WO2018180498A1 - Optical film, polarizing plate and production method - Google Patents

Abstract

An optical film which is formed from a stretched resin and has Re(590), |Rth(590)|, |Re(400) - Re(800)| and |Rth(400) - Rth(800)| within specific ranges, while having a tensile modulus of elasticity of 1,500 MPa or more and a tear strength of 0.6 N/mm or more; a polarizing plate which is provided with this optical film; and a method for producing this optical film. The resin preferably contains a polymer that has an aromatic vinyl compound hydride unit (a) and a diene compound hydride unit (b).

Description

Optical film, polarizing plate, and manufacturing method

The present invention relates to an optical film, a polarizing plate, and a production method thereof.

In an optical device such as a display device, the use of a resin optical film is widely performed. Furthermore, optical films having a small retardation are known as examples of such optical films (for example, Patent Documents 1 to 3). Such a low retardation optical film can be used as a protective film for protecting a polarizer in a polarizing plate. Specifically, a display device having good viewing angle characteristics can be configured by using a low retardation optical film as a polarizer protective film.

JP 2010-286841 A (corresponding publication: US Patent Application Publication No. 2008/309860) JP 2011-13378 A JP-T-2011-523668 (corresponding publication: US Patent Application Publication No. 2011/038045)

The low retardation optical film is required to be capable of manufacturing and processing the film with high efficiency and high durability of the film in addition to the small retardation. For example, it is required that the film can be easily produced as a long film having a large area by stretching, and that the film can be easily cut and conveyed without causing defects. Moreover, it is calculated | required that defects, such as generation | occurrence | production of a curl, do not generate | occur | produce in the environment which uses a film as a polarizer protective film.

However, it was difficult to obtain an optical film excellent in all the characteristics described above.

Accordingly, an object of the present invention is an optical film having a small phase difference, can be easily produced as a long film having a large area by stretching, can be easily cut and conveyed, and has high durability, and a method for producing the same. Is to provide.
A further object of the present invention is to provide a polarizing plate that can realize a display device with good viewing angle characteristics, can be easily manufactured, and has high durability.

The present invention is as follows.

[1] An optical film made of a stretched resin, which satisfies the following formulas (1) to (4):
0 nm ≦ Re (590) ≦ 3 nm (1)
| Rth (590) | ≦ 3 nm (2)
| Re (400) −Re (800) | ≦ 1 nm (3)
| Rth (400) −Rth (800) | ≦ 1 nm (4)
(However,
Re (400) is an in-plane retardation at a wavelength of 400 nm of the optical film,
Re (590) is an in-plane retardation at a wavelength of 590 nm of the optical film,
Re (800) is the in-plane retardation at a wavelength of 800 nm of the optical film,
Rth (400) is the thickness direction retardation of the optical film at a wavelength of 400 nm,
Rth (590) is a retardation in the thickness direction at a wavelength of 590 nm of the optical film,
Rth (800) is a thickness direction retardation of the optical film at a wavelength of 800 nm. )
The tensile modulus is 1500 MPa or more,
An optical film having a tear strength of 0.6 N / mm or more.
[2] The optical film according to [1], wherein the resin includes a polymer having an aromatic vinyl compound hydride unit (a) and a diene compound hydride unit (b).
[3] The polymer is
One block B per molecule having the diene compound hydride unit (b);
One block A1 per molecule connected to one end of the block B and having the aromatic vinyl compound hydride unit (a);
The optical film according to [2], which is a triblock copolymer that is connected to the other end of the block B and includes one block A2 per molecule having the aromatic vinyl compound hydride unit (a). .
[4] In the triblock copolymer, the ratio (A1 + A2) / B of the total weight of the block A1 and the block A2 to the weight of the block B is 80/20 or more and 88/12 or less. [3] The optical film according to [3].
[5] The aromatic vinyl compound hydride unit (a) is a structural unit having a structure obtained by polymerizing styrene and hydrogenating,
The optical film according to any one of [2] to [4], wherein the diene compound hydride unit (b) is a structural unit having a structure obtained by polymerizing and hydrogenating isoprene.
[6] A polarizing plate comprising a polarizer and the optical film described in any one of [1] to [5].
[7] The method for producing an optical film according to any one of [1] to [5],
The glass transition temperature of the resin is Tg,
The manufacturing method including extending | stretching the film before extending | stretching which consists of said resin by the draw ratio of 1.1 times or more and 3.0 times or less in the temperature of (Tg + 10) degreeC or more and (Tg + 45) degreeC or less.

According to the present invention, an optical film that has a small retardation, can be easily manufactured as a long film with a large area by stretching, can be easily cut and conveyed, and has high durability, and a manufacturing method thereof are provided. can do.
According to the present invention, it is also possible to provide a polarizing plate that can realize a display device with good viewing angle characteristics, can be easily manufactured, and has high durability.

FIG. 1 is a rear view of the trimming apparatus used for trimming in the embodiment as viewed from the downstream side in the conveyance direction of the optical film.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and exemplifications, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

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

In the following description, the in-plane retardation Re of the film is a value represented by Re = (nx−ny) × d unless otherwise specified. The thickness direction retardation Rth of the film is a value represented by Rth = [{(nx + ny) / 2} −nz] × d. Here, nx represents a refractive index in a direction (in-plane direction) perpendicular to the thickness direction of the film and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the film and perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. These phase differences Re and Rth can be measured using, for example, a commercially available automatic birefringence meter. The phase differences Re and Rth are evaluated for light having a wavelength of 590 nm.

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

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

[1. Optical film material: block copolymer]
The optical film of the present invention is made of a stretched resin.
A film made of a stretched resin is a film obtained by stretching a resin by forming it into a film shape and further subjecting it to a stretching process. In the present application, a film before being subjected to such a stretching process may be referred to as a “film before stretching”.

The resin constituting the optical film may be a resin containing a block copolymer having an aromatic vinyl compound hydride unit (a) and a diene compound hydride unit (b). In the present application, such a copolymer may be simply referred to as a block copolymer. Further, a resin containing a block copolymer may be simply referred to as a block copolymer resin.

The block copolymer has one diene compound hydride unit (b), one block B per molecule, and one molecule connected to one end of the block B and having an aromatic vinyl compound hydride unit (a). A triblock copolymer comprising one block A1 and one block A2 connected to the other end of the block B and having an aromatic vinyl compound hydride unit (a) may be used. By adopting a block copolymer resin as the resin constituting the optical film, an optical film particularly excellent in terms of low phase difference, ease of cutting and transport, durability, etc. is particularly easy as a long film with a large area. Can be manufactured.

The aromatic vinyl compound hydride unit (a) is a repeating unit having the same structure as a repeating unit obtained by polymerizing an aromatic vinyl compound and then hydrogenating an unsaturated bond thereof. For example, the following structural formula ( It is a repeating unit represented by 1). However, the aromatic vinyl compound hydride unit (a) is not limited depending on the production method.
In the following examples of units, those having stereoisomers can use any of the stereoisomers. Blocks A1, A2 and B may include a plurality of different types of units. Further, the block copolymer may be a mixture of plural kinds of polymers including plural kinds of different blocks. The structure of the block copolymer, the hydrogenation rate, etc. can be confirmed by NMR method.

In the 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 the 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 (halogen atom, alkoxy group, hydroxyl group, ester group, cyano group, amide group, imide group, or silyl group). Among them, R ¹ , R ² and R ³ are preferably a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms from the viewpoints of heat resistance, low birefringence and mechanical strength. The chain hydrocarbon group is preferably a saturated hydrocarbon group, and more preferably an alkyl group.

The molecular weight of each of the blocks A1 and A2 is preferably 1000 or more, more preferably 2000 or more, even more preferably 3000 or more, preferably 100,000 or less, more preferably 90000 or less, and even more preferably 80000 or less. When the molecular weights of the blocks A1 and A2 are equal to or higher than the lower limit, an advantage that the elastic modulus of the film is improved is obtained. When the molecular weight is equal to or lower than the upper limit, an advantage that the impact resistance of the film is improved is obtained. The molecular weight of block A1 and the molecular weight of block A2 may be the same or different.

In a preferred example, the aromatic vinyl compound hydride unit (a) is a structural unit having a structure obtained by polymerizing styrene and hydrogenating it. More specifically, a preferred example of the aromatic vinyl compound hydride unit (a) includes a unit represented by the following structural formula (1-1).

The diene compound hydride unit (b) has the same structure as the repeating unit obtained by polymerizing the diene compound and then hydrogenating the unsaturated bond if the resulting polymer has an unsaturated bond. It is a repeating unit having. The diene compound hydride unit (b) is preferably a repeating unit having the same structure as the repeating unit obtained by polymerizing the conjugated diene compound and then hydrogenating the unsaturated bond. Examples of the diene compound hydride unit (b) include a unit represented by the following structural formula (2) and a unit represented by the structural formula (3). However, the diene compound hydride unit (b) is not limited depending on its production method.

In the 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 these, R ⁴ to R ⁹ are preferably a hydrogen atom and a chain hydrocarbon group having 1 to 6 carbon atoms from the viewpoints of heat resistance, low birefringence, mechanical strength, and the like. The chain hydrocarbon group is preferably a saturated hydrocarbon group, and more preferably an alkyl group.

In the structural formula (3), R ¹⁰ to R ¹⁵ each independently represent 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, R ¹⁰ to R ¹⁵ are preferably 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. The chain hydrocarbon group is preferably a saturated hydrocarbon group, and more preferably an alkyl group.

The molecular weight of the block B is preferably 500 or more, more preferably 1000 or more, still more preferably 2000 or more, preferably 50000 or less, more preferably 30000 or less, and even more preferably 20000 or less. The advantage that the impact resistance is improved when the molecular weight of the block B is equal to or higher than the lower limit is obtained, and the advantage that the elastic modulus is improved when the molecular weight is lower than the upper limit is obtained.

In a preferred example, the diene compound hydride unit (b) is a structural unit having a structure obtained by polymerizing isoprene and hydrogenating it. More specifically, units represented by the following structural formulas (2-1) to (2-3) can be given.

　トリブロック共重合体において、ブロックＡ１及びブロックＡ２の合計の重量と、ブロックＢの重量との比（Ａ１＋Ａ２）／Ｂは、好ましくは８０／２０以上、より好ましくは８２／１８以上であり、好ましくは８８／１２以下、より好ましくは８６／１４以下である。（Ａ１＋Ａ２）／Ｂをこの範囲内とすることにより、光学フィルムのＲｅを所望の小さい値に収めることができる。

In the triblock copolymer, the ratio (A1 + A2) / B of the total weight of the block A1 and the block A2 to the weight of the block B is preferably 80/20 or more, more preferably 82/18 or more, preferably Is 88/12 or less, more preferably 86/14 or less. By setting (A1 + A2) / B within this range, Re of the optical film can be kept within a desired small value.

The triblock copolymer may have any block other than the blocks A1, A2 and B as long as the effects of the present invention are not significantly impaired. The triblock copolymer may also contain any unit other than the aromatic vinyl compound hydride unit (a) and the diene compound hydride unit (b) as long as the effects of the present invention are not significantly impaired. However, from the viewpoint of exhibiting the effects of the present invention more remarkably, the number of the arbitrary blocks and the arbitrary units is preferably small. The weight ratio of the arbitrary block in the triblock copolymer is not uniform depending on the use of the film, but is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less. It is particularly preferred that any block is not included. The weight ratio of the arbitrary unit in the triblock copolymer is not uniform depending on the use of the film, but is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less. It is particularly preferred that any unit is not included.

The weight average molecular weight Mw of the triblock copolymer is preferably 50,000 or more, more preferably 55,000 or more, still more preferably 60,000 or more, preferably 100,000 or less, more preferably 90, 000 or less, and more preferably 80,000 or less. When the weight average molecular weight Mw is equal to or higher than the lower limit, the impact resistance of the film can be improved, and when the weight average molecular weight Mw is equal to or lower than the upper limit, the viscosity of the polymer can be lowered and the moldability can be improved.

The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the triblock copolymer is preferably 2 or less, more preferably 1.7 or less, and even more preferably 1.5 or less. When Mw / Mn is within such a range, the polymer viscosity can be lowered to improve the moldability.

The glass transition temperature Tg _A of the triblock copolymer is preferably 110 ° C. or higher, more preferably 115 ° C. or higher, even more preferably 120 ° C. or higher, preferably 150 ° C. or lower, more preferably 148 ° C. or lower, More preferably, it is 145 degrees C or less. When the glass transition temperature of the triblock copolymer is at least the above lower limit, the advantage that the heat resistance of the film is improved is obtained, and when it is not more than the upper limit, the advantage is obtained that the processing temperature is lowered and the moldability is increased. . As the glass transition temperature Tg _A of the triblock copolymer, a higher numerical value can be adopted when a plurality of glass transition temperatures are observed.

The block copolymer is prepared by preparing monomers corresponding to each of the aromatic vinyl compound hydride block and the diene compound hydride block, and performing block polymerization to obtain a polymer, and then hydrogenating the obtained polymer. It can manufacture by performing.

Examples of monomers corresponding to aromatic vinyl compound hydride blocks include styrene, α-methyl styrene, α-ethyl styrene, α-propyl styrene, α-isopropyl styrene, α-t-butyl styrene, 2-methyl. Styrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, Styrenes such as monofluorostyrene and 4-phenylstyrene; vinylcyclohexanes such as vinylcyclohexane and 3-methylisopropenylcyclohexane; 4-vinylcyclohexene, 4-isopropenylcyclohexene, 1-methyl-4-vinylcyclohexene, 1- Methyl-4-isop And vinylcyclohexenes such as lopenylcyclohexene, 2-methyl-4-vinylcyclohexene, 2-methyl-4-isopropenylcyclohexene; and combinations thereof.

Examples of monomers corresponding to diene compound hydride blocks include chain conjugated dienes such as butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Class; these combinations are listed alongside.

The specific procedure for polymerization and hydrogenation is not particularly limited. Polymerization and hydrogenation can be carried out, for example, by the method described in JP2011-13378.

The resin constituting the optical film may contain an optional component other than the block copolymer. Examples of optional components include ultraviolet absorbers; inorganic fine particles; stabilizers such as antioxidants, heat stabilizers and near infrared absorbers; resin modifiers such as lubricants and plasticizers; colorants such as dyes and pigments; Antistatic agents; and combinations thereof. From the viewpoint of remarkably exhibiting the effect of the present invention, the amount of the optional component is preferably small. The specific amount of the optional component depends on the use and thickness of the film of the present invention, but is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, for example, with respect to 100 parts by weight of the block copolymer. More preferred are parts by weight or less. Among these, it is particularly preferable that other components are not included.

[2. Properties of optical film)
The optical film of the present invention satisfies the following formulas (1) to (4).
0 nm ≦ Re (590) ≦ 3 nm (1)
| Rth (590) | ≦ 3 nm (2)
| Re (400) −Re (800) | ≦ 1 nm (3)
| Rth (400) −Rth (800) | ≦ 1 nm (4)
In the formula, Re (400) is an in-plane direction retardation of the optical film at a wavelength of 400 nm, Re (590) is an in-plane direction retardation of the optical film at a wavelength of 590 nm, and Re (800) is Rth (400) is the thickness direction retardation of the optical film at a wavelength of 400 nm, and Rth (590) is the thickness of the optical film at a wavelength of 590 nm. Rth (800) is the thickness direction retardation of the optical film at a wavelength of 800 nm.

Re (590) is 3 nm or less, preferably 2 nm or less. The lower limit of Re (590) is ideally 0 nm. | Rth (590) | is 3 nm or less, preferably 1 nm or less. The lower limit of Rth (590) is ideally 0 nm. | Re (400) −Re (800) | is 1 nm or less, preferably 0.8 nm or less. The lower limit of | Re (400) −Re (800) | is ideally 0 nm. | Rth (400) −Rth (800) | is 1 nm or less, preferably 0.8 nm or less. The lower limit of | Rth (400) −Rth (800) | is ideally 0 nm. The optical film of the present invention can be preferably used in applications such as a polarizer protective film as a low retardation optical film by satisfying the formulas (1) to (4).

The optical film of the present invention has a tensile modulus and tear strength within a specific range. The tensile elastic modulus is 1500 MPa or more, preferably 1600 MPa or more, and the tear strength is 0.6 N / mm or more, preferably 0.8 N / mm or more. Although the upper limit of a tensile elasticity modulus is not specifically limited, For example, it can be 4000 MPa or less. The upper limit of the tear strength is not particularly limited, but may be, for example, 2.0 N / mm or less. By having such a tensile elastic modulus and tear strength, the optical film can be easily cut and conveyed without causing defects. Moreover, in an environment where the optical film is used as a polarizer protective film, problems such as the occurrence of curling can be reduced.

The optical film having the optical properties and mechanical properties described above can be easily selected by appropriately selecting the resin constituting the film from those described above and appropriately selecting the manufacturing conditions from those described below. Can be manufactured.

The optical film of the present invention has a total light transmittance of preferably 80% or more, more preferably 90% or more, from the viewpoint of stably exhibiting the function as an optical member.

The optical film of the present invention can be produced as a long film and further cut into a desired dimension when used. When the optical film of the present invention is produced as a long film, the dimension in the width direction can be set to, for example, 1000 mm to 3000 mm.

The thickness of the optical film of the present invention is preferably 10 μm or more, more preferably 15 μm or more, still more preferably 20 μm or more, preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. When used as a polarizing plate protective film by making the thickness of the optical film above the lower limit, there is an advantage that handling properties such as prevention of damage to the polarizing plate are improved, and by making the thickness below the upper limit, the polarizing plate is made thin. There is an advantage that can be.

The optical film of the present invention is usually a transparent layer and transmits visible light well. Although the specific light transmittance is not uniform depending on the use of the film of the present invention, the light transmittance at a wavelength of 420 to 780 nm is preferably 85% or more, more preferably 88% or more. Since the optical film has such a high light transmittance at a wavelength of 420 to 780 nm, when the optical film is mounted on a display device such as a liquid crystal display device, it is possible to suppress a decrease in luminance particularly during long-term use.

[3. Manufacturing method of optical film]
The optical film of the present invention can be produced by a production method in which a pre-stretch film is prepared using the above-described resin as a material and the pre-stretch film is stretched. Preparation and stretching of the pre-stretched film can be performed, for example, by the method described in JP2011-13378A. By stretching, the optical film can be easily produced as a long film having a large area.

The optical film of the present invention can be preferably manufactured by a manufacturing method in which a pre-stretch film is stretched at a specific stretch ratio at a specific temperature range. The stretching temperature can be defined as a relative value with respect to the glass transition temperature Tg of the resin constituting the film before stretching. The stretching temperature is preferably (Tg + 10) ° C. or higher, more preferably (Tg + 15) ° C. or higher, preferably (Tg + 45) ° C. or lower, more preferably (Tg + 40) ° C. or lower. The draw ratio is preferably 1.1 times or more, more preferably 1.15 times or more, preferably 3.0 times or less, more preferably 2.75 times or less. By setting the stretching direction and the stretching ratio within such ranges, the optical film can be made into a long film having a large area by stretching, and the retardation of the optical film can be reduced. In particular, by adopting the block copolymer resin described above as the resin constituting the optical film, and by setting the stretching temperature and magnification within the specific range described above, the phase difference is small, An optical film that can be easily transported and has high durability can be easily manufactured as a long film having a large area.

[4. Application of optical film: Polarizing plate]
The optical film of the present invention can be suitably used as a protective film for protecting other layers in a display device such as a liquid crystal display device. Especially, the optical film of this invention is suitable as a polarizer protective film, and is especially suitable as an inner side polarizer protective film of a display apparatus.

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

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

By providing the optical film of the present invention, the polarizing plate of the present invention can realize a display device having good viewing angle characteristics based on the low phase difference. Since the optical film of the present invention can be easily manufactured and has high durability, the polarizing plate of the present invention can also be easily manufactured and can be a highly polarizing plate.

Although the number of polarizers and protective films provided in the polarizing plate is arbitrary, the polarizing plate of the present invention can usually comprise one layer of polarizer and two layers of protective films provided on both sides thereof. Of these two protective films, both may be the optical film of the present invention, and only one of them may be the optical film of the present invention. In particular, in a liquid crystal display device including 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, the optical film of the present invention is used as a protective film used at a position closer to the liquid crystal cell than the polarizer. It is particularly preferred to provide a film. By having such a configuration, it is possible to easily configure a liquid crystal display device having a good display quality with small light leakage and color unevenness at an oblique viewing angle.

When the polarizing plate of the present invention includes any other protective film in addition to the optical film of the present invention, a known protective film can be appropriately selected as the optional protective film. For example, a film made of a resin containing an alicyclic structure-containing polymer can be used. More specifically, a film made of a resin such as “ZEONOR” (manufactured by Nippon Zeon Co., Ltd.) can be used.

When the polarizing plate of the present invention is provided in a liquid crystal display device, the liquid crystal display device is not particularly limited, and may be a liquid crystal display device of any type. Among them, a liquid crystal display device including an IPS mode liquid crystal cell is particularly preferable because the optical film of the present invention has a remarkable effect of suppressing light leakage at an oblique viewing angle and suppressing color unevenness.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

〔Evaluation methods〕
[Molecular weight]
The weight average molecular weight and number average molecular weight of the polymer (block copolymer and polymer as an intermediate for production thereof) were measured at 38 ° C. as a standard polystyrene equivalent value by GPC using THF as an eluent. As a measuring apparatus, HLC8020GPC manufactured by Tosoh Corporation was used.

[Re and Rth]
Re and Rth of the optical film were measured by using “AxoScan” manufactured by AXOMETRICS at wavelengths of 400, 590, and 800 nm, R ₀ (retardation observed from 0 ° polar angle), R ₄₀ (polar angle 40 ° direction). The retardation Re in the in-plane direction and the retardation Rth in the thickness direction were calculated from the retardation observed from 1) and the average refractive index.

[Tensile modulus]
The tensile elastic modulus of the optical film was measured according to JIS K7162. However, the test piece was prepared according to JIS K7127-1B. The tensile speed was measured as 5 mm / min. Both the measurement by the tension along the longitudinal direction of the long optical film and the measurement by the tension along the width direction were performed, and the average value thereof was taken as the measurement value.

(Tear strength)
The tear strength of the optical film was measured according to the trouser tear method (JIS K7128-1). Both the measurement by tearing along the longitudinal direction of the long optical film and the measurement by tearing along the width direction were performed, and the average value thereof was taken as the measurement value.

[Evaluation method of transportability of optical film]
The long optical film was transported horizontally along the film longitudinal direction at a transport speed of 5 m / min. The conveyed optical film was continuously trimmed using the trimming apparatus shown in FIG. Trimming was performed for 30 minutes during which no film breakage occurred.
Trimming of the optical film was continued for 30 minutes while conveying the optical film in the longitudinal direction at a conveyance speed of 5 m / min. And what the fracture | rupture of the optical film caused by the crack by trimming generate | occur | produced was determined to be bad, and what was not generate | occur | produced such a fracture | rupture was determined to be favorable. Here, the breakage of the optical film refers to a phenomenon in which the optical film is cut in a direction other than the longitudinal direction.

FIG. 1 is a rear view of the trimming apparatus used for trimming as viewed from the downstream side in the optical film transport direction. For convenience of illustration, the lower blade 122 in FIG. 1 is shown by a longitudinal sectional view taken along a plane passing through the rotation shaft 122C. The trimming device 120 is a pair of devices aligned in the TD direction (direction parallel to the width direction of the film being conveyed). In the trimming step, the long optical film is transported in the horizontal direction, and the dish-shaped upper blade 121 disposed on the upper side of the optical film transport path is rotated around the rotation shaft 121C, so that A part of the outer periphery is rotated by rotating a bowl-shaped lower blade 122 with a part thereof in contact with the upper surface of the optical film and arranged on the lower side of the conveyance path of the optical film about the rotation shaft 122C. Was brought into contact with the lower surface of the optical film. The rotating shaft 121C of the upper blade 121 and the rotating shaft 122C of the lower blade 122 are both arranged in a direction parallel to the TD direction. The upper blade 121 and the lower blade 122 were overlapped so as to shear the optical film, and the saddle-shaped lower blade 122 was arranged so that the edge protruded to the side surface side of the upper blade 121. By carrying an optical film between the upper blade 121 and the lower blade 122 of such a trimming device, continuous trimming of the optical film is achieved, and the optical film is cut into the center of the cut optical film 11; Separated into end films 12 at both ends.

[Viewing angle characteristics]
A commercially available television receiver was prepared as an IPS type liquid crystal display device.
The polarizing plate on the viewing side of this television receiver (that is, the polarizing plate closer to the display surface) was removed, and the polarizing plate produced in the example or comparative example was attached instead. The orientation of the polarizing plate was adjusted so that the optical film was on the light source side and the absorption axis of the polarizer was the same as the orientation of the polarizer in the polarizing plate originally provided in the television receiver.
The television receiver was set in a black display state (a state in which a black color was displayed on the entire display surface), and the display surface was observed. The observation was performed in the range of the azimuth angle of 0 ° to 180 ° from the direction where the polar angle with respect to the display surface is about 40 °. As a result of observation, when a color such as a bluish color was confirmed on the display surface, it was determined to be bad, and when the color was not confirmed, it was determined to be good.

〔curl〕
The polarizing plate produced in the example or the comparative example was cut to obtain a square film piece of 100 mm × 100 mm. The surface on the optical film side of the obtained film piece was subjected to corona treatment. The corona treatment was performed under the same conditions as those performed in the production of the polarizing plate. The corona-treated surface of the polarizing plate was bonded to an optical glass (Corning EagleXG thickness 0.7 mm) through a layer of an adhesive (CS9621T manufactured by Nitto Denko Corporation) to obtain a bonded product.

The paste was subjected to a thermal shock test. The thermal shock test was performed using a thermal shock tester (manufactured by Espec). The conditions of the thermal shock test were 70 ° C. for 30 minutes followed by −40 ° C. for 30 minutes, and 100 cycles were repeated. After completion of the thermal shock test, the bonded product was taken out. When the end of the polarizing plate was lifted by 2 mm or more due to the curling of the polarizing plate, it was determined to be defective, and when the lifting amount was less than 2 mm, it was determined to be good.

[Example 1]
(1-1. First stage reaction: elongation of aromatic vinyl compound hydride block A1)
A stainless steel reactor equipped with a stirrer and thoroughly dried and purged with nitrogen was charged with 320 parts of dehydrated cyclohexane, 75 parts of styrene and 0.38 part of dibutyl ether, and stirred at 60 ° C. to give an n-butyllithium solution. (15 wt% hexane solution) 0.41 part was added to initiate the polymerization reaction, and the first stage polymerization reaction was carried out for 1 hour. At 1 hour after the start of the reaction, a sample was sampled from the reaction mixture and analyzed by gas chromatography (GC). As a result, the polymerization conversion was 99.5%.

(1-2. Second Stage Reaction: Extension of Diene Compound Hydride Block)
To the reaction mixture obtained in the step (P1-1), 15 parts of isoprene was added, and then the second stage polymerization reaction was started to carry out the polymerization reaction for 1 hour. At 1 hour after the start of the second stage polymerization reaction, a sample was sampled from the reaction mixture and analyzed by GC. As a result, the polymerization conversion was 99.5%.

(1-3. Third stage reaction: elongation of aromatic vinyl compound hydride block A2)
To the reaction mixture obtained in the step (1-2), 10 parts of styrene was added, and then the third stage polymerization reaction was started. At 1 hour after the start of the third stage polymerization reaction, a sample was sampled from the reaction mixture, and the weight average molecular weight Mw and number average molecular weight Mn of the copolymer were measured. Moreover, as a result of analyzing the sample sampled at this time by GC, the polymerization conversion was almost 100%. Immediately thereafter, 0.2 part of isopropyl alcohol was added to the reaction mixture to stop the reaction. As a result, a mixture containing a copolymer having a triblock molecular structure of styrene-isoprene-styrene was obtained.
The obtained copolymer was a copolymer having a triblock molecular structure in a weight ratio of styrene / isoprene / styrene = 75/15/10.

(1-4. Fourth stage reaction: hydrogenation)
Next, the mixture containing the block copolymer obtained in the step (1-3) is transferred to a pressure-resistant reactor equipped with a stirrer, and a diatomaceous earth-supported nickel catalyst (manufactured by JGC Catalysts & Chemicals, Inc.) is used as a hydrogenation catalyst. E22U ", nickel loading 60%) 8.0 parts and dehydrated cyclohexane 100 parts were added and mixed. The inside of the reactor was replaced with hydrogen gas, and hydrogen was supplied while stirring the solution. A hydrogenation reaction was performed at a temperature of 190 ° C. and a pressure of 4.5 MPa for 6 hours. A reaction solution containing a block copolymer in which the copolymer was hydrogenated by a hydrogenation reaction was obtained.
After completion of the hydrogenation reaction, the reaction solution was filtered to remove the hydrogenation catalyst, and then the phenolic antioxidant pentaerythrityl tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) ) Propionate] ("Songnox 1010" manufactured by Matsubara Sangyo Co., Ltd.) 2.0 parts of xylene solution in which 0.1 part was dissolved was added and dissolved.
Next, the above solution is mixed with cyclohexane, xylene and other volatile components as solvents from a solution at a temperature of 260 ° C. and a pressure of 0.001 MPa or less using a cylindrical concentrating dryer (“Contro” manufactured by Hitachi, Ltd.). Removed. The molten polymer was extruded into a strand form from a die, and after cooling, 95 parts of block copolymer pellets were produced by a pelletizer.
The block copolymer contained in the obtained pellets had a weight average molecular weight (Mw) of 65,000, a molecular weight distribution (Mw / Mn) of 1.25, and a hydrogenation rate of almost 100%.

(1-5. Optical film)
The pellets obtained in the step (1-4) were heated and melted and molded by extrusion to obtain a long original film. The thickness of the raw film was 48 μm.
The raw film was stretched in the width direction by a tenter stretching machine. The stretching temperature was 160 ° C. and the stretching ratio was 1.2 times. By such stretching, an optical film having a thickness of 40 μm was obtained.
About the obtained optical film, Re (590), Rth (590), Re (400) -Re (800), Rth (400) -Rth (800), tensile elastic modulus and tear strength were measured, and the transportability was measured. evaluated.

(1-6. Polarizing plate)
One side of the optical film obtained in the step (1-5) and one side of the polarizer protective film were subjected to corona treatment. As the polarizer protective film, a film made of a resin containing an alicyclic structure-containing polymer (trade name “Zeonor Film ZF14”, manufactured by Nippon Zeon Co., Ltd., glass transition temperature 136 ° C., thickness 40 μm) was used. A corona treatment device (manufactured by Kasuga Denki Co., Ltd.) was used for the corona treatment. The condition of the corona treatment was a discharge amount of 50 W · min / m ² .

These films and a polarizer were bonded together to obtain a multilayer film. As the polarizer, a polyvinyl alcohol polarizer (thickness: 23 μm) was used. Bonding is an arrangement in which the polarizer and the corona-treated surface of the optical film and the polarizer protective film face each other, and these are overlapped through a layer of adhesive (Toyochem Dynaleo CRB series), and a roll laminator is used. This was done by pressure bonding.

The resulting multilayer film was irradiated with UV. UV irradiation is performed by using a UV irradiation apparatus (manufactured by Fusion) equipped with a high-pressure mercury light source under the conditions of a peak illuminance of 350 mW / cm ² and an integrated light quantity of 500 mJ / cm ² from the light source to the surface on the optical film side. Performed by irradiation. By this UV irradiation, the adhesive was cured to obtain a polarizing plate having a layer structure of (polarizer protective film) / (adhesive layer) / (polarizer) / (adhesive layer) / (optical film).
The obtained polarizing plate was evaluated for viewing angle characteristics and curl.

[Example 2]
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
In step (1-5), the extrusion conditions were changed, and the thickness of the raw film was set to 60 μm.
In step (1-5), the draw ratio was changed to 1.5 times. The thickness of the obtained optical film was 40 μm.

Example 3
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
In step (1-5), the extrusion molding conditions were changed, and the thickness of the raw film was 120 μm.
In step (1-5), the draw ratio was changed to 3.0 times. The thickness of the obtained optical film was 40 μm.

Example 4
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
The amount of styrene used in step (1-1) was changed to 60 parts, the amount of isoprene used in step (1-2) was changed to 20 parts, and the amount of styrene used in step (1-3) was changed to 20 parts. Changed to the department. The copolymer obtained in the step (1-3) was a copolymer having a triblock molecular structure with a weight ratio of styrene / isoprene / styrene = 60/20/20. Thereafter, the block copolymer contained in the obtained pellet had a weight average molecular weight (Mw) of 65,000, a molecular weight distribution (Mw / Mn) of 1.24, and a hydrogenation rate of almost 100%.
In step (1-5), the extrusion molding conditions were changed, and the thickness of the raw film was set to 100 μm.
In step (1-5), the draw ratio was changed to 2.5 times. The thickness of the obtained optical film was 40 μm.

Example 5
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
-The amount of styrene used in step (1-1) was changed to 78 parts, the amount of isoprene used in step (1-2) was changed to 12 parts, and the amount of styrene used in step (1-3) was 10 parts. Changed to the department. The copolymer obtained in the step (1-3) was a copolymer having a triblock molecular structure with a weight ratio of styrene / isoprene / styrene = 78/12/10. Thereafter, the block copolymer contained in the obtained pellet had a weight average molecular weight (Mw) of 64,000, a molecular weight distribution (Mw / Mn) of 1.33, and a hydrogenation rate of almost 100%.
In step (1-5), the extrusion molding conditions were changed, and the thickness of the raw film was set to 100 μm.
In step (1-5), the draw ratio was changed to 2.5 times. The thickness of the obtained optical film was 40 μm.

[Comparative Example 1]
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
In step (1-5), the extrusion molding conditions were changed, and the thickness of the raw film was 40 μm.
In Step (1-5), the original film was directly obtained as an optical film without stretching.

[Comparative Example 2]
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
-The amount of styrene used in step (1-1) was changed to 60 parts, the amount of isoprene used in step (1-2) was changed to 30 parts, and the amount of styrene used in step (1-3) was 10 parts. Changed to the department. The copolymer obtained in the step (1-3) was a copolymer having a triblock molecular structure with a weight ratio of styrene / isoprene / styrene = 60/30/10. Thereafter, the block copolymer contained in the obtained pellet had a weight average molecular weight (Mw) of 65,000, a molecular weight distribution (Mw / Mn) of 1.44, and a hydrogenation rate of almost 100%.
In step (1-5), the extrusion conditions were changed, and the thickness of the raw film was set to 60 μm.
In step (1-5), the draw ratio was changed to 1.5 times. The thickness of the obtained optical film was 40 μm.

[Comparative Example 3]
The optical film and the polarizing plate were obtained and evaluated by the same operation as in Example 1 except for the following changes.
-The amount of styrene used in step (1-1) was changed to 80 parts, the amount of isoprene used in step (1-2) was changed to 10 parts, and the amount of styrene used in step (1-3) was changed to 10 parts. Changed to the department. The copolymer obtained in the step (1-3) was a copolymer having a triblock molecular structure with a weight ratio of styrene / isoprene / styrene = 80/10/10. Thereafter, the block copolymer contained in the obtained pellet had a weight average molecular weight (Mw) of 64000, a molecular weight distribution (Mw / Mn) of 1.44, and a hydrogenation rate of almost 100%.
In step (1-5), the extrusion conditions were changed, and the thickness of the raw film was set to 60 μm.
In step (1-5), the draw ratio was changed to 1.5 times. The thickness of the obtained optical film was 40 μm.

[Comparative Example 4]
A film made of a resin containing an alicyclic structure-containing polymer (trade name “Zeonor Film ZF14”, manufactured by Nippon Zeon Co., Ltd., glass transition temperature 136 ° C., thickness 40 μm) was directly evaluated as an optical film. Further, a polarizing plate was obtained and evaluated in the same manner as in (1-6) of Example 1, except that this film was used instead of the optical film obtained in (1-5).

[Comparative Example 5]
A triacetylcellulose film (“Zerotac (registered trademark)” manufactured by Konica Minolta, Inc., thickness 40 μm) was evaluated as an optical film as it was. Further, a polarizing plate was obtained and evaluated in the same manner as in (1-6) of Example 1, except that this film was used instead of the optical film obtained in (1-5).

Tables 1 and 2 show the results of Examples and Comparative Examples.

St / IP / St: The type of polymer constituting the optical film. In the case of a styrene-isoprene-styrene triblock copolymer, the block weight ratio. COP: cycloolefin polymer, TAC: triacetyl cellulose.

From the results of Tables 1 and 2, it can be seen that the optical film and the polarizing plate of the present invention are excellent in curling suppression and trimming properties and can constitute a liquid crystal display device having good viewing angle characteristics.

11: Cut optical film 12: End film 120: Trimming device 121: Upper blade 121C: Rotating shaft 122: Lower blade 122C: Rotating shaft

Claims (7)

An optical film made of a stretched resin, which satisfies the following formulas (1) to (4):
0 nm ≦ Re (590) ≦ 3 nm (1)
| Rth (590) | ≦ 3 nm (2)
| Re (400) −Re (800) | ≦ 1 nm (3)
| Rth (400) −Rth (800) | ≦ 1 nm (4)
(However,
Re (400) is an in-plane retardation at a wavelength of 400 nm of the optical film,
Re (590) is an in-plane retardation at a wavelength of 590 nm of the optical film,
Re (800) is the in-plane retardation at a wavelength of 800 nm of the optical film,
Rth (400) is the thickness direction retardation of the optical film at a wavelength of 400 nm,
Rth (590) is a retardation in the thickness direction at a wavelength of 590 nm of the optical film,
Rth (800) is a thickness direction retardation of the optical film at a wavelength of 800 nm. )
The tensile modulus is 1500 MPa or more,
An optical film having a tear strength of 0.6 N / mm or more. The optical film according to claim 1, wherein the resin comprises a polymer having an aromatic vinyl compound hydride unit (a) and a diene compound hydride unit (b). The polymer is
One block B per molecule having the diene compound hydride unit (b);
One block A1 per molecule connected to one end of the block B and having the aromatic vinyl compound hydride unit (a);
3. The optical film according to claim 2, wherein the optical film is a triblock copolymer which is connected to the other end of the block B and has one block A2 per molecule having the aromatic vinyl compound hydride unit (a). . In the triblock copolymer, the ratio (A1 + A2) / B of the total weight of the block A1 and the block A2 to the weight of the block B is 80/20 or more and 88/12 or less. The optical film described in 1. The aromatic vinyl compound hydride unit (a) is a structural unit having a structure obtained by polymerizing and hydrogenating styrene,
The optical film according to any one of claims 2 to 4, wherein the diene compound hydride unit (b) is a structural unit having a structure obtained by polymerizing isoprene and hydrogenating it. A polarizing plate comprising a polarizer and the optical film according to any one of claims 1 to 5. A method for producing an optical film according to any one of claims 1 to 5,
The glass transition temperature of the resin is Tg,
The manufacturing method including extending | stretching the film before extending | stretching which consists of said resin by the draw ratio of 1.1 times or more and 3.0 times or less in the temperature of (Tg + 10) degreeC or more and (Tg + 45) degreeC or less.

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