KR102557788B1 - optical film - Google Patents

Abstract

An optical film made of a thermoplastic resin, wherein the thermoplastic resin comprises two or more polymer blocks [D] per molecule, mainly composed of a cyclic hydrocarbon group-containing compound hydride unit [I], and a chain hydrocarbon compound hydride unit. [II], or a hydrogenated block copolymer [G] containing at least one polymer block [E] per molecule mainly composed of a combination of the above unit [I] and the above unit [II], and the above 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 modulus of the thermoplastic resin, G″ is the loss modulus of the thermoplastic resin, and (η| _ε=2 - η| _ε=1 ) is the slope of the elongational viscosity of the thermoplastic resin.

Description

optical film

The present invention relates to an optical film.

BACKGROUND OF THE INVENTION Various optical films are installed in display devices such as liquid crystal display devices. For example, a liquid crystal display device usually includes a polarizing plate, and the polarizing plate usually includes a polarizer made of resin such as polyvinyl alcohol, and a protective film for protecting the polarizer. As a material for the protective film, various materials have been proposed. For example, use of a block copolymer containing a block of an aromatic vinyl compound hydride and a block of a diene compound hydride has been proposed (Patent Documents 1 and 2). An optical film can be efficiently manufactured by extrusion molding, for example.

International Publication No. 2017 / 086265 Japanese Laid-Open Patent Publication No. 2010-031253

However, when an optical film is manufactured by extrusion molding using a resin containing a block copolymer as a material, draw resonance may occur, resulting in large film thickness nonuniformity.

Therefore, the objective of this invention is to provide the optical film which can reduce the film thickness nonuniformity by generation|occurrence|production of draw resonance in extrusion molding, and can manufacture it efficiently as a thing of high quality.

As a result of examination in order to solve the said subject, this inventor discovered that the said subject was solvable by employ|adopting a specific thermoplastic resin as a material which comprises an 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,

Two or more polymer blocks [D] per molecule, the main component of which is a cyclic hydrocarbon group-containing compound hydride unit [I];

Chain hydrocarbon compound hydride unit [II], or one or more polymer blocks per molecule [E] having as a main component a combination of the above unit [I] and the above unit [II]

Including a hydrogenated block copolymer [G] containing,

The thermoplastic resin is an optical film that satisfies Formula (1) or Formula (2):

G''/G' > 0.95 Equation (1)

(η| _ε=2 - η| _ε=1 ) > -1.0 × 10 ⁴ Pa·s Equation (2)

Where, G' is the storage modulus of the thermoplastic resin, G'' is the loss modulus of the thermoplastic resin,

The storage modulus and loss modulus are values measured under the condition of Ts + 90 ° C., 1 rad / sec,

(η| _ε=2 - η| _ε=1 ) is the slope of the extensional viscosity of the thermoplastic resin,

The elongational viscosity is a value measured under conditions of Ts + 80 ° C., 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 absolute value |Rth| of the front retardation Re and the retardation in the thickness direction are 3 nm or less.

[3] The cyclic hydrocarbon group-containing compound hydride unit [I] is an aromatic vinyl compound hydride unit,

The optical film according to [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 nonuniformity by generation|occurrence|production of draw resonance in extrusion molding is reduced, and the optical film which can be efficiently manufactured as a high quality thing is provided.

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 can be implemented with arbitrary changes within a range not departing from the scope of the claims of the present invention and their equivalents.

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

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

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

In addition, that a specific polymeric unit has a positive intrinsic birefringence value means that a polymer composed of only the polymerized unit has a positive intrinsic birefringence value, and that a specific polymeric unit has a negative intrinsic birefringence value, It means that the polymer consisting only of the said polymerization unit has a negative intrinsic birefringence value. Therefore, the positive or negative of the intrinsic birefringence value of the polymerized unit can be easily determined by preparing a homopolymer composed only of the polymerized unit, forming the polymer into a molded product of an arbitrary shape, stretching the molded product, and measuring the optical properties. can In general, it is known that many of the polymerized units of hydrocarbons such as alkenes and dienes and their hydrides have a positive intrinsic birefringence value, while polymers of hydrocarbons having aromatic rings in side chains such as styrene and vinylnaphthalene and their hydrides It is known that many of the compounds having a cyclic hydrocarbon group have a negative intrinsic birefringence value.

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

In the following description, "polarizing plate" includes not only rigid members but also members having flexibility such as, for example, resin films, unless otherwise indicated.

[One. Outline 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 only of a specific thermoplastic resin.

The thermoplastic resin constituting 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 hydrocarbon group-containing compound hydride unit [I] as a main component. The polymer block [E] is a block containing as a main component a chain hydrocarbon compound hydride unit [II] or a combination of units [I] and units [II]. 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, the expression of the retardation of the optical film can be suppressed. As a result, an optical film of 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 a structural unit having a structure obtained by polymerizing a cyclic hydrocarbon group-containing compound and, if the unit obtained by such polymerization has an unsaturated bond, hydrogenating the unsaturated bond. am. However, the cyclic hydrocarbon group-containing compound hydride unit [I] includes units 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 the unsaturated bond. However, the aromatic vinyl compound hydride unit [I] includes units obtained by any production method as long as it has the structure.

Similarly, in this application, a structural unit having a structure obtained by, for example, polymerizing styrene and hydrogenating the unsaturated bond may be referred to as a styrene hydride unit. Styrene hydride units also include units obtained by any manufacturing method as long as they have the structure.

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

[Formula 1]

In structural formula (1), R ^c represents an alicyclic hydrocarbon group. Examples of R ^c include cyclohexyl groups such as cyclohexyl groups; Decahydronaphthyl groups etc. are mentioned.

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, and an imide group. , A silyl group, or 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, as R ¹ , R ² and R ³ , from the viewpoints of heat resistance, low birefringence and mechanical strength, any one of a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms is preferable. As the chain hydrocarbon group, a saturated hydrocarbon group is preferable, and an alkyl group is more preferable.

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

[Formula 2]

As for the exemplified product of the cyclic hydrocarbon group-containing compound hydride unit [I], which has stereoisomers, any stereoisomers can be used. Cyclic hydrocarbon group-containing compound hydride unit [I] may be used alone or in combination of two or more at an arbitrary ratio.

[3. chain hydrocarbon compound hydride unit [II]]

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

Similarly, in this application, a structural unit having a structure obtained by, for example, polymerizing isoprene and hydrogenating the unsaturated bond may be referred to as an isoprene hydride unit. An 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 structural units represented by the following structural formula (2) and structural units represented by structural formula (3).

[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, or a silyl group. , or 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, as R ⁴ to R ⁹ , any one of a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms is preferable from the viewpoints 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.

[Formula 4]

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, or a silyl group. , or 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, as R ¹⁰ to R ¹⁵ , any one of a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms is preferable from the viewpoints 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 preferable 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.

[Formula 5]

Among the examples of chain hydrocarbon compound hydride unit [II], any stereoisomers of those having stereoisomers can be used. Chain hydrocarbon compound hydride units [II] may be used singly or in combination of two or more 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] per molecule connected to both ends thereof. That is, the hydrogenated block copolymer [G] includes one block [E] per molecule; one block [Da] per molecule connected to one end of the block [E] and having a compound hydride unit [I] containing a cyclic hydrocarbon group; [Da]-[E]-[ Db] is preferred.

It is preferable that the thermoplastic resin contains 85% by mass or more of the hydrogenated block copolymer [G]. As the hydrogenated block copolymer [G], only one type of polymer may be included, but two or more types of polymers may be included. Preferably, the thermoplastic resin contains two or more types of polymers as the hydrogenated block copolymer [G]. When the thermoplastic resin contains two or more types of polymers as the hydrogenated block copolymer [G], a thermoplastic resin having desired characteristics can be easily prepared.

In particular, the thermoplastic resin preferably contains a plurality of triblock copolymers having different symmetries as the hydrogenated block copolymer [G]. In the present application, the symmetry of the triblock copolymer [Da]-[E]-[Db] refers to the ratio Da/Db of the weight Da of the block [Da] and the weight Db of the block [Db] (provided that Da ≥ Db) Regarding the properties, a triblock copolymer with a small Da / Db and 1 or close to 1 is called a triblock copolymer with high symmetry, and a triblock copolymer with a large Da / Db is called a triblock copolymer with low symmetry. It is said.

As a preferred example, an example in which the thermoplastic resin includes, as the hydrogenated block copolymer [G], a triblock copolymer [G _X ] with low symmetry and a triblock copolymer [G _Y ] with high symmetry will be described below. . In this example, the triblock copolymer [G _X ] is a triblock copolymer comprising blocks [Da _X ] and [Db _X ] as polymer blocks [D], and blocks [E _X ] as polymer blocks [E]. It is a combination [Da _X ]-[E _X ]-[Db _X ]. The triblock copolymer [G _Y ] is a triblock copolymer [Da Y ] comprising blocks [Da _Y ] and [Db _Y ] as polymer blocks [D], and blocks [E _Y ] as polymer blocks [E _] . -[E _Y ]-[Db _Y ].

The weight ratio _DaX / _DbX of the blocks [ _DaX ] and [ _DbX ] in the triblock copolymer [ _GX ] is 3 or more, preferably 4 or more, more preferably 5 or more, preferably 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, and more preferably 1.5 or less. . By including these triblock copolymers [G _X ] and [G _Y ] having different symmetrical properties, the advantages of the asymmetric triblock copolymer, such as having both heat resistance and toughness, are obtained, while also generating draw resonance. The film thickness nonuniformity due to this can be reduced, and it can be set as an optical film with few film thickness nonuniformities.

The preferable ratio of the triblock copolymer [G _X ] with low symmetry and the triblock copolymer [G _Y ] with high symmetry in the thermoplastic resin can be appropriately adjusted within a range where an optical film having desired characteristics is obtained. The ratio of the triblock copolymer [G _{X ] to the sum 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 (Da + Db)/E is preferably within a specific range. Specifically, the weight ratio (Da + Db)/E is preferably 65/35 or more, more preferably 70/30 or more, and preferably 90/10 or less, more preferably 85/15 or less. When the thermoplastic resin contains a plurality of types of polymers as the hydrogenated block copolymer [G], it is preferable that the weight ratio (Da + Db)/E in all of them is within the above range.

The weight average molecular weight Mw of the hydrogenated block copolymer [G] in the thermoplastic resin is preferably 40000 or more, more preferably 55000 or more, particularly preferably 60000 or more, preferably 85000 or less, more preferably 80000 or less, particularly preferably 75000 or less. When the weight average molecular weight Mw is within the above range, an optical film having desirable properties can be easily obtained. When the thermoplastic resin contains a plurality of types of polymers as the hydrogenated block copolymer [G], it is preferable that the hydrogenated block copolymer as the main component is within the above range.

Block [Da] and block [Db] are each independently preferably composed of only a cyclic hydrocarbon group-containing compound hydride unit [I], but may include any unit other than the cyclic hydrocarbon group-containing compound hydride unit [I]. can include 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 arbitrary structural units 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.

Block [E] is preferably composed only of chain hydrocarbon compound hydride unit [II], or composed of only cyclic hydrocarbon group-containing compound hydride unit [I] and chain hydrocarbon compound hydride unit [II], It may include arbitrary units other than units [I] and [II]. Examples of the arbitrary structural units include structural units based on vinyl compounds other than units [I] and [II]. The content of arbitrary structural units 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] includes a cyclic hydrocarbon group-containing compound hydride unit [I] and a chain hydrocarbon compound hydride unit [II], the weight ratio of the units [I] and [II] in the block [E] [ 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 units [I] and [II] is within the above range, an optical film having desirable properties can be easily obtained. Specifically, by including the unit [I] having a negative intrinsic birefringence value and the unit [II] normally having a positive intrinsic birefringence value in a preferred ratio, the occurrence of phase difference in the optical film can be suppressed. As a result, an optical film of 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 method for producing the hydrogenated block copolymer [G] can be employed. The hydrogenated block copolymer [G] is, for example, a polymer obtained by preparing monomers corresponding to the cyclic hydrocarbon group-containing compound hydride unit [I] and the chain hydrocarbon compound hydride unit [II], and polymerizing them. It can be produced by hydrogenating [F]. Specific production can be performed by suitably combining the method described in International Publication No. WO2016/152871 and other known methods, for example. The hydrogenation rate in the hydrogenation reaction is usually 90% or more, preferably 95% or more, and more preferably 97% or more. By increasing the hydrogenation rate, the low birefringence and thermal stability of the hydrogenated block copolymer [G] can be improved. The hydrogenation rate can be measured by ¹ H-NMR.

The thermoplastic resin may consist only of the hydrogenated block copolymer [G], or may contain arbitrary components 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, reinforcing agents, antiblocking agents, antifogging agents, release agents, pigments, organic or inorganic fillers, neutralizers, lubricants, decomposers, metal deactivators, antifouling agents, and antibacterial agents. The content of the optional component is preferably 0.5 to 5% by weight per 100% by weight of the thermoplastic resin.

[5. Characteristics of thermoplastic resin]

A thermoplastic resin satisfies one or both of Formulas (1) and (2).

G''/G' > 0.95 Equation (1)

(η| _ε=2 - η| _ε=1 ) > -1.0 × 10 ⁴ Pa·s Equation (2)

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

The storage modulus and loss modulus are values measured by dynamic viscoelasticity measurement under conditions of Ts+90°C and 1 rad/sec. Ts is the softening temperature of the thermoplastic resin. In the measurement of the modulus of elasticity, 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 a thermoplastic resin can be obtained by TMA (thermomechanical analysis). Specifically, the thermoplastic resin to be measured is made into a sheet having a width of 5 mm × a length of 20 mm × a thickness of 0.5 mm, and the temperature is changed in a state in which 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 referred to as the softening temperature Ts. As the measuring device, TMA/SS7100 (manufactured by SI Nanotechnology Co., Ltd.) can be used. The softening temperature Ts of the thermoplastic resin is not particularly limited, but may be 100 to 150°C.

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

In the present application, the gradient of the extensional viscosity refers to the gradient of the extensional viscosity in the relationship between the extensional deformation and the 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 × a thickness of 0.5 mm, and the relationship between elongational deformation and elongational viscosity is determined under the condition of a strain rate of 1 s ^-1 at Ts + 80 ° C. The slope can be obtained from measured values at elongation strains 1 and 2 or values close to them (for example, values within the ranges of 1 ± 0.05 and 2 ± 0.05). As a measuring device, a rheometer MCR302 manufactured by Anton paar can be used.

According to the findings of the present inventors, when the thermoplastic resin satisfies one or both of formulas (1) and (2), it is possible to reduce film thickness nonuniformity due to draw resonance generated in the manufacture of an optical film, An optical film can be efficiently produced as a high quality one.

[6. Optical film characteristics and dimensions, etc.]

The absolute value |Rth| of the front retardation Re and the thickness direction retardation Rth of the optical film of the present invention is preferably 3 nm or less, 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). Although the lower limits of Re and |Rth| are not particularly limited, they are all ideally 0. When the film thickness fluctuates periodically due to phenomena such as draw resonance, observation is performed in a range where the period of the film thickness is observed, and the average values 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 nonuniformity by employing the specific thermoplastic resin described above as a 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 setting the thickness to the lower limit of the above range or more, when used as a polarizing plate protective film, the breakage prevention ability and handling properties of the polarizing plate can be improved, and by setting the thickness to the upper limit or less, the polarizing plate can be made thin.

Since the optical film of the present invention can be produced with reduced film thickness nonuniformity due to the occurrence of draw resonance, the film thickness nonuniformity can be reduced. The film thickness nonuniformity can be calculated according to the following formula from the maximum thickness t _max , the minimum thickness t _min , and the average thickness t _ave in the period in which the film thickness is observed in a range where the film thickness cycle is observed.

Film thickness non-uniformity (%) = ((t _max - t _min )/t _ave ) × 100

The film thickness nonuniformity of the optical film of the present invention is preferably 20% or less, more preferably 10% or less. When the film thickness nonuniformity is such a low value, the optical film can be used particularly suitably 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. A specific light transmittance can be appropriately selected depending on the use of the film of the present invention. For example, the light transmittance in the wavelength range 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. Manufacturing method of optical film]

The manufacturing method of the optical film of this invention is not specifically limited, Any manufacturing method can be employ|adopted. For example, a manufacturing method including the following steps S1 and S2 can be employed.

Step S1: A step of mixing a triblock copolymer [G _X ] with low symmetry and a triblock copolymer [G _Y ] with high symmetry to obtain a mixture.

Process S2: A process of obtaining an optical film by molding the mixture by an extrusion molding method.

Below, the said manufacturing method is demonstrated as a manufacturing method of the optical film of this invention.

Step S1 can be, for example, a step of obtaining a pellet-shaped molding containing the triblock copolymer [G _X ] and the triblock copolymer [G _Y ]. Specifically, it can be performed by mixing pellets of the triblock copolymer [G _X ] and pellets of the triblock copolymer [G _Y ] to obtain 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 in which an optional component is added as needed. The ratio of the triblock copolymer [G _X ] and the triblock copolymer [G _Y ] in the mixture can be set to these preferable ratios in the thermoplastic resin described above.

Step S2 can be performed by a normal extrusion molding method. When molding is performed by the extrusion molding method, efficient production is possible. However, when a triblock copolymer [G _X ] is used as a molding material, draw resonance tends to occur. According to what the present inventors found out, by using a mixture of a triblock copolymer [G _X ] and a triblock copolymer [G _Y ] as a material, the occurrence of such film thickness nonuniformity due to draw resonance can be reduced.

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

The thermoplastic resin molded into the shape of a film can be used as the optical film of the present invention as it is. Alternatively, the thermoplastic resin molded into the shape of a film may be further subjected to an arbitrary treatment, and the resultant product may be used as the optical film of the present invention. As such an arbitrary process, a stretching process is mentioned. By appropriately adjusting the ratio of the materials constituting the thermoplastic resin, it is possible to reduce the retardation that develops in the film by stretching, and thus, by performing such a stretching treatment, an optical film having a thin thickness and a large area and good quality can be easily produced. It becomes possible to manufacture

[8. Use of optical film: polarizer]

The optical film of the present invention has high heat resistance, low water vapor transmission rate, low Re and |Rth| Since it has such characteristics, it can be used suitably as a protective film which protects another layer in display devices, such as a liquid crystal display device. In particular, the optical film of the present invention can function particularly well as a polarizer protective film.

Specifically, the polarizing plate provided with these can be obtained by combining the optical film of this invention and a polarizer layer. In a polarizing plate, an optical film can function as a polarizer protective film. The polarizing plate may further include an adhesive layer for adhering them between the optical film and the polarizer layer.

The polarizer layer is not particularly limited, and any known polarizer layer can be used. After making materials, such as iodine and a dichroic dye, adsorb|suck to the polyvinyl alcohol film as an example of a polarizer, what carried out the extending|stretching process is mentioned. As the adhesive constituting the adhesive layer, those using various polymers as base polymers are exemplified. Examples of such base polymers include, for example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyethers, and synthetic rubbers.

Although the number of layers of the polarizer layer and protective film included in the polarizing plate is arbitrary, the polarizing plate can usually be equipped with one layer of polarizer layer and two layers of protective films formed on both surfaces thereof. Among these two layers of protective films, both may be the optical film of the present invention, and only either one 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 this liquid crystal cell, as a protective film used at a position on the light source side rather than the polarizer on the display surface side, the present invention It is particularly preferable to provide an optical film of By having this configuration, high film thickness uniformity, low Re and |Rth| It is possible to easily construct a liquid crystal display device having good display quality by making use of such characteristics.

Example

Hereinafter, the present invention will be described in detail by showing examples. However, the present invention is not limited to the examples shown below, and can be implemented with arbitrary changes within a range not departing from the scope of the claims of the present invention and their equivalents.

In the following description, "%" and "parts" representing quantities are based on weight unless otherwise indicated. In addition, the operation described below was performed in normal temperature and normal pressure atmosphere unless otherwise indicated.

[Assessment Methods]

(softening temperature)

A pellet of the thermoplastic resin to be measured was 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, they were melted and kneaded with a twin screw extruder, molded into pellets, and subjected to a hot press.

The obtained film was cut out to make a sample having a shape of 5 mm × 20 mm, and this was subjected to TMA (thermo-mechanical analysis). As a measuring device, TMA/SS7100 (manufactured by SI Nanotechnology Co., Ltd.) 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)

A thermoplastic resin pellet to be measured was 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, they were melted and kneaded with a twin screw extruder, molded into pellets, and subjected to a hot press.

The obtained sheet was used as a sample, and this was used for measurement of dynamic viscoelasticity. As the measuring device, a strain-controlled viscoelasticity measuring device (parallel plate method) manufactured by TA Instruments was used. The measurement conditions were a temperature increase rate of 5°C/min and a frequency of 1 rad/sec. By these measurements, the temperature distribution of the storage modulus G' and loss modulus G'' was obtained. Based on this, G' and G'' at Ts+90°C were determined.

(elongational viscosity)

A thermoplastic resin pellet to be measured was 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, they were melted and kneaded with a twin screw extruder, molded into pellets, and subjected to a hot press.

The obtained sheet was cut out to make a sample having a shape of 5 mm x 15 mm, and used for measurement of elongational viscosity. As a measuring device, a rheometer MCR302 manufactured by Anton paar was used. The measurement conditions were a temperature of Ts+80°C and a strain rate of 1 s ^-1 . The relationship between elongational strain and elongational viscosity (Pa s) is obtained, and the elongational strain and elongational viscosity values at elongational strain 1 or values close thereto, and the elongational strain and elongational viscosity at elongational strain 2 or values close thereto From the values, the slope of the extensional viscosity (η| _{ε = 2} - η| _{ε = 1} ) was determined.

(front phase difference Re and thickness direction phase difference Rth)

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

(film thickness)

The film thickness of the central part in the width direction of the conveyed long optical film was continuously measured. As a measuring device, a two-dimensional film thickness gauge manufactured by K.S.I. was used. Observation was performed in a range in which the period of the film thickness was observed, and the maximum thickness t _max , minimum thickness t _min , and average thickness t _ave in the period were determined. Based on these, film thickness unevenness (%) was calculated according to the following formula.

Film thickness non-uniformity (%) = ((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 stirring device and sufficiently purged with nitrogen. While stirring the whole at 60 DEG C, 5.6 parts of n-butyllithium (15% cyclohexane solution) was added to initiate polymerization. Then, the whole was stirred at 60 degreeC for 60 minutes. The reaction temperature was maintained at 60°C until the reaction was stopped. As a result of analyzing the reaction solution at this point (first polymerization step) by GC (gas chromatography) and GPC (gel permeation chromatography), the polymerization conversion rate was 99.4%.

Next, 15 parts of dehydrated isoprene was continuously added to the reaction solution over 40 minutes, and stirring was continued for 30 minutes after the addition was completed. At this point (second polymerization stage), the reaction solution was analyzed by GC and GPC, and the polymerization conversion rate was 99.8%.

Thereafter, 10 parts of dehydrated styrene was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the mixture was stirred for 30 minutes as it was. At this point (third polymerization stage), the reaction solution was analyzed by GC and GPC, and the polymerization conversion was approximately 100%.

Here, by adding 1.0 part of isopropyl alcohol to stop the reaction, a polymer solution containing [Da]-[E]-[Db] type block copolymer [F1] was obtained. In the obtained block copolymer [F1], Mw[F1] = 82,400 and Mw/Mn were 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, 4.0 parts of a diatomaceous earth-supported nickel catalyst (product name "E22U", nickel loading 60%, manufactured by Nikki Catalyst Chemicals Co., Ltd.) , and 30 parts of dehydrated cyclohexane were added and mixed. The inside of the reactor was substituted with hydrogen gas, hydrogen was further supplied while stirring the solution, and a hydrogenation reaction was performed at a temperature of 190°C and a pressure of 4.5 MPa for 6 hours.

A hydrogenated block copolymer [G1] was contained in the reaction solution obtained by the hydrogenation reaction. The Mw [G1] of the hydrogenated block copolymer was 71,800, the molecular weight distribution Mw/Mn was 1.30, and the hydrogenation rate was approximately 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)propio, a phenolic antioxidant 2.0 part of xylene solution in which 0.3 part of Nate] (product name "AO60", manufactured by ADEKA) was added and dissolved to obtain a solution.

Next, the solution is 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.) to remove cyclohexane, xylene and other volatile components from the solution Thus, a molten resin was obtained. This was extruded from a die into a strand shape, cooled, and formed into pellets by a pelletizer. In this way, 95 parts of pellets of Resin [G1] containing the hydrogenated block copolymer [G1] were prepared.

The hydrogenated block copolymer [G1] in the obtained resin [G1] was 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 stirring device and sufficiently purged with nitrogen. While stirring the whole at 60 DEG C, 5.6 parts of n-butyllithium (15% cyclohexane solution) was added to initiate polymerization. Then, the whole was stirred at 60 degreeC for 60 minutes. The reaction temperature was maintained at 60°C until the reaction was stopped. As a result of analyzing the reaction solution by GC and GPC at this time point (first polymerization stage), the polymerization conversion rate was 99.4%.

Next, 20 parts of dehydrated isoprene was continuously added to the reaction solution over 40 minutes, and stirring was continued for 30 minutes after the addition was completed. At this point (second polymerization stage), the reaction solution was analyzed by GC and GPC, and the polymerization conversion rate was 99.8%.

Thereafter, 10 parts of dehydrated styrene was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the mixture was stirred for 30 minutes as it was. At this point (third polymerization stage), the reaction solution was analyzed by GC and GPC, and the polymerization conversion was approximately 100%.

Here, by adding 1.0 part of isopropyl alcohol to stop the reaction, a polymer solution containing [Da]-[E]-[Db] type block copolymer [F2] was obtained. In the obtained block copolymer [F2], Mw[F2] = 83,400 and Mw/Mn were 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, 4.0 parts of a diatomaceous earth supported nickel catalyst (product name "E22U", nickel supported amount 60%, manufactured by Nikki Catalyst Chemicals Co., Ltd.) , and 30 parts of dehydrated cyclohexane were added and mixed. The inside of the reactor was substituted with hydrogen gas, and hydrogen was supplied while stirring the solution, and a hydrogenation reaction was performed at a temperature of 190°C and a pressure of 4.5 MPa for 6 hours.

A hydrogenated block copolymer [G2] was contained in the reaction solution obtained by the hydrogenation reaction. Mw[G2] of hydrogenated block copolymer [G2] was 72,800, molecular weight distribution Mw/Mn was 1.30, and hydrogenation rate was approximately 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)propio, a phenolic antioxidant 2.0 part of xylene solution in which 0.3 part of Nate] (product name "AO60", manufactured by ADEKA) was added and dissolved to obtain a solution.

Next, the solution is 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.) to remove cyclohexane, xylene and other volatile components from the solution Thus, a molten resin was obtained. This was extruded from a die into a strand shape, cooled, and formed into pellets by a pelletizer. In this way, 95 parts of pellets of the resin [G2] containing the hydrogenated block copolymer [G2] were prepared.

The hydrogenated block copolymer [G2] in the obtained resin [G2] was Mw[G2] = 69,500, Mw/Mn = 1.30, and Ts = 138°C.

[Production Example 3]

(P3 - 1. Block copolymer [F3])

256 parts of dehydrated cyclohexane, 25.0 parts of dehydrated styrene, and 0.65 part of n-dibutyl ether were put into a stainless steel reactor equipped with a stirring device that was sufficiently dried and purged with nitrogen, and n-butyllithium (15 parts) was stirred while stirring at 60 ° C. % cyclohexane solution) was added to initiate the polymerization reaction. Furthermore, it was made to react at 60 degreeC for 60 minutes, stirring. The polymerization conversion rate at this point was 99.5% (measured by gas chromatography, the same applies hereinafter). 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 point 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 approximately 100%. Subsequently, 0.5 part of isopropyl alcohol was added to the reaction solution to stop the reaction, and a polymerization reaction solution containing 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 as a hydrogenation catalyst, silica-alumina supported nickel catalyst (E22U, nickel supported 60%; manufactured by Nikki Chemical Industry Co., Ltd.) 4.0 parts and dehydration 350 parts of cyclohexane were added and mixed. The inside of the reactor was substituted with hydrogen gas, and hydrogen was supplied while stirring the solution, and a hydrogenation reaction was performed 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. To the filtrate, a phenolic antioxidant, pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (manufactured by Koyo Chemical Research Laboratories, product name "Songnox1010") 」) 1.0 part of a xylene solution in which 0.1 part was dissolved was added and dissolved. Next, the solution was removed from the solution using a cylindrical concentrating dryer (manufactured by Hitachi, product name “Contro”) at a temperature of 260° C. and a pressure of 0.001 MPa or less to remove cyclohexane as a solvent, xylene, and other volatile components from the solution. did After continuously filtering the molten polymer at a temperature of 260°C with a polymer filter (manufactured by Fuji Filter Co., Ltd.) equipped with a stainless steel sintered filter with a pore diameter of 20 µm connected to a concentrating dryer, the molten polymer is extruded into strands from a die After cooling, it was molded into pellets by a pelletizer. As a result, pellets of 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 containing a repeating unit derived from styrene (St) and a block containing a repeating unit derived from isoprene (Ip). The weight ratio of each block is was St : Ip : St = 25 : 50 : 25. The Mw of this hydrogenated block copolymer [G3] was 45,100, the Mw/Mn was 1.04, and the main chain and aromatic ring hydrogenation rates were approximately 100%.

[Example 1]

(1 - 1. Thermoplastic resin)

80 parts of pellets of Resin [G1] obtained in Production Example 1 and 20 parts of pellets of Resin [G3] obtained in Production Example 3 were mixed to obtain mixed pellets. For this mixed pellet, softening temperature, dynamic viscoelasticity and extensional viscosity were measured.

(1 - 2. Optical Film)

Extrusion molding was performed by heating and melting the mixed pellets obtained in (1-1) with an extruder (manufactured by Optical Control System), and extruding them into a film shape in that state. In this way, 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 phase difference and film thickness of the conveyed optical film were measured immediately before winding on the winding shaft, and Re, Rth, and film thickness nonuniformity were calculated|required.

[Example 2]

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

[Comparative Example 1]

An optical film was obtained and evaluated in the same manner as in Example 1, except that the pellets of Resin [G1] obtained in Production Example 1 were used as they were instead of the mixed pellets.

[Comparative Example 2]

An optical film was obtained and evaluated in the same manner as in Example 1, except that the pellets of Resin [G2] obtained in Production Example 2 were used as they were instead of the mixed pellets.

[Comparative Example 3]

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

[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 constituting the mixed pellets was changed to 90 parts and the ratio of the resin [G3] pellets to 10 parts. .

[Comparative Example 5]

An optical film was obtained and evaluated in the same manner as in Example 1, except that pellets of Resin G4 (manufactured by Nippon Zeon Co., Ltd., Ts = 128° C.) containing an amorphous alicyclic structure-containing polymer were used instead of the mixed pellets. .

Table 1 shows the results of Examples and Comparative Examples.

※Blend ratio: Ratio of triblock copolymer with low symmetry (copolymer [G1] or [G2]) and triblock copolymer with high symmetry (copolymer [G3]).

As is clear from the results of Examples and Comparative Examples, the optical films of Example 1 and Example 2 obtained slopes of G''/G' and elongational viscosity that satisfy the requirements of the present invention by blending a plurality of types of polymers. , compared to the optical film of the comparative example, it was able to set it as an optical film in which both low retardation and suppressed film thickness nonuniformity were achieved.

Claims (3)

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