - ny) × d unless otherwise specified. Also, the birefringence in the in-plane direction of the film is given by the value (nx - ny) unless otherwise specified, and therefore expressed as Re / d. Furthermore, the retardation Rth in the thickness direction of the film is given by the value Rth = [{(nx + ny) / 2} - nz] × d unless otherwise specified. Also, the birefringence in the thickness direction of the film is given by the value [{(nx + ny) / 2} - nz] unless otherwise specified, and therefore expressed as Rth / d. Furthermore, the NZ coefficient of the film is given by the value (nx - nz) / (nx - ny) unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the aforementioned in-plane direction of the film that is perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of the film. 'd' represents the film thickness. The measurement wavelength is 590 nm unless otherwise specified.

[0014] In the following explanation, unless otherwise specified, a material with positive intrinsic birefringence means a material whose refractive index in the stretching direction is greater than its refractive index in the direction perpendicular to it. Similarly, unless otherwise specified, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is less than its refractive index in the direction perpendicular to it. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0015] In the following description, "long film" refers to a film having a length of five times or more its width, preferably 10 times or more its width, and specifically a film long enough to be rolled up for storage or transport. There is no particular upper limit on the length, but it is usually 100,000 times or less its width.

[0016] In the following description, the terms "parallel," "perpendicular," and "orthogonal" of the elements may include errors within a range that does not impair the effects of the present invention, for example, within a range of ±5°, unless otherwise specified.

[0017] In the following description, the longitudinal direction of a long film is usually parallel to the film transport direction in the manufacturing line. The MD direction (machine direction) is the film transport direction in the manufacturing line and is usually parallel to the longitudinal direction of a long film. Furthermore, the TD direction (transverse direction) is the direction parallel to the film surface and perpendicular to the MD direction, and is usually parallel to the width direction of a long film.

[0018] [1. Overview of the phase difference film according to the first embodiment] The phase difference film according to the first embodiment of the present invention is formed from a resin containing a crystalline polymer, has an NZ coefficient of less than 1.0, and exhibits low haze. Such a phase difference film could not be realized with conventional technology, but has been realized for the first time with the present invention. By providing this phase difference film in, for example, a display device, it is possible to improve the clarity of the image displayed on the display device while also improving display quality such as viewing angle, contrast, and image quality.

[0019] Conventionally, there has been a need for technical means to improve display quality while increasing the clarity of images displayed on display devices, but it has been difficult to materialize such technical means. In one respect, the phase difference film according to the first embodiment can be said to be the first to achieve the materialization of the aforementioned technical means.

[0020] [2. Crystalline resin contained in phase difference film] The phase difference film according to the first embodiment is formed of a resin containing a crystalline polymer. "Crystalline polymer" refers to a polymer having a melting point Tm. That is, "crystalline polymer" refers to a polymer whose melting point can be observed using a differential scanning calorimeter (DSC). In the following description, a crystalline polymer may be referred to as a "crystalline polymer." Furthermore, a resin containing a crystalline polymer may be referred to as a "crystalline resin." This crystalline resin is preferably a thermoplastic resin.

[0021] Crystalline polymers are preferably positive intrinsic birefringence. By using crystalline polymers with positive intrinsic birefringence, phase difference films with an NZ coefficient of less than 1.0 can be easily manufactured.

[0022] Crystalline polymers preferably contain alicyclic structures. By using crystalline polymers containing alicyclic structures, the mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and lightweight properties of the phase difference film can be improved. A polymer containing an alicyclic structure refers to a polymer that has an alicyclic structure within its molecule. Such polymers containing alicyclic structures may be polymers or hydrides obtained by polymerization reactions using cyclic olefins as monomers, for example.

[0023] Examples of alicyclic structures include cycloalkane and cycloalkene structures. Among these, cycloalkane structures are preferred because they easily yield phase difference films with excellent properties such as thermal stability. The number of carbon atoms in a single alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. By having the number of carbon atoms in a single alicyclic structure within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

[0024] In a crystalline polymer containing an alicyclic structure, the proportion of structural units having an alicyclic structure 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 structural units having an alicyclic structure as described above, heat resistance can be improved. The proportion of structural units having an alicyclic structure to all structural units may be 100% by weight or less. Furthermore, in a crystalline polymer containing an alicyclic structure, the remainder other than structural units having an alicyclic structure is not particularly limited and can be appropriately selected according to the intended use.

[0025] Examples of crystalline polymers containing an alicyclic structure include polymers (α) to (δ) listed below. Among these, polymer (β) is preferred because it is easier to obtain a phase difference film with excellent heat resistance. Polymer (α): A ring-opening polymer of a cyclic olefin monomer that is crystalline. Polymer (β): A hydride of polymer (α) that is crystalline. Polymer (γ): An addition polymer of cyclic olefin monomers that is crystalline. Polymer (δ): A hydride of polymer (γ) that is crystalline.

[0026] Specifically, as crystalline polymers containing an alicyclic structure, ring-opened polymers of dicyclopentadiene that are crystalline, and hydrides of ring-opened polymers of dicyclopentadiene that are crystalline are more preferred. Among these, hydrides of ring-opened polymers of dicyclopentadiene that are crystalline are particularly preferred. Here, a ring-opened polymer of dicyclopentadiene refers to a polymer in which the proportion of structural units derived from dicyclopentadiene to the total structural units is usually 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.

[0027] The hydride of a ring-opening polymer of dicyclopentadiene preferably has a high proportion of racemo-dyads. Specifically, the proportion of racemo-dyads in the repeating units of the hydride of a ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high proportion of racemo-dyads indicates high syndiotactic stereoregularity. Therefore, the higher the proportion of racemo-dyads, the higher the melting point of the hydride of the ring-opening polymer of dicyclopentadiene tends to be. The proportion of the racemo dyad is described in the examples below. 13 It can be determined by analyzing the C-NMR spectrum.

[0028] As the polymers (α) to polymers (δ) mentioned above, polymers obtained by the manufacturing method disclosed in International Publication No. 2018 / 062067 may be used.

[0029] The melting point Tm of the crystalline polymer is preferably 200°C or higher, more preferably 230°C or higher, and preferably 290°C or lower. By using a crystalline polymer having such a melting point Tm, a phase difference film with an even better balance of moldability and heat resistance can be obtained.

[0030] Typically, crystalline polymers have a glass transition temperature (Tg). While the specific glass transition temperature (Tg) of a crystalline polymer is not particularly limited, it is usually between 85°C and 170°C.

[0031] The glass transition temperature (Tg) and melting point (Tm) of a polymer can be measured by the following method. First, the polymer is melted by heating, and the molten polymer is rapidly cooled with dry ice. Then, using this polymer as a test specimen, the glass transition temperature (Tg) and melting point (Tm) of the polymer can be measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode).

[0032] The weight-average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, preferably 1,000,000 or less, and more preferably 500,000 or less. Crystalline polymers having such a weight-average molecular weight offer an excellent balance between moldability and heat resistance.

[0033] The molecular weight distribution (Mw / Mn) of the crystalline polymer is preferably 1.0 or higher, more preferably 1.5 or higher, preferably 4.0 or lower, and more preferably 3.5 or lower. Here, Mn represents the number-average molecular weight. Crystalline polymers having such a molecular weight distribution exhibit excellent moldability.

[0034] The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of a polymer can be measured as polystyrene equivalent values ​​by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent.

[0035] There are no particular restrictions on the degree of crystallinity of the crystalline polymer contained in the phase difference film, but it is usually above a certain level. The specific range of crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The degree of crystallinity of crystalline polymers can be measured by X-ray diffraction.

[0036] Crystalline polymers may be used individually or in combination of two or more types in any ratio.

[0037] The proportion of crystalline polymer in the crystalline resin is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of crystalline polymer is above the lower limit of the above range, the birefringence and heat resistance of the phase difference film can be improved. The upper limit of the proportion of crystalline polymer may be 100% by weight or less.

[0038] Crystalline resins may contain optional components in addition to the crystalline polymer. These optional components include, for example, antioxidants such as phenolic antioxidants, phosphorus antioxidants, and sulfur antioxidants; light stabilizers such as hindered amine light stabilizers; waxes such as petroleum waxes, Fischer-Tropsch waxes, and polyalkylene waxes; nucleating agents such as sorbitol compounds, metal salts of organic phosphoric acids, metal salts of organic carboxylic acids, kaolin, and talc; diaminostilbene derivatives, coumarin derivatives, and azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, benzimi). Examples include fluorescent whitening agents such as dazole derivatives and benzothiasol derivatives, carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolon 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 fibers; colorants; flame retardants; flame retardant additives; antistatic agents; plasticizers; near-infrared absorbers; lubricants; 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.

[0039] [3. NZ coefficient of phase difference film] The NZ coefficient of the phase difference film according to the first embodiment of the present invention is typically less than 1.0. When a phase difference film having an NZ coefficient of less than 1.0 is installed in a display device, it is possible to improve the display quality of the display device, such as the viewing angle, contrast, and image quality.

[0040] The specific value of the NZ coefficient of the phase difference film can be arbitrary depending on the application of the phase difference film, and may be, for example, less than 0.8, less than 0.6, or less than 0.4. The lower limit of the NZ coefficient of the phase difference film is arbitrary, and may be, for example, greater than -1000, greater than -500, greater than -100, greater than -40, or greater than -20. In particular, since manufacturing using conventional technology has been especially difficult, it is preferable that the NZ coefficient of the phase difference film be greater than 0.0.

[0041] The NZ coefficient of a film can be calculated from the in-plane retardation Re and the thickness-direction retardation Rth of the film.

[0042] [4. Haze in phase-contrast film] The haze of the phase difference film according to the first embodiment of the present invention is typically less than 1.0%, preferably less than 0.8%, more preferably less than 0.5%, and ideally 0.0%. A phase difference film with such low haze can improve the clarity of images displayed on a display device when installed in that device.

[0043] The haze of the film can be measured using a haze meter (for example, the "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

[0044] [5. Organic solvents contained in phase contrast films] The phase difference film according to the first embodiment of the present invention may contain an organic solvent. This organic solvent is typically incorporated into the film in the second step of the manufacturing method described in the second embodiment.

[0045] In the second step, all or part of the organic solvent incorporated into the film may penetrate into the polymer. Therefore, even if drying is performed at a temperature above the boiling point of the organic solvent, it is difficult to completely remove the solvent. Consequently, phase contrast films typically contain organic solvents.

[0046] As the aforementioned organic solvent, one that does not dissolve crystalline polymers may be used. Preferred organic solvents include, for example, hydrocarbon solvents such as toluene, limonene, and decalin; and carbon disulfide. The organic solvent may be one type or two or more types.

[0047] The ratio of organic solvent contained in the phase difference film to 100% of the phase difference film's weight (solvent content) is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 0.1% by weight or less.

[0048] The solvent content of the retardation film can be measured by the measuring method described in the examples.

[0049] [6. Other properties of the retardation film] The retardation film usually has a large birefringence in at least one of the in-plane direction and the thickness direction. Specifically, the retardation film usually has a birefringence Re / d in the in-plane direction of 1.0×10 -3 or more, and an absolute value of birefringence |Rth / d| in the thickness direction of 1.0×10 -3 or more.

[0050] Specifically, the birefringence Re / d in the in-plane direction of the retardation film is usually 1.0×10 -3 or more, preferably 3.0×10 -3 or more, particularly preferably 5.0×10 -3 or more. There is no upper limit, for example, it may be 2.0×10 -2 or less, 1.5×10 -2 or less, or 1.0×10 -2 or less. However, when the absolute value of birefringence |Rth / d| in the thickness direction of the retardation film is 1.0×10 -3 or more, the birefringence Re / d in the in-plane direction of the retardation film may be outside the above range.

[0051] Also, the absolute value of birefringence |Rth / d| in the thickness direction of the retardation film is usually 1.0×10 -3 or more, preferably 3.0×10 -3 or more, particularly preferably 5.0×10 -3 or more. There is no upper limit, for example, it may be 2.0×10 -2 or less, 1.5×10 -2 or less, or 1.0×10 -2 or less. However, when the birefringence Re / d in the in-plane direction of the retardation film is 1.0×10 -3 or more, the absolute value of birefringence |Rth / d| in the thickness direction of the retardation film may be outside the above range.

[0052] The in-plane retardation Re value of a phase difference film can be set according to the application of the phase difference film. The specific in-plane retardation Re of the phase difference film may be, for example, preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 3 nm or less. In this case, the phase difference film can function as a positive C plate or a negative C plate.

[0053] Furthermore, the specific in-plane retardation Re of the phase difference film may be, for example, preferably 100 nm or more, more preferably 110 nm or more, particularly preferably 120 nm or more, and also preferably 180 nm or less, more preferably 170 nm or less, particularly preferably 160 nm or less. In this case, the phase difference film can function as a quarter-wave plate.

[0054] Furthermore, the specific in-plane retardation Re of the phase difference film may be, for example, preferably 245 nm or more, more preferably 265 nm or more, particularly preferably 270 nm or more, and also preferably 320 nm or less, more preferably 300 nm or less, particularly preferably 295 nm or less. In this case, the phase difference film can function as a half-wave plate.

[0055] The value of the retardation Rth in the thickness direction of the phase difference film can be set according to the application of the phase difference film. The specific retardation Rth in the thickness direction of the phase difference film is preferably 200 nm or more, more preferably 250 nm or more, and particularly preferably 300 nm or more. The upper limit may be 10,000 nm or less.

[0056] Film retardation can be measured using a phase difference meter (for example, the "AxoScan OPMF-1" from AXOMETRICS).

[0057] Since the phase difference film is an optical film, it is preferable that it has high transparency. The specific total light transmittance of the phase difference film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The total light transmittance of the phase difference film can be measured using an ultraviolet-visible spectrometer in the wavelength range of 400 nm to 700 nm.

[0058] The thickness d of the phase difference film can be appropriately set according to the application of the phase difference film. The specific thickness d of the phase difference film is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 20 μm or more, preferably 200 μm or less, more preferably 100 μm or less, and particularly preferably 50 μm or less. When the thickness d of the phase difference film is above the lower limit of the above range, handling properties can be improved and strength can be increased. Also, when the thickness d of the phase difference film is below the upper limit, winding of long lengths of phase difference film is easy.

[0059] The phase difference film may be a single-fed film or a long-length film.

[0060] The phase difference film according to the first embodiment described above can be manufactured by the manufacturing method described in the second embodiment later.

[0061] [7. Overview of the manufacturing method for phase difference film according to the second embodiment] A method for manufacturing a phase difference film according to a second embodiment of the present invention includes: a first step of preparing an optically isotropic resin film formed from a crystalline resin containing a crystalline polymer; and a second step of contacting this resin film with an organic solvent to change its birefringence in the thickness direction. In this manufacturing method, the NZ coefficient of the resin film can be adjusted in the second step, so that a phase difference film having an NZ coefficient of less than 1.0 can be easily manufactured.

[0062] The inventors surmise that the mechanism by which this manufacturing method yields a phase difference film having an NZ coefficient of less than 1.0 is as follows. However, the technical scope of the present invention is not limited by the mechanism described below.

[0063] When an optically isotropic resin film formed from a crystalline resin is brought into contact with an organic solvent in the second step, the organic solvent penetrates into the resin film. The action of the penetrating organic solvent causes micro-Brownian motion in the molecules of the crystalline polymer within the film, and the molecular chains of the film become oriented. According to the inventors' research, it is possible that solvent-induced crystallization of the crystalline polymer may occur during this molecular chain orientation.

[0064] Incidentally, the surface area of ​​the resin film is larger on the front and back surfaces, which are the main surfaces. Therefore, the penetration rate of the organic solvent is greater in the thickness direction, passing through the front or back surface. Consequently, the orientation of the molecules of the crystalline polymer can proceed so that the molecules of the polymer are oriented in the thickness direction.

[0065] The orientation of the crystalline polymer molecules in the thickness direction in this manner adjusts the NZ coefficient of the resin film. Therefore, the resin film after contact with the organic solvent can be obtained as a phase difference film having an NZ coefficient of less than 1.0. The ability to adjust the NZ coefficient simply by bringing an optically isotropic resin film into contact with an organic solvent is useful in facilitating the manufacture of phase difference films.

[0066] The method for manufacturing a phase difference film according to the second embodiment of the present invention may include any additional steps in combination with the first and second steps described above. For example, the method for manufacturing a phase difference film may include a third step of stretching the resin film after the second step, or a fourth step of heat-treating the resin film after the second step. When these optional steps are performed, a phase difference film can be obtained as a resin film whose properties have been adjusted by these optional steps.

[0067] [8. First step: Preparing the resin film] In the first step, an optically isotropic resin film is prepared, which is made of a crystalline resin containing a crystalline polymer. In the following explanation, the resin film before contact with the organic solvent in the second step may be referred to as the "raw film" as appropriate.

[0068] The crystalline resin used as the material for the optically isotropic base film prepared in the first step may be the same as the crystalline resin described in the first embodiment. However, it is preferable that the degree of crystallinity of the crystalline polymer contained in the base film is low. Specifically, the degree of crystallinity is preferably less than 10%, more preferably less than 5%, and particularly preferably less than 3%. If the degree of crystallinity of the crystalline polymer contained in the base film before contact with the organic solvent is low, many molecules of the crystalline polymer can be oriented in the thickness direction by contact with the organic solvent, making it possible to adjust the NZ coefficient over a wide range.

[0069] The base film is an optically isotropic resin film. That is, the base film is a film with a small in-plane birefringence Re / d and a small absolute value of birefringence |Rth / d| in the thickness direction. Specifically, the in-plane birefringence Re / d of the base film is usually 1.0 × 10⁻⁶. -3 Less than 0.5 × 10 -3 Less than, more preferably 0.3 × 10 -3 It is less than . Also, the absolute value of the birefringence in the thickness direction of the raw film |Rth / d| is usually 1.0 × 10 -3 Less than 0.5 × 10 -3 Less than, more preferably 0.3 × 10 -3It is less than [value missing]. Having optical isotropy in this way indicates that the orientation of the molecules of the crystalline polymer contained in the base film is low, and that it is substantially in an unoriented state. When such an optically isotropic resin film is used as the base film, precise control of the optical properties of the base film is unnecessary, and therefore precise control of the orientation of the molecules of the crystalline polymer is unnecessary, thus simplifying the manufacturing method of the phase difference film. Furthermore, when an optically isotropic resin film is used as the base film, a phase difference film with low haze can usually be obtained.

[0070] The base film preferably has a low organic solvent content, and more preferably does not contain any organic solvent. The ratio of organic solvent contained in the base film to 100% of its weight (solvent content) is preferably 1% or less, more preferably 0.5% or less, particularly preferably 0.1% or less, and ideally 0.0%. By having a small amount of organic solvent in the base film before contact with the organic solvent, many crystalline polymer molecules can be oriented in the thickness direction upon contact with the organic solvent, thus enabling adjustment of the NZ coefficient over a wide range.

[0071] The solvent content of the raw film can be measured by its density.

[0072] The haze of the raw film is preferably less than 1.0%, preferably less than 0.8%, more preferably less than 0.5%, and ideally 0.0%. The smaller the haze of the raw film, the easier it is to reduce the haze of the resulting phase difference film.

[0073] The thickness of the base film is preferably set according to the thickness of the phase difference film to be manufactured. Typically, the thickness increases when the film is brought into contact with an organic solvent in the second step. On the other hand, if stretching is performed in the third step, the thickness decreases due to the stretching. Therefore, the thickness of the base film may be set considering the changes in thickness in the steps from the second step onward as described above.

[0074] The raw film roll may be a single-sheet film, but a long roll of film is preferable. By using a long roll of raw film, continuous production of phase difference film by the roll-to-roll method is possible, thereby effectively increasing the productivity of phase difference film.

[0075] As a method for manufacturing the raw film, resin molding methods such as injection molding, extrusion molding, press molding, inflation molding, blow molding, calendering, casting, and compression molding are preferred because they yield a raw film that does not contain organic solvents. Among these, extrusion molding is preferred because it allows for easy control of the thickness.

[0076] The manufacturing conditions in the extrusion molding method are preferably as follows: The cylinder temperature (molten resin temperature) is preferably Tm or higher, more preferably Tm+20°C or higher, preferably Tm+100°C or lower, and more preferably Tm+50°C or lower. The cooling body that the extruded molten resin first contacts is not particularly limited, but a cast roll is usually used. The temperature of this cast roll is preferably Tg-50°C or higher, preferably Tg+70°C or lower, and more preferably Tg+40°C or lower. Furthermore, the cooling roll temperature is preferably Tg-70°C or higher, more preferably Tg-50°C or higher, preferably Tg+60°C or lower, and more preferably Tg+30°C or lower. When a raw film is manufactured under these conditions, a raw film with a thickness of 1 μm to 1 mm can be easily manufactured. Here, "Tm" represents the melting point of the crystalline polymer, and "Tg" represents the glass transition temperature of the crystalline polymer.

[0077] [9. Second step: Contact between resin film and organic solvent] In the second step, the resin film prepared in the first step as the raw material film is brought into contact with an organic solvent. The organic solvent can be one that can penetrate the resin film without dissolving the crystalline polymer contained in the resin film, and examples include hydrocarbon solvents such as toluene, limonene, and decalin; and carbon disulfide. There may be one or more types of organic solvents.

[0078] The method of contact between the resin film and the organic solvent is arbitrary. Examples of contact methods include a spray method in which the organic solvent is sprayed onto the resin film; a coating method in which the organic solvent is applied to the resin film; and an immersion method in which the resin film is immersed in the organic solvent. Among these, the immersion method is preferred because it allows for easy continuous contact.

[0079] The temperature of the organic solvent brought into contact with the resin film can be arbitrary as long as the organic solvent remains in a liquid state, and therefore can be set within a range above the melting point and below the boiling point of the organic solvent.

[0080] The contact time between the resin film and the organic solvent is not particularly specified, but is preferably 0.5 seconds or more, more preferably 1.0 second 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. When the contact time is above the lower limit of the above range, the NZ coefficient can be effectively adjusted by contact with the organic solvent. On the other hand, the amount of adjustment of the NZ coefficient tends not to change significantly even if the immersion time is increased. Therefore, when the contact time is below the upper limit of the above range, productivity can be increased without impairing the quality of the phase difference film.

[0081] In the second step, contact with an organic solvent changes the birefringence Rth / d in the thickness direction of the resin film. This adjusts the NZ coefficient, resulting in an NZ coefficient of less than 1.0. The amount of change in the birefringence Rth / d in the thickness direction of the resin film caused by contact with the organic solvent is preferably 1.0 × 10⁻⁶. -3 The above is more 2.0 × 10 -3 The above is particularly preferable to 5.0 × 10-3 The above, preferably 50.0 × 10 -3 More preferably 30.0 × 10 -3 The following is particularly preferred: 20.0 × 10 -3 The following applies: The change in birefringence Rth / d in the thickness direction refers to the absolute value of the change in birefringence Rth / d in the thickness direction.

[0082] The in-plane birefringence Re / d of the resin film may or may not change upon contact with an organic solvent. From the viewpoint of simplifying the control of the in-plane retardation Re of the phase difference film, it is preferable that the change in the in-plane birefringence Re / d of the resin film upon contact with an organic solvent is small, and more preferably that no change occurs. The amount of change in the in-plane birefringence Re / d of the resin film upon contact with an organic solvent is preferably 0.0 × 10⁻⁶. -3 ~2.0×10 -3 , comfortably 0.0 × 10 -3 ~1.0×10 -3 Particularly preferred is 0.0 × 10 -3 ~0.5 × 10 -3 Therefore, the change in birefringence Re / d in the in-plane direction mentioned above represents the absolute value of the change in birefringence Re / d in the in-plane direction.

[0083] In the second step, the thickness of the resin film typically increases as the organic solvent, upon contact with the resin film, penetrates into the film. The lower limit of the rate of change in the thickness of the resin film at this time may be, for example, 10% or more, 20% or more, or 30% or more. The upper limit of the rate of change in thickness may be, for example, 80% or less, 50% or less, or 40% or less. The rate of change in the thickness of the resin film is the ratio obtained by dividing the amount of change in the thickness of the resin film by the thickness of the original film (i.e., the resin film before contact with the organic solvent).

[0084] As described above, the second step changes the birefringence Rth / d in the thickness direction of the resin film. Therefore, if the change in birefringence Rth / d in the thickness direction due to the second step results in a resin film with desired optical properties, that resin film can be obtained as a phase difference film. Furthermore, in the manufacturing method according to the second embodiment, any additional process may be applied to the resin film after the second step has been performed.

[0085] [10. Third step: Stretching of the resin film] In the method for manufacturing a phase difference film according to the second embodiment of the present invention, a third step of stretching the resin film may be included after the second step. Stretching allows the molecules of the crystalline polymer contained in the resin film to be oriented in a direction corresponding to the stretching direction. Therefore, the third step allows for adjustment of optical properties such as the in-plane birefringence Re / d, in-plane retardation Re, thickness-direction birefringence Rth / d, thickness-direction retardation Rth, and NZ coefficient of the resin film, as well as the thickness d.

[0086] There are no restrictions on the stretching direction; for example, it can be in the longitudinal direction, the width direction, or an oblique direction. Here, an oblique direction refers to a direction perpendicular to the thickness direction, and neither parallel nor perpendicular to the width direction. Furthermore, the stretching direction may be one direction or two or more directions. Therefore, stretching methods include, for example, uniaxial stretching methods such as stretching the resin film uniaxially in the longitudinal direction (longitudinal uniaxial stretching method) and stretching the resin film uniaxially in the width direction (transverse uniaxial stretching method); biaxial stretching methods such as simultaneous biaxial stretching, in which the resin film is stretched in the longitudinal direction and simultaneously in the width direction, and sequential biaxial stretching, in which the resin film is stretched in one direction (longitudinal or width direction) and then in the other direction; and stretching the resin film obliquely (oblique stretching method).

[0087] The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or 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. It is desirable to appropriately set the specific stretching ratio according to factors such as the optical properties, thickness, and strength of the phase difference film to be manufactured. When the stretching ratio is above the lower limit of the above range, the birefringence can be greatly changed by stretching. Also, when the stretching ratio is below the upper limit of the above range, the direction of the slow axis can be easily controlled and the breakage of the resin film can be effectively suppressed.

[0088] The stretching temperature is preferably "Tg + 5°C" or higher, more preferably "Tg + 10°C" or higher, preferably "Tg + 100°C" or lower, and more preferably "Tg + 90°C" or lower. Here, "Tg" represents the glass transition temperature of the crystalline polymer. When the stretching temperature is above the lower limit of the above range, the resin film can be sufficiently softened and stretched uniformly. Furthermore, when the stretching temperature is below the upper limit of the above range, the hardening of the resin film due to the progression of crystallization of the crystalline polymer can be suppressed, allowing for smooth stretching and enabling the expression of large birefringence through stretching. In addition, it is usually possible to reduce the haze of the resulting resin film and improve its transparency.

[0089] By performing the stretching process described above, a stretched film can be obtained as a stretched resin film. As described above, since the birefringence may change due to the stretching in the third step, the NZ coefficient can be adjusted. Therefore, if a resin film with desired optical properties can be obtained as a stretched film by the stretching in the third step, that resin film can be obtained as a phase difference film.

[0090] [11. Fourth step: Heat treatment of the resin film] In the method for manufacturing a phase difference film according to the second embodiment of the present invention, a fourth step may be included after the second step, in which the resin film is subjected to heat treatment. When the method for manufacturing a phase difference film includes a third step, the fourth step is usually performed after the third step. Heat treatment can promote the crystallization of the crystalline polymer contained in the resin film, thereby increasing the orientation of the crystalline polymer. Heat treatment can also reduce the amount of organic solvent contained in the resin film. Therefore, the optical properties of the resin film can be adjusted according to the fourth step.

[0091] The heat treatment temperature is typically above the glass transition temperature Tg of the crystalline polymer and below the melting point Tm of the crystalline polymer. More specifically, the heat treatment temperature is preferably above Tg°C, more preferably above Tg+10°C, preferably below Tm-20°C, and more preferably below Tm-40°C. Within this temperature range, the crystallization of the crystalline polymer can be rapidly promoted while suppressing clouding due to the progression of crystallization.

[0092] The heat treatment processing time is preferably 1 second or more, more preferably 5 seconds or more, preferably 30 minutes or less, and more preferably 15 minutes or less.

[0093] As described above, the birefringence can be changed by the heat treatment in the fourth step, allowing for adjustment of the NZ coefficient. Therefore, if a resin film with desired optical properties is obtained by the heat treatment in the fourth step, that resin film can be obtained as a phase difference film.

[0094] [12. Other processes] The method for manufacturing a phase difference film may include any additional steps in addition to the steps described above. The method for manufacturing a phase difference film may include, for example, a step after the second step to remove organic solvents adhering to the resin film. Examples of methods for removing organic solvents include drying and wiping.

[0095] The method for manufacturing a phase difference film may include, for example, a step of preheating the resin film to the stretching temperature before the third step. Usually, the preheating temperature and the stretching temperature are the same, but they may be different. The preheating temperature is preferably T1-10°C or more, more preferably T1-5°C or more, preferably T1+5°C or less, and more preferably T1+2°C or less, relative to the stretching temperature T1. The preheating time is arbitrary, preferably 1 second or more, more preferably 5 seconds or more, and also preferably 60 seconds or less, more preferably 30 seconds or less.

[0096] If the method for manufacturing a phase difference film includes a third or fourth step, the resin film after those steps may contain residual stress. Therefore, the method for manufacturing a phase difference film may include, for example, a step of a relaxation treatment to remove residual stress by thermally shrinking the resin film. In the relaxation treatment, residual stress can usually be removed by causing thermal shrinkage of the resin film within an appropriate temperature range while maintaining the resin film flat.

[0097] According to the manufacturing method described above, a long phase difference film can be manufactured using a long roll of raw film. The manufacturing method for the phase difference film may include a step of winding the long phase difference film thus manufactured into a roll. Furthermore, the manufacturing method for the phase difference film may include a step of cutting the long phase difference film into a desired shape.

[0098] [13. Phase difference film to be manufactured] According to the manufacturing method of the second embodiment of the present invention described above, the birefringence can be adjusted by a simple step of contacting the raw film with an organic solvent, so that a phase difference film having a desired NZ coefficient can be easily manufactured. Therefore, according to this manufacturing method, a phase difference film with an NZ coefficient of less than 1.0 can be easily obtained.

[0099] The NZ coefficient of the phase difference film produced by the manufacturing method according to the second embodiment may, in detail, be the same as the NZ coefficient of the phase difference film according to the first embodiment. Furthermore, the phase difference film produced by the manufacturing method according to the second embodiment may also be the same as the phase difference film according to the first embodiment in terms of properties other than the NZ coefficient. Therefore, the phase difference film produced by the manufacturing method according to the second embodiment may have the same properties as the phase difference film according to the first embodiment, such as the crystalline resin contained in the phase difference film; the haze of the phase difference film; the amount of organic solvent contained in the phase difference film; the retardation Re and Rth of the phase difference film; the birefringence Re / d and Rth / d of the phase difference film; the total light transmittance of the phase difference film; and the thickness of the phase difference film.

[0100] [14.Applications] The phase difference film according to the first embodiment described above, and the phase difference film manufactured by the manufacturing method according to the second embodiment, can be installed in a display device, for example. In this case, the phase difference film can improve the display quality, such as the viewing angle, contrast, and image quality, of the image displayed on the display device. [Examples]

[0101] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and can be modified and implemented as appropriate without departing from the scope of the claims and equivalents of the present invention. In the following explanation, "%" and "parts" refer to weight unless otherwise specified. Furthermore, the operations described below were performed under normal temperature and pressure conditions unless otherwise specified.

[0102] [Evaluation Method] (Method for measuring the weight-average molecular weight Mw and number-average molecular weight Mn of polymers) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polymer were measured as polystyrene equivalents using a gel permeation chromatography (GPC) system (Tosoh Corporation, "HLC-8320"). An H-type column (Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The measurement temperature was 40°C.

[0103] (Method for measuring the hydrogenation rate of polymers) The hydrogenation rate of the polymer is orthodichlorobenzene-d 4 Using as a solvent, at 145°C, 1 The measurement was performed by 1H-NMR.

[0104] (Method for measuring glass transition temperature Tg and melting point Tm) The glass transition temperature (Tg) and melting point (Tm) of the polymer were measured as follows. First, the polymer was melted by heating, and the molten polymer was rapidly cooled with dry ice. Subsequently, using this polymer as a test specimen, the glass transition temperature (Tg) and melting point (Tm) of the polymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode).

[0105] (Method for measuring the ratio of racemo-dyad in polymers) The ratio of racemo-dyads in the polymer was measured as follows: orthodichlorobenzene-d 4 Using [the solvent], the polymer was subjected to an inverse-gated decoupling method at 200°C. 13 ¹¹NMR measurements were performed. 13 In the results of the 1C NMR measurement, orthodichlorobenzene-d 4 Using the 127.5 ppm peak as the reference shift, we identified a 43.35 ppm signal from the meso-dyad and a 43.43 ppm signal from the racemo-dyad. Based on the intensity ratio of these signals, we determined the proportion of racemo-dyad in the polymer.

[0106] (Method for measuring film retardation Re and Rth, and NZ coefficient) The in-plane retardation Re, thickness-direction retardation Rth, and NZ coefficient of the film were measured using a phase difference meter (AXOMETRICS "AxoScan OPMF-1"). The measurement wavelength was 590 nm.

[0107] (Method for measuring film thickness) The film thickness was measured using a contact-type thickness gauge (MITUTOYO, Code No. 543-390).

[0108] (Method for measuring film haze) The film haze was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0109] (Method for measuring the solvent content of phase difference film) The weight of the raw film (resin film before solvent immersion) used to manufacture the phase difference film as a sample was measured by thermogravimetric analysis (TGA: under a nitrogen atmosphere, heating rate of 10°C / min, 30°C to 300°C). Weight of the raw film at 30°C (W) O Weight W of the raw film at temperatures from 30°C to 300°C O Subtracting (300℃) gives the weight loss ΔW of the raw film at 300℃. O The following was determined. The raw film rolls used in the examples and comparative examples described later were manufactured by melt extrusion and therefore do not contain solvents. Therefore, the weight loss ΔW of this raw film roll is O This was adopted as a reference in equation (X), which will be described later.

[0110] Furthermore, the weight of the phase difference film used as a sample was measured by thermogravimetric analysis (TGA: under a nitrogen atmosphere, heating rate of 10°C / min, 30°C to 300°C), as described above. Weight W of the phase difference film at 30°C R Weight W of phase difference film at temperatures from 30°C to 300°C R Subtracting (300℃) gives the weight loss ΔW of the phase difference film at 300℃. R They sought it.

[0111] The weight loss ΔW of the raw film at 300°C as described above. O , and the weight loss ΔW of the phase difference film at 300℃ R Therefore, the solvent content of the phase difference film was calculated using the following formula (X). Solvent content (%) = {(ΔW R -ΔW O ) / W R (30℃) × 100 (X)

[0112] [Production Example 1: Production of a crystalline resin containing a hydride of a ring-opening polymer of dicyclopentadiene] A metal pressure reactor was thoroughly dried and then purged with nitrogen. To this metal pressure reactor, 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo-isomer content of 99% or more) (30 parts of dicyclopentadiene), and 1.9 parts of 1-hexene were added, and the mixture was heated to 53°C.

[0113] A solution was prepared by dissolving 0.014 parts of tetrachlorotungstenphenylimide (tetrahydrofuran) complex in 0.70 parts of toluene. To this solution, 0.061 parts of a 19% diethylaluminum ethoxide / n-hexane solution were added and the mixture was stirred for 10 minutes to prepare a catalyst solution. This catalyst solution was added to a pressure reactor to initiate the ring-opening polymerization reaction. The reaction was then carried out for 4 hours at a temperature of 53°C to obtain a solution of the ring-opened polymer of dicyclopentadiene. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained ring-opened polymer of dicyclopentadiene were 8,750 and 28,100, respectively, and the molecular weight distribution (Mw / Mn) was 3.21.

[0114] To 200 parts of the solution of the obtained ring-opened polymer of dicyclopentadiene, 0.037 parts of 1,2-ethanediol were added as a stopping agent, and the mixture was heated to 60°C and stirred for 1 hour to stop the polymerization reaction. To this, 1 part of a hydrotalcite-like compound (Kyowa Chemical Industry Co., Ltd. "Kyoword® 2000") was added, and the mixture was heated to 60°C and stirred for 1 hour. Subsequently, 0.4 parts of a filtration aid (Showa Chemical Industry Co., Ltd. "Radiolite® #1500") was added, and the adsorbent and solution were filtered off using a PP pleated cartridge filter (ADVANTEC Toyo Co., Ltd. "TCP-HX").

[0115] To 200 parts (30 parts polymer) of a filtered solution of the ring-opened polymer of dicyclopentadiene, 100 parts of cyclohexane were added, and 0.0043 parts of chlorohydridecarbonyltris(triphenylphosphine)ruthenium were added. A hydrogenation reaction was carried out at a hydrogen pressure of 6 MPa and 180°C for 4 hours. This yielded a reaction solution containing the hydride of the ring-opened polymer of dicyclopentadiene. The hydride precipitated from this reaction solution, forming a slurry solution.

[0116] The hydride and solution contained in the reaction mixture were separated using a centrifuge and dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a crystalline ring-opening polymer hydride. The hydrogenation rate of this hydride was 99% or higher, the glass transition temperature (Tg) was 93°C, the melting point (Tm) was 262°C, and the racemo-dyad ratio was 89%.

[0117] 100 parts of the obtained hydride of the ring-opening polymer of dicyclopentadiene were mixed with 1.1 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane; "Irganox® 1010" manufactured by BASF Japan), and then fed into a twin-screw extruder (product name "TEM-37B", manufactured by Toshiba Machine Co., Ltd.) equipped with four die holes with an inner diameter of 3 mmΦ. The mixture of the hydride of the ring-opening polymer of dicyclopentadiene and the antioxidant was formed into strands by hot melt extrusion, and then shredded with a strand cutter to obtain pellet-shaped crystalline resin. The operating conditions of the twin-screw extruder were as follows. Barrel temperature setting = 270~280℃ Die setting temperature = 250℃ • Screw rotation speed = 145 rpm

[0118] [Example 1] (1-1. First process: Manufacturing of the raw film roll) The crystalline resin produced in Production Example 1 was molded using a thermal melt extrusion film molding machine equipped with a T-die (Optical Control Systems' "Measuring Extruder Type Me-20 / 2800V3"), and wound onto a roll at a speed of 1.5 m / min to obtain a resin film (thickness 50 μm) as a long roll of raw material film with a width of approximately 120 mm. The operating conditions of the film molding machine were as follows. Barrel setting temperature = 280℃~300℃ Die temperature = 270℃ • Screw rotation speed = 30 rpm Cast roll temperature = 80°C

[0119] (1-2. Second step: Contact between the raw film and the processing solvent) The resin film was cut to 100 mm x 100 mm. Regression was measured using a phase difference meter, and the in-plane retardation Re = 5 nm and the thickness-direction retardation Rth = 6 nm were found. Since this resin film is manufactured by thermal melt extrusion at high temperatures (280°C to 300°C) as described above, it is assumed that the resin film does not contain solvent, and therefore its solvent content was assumed to be 0.0%.

[0120] A tray was filled with toluene as the processing solvent, and the resin film was immersed in the toluene for 5 seconds. After that, the resin film was removed from the toluene, and the surface was wiped with gauze. The obtained resin film was evaluated as a phase difference film using the method described above. As a result, the in-plane retardation Re = 9 nm, the retardation Rth = -575 nm in the thickness direction, the thickness was 64 μm, and the haze Hz was 0.4%.

[0121] [Example 2] In step (1-1) above, the thickness of the resin film used as the base film was changed to 20 μm by adjusting the winding speed (line speed) of the film onto the roll. Furthermore, in step (1-2) above, the immersion time of the resin film in the processing solvent (in this case, toluene) was changed to 1 second. Except for the matters mentioned above, the phase difference film was manufactured and evaluated using the same procedure as in Example 1.

[0122] [Example 3] In step (1-1) above, the thickness of the resin film used as the base film was changed to 100 μm by adjusting the winding speed (line speed) of the film onto the roll. Furthermore, in step (1-2) above, the immersion time of the resin film in the processing solvent (in this case, toluene) was changed to 60 seconds. Except for the matters mentioned above, the phase difference film was manufactured and evaluated using the same procedure as in Example 1.

[0123] [Example 4] A stretching device (SDR-562Z, manufactured by Eto Corporation) was prepared. This stretching device was equipped with clips capable of gripping the edges of a rectangular resin film and an oven. There were 24 clips in total: 5 per side of the resin film and 1 at each vertex of the resin film. The resin film could be stretched by moving these clips. In addition, there were two ovens, which could be set to stretching temperature and heat treatment temperature, respectively. Furthermore, with the aforementioned stretching device, the resin film could be transferred from one oven to the other while still being gripped by the clips.

[0124] A resin film was manufactured as a raw material film and the resin film was brought into contact with toluene using the same method as in Example 1. The resin film, after contact with toluene, was mounted on the stretching apparatus described above, and the resin film was treated at a preheating temperature of 110°C for 10 seconds. Subsequently, the resin film was stretched at a stretching temperature of 110°C, with a longitudinal stretching ratio of 1x, a transverse stretching ratio of 1.5x, and a stretching speed of 1.5x / 10 seconds. The "longitudinal stretching ratio" refers to the stretching ratio in the direction corresponding to the longitudinal direction of the long roll of original film, and the "transverse stretching ratio" refers to the stretching ratio in the direction corresponding to the width direction of the long roll of original film. This resulted in a stretched film as a resin film that had undergone stretching treatment. This stretched film was evaluated as a phase difference film using the method described above. As a result, the in-plane retardation Re = 347 nm, the thickness-direction retardation Rth = -12 nm, the thickness was 47 μm, and the haze Hz was 0.4%.

[0125] [Example 5] The thickness of the resin film used as the base film was changed to 35 μm by adjusting the winding speed (line speed) of the film onto the roll. Except for the above, the phase difference film was manufactured and evaluated using the same method as in Example 4.

[0126] In this Example 5, the thickness of the resin film obtained after contact with toluene (resin film before stretching) was 47 μm, and the retardation Rth in the thickness direction was -420 nm.

[0127] [Example 6] During the stretching of the resin film using a stretching device, the transverse stretching ratio was changed to 1.3 times. Except for the above, the phase difference film was manufactured and evaluated using the same method as in Example 4.

[0128] [Example 7] Using the same method as in Example 4, a resin film was manufactured as a raw material, the resin film was brought into contact with toluene, and the resin film was stretched.

[0129] The stretched resin film, held in place by clips, was moved to a heat treatment oven and heat-treated at 170°C for 20 seconds. The stretched film after this heat treatment was evaluated as a phase difference film using the method described above. The results showed an in-plane retardation Re = 378 nm, a thickness retardation Rth = -10 nm, a thickness of 44 μm, and a haze Hz of 0.4%.

[0130] [Example 8] The heat treatment time was changed to 10 minutes. Except for the above, the phase difference film was manufactured and evaluated using the same method as in Example 7.

[0131] [Example 9] The thickness of the resin film used as the base film was changed to 30 μm by adjusting the winding speed (line speed) of the film onto the roll. In addition, the transverse stretching ratio was changed to 1.7 times when stretching the resin film using a stretching device. Except for the above, the phase difference film was manufactured and evaluated using the same method as in Example 4.

[0132] In this Example 9, the thickness of the resin film obtained after contact with toluene (resin film before stretching) was 41 μm, and the retardation Rth in the thickness direction was -370 nm.

[0133] [Example 10] The thickness of the resin film used as the base film was changed to 33 μm by adjusting the winding speed (line speed) of the film onto the roll. In addition, the transverse stretching ratio was changed to 1.4 times when stretching the resin film using a stretching device. Except for the above, the phase difference film was manufactured and evaluated using the same method as in Example 4.

[0134] In this Example 10, the thickness of the resin film obtained after contact with toluene (resin film before stretching) was 44 μm, and the retardation Rth in the thickness direction was -390 nm.

[0135] [Example 11] The type of processing solvent was changed from toluene to limonene. Except for the above, the phase difference film was manufactured and evaluated using the same method as in Example 1.

[0136] [Example 12] The type of processing solvent was changed from toluene to decalin. Also, the immersion time of the resin film in the processing solvent (decalin in this case) was changed to 60 seconds. Except for the above changes, the phase difference film was manufactured and evaluated using the same method as in Example 1.

[0137] [Comparative Example 1] A long resin film was manufactured using the same method as in step (1-1) of Example 1. The obtained resin film was cut to 100 mm x 100 mm. The cut resin film was attached to the stretching apparatus and treated at a preheating temperature of 110°C for 10 seconds. Thereafter, the resin film was stretched at a stretching temperature of 110°C, with a longitudinal stretching ratio of 1x, a transverse stretching ratio of 1.5x, and a stretching speed of 1.5x / 10 seconds. After stretching, the in-plane retardation Re = 62 nm, the thickness-direction retardation Rth = 77 nm, the thickness was 33 μm, and the haze Hz was 0.1%.

[0138] The stretched resin film was used as the raw material and brought into contact with toluene as the processing solvent. Specifically, a tray was filled with toluene, and the stretched resin film was immersed in the toluene for 5 seconds. After that, the resin film was removed from the toluene, and the surface was wiped with gauze. The resulting resin film was evaluated as a phase difference film using the method described above.

[0139] [Comparative Example 2] A long resin film was manufactured using the same method as in step (1-1) of Example 1. The obtained resin film was cut to 100 mm x 100 mm. The cut resin film was attached to the stretching apparatus and treated at a preheating temperature of 110°C for 10 seconds. Thereafter, the resin film was stretched at a stretching temperature of 110°C, with a longitudinal stretching ratio of 1x, a transverse stretching ratio of 2x, and a stretching speed of 1.5x / 10 seconds. After stretching, the in-plane retardation Re = 91 nm, the thickness-direction retardation Rth = 85 nm, the thickness was 25 μm, and the haze Hz was 0.1%.

[0140] The stretched resin film was used as the raw material and brought into contact with toluene as the processing solvent. Specifically, a tray was filled with toluene, and the stretched resin film was immersed in the toluene for 5 seconds. After that, the resin film was removed from the toluene, and the surface was wiped with gauze. The resulting resin film was evaluated as a phase difference film using the method described above.

[0141] [Comparative Example 3] A long resin film was manufactured using the same method as in step (1-1) of Example 1. The obtained resin film was cut into 100 mm x 100 mm pieces. Shrinkable films were laminated to both sides of the cut resin film to obtain a multilayer film. The shrinkable film had the property of shrinking by 20% vertically and 25% horizontally at 145°C.

[0142] The multilayer film was attached to the stretching apparatus and treated at a preheating temperature of 145°C for 5 seconds. Then, the multilayer film was stretched at a stretching temperature of 145°C with a longitudinal stretching ratio of 0.8 and a transverse stretching ratio of 1.2. After stretching, the shrinkage film was removed from the multilayer film to obtain a resin film as a phase difference film. This resin film was evaluated using the method described above.

[0143] [result] The results of the above-mentioned examples and comparative examples are shown in the table below. In the table below, the meanings of the abbreviations are as follows. COP: A hydride of a ring-opening polymer of dicyclopentadiene. d: Thickness. Re: In-plane lettering. Rth: Regression in the thickness direction. Hz: Haze.

[0144] [Table 1]

[0145] [Table 2]

[0146] [Consider] As shown in Comparative Example 3, it was possible to produce a film with an NZ coefficient of less than 1.0 using a manufacturing method that combined stretching and shrinking of the film. However, controlling this combination of stretching and shrinking was complex. Furthermore, the film obtained in Comparative Example 3 had low birefringence and could not be used as a phase difference film. Therefore, it has not been possible to easily manufacture a phase difference film with an NZ coefficient of less than 1.0.

[0147] Furthermore, as shown in Comparative Example 2, even when an optically anisotropic raw film was brought into contact with an organic solvent, it was not possible to easily produce a phase difference film having an NZ coefficient of less than 1.0. Moreover, the phase difference film obtained in Comparative Example 2 exhibited significant haze, which is likely to result in poor image clarity when installed in a display device.

[0148] As shown in Comparative Example 1, when using a base film in which the orientation of crystalline polymer molecules is appropriately controlled by appropriately adjusting the optical properties, it is sometimes possible to produce a phase difference film with an NZ coefficient of less than 1.0, even if the base film is optically anisotropic. However, as can be seen from the fact that an NZ coefficient of less than 1.0 was not obtained in Comparative Example 2, which also used an optically anisotropic base film, when using an optically anisotropic base film, it is necessary to precisely control the optical properties of the base film in order to achieve an NZ coefficient of less than 1.0, and therefore it is necessary to precisely control the orientation of the crystalline polymer molecules contained in the base film. Consequently, when using an optically anisotropic base film, the control becomes complicated, and the simple production of phase difference films cannot be realized. In addition, the phase difference film of Comparative Example 1, like the phase difference film of Comparative Example 2, had a large haze.

[0149] In contrast, in the examples, a phase difference film having an NZ coefficient of less than 1.0 was obtained by a simple method of contacting an optically isotropic raw film with an organic solvent. Furthermore, all of the obtained phase difference films exhibited sufficiently low haze. Therefore, from the results of these examples, it was confirmed that a phase difference film with an NZ coefficient of less than 1.0 can be easily produced by the manufacturing method of the present invention, and that the haze of the produced phase difference film can be reduced.

Claims

1. A phase difference film formed from a resin containing a crystalline polymer, The crystalline polymer contains an alicyclic structure, The NZ coefficient is less than 1.0, and The haze is less than 1.0%. 1.0 × 10 －３ The above in-plane birefringence Re / d, and 1.0 × 10 －３ Having at least one of the absolute values ​​of the birefringence in the thickness direction |Rth / d|, A phase difference film wherein the phase difference film contains an organic solvent, and the ratio of the organic solvent contained in the phase difference film to 100% of the weight of the phase difference film (solvent content) is 3.2% by weight or more and 10% by weight or less.

2. The phase difference film according to claim 1, wherein the crystalline polymer has positive intrinsic birefringence.

3. The phase difference film according to claim 1, wherein the NZ coefficient of the phase difference film is greater than 0.0 and less than 1.

0.

4. The phase difference film according to claim 1, wherein the organic solvent is a hydrocarbon solvent.

5. The phase difference film according to claim 1, wherein the crystalline polymer is a hydride of a ring-opening polymer of dicyclopentadiene.

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