CN116685455A

CN116685455A - Birefringent film, method for producing same, and method for producing optical film

Info

Publication number: CN116685455A
Application number: CN202180085500.8A
Authority: CN
Inventors: 柴田祐二
Original assignee: Zeon Corp
Current assignee: Zeon Corp
Priority date: 2020-12-28
Filing date: 2021-12-15
Publication date: 2023-09-01
Also published as: JPWO2022145238A1; WO2022145238A1; TW202231705A; KR20230121748A

Abstract

The present invention relates to a birefringent film comprising a solvent A, a solvent B, and a polymer having crystallinity, wherein the boiling point Bp (SA) (DEGC) of the solvent A and the boiling point Bp (SB) (DEGC) of the solvent B satisfy Bp (SA) -Bp (SB) > 5, and wherein the total content of the solvent A and the solvent B in the birefringent film is 0.01 wt% or more and 3 wt% or less, and Rth is not more than-100 nm. The present invention relates to a method for producing a film, comprising a step of bringing a specific film into contact with a mixed solvent containing a solvent A and a solvent B, and changing the birefringence of the film in the thickness direction.

Description

Birefringent film, method for producing same, and method for producing optical film

Technical Field

The present invention relates to a birefringent film that can be usefully used for manufacturing an optical film, a method for manufacturing the birefringent film, and a method for manufacturing the optical film.

Background

Conventionally, resin films having specific optical characteristics have been used for optical applications. For example, a film whose NZ coefficient satisfies 0 < NZ < 1 is called a three-dimensional phase difference film. It is known that when the three-dimensional retardation film is provided in a display device such as a liquid crystal display device, the following effects can be exhibited: that is, the coloring of the display surface viewed from the oblique direction is reduced.

The three-dimensional retardation film has a larger retardation in the z-axis direction (i.e., thickness direction) than in the y-axis direction (i.e., in-plane direction orthogonal to the in-plane slow-axis direction). Therefore, a conventional method for producing a retardation film, such as a resin for an optical film having positive intrinsic birefringence, cannot be used by simply stretching the film. Therefore, it has been proposed to produce a three-dimensional retardation film or a film similar to the three-dimensional retardation film by combining a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence (for example, patent documents 1 to 2).

Prior art literature

Patent literature

Patent document 1: international publication No. 2019/188205;

patent document 2: international publication No. 2020/137409.

Disclosure of Invention

Problems to be solved by the invention

The heretofore proposed method for producing a three-dimensional retardation film which combines a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence has such a problem that: complicated stretching steps, bonding steps after stretching, positioning effort, and the like are required.

Accordingly, an object of the present invention is to provide a means for easily producing a three-dimensional retardation film that can exhibit a good effect.

Solution for solving the problem

If a film having a small retardation Rth in the thickness direction (particularly, a film having a negative Rth and a large absolute value) can be easily obtained, a three-dimensional retardation film can be easily produced by a simple operation (one-time uniaxial stretching or the like) based on this. Accordingly, the present inventors have studied a film which has a small Rth and can be easily produced in order to solve the above-described problems.

In the course of this study, the present inventors studied the following: a resin film containing a polymer having crystallinity is brought into contact with a solvent to form a state in which the solvent is impregnated into the resin, whereby the birefringence of the film in the thickness direction is changed, and a film having a small Rth is produced. However, in the course of the investigation, when the solvent is impregnated into the resin, there is a problem that a large amount of solvent remains in the film. When a large amount of solvent remains, such an undesirable phenomenon occurs: in a display device manufactured using the film, a solvent gradually volatilizes from the film, and the film is deteriorated with time in use, or adversely affects other members of the device. In addition, since the film having a large amount of solvent remaining therein volatilizes the solvent in the subsequent step, an explosion-proof device must be used in the subsequent step. On the other hand, if drying is performed at high temperature for a long period of time in the film production process in order to reduce the amount of residual solvent, the quality of the film is degraded.

In order to reduce the amount of residual solvent, it is considered to use a solvent having a low boiling point. However, according to the studies of the present inventors, a solvent which can sufficiently change birefringence in the thickness direction by acting on a polymer having crystallinity is limited to a solvent having a boiling point higher than the glass transition temperature of the polymer having crystallinity, and a solvent having both a large effect of changing birefringence and high volatility has not been found.

However, the present inventors have further studied and as a result, have found that a combination of a plurality of specific solvents gives a good balance between the high level of birefringence change effect and the high volatility, and as a result, a film exhibiting a good effect as a member for producing a three-dimensional retardation film can be easily produced. The present invention has been completed based on this finding.

Namely, the present invention includes the following.

[1] A birefringent film comprising a solvent A, a solvent B, and a polymer having crystallinity, wherein,

the boiling point Bp (SA) (DEGC) of the solvent A and the boiling point Bp (SB) (DEGC) of the solvent B satisfy Bp (SA) -Bp (SB) > 5,

the total content of the solvent A and the solvent B in the birefringent film is 0.01 wt% or more and 3 wt% or less,

the birefringent film meets Rth of less than or equal to-100 nm.

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

[3] The birefringent film according to [1] or [2], wherein the intrinsic birefringence value of the polymer having crystallinity is positive.

[4] The birefringent film according to any one of [1] to [3], wherein the polymer having crystallinity contains an alicyclic structure.

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

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

[7] A method for producing the birefringent film according to any one of [1] to [6], wherein the method comprises the steps of:

a step (I) of melt-extruding a resin (pA) containing a polymer having crystallinity to form a film (pA); and

and (II) bringing the film (pA) into contact with a mixed solvent containing the solvent A and the solvent B, impregnating the resin (pA) with the solvent, and changing the birefringence of the film (pA) in the thickness direction to form a film (qA).

[8] A method for producing an optical film, comprising the steps of:

a step of obtaining a birefringent film by the production method described in [7 ]; and

and (III) stretching the birefringent film.

Effects of the invention

According to the present invention, a method for producing a three-dimensional retardation film capable of exhibiting a good effect, a birefringent film which can be usefully used for producing the three-dimensional retardation film, and a method for producing the birefringent film are provided.

Detailed Description

The present invention will be described in detail with reference to the following embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be arbitrarily modified and implemented within a range not departing from the scope of the claims and their equivalents.

In the following description, unless otherwise specified, the in-plane retardation Re of a layered structure such as a film is a value represented by re= (nx-ny) ×d. The retardation Rth of the layered structure in the thickness direction is a value represented by rth= [ { (nx+ny)/2 } -nz ] ×d, unless otherwise specified. The NZ coefficient of the layered structure is a value represented by (nx-NZ)/(nx-ny) unless otherwise specified.

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

In the following description, unless otherwise specified, a material having positive intrinsic birefringence refers to a material having a refractive index in the stretching direction that is larger than a refractive index in the direction perpendicular thereto. The material having negative intrinsic birefringence is a material having a refractive index in the stretching direction smaller than that in the direction perpendicular thereto unless otherwise specified. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

In the following description, the term "long film" refers to a film having a length of 5 times or more, preferably 10 times or more, with respect to the width, and specifically refers to a film having a length of such a degree that it can be wound into a roll and stored or transported. The upper limit of the length is not particularly limited, and is usually 10 ten thousand times or less relative to the width.

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

[ birefringent film ]

The birefringent film of the present invention is a film comprising a solvent a, a solvent B, and a polymer having crystallinity. Specifically, the birefringent film of the present invention may be a film composed of a crystalline resin containing a polymer having crystallinity as a main component and further containing a plurality of solvents in specific amounts described below.

[ Polymer having crystallinity ]

"Polymer having crystallinity" means a polymer having a melting point Tm. That is, the "polymer having crystallinity" means a polymer whose melting point can be observed using a Differential Scanning Calorimeter (DSC). In the following description, a polymer having crystallinity is sometimes referred to as "crystalline polymer". The resin containing the crystalline polymer as a main component can exhibit characteristics based on the crystalline polymer. Such resins are sometimes referred to as crystalline resins. The crystalline resin is preferably a thermoplastic resin.

The crystalline polymer preferably has positive intrinsic birefringence, and thus the crystalline resin has a positive intrinsic birefringence value. By using a crystalline resin and a resin having positive intrinsic birefringence, a birefringent film satisfying the requirements of the present invention (in particular, requirements of Rth. Ltoreq. -100 nm) can be produced particularly easily, and a three-dimensional retardation film can be produced easily using such a birefringent film.

The crystalline polymer is not particularly limited, and may be, for example, a polyester such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN); polyolefin such as Polyethylene (PE) and polypropylene (PP), etc., preferably contains an alicyclic structure. By using the crystalline polymer having an alicyclic structure, the mechanical properties, heat resistance, transparency, low hygroscopicity, dimensional stability, and light weight of the film can be improved. The polymer having an alicyclic structure means a polymer having an alicyclic structure in a molecule. Such a polymer having an alicyclic structure may be, for example, a polymer obtainable by polymerization using a cyclic olefin as a monomer or a hydride thereof.

Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure. Among them, a cycloalkane structure is preferable in terms of easy obtaining of a retardation film excellent in characteristics such as thermal stability. The number of carbon atoms contained in the 1 alicyclic structure is preferably 4 or more, more preferably 5 or more, still more preferably 30 or less, still more preferably 20 or less, and particularly preferably 15 or less. By setting the number of carbon atoms contained in the 1 alicyclic structure within the above range, mechanical strength, heat resistance, and moldability can be highly balanced.

In the crystalline polymer having an alicyclic structure, the proportion of the structural unit having an alicyclic structure to the total 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 the structural unit having an alicyclic structure as described above, heat resistance can be improved. The proportion of the structural unit having an alicyclic structure to the total structural units may be 100% by weight or less. In addition, in the crystalline polymer having an alicyclic structure, the remaining portion other than the structural unit having an alicyclic structure is not particularly limited, and can be appropriately selected according to the purpose of use.

Examples of the crystalline polymer having an alicyclic structure include the following polymers (α) to (δ). Among them, the polymer (. Beta.) is preferable in that a retardation film excellent in heat resistance can be easily obtained.

Polymer (α): a ring-opening polymer of a cyclic olefin monomer having crystallinity.

Polymer (β): a hydride of the polymer (. Alpha.) having crystallinity.

Polymer (γ): addition polymers of cyclic olefin monomers having crystallinity.

Polymer (δ): a polymer (. Gamma.) hydride having crystallinity.

Specifically, as the crystalline polymer having an alicyclic structure, a ring-opening polymer of dicyclopentadiene having crystallinity and a hydride of the ring-opening polymer of dicyclopentadiene having crystallinity are more preferable. Among them, a hydrogenated product of a ring-opening polymer of dicyclopentadiene having crystallinity is particularly preferable. The ring-opening polymer of dicyclopentadiene is 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.

The hydrogenated product of the ring-opening polymer of dicyclopentadiene preferably has a high proportion of syndiotactic dyads. Specifically, the proportion of the syndiotactic diad group of the repeating unit in the hydrogenated product of the ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, particularly preferably 85% or more. A high proportion of syndiotactic diads means a high syndiotacticity. Thus, the higher the proportion of the syndiotactic diad, the higher the melting point of the hydrogenated ring-opening polymer of dicyclopentadiene tends to be.

The ratio of the syndiotactic diad groups can be based on the following examples ¹³ C-NMR spectroscopy.

As the above polymers (α) to (δ), polymers obtained by the production method disclosed in international publication No. 2018/062067 can be used.

The melting point Tm of the crystalline polymer is preferably 200℃or higher, more preferably 230℃or higher, and still more preferably 290℃or lower. By using a crystalline polymer having such a melting point Tm, a birefringent film having further excellent balance between moldability and heat resistance can be obtained.

In general, since a crystalline polymer has a glass transition temperature, a crystalline resin containing a crystalline polymer as a main component can also observe a glass transition temperature based on the glass transition temperature of the crystalline polymer. The glass transition temperature TgP of the crystalline polymer is usually 85℃or higher and usually 170℃or lower.

The glass transition temperature TgP and the melting point Tm of the polymer can be determined by the following methods. First, the polymer was melted by heating, and the melted polymer was rapidly cooled with dry ice. Next, the glass transition temperature TgP and the melting point Tm of the polymer can be measured using a Differential Scanning Calorimeter (DSC) at a temperature rise rate (temperature rise pattern) of 10 ℃/min using the polymer as a test object.

The weight average molecular weight (Mw) of the crystalline polymer is preferably 1000 or more, more preferably 2000 or more, preferably 1000000 or less, more preferably 500000 or less. The crystalline polymer having such a weight average molecular weight is excellent in balance between molding processability 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, preferably 4.0 or less, more preferably 3.5 or less. Here, mn represents a number average molecular weight. The crystalline polymer having such a molecular weight distribution is excellent in molding processability.

The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymer can be measured as polystyrene equivalent values by Gel Permeation Chromatography (GPC) using tetrahydrofuran as a developing solvent.

The crystallinity of the crystalline polymer contained in the film of the present invention is not particularly limited, and is usually higher than a certain level. In the case of measuring the crystallinity of the resin containing the crystalline polymer, the specific crystallinity is preferably in the range of 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The upper limit of the crystallinity can be 100% or less. The crystallinity can be measured by an X-ray diffraction method.

The crystalline polymer may be used alone or in combination of 2 or more kinds in any ratio.

The crystalline polymer contained in the birefringent film of the present invention is preferably 50 wt% or more, more preferably 70 wt% or more, and particularly preferably 90 wt% or more. When the ratio of the crystalline polymer is not less than the above lower limit, the film can be improved in the appearance of birefringence and heat resistance. The upper limit of the proportion of the crystalline polymer can be 99.99% by weight or less.

[ solvent ]

The birefringent film of the present invention can comprise solvent a and solvent B as a variety of solvents. These solvents are generally absorbed into the film in step (II) of the production method of the present invention.

All or part of the solvent absorbed into the film in the step (II) can enter the crystalline polymer. Therefore, even if the solvent is dried at a boiling point or higher, it is difficult to easily and completely remove the solvent. Thus, the birefringent films of the present invention typically comprise a solvent.

For solvents A and B, their boiling points have a particular relationship. That is, the boiling point Bp (SA) (. Degree. C.) of the solvent A and the boiling point Bp (SB) (. Degree. C.) of the above-mentioned solvent B satisfy Bp (SA) -Bp (SB). Gtoreq.5 (. Degree. C.).

Bp (SA) -Bp (SB) is 5℃or higher, preferably 10℃or higher. According to the findings of the present inventors, by using solvents a and B having such a relationship of Bp (SA) and Bp (SB) in combination, it is possible to greatly vary the degree to which the polymer having crystallinity is birefringent in the thickness direction to be able to become a material for forming a three-dimensional retardation film, and also to easily volatilize and remove the solvent from the film. The upper limit of Bp (SA) -Bp (SB) is not particularly limited, and may be, for example, 100℃or lower.

In the case where the birefringent film of the present invention contains a mixture of three or more solvents as the solvent, if the above-described requirements are satisfied when two of them are solvent a and solvent B, the birefringent film can be made to satisfy the above-described requirements. In this case, the total of the solvent a and the solvent B may be preferably 50% by weight or more, more preferably 70% by weight or more based on the entire solvent.

The ratio of the solvent a and the solvent B to the total of the solvent a and the solvent B can be varied by appropriately adjusting the amounts used in the production process so that the desired magnitude and volatility of the birefringent change effect can be exhibited. Specifically, the weight ratio of the solvent A to the solvent B can be preferably 3:7 to 99:1, more preferably 4:6 to 9:1.

The total content of the solvent a and the solvent B in the birefringent film of the present invention is 3 wt% or less, preferably 2 wt% or less. By setting the total content of the solvent a and the solvent B to the above upper limit or less, such an undesirable phenomenon can be effectively suppressed: the birefringent film deteriorates with time in use or adversely affects other components of the device in which the birefringent film is mounted. On the other hand, when the birefringent film is produced in a process including the process (II) of the production method of the present invention, 0.01 wt% or more of the solvent can remain. The lower limit of the proportion of the residual solvent may be 0.1 wt% or more.

The type, composition and content ratio of the solvent in the film can be analyzed by an appropriate analysis method. The total content of the solvents in the film can be measured by thermogravimetric analysis.

The solvent contained in the birefringent film of the present invention can be an organic solvent in which the crystalline polymer is not dissolved. Examples of the preferable organic solvent include hydrocarbon solvents such as toluene, decalin, hexane, and limonene; ethers such as tetrahydrofuran; ketones such as methyl ethyl ketone; chlorobenzene; and carbon disulfide.

Specific examples of the combination of the solvent a and the solvent B include a combination of toluene and methyl ethyl ketone, and a combination of toluene and hexane. By using these combinations in the manufacturing process of the birefringent film, the birefringent film including them can be manufactured more easily at normal temperature while exhibiting the desired magnitude and volatility of the birefringent change effect.

In the birefringent film of the present invention, the boiling point Bp (SA) of the solvent a and the boiling point Bp (SB) of the solvent B and the glass transition temperature TgP of the crystalline polymer preferably have a specific relationship. Specifically, they preferably satisfy the relationship of Bp (SA). Gtoreq. TgP and Bp (SB). Ltoreq. TgP. Regarding their relationship, the value of Bp (SA) -TgP is preferably 10℃or higher, more preferably 20℃or higher. The value of TgP-Bp (SB) is preferably 5℃or higher, more preferably 10℃or higher. By making them satisfy this relationship, the magnitude and volatility of the desired birefringence change effect can be better exhibited. The upper limit of the Bp (SA) -TgP value is not particularly limited, and may be, for example, 200 ℃ or lower. The upper limit of the value of TgP-Bp (SB) is not particularly limited, and may be, for example, 100℃or lower.

The birefringent film of the present invention can contain any component in addition to the crystalline polymer and the solvent. Examples of the optional component include: antioxidants such as phenol 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, talc, and the like; fluorescent whitening agents such as diaminostilbene derivatives, coumarin derivatives, azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, benzimidazole derivatives, and benzothiazole derivatives), carbazole derivatives, pyridine derivatives, naphthalene dicarboxylic acid derivatives, and imidazole derivatives; ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fiber; a colorant; a flame retardant; a flame retardant aid; an antistatic agent; a plasticizer; a near infrared ray absorber; a slip agent; a filler; and any polymer other than crystalline polymers such as soft polymers. Any one of the components may be used alone or in combination of 2 or more of the components in any ratio.

[ optical Properties ]

In the birefringent film of the present invention, the retardation Rth in the thickness direction thereof satisfies Rth of-100 nm. Rth is preferably-150 nm or less, more preferably-200 nm or less. When a film having such a small Rth is used, a three-dimensional retardation film can be easily produced by a simple operation (one-time uniaxial stretching or the like). The lower limit of Rth is not particularly limited, and may be, for example, -1000nm or more.

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

[ other physical Properties ]

The thickness of the birefringent film of the present invention can be appropriately adjusted to a thickness that can obtain desired optical characteristics. The thickness of the birefringent film is preferably 10 μm or more, more preferably 15 μm or more, and on the other hand, preferably 200 μm or less, more preferably 150 μm or less. In general, an optical film used for a device such as a display device needs to have a thickness of a certain level or more in order to exhibit optical characteristics, and on the other hand, needs to be thin in order to reduce the thickness of the device. The birefringent film of the present invention can be formed as follows by satisfying the requirements of the present invention: the manufacture of an optical film satisfying desired optical characteristics even when the thickness is thin is facilitated.

In one embodiment, the birefringent film of the present invention may be a processed product of a melt-extruded film. Specifically, as described in the production method of the present invention described later, a resin containing a polymer having crystallinity is melt-extruded to form a film, and the film is further processed to obtain the birefringent film of the present invention.

[ method for producing birefringent film ]

The birefringent film of the present invention can be produced by a production method comprising the following steps (I) to (II). Hereinafter, the method of producing the birefringent film according to the present invention will be described.

Step (I): and (c) a step of melt-extruding the resin (pA) containing the crystalline polymer to form a film (pA).

Step (II): and a step of forming a film (qA) by bringing the film (pA) into contact with a mixed solvent containing the solvent a and the solvent B, impregnating the resin (pA) with the solvent, and changing the birefringence of the film (pA) in the thickness direction.

[ procedure (I) ]

Step (I) is to form a film of a resin (pA) containing a crystalline polymer by melt extrusion molding, thereby obtaining a film (pA). Specifically, the crystalline resin (pA) is melt-extruded by an extrusion apparatus having a die for usual extrusion molding, whereby a film (pA) of the crystalline resin (pA) can be formed into a long film. The conditions for film formation can be appropriately adjusted according to the properties of the crystalline resin (pa). The thickness of the film (pA) formed in the step (I) is not particularly limited, and may be appropriately adjusted so that the thickness of the birefringent film or the optical film as a product is a desired value. The film (pA) may be a film having optical anisotropy, and in particular, the birefringent film of the present invention can be easily produced by supplying the film to a subsequent step even in a state where the film does not have optical anisotropy.

[ procedure (II) ]

In the step (II), the film (pA) is brought into contact with a mixed solvent containing the solvent a and the solvent B. Examples of the respective kinds of the solvent a and the solvent B, and combinations thereof are as described above.

The mixed solvent is composed of only the solvent a and the solvent B, or the solvent a and the solvent B are the main components. The total ratio of the solvent a and the solvent B in the mixed solvent may be preferably 50% by weight or more, and more preferably 70% by weight or more.

The ratio of the solvent a and the solvent B to the total of the solvent a and the solvent B, respectively, can be appropriately adjusted to exhibit a desired large birefringence change effect and volatility. Specifically, the weight ratio of the solvent A to the solvent B can be preferably 3:7 to 99:1, more preferably 4:6 to 9:1.

The contact in the step (II) can be achieved by any operation. Examples of the contact operation include a spraying method in which a mixed solvent is sprayed on the surface of the film (pA); a coating method of coating a mixed solvent on the surface of the film (pA); and an immersion method in which the membrane (pA) is immersed in a mixed solvent. The impregnation method is preferable from the viewpoint of easiness of continuous contact. However, in the case where it is necessary to control the amount of the mixed solvent to be contacted by the coating thickness or the like, the spraying method and the coating method can be preferably performed.

The temperature of the mixed solvent at the time of contact in the step (II) is arbitrary within a range in which the mixed solvent can be maintained in a liquid state, and thus, a range of a melting point of the mixed solvent or higher (typically, a melting point of a solvent having a highest melting point among solvents constituting the mixed solvent or higher) and a boiling point or lower (typically, a boiling point of a solvent having a lowest boiling point among solvents constituting the mixed solvent or lower) can be set. However, from the viewpoint of ease of handling, it is preferable that the solvent constituting the mixed solvent is a combination of substances which are liquid at ordinary temperature and can exhibit a desired birefringence change effect at ordinary temperature, and the operation is performed at ordinary temperature.

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

In the case where the film (pA) is brought into contact with the mixed solvent by the coating of the mixed solvent, the coating thickness calculated from the coating area and the supply amount of the mixed solvent can be appropriately adjusted. The coating thickness is preferably 5 μm or more, more preferably 10 μm or more, and can be preferably 100 μm or less.

When the contact time or the coating thickness is equal to or more than the lower limit value, the birefringence of the birefringent film can be effectively adjusted by contact with the mixed solvent. On the other hand, even if the contact time is made longer than the upper limit or the coating thickness is made thicker than the upper limit, the amount of birefringence adjustment tends not to be changed significantly. In this way, when the contact time or the coating thickness is equal to or less than the upper limit value, productivity can be improved without impairing the quality of the birefringent film.

As a result of the contact with the mixed solvent in the step (II), the thickness of the film (pA) and the birefringence in the thickness direction change to form a film (qA). Such a change due to contact with the mixed solvent is difficult to be obtained by a usual method for producing a retardation film, such as simply stretching a resin for an optical film. Accordingly, as a result of this variation, the birefringent film of the present invention can be easily manufactured.

As a result of the step (II), the obtained film (qA) can be directly used as the birefringent film of the present invention. Alternatively, the obtained film may be further subjected to any treatment to obtain the birefringent film of the present invention. As an example of any process, a process of removing the solvent adhering to the film can be included. Examples of the method for removing the solvent include drying and wiping.

Since the film (qA) has undergone the step (II), the refractive index in the thickness direction thereof can be greatly changed from the state of the film (pA). For example, the film (pA) is optically isotropic, and Rth is 0nm or a value close thereto, whereas the film (qA) as a birefringent film having optical characteristics of Rth of-100 nm can be easily obtained by the step (II), and it is difficult to obtain such optical characteristics by a usual method for producing a retardation film such as simply stretching a resin for an optical film.

[ method for producing optical film ]

The method for manufacturing an optical film of the present invention comprises: a step of obtaining a birefringent film by the method for producing a birefringent film according to the present invention; and (III) stretching the birefringent film. Specifically, the method for producing an optical film of the present invention can be carried out by obtaining the film (qA) through the steps (I) to (II) described above and further stretching the film. By this stretching, the polymer molecules contained in the film (qA) are oriented in a direction along with the stretching direction. Since the film (qA) is subjected to the step (II), an optical film having optical characteristics which are difficult to obtain by a usual method for producing a retardation film, such as simply stretching a resin for an optical film, can be easily obtained.

The stretching in the step (III) may be uniaxial stretching or biaxial stretching or more. The number of stretching may be one or two or more times. Preferably, the stretching is one-time uniaxial stretching or biaxial stretching, and the biaxial stretching is as follows: stretching in one direction and stretching in the other direction are performed simultaneously or sequentially. Since the film (qA) is subjected to the step (II), an optical film having optical characteristics which are difficult to obtain by a usual method for producing a retardation film can be easily obtained by such simple stretching.

In the case of uniaxial stretching, stretching may be free-end uniaxial stretching or fixed-end uniaxial stretching. The free-end uniaxial stretching of the film means uniaxial stretching performed in such a manner as to allow shrinkage in a direction orthogonal to the stretching direction among in-plane directions. In contrast, the fixed-end uniaxial stretching refers to uniaxial stretching performed such that the dimension in the direction orthogonal to the stretching direction is fixed and shrinkage in that direction is not allowed (i.e., stretching in which the stretching magnification in the direction orthogonal to the stretching direction is set to 1 time).

The stretching direction in the step (III) is not limited, and examples thereof include a longitudinal direction, a width direction, and an oblique direction. Here, the oblique direction means a direction that makes an angle of neither 0 ° nor 90 ° with the width direction (i.e., a direction that makes an angle of more than 0 ° and less than 90 ° with the width direction) among directions perpendicular to the thickness direction.

When a film having the same optical characteristics is to be produced by a production method not involving the step (III), a more complicated stretching step and a more complicated resin film structure are generally required, which is disadvantageous from the viewpoint of production efficiency. In contrast, in the production method of the present invention, the optical film can be obtained by a simpler process, and therefore, it is advantageous from the viewpoints of production efficiency and product quality.

The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, still more preferably 20.0 times or less, still more preferably 10.0 times or less, still more preferably 5.0 times or less, and particularly preferably 2.0 times or less. The specific stretching ratio is preferably set appropriately according to factors such as optical characteristics, thickness, and strength of the optical film as a product. When the draw ratio is equal to or greater than the lower limit, the birefringence can be significantly changed by drawing. In addition, when the draw ratio is equal to or less than the upper limit, the direction of the slow axis can be easily controlled, and the film breakage can be effectively suppressed.

The stretching temperature can be defined in accordance with the glass transition temperature TgP of the crystalline polymer. The stretching temperature is preferably "TgP +5" or higher, more preferably "TgP +10" or higher, preferably "TgP +100" or lower, more preferably "TgP +90" or lower. When the stretching temperature is equal to or higher than the lower limit, the film can be sufficiently softened and stretched uniformly. In addition, when the stretching temperature is equal to or lower than the upper limit, the film can be prevented from being cured due to the progress of crystallization of the crystalline polymer, so that the stretching can be smoothly performed, and a large birefringence can be exhibited by the stretching. Further, the haze of the obtained optical film can be reduced and the transparency can be improved. Further, by stretching at this temperature, the crystallinity of the crystalline polymer increases, and as a result, the optical properties of the obtained optical film can be easily adjusted to a desired range.

Since the birefringence can be changed by the step (III), the NZ coefficient can be adjusted. Thus, an optical film having desired optical characteristics can be obtained by stretching in the step (III). The film (sA) obtained as a result of the step (III) can be directly used as an optical film of a product. Or the obtained film may be further subjected to any treatment to obtain a product. Examples of the optional step include a heat treatment in which the dimensions after stretching are maintained, a relaxation treatment in which the dimensions after stretching are reduced, and the like, to adjust the birefringence.

The NZ coefficient NZ (rA) of the optical film obtained by the method for producing an optical film of the present invention can be less than 1. Specifically, 0 < NZ (rA) < 1 can be satisfied. Such a film can be usefully used as a so-called three-dimensional retardation film. NZ (rA) is preferably 0.2 or more, and on the other hand, preferably 0.8 or less. When NZ (rA) is set to this range, the effect of reducing the coloring of the display surface when viewed from the oblique direction can be particularly well exhibited when the optical film is provided in a display device such as a liquid crystal display device.

[ use ]

The birefringent film of the present invention and the optical film produced using the birefringent film of the present invention can be used as a component of an optical device such as a display device, after being processed into a desired shape such as a rectangle, if necessary. When the birefringent film and the optical film of the present invention are used as components of a display device, the viewing angle, contrast, image quality, and other display qualities of an image displayed by the display device can be improved.

Examples (example)

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented within a range not departing from the scope of the claims and the equivalents thereof.

In the following description, unless otherwise indicated, "%" and "parts" representing amounts are weight basis. The operations described below are performed under normal temperature and normal pressure conditions unless otherwise specified.

[ evaluation method ]

(method for measuring weight average molecular weight Mw and number average molecular weight Mn of Polymer)

The weight average molecular weight Mw and the number average molecular weight Mn of the polymer were measured as polystyrene equivalent values using a Gel Permeation Chromatography (GPC) system (manufactured by Tosoh corporation, "HCL-8320"). 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 at the time of measurement was 40 ℃.

(method for measuring hydrogenation Rate of Polymer)

The hydrogenation rate of the polymer is that of ortho-dichlorobenzene-d ⁴ As solvent, at 145 DEG C ¹ H-NMR measurement was performed.

[ method for measuring glass transition temperature Tg and melting Point Tm ]

The glass transition temperature Tg and melting point Tm of the polymer are measured as follows. First, the polymer was melted by heating, and the melted polymer was rapidly cooled with dry ice. Next, using the polymer as a test body, the glass transition temperature Tg and the melting point Tm of the polymer were measured at a temperature rise rate (temperature rise pattern) of 10 ℃/min using a Differential Scanning Calorimeter (DSC).

(method for measuring the proportion of the syndiotactic diad of Polymer)

The proportion of the syndiotactic polymer diads was measured as follows. O-dichlorobenzene-d ⁴ As solvent, the polymer was subjected to reverse-gated decoupling (reverse-gated decoupling) at 200℃ ¹³ C-NMR measurement. According to the following ¹³ Results of C-NMR measurement with o-dichlorobenzene-d ⁴ The peak at 127.5ppm was shifted on the basis to identify a 43.35ppm signal from the isotactic diad and a 43.43ppm signal from the syndiotactic diad. Based on the intensity ratio of these signals, the proportion of the syndiotactic diads of the polymer was determined.

(method for measuring optical characteristics such as retardation Re and Rth of film)

Optical characteristics such as in-plane retardation Re and retardation in the thickness direction Rth of the film were measured by a retardation meter (manufactured by axome corporation, "AxoScan OPMF-1"). The measurement wavelength was 590nm.

(method for measuring film thickness)

The thickness of the film was measured using a contact thickness meter (Code No.543-390, manufactured by Sanfeng Co.).

(method for measuring total content of solvents)

The weight of the film (pA) was measured by thermogravimetric analysis (TGA: temperature rise rate of 10 ℃/min, 30 ℃ C. To 300 ℃ C. Under nitrogen atmosphere). Weight W of film (pA) from 30 DEG C _O (30 ℃) minus the weight W of the 300℃film _O (300 ℃ C.) and a weight reduction amount ΔW of the film at 300 ℃ C. Was obtained _O . The films (pA) used in examples and comparative examples described later were produced by the melt extrusion method, and therefore contained no solvent. Thus, the weight reduction ΔW of the membrane (pA) is used _O The following formula (X) is used as a reference.

The weight of the film to be measured was measured by thermogravimetric analysis (TGA: temperature rise rate 10 ℃ C./min, 30 ℃ C. -300 ℃ C.) in the same manner as described above. Weight W of film from 30 DEG C _R (30 ℃) minus the weight W of the 300℃film _R (300 ℃ C.) and a weight reduction amount ΔW of the film at 300 ℃ C. Was obtained _R 。

By the following formula (X), the weight of the film (pA) at 300℃was reduced by a small amount of ΔW _O And a weight reduction amount ΔW of a film to be measured at 300 ℃ _R The total content of solvents in the film was calculated.

Total content (%) = { (Δw) of solvents _R -ΔW _o )/W _R (30 ℃ C.) } ×100 (X) [ preparation example 1. Preparation of crystalline resin comprising a hydride of a Ring-opened Polymer of dicyclopentadiene]

After the metal pressure-resistant reactor was sufficiently dried, nitrogen substitution was performed. To this metal pressure-resistant reactor were added 154.5 parts of cyclohexane, 42.8 parts of a cyclohexane solution (30 parts as dicyclopentadiene) having a concentration of 70% of dicyclopentadiene (the content of the internal form of which is 99% or more), and 1.9 parts of 1-hexene, and the mixture was heated to 53 ℃.

A solution was prepared by dissolving 0.014 parts of tungsten tetrachloride-phenylimide (tetrahydrofuran) complex in 0.70 parts of toluene. To this solution, 0.061 parts of a 19% strength diethyl aluminum ethoxide/n-hexane solution was added and stirred for 10 minutes to prepare a catalyst solution. The catalyst solution was added to a pressure-resistant reactor to initiate ring-opening polymerization. Then, the reaction was carried out at 53℃for 4 hours to obtain a solution of a ring-opening polymer of dicyclopentadiene. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the obtained ring-opened polymer of dicyclopentadiene were 8750 and 28100, respectively, and the molecular weight distribution (Mw/Mn) thereof was found to be 3.21.

To 200 parts of the obtained solution of the ring-opening polymer of dicyclopentadiene, 0.037 part of 1, 2-ethylene glycol as a terminator was added, and the mixture was heated to 60℃and stirred for 1 hour to terminate the polymerization. At this time, 1 part of a hydrotalcite-like compound (Kyowa (registered trademark) 2000, manufactured by Kyowa chemical industry Co., ltd.) was added, heated to 60℃and stirred for 1 hour. Then, 0.4 part of a filter aid (manufactured by Showa chemical industry Co., ltd., "radio (registered trademark) # 1500") was added, and the adsorbent and the solution were separated by filtration using a polypropylene pleated cartridge filter (manufactured by ADVANTEC Toyo Co., ltd., "TCP-HX").

To 200 parts of the filtered solution of the ring-opening polymer of dicyclopentadiene (30 parts of the polymer amount) was added 100 parts of cyclohexane, and 0.0043 parts of tris (triphenylphosphine) ruthenium chlorohydrocarbonyl was added, and hydrogenation was carried out at a hydrogen pressure of 6MPa and a temperature of 180℃for 4 hours. Thus, a reaction solution containing a hydrogenated product of a ring-opening polymer of dicyclopentadiene was obtained. In this reaction solution, a hydride is precipitated to form a slurry solution.

The hydride contained in the reaction solution was separated from the solution by using a centrifugal separator, and dried under reduced pressure at 60℃for 24 hours to obtain 28.5 parts of a hydride of a ring-opening polymer of dicyclopentadiene having crystallinity. The hydrogenation rate of the hydride is more than 99%, the glass transition temperature TgP is 93 ℃, the melting point Mp is 262 ℃, and the proportion of the syndiotactic diad is 89%.

To 100 parts of the obtained hydrogenated ring-opening polymer of dicyclopentadiene, 1.1 parts of antioxidant (tetrakis [ methylene-3- (3 ',5' -di-t-butyl-4 ' -hydroxyphenyl) propionate ] methane, "Irganox (registered trademark) 1010" manufactured by Basfujapan) was mixed, and then added to a biaxial extruder (product name "TEM-37B" manufactured by Toshiba machinery Co., ltd.) having 4 die holes with an inner diameter of 3mm phi. After molding a mixture of a hydrogenated ring-opening polymer of dicyclopentadiene and an antioxidant into a strand shape by hot melt extrusion molding, the strand was cut in a wire cutter to obtain a crystalline resin (pa) in a pellet shape. The operation conditions of the twin-screw extruder described above are as follows.

Barrel set temperature=270 to 280 DEG C

Die set temperature=250℃

Screw speed = 145rpm

Example 1

(1-1. Process (I) production of Membrane (pA))

The crystalline resin (pA) produced in production example 1 was molded using a hot-melt extrusion film molding machine (product of Optical Control Systems Co., ltd. "Measuring Extruder Type Me-20/2800V 3") having a T die, and wound into a roll at a speed of 1.5 m/min to obtain a long film (pA) having a width of about 120mm (thickness 50 μm). The operation conditions of the film forming machine are as follows.

Barrel set temperature=280 to 300 DEG C

Die temperature=270℃

Screw speed = 30rpm

Casting roll temperature=80℃

( 1-2, step (II): contact of Membrane (pA) with Mixed solvent )

The film (pA) was cut into a rectangular film (pA) of 100mm by 100 mm. The optical properties of the film (pA) were measured. The in-plane retardation Re of the film (pA) was 5nm, and the retardation Rth in the thickness direction was 6nm. Since this resin film is produced by hot melt extrusion at a high temperature (280 to 300 ℃) as described above, the resin film is considered to contain no solvent, and therefore the solvent content thereof is set to 0.0%.

1, the method comprises the following steps: 1 (weight ratio) toluene (boiling point Bp (SA) =110.6 ℃) and methyl ethyl ketone (boiling point Bp (SB) =79.6 ℃) were mixed to prepare a mixed solvent M1.

The flat-bottom square dish (vat) was filled with the mixed solvent M1, and the rectangular film (pA) was immersed therein for 5 seconds. Then, the film (pA) was taken out of the mixed solvent M1, the solvent on the film surface was wiped off with gauze, and the film was dried in a drying oven at 90℃for 1 minute to obtain a birefringent film (qA).

The birefringent film (qA) was evaluated for optical properties and physical properties. The in-plane retardation Re of the birefringent film (qA) was 18nm, the thickness-direction retardation Rth was-292 nm, the thickness was 64 μm, the crystallinity was 13%, and the total content of solvents was 2%.

Example 2

Toluene and n-hexane (boiling point Bp (SB) =68.7 ℃) were mixed at 1:1 (weight ratio) to prepare a mixed solvent M2.

A birefringent film (qA) was obtained and evaluated in the same manner as in example 1, except that the mixed solvent M2 was used instead of the mixed solvent M1. The in-plane retardation Re of the birefringent film (qA) was 18nm, the thickness-direction retardation Rth was-354 nm, the thickness was 64 μm, the crystallinity was 14%, and the total content of the solvents was 1.7%.

Comparative example 1

A birefringent film (qA) was obtained and evaluated in the same manner as in example 1, except that toluene was used instead of the mixed solvent M1. The in-plane retardation Re of the birefringent film (qA) was 20nm, the thickness-direction retardation Rth was-575 nm, the thickness was 64 μm, the crystallinity was 15%, and the total content of solvents was 6.2%.

Comparative example 2

A birefringent film (qA) was obtained and evaluated in the same manner as in example 1, except that methyl ethyl ketone was used instead of the mixed solvent M1. The in-plane retardation Re of the birefringent film (qA) was 12nm, the thickness-direction retardation Rth was-17 nm, the thickness was 64 μm, the crystallinity was 3%, and the total content of solvents was 0.8%.

The summaries and evaluation results of examples 1 to 2 and comparative examples 1 to 2 are shown in table 1 below.

TABLE 1

Example 3

A stretching apparatus (SDR-562Z, manufactured by ETO Co., ltd.) was prepared. The stretching device includes an oven and a clamp capable of holding an end portion of a rectangular resin film. In total, 24 jigs were provided, 5 jigs were provided on each 1 side of the resin film, and 1 jig was provided on each vertex of the resin film, and stretching of the resin film was enabled by moving these jigs. In addition, the number of ovens is 2, and the stretching temperature and the heat treatment temperature can be set separately. Further, in this stretching apparatus, the movement of the resin film from one oven to another oven can be directly performed in a state of being held by a jig.

The birefringent film (qA) obtained in example 1 was mounted in a stretching apparatus, and the birefringent film (qA) was treated at a preheat temperature of 110 ℃ for 10 seconds. Then, the birefringent film (qA) was stretched at a stretching temperature of 110 ℃, a longitudinal stretching ratio of 1 time, a transverse stretching ratio of 1.5 times, and a stretching speed of 1.5 times/10 seconds. The "longitudinal stretching ratio" mentioned above means a stretching ratio in a direction coincident with the longitudinal direction of the long raw material film, and the "transverse stretching ratio" means a stretching ratio in a direction coincident with the width direction of the long raw material film. Thus, the birefringent film (qA) was subjected to stretching treatment to obtain an optical film (rA).

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

As is clear from the results of examples and comparative examples, according to the production method of the present invention, both the magnitude of the effect of the birefringence change and the volatility are compatible, and as a result, a film exhibiting a good effect as a member for producing a three-dimensional retardation film can be easily produced.

Claims

1. A birefringent film comprising a solvent A, a solvent B, and a polymer having crystallinity,

the boiling point Bp (SA) (DEGC) of the solvent A and the boiling point Bp (SB) (DEGC) of the solvent B meet the conditions of Bp (SA) -Bp (SB) not less than 5,

the birefringent film meets Rth of less than or equal to-100 nm.

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

3. The birefringent film according to claim 1 or 2, wherein the polymer having crystallinity has an intrinsic birefringence value of positive.

4. The birefringent film according to any one of claims 1 to 3, wherein the polymer having crystallinity contains an alicyclic structure.

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

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

7. A method for producing the birefringent film according to any one of claims 1 to 6, comprising the steps of:

and (II) bringing the film (pA) into contact with a mixed solvent containing the solvent A and the solvent B, impregnating the resin (pA) with the mixed solvent, and changing the birefringence of the film (pA) in the thickness direction to form a film (qA).

8. A method for producing an optical film, comprising the steps of:

a step of obtaining a birefringent film by the production method according to claim 7; and

and (III) stretching the birefringent film.