JP7639334B2 - Optical film, its manufacturing method and use - Google Patents

Description

The present invention relates to an optical film, its manufacturing method, and uses.

Resin films with specific optical properties have been used for optical purposes. For example, a film with an NZ coefficient that satisfies 0<NZ<1 is called a three-dimensional retardation film. It is known that when a three-dimensional retardation film is provided in a display device such as a liquid crystal display device, it can exert an effect of reducing coloring of the display surface when viewed from an oblique direction.

Three-dimensional retardation films have a greater retardation in the z-axis direction (i.e., thickness direction) than in the y-axis direction (i.e., in-plane direction perpendicular to the in-plane slow axis direction). Therefore, they cannot be manufactured by a normal retardation film manufacturing method, such as simply stretching a resin for optical films that has a normal positive intrinsic birefringence. For this reason, it has been proposed to manufacture three-dimensional retardation films or similar films by combining resins with positive and negative intrinsic birefringence (e.g., Patent Documents 1 and 2).

International Publication No. 2019/188205 International Publication No. 2020/137409

The manufacturing method of three-dimensional retardation film that combines resins with positive and negative intrinsic birefringence that have been proposed so far has problems such as requiring a complicated stretching process and a lamination process after stretching, which requires a lot of work for positioning. In particular, it is difficult to easily manufacture a film with reverse wavelength dispersion. In addition, in such a combination, it is required to increase the ratio of resins with negative intrinsic birefringence to a certain extent, but since resins with negative intrinsic birefringence generally have low mechanical strength, a problem of low mechanical strength may occur when the ratio of such resins is increased. In addition, when the film is manufactured as a long film, if the manufacturing process includes a process of stretching in the width direction, there is a significant problem that curling of the ends of the film in the width direction during transport of the long film occurs easily. In addition, when such a long film is made into a film roll, there is also a problem that the roll shape is deformed and the film is easily deteriorated during storage of the film roll.

The object of the present invention is therefore to provide a film that can exhibit good effects as a three-dimensional retardation film, is easy to transport and store, and can be easily manufactured, and a manufacturing method that can easily manufacture a film that can exhibit good effects as a three-dimensional retardation film.

The present inventors have conducted studies to solve the above problems, and as a result, have found that the above problems can be solved by combining a film that uses a specific material and exhibits desired optical properties with a specific protective film, and have thus completed the present invention.
That is, the present invention includes the following.

[1] A long optical film comprising a film A made of a crystalline resin (a) and a protective film B provided on one surface of the film A,
a thickness DA of the film A and a thickness DB of the protective film B satisfy DB/DA>2;
The optical film, wherein the NZ coefficient of the film A is less than 1.
[2] The optical film according to [1], wherein the crystalline resin (a) has a positive intrinsic birefringence value.
[3] The optical film according to [1] or [2], wherein the crystalline resin (a) contains an alicyclic structure-containing polymer.
[4] The protective film B is made of material (b),
[1] to [3], wherein the glass transition temperature Tg(a) (°C) of the crystalline resin (a) and the glass transition temperature Tg(b) (°C) of the material (b) satisfy Tg(b) ≧ Tg(a) + 35.
[5] A method for producing the optical film according to any one of [1] to [4],
A step (I) of preparing a film pA made of a crystalline resin (a);
A step (II) of laminating a protective film B onto one surface of the film pA;
and (III) a step of contacting the other surface of the film pA with a solvent to change the birefringence in the thickness direction of the film pA to form the film A.
[6] The method for producing an optical film according to [5], further comprising a step (IV) of co-stretching the film A and the protective film B after the step (III).
[7] A method for producing a retardation film, comprising: a step of producing the optical film by the production method according to [5] or [6]; and a step (V) of peeling the protective film B from the optical film.

The present invention provides a film that can exhibit good effects as a three-dimensional retardation film, is easy to transport and store, and can be easily manufactured, as well as a manufacturing method that can easily manufacture a film that can exhibit good effects as a three-dimensional retardation film.

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 may be modified as desired without departing from the scope of the claims of the present invention and their equivalents.

In the following description, the in-plane retardation Re of a layered structure (such as a film or a layer that constitutes part of a film made up of multiple layers) is a value expressed as Re = (nx - ny) x d, unless otherwise specified. The retardation Rth in the thickness direction of a layered structure is a value expressed as Rth = [{(nx + ny)/2} - nz] x d, unless otherwise specified. The NZ coefficient of a layered structure is a value expressed as (nx - nz)/(nx - ny), unless otherwise specified.

nx represents the refractive index in a direction perpendicular to the thickness direction of the layered structure (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the in-plane direction of the layered structure that is perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the layered structure. d represents the thickness of the layered structure. The measurement wavelength is 590 nm unless otherwise specified.

In the following description, unless otherwise specified, a material with positive intrinsic birefringence means a material whose refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to the stretching direction. Furthermore, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction, unless otherwise specified. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

In the following description, a "long" film refers to a film that is 5 times or more longer than its width, preferably 10 times or more longer, specifically a film that is long enough to be wound into a roll for storage or transportation. There is no particular upper limit on the length, but it is usually 100,000 times or less longer than the width.

In the following description, the slow axis of a layered structure is the in-plane slow axis unless otherwise specified.

[Optical Film]
The optical film of the present invention is a long optical film comprising a film A made of a crystalline resin (a) and a protective film B provided on one surface of the film A.

Film A has an NZ coefficient of less than 1. Specifically, the NZ coefficient NZ(A) of film A can satisfy 0<NZ(A)<1 or NZ(A)<0. The former can be useful as a so-called three-dimensional retardation film. The latter can be useful as a material for producing a three-dimensional retardation film. In other words, it can be easily converted into a film that satisfies 0<NZ(A)<1 by a simple process such as uniaxial stretching.

When film A satisfies 0<NZ(A)<1, NZ(A) is greater than 0, preferably 0.2 or greater, and smaller than 1, preferably 0.8 or less. When NZ(A) is in this range, when the optical film is provided in a display device such as a liquid crystal display device, it is possible to particularly effectively exhibit the effect of reducing coloring of the display surface when viewed from an inclined direction. On the other hand, when film A satisfies NZ(A)<0, NZ(A) is preferably 0.7 or less, more preferably 0.6 or less. The lower limit of NZ(A) is not particularly limited, but can be 0.3 or more.

In the optical film of the present invention, the thickness DA of film A and the thickness DB of protective film B satisfy DB/DA>2. Specifically, the thickness ratio DB/DA is greater than 2, preferably 2.1 or more, and more preferably 2.2 or more. The upper limit of the thickness ratio DB/DA is not particularly limited, but may be 5 or less. In general, optical films used in devices such as display devices require a certain degree of thickness to exhibit optical properties, but are also required to be thin in order to make the device thinner. By satisfying the requirements of the present invention, the optical film of the present invention can be a film in which film A satisfies the desired optical properties even if it is thin.

The thickness of film A can be adjusted appropriately to obtain the desired optical characteristics. The thickness of film A is preferably 10 μm or more, more preferably 20 μm or more, and preferably 200 μm or less, more preferably 100 μm or less. The thickness of protective film B can be adjusted appropriately to a thickness that satisfies the above-mentioned requirements and that can optimally exhibit the function of a protective film. The thickness of protective film B is preferably 50 μm or more, more preferably 100 μm or more, and preferably 500 μm or less, more preferably 300 μm or less.

The optical film of the present invention may have two or more layers of film A and may have two or more layers of protective film B, but in a preferred embodiment, it has only one layer of film A and only one layer of protective film. When it has two or more layers of film A, the sum of their thicknesses can be considered to be the thickness of film A described above. When it has two or more layers of film B, the sum of their thicknesses can be considered to be the thickness of film B described above.

In the prior art, no film is known that satisfies NZ(A)<0 and has a thickness ratio DB/DA that satisfies the above requirement, and in this respect the optical film of the present invention is novel. In the present invention, such an optical film is achieved by using a crystalline resin as the material for film A and adjusting the birefringence in the thickness direction by a specific manufacturing method described below.

The degree of crystallinity of the crystalline polymer contained in film A is not particularly limited, but is usually high to a certain degree. The specific range of the degree of crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The degree of crystallinity of the crystalline polymer can be measured by X-ray diffraction.

[Materials Constituting Film A]
The crystalline resin (a) constituting the film A may be a resin containing a polymer having crystallinity. The "polymer having crystallinity" refers to a polymer having a melting point Tm. That is, the "polymer having crystallinity" refers to a polymer whose melting point can be observed by a differential scanning calorimeter (DSC). In the following description, the polymer having crystallinity may be referred to as a "crystalline polymer". The crystalline resin is preferably a thermoplastic resin.

It is preferred that the crystalline polymer has a positive intrinsic birefringence, so that the crystalline resin (a) has a positive intrinsic birefringence value. By using a crystalline resin having a positive intrinsic birefringence, it is particularly easy to produce an optical film that satisfies the requirements of the present invention, in particular the requirement that NZ(A)<1.

The crystalline polymer may be, for example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene (PE) and polypropylene (PP); and the like, but is not particularly limited, and 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 light weight of the retardation film can be improved. A polymer containing an alicyclic structure refers to a polymer having an alicyclic structure in the molecule. Such a polymer containing an alicyclic structure may be, for example, a polymer obtained by a polymerization reaction using a cyclic olefin as a monomer, or a hydrogenated product thereof.

Examples of alicyclic structures include cycloalkane structures and cycloalkene structures. Among these, cycloalkane structures are preferred because retardation films with excellent properties such as thermal stability are easily obtained. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the number of carbon atoms contained in one alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

In a crystalline polymer containing an alicyclic structure, the ratio 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 ratio of structural units having an alicyclic structure as described above, heat resistance can be improved. The ratio of structural units having an alicyclic structure to all structural units can be 100% by weight or less. In addition, in a crystalline polymer containing an alicyclic structure, the remainder other than the structural units having an alicyclic structure is not particularly limited and can be appropriately selected depending on the purpose of use.

Examples of the crystalline polymer containing an alicyclic structure include the following polymer (α) to polymer (δ). Among these, polymer (β) is preferred because it is easy to obtain a retardation film having excellent heat resistance.
Polymer (α): A ring-opening polymer of a cyclic olefin monomer, which has crystallinity.
Polymer (β): A hydrogenated product of polymer (α) and has crystallinity.
Polymer (γ): An addition polymer of a cyclic olefin monomer, which has crystallinity.
Polymer (δ): A hydrogenated polymer (γ) having crystallinity.

Specifically, as the crystalline polymer containing an alicyclic structure, a ring-opening polymer of dicyclopentadiene having crystallinity and a hydrogenated ring-opening polymer of dicyclopentadiene having crystallinity are more preferable. Among them, a hydrogenated ring-opening polymer of dicyclopentadiene having crystallinity is particularly preferable. Here, a ring-opening polymer of dicyclopentadiene refers to a polymer in which the ratio of structural units derived from dicyclopentadiene to all 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.

The hydrogenated ring-opening polymer of dicyclopentadiene preferably has a high ratio of racemo dyads. Specifically, the ratio of racemo dyads in the repeating units of the hydrogenated ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high ratio of racemo dyads indicates high syndiotactic stereoregularity. Therefore, the higher the ratio of racemo dyads, the higher the melting point of the hydrogenated ring-opening polymer of dicyclopentadiene tends to be.
The ratio of the racemo dyads can be determined based on the ¹³ C-NMR spectrum analysis described in the Examples below.

As the above polymer (α) to polymer (δ), polymers obtained by the manufacturing method disclosed in WO 2018/062067 can be used.

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, an optical film with an even better balance between moldability and heat resistance can be obtained.

Usually, a crystalline polymer has a glass transition temperature, and therefore a glass transition temperature can be observed for the crystalline resin (a) whose main component is a crystalline polymer. The glass transition temperature Tg(a) of the crystalline resin (a) is not particularly limited, but is usually 85°C or higher and usually 170°C or lower.

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. Next, 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).

The weight average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, and preferably 1,000,000 or less, more preferably 500,000 or less. A crystalline polymer having such a weight average molecular weight has an excellent balance between moldability and heat resistance.

The molecular weight distribution (Mw/Mn) of the crystalline polymer is preferably 1.0 or more, more preferably 1.5 or more, and preferably 4.0 or less, more preferably 3.5 or less. Here, Mn represents the number average molecular weight. A crystalline polymer having such a molecular weight distribution has excellent moldability.

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

The crystalline polymer may be used alone or in any combination of two or more types in any ratio.

The proportion of the crystalline polymer in the crystalline resin (a) 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 the crystalline polymer is equal to or more than the lower limit, the birefringence expression and heat resistance of film A can be improved. The upper limit of the proportion of the crystalline polymer can be 100% by weight or less.

The crystalline resin (a) may contain optional components in addition to the crystalline polymer. Optional components include, for example, antioxidants such as phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants; light stabilizers such as hindered amine-based light stabilizers; waxes such as petroleum wax, Fischer-Tropsch wax, and polyalkylene wax; nucleating agents such as sorbitol-based 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, benzoimide derivatives, and benzoyl ester derivatives). Examples of the optional components include fluorescent brighteners such as benzothiazole derivatives, carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolone 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 assistants; antistatic agents; plasticizers; near-infrared absorbers; lubricants; fillers; and any polymer other than a crystalline polymer, such as a soft polymer. One type of optional component may be used alone, or two or more types may be used in any ratio.

[Organic solvent contained in crystalline resin (a)]
The crystalline resin (a) constituting the film A may contain a solvent such as an organic solvent. This solvent is usually incorporated into the film in step (III) of the production method of the present invention.

All or part of the solvent incorporated into the film in step (III) may penetrate into the polymer. Therefore, even if drying is performed at or above the boiling point of the solvent, it is difficult to completely remove the solvent. Therefore, film A usually contains a solvent.

The solvent may be an organic solvent that does not dissolve the crystalline polymer. Preferred organic solvents include, for example, hydrocarbon solvents such as toluene, limonene, and decalin; and carbon disulfide. The type of organic solvent may be one type or two or more types.

The ratio of the organic solvent contained in the crystalline resin (a) to 100% by 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.

[Materials Constituting Protective Film B]
A preferred example of the material constituting the protective film B is the material (b) described below.
As the material (b), a thermoplastic resin is usually used. The thermoplastic resin constituting the material (b) usually contains a polymer and may further contain any component as necessary. The polymer may usually be an amorphous polymer that does not have crystallinity.

Examples of polymers that can be included in the material (b) include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester polymers, polyethersulfone; polysulfone; polyarylsulfone; polyvinyl chloride; polymers containing an alicyclic structure such as norbornene-based polymers; rod-shaped liquid crystal polymers, etc. One type of polymer may be used alone, or two or more types may be used in combination at any ratio. The polymer may be a homopolymer or a copolymer. Among these, polymers containing an alicyclic structure are preferred because they have excellent mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and light weight.

A polymer containing an alicyclic structure has a structural unit containing an alicyclic structure. The polymer containing an alicyclic structure may have an alicyclic structure in the main chain, or may have an alicyclic structure in the side chain. Among these, from the viewpoints of mechanical strength and heat resistance, a polymer containing an alicyclic structure in the main chain is preferred.

Examples of alicyclic structures include saturated alicyclic hydrocarbon (cycloalkane) structures and unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structures. Among these, from the viewpoint of mechanical strength and heat resistance, cycloalkane structures and cycloalkene structures are preferred, and cycloalkane structures are particularly preferred.

The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less per alicyclic structure. When the number of carbon atoms constituting the alicyclic structure is within the above range, the mechanical strength, heat resistance, and moldability of the resin containing the alicyclic structure-containing polymer are highly balanced.

The proportion of structural units having an alicyclic structure in the alicyclic structure-containing polymer may be appropriately selected depending on the intended use, and is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of structural units having an alicyclic structure in the alicyclic structure-containing polymer is within this range, the transparency and heat resistance of the resin are good.

Examples of alicyclic structure-containing polymers that may be included in material (b) include norbornene-based polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrogenated versions of these. Among these, norbornene-based polymers are preferred due to their good transparency and moldability.

Examples of norbornene-based polymers and their hydrogenated products include ring-opening polymers of monomers having a norbornene structure and their hydrogenated products; addition polymers of monomers having a norbornene structure and their hydrogenated products. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer that can be copolymerized therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer that can be copolymerized therewith. Examples of these polymers include the polymers disclosed in, for example, JP 2002-321302 A. Among these, the hydrogenated ring-opening polymer of a monomer having a norbornene structure is particularly suitable from the standpoints of moldability, heat resistance, low moisture absorption, dimensional stability, and light weight.

Specific examples of norbornene-based polymers and their hydrogenated products include "ZEONOR" manufactured by Zeon Corporation; "ARTON" manufactured by JSR Corporation; and "TOPAS" manufactured by TOPAS ADVANCED POLYMERS.

The weight average molecular weight (Mw) of the polymer that can be contained in material (b) is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and preferably 100,000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight average molecular weight is in such a range, the mechanical strength and moldability of the protective film are highly balanced.

The molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of the polymer that can be contained in material (b) is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, and is preferably 4.0 or less, more preferably 3.5 or less, particularly preferably 3.0 or less. When the molecular weight distribution is equal to or more than the lower limit of the above range, the productivity of the polymer can be increased and the manufacturing cost can be reduced. When it is equal to or less than the upper limit, the amount of low molecular weight components is reduced, thereby suppressing relaxation during exposure to high temperatures and improving the stability of the protective film.

The weight average molecular weight Mw and number average molecular weight Mn of the polymer can be measured in polyisoprene equivalent values by gel permeation chromatography (hereinafter abbreviated as "GPC") using cyclohexane as a solvent. If the polymer is not soluble in cyclohexane, they can be measured in polystyrene equivalent values by GPC using toluene as a solvent.

The amount of polymer contained in material (b) is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 80% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight, and particularly preferably 95% by weight to 100% by weight, relative to 100% by weight of the resin that forms the resin film. When the amount of polymer is within the above range, the properties of the polymer can be effectively exhibited.

The material (b) may contain optional components other than the polymer. Examples of optional components include additives such as colorants such as pigments and dyes; plasticizers; fluorescent whitening agents; dispersants; heat stabilizers; light stabilizers; UV absorbers; antistatic agents; antioxidants; fine particles; and surfactants. These components may be used alone or in combination of two or more types in any ratio.

Usually, material (b) is a resin whose main component is a polymer having a glass transition temperature, and therefore, a glass transition temperature can also be observed for material (b). The glass transition temperature Tg(b) of material (b) is preferably 90°C or higher, more preferably 100°C or higher, particularly preferably 110°C or higher, and preferably 200°C or lower, more preferably 190°C or lower, particularly preferably 180°C or lower. When the glass transition temperature Tg(b) of material (b) is equal to or higher than the lower limit, the durability of protective film B in a high-temperature environment can be improved. When the glass transition temperature Tg(b) of material (b) is equal to or lower than the upper limit, the stretching process of the multilayer film including protective film B can be performed smoothly.

The glass transition temperature Tg(b) of the material (b) is preferably relatively higher than the glass transition temperature Tg(a) of the crystalline resin (a). Specifically, it is preferable that Tg(b) ≧ Tg(a), it is preferable that Tg(b) ≧ Tg(a) + 30 (°C), and it is more preferable that Tg(b) ≧ Tg(a) + 35 (°C). By having the ratio of Tg(a) and Tg(b) within the above range, it is possible to perform co-stretching of the crystalline resin (a) with the material (b) providing good support therefor, and as a result, it is possible to easily manufacture the optical film of the present invention having the desired optical properties.

[Any layer]
The optical film of the present invention may be composed of only the film A and the protective film B, but may further include any layer. For example, it may include an adhesive layer that is interposed between the film A and the protective film B and bonds them together with an appropriate adhesive strength.

[Method for producing optical film]
The optical film of the present invention can be produced by a production method including the following steps (I) to (III). Such a production method will be described below as a method for producing the optical film of the present invention. The method for producing the optical film of the present invention can further include the following step (IV) in addition to the steps (I) to (III).
Step (I): A film pA made of a crystalline resin (a) is prepared.
Step (II): A protective film B is laminated to one surface of the film pA.
Step (III): The other surface of film pA is brought into contact with a solvent to change the birefringence in the thickness direction of film pA to form film A.
Step (IV): After step (III), film A and protective film B are co-stretched.

In the description of this application, the film A and protective film B that have been subjected to step (III) and before being subjected to step (IV), and the film A and protective film B that have been subjected to step (IV) may be referred to by the same name, but in the following description, when it is necessary to distinguish between them for the sake of convenience, the former will be referred to as film qA and protective film qB, and the latter as film rA and protective film rB.

In the following, the film obtained as a result of step (II) and having film pA and protective film B may be referred to as multilayer film (II). Similarly, among the optical films of the present invention, the optical film obtained as a result of step (III) may be referred to as optical film (III), and the optical film obtained as a result of performing step (III) and step (IV) may be referred to as optical film (IV).

[Step (I)]
Step (I) can be carried out by any process capable of forming the crystalline resin (a) into a film shape. Molding by melt extrusion molding is preferred from the viewpoint of efficiently producing a long film pA. Specifically, a long film pA of the crystalline resin (a) can be formed by melt extrusion molding the crystalline resin (a) in an extrusion device equipped with a die for normal extrusion molding. The molding conditions can be appropriately adjusted according to the properties of the crystalline resin (a). The thickness of the film pA prepared in step (I) is not particularly limited, and can be appropriately adjusted so that the thickness of the film A (film qA or film rA) in the optical film as a product has a desired value. The film pA may be a film having optical anisotropy, but even if it does not have optical anisotropy, the optical film of the present invention can be easily produced by subjecting it to the subsequent steps.

[Step (II)]
The step (II) can be carried out by preparing a protective film B separately from the film pA and laminating them together. By such lamination, a multilayer film (II) including the film pA and the protective film is obtained.

The protective film B used in step (II) may be a film of the material (b) described above. A commercially available film may be used as the protective film B used in step (II). In addition, a multilayer film (II) having a layer structure of (film pA)/(adhesive layer)/(protective film B) may be obtained by preparing a multilayer film having a multilayer structure including the protective film B and an adhesive layer and laminating this with the film pA.

[Step (III)]
In step (III), a solvent is brought into contact with the surface of the film pA opposite to the surface to which the protective film B is attached. As the solvent, a solvent that can penetrate into the crystalline resin (a) without dissolving the resin can be appropriately selected. As the solvent, an organic solvent is usually used. Examples of the organic solvent include hydrocarbon solvents such as toluene, limonene, and decalin; and carbon disulfide. The type of solvent may be one type or two or more types.

The contact in step (III) can be achieved by any operation. Examples of the contact operation include a spray method in which a solvent is sprayed onto the surface of the film pA side of the multilayer film (II); a coating method in which a solvent is applied to the surface of the film pA side; and an immersion method in which the multilayer film (II) is immersed in a solvent. From the viewpoint of facilitating continuous contact, the immersion method is preferred. However, when the protective film B is a material that is easily dissolved by contact with a solvent, an operation that can achieve contact of the solvent with only one side of the film (II) is preferred, and such an operation is an operation other than the immersion method, and specifically, it can be a spray method or a coating method.

The temperature of the solvent during contact in step (III) can be any temperature within the range in which the solvent can remain in a liquid state, and therefore can be set within the range of the melting point or higher and the boiling point or lower of the solvent.

When the multilayer film (II) is contacted with the solvent by immersion, the contact time is preferably 0.5 seconds or more, more preferably 1.0 second or more, particularly preferably 5.0 seconds or more, and is preferably 120 seconds or less, more preferably 80 seconds or less, particularly preferably 60 seconds or less.
When the multilayer film (II) and the solvent are brought into contact with each other by coating the solvent, the coating thickness calculated from the coating area and the amount of the solvent supplied can be appropriately adjusted. The coating thickness is preferably 5 μm or more, more preferably 10 μm or more, and is preferably 100 μm or less.
When the contact time or coating thickness is equal to or greater than the lower limit, the NZ coefficient of the film A can be effectively adjusted by contact with the solvent. On the other hand, even if the contact time is longer than the upper limit or the coating thickness is thicker than the upper limit, the adjustment amount of the NZ coefficient tends not to change significantly. Therefore, when the contact time or coating thickness is equal to or less than the upper limit, the productivity can be increased without impairing the quality of the film A.

The multilayer film that has undergone step (III) may be used as is as the optical film (III) of the present invention. Alternatively, the multilayer film that has undergone step (III) may be subjected to an optional step and then used as the optical film (III) of the present invention. For example, the film that has undergone step (III) may be heated while maintaining its dimensions to increase the crystallinity.

As a result of contact with the solvent in step (III), the refractive index of film pA changes to film qA, and an optical film (III) comprising film qA and protective film qB is obtained. When film pA changes to film qA, the thickness may increase in addition to the change in refractive index. Such a change brought about by contact with the solvent is difficult to obtain by a normal retardation film manufacturing method, such as simply stretching a resin for an optical film. Therefore, as a result of such a change, the optical film of the present invention can be easily manufactured.

The film qA in the optical film (III) has an NZ coefficient NZ(qA) of less than 1, and specifically, can satisfy NZ(qA)<0. Therefore, the film qA in the optical film (III) can be easily converted into a film that satisfies 0<NZ(A)<1 by a simple process such as the uniaxial stretching in step (IV). NZ(qA) is preferably 0.7 or less, more preferably 0.6 or less. The lower limit of NZ(A) is not particularly limited, but can be 0.3 or more.

[Step (IV)]
In step (IV), after step (III), the film qA and the protective film qB are co-stretched. Specifically, the optical film (III) obtained in step (III) is stretched to co-stretch the film qA and the protective film qB. By such co-stretching, all layers included in the optical film (III) are stretched at the same stretching ratio and in the same stretching direction, and the polymer molecules included in these layers are oriented in a direction according to the stretching direction. Since the optical film (III) has undergone step (III), as a result of step (IV), an optical film (IV) having optical properties that are difficult to obtain by a normal retardation film manufacturing method such as simply stretching a resin for an optical film can be easily obtained.

The stretching in step (IV) may be uniaxial stretching or biaxial or more stretching. The number of stretching times may be one or more. A single uniaxial stretching is preferred. Since the optical film (III) has been subjected to step (III), such a single uniaxial stretching can easily produce an optical film (IV) with optical properties that are difficult to obtain by a conventional retardation film manufacturing method.

There are no limitations on the stretching direction in step (IV), and examples include the longitudinal direction, the width direction, and the diagonal direction. Here, the diagonal direction refers to a direction perpendicular to the thickness direction, and an angle between the width direction and the direction is neither 0° nor 90° (i.e., an angle between the width direction and the direction is greater than 0° and less than 90°).

When attempting to produce a film having optical properties equivalent to the optical film (IV) of the present invention using a manufacturing method that does not include step (III), multiple complex stretching steps are usually required. When developing optical properties through stretching, the stretching conditions must be strictly controlled, and therefore the large number of stretching steps is a major disadvantage in terms of manufacturing efficiency. In contrast, the manufacturing method of the present invention is advantageous in terms of manufacturing efficiency, since the optical film (IV) of the present invention can be obtained by only uniaxial stretching.

The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, and is 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 set the specific stretching ratio appropriately depending on factors such as the optical properties, thickness, and strength of the optical film (IV) that is the product. When the stretching ratio is equal to or greater than the lower limit, the birefringence can be significantly changed by stretching. Also, when the stretching ratio is equal to or less than the upper limit, the direction of the slow axis can be easily controlled and breakage of the film can be effectively suppressed.

The stretching temperature can be specified relative to the glass transition temperature Tg(a) of the crystalline resin (a). The stretching temperature is preferably "Tg(a)+5"°C or higher, more preferably "Tg(a)+10"°C or higher, and preferably "Tg(a)+100"°C or lower, more preferably "Tg(a)+90"°C or lower. When the stretching temperature is equal to or higher than the lower limit, the film can be sufficiently softened and stretched uniformly. When the stretching temperature is equal to or lower than the upper limit, the film can be stretched smoothly, since the film hardening caused by the progress of crystallization of the crystalline polymer can be suppressed, and large birefringence can be expressed by stretching. Furthermore, the haze of the optical film (IV) obtained can usually be reduced to increase its transparency. In addition, by performing stretching at such a temperature, the crystallinity of the crystalline resin (a) is increased, and the optical properties of the film A of the optical film (IV) obtained as a result can be easily adjusted to the desired range.

Since the birefringence can be changed by step (IV), the NZ coefficient can be adjusted. Thus, the stretching in step (IV) produces an optical film (IV) having the desired optical properties. The film obtained in step (IV) can be used as is as the optical film (IV) of the present invention. Alternatively, the obtained film can be further subjected to any processing to produce the optical film (IV) of the present invention. Examples of optional processing include adjustment of birefringence by heat treatment while maintaining the stretched dimensions or relaxation treatment by shrinking the stretched dimensions.

The film rA in the optical film (IV) has an NZ coefficient NZ(rA) of less than 1. Specifically, it can satisfy 0<NZ(A)<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 preferably 0.8 or less. When NZ(rA) is in this range, when the optical film is provided in a display device such as a liquid crystal display device, it can exhibit a particularly good effect of reducing coloring of the display surface when viewed from an inclined direction.

[Other steps]
The method for producing an optical film of the present invention may further include any step in combination with the above-mentioned steps. For example, after step (III), the method may include a step of removing the solvent attached to the film. Examples of the method for removing the solvent include drying and wiping.

The long optical film (III) obtained in step (III) and the long optical film (IV) obtained in step (IV) can be wound into a roll as necessary to form a film roll.

[Method for producing retardation film]
The optical films of the present invention (optical film (III) and optical film (IV)) can be used for optical purposes as they are, but can also be subjected to a step of peeling off the protective film B from the optical film, and only the remaining film A can be used as a retardation film.

[Application]
The optical film of the present invention and the retardation film of the present invention can be processed into a desired shape such as a rectangle as necessary and used as a component of an optical device such as a display device. When the optical film of the present invention or the retardation film of the present invention is used as a component of a display device, the display quality such as the viewing angle, contrast, and image quality of an image displayed on the display device can be improved.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be modified and carried out as desired without departing from the scope of the claims of the present invention and the scope of equivalents thereto.
In the following description, the units "%" and "parts" expressing amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out under normal temperature and pressure conditions unless otherwise specified.

(Method of measuring weight average molecular weight Mw and number average molecular weight Mn of polymer)
The weight average molecular weight Mw and number average molecular weight Mn of the polymer were measured as polystyrene equivalent values using a gel permeation chromatography (GPC) system ("HLC-8320" manufactured by Tosoh Corporation). In the measurement, an H-type column (manufactured by Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The temperature during the measurement was 40° C.

(Method of measuring hydrogenation rate of polymer)
The hydrogenation rate of the polymer was measured by ¹ H-NMR measurement at 145° C. using orthodichlorobenzene- ^d4 as a solvent.

(Method of 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 melted polymer was quenched with dry ice. Then, 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) using the polymer as a test specimen.

(Method for measuring the ratio of racemo-dyads in polymers)
The ratio of the racemo-dyad in the polymer was measured as follows. The polymer was subjected to ¹³ C-NMR measurement by applying the inverse-gated decoupling method at 200°C using orthodichlorobenzene- ^d4 as a solvent. In the results of this ¹³ C-NMR measurement, a signal at 43.35 ppm derived from the meso-dyad and a signal at 43.43 ppm derived from the racemo-dyad were identified, with the peak at 127.5 ppm of orthodichlorobenzene- ^d4 as the reference shift. The ratio of the racemo-dyad in the polymer was calculated based on the intensity ratio of these signals.

(Method of measuring optical properties of film)
The in-plane retardation Re, thickness retardation Rth and NZ coefficient of the optical film were measured at a wavelength of 590 nm using a birefringence meter (Axometrics'"AxoScan") The measurements were performed at multiple points at 5 cm intervals in the width direction of the film, and the average value of the measurements at each point was used as the measurement result.

(Method of measuring film thickness)
The thickness was measured at multiple points at 5 cm intervals across the width of the film using a snap gauge (Mitutoyo ID-C112BS). The average of these measurements was calculated to determine the average thickness of the film.

(Crystallization degree)
The crystallinity (%) of the crystalline polymer was measured by X-ray diffraction method.

(Curl Evaluation)
A piece of film was cut from the center of the width direction of the long film to be evaluated to obtain a rectangular sample of 100 mm length x 100 mm width. The sample was placed on a flat stage and left at 23°C for 1 hour. After that, the height of the four corners of the sample lifted from the stage was measured with a ruler. The average value of the measurement results at the four points was taken as the curl amount of the film. The curl amount was evaluated according to the following criteria.
Good: The curl amount is less than 4 mm.
Poor: The curl amount is 4 mm or more.

(Winding deformation evaluation)
Immediately after obtaining the film roll of the long film to be measured, the deformation state of the winding of the film roll was evaluated according to the following criteria.
5: No deformation of the winding at all 4: Almost no deformation of the winding 3: Slight deformation of the winding 2: Clear deformation of the winding 1: Major deformation of the winding In practical terms, a rating of 4 or above is a usable level.

(Evaluation of deterioration over time during rolling)
The film roll of the long film to be measured was stored for about 2 weeks under a high temperature (38°C) and high humidity (75%) atmosphere, and then the film was unwound from the film roll, and the protective film was peeled off in the middle of the roll (i.e., at the middle part in the longitudinal direction of the film) to obtain a retardation film consisting of only film A. A rectangular area of 100 cm x 100 cm of the obtained retardation film was visually observed for the presence or absence of folds and wrinkles with a diameter of 1 mm or more, and evaluated according to the following criteria.
A: No folds or wrinkles.
Δ: The total number of folds and wrinkles is less than 5.
×: The total number of folds and wrinkles is 5 or more.

[Production Example 1: Hydrogenated product of ring-opened polymer of dicyclopentadiene]
A metallic pressure-resistant reactor was thoroughly dried and then purged with nitrogen, and 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo isomer content of 99% or more) (30 parts as the amount of dicyclopentadiene), and 1.8 parts of 1-hexene were added to the metallic pressure-resistant reactor, and the reactor was heated to 53°C.

A solution was prepared by dissolving 0.014 parts of tetrachlorotungsten phenylimide (tetrahydrofuran) complex in 0.70 parts of toluene, and 0.061 parts of a 19% diethylaluminum ethoxide/n-hexane solution was added to the solution and stirred for 10 minutes to prepare a catalyst solution.
The catalyst solution was added to the mixture in the pressure-resistant reactor to initiate the ring-opening polymerization reaction. The reaction was then continued for 4 hours while maintaining the temperature at 53° C., to obtain a solution of a ring-opening polymer of dicyclopentadiene.
The number average molecular weight (Mn) and weight average molecular weight (Mw) of the resulting ring-opened polymer of dicyclopentadiene were 8,830 and 29,800, respectively, and the molecular weight distribution (Mw/Mn) calculated from these was 3.37.

0.037 parts of 1,2-ethanediol was added as a terminator to 200 parts of the resulting solution of ring-opened dicyclopentadiene polymer, and the mixture was heated to 60°C and stirred for 1 hour to terminate the polymerization reaction. 1 part of a hydrotalcite-like compound (Kyowa Chemical Industry Co., Ltd.'s "Kyoward (registered trademark) 2000") was added to the solution, which was then heated to 60°C and stirred for 1 hour. 0.4 parts of a filter aid (Showa Chemical Industry Co., Ltd.'s "Radiolight (registered trademark) #1500") was then added, and the adsorbent and the solution were filtered using a PP pleated cartridge filter (Advantec Toyo Co., Ltd.'s "TCP-HX").

100 parts of cyclohexane were added to 200 parts of the filtered ring-opening polymer solution (polymer amount 30 parts), and 0.0043 parts of chlorohydridocarbonyltris(triphenylphosphine)ruthenium was added, and a hydrogenation reaction was carried out at 6 MPa hydrogen pressure and 180°C for 4 hours. This produced a reaction liquid containing a hydride of the ring-opening polymer of dicyclopentadiene. The hydride precipitated from this reaction liquid, forming a slurry solution.

The hydride and the solution contained in the reaction liquid 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 of dicyclopentadiene. The hydrogenation rate of this hydride was 99% or more, the glass transition temperature Tg was 97°C, the melting point Tm was 266°C, and the racemo-dyad ratio was 89%.

[Production Example 2: Pellets of Crystalline Resin (a)]
Crystalline resin (a) was obtained by mixing 100 parts of the hydrogenated product of the ring-opening polymer of dicyclopentadiene obtained in Production Example 1 with 0.5 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane;"Irganox (registered trademark) 1010" manufactured by BASF Japan Ltd.).

The obtained crystalline resin (a) was fed into a twin-screw extruder (Toshiba Machine Co., Ltd., "TEM-37B") equipped with four die holes with an inner diameter of 3 mm. The resin was subjected to hot melt extrusion molding using the twin-screw extruder to form a strand-shaped molded body. This molded body was chopped with a strand cutter to obtain pellets of crystalline resin (a).

Example 1
(1-1. Step (I): Film pA)
The pellets of crystalline resin (a) obtained in Production Example 2 were fed to a hot melt extrusion film molding machine equipped with a T-die. Using this film molding machine, the crystalline resin (a) was formed into a film under the following operating conditions, and taken up on a roll at a speed of 27 m/min.
・Barrel temperature setting: 280℃～290℃
Die temperature: 270°C
Screw rotation speed: 145 rpm
Cast roll temperature: 70°C
Thus, a long film pA made of the crystalline resin (a) was obtained. The obtained film pA had a width of 120 mm and a thickness of 68 μm.

At a wavelength of 590 nm, the in-plane retardation Re(pA) of film pA was 5 nm, the thickness retardation Rth(pA) was 5 nm, and the slow axis direction was the width direction rather than the longitudinal direction.

(1-2. Step (II): Attachment of Protective Film B)
A protective film with an adhesive layer (a film having protective film B and an adhesive layer) was prepared. Protective film B in the protective film with an adhesive layer (product name "ZEONORFILM ZF14-188", manufactured by Zeon Corporation) was a film made of a material (b) (glass transition temperature 137°C) containing an alicyclic structure-containing polymer having a thickness of 188 µm. Protective film B had an in-plane retardation of 10 nm and a thickness retardation of 15 nm at a wavelength of 590 nm.

A protective film with an adhesive layer was attached to one surface of the film pA obtained in (1-1) with the adhesive layer side facing in contact. This resulted in a multilayer film (II) having a layer structure of (film pA)/(adhesive layer)/(protective film B). The ratio of (protective film B thickness)/(film pA thickness) was 2.76.

(1-3. Step (III): Solvent Contact)
The multilayer film (II) obtained in (1-2) was continuously transported along the longitudinal direction, and toluene was applied to the surface of the film pA in the multilayer film (II) opposite to the protective film B using a die coater. This operation changed the birefringence in the thickness direction of the film pA to film qA, and an optical film (III) having a layer structure of (film qA)/(adhesive layer)/(protective film B) was obtained. The optical film (III) was wound around a core to form a film roll.

(1-4. Step (IV): Co-stretching)
The optical film (III) obtained in (1-3) was unwound from the film roll and stretched using a stretching machine. This stretching machine has a structure equipped with a plurality of clips capable of gripping both ends of the film, and the film can be stretched by moving the clips. The stretching temperature was 145° C., the stretching direction was the film width direction, and the stretching ratio was 1.15 times, and fixed-end uniaxial stretching was performed. By this operation, the optical film (III) was stretched, and the optical anisotropy of the film qA was changed to film rA, and an optical film (IV) having a layer structure of (film rA)/(adhesive layer)/(protective film B) was obtained. The optical film (IV) was wound around a winding core to obtain a film roll. The total length of the obtained film was 1000 m.

(1-5. Evaluation)
In the optical film (IV) obtained in (1-4), the thickness of the film rA was 70 μm, and the thickness of the protective film B was 164 μm. Therefore, the ratio of (thickness of protective film B)/(thickness of film rA) was 2.34.
The in-plane retardation Re(rA) of film rA at a wavelength of 590 nm was 125 nm, the thickness direction retardation Rth(rA) was −7 nm, the NZ coefficient was 0.44, and the slow axis direction was perpendicular to the longitudinal direction. The crystallinity of film rA was measured to be 25%.

The optical film (IV) and its film roll were evaluated for curl, deformation during rolling, and deterioration over time during rolling.

Example 2
Except for the fact that the stretching ratio of the co-stretching in (1-4) was 1.00 times, the same operation as in Example 1 was carried out and evaluation was performed. That is, in the step (1-4), stretching was not performed, and the film was moved and heated in a stretching machine at a temperature of 145° C. while maintaining the film dimensions, and an optical film was produced and evaluated.

Comparative Example 1
The protective film B in (1-2) was not laminated. That is, in (1-3), the film pA obtained in (1-1) was used as it was instead of the multilayer film (II) obtained in (1-2), and the evaluation was performed in the same manner as in Example 1.

Comparative Example 2
In (1-2), a protective film B different from that used in (1-2) (product name "ZEONORFILM ZF14-040", manufactured by Zeon Corporation, made of the same material as that used in (1-2), thickness 40 μm) was used, and the evaluation was performed in the same manner as in Example 1.

The operation overview and evaluation results of the examples and comparative examples are shown in Table 1.

As is clear from the results of the Examples and Comparative Examples, the optical film of the present invention obtained by the manufacturing method of the present invention has a film A with an NZ coefficient of less than 1, and yet is a film in which curling, deformation of the wound shape of the film roll, and film deterioration are suppressed.

Claims (6)

A long optical film comprising a film A made of a crystalline resin (a) and a protective film B provided on one surface of the film A,
a thickness DA of the film A and a thickness DB of the protective film B satisfy DB/DA>2;
The NZ coefficient of the film A is less than 1;
The protective film B is made of material (b),
An optical film, wherein the glass transition temperature Tg(a) (°C) of the crystalline resin (a) and the glass transition temperature Tg(b) (°C) of the material (b) satisfy Tg(b) ≧ Tg(a) + 35 . The optical film according to claim 1, wherein the intrinsic birefringence value of the crystalline resin (a) is positive. The optical film according to claim 1 or 2, wherein the crystalline resin (a) contains an alicyclic structure-containing polymer. A method for producing the optical film according to any one of claims 1 to 3 ,
A step (I) of preparing a film pA made of a crystalline resin (a);
A step (II) of laminating a protective film B onto one surface of the film pA;
and (III) a step of contacting the other surface of the film pA with a solvent to change the birefringence in the thickness direction of the film pA to form the film A. The method for producing an optical film according to claim 4 , further comprising, after the step (III), a step (IV) of co-stretching the film A and the protective film B. A method for producing a retardation film, comprising: a step of producing the optical film by the production method according to claim 4 or 5 ; and a step (V) of peeling the protective film B from the optical film.