WO2022145174A1

WO2022145174A1 - Optical film and manufacturing method therefor

Info

Publication number: WO2022145174A1
Application number: PCT/JP2021/044567
Authority: WO
Inventors: 浩成摺出寺; 恭輔井上
Original assignee: 日本ゼオン株式会社
Priority date: 2020-12-28
Filing date: 2021-12-03
Publication date: 2022-07-07
Also published as: TW202239832A; JPWO2022145174A1

Abstract

An optical film comprising a resin that includes a polymer with a crystalline property, wherein the absolute value of the retardation Rth in the thickness direction is 15 nm or less, the in-plane retardation Re is 10 nm or less, and the thermal expansion coefficient is 0% to 7.5%.

Description

Optical film and its manufacturing method

The present invention relates to an optical film and a method for manufacturing the same.

A resin containing a crystalline polymer is generally superior in heat resistance to a resin containing an amorphous polymer. Therefore, a resin containing a crystalline polymer is used as a material for an optical film that is required to have heat resistance (Patent Documents 1 and 2).

International Publication No. 2018/061841 (Corresponding Foreign Gazette: US Patent Application Publication No. 2019/255757) International Publication No. 2018/124137

When the optical film is used as a protective film for an optical element such as a polarizing element, it is preferable that the optical film does not change the optical characteristics required for the optical element.
However, when an optical film made of a resin containing a crystalline polymer is combined with another optical element, the original optical characteristics of the optical element may be significantly changed. For example, when a polarizing plate in which a polarizing element and an optical film are combined is incorporated into an image display device, the optical film may change the color tone when observed from an inclined direction.
On the other hand, the optical element can be used in a high temperature environment. Therefore, in order to use it in combination with an optical element, it is preferable that the optical film is less deformed at a high temperature, and for example, it is preferable that the occurrence of wrinkles at a high temperature is reduced.
Therefore, it is an optical film made of a crystalline resin, and when combined with other optical elements, the original optical characteristics of the optical element are not significantly changed, and the occurrence of wrinkles at high temperatures is reduced. A film and a method for manufacturing the optical film are required.

As a result of diligent studies to solve the above problems, the present inventor has formed an optical film from a resin having crystalline properties, and the retardation Rth, the in-plane retardation, and the heat of the optical film in the thickness direction of the optical film. We have found that the above problems can be solved by keeping the expansion rate within a predetermined range, and have completed the present invention.
That is, the present invention provides the following.

[1] It is made of a resin containing a crystalline polymer.
The absolute value of retardation Rth in the thickness direction is 15 nm or less.
In-plane retardation Re is 10 nm or less,
An optical film having a coefficient of thermal expansion of 0% or more and 7.5% or less.
[2] The optical film has a first surface and a second surface.
The central part, which is the part including the center in the thickness direction,
The first outer portion, which is outside in the thickness direction with respect to the central portion and includes the first surface, and the first outer portion.
It is composed of a second outer portion, which is outside in the thickness direction with respect to the central portion and is a portion including the second surface.
The retardation Rth in the thickness direction is positive in the central portion, and the retardation Rth is positive.
The retardation Rth in the thickness direction is negative in at least one of the first outer portion and the second outer portion.
The optical film according to [1].
[3] The optical film according to [1] or [2], which is long.
[4] The optical film according to any one of [1] to [3], wherein the intrinsic birefringence value of the resin containing the crystalline polymer is positive.
[5] The method for producing an optical film according to any one of [1] to [4].
Step (1) of extruding a resin containing a crystalline polymer to obtain a film (a).
A step (2) of applying a solvent on at least one of the two surfaces of the film (a) to form a solvent layer to obtain a film (a'), and the film (a'. ) To dry the solvent layer to obtain a film (b), which comprises the step (3).
Here, the total thickness of the solvent layer formed on at least one surface of the film (a) in the step (2) is 10 μm or less.
Manufacturing method of optical film.

According to the present invention, an optical film made of a crystalline resin does not significantly change the original optical characteristics of the optical element when combined with other optical elements, and the occurrence of wrinkles at high temperatures is reduced. It is possible to provide an optical film and a method for manufacturing the optical film.

FIG. 1 is a sectional view schematically showing an optical film according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail by showing embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be arbitrarily modified and carried out without departing from the scope of claims of the present invention and the equivalent scope thereof.

In the following description, the "long" film means a film having a length of 5 times or more with respect to the width, preferably a film having a length of 10 times or more, and specifically, a roll. A film that has a length that allows it to be rolled up and stored or transported. The upper limit of the length of the film is not particularly limited and may be, for example, 100,000 times or less with respect to the width.

In the following description, the angle formed by the optical axis (slow phase axis, transmission axis, absorption axis, etc.) of each layer in the member having a plurality of layers is the angle when the layer is viewed from the thickness direction unless otherwise specified. Represents.

In the following description, the diagonal direction of a long film indicates an in-plane direction of the film, which is neither parallel nor perpendicular to the longitudinal direction of the film, unless otherwise specified.

In the following description, the front direction of a certain film means the normal direction of the main surface of the film, and specifically, the direction of the polar angle 0 ° and the azimuth angle 0 ° of the main surface, unless otherwise specified. Point to.

In the following description, the tilting direction of a film means a direction that is neither parallel nor perpendicular to the main surface of the film, and specifically, the polar angle of the main surface is larger than 0 ° and 90. Points in a range smaller than °.

In the following description, a material having a positive intrinsic birefringence means a material in which the refractive index in the stretching direction is larger than the refractive index in the direction perpendicular to it, unless otherwise specified. Further, the material having a negative intrinsic birefringence means a material in which the refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the refractive index, unless otherwise specified. The value of the intrinsic birefringence can be calculated from the permittivity distribution.

In the following description, the in-plane retardation Re of the layer or film is a value represented by Re = (nx-ny) × d unless otherwise specified. Further, the retardation Rth in the thickness direction of the layer or the film is a value represented by Rth = [{(nx + ny) / 2} -nz] × d unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer or film (in-plane direction) and in the direction giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the layer or film and orthogonal to the direction of nx. nz represents the refractive index in the thickness direction of the layer or film. d represents the thickness of the layer or film. The measurement wavelength is 590 nm unless otherwise specified.

In the following description, unless the directions of the elements are "parallel", "vertical" and "orthogonal", they are within the range that does not impair the effect of the present invention, for example, ± 3 °, ± 2 ° or ± 1 °. It may include an error within the range of.

In the following description, the longitudinal direction of the long film is usually parallel to the film transport direction in the production line. Further, the MD direction (machine direction) is the transport direction of the film in the production line, and is usually parallel to the longitudinal direction of the long film. Further, the TD direction (transverse direction) is a direction parallel to the film surface, a direction perpendicular to the MD direction, and usually parallel to the width direction of a long film.

[1. Overview of optical film]
The optical film according to the embodiment of the present invention is made of a resin containing a polymer having crystallinity, the absolute value of the retardation Rth in the thickness direction is 15 nm or less, and the in-plane retardation Re is 10 nm or less. Yes, the coefficient of thermal expansion is 0% or more and 7.5% or less.
When the optical film of the present embodiment is combined with other optical elements, the original optical characteristics of the optical elements are not significantly changed, and the occurrence of wrinkles at high temperatures is reduced. Even if the optical film of the present embodiment is incorporated into an image display device as a polarizing plate in combination with a polarizing element, for example, the color tone when observed from an inclined direction does not change significantly.

[1.1. Optical film material]
The optical film according to the present embodiment is made of a resin containing a polymer having crystallinity, and is formed of the resin.

The "polymer having crystallinity" represents a polymer having a melting point Tm. That is, the "polymer having crystallinity" represents a polymer whose melting point can be observed with a differential scanning calorimeter (DSC). In the following description, a polymer having crystallinity may be referred to as a “crystalline polymer”. Further, a resin containing a crystalline polymer may be referred to as a "crystalline resin". This crystalline resin is preferably a thermoplastic resin.

The crystalline polymer preferably has a positive intrinsic birefringence. By using a crystalline polymer having positive intrinsic birefringence, an optical film having desired optical properties can be easily produced.

The crystalline polymer may be, for example, a polyester such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN); a polyolefin such as polyethylene (PE) or polypropylene (PP); and is not particularly limited. It preferably contains an alicyclic structure. By using the crystalline polymer containing an alicyclic structure, the mechanical properties, heat resistance, transparency, low hygroscopicity, dimensional stability and lightness of the optical film can be improved. The polymer containing an alicyclic structure represents a polymer having an alicyclic structure in the molecule. The polymer containing such an alicyclic structure can be, for example, a polymer obtained by a polymerization reaction 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 these, the cycloalkane structure is preferable because it is easy to obtain an optical film having excellent properties such as thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. be. 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 the crystalline polymer containing an alicyclic structure, the ratio of the structural unit having an alicyclic structure to all the structural units is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight. % Or more. Heat resistance can be improved by increasing the proportion of structural units having an alicyclic structure as described above. The ratio of structural units having an alicyclic structure to all structural units may be 100% by weight or less. Further, in the crystalline polymer containing an alicyclic structure, the balance other than the structural unit having an alicyclic structure is not particularly limited and may be appropriately selected depending on the purpose of use.

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

Specifically, the crystalline polymer containing an alicyclic structure includes a ring-opening polymer of dicyclopentadiene having crystalline property and a hydride of a ring-opening polymer of dicyclopentadiene. Those having crystalline properties are more preferable. Of these, a hydride of a ring-opening polymer of dicyclopentadiene, which has crystallinity, is particularly preferable. Here, in the open-ring polymer of dicyclopentadiene, the ratio of the structural unit derived from dicyclopentadiene to all the structural units is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more. More preferably, it refers to a polymer of 100% by weight.

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

As the polymer (α) to the polymer (δ), a polymer 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 ° 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 having a better balance between moldability and heat resistance can be obtained.

Normally, the crystalline polymer has a glass transition temperature Tg. The specific glass transition temperature Tg of the crystalline polymer 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 the polymer can be measured by the following methods. First, the polymer is melted by heating, and the melted polymer is rapidly cooled with dry ice. Subsequently, using this polymer as a test piece, the glass transition temperature Tg and melting point Tm of the polymer were measured at a heating rate of 10 ° C./min (heating mode) using a differential scanning calorimeter (DSC). Can be measured.

The weight average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, preferably 1,000,000 or less, and more preferably 500,000 or less. A crystalline polymer having such a weight average molecular weight has an excellent 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, and more preferably 3.5 or less. Here, Mn represents a number average molecular weight. A 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 optical film is not particularly limited, but is usually higher than a certain level. The high crystallinity of the crystalline polymer contained in the optical film can be confirmed by the magnitude of the coefficient of thermal expansion described later. The smaller the coefficient of thermal expansion of the optical film, the higher the crystallinity of the crystalline polymer contained in the optical film.
The specific range of crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more.
The crystallinity of the crystalline polymer can be measured by X-ray diffraction.

As the crystalline polymer, one type may be used alone, or two or more types may be used in combination at any ratio.

The proportion of the crystalline polymer in the crystalline resin is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the ratio of the crystalline polymer is not more than the lower limit of the above range, the heat resistance of the optical film can be enhanced. The upper limit of the proportion of the crystalline polymer may be 100% by weight or less.

The crystalline resin may contain any component in addition to the crystalline polymer. Optional components include, for example, antioxidants such as phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants; light stabilizers such as hindered amine-based light stabilizers; petroleum-based waxes, Fishertroph waxes, etc. Waxes such as polyalkylene wax; sorbitol compounds, metal salts of organic phosphates, metal salts of organic carboxylic acids, nucleating agents such as kaolin and talc; diaminostilben derivatives, coumarin derivatives, azole derivatives (eg, benzoxazole derivatives, etc.) Fluorowhitening agents such as benzotriazole derivatives, benzoimidazole derivatives, and benzothiazole derivatives), carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolone derivatives; benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, benzotriazole-based UV absorbers such as UV absorbers; Inorganic fillers such as talc, silica, calcium carbonate, glass fibers; Colorants; Flame retardants; Flame retardant aids; Antistatic agents; Plastics; Near infrared absorbers; Lubricants; Fillers ; And any polymer other than the crystalline polymer, such as a soft polymer; and the like. As the arbitrary component, one kind may be used alone, or two or more kinds may be used in combination at any ratio.

[1.2. Characteristics of optical film]
(Letteration Rth in the thickness direction)
In the optical film of the present embodiment, the absolute value of retardation Rth in the thickness direction is usually 15 nm or less, preferably 3 nm or less, more preferably 1 nm or less, usually 0 nm or more, and ideally 0 nm. When the absolute value of the retardation Rth in the thickness direction is equal to or less than the upper limit value, it is possible to prevent the optical characteristics of the optical element from being significantly changed when combined with other optical elements. For example, when an optical film is used as an element of an image display device (for example, a protective film for a polarizing element), it is possible to reduce a change in the tint of an image when observed from an inclined direction.

In the optical film of the present embodiment, it is preferable that the sign of the retardation Rth in the thickness direction (hereinafter, "letteration in the thickness direction" is also simply referred to as "Rth") changes in the thickness direction. Specifically, it is preferable that the Rth code is different between the central portion in the thickness direction of the optical film and at least one of the first outer portion and the second outer portion of the optical film, and the Rth of the central portion. It is more preferable that the sign is positive and the sign of at least one of the first outer portion and the second outer portion is negative, and the sign of Rth in the central portion is positive and the first outer portion. And it is more preferable that the sign of Rth of both of the second outer portions is negative. By providing the optical film with the above-mentioned preferable configuration, it is possible to easily realize the lettering within a desired range.

FIG. 1 is a sectional view schematically showing an optical film according to an embodiment of the present invention. The optical film 100 is composed of a central portion 110, a first outer portion 121, and a second outer portion 122.
The optical film 100 has a first surface 100U and a second surface 100D. The center 111 in the thickness direction of the optical film 100 is a surface equidistant from the first surface 100U and the second surface 100D. The central portion 110 is a portion including the central 111 in the thickness direction. The first outer portion 121 is located outside the central portion 110 in the thickness direction and includes the first surface 100U. The second outer portion 122 is located outside the central portion 110 in the thickness direction and includes the second surface 100D.

The Rth value of the central portion 110 is positive, and the Rth value of the first outer portion 121 and the second outer portion 122 are both negative.

As described above, the optical film 100 in which the Rth value of the central portion 110 is positive and the Rth value of the first outer portion 121 and the second outer portion 122 is negative is manufactured from the crystalline resin by extrusion molding. It can be produced by a production method including coating an organic solvent on both sides of the extruded film to form a solvent layer. The reason why the optical film 100 can be manufactured by this manufacturing method is presumed as follows, but the present invention is not limited.

It is considered that the extruded film is slightly stretched in the transport direction when the crystalline resin is extruded, and the thickness direction retardation Rth has a positive value.
By applying a solvent on both sides of the extruded film, the solvent penetrates into the extruded film. It is considered that the action of the infiltrated solvent causes microBrownian motion in the molecules of the crystalline polymer in the extruded film, and the molecular chains of the extruded film are oriented.

By the way, the surface area of the extruded film is large on the front surface and the back surface, which are the main surfaces. Therefore, as for the infiltration rate of the solvent, the infiltration rate in the thickness direction through the front surface or the back surface is high. Then, the orientation of the molecular chains of the crystalline polymer can proceed so that the molecules of the polymer are oriented in the thickness direction. Further, by applying the solvent to the extruded film instead of immersing the extruded film in the solvent, the solvent penetrates into the outer portion in the thickness direction of the extruded film, but reaches the central portion in the thickness direction of the extruded film. It is thought that it will not be reached.
As a result, the Rth in the central portion of the optical film is a positive value that is the same as or close to the value of the extruded film before the solvent is applied, and the first outer portion and the second outer portion of the optical film. It is considered that the refractive index in the thickness direction becomes large and Rth becomes a negative value.

When the solvent is applied only on one side of the extruded film, the outer part of the optical film including the surface coated with the solvent has a large refractive index in the thickness direction, and the outer part has a negative Rth. It is considered to be a value. Further, it is considered that the outer portion of the optical film including the surface not coated with the solvent has a positive Rth value as in the central portion.

(In-plane Letteration Re)
The optical film of the present embodiment has an in-plane retardation Re of usually 10 nm or less, preferably 5 nm or less, more preferably 3 nm or less, and usually 0 nm or more. When the in-plane retardation Re is not more than the upper limit value, the influence of the optical film on the original optical characteristics of the optical element can be reduced when the optical film is used as a protective film for the optical element.

The film retardation can be measured using a phase difference meter (for example, "AXoScan OPMF-1" manufactured by AXOMETRICS).

(Coefficient of thermal expansion)
The optical film of the present embodiment has a coefficient of thermal expansion of usually 7.5% or less, preferably 7% or less, more preferably 6.5% or less, and usually 0% or more. When the coefficient of thermal expansion of the optical film is not more than the upper limit value, the heat resistance of the optical film can be improved.

Here, the coefficient of thermal expansion is a value measured under the following conditions.
A sample is obtained by cutting out an optical film into a rectangular shape. This cutting is performed so that the longitudinal direction of the rectangular sample coincides with the MD direction (longitudinal direction in the long film) or the TD direction (width direction in the long film) of the film.
With a tension of 50 mN applied in the longitudinal direction of the obtained sample, the linear expansion ΔL from a temperature of 20 ° C. to 130 ° C. is measured at a heating rate of 10 ° C./min.
Divide the measured value of linear expansion ΔL by the original length (that is, the length L before linear expansion) to obtain the coefficient of thermal expansion (%) in the MD and TD directions according to the following formula, and calculate the average value. The coefficient of thermal expansion of the optical film is _RTMA (%).
Coefficient of thermal expansion (%) = (ΔL / L) × 100

The coefficient of thermal expansion _RTMA of the optical film measured under the above conditions can be an index of the degree of crystallinity of the crystalline resin contained in the optical film. The smaller the coefficient of thermal expansion _RTMA of the optical film, the higher the crystallinity of the crystalline resin contained in the optical film tends to be.
When the coefficient of thermal expansion of the optical film is within the above range, the heat resistance of the optical film can be improved.

(Thickness)
The thickness of the optical film can be appropriately set according to the application of the optical film. The thickness d of the optical film is preferably 5 μm or more, more preferably 10 μm or more, preferably 80 μm or less, and more preferably 70 μm or less. When the thickness d of the optical film is not less than the lower limit of the above range, the handleability can be improved and the strength can be increased. Further, when the thickness d of the optical film is not more than the upper limit value, it is easy to wind the long optical film.

The optical film of the present embodiment may be a single-wafer film or a long film. Optical films are usually manufactured as long films. Long optical films can be efficiently combined with other long optical elements using the roll-to-roll method. Therefore, the optical film is preferably long.

(transparency)
The optical film of the present embodiment preferably has high transparency. The specific total light transmittance of the optical film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The total light transmittance of the optical film is usually 100% or less. The total light transmittance of the optical film can be measured in the wavelength range of 400 nm to 700 nm using an ultraviolet / visible spectrometer.

[2. Optical film manufacturing method]
The optical film of the present embodiment can be produced by any method. For example, the optical film can be manufactured by a manufacturing method including the following steps.
Step (1): A step of extruding a resin containing a crystalline polymer to obtain a film (a).
Step (2): A step of applying a solvent on at least one of the two surfaces of the film (a) to form a solvent layer to obtain a film (a').
Step (3): A step of drying the solvent layer of the film (a') to obtain the film (b).
The normal step (2) is performed after the step (1). The normal step (3) is performed after the step (2). The method for producing an optical film of the present embodiment may include any step in addition to the steps (1) to (3).

[2.1. Process (1)]
In the step (1), the resin containing the crystalline polymer is extruded to obtain a film (a).
The resin containing the crystalline polymer used in the step (1) can be the same as the resin containing the crystalline polymer contained in the optical film. However, the crystallinity of the crystalline polymer contained in the film (a) is preferably small. The specific crystallinity is preferably less than 10%, more preferably less than 5%, and particularly preferably less than 3%. When the crystallinity of the crystalline polymer contained in the film (a) before coating with the organic solvent is low, it is easy to control the retardation Rth in the thickness direction of the optical film by the amount of coating of the organic solvent. It becomes.

The manufacturing conditions by the extrusion molding method are as follows, for example.
The cylinder temperature (molten resin temperature) is preferably Tm or higher, more preferably "Tm + 20 ° C" or higher, preferably "Tm + 100 ° C" or lower, and more preferably "Tm + 50 ° C" or lower. Further, the cooling body that the molten resin extruded into a film comes into contact with first is not particularly limited, but a cast roll is usually used. The cast roll temperature is preferably "Tg-50 ° C." or higher, preferably "Tg + 70 ° C." or lower, and more preferably "Tg + 40 ° C." or lower. Further, the cooling roll temperature is preferably "Tg −70 ° C.” or higher, more preferably “Tg −50 ° C.” or higher, preferably “Tg + 60 ° C.” or lower, and more preferably “Tg + 30 ° C.” or lower. When the film (a) is manufactured under such conditions, the film (a) having a thickness of 1 μm to 1 mm can be easily manufactured. Here, "Tm" represents the melting point of the crystalline polymer, and "Tg" represents the glass transition temperature of the crystalline polymer.

The thickness of the film (a) is preferably set according to the thickness of the optical film to be manufactured. Usually, by applying the solvent to the film (a) in the step (2), the thickness of the film is increased. On the other hand, when the method for producing an optical film includes a stretching step, the thickness of the film is reduced by stretching. Therefore, the thickness of the film (a) may be set in consideration of the change in the thickness in the step after the step (1) as described above.
According to extrusion molding, the thickness of the film (a) can be easily controlled.

The film (a) may be a single-wafer film, but is preferably a long film. By using the long film (a), the optical film can be continuously produced by the roll-to-roll method, so that the productivity of the optical film can be effectively increased.

The film (a) preferably has a small content of the organic solvent, and more preferably does not contain the organic solvent. The ratio (solvent content) of the organic solvent contained in the film (a) to 100% by weight of the film (a) is preferably 1% or less, more preferably 0.5% or less, still more preferably 0.1%. It is less than or equal to, ideally 0.0%. Since the amount of the organic solvent contained in the film (a) before applying the organic solvent is small, it becomes easy to control the retardation Rth in the thickness direction of the optical film by the amount of the organic solvent applied.

According to extrusion molding, a film (a) having a small content of organic solvent and usually containing no organic solvent can be obtained.

The solvent content of the film (a) can be measured by the density.

The in-plane retardation Re of the film (a) is preferably 10 nm or less, more preferably 8 nm or less, still more preferably 5 nm or less, and usually 0 nm or more.
The retardation Rth of the film (a) in the thickness direction is preferably 15 nm or less, more preferably 10 nm or less, still more preferably 8 nm or less, preferably 0 nm or more, more preferably 0.5 nm or more, still more preferably 1 nm or more. Is.
Such a low phase difference of the film (a) makes it easy to adjust the phase difference of the optical film to a desired range.

[2.2. Process (2)]
In the step (2), a solvent is applied on at least one surface of the two surfaces of the film (a) to form a solvent layer to obtain a film (a').
By the step (2), a film having a changed refractive index in the thickness direction in the vicinity of the surface can be obtained.

The solvent is usually an organic solvent. As the organic solvent, a solvent that does not dissolve the crystalline polymer can be used. Examples of preferable organic solvents include hydrocarbon solvents such as toluene, limonene and decalin; carbon disulfide; preferably toluene. The type of the organic solvent may be one kind or two or more kinds.

Of the two surfaces (two main surfaces) of the film (a), the solvent may be applied on one surface, or the solvent may be applied on both of the two surfaces. As the coating method, a method capable of controlling the thickness of the solvent layer formed on the surface of the film (a) by coating is preferably used.
Examples of the coating method include a wire bar coating method, a spray method, a roll coating method, a gravure coating method, a die coating method, a curtain coating method, a slide coating method, and an extrusion coating method, and the die coating method is preferable.

The total thickness of the solvent layer formed on at least one surface of the film (a) is usually 10 μm or less, preferably 9 μm or less, more preferably 8 μm or less, and usually larger than 0 μm.
Here, the total thickness is the total thickness of the two solvent layers when the solvent is applied to both of the two surfaces of the film (a) to form the two solvent layers, and the film (a). When the solvent is applied to only one of the two surfaces to form only one solvent layer, it is the thickness of the one solvent layer.

By keeping the total thickness of the solvent layer within the above range, the absolute value of the retardation Rth in the thickness direction of the optical film can be adjusted to a desired range.
As the total thickness of the solvent layer is increased, the retardation Rth in the thickness direction of the film (b) tends to be smaller. The absolute value of the retardation Rth in the thickness direction of the film (b) can be adjusted by adjusting the total thickness of the solvent layer according to the value of the retardation Rth in the thickness direction of the film (a).
Further, by keeping the total thickness of the solvent layer within the above range, it is possible to reduce the occurrence of wrinkles in the film conveyed in the step (3) and improve the handleability of the film.

[2.3. Process (3)]
In the step (3), the solvent layer of the film (a') is dried to obtain the film (b). Thereby, the solvent in the solvent layer can be removed.
As the drying method, any method can be adopted depending on the boiling point of the solvent used. Examples of the drying method include natural drying, heat drying, vacuum drying, vacuum heating drying and the like.

Part or all of the solvent in the solvent layer coated in the step (2) can be incorporated into the film (a') and enter the inside of the polymer. Therefore, in the step (3), it is difficult to completely remove the solvent from the film (a') even if the film is dried above the boiling point of the solvent. Therefore, the film (b) may contain a solvent.

By adjusting the total thickness of the solvent layer in the step (2), the size of the retardation Rth in the thickness direction can be adjusted in the film (b). By adjusting the total thickness of the solvent layer in the step (2), if a film (b) having desired optical characteristics can be obtained, the film (b) can be obtained as an optical film.

[2.4. Process (4)]
The method for producing the optical film may optionally include the step (4) in addition to the steps (1) to (3). The step (4) is a step of stretching the film (b) obtained in the step (3).
By stretching, the molecules of the crystalline polymer contained in the film (b) can be oriented in a direction corresponding to the stretching direction. Therefore, according to the step (4), optical characteristics such as birefringence Re / d in the in-plane direction, birefringence Re / d in the thickness direction, birefringence Rth / d in the thickness direction, and retardation Rth in the thickness direction of the film (b). In addition, the thickness d can be adjusted.

There is no limitation on the stretching direction, and examples thereof include a longitudinal direction, a width direction, and an oblique direction. Here, the diagonal direction is a direction perpendicular to the thickness direction and is neither parallel nor perpendicular to the width direction. Further, the stretching direction may be one direction or two or more directions. Therefore, as the stretching method, for example, a uniaxial stretching method such as a method of uniaxially stretching the film in the longitudinal direction (longitudinal uniaxial stretching method), a method of uniaxially stretching the film in the width direction (horizontal uniaxial stretching method); Biaxial stretching method such as simultaneous biaxial stretching method in which the film is stretched in the direction and width direction at the same time, and sequential biaxial stretching method in which the film is stretched in one of the longitudinal direction and the width direction and then stretched in the other direction; A method of stretching in a direction (diagonal stretching method); and the like can be mentioned.
As another example of the uniaxial stretching method, there are a fixed uniaxial stretching method in which the end portion of the film is fixed, and a free uniaxial stretching method in which the end portion of the film is not fixed.

The draw ratio is preferably 1 time or more, more preferably 1.01 times or more, preferably 1.5 times or less, and more preferably 1.4 times or less. It is desirable that the specific draw ratio is appropriately set according to factors such as the optical characteristics, thickness, and strength of the film (b) to be stretched.
When the stretching ratio is equal to or higher than the lower limit of the above range, the birefringence can be significantly changed by stretching. Further, when the draw ratio is not more than the upper limit of the above range, the direction of the slow phase axis can be easily controlled and the breakage of the film can be effectively suppressed.

The stretching temperature is preferably "Tg + 5 ° C." or higher, more preferably "Tg + 10 ° C." or higher, preferably "Tg + 100 ° C." or lower, and more preferably "Tg + 90 ° C." or lower. Here, "Tg" represents the glass transition temperature of the crystalline polymer. When the stretching temperature is equal to or higher than the lower limit of the above range, the film (b) can be sufficiently softened and stretched uniformly. Further, when the stretching temperature is not more than the upper limit of the above range, the curing of the film (b) due to the progress of crystallization of the crystalline polymer can be suppressed, so that stretching can be smoothly performed. In addition, birefringence can be significantly changed by stretching. In addition, the haze of the film, usually obtained after stretching, can be reduced to increase transparency.

By performing the above stretching treatment, a film (c) as a stretched film (b) can be obtained. As described above, since the birefringence can be changed by the stretching in the step (4), the thickness direction retardation Rth of the film (c) can be adjusted. Therefore, by stretching the film (b) by the step (4), the optical characteristics of the film (c) can be adjusted to a desired range as an optical film, and the film (c) can be obtained as an optical film.

The step (4) may further include any of the following steps in addition to the step of stretching the film (b) (referred to as step (4b)).
Step (4a): A step of preheating the film (b).
Step (4c): A step of heat-treating the film (b).
Step (4d): A step of cooling the film (c).

When step (4) includes step (4a), step (4a) is performed before normal step (4b).
When step (4) includes step (4c), step (4c) is performed after normal step (4b).
When the step (4) includes the step (4d), the step (4d) is performed after the normal steps (4a) to (4c).

By heat treatment, the crystallinity of the crystalline polymer contained in the stretched film (b) can be promoted, and the coefficient of thermal expansion can usually be lowered. Therefore, the heat resistance of the optical film can be improved by the step (4c).

The heat treatment temperature is usually equal to or higher than the glass transition temperature of the crystalline polymer and lower than the melting point of the crystalline polymer of Tm. More specifically, the heat treatment temperature is preferably Tg ° C. or higher, more preferably Tg + 10 ° C. or higher, preferably Tm-20 ° C. or lower, and more preferably Tm-40 ° C. or lower. In the above temperature range, crystallization of the crystalline polymer can be rapidly promoted while suppressing white turbidity due to the progress of crystallization.

The heat treatment treatment time is preferably 1 second or longer, more preferably 5 seconds or longer, preferably 30 minutes or shorter, and more preferably 15 minutes or shorter.

The preheating temperature in the step (4a) is usually the same as the stretching temperature in the step (4b), but may be different. The preheating temperature is preferably T1-10 ° C. or higher, more preferably T1-5 ° C. or higher, preferably T1 + 5 ° C. or lower, and more preferably T1 + 2 ° C. or lower with respect to the stretching temperature T1. The preheating time is arbitrary, preferably 1 second or longer, more preferably 5 seconds or longer, and preferably 60 seconds or shorter, more preferably 30 seconds or shorter.

The cooling temperature in the step (4d) is set lower than the heating temperature in the step (step (4b) or step (4c)) performed before the step (4d). The cooling time is arbitrary, preferably 1 second or longer, more preferably 5 seconds or longer, and preferably 30 seconds or shorter, more preferably 20 seconds or shorter.

When the method for manufacturing the optical film includes the step (4), the optical film after the step (4) may contain residual stress. Therefore, the method for producing an optical film may include, for example, a step of thermally shrinking the stretched film to remove residual stress. In the relaxation treatment, residual stress can usually be removed by causing the film to undergo thermal shrinkage in an appropriate temperature range while keeping the stretched film flat.

According to the above-mentioned manufacturing method, a long film (a) can be manufactured from a crystalline resin, and a long optical film can be manufactured from the film (a). The method for producing an optical film may include a step of winding the long optical film thus produced into a roll shape. Further, the method for producing an optical film may include a step of cutting a long optical film into a desired shape.

[3. Applications of optical film]
When the optical film of the present embodiment is combined with other optical elements, the original optical characteristics of the optical elements are not significantly changed, and the occurrence of wrinkles at high temperatures is reduced. Therefore, the optical film of the present embodiment is suitable for optical applications such as a protective film for an optical element and a base film for forming an optical element.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples shown below, and may be arbitrarily modified and carried out without departing from the scope of claims of the present invention and the equivalent scope thereof.

In the following explanation, "%" and "part" indicating the amount are based on weight unless otherwise specified. Further, the operations described below were performed under the conditions of normal temperature (20 ° C. ± 15 ° C.) and atmospheric pressure (1 atm) 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 (“HLC-8320” manufactured by Tosoh Corporation). At the time of 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 ° C.

(Measuring method of hydrogenation rate of polymer)
The hydrogenation rate of the polymer was measured by ¹ H-NMR at 145 ° C. using orthodichlorobenzene _- d4 as a solvent.

(Measurement method of glass transition temperature Tg and melting point Tm)
The glass transition temperature Tg and the melting point Tm of the polymer were measured as follows. First, the polymer was melted by heating, and the melted polymer was rapidly cooled with dry ice. Subsequently, using this polymer as a test piece, the glass transition temperature Tg and melting point Tm of the polymer were measured at a heating rate of 10 ° C./min (heating mode) using a differential scanning calorimeter (DSC). It was measured.

(Confirmation of the sign of the intrinsic birefringence value)
The film to be measured was cut to a size of 50 mm × 150 mm to obtain a film piece. As a measuring device, a tensile tester with a constant temperature and humidity chamber (“5564 type” manufactured by Instron) was used to freely uniaxially stretch the film piece. The stretching temperature was (Tg + 15 ° C. of the resin forming the film), and the tensile speed was 1.5 times / min.
After that, the slow-phase axial direction of the stretched film piece is determined by "AXoScan OPMF-1" manufactured by AXOMETRICS, and when the stretched direction and the slow-phase axial direction are parallel, the intrinsic birefringence of the resin constituting the film piece is determined. Is positive, and when the stretching direction and the slow-phase axial direction are perpendicular to each other, the intrinsic birefringence of the resin constituting the film piece is negative.

(Measuring method of racemic diad ratio of polymer)
The ratio of racemic diads in the polymer was measured as follows. ¹³ C-NMR measurement of the polymer was carried out by applying the inverted-gated decoupling method at 200 ° C. using ordichlorobenzene _- d4 as a solvent. In the results of this ¹³ C-NMR measurement, the signal of 43.35 ppm derived from meso-diad and the signal of 43.43 ppm derived from racemic diad were used as the reference shift with the peak of 127.5 ppm of orthodichlorobenzene _- d4 as a reference shift. Was identified. Based on the intensity ratios of these signals, the proportion of racemic diads in the polymer was determined.

(Measurement method of Re and Rth)
The in-plane retardation Re and the thickness direction retardation Rth of the film were measured by "AXoScan OPMF-1" manufactured by AXOMETRICS. At this time, the measurement was performed at a wavelength of 590 nm.

(Confirmation of Rth sign in the center and outside of the film)
The retardation Rth in the thickness direction of the film to be measured was measured and set to Rth0. The measurement was performed by "AXoScan OPMF-1" manufactured by AXOMETRICS. The measurement was performed at a wavelength of 590 nm. The following measurements were also performed with a similar device at a measurement wavelength of 590 nm.
Then, while wetting the surface of the film with water, the film was thinned by scraping a thickness of 1 μm from one surface of the film with sandpaper (Nos. 4000, 8000, 15000).
Next, the retardation Rth in the thickness direction of the thinned film was measured and set to Rth1. The operation of scraping a 1 μm surface layer from one surface of the film to thin the film and then measuring the retardation Rth of the thinned film is that the retardation Rth1 in the thickness direction of the thinned film has a code different from the code of Rth0. I repeated until it became. However, even if the surface layer is scraped to the center in the thickness direction of the film, if the sign of the retardation Rth1 in the thickness direction is not different from that of Rth0, the operation of scraping the surface layer of the film is completed.
If Rth1 has a code different from the code of Rth0 while the surface layer is scraped to the center in the thickness direction of the film, the code of retardation Rth in the thickness direction of the central portion of the film to be measured is opposite to that of Rth0. It is a code, and the code of the retardation Rth in the thickness direction of the first outer part and the second outer part is the same as the code of Rth0.
If the sign of the lettering Rth1 in the thickness direction does not differ from that of Rth0 even if the surface layer is scraped to the center in the thickness direction of the film, the lettering in the thickness direction of the center part, the first outer part, and the second outer part It is assumed that Rth has the same code as Rth0, respectively.

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

(Measurement method of thermal expansion coefficient _RTMA of film)
The film was cut into strips (rectangular) having a size of 5 mm × 20 mm to obtain a sample. This cutting was performed so that the longitudinal direction of the strip-shaped sample coincided with the MD direction (longitudinal direction in the long film) or the TD direction (width direction in the long film) of the film.
With a tension of 50 mN applied in the longitudinal direction of this sample, linear expansion from a temperature of 20 ° C. to 130 ° C. was measured at a heating rate of 10 ° C./min. The measurement was performed using a thermomechanical analyzer (“TMA / SS7100” manufactured by SSI Nanotechnology Co., Ltd.). The measured linear expansion value is divided by the original length (that is, the length before linear expansion) to obtain the coefficient of thermal expansion (%) in the MD and TD directions, and the average value is the coefficient of thermal expansion _RTMA . It was set to (%).

(Evaluation of viewing angle characteristics)
A commercially available IPS liquid crystal display device (manufactured by LG Display) was prepared. The liquid crystal display device is a so-called O-mode device in which the pretilt angle of the liquid crystal cell is 1 ° and the absorption axis of the backlight side polarizing element is parallel to the slow axis of the liquid crystal cell when no voltage is applied. Is. The absorption axis of the viewing side polarizing element and the absorption axis of the backlight side polarizing element are orthogonal to each other. The liquid crystal display device was disassembled, the film to be evaluated was inserted between the backlight side polarizing element and the liquid crystal cell, and the film was reassembled to obtain a liquid crystal display device for evaluation. The liquid crystal display device includes, from the visual side, a visual viewing side polarizing element, a color filter, a liquid crystal cell, the film, a backlight side polarizing element, and a backlight in this order. The color of the obtained liquid crystal display device was evaluated at a polar angle of 60 °. Specifically, the slow-phase axial directions of the liquid crystal cell provided in the liquid crystal display device in a state where no voltage is applied are set to azimuth angles of 0 ° and 180 °, and the azimuth angles are 45 °, 135 °, 225 °, and 315 °. The color was evaluated.
Good; the color is black.
Defective; the color is red or blue.

(Number of wrinkles after 105 ° C heat resistance test)
In an environment of room temperature of 23 ° C., the film to be evaluated was cut into a square having a size of 150 mm × 150 mm and used as a sample film. This sample film was heated in an oven at 105 ° C. for 100 hours and then cooled to 23 ° C. (room temperature). The number of wrinkles generated on the cooled sample film was measured. The evaluation criteria are as follows.
Ryo: There are no wrinkles.
Possible: There is one wrinkle.
Defective: There are two or more wrinkles.

(Evaluation of handleability)
The wrinkles of the film generated during the transportation of the film (b) were visually confirmed.
The evaluation criteria are as follows.
Good: No wrinkles or only small wrinkles that did not break the film.
Defective: Wrinkles large enough to break the film occurred.

[Manufacturing example 1. Production of crystalline resin A]
The pressure resistant reactor made of metal was sufficiently dried and then replaced with nitrogen. In this metal pressure resistant reactor, 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo content of 99% or more) (30 parts as the amount of dicyclopentadiene), and 1- 1.9 parts of hexene was added and heated to 53 ° C.

0.014 parts of the tetrachlorotungsten phenylimide (tetrahydrofuran) complex was dissolved in 0.70 parts of toluene to prepare a solution. To this solution, 0.061 part of a diethylaluminum ethoxide / n-hexane solution having a concentration of 19% was added and stirred for 10 minutes to prepare a catalytic solution. This catalyst solution was added to a pressure resistant reactor to initiate a ring-opening polymerization reaction. Then, the reaction was carried out for 4 hours while maintaining 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 obtained ring-opening polymer of dicyclopentadiene are 8,750 and 28,100, respectively, and the molecular weight distribution (Mw / Mn) obtained from these. Was 3.21.

To 200 parts of the obtained solution of the ring-opening polymer of dicyclopentadiene, 0.037 parts of 1,2-ethanediol was added as a terminator, heated to 60 ° C., and stirred for 1 hour to stop the polymerization reaction. I let you. A part of a hydrotalcite-like compound (“Kyoward (registered trademark) 2000” manufactured by Kyowa Chemical Industry Co., Ltd.) was added thereto, and the mixture was heated to 60 ° C. and stirred for 1 hour. After that, 0.4 part of a filtration aid ("Radiolite (registered trademark) # 1500" manufactured by Showa Kagaku Kogyo Co., Ltd.) was added, and a PP pleated cartridge filter ("TCP-HX" manufactured by ADVANTEC Toyo Co., Ltd.) was used as an adsorbent. The solution was filtered off.

To 200 parts of a solution of a ring-opening polymer of dicyclopentadiene after filtration (polymer amount: 30 parts), 100 parts of cyclohexane is added, 0.0043 parts of chlorohydride carbonyltris (triphenylphosphine) ruthenium is added, and hydrogen is added. The hydrogenation reaction was carried out at a pressure of 6 MPa and 180 ° C. for 4 hours. As a result, a reaction solution containing a hydride of a ring-opening polymer of dicyclopentadiene was obtained. In this reaction solution, hydride was precipitated to form a slurry solution.

The hydride contained in the reaction solution and the solution were separated using a centrifuge and dried under reduced pressure at 60 ° C. for 24 hours to obtain a hydride of a crystallized dicyclopentadiene ring-opening polymer 28. I got 5 copies. The hydrogenation rate of this hydride was 99% or more, the glass transition temperature Tg was 93 ° C., the melting point (Tm) was 267 ° C., and the ratio of racemo diad was 89%.

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

[Example 1]
(1-1. Step (1): Production of film made of crystalline resin A)
The crystalline resin A produced in Production Example 1 is molded using a heat melt extrusion film molding machine equipped with a T-die to obtain an extruded film (thickness 38 μm) as a long film (a) having a width of about 400 mm. rice field. The obtained extruded film was wound into a roll. The evaluation results of the film (a) are as shown in the table below. Further, as a result of confirming the sign of the intrinsic birefringence value of the crystalline resin A using the film (a), the sign of the intrinsic birefringence value of the crystalline resin A was “positive”.
The operating conditions of the film forming machine were as follows.
・ Barrel set temperature = 280 ° C to 300 ° C
・ Die temperature = 270 ℃
・ Cast roll temperature = 80 ℃

(1-2. Process (2): Coating process)
The extruded film is unwound from the roll of the extruded film as the film (a) produced in (1-1), and toluene is spread on both sides of the extruded film with a die coater to a thickness of 2 μm per side (that is, a total thickness of 4 μm on both sides). ) Was applied. As a result, a toluene layer as a solvent layer was formed on each of the two surfaces of the film (a), and the film (a') was obtained. The total thickness of the solvent layers formed on the two surfaces of the film (a') is 4 μm.

(1-3. Step (3): Drying step)
Then, the film (a') was heated and dried in an oven at 100 ° C. for 2 minutes to obtain a long film (b). The obtained film (b) was wound into a roll form. The evaluation results of the film (b) are as shown in the table below.

(1-4. Step (4): Stretching heating step)
The film (b) is supplied to a transverse stretching machine using the tenter method, and while adjusting the take-up tension and the tenter chain tension, the film (c) is fixed and uniaxially stretched 1.1 times in the lateral direction to form an optical film (c). ) Was produced. Stretching was performed by preheating (4a): film (b) to 160 ° C, then; (4b): preheated film (b) at 160 ° C, and then; (4c): stretched film (b). ) Was kept tense at a temperature of 160 ° C. to promote crystallization, and then; (4d): the crystallized film (b) was cooled at a temperature of 100 ° C.;
The thickness of the film (c) was 35 μm. The evaluation results of the film (c) are as shown in the table below.

[Example 2]
An optical film was obtained in the same manner as in Example 1 except that the following items were changed. The thickness of the film (b) was 38 μm.
-In (1-2. Step (2)), the thickness of the toluene to be coated was changed to a thickness of 1.1 μm per one side (that is, a total thickness of 2.2 μm on both sides).
(1-4. Step (4)) was not performed on the film (b), and the obtained film (b) was evaluated as an optical film.

[Comparative Example 1]
An optical film was obtained in the same manner as in Example 1 except that the following items were changed.
-The film (a) was evaluated as an optical film without performing (1-2. Step (2)) to (1-4. Step (4)).

[Comparative Example 2]
An optical film was obtained in the same manner as in Example 1 except that the following items were changed.
-(1-2. Step (2)) and (1-3. Step (3)) were not performed.
-In (1-4. Step (4)), the film (a) obtained in (1-1. Step (1)) was used instead of the film (b).

[Comparative Example 3]
An optical film was obtained in the same manner as in Example 1 except that the following items were changed.
-In (1-2. Step (2)), the thickness of the toluene to be coated was changed to a thickness of 6 μm per one side (that is, a total thickness of 12 μm on both sides).
-In (1-4. Step (4)), instead of fixed uniaxial stretching using a transverse stretching machine, the film (b) was freely uniaxially stretched according to the following method to obtain a film (c).
As the stretching machine, a roll longitudinal stretching machine equipped with four preheating rolls, two stretching rolls, and two cooling rolls in this order was used. This roll longitudinal stretching machine is a device that stretches by providing a difference in the rotation speeds of the two stretching rolls. The temperature of all four preheating rolls was set to 100 ° C. The temperatures of the two stretch rolls were all set to 160 ° C. The temperatures of the two cooling rolls were all set to 60 ° C. The rotation speeds of the two stretching rolls were adjusted, and the film (b) was stretched uniaxially at a magnification of 1.1 times.

[Comparative Example 4]
An optical film was obtained in the same manner as in Example 1 except that the following items were changed.
-In (1-2. Step (2)), the thickness of the toluene to be coated was changed to a thickness of 30 μm per one side (that is, a total thickness of 60 μm on both sides).
-In (1-4. Step (4)), instead of fixed uniaxial stretching using a transverse stretching machine, the film (b) was freely uniaxially stretched to obtain a film (c). The free uniaxial stretching was performed in the same operation as in Comparative Example 3.

[Comparative Example 5]
An optical film was obtained in the same manner as in Example 1 except that the following items were changed.
-The film (b) was obtained by performing the following solvent dipping step on the film (a) without performing the steps (1-2. Step (2)) and (1-3. Step (3)). ..
The film (a) was immersed in toluene by passing the film (a) through a bathtub filled with toluene. The time for the film (a) to pass through the bathtub (that is, the time for the film (a) to come into contact with toluene) was 5 seconds. The film (a) passed through the bathtub was passed through an oven at 80 ° C. to dry the film (a) immersed in toluene to obtain a film (b).
-In (1-4. Step (4)), the stretching temperature and the stretching ratio were changed as follows to obtain a film (c).
The draw ratio was 1.5 times. Stretching was performed by preheating (4a): film (b) to 110 ° C, then; (4b): preheated film (b) at 110 ° C, and then; (4c): stretched film (b). ) Was kept tense at a temperature of 170 ° C. to promote crystallization, and then; (4d): the crystallization-promoted film (b) was cooled at a temperature of 100 ° C.;

[result]
The production conditions, physical properties, and evaluations of the optical films obtained in Examples and Comparative Examples are shown in Table 1 or Table 2. In the table below, the abbreviations have the following meanings.
"COP": A resin containing a hydride of the ring-opening polymer of dicyclopentadiene obtained in Production Example 1 and which is crystalline. "Rsa": Lettering Rth in the thickness direction of the film (a).
"Rea": In-plane lettering Re of film (a)
"Rthb": Lettering Rth in the thickness direction of the film (b)
"Reb": In-plane lettering Re of film (b)
"Rthc": Lettering Rth in the thickness direction of the film (c)
"Rec": In-plane lettering Re of film (c)
" _RTMA ": Thermal expansion coefficient of film "Fixed": Fixed uniaxial stretching "Free": Free uniaxial stretching

From the above results, the following matters can be understood.
The optical film of Example 1 (film (c)) and the optical film of Example 2 (film (b)) have an absolute value of retardation of 15 nm or less in the thickness direction and an in-plane retardation Re of 10 nm or less. R _TMA is 0% or more and 7.5% or less. The optical film of the example has a good evaluation of the viewing angle characteristic, and the number of wrinkles generated in the 105 ° C. heat resistance test is small.

On the other hand, the optical film of Comparative Example 1 having an _RTMA of 7.5% or more has a large number of wrinkles generated in the 105 ° C. heat resistance test. Further, the optical films of Comparative Examples 2 to 5 in which the absolute value of the retardation in the thickness direction is larger than 15 nm or the in-plane retardation Re is larger than 10 nm have a poor evaluation of the viewing angle characteristics, and are inherent in the polarizing element. It can be seen that the optical characteristics are greatly changed.

Further, the optical films of Comparative Examples 1 and 2 obtained by the manufacturing method not including the step (2) and the step (3), and the comparative example obtained by the manufacturing method having a coating thickness larger than 10 μm in the step (2). The optical films of 3 to 5 have poor viewing angle characteristics.

The above results show that when the optical film according to the present invention is combined with other optical elements, the original optical characteristics of the optical elements do not change significantly, and wrinkles occur at high temperatures (wrinkles in the 105 ° C. heat resistance test). It indicates that the occurrence) is reduced.

100 Optical film

100U First surface

100D Second surface 110 Central part 111 Thickness direction center 121 First outer part 122 Second outer part

Claims

It consists of a resin containing a crystalline polymer.
The absolute value of retardation Rth in the thickness direction is 15 nm or less.
In-plane retardation Re is 10 nm or less,
An optical film having a coefficient of thermal expansion of 0% or more and 7.5% or less.
The optical film has a first surface and a second surface,
The central part, which is the part including the center in the thickness direction,
The first outer portion, which is outside in the thickness direction with respect to the central portion and includes the first surface, and the first outer portion.
It is composed of a second outer portion, which is outside in the thickness direction with respect to the central portion and is a portion including the second surface.
The retardation Rth in the thickness direction is positive in the central portion, and the retardation Rth is positive.
The retardation Rth in the thickness direction is negative in at least one of the first outer portion and the second outer portion.
The optical film according to claim 1.
The optical film according to claim 1 or 2, which is long.
The optical film according to any one of claims 1 to 3, wherein the intrinsic birefringence value of the resin containing the crystalline polymer is positive.
The method for manufacturing an optical film according to any one of claims 1 to 4.
Step (1) of extruding a resin containing a crystalline polymer to obtain a film (a).
A step (2) of applying a solvent on at least one of the two surfaces of the film (a) to form a solvent layer to obtain a film (a'), and the film (a'. ) To dry the solvent layer to obtain a film (b), which comprises the step (3).
Here, the total thickness of the solvent layer formed on at least one surface of the film (a) in the step (2) is 10 μm or less.
Manufacturing method of optical film.
The method for producing an optical film according to claim 5, further comprising a step (4) of stretching the film (b).