JPWO2019026625A1 - Optical film - Google Patents

Abstract

An optical film made of a thermoplastic resin, wherein the thermoplastic resin contains two or more polymer blocks [D] per molecule containing a hydride unit [I] of a cyclic hydrocarbon group-containing compound as a main component. , A chain hydrocarbon compound hydride unit [II], or one or more polymer blocks [E] per molecule containing the combination of the unit [I] and the unit [II] as a main component The block copolymer [G] is included, and the thermoplastic resin satisfies G″/G′>0.95 or (η|ε=2-η|ε=1)>−1.0×10 4 Pa·s Where G′ is the storage elastic modulus of the thermoplastic resin, G″ is the loss elastic modulus of the thermoplastic resin, and (η|ε=2-η|ε=1) is the elongation of the thermoplastic resin. It is the slope of viscosity.

Description

The present invention relates to an optical film.

A display device such as a liquid crystal display device is provided with various optical films. For example, a liquid crystal display device usually includes a polarizing plate, and such a polarizing plate usually includes a polarizer made of a resin such as polyvinyl alcohol, and a protective film for protecting the polarizer. Various materials have been proposed as materials for the protective film. For example, it has been proposed to use a block copolymer containing a block of an aromatic vinyl compound hydride and a block of a diene compound hydride (Patent Documents 1 and 2). The optical film can be efficiently manufactured by, for example, extrusion molding.

International Publication No. 2017/086265 JP, 2010-031253, A

However, when an optical film is manufactured by extrusion molding using a resin containing a block copolymer as a material, draw resonance may occur and the film thickness unevenness may increase.

Therefore, it is an object of the present invention to provide an optical film in which film thickness unevenness due to generation of draw resonance in extrusion molding is reduced and which can be efficiently manufactured as a high quality film.

As a result of studies to solve the above problems, the present inventor has found that the above problems can be solved by adopting a specific thermoplastic resin as a material forming the optical film.
That is, according to the present invention, the following [1] to [3] are provided.

[1] An optical film made of a thermoplastic resin,
The thermoplastic resin is
Two or more polymer blocks [D] per molecule having a cyclic hydride group-containing compound hydride unit [I] as a main component;
A chain hydrocarbon compound hydride unit [II], or a hydrogenation block containing one or more polymer blocks [E] per molecule containing the combination of the unit [I] and the unit [II] as a main component Including a copolymer [G],
The thermoplastic resin satisfies the formula (1) or the formula (2):
G"/G'>0.95 Formula (1)
(Η| _ε=2 −η| _ε=1 )>−1.0×10 ⁴ Pa·s Formula (2)
Where G′ is the storage elastic modulus of the thermoplastic resin, G″ is the loss elastic modulus of the thermoplastic resin,
The storage elastic modulus and the loss elastic modulus are values measured under the conditions of Ts+90° C. and 1 rad/sec,
(Η| _ε=2- η| _{ε= 1} ) is the slope of extensional viscosity of the thermoplastic resin,
The extensional viscosity is a value measured under the conditions of Ts+80° C. and 1 s ⁻¹ ,
Ts is the softening temperature of the thermoplastic resin measured by TMA.
[2] The optical film according to [1], wherein both the front retardation Re and the absolute value |Rth| of the retardation in the thickness direction are 3 nm or less.
[3] The cyclic hydride group-containing compound hydride unit [I] is an aromatic vinyl compound hydride unit,
The optical film as described in [1] or [2], wherein the chain hydrocarbon compound hydride unit [II] is a conjugated diene compound hydride unit.

ADVANTAGE OF THE INVENTION According to this invention, the film thickness unevenness by the generation of draw resonance in extrusion molding is reduced, and the optical film which can be efficiently manufactured as a high quality film is provided.

Hereinafter, the present invention will be described in detail by showing embodiments and exemplifications. However, the present invention is not limited to the embodiments and exemplifications shown below, and may be implemented by being arbitrarily modified within the scope of the claims of the present invention and the scope of equivalents thereof.

In the following description, the front phase difference Re of a certain layer has a value represented by Re=(nx−ny)×d, and the phase difference Rth in the thickness direction of a certain layer is Rth=[{( nx+ny)/2}-nz]×d. nx represents the refractive index in the in-plane direction of the layer (direction perpendicular to the thickness direction) and gives the maximum refractive index, and ny is the in-plane direction of the layer and orthogonal to the nx direction. , Nz represents the refractive index in the thickness direction of the layer, and d represents the thickness of the layer.

In the following description, the measurement wavelength of the refractive index is 590 nm unless otherwise specified.

In the following description, whether the intrinsic birefringence value of the resin is positive or negative is defined by the behavior of the refractive index of the resin molded product when the molded product is stretched. That is, a resin having a positive intrinsic birefringence value is a resin in which the refractive index of the molded product in the stretching direction is higher than that before stretching. The resin having a negative intrinsic birefringence value is a resin in which the refractive index of the molded product in the stretching direction is smaller than that before stretching. The intrinsic birefringence value can be calculated from the dielectric constant distribution.

Furthermore, a certain specific polymerized unit has a positive intrinsic birefringence value means that a polymer composed of only the polymerized unit has a positive intrinsic birefringence value, and a specific polymerized unit has a negative intrinsic birefringence value. Having a birefringence value means that a polymer composed of only the polymerized units has a negative intrinsic birefringence value. Therefore, the positive and negative of the intrinsic birefringence value of the polymerized unit, the homopolymer consisting only of the polymerized unit is prepared, the polymer into a molded article of any shape, the molded article is stretched, and the optical characteristics are measured. By doing so, it can be easily determined. It is generally known that many polymerized units of hydrocarbons such as alkenes and dienes and their hydrides have a positive intrinsic birefringence value, while carbonized units having an aromatic ring in the side chain such as styrene and vinylnaphthalene. It is known that many polymers of hydrogen and their hydrides having a cyclic hydrocarbon group have a negative intrinsic birefringence value.

In the following description, the cyclic hydrocarbon group is a hydrocarbon group having a cyclic structure such as an aromatic ring, cycloalkane, and cycloalkene. The chain hydrocarbon compound is a hydrocarbon compound that does not contain such a cyclic hydrocarbon group.

In the following description, the term “polarizing plate” includes not only a rigid member but also a flexible member such as a resin film unless otherwise specified.

[1. Overview of optical film]
The optical film of the present invention is an optical film made of a specific thermoplastic resin. That is, the optical film of the present invention is an optical film composed of only a specific thermoplastic resin.

The thermoplastic resin forming the optical film contains a specific hydrogenated block copolymer [G]. The hydrogenated block copolymer [G] contains two or more polymer blocks [D] and one or more polymer blocks [E]. The polymer block [D] is a block containing a cyclic hydride group-containing compound hydride unit [I] as a main component. The polymer block [E] is a block containing a chain hydrocarbon compound hydride unit [II] or a combination of the unit [I] and the unit [II] as a main component. Unit [I] usually has a negative intrinsic birefringence value, while unit [II] usually has a positive intrinsic birefringence value. When the hydrogenated block copolymer [G] contains these units in combination, expression of retardation of the optical film can be suppressed. As a result, an optical film with a low retardation suitable for use as a polarizing plate protective film can be easily obtained.

[2. Cyclic hydrocarbon group-containing compound hydride unit [I]
The cyclic hydrocarbon group-containing compound hydride unit [I] is obtained by polymerizing a cyclic hydrocarbon group-containing compound, and further, if the unit obtained by such polymerization has an unsaturated bond, the unsaturated bond is formed. It is a structural unit having a structure obtained by hydrogenation. However, the cyclic hydrocarbon group-containing compound hydride unit [I] includes a unit obtained by any production method as long as it has the structure.

The cyclic hydrocarbon group-containing compound hydride unit [I] is preferably a structural unit obtained by polymerization of an aromatic vinyl compound. More specifically, it is a structural unit (aromatic vinyl compound hydride unit [I]) having a structure obtained by polymerizing an aromatic vinyl compound and hydrogenating its unsaturated bond. However, the aromatic vinyl compound hydride unit [I] includes a unit obtained by any manufacturing method as long as it has the structure.

Similarly, in the present application, for example, a structural unit having a structure obtained by polymerizing styrene and hydrogenating its unsaturated bond may be referred to as a styrene hydride unit. The styrene hydride unit also includes a unit obtained by any manufacturing method as long as it has the structure.

Examples of the aromatic vinyl compound hydride unit [I] include a structural unit represented by the following structural formula (1).

In Structural Formula (1), R ^c represents an alicyclic hydrocarbon group. Examples of R ^c include cyclohexyl groups such as cyclohexyl group; decahydronaphthyl groups and the like.

In Structural Formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom, a chain hydrocarbon group, a halogen atom, an alkoxy group, a hydroxyl group, an ester group, a cyano group, an amide group or an imide group. Represents a chain hydrocarbon group substituted with a silyl group or a polar group (a halogen atom, an alkoxy group, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group, or a silyl group). Among them, R ¹ , R ² and R ³ are preferably any one of a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms from the viewpoint of heat resistance, low birefringence and mechanical strength. .. As the chain hydrocarbon group, a saturated hydrocarbon group is preferable, and an alkyl group is more preferable.

Specific preferred examples of the aromatic vinyl compound hydride unit [I] include structural units represented by the following formula (1-1). The structural unit represented by the formula (1-1) is a styrene hydride unit.

Any of the stereoisomers of the cyclic hydride-containing compound hydride unit [I] having stereoisomers can be used. As the cyclic hydride group-containing compound hydride unit [I], only one type may be used, or two or more types may be used in combination at any ratio.

[3. Chain hydrocarbon compound hydride unit [II]]
The chain hydrocarbon compound hydride unit [II] is obtained by polymerizing a chain hydrocarbon compound and further hydrogenating the unsaturated bond if the unit obtained by such polymerization has an unsaturated bond. Is a structural unit having a structure described below. However, the chain hydrocarbon compound hydride unit [II] includes a unit obtained by any production method as long as it has the structure.

The chain hydrocarbon compound hydride unit [II] is preferably a structural unit obtained by polymerization of a diene compound. More specifically, a structural unit having a structure obtained by polymerizing a diene compound and further hydrogenating the unsaturated bond, if the unit obtained by such polymerization has an unsaturated bond (diene compound hydrogen Compound unit [II]). However, the diene compound hydride unit [II] includes a unit obtained by any manufacturing method as long as it has the structure.

Similarly, in the present application, a structural unit having a structure obtained by polymerizing isoprene and hydrogenating its unsaturated bond may be referred to as an isoprene hydride unit. The isoprene hydride unit also includes a unit obtained by any manufacturing method as long as it has the structure.

The diene compound hydride unit [II] is preferably a structural unit obtained by polymerization of a conjugated diene compound. More specifically, it is preferably a structural unit (conjugated diene compound hydride unit) having a structure obtained by polymerizing a conjugated diene compound such as a chain conjugated diene compound and hydrogenating the unsaturated bond. Examples thereof include a structural unit represented by the following structural formula (2) and a structural unit represented by the structural formula (3).

In Structural Formula (2), R ^{4 to} R ⁹ are each independently a hydrogen atom, a chain hydrocarbon group, a halogen atom, an alkoxy group, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group, a silyl group. Or represents a chain hydrocarbon group substituted with a polar group (halogen atom, alkoxy group, hydroxyl group, ester group, cyano group, amide group, imide group, or silyl group). Among them, R ^{4 to} R ⁹ are preferably any one of a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms from the viewpoint of heat resistance, low birefringence, mechanical strength and the like. As the chain hydrocarbon group, a saturated hydrocarbon group is preferable, and an alkyl group is more preferable.

In Structural Formula (3), R ^{10 to} R ¹⁵ are each independently a hydrogen atom, a chain hydrocarbon group, a halogen atom, an alkoxy group, a hydroxyl group, an ester group, a cyano group, an amide group, an imide group, a silyl group. Or represents a chain hydrocarbon group substituted with a polar group (halogen atom, alkoxy group, hydroxyl group, ester group, cyano group, amide group, imide group, or silyl group). Among them, R ^{10 to} R ¹⁵ are preferably any one of a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms from the viewpoint of heat resistance, low birefringence, mechanical strength and the like. As the chain hydrocarbon group, a saturated hydrocarbon group is preferable, and an alkyl group is more preferable.

Specific preferred examples of the diene compound hydride unit [II] include structural units represented by the following formulas (2-1) to (2-3). The structural units represented by formulas (2-1) to (2-3) are isoprene hydride units.

Any of the stereoisomers of the chain hydrocarbon compound hydride unit [II] having stereoisomers can be used. As the chain hydrocarbon compound hydride unit [II], only one type may be used, or two or more types may be used in combination at an arbitrary ratio.

[4. Details of Hydrogenated Block Copolymer [G]]
The hydrogenated block copolymer [G] preferably has a triblock molecular structure having one block [E] per molecule and two blocks [D] connected to both ends thereof per molecule. That is, the hydrogenated block copolymer [G] has one block [E] per molecule; and a cyclic hydride group-containing compound hydride unit [I] linked to one end of the block [E], One block [Da] per molecule; one block [Db] per molecule having a cyclic hydrocarbon group-containing compound hydride unit [I] linked to the other end of the block [E]; It is preferably a triblock copolymer [Da]-[E]-[Db] containing.

The thermoplastic resin preferably contains the hydrogenated block copolymer [G] in an amount of 85% by mass or more. The hydrogenated block copolymer [G] may contain only one kind of polymer, but may contain two or more kinds of polymers. Preferably, the thermoplastic resin contains two or more polymers as the hydrogenated block copolymer [G]. When the thermoplastic resin contains two or more kinds of polymers as the hydrogenated block copolymer [G], a thermoplastic resin having desired properties can be easily prepared.

In particular, the thermoplastic resin preferably contains, as the hydrogenated block copolymer [G], a plurality of triblock copolymers having different symmetries. In the present application, the symmetry of the triblock copolymer [Da]-[E]-[Db] means the ratio Da of the weight Da of the block [Da] and the weight Db of the block [Db] (provided that Da≧Da). A triblock copolymer having a small Da/Db value of 1 or close to 1 is a triblock copolymer having a high symmetry, which is a property relating to Db, and a triblock copolymer having a large Da/Db is a symmetry Low triblock copolymer.

As a preferred example, the thermoplastic resin contains, as the hydrogenated block copolymer [G], a triblock copolymer [G _X ] having low symmetry and a triblock copolymer [G _Y ] having high symmetry. Will be described below. In this example, a triblock copolymer _{[G X]} includes blocks [Da _X] as the polymer block [D] and _[Db X], as well as a block _{[E X]} as the polymer block [E] triblock copolymer _{[Da X] - [E X} ] - a [Db _X]. The triblock copolymer [G _Y ] is a triblock copolymer including the blocks [Da _Y ] and [Db _Y ] as the polymer block [D] and the block [E _Y ] as the polymer block [E]. The combination is [Da _Y ]-[E _Y ]-[Db _Y ].

The weight ratio Da _X /Db _X of the blocks [Da _X ] and [Db _X ] in the triblock copolymer [G _X ] is 3 or more, preferably 4 or more, more preferably 5 or more, and preferably It is 11 or less, more preferably 10 or less, and particularly preferably 9 or less. The weight ratio Da _Y /Db _Y of the blocks [Da _Y ] and [Db _Y ] in the triblock copolymer [G _Y ] is 1 or more and less than 3, preferably 2 or less, more preferably 1.5. It is as follows. By including such triblock copolymers [G _X ] and [G _Y ] having different symmetries, while enjoying the advantages of the asymmetric triblock copolymer having both heat resistance and toughness, In addition, it is possible to reduce the film thickness unevenness due to the occurrence of draw resonance, and to obtain an optical film with less film thickness unevenness.

The preferable ratio of the triblock copolymer [G _X ] having a low symmetry and the triblock copolymer [G _Y ] having a high symmetry in the thermoplastic resin is appropriately set within a range in which an optical film having desired properties can be obtained. Can be adjusted. The ratio of the triblock copolymer [G _X ] to the total of the triblock copolymer [G _X ] and the triblock copolymer [G _Y ] is preferably 70% by weight or more, more preferably 75% by weight or more. On the other hand, it is preferably 85% by weight or less, more preferably 83% by weight or less.

Regarding the hydrogenated block copolymer [G] in the thermoplastic resin, the weight ratio of the total of the block [Da] and the block [Db] to the block [E] is used from the viewpoint of easily obtaining an optical film having preferable properties. It is preferable that (Da+Db)/E is within a specific range. Specifically, the weight ratio (Da+Db)/E is preferably 65/35 or more, more preferably 70/30 or more, preferably 90/10 or less, more preferably 85/15 or less. When the thermoplastic resin contains a plurality of kinds of polymers as the hydrogenated block copolymer [G], the weight ratio (Da+Db)/E in the whole of them is preferably within the above range.

The weight average molecular weight Mw of the hydrogenated block copolymer [G] in the thermoplastic resin is preferably 40,000 or more, more preferably 55,000 or more, particularly preferably 60,000 or more, preferably 85,000 or less, more preferably 80,000 or less, It is particularly preferably 75,000 or less. When the weight average molecular weight Mw is within the above range, an optical film having preferable characteristics can be easily obtained. When the thermoplastic resin contains a plurality of types of polymers as the hydrogenated block copolymer [G], the hydrogenated block copolymer as the main component is preferably within the above range.

It is preferable that each of the block [Da] and the block [Db] independently comprises only the cyclic hydrocarbon group-containing compound hydride unit [I], but other than the cyclic hydrocarbon group-containing compound hydride unit [I]. Can include any unit. Examples of the optional structural unit include structural units based on vinyl compounds other than the cyclic hydrocarbon group-containing compound hydride unit [I]. The content of any structural unit in the block [D] is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 1% by weight or less.

The block [E] is composed of only a chain hydrocarbon compound hydride unit [II], or is composed only of a cyclic hydrocarbon group-containing compound hydride unit [I] and a chain hydrocarbon compound hydride unit [II]. However, it may contain any unit other than the units [I] and [II]. Examples of the optional structural unit include structural units based on vinyl compounds other than the units [I] and [II]. The content of any structural unit in the block [E] is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 1% by weight or less.

When the block [E] contains a cyclic hydride group-containing compound hydride unit [I] and a chain hydrocarbon compound hydride unit [II], the units [I] and [II] in the block [E] The weight ratio [I]/[II] is preferably 0.1 or more, more preferably 0.2 or more, particularly preferably 0.3 or more, preferably 1.5 or less, more preferably 1.4 or less. And particularly preferably 1.3 or less.

The weight ratio [I]/[II] of the units [I] and [II] in the entire hydrogenated block copolymer [G] is preferably 70/30 or more, more preferably 75/25 or more. , Preferably 90/10 or less, more preferably 85/15 or less. When the ratio of the units [I] and [II] is within the above range, an optical film having preferable characteristics can be easily obtained. Specifically, by containing a unit [I] having a negative intrinsic birefringence value and a unit [II] usually having a positive intrinsic birefringence value in a preferable ratio, the retardation of the optical film is expressed. Can be suppressed. As a result, an optical film with a low retardation suitable for use as a polarizing plate protective film can be easily obtained.

The method for producing the hydrogenated block copolymer [G] is not particularly limited, and any production method can be adopted. As the hydrogenated block copolymer [G], for example, a monomer corresponding to the cyclic hydrocarbon group-containing compound hydride unit [I] and the chain hydrocarbon compound hydride unit [II] is prepared, and these are prepared. It can be produced by polymerizing and polymerizing the obtained polymer [F]. Specific production can be carried out by appropriately combining, for example, the method described in International Publication WO2016/152871 and other known methods. The hydrogenation rate in the hydrogenation reaction is usually 90% or more, preferably 95% or more, more preferably 97% or more. By increasing the hydrogenation rate, the low birefringence and thermal stability of the hydrogenated block copolymer [G] can be increased. The hydrogenation rate can be measured by ¹ H-NMR.

The thermoplastic resin may be composed of only the hydrogenated block copolymer [G] or may contain an arbitrary component other than the hydrogenated block copolymer [G]. Examples of optional components include ultraviolet absorbers, antioxidants, heat stabilizers, light stabilizers, antistatic agents, dispersants, chlorine scavengers, flame retardants, crystallization nucleating agents, strengthening agents, antiblocking agents, antifogging agents. Agents, release agents, pigments, organic or inorganic fillers, neutralizing agents, lubricants, decomposing agents, metal deactivators, antifouling agents, and antibacterial agents. The content of the optional component is preferably 0.5 to 5% by weight based on 100% by weight of the thermoplastic resin.

[5. Characteristics of thermoplastic resin]
The thermoplastic resin satisfies one or both of formula (1) and formula (2).
G"/G'>0.95 Formula (1)
(Η| _ε=2 −η| _ε=1 )>−1.0×10 ⁴ Pa·s Formula (2)

In the formula (1), G′ is the storage elastic modulus of the thermoplastic resin, and G″ is the loss elastic modulus of the thermoplastic resin. The value of G″/G′ is more preferably 1.2 or more, It is more preferably 1.3 or more. The upper limit of the value of G″/G′ is not particularly limited, but may be 10.0 or less, for example.

The storage elastic modulus and the loss elastic modulus are values measured by dynamic viscoelasticity measurement under the conditions of Ts+90° C. and 1 rad/sec. Ts is the softening temperature of the thermoplastic resin. In measuring the elastic modulus, the thermoplastic resin to be measured can be molded into a sheet shape and used as a sample for measurement. As the measuring device, a strain control type viscoelasticity measuring device (parallel plate method) manufactured by TA Instruments can be used.

The softening temperature Ts of the thermoplastic resin can be obtained by TMA (thermomechanical analysis). Specifically, the thermoplastic resin to be measured is a sheet having a width of 5 mm, a length of 20 mm, and a thickness of 0.5 mm, and the temperature is changed while a tension of 50 mN is applied in the longitudinal direction of the sample. The temperature (° C.) when the linear expansion changes by 3% can be defined as the softening temperature Ts. As the measuring device, TMA/SS7100 (manufactured by SII Nanotechnology Inc.) can be used. The softening temperature Ts of the thermoplastic resin is not particularly limited, but may be 100 to 150°C.

In the formula (2), (η| _ε=2- η| _{ε =1} ) is the slope of elongational viscosity of the thermoplastic resin. The gradient (η| _ε=2- η| _{ε= 1} ) is more preferably −9.0×10 ³ Pa·s or more, still more preferably −8.0×10 ³ Pa·s or more. The upper limit of the inclination is not particularly limited, but may be 1.0×10 ² Pa·s or less, for example.

In the present application, the slope of extensional viscosity refers to the slope of extensional viscosity in the relationship between extensional strain and extensional viscosity of the thermoplastic resin. More specifically, the thermoplastic resin to be measured is a sheet having a width of 5 mm, a length of 20 mm, and a thickness of 0.5 mm, and the relationship between the elongation strain and the elongation viscosity is calculated at a strain rate of 1 s ⁻¹ at Ts+80° C. .. The slope can be obtained from the measured values at the elongation strains 1 and 2 or values close thereto (for example, values within the range of 1±0.05 and 2±0.05). An Rheometer MCR302 manufactured by Anton Paar can be used as the measuring device.

The present inventors have found that the thermoplastic resin satisfies one or both of the formula (1) and the formula (2) to reduce film thickness unevenness due to draw resonance generated in the production of an optical film. Therefore, the optical film can be efficiently manufactured as a high quality product.

[6. Characteristics and dimensions of optical film]
The absolute value |Rth| of both the front retardation Re and the thickness direction retardation Rth of the optical film of the present invention is preferably 3 nm or less, and more preferably 2 nm or less. The values of Re and Rth can be measured using a phase difference meter (for example, Axoscan, manufactured by AXOMETRICS). The lower limits of Re and |Rth| are not particularly limited, but both are ideally 0. When the film thickness periodically changes due to a phenomenon such as draw resonance, observation is performed within a range in which the film thickness cycle is observed, and the average value thereof can be used as Re and Rth of the optical film.

The optical film of the present invention can achieve both low retardation and low film thickness unevenness by employing the above-mentioned specific thermoplastic resin as the resin constituting the film.

The thickness of the optical film of the present invention is usually 10 μm or more, preferably 15 μm or more, more preferably 20 μm or more, and usually 75 μm or less, preferably 60 μm or less, more preferably 50 μm or less. By making the thickness not less than the lower limit of the above range, it is possible to improve the damage preventing ability and handling property of the polarizing plate when used as a polarizing plate protective film, and making the thickness thinner than the upper limit makes the polarizing plate thinner You can

Since the optical film of the present invention can be manufactured with reduced film thickness unevenness due to generation of draw resonance, the film thickness unevenness can be made small. The film thickness unevenness can be calculated from the maximum thickness t _max , the minimum thickness t _min , and the average thickness t _ave by observing the film thickness within a range in which the film thickness cycle is observed, according to the following formula.
Thickness unevenness (%)=((t _max −t _min )/t _ave )×100

The thickness unevenness of the optical film of the present invention can be preferably 20% or less, more preferably 10% or less. Due to such a low value of unevenness in film thickness, the optical film can be particularly suitably used for applications such as a polarizing plate protective film.

The optical film of the present invention is usually a transparent layer and transmits visible light well. The specific light transmittance can be appropriately selected according to the application of the film of the present invention. For example, the light transmittance at a wavelength of 420 to 780 nm is preferably 85% or more, more preferably 88% or more. By having such a high light transmittance, the optical film can be particularly suitably used for applications such as a polarizing plate protective film.

[7. Optical film production method]
The manufacturing method of the optical film of the present invention is not particularly limited, and any manufacturing method can be adopted. For example, a manufacturing method including the following steps S1 and S2 can be adopted.
Step S1: A step of mixing a triblock copolymer [G _X ] having low symmetry and a triblock copolymer [G _Y ] having high symmetry to obtain a mixture.
Step S2: A step of molding the mixture by an extrusion molding method to obtain an optical film.
Below, the said manufacturing method is demonstrated as a manufacturing method of the optical film of this invention.

The step S1 can be, for example, a step of obtaining a pellet-shaped molded product containing the triblock copolymer [G _X ] and the triblock copolymer [G _Y ]. Specifically, it can be performed by mixing the pellets of the triblock copolymer [G _X ] and the pellets of the triblock copolymer [G _Y ] into mixed pellets. Alternatively, it can be performed by melting the triblock copolymer [G _X ] and the triblock copolymer [G _Y ] and molding the melt into a pellet shape. In addition to these steps, mixing may be performed by adding optional components as necessary. The proportions of the triblock copolymer [G _X ] and the triblock copolymer [G _Y ] in the mixture can be the above-mentioned preferable proportions in the thermoplastic resin.

Step S2 can be performed by a usual extrusion molding method. When the molding is performed by the extrusion molding method, efficient manufacturing is possible. However, when a triblock copolymer [G _X ] is used as a molding material, draw resonance is likely to occur. According to the finding of the present inventor, by using a mixture of a triblock copolymer [G _X ] and a triblock copolymer [G _Y ] as a material, generation of film thickness unevenness due to such draw resonance is reduced. can do.

A long film can be obtained by molding by the extrusion molding method. The long film refers to a shape having a length 5 times or more the width, preferably 10 times or more, and specifically, is wound into a roll or stored or It refers to the shape of a film that is long enough to be transported. The upper limit of the ratio of the length to the width is not particularly limited, but may be 100,000 times or less, for example.

The thermoplastic resin molded into a film shape can be used as it is as the optical film of the present invention. Alternatively, the thermoplastic resin molded into the shape of a film may be further subjected to any treatment, and the product thus obtained may be used as the optical film of the present invention. Examples of such optional treatment include stretching treatment. By appropriately adjusting the proportion of the material that constitutes the thermoplastic resin, it is possible to reduce the retardation that appears in the film by stretching. Therefore, by performing such stretching, the thickness is thin and the area is large and the quality is high. It becomes possible to easily manufacture an optical film having good quality.

[8. Optical film application: Polarizing plate]
The optical film of the present invention has properties such as high heat resistance, low water vapor transmission rate, low Re and |Rth|, and thus is suitably used as a protective film for protecting other layers in a display device such as a liquid crystal display device. sell. In particular, the optical film of the present invention can function particularly well as a polarizer protective film.

Specifically, the optical film of the present invention and a polarizer layer can be combined to obtain a polarizing plate including them. In the polarizing plate, the optical film can function as a polarizer protective film. The polarizing plate may further include an adhesive layer between the optical film and the polarizer layer for bonding them.

The polarizer layer is not particularly limited, and any known polarizer layer can be used. Examples of the polarizer include those obtained by adsorbing a material such as iodine and a dichroic dye on a polyvinyl alcohol film and then stretching the polyvinyl alcohol film. Examples of the adhesive constituting the adhesive layer include those using various polymers as base polymers. Examples of such base polymers include, for example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyethers, and synthetic rubbers.

Although the number of polarizer layers and protective film layers included in the polarizing plate is arbitrary, the polarizing plate can usually include one polarizer layer and two protective films provided on both surfaces thereof. Of such two-layer protective films, both may be the optical film of the present invention, or only one of them may be the optical film of the present invention. In particular, in a liquid crystal display device having a light source and a liquid crystal cell and having polarizing plates on both the light source side and the display surface side of the liquid crystal cell, as a protective film used at a position closer to the light source than the display surface side polarizer, It is particularly preferred to include the inventive optical film. By having such a configuration, it is possible to easily configure a liquid crystal display device having good display quality by making use of high film thickness uniformity and low characteristics such as Re and |Rth|.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples described below, and may be implemented by being arbitrarily modified within the scope of the claims of the present invention and the scope of equivalents thereof.
In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. Unless otherwise specified, the operations described below were performed in the normal temperature and normal pressure atmosphere.

〔Evaluation method〕
(Softening temperature)
The thermoplastic resin pellets to be measured were hot pressed to obtain a film having a thickness of 0.05 mm. However, when the pellets to be measured were mixed pellets composed of a plurality of types of pellets, the pellets were melted by a twin-screw extruder, kneaded, molded into pellets, and subjected to hot pressing.
The obtained film was cut out and used as a sample having a shape of 5 mm×20 mm, which was subjected to TMA (thermo-mechanical analysis). As the measuring device, TMA/SS7100 (manufactured by SII Nanotechnology Inc.) was used. In TMA, the temperature was changed while a tension of 50 mN was applied in the longitudinal direction of the sample. The temperature (° C.) when the linear expansion changed by 3% was defined as the softening temperature Ts.

(Dynamic viscoelasticity)
The thermoplastic resin pellets to be measured were hot pressed to obtain a sheet having a thickness of 2 mm. However, when the pellets to be measured were mixed pellets composed of a plurality of types of pellets, the pellets were melted by a twin-screw extruder, kneaded, molded into pellets, and subjected to hot pressing.
The obtained sheet was used as a sample and subjected to measurement of dynamic viscoelasticity. As a measuring device, a strain control type viscoelasticity measuring device (parallel plate method) manufactured by TA Instruments was used. The measurement conditions were a temperature rising rate of 5° C./min and a frequency of 1 rad/sec. By such measurement, temperature dispersion of storage elastic modulus G′ and loss elastic modulus G″ was obtained. Based on this, G′ and G″ at Ts+90° C. were obtained.

(Extension viscosity)
The thermoplastic resin pellets to be measured were hot pressed to obtain a sheet having a thickness of 0.5 mm. However, when the pellets to be measured were mixed pellets composed of a plurality of types of pellets, the pellets were melted by a twin-screw extruder, kneaded, molded into pellets, and subjected to hot pressing.
The obtained sheet was cut out and used as a sample with a shape of 5 mm×15 mm, and the extensional viscosity was measured. An Rheometer MCR302 manufactured by Anton Paar was used as a measuring device. The measurement conditions were temperature Ts+80° C. and strain rate 1s ⁻¹ . The relationship between the elongation strain and the elongation viscosity (Pa·s) is obtained, and from the values of the elongation strain and the elongation viscosity at the elongation strain 1 or a value close thereto, and the values of the elongation strain and the elongation viscosity at the elongation strain 2 or a value close thereto, The slope of elongational viscosity (η| _ε=2- η| _ε=1 ) was determined.

(Front phase difference Re and thickness direction phase difference Rth)
The front retardation Re and the absolute value |Rth| of the retardation in the thickness direction of the optical film were measured at a wavelength of 590 nm. As the measuring device, a phase difference measuring device (product name “Axoscan” manufactured by Axometric) was used. Since the film thickness periodically fluctuated due to the draw resonance, the film thickness was observed within the range in which the period was observed, and the average values thereof were taken as the front retardation Re and the thickness direction retardation Rth.

(Film thickness)
The thickness of the conveyed long optical film in the widthwise central portion was continuously measured. A two-dimensional film thickness meter manufactured by KSE Co. was used as a measuring device. Observation was performed within a range in which the film thickness cycle was observed, and the maximum thickness t _max , the minimum thickness t _min , and the average thickness t _ave in the cycle were determined. Based on these, the film thickness unevenness (%) was calculated according to the following formula.
Thickness unevenness (%)=((t _max −t _min )/t _ave )×100

[Production Example 1]
(P1-1. Block copolymer [F1])
270 parts of dehydrated cyclohexane, 75 parts of dehydrated styrene, and 7.0 parts of dibutyl ether were placed in a reactor equipped with a stirrer and whose inside was sufficiently replaced with nitrogen. While stirring the whole volume at 60° C., 5.6 parts of n-butyllithium (15% cyclohexane solution) was added to initiate polymerization. The whole volume was subsequently stirred at 60° C. for 60 minutes. The reaction temperature was maintained at 60°C until the reaction was stopped. At this point (first stage of polymerization), the reaction liquid was analyzed by GC (gas chromatography) and GPC (gel permeation chromatography), and as a result, the polymerization conversion rate was 99.4%.

Next, 15 parts of dehydrated isoprene was continuously added to the reaction liquid over 40 minutes, and after completion of the addition, stirring was continued for 30 minutes. At this point (second stage of polymerization), the reaction liquid was analyzed by GC and GPC, and as a result, the conversion of polymerization was 99.8%.
Then, 10 parts of dehydrated styrene was further added to the reaction solution continuously over 30 minutes, and after the addition was completed, the mixture was stirred for 30 minutes as it was. At this point (third stage of polymerization), the reaction solution was analyzed by GC and GPC, and as a result, the polymerization conversion rate was almost 100%.

Here, 1.0 part of isopropyl alcohol was added to stop the reaction to obtain a polymer solution containing a [Da]-[E]-[Db] type block copolymer [F1]. In the obtained block copolymer [F1], Mw[F1]=82,400, Mw/Mn was 1.32, and wA:wB=85:15.

(P1-2. Hydrogenated block copolymer [G1])
The polymer solution obtained in (P1-1) was transferred to a pressure resistant reactor equipped with a stirrer, and as a hydrogenation catalyst, a diatomaceous earth supported nickel catalyst (product name "E22U", nickel supported amount 60%, JGC catalyst). (Manufactured by Kasei) 4.0 parts and 30 parts of dehydrated cyclohexane were added and mixed. The inside of the reactor was replaced with hydrogen gas, hydrogen was supplied while stirring the solution, and a hydrogenation reaction was carried out at a temperature of 190° C. and a pressure of 4.5 MPa for 6 hours.
The reaction solution obtained by the hydrogenation reaction contained the hydrogenated block copolymer [G1]. The hydrogenated block copolymer had an Mw[G1] of 71,800, a molecular weight distribution Mw/Mn of 1.30, and a hydrogenation rate of almost 100%.

After completion of the hydrogenation reaction, the reaction solution was filtered to remove the hydrogenation catalyst, and then pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl) which was a phenolic antioxidant. ) Propionate] (product name "AO60", manufactured by ADEKA), 2.0 parts of xylene solution containing 0.3 parts thereof was added and dissolved to obtain a solution.
Next, the solution was treated at a temperature of 260° C. and a pressure of 0.001 MPa or less using a cylindrical concentrating dryer (product name “Contro”, manufactured by Hitachi, Ltd.), and cyclohexane, xylene, and other volatile components were removed from the solution. Was removed to obtain a molten resin. This was extruded in a strand form from a die, cooled, and formed into pellets by a pelletizer. This produced 95 parts of pellets of the resin [G1] containing the hydrogenated block copolymer [G1].
The hydrogenated block copolymer [G1] in the obtained resin [G1] had Mw[G1]=68,500, Mw/Mn=1.30 and Ts=139° C.

[Production Example 2]
(P2-1. Block copolymer [F2])
270 parts of dehydrated cyclohexane, 70 parts of dehydrated styrene and 7.0 parts of dibutyl ether were placed in a reactor equipped with a stirrer and the inside of which was sufficiently replaced with nitrogen. While stirring the whole volume at 60° C., 5.6 parts of n-butyllithium (15% cyclohexane solution) was added to initiate polymerization. The whole volume was subsequently stirred at 60° C. for 60 minutes. The reaction temperature was maintained at 60°C until the reaction was stopped. At this point (first stage of polymerization), the reaction solution was analyzed by GC and GPC, and as a result, the polymerization conversion rate was 99.4%.

Next, 20 parts of dehydrated isoprene was continuously added to the reaction liquid over 40 minutes, and after the addition was completed, stirring was continued for 30 minutes as it was. At this point (second stage of polymerization), the reaction liquid was analyzed by GC and GPC, and as a result, the conversion of polymerization was 99.8%.
Then, 10 parts of dehydrated styrene was further added to the reaction solution continuously over 30 minutes, and after the addition was completed, the mixture was stirred for 30 minutes as it was. At this point (third stage of polymerization), the reaction solution was analyzed by GC and GPC, and as a result, the polymerization conversion rate was almost 100%.

Here, 1.0 part of isopropyl alcohol was added to stop the reaction to obtain a polymer solution containing a [Da]-[E]-[Db] type block copolymer [F2]. In the obtained block copolymer [F2], Mw[F2]=83,400, Mw/Mn was 1.32, and wA:wB=80:20.

(P2-2. Hydrogenated block copolymer [G2])
The polymer solution obtained in (P2-1) was transferred to a pressure resistant reactor equipped with a stirrer, and as a hydrogenation catalyst, a diatomaceous earth supported nickel catalyst (product name "E22U", nickel supported amount 60%, JGC catalyst). (Manufactured by Kasei) 4.0 parts and 30 parts of dehydrated cyclohexane were added and mixed. The inside of the reactor was replaced with hydrogen gas, hydrogen was supplied while stirring the solution, and a hydrogenation reaction was carried out at a temperature of 190° C. and a pressure of 4.5 MPa for 6 hours.
The reaction solution obtained by the hydrogenation reaction contained the hydrogenated block copolymer [G2]. The hydrogenated block copolymer [G2] had an Mw[G2] of 72,800, a molecular weight distribution Mw/Mn of 1.30 and a hydrogenation rate of almost 100%.

After completion of the hydrogenation reaction, the reaction solution was filtered to remove the hydrogenation catalyst, and then pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl) which was a phenolic antioxidant. ) Propionate] (product name "AO60", manufactured by ADEKA), 2.0 parts of xylene solution containing 0.3 parts thereof was added and dissolved to obtain a solution.
Next, the solution was treated at a temperature of 260° C. and a pressure of 0.001 MPa or less using a cylindrical concentrating dryer (product name “Contro”, manufactured by Hitachi, Ltd.), and cyclohexane, xylene, and other volatile components were removed from the solution. Was removed to obtain a molten resin. This was extruded in a strand form from a die, cooled, and formed into pellets by a pelletizer. This produced 95 parts of pellets of the resin [G2] containing the hydrogenated block copolymer [G2].
The hydrogenated block copolymer [G2] in the obtained resin [G2] had Mw[G2]=69,500, Mw/Mn=1.30 and Ts=138°C.

[Production Example 3]
(P3-1. Block copolymer [F3])
A fully dried and nitrogen-substituted stainless steel reactor equipped with a stirrer was charged with 256 parts of dehydrated cyclohexane, 25.0 parts of dehydrated styrene, and 0.65 part of n-dibutyl ether, and stirred at 60°C. 1.35 parts of n-butyllithium (15% cyclohexane solution) was added to initiate the polymerization reaction. Furthermore, the mixture was reacted at 60° C. for 60 minutes while stirring. The polymerization conversion rate at this time was 99.5% (measured by gas chromatography, the same applies below). Next, 50.0 parts of dehydrated isoprene was added, and stirring was continued at the same temperature for 30 minutes. The polymerization conversion rate at this time was 99%. Thereafter, 25.0 parts of dehydrated styrene was further added, and the mixture was stirred at the same temperature for 60 minutes. The polymerization conversion rate at this point was almost 100%. Next, 0.5 part of isopropyl alcohol was added to the reaction solution to stop the reaction, and a polymerization reaction solution containing the block copolymer [F3] was obtained. The weight average molecular weight (Mw) of the obtained block copolymer [F3] was 44,900, and the molecular weight distribution (Mw/Mn) was 1.03.

(P3-2. Hydrogenated block copolymer [G3])
The polymerization reaction solution obtained in (P3-1) was transferred to a pressure resistant reactor equipped with a stirrer, and a silica-alumina-supporting nickel catalyst (E22U, nickel loading 60%; manufactured by JGC Corporation) as a hydrogenation catalyst. ) 4.0 parts and 350 parts of dehydrated cyclohexane were added and mixed. The inside of the reactor was replaced with hydrogen gas, hydrogen was further supplied while stirring the solution, and a hydrogenation reaction was carried out at a temperature of 170° C. and a pressure of 4.5 MPa for 6 hours.

After completion of the hydrogenation reaction, the reaction solution was filtered to remove the hydrogenation catalyst. In the filtrate, pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] which is a phenolic antioxidant (manufactured by Koyo Chemical Laboratory Co., Ltd., product name "Songnox 1010"). ) 0.1 part of xylene solution 1.0 part was added and dissolved. Then, using a cylindrical concentrating dryer (manufactured by Hitachi, Ltd., product name "Contro"), the solution is evaporated from the solution at a temperature of 260°C and a pressure of 0.001 MPa or less by using cyclohexane, xylene and other solvents. The component was removed. The molten polymer was continuously filtered at a temperature of 260° C. by a polymer filter (manufactured by Fuji Filter Co.) equipped with a stainless sintered filter having a pore diameter of 20 μm connected to a concentrating dryer, and then the molten polymer was formed into a strand from a die. After extruding and cooling, it was formed into pellets by a pelletizer. Thereby, pellets of the resin [G3] containing the hydrogenated block copolymer [G3] were obtained.

The obtained hydrogenated block copolymer [G3] is a ternary block copolymer composed of a block (St) containing a repeating unit derived from styrene and a block (Ip) containing a repeating unit derived from isoprene. The weight ratio of each block was St:Ip:St=25:50:25. The hydrogenated block copolymer [G3] had an Mw of 45,100, an Mw/Mn of 1.04, and the hydrogenation rates of the main chain and the aromatic ring were almost 100%.

[Example 1]
(1-1. Thermoplastic resin)
80 parts of resin [G1] pellets obtained in Production Example 1 and 20 parts of resin [G3] pellets obtained in Production Example 3 were mixed to obtain mixed pellets. The softening temperature, dynamic viscoelasticity and extensional viscosity of the mixed pellets were measured.

(1-2. Optical film)
The mixed pellet obtained in (1-1) was heated and melted in an extruder (manufactured by Optical Control System) and extruded into a film shape in that state to perform extrusion molding. As a result, a long optical film having a thickness of 40 μm was continuously formed. The formed optical film was wound around a winding shaft to obtain a film roll. The retardation and the film thickness of the optical film conveyed immediately before being wound on the winding shaft were measured, and Re, Rth and the film thickness unevenness were obtained.

[Example 2]
An optical film was obtained and evaluated by the same operation as in Example 1 except that the pellets of the resin [G2] obtained in Production Example 2 were used instead of the pellets of the resin [G1] obtained in Production Example 1.

[Comparative Example 1]
An optical film was obtained and evaluated by the same operation as in Example 1 except that the pellet of the resin [G1] obtained in Production Example 1 was used as it was instead of the mixed pellet.

[Comparative Example 2]
An optical film was obtained and evaluated by the same operation as in Example 1 except that the pellet of the resin [G2] obtained in Production Example 2 was used as it was instead of the mixed pellet.

[Comparative Example 3]
An optical film was obtained and evaluated by the same operation as in Example 1 except that the proportion of the resin [G1] pellets and the proportion of the resin [G3] pellets constituting the mixed pellets were changed to 90 parts and 10 parts, respectively. did.

[Comparative Example 4]
An optical film was obtained and evaluated by the same operation as in Example 2 except that the ratio of the resin [G2] pellets and the ratio of the resin [G3] pellets constituting the mixed pellets were changed to 90 parts and 10 parts, respectively. did.

[Comparative Example 5]
An optical film was prepared in the same manner as in Example 1 except that pellets of resin G4 (manufactured by Zeon Corporation, Ts=128° C.) containing an amorphous alicyclic structure-containing polymer were used instead of the mixed pellets. Obtained and evaluated.

The results of Examples and Comparative Examples are shown in Table 1.

*Blend ratio: A ratio of a triblock copolymer having low symmetry (copolymer [G1] or [G2]) and a triblock copolymer having high symmetry (copolymer [G3]).

As is clear from the results of the Examples and Comparative Examples, the optical films of Examples 1 and 2 in which G″/G′ and the elongation viscosity gradient satisfying the requirements of the present invention were obtained by blending a plurality of types of polymers were used. In comparison with the optical film of Comparative Example, it was possible to obtain an optical film having both low retardation and suppressed unevenness in film thickness.

Claims (3)

An optical film made of a thermoplastic resin,
The thermoplastic resin is
Two or more polymer blocks [D] per molecule having a cyclic hydride group-containing compound hydride unit [I] as a main component;
A chain hydrocarbon compound hydride unit [II], or a hydrogenation block containing one or more polymer blocks [E] per molecule containing the combination of the unit [I] and the unit [II] as a main component Including a copolymer [G],
The thermoplastic resin satisfies the formula (1) or the formula (2):
G"/G'>0.95 Formula (1)
(Η| _ε=2 −η| _ε=1 )>−1.0×10 ⁴ Pa·s Formula (2)
Where G′ is the storage elastic modulus of the thermoplastic resin, G″ is the loss elastic modulus of the thermoplastic resin,
The storage elastic modulus and the loss elastic modulus are values measured under the conditions of Ts+90° C. and 1 rad/sec,
(Η| _ε=2- η| _{ε= 1} ) is the gradient of the extensional viscosity of the thermoplastic resin, and the extensional viscosity is a value measured under the conditions of Ts+80° C. and 1s ⁻¹ ,
Ts is the softening temperature of the thermoplastic resin measured by TMA. The optical film according to claim 1, wherein both the front phase difference Re and the absolute value |Rth| of the phase difference in the thickness direction are 3 nm or less. The cyclic hydride group-containing compound hydride unit [I] is an aromatic vinyl compound hydride unit,
The optical film according to claim 1, wherein the chain hydrocarbon compound hydride unit [II] is a conjugated diene compound hydride unit.