WO2018003154A1

WO2018003154A1 - Optical compensation film having wide viewing angle and high contrast

Info

Publication number: WO2018003154A1
Application number: PCT/JP2017/002021
Authority: WO
Inventors: 真典松本; 哲央野口; 藤掛　英夫; 石鍋　隆宏
Original assignee: デンカ株式会社; 国立大学法人東北大学
Priority date: 2016-06-30
Filing date: 2017-01-20
Publication date: 2018-01-04
Also published as: CN109416427B; KR20190025932A; JP6711914B2; KR102576933B1; CN109416427A; JPWO2018003154A1

Abstract

Provided is a liquid crystal display device having excellent viewing angle characteristics and a high contrast ratio even in an oblique direction. This optical compensation film is configured from a film A that satisfies formulas (1) through (3) laminated on a film B that satisfies formulas (4) and (5). The film B is a copolymer composed of an aromatic vinyl monomer unit, an unsaturated dicarboxylic acid anhydride monomer unit, and a (meth)acrylic acid ester monomer unit. An in-plane phase difference Re is a value defined by a formula (6) and a thickness-direction phase difference Rth is a value defined by a formula (7), the Re(450), Re(550), and Re(650) representing in-plane phase differences for wavelengths 450 nm, 550 nm and 650 nm, Rth(550) representing a thickness-direction phase difference for a wavelength 550 nm, nx representing a refractive index along the slow axis direction of the film, ny representing a refractive index along the fast axis direction of the film, nz representing a refractive index along the thickness direction of the film, and d representing the thickness of the film. Re(450) < Re(550) < Re(650) (1) 25 nm ≤ Re(550) ≤ 280 nm (2) 12 nm ≤ Rth(550) ≤ 95 nm (3) 0 nm ≤ Re(550) ≤ 140 nm (4) −140 nm ≤ Rth(550) ≤ 0 nm (5) Re = (nx − ny) × d (6) Rth = {(nx + ny) ÷ 2 − nz} × d (7)

Description

Wide viewing angle high contrast optical compensation film

The present invention relates to an optical compensation film for providing a liquid crystal display device having excellent viewing angle characteristics and a high contrast ratio even in an oblique direction.

Transparent resins are used in various applications such as home appliance parts, food containers, and miscellaneous goods. In recent years, the liquid crystal display device is frequently used for optical parts such as a thin liquid crystal display element and an electroluminescence element instead of the cathode ray tube type television monitor.

A stretched film obtained by uniaxially or biaxially stretching a resin film is widely used as an optical compensation film for liquid crystal displays. As a typical optical compensation film, there is a retardation film, and a λ / 2 plate for converting the vibration direction of polarized light and a λ / 4 plate for converting circularly polarized light into linearly polarized light or linearly polarized light into circularly polarized light are widely used. It has been.

The retardation film is required to optically compensate in a wide visual field range, and it is an extremely important characteristic that the retardation does not change even for incident light in an oblique direction. For such required characteristics, Patent Document 1 discloses a liquid crystal display device including a laminate of a transparent stretched film having negative orientation birefringence and a transparent stretched film having positive orientation birefringence. Has been.

In Patent Document 2, a stretched film exhibiting negative orientation birefringence and a stretched film exhibiting positive orientation birefringence are laminated so that the slow axes of the stretched films are parallel to each other. A method for widening the viewing angle of a liquid crystal display device by using an optical compensation film having a phase difference (Re) of 60 to 300 nm and an alignment parameter (Nz) within a range of 0.5 ± 0.1 is disclosed. . Furthermore, it is disclosed that the stretched film showing negative intrinsic birefringence is a resin composition of a copolymer composed of an α-olefin and an N-phenyl-substituted maleimide and an acrylonitrile-styrene copolymer.

Examples of thermoplastic resins exhibiting positive orientation birefringence include polycarbonate and amorphous cyclic polyolefin, which are excellent in heat resistance, transparency, film strength, and retardation development. It is used. On the other hand, as a thermoplastic resin exhibiting negative orientation birefringence, there are very few examples of practical use because heat resistance, transparency, film strength, and retardation development are inferior. A plurality of stretched films exhibiting positive orientation birefringence are bonded together at an appropriate angle. Therefore, the optical compensation design is complicated and expensive, and the optical compensation performance is insufficient.

In response to these requirements, Patent Document 3 and Patent Document 4 include a thermoplastic resin copolymer excellent in transparency, heat resistance, film moldability, film strength, and retardation development, and negative orientation birefringence. The retardation film described in Patent Document 3 and Patent Document 4 uses a cyclic polyolefin as a thermoplastic resin exhibiting positive orientation birefringence. Patent Document 5 proposes a so-called reverse wavelength dispersion film in which the in-plane retardation increases as the wavelength increases.

JP-A-2-256603 JP 2007-24940 A WO2014 / 021265 WO2015 / 033877 JP 2013-164501 A

However, the methods described in Cited Document 3 and Cited Document 4 are insufficient to have high contrast characteristics. Further, in Patent Document 5, it is expected that a high contrast characteristic is exhibited by a film with reverse wavelength dispersion, and a high contrast from the front is obtained, but the contrast characteristic from an oblique direction is insufficient.

An object of the present invention is to provide an optical compensation film for providing a liquid crystal display device having excellent viewing angle characteristics and having a high contrast ratio even in an oblique direction.

The present inventors have studied to obtain a high contrast ratio even in an oblique direction with excellent viewing angle characteristics, and as a result, the in-plane phase difference Re and thickness are obtained. Positive birefringent film A having directional retardation Rth within a specific range, and negative birefringent film having in-plane retardation Re and thickness direction retardation Rth corresponding to directional retardation Rth within a specific range It was found that by combining B, an optical compensation film for providing a liquid crystal display device having a high contrast ratio even in an oblique direction can be provided, and the present invention has been completed. The optical compensation film obtained by the method of the present invention can be used for a liquid crystal display device.

The gist of the present invention is as follows.
(1) A film A satisfying (Expression 1) to (Expression 3) and a film B satisfying (Expression 4) and (Expression 5) are laminated, and the film B is an aromatic vinyl monomer unit, It is a copolymer comprising an unsaturated dicarboxylic acid anhydride monomer unit and a (meth) acrylic acid ester monomer unit, and Re (450), Re (550) and Re (650) have a wavelength of 450 nm. In-plane retardation at 550 nm and 650 nm, Rth (550) indicates a thickness direction retardation at a wavelength of 550 nm, a refractive index in the slow axis direction of the film is nx, a refractive index in the fast axis direction of the film is ny, and the film When the refractive index in the thickness direction is nz and the film thickness is d, the in-plane retardation Re is a value defined by (Expression 6), and the thickness direction retardation Rth is a value defined by (Expression 7). Compensation film.
(Formula 1) Re (450) <Re (550) <Re (650)
(Formula 2) 25 nm ≦ Re (550) ≦ 280 nm
(Formula 3) 12 nm ≦ Rth (550) ≦ 95 nm
(Formula 4) 0 nm ≦ Re (550) ≦ 140 nm
(Formula 5) −140 nm ≦ Rth (550) ≦ 0 nm
(Expression 6) Re = (nx−ny) × d
(Expression 7) Rth = {(nx + ny) ÷ 2-nz} × d
(2) The optical compensation film according to (1), wherein the Nz coefficient of the film A satisfies (Equation 8), and the Nz coefficient is a value defined by (Equation 9).
(Formula 8) 0.6 ≦ Nz ≦ 1.2
(Formula 9) Nz = (nx−nz) / (nx−ny)
(3) The optical compensation film according to any one of (1) and (2), wherein the film B is a positive C plate, and the positive C plate is a film satisfying (Equation 10).
(Formula 10) nx = ny <nz
(4) The optical compensation film according to any one of (1) and (2), wherein the film B is a negative A plate, and the negative A plate is a film satisfying (Equation 11).
(Formula 11) ny <nz = nx
(5) The film A satisfies (Expression 12), (Expression 13), and (Expression 14), and the film B satisfies (Expression 15) and (Expression 16). Optical compensation film.
(Formula 12) 0.8 ≦ Nz ≦ 1.2
(Formula 13) 120 nm ≦ Re (550) ≦ 170 nm
(Formula 14) 55 nm ≦ Rth (550) ≦ 90 nm
(Formula 15) Re (550) = 0
(Expression 16) −120 nm ≦ Rth (550) ≦ −70 nm
(6) The film A satisfies (Expression 17), (Expression 18), and (Expression 19), and the film B satisfies (Expression 20) and (Expression 21). Optical compensation film.
(Formula 17) 0.6 ≦ Nz ≦ 0.8
(Formula 18) 170 nm ≦ Re (550) ≦ 230 nm
(Formula 19) 15 nm ≦ Rth (550) ≦ 55 nm
(Equation 20) Re (550) = 0
(Formula 21) −70 nm ≦ Rth (550) ≦ −20 nm
(7) The optical compensation film according to (4), wherein the film A satisfies (Formula 22) and (Formula 23), and the film B satisfies (Formula 24) and (Formula 25).
(Formula 22) 70 nm ≦ Re (550) ≦ 120 nm
(Formula 23) 30 nm ≦ Rth (550) ≦ 60 nm
(Formula 24) 70 nm ≦ Re (550) ≦ 120 nm
(Formula 25) −60 nm ≦ Rth (550) ≦ −30 nm
(8) A liquid crystal display device using the optical compensation film according to any one of (1) to (7).

According to the present invention, an optical compensation film for providing a liquid crystal display device having excellent viewing angle characteristics and a high contrast ratio even in an oblique direction can be provided by a simple method.

It is the schematic which shows the structure combined when the film B is made into the positive C plate. It is the schematic which shows the structure combined when the film B is made into the negative A plate.

<Explanation of terms>
In the present specification, the description “A to B” means not less than A and not more than B. In addition, the “Nz coefficient” may be represented by “Nz” in the formula.

Hereinafter, embodiments of the present invention will be described in detail.

In the present invention, by combining the film A and the film B having specific optical characteristics, an optical compensation film having a high contrast ratio even in an oblique viewing angle is possible. That is, a positive birefringent film A having a reverse wavelength dispersion characteristic in which the in-plane retardation becomes smaller as the wavelength is shorter, and has an in-plane retardation Re and a thickness direction retardation Rth within a specific range, By combining the negative birefringent film B having the corresponding in-plane retardation Re and thickness direction retardation Rth within a specific range, a high contrast ratio can be realized even in an oblique viewing angle.

The film A used for the optical compensation film of the present invention is characterized by satisfying the following (formula 1) to (formula 3).
(Formula 1) Re (450) <Re (550) <Re (650)
(Formula 2) 25 nm ≦ Re (550) ≦ 280 nm
(Formula 3) 12 nm ≦ Rth (550) ≦ 95 nm
Here, Re (450), Re (550), and Re (650) indicate in-plane retardation at wavelengths of 450 nm, 550 nm, and 650 nm, and Rth (550) indicates a thickness direction retardation at a wavelength of 550 nm.
Note that the slow axis of the film, that is, the refractive index in the axial direction where the refractive index in the film plane is maximum is nx, the fast axis of the film, that is, the refractive index in the axial direction perpendicular to the slow axis, ny, When the refractive index in the thickness direction is nz and the film thickness is d, the in-plane retardation Re is a value defined by (Expression 6), and the thickness direction retardation Rth is a value defined by (Expression 7).
(Expression 6) Re = (nx−ny) × d
(Expression 7) Rth = {(nx + ny) ÷ 2-nz} × d

Film A has the characteristics of Re (450) <Re (550) <Re (650), 25 nm ≦ Re (550) ≦ 280 nm, and 12 nm ≦ Rth (550) ≦ 95 nm. An optical compensation film having a high contrast ratio at a viewing angle can be produced.

The Nz coefficient of the film A preferably satisfies the following (Equation 8) in producing an optical compensation film having a high contrast ratio at an oblique viewing angle.
(Formula 8) 0.6 ≦ Nz ≦ 1.2
The Nz coefficient is a value defined by (Equation 9).
(Formula 9) Nz = (nx−nz) / (nx−ny)

The thermoplastic resin that can be used for the film A is not particularly limited as long as it satisfies (Formula 1) to (Formula 3). For example, the thermoplastic resin described in JP2012-150477A, There are polycarbonate resins such as a copolymer of 9-bis [4- (2-hydroxyethoxy) phenyl] fluorene and isosorbide. The resin that can be used for the film A may be used alone or in combination of two or more.

The production method of the film A is not particularly limited. For example, after forming an unstretched film by a melt extrusion method, a solution casting method, or the like, the unstretched film is uniaxially formed by a roll stretching method, a tenter stretching method, or the like. Or it can produce by extending | stretching biaxially.

The film B used for the optical compensation film of the present invention satisfies the following (formula 4) to (formula 5).
(Formula 4) 0 nm ≦ Re (550) ≦ 140 nm
(Formula 5) −140 nm ≦ Rth (550) ≦ 0 nm

If the film B satisfies 0 nm ≦ Re (550) ≦ 140 nm and −140 nm ≦ Rth (550) ≦ 0 nm, an optical compensation film having a high contrast ratio at an oblique viewing angle can be produced.

The thermoplastic resin that can be used for the film B is a copolymer comprising an aromatic vinyl monomer unit, an unsaturated dicarboxylic anhydride monomer unit, and a (meth) acrylic acid ester monomer unit.

Aromatic vinyl monomer units include styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, 2,4-dimethyl styrene, ethyl styrene, p-tert-butyl styrene, α-methyl styrene, α Examples thereof include units derived from styrene monomers such as -methyl-p-methylstyrene. Of these, styrene units are preferred. These aromatic vinyl monomer units may be one type or a combination of two or more types.

Examples of the unsaturated dicarboxylic acid anhydride monomer unit include units derived from respective anhydride monomers such as maleic acid anhydride, itaconic acid anhydride, citraconic acid anhydride, and aconitic acid anhydride. Among these, maleic anhydride units are preferable. The unsaturated dicarboxylic acid anhydride monomer unit may be one type or a combination of two or more types.

Examples of the (meth) acrylic acid ester monomer unit include methyl methacrylate monomers such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, dicyclopentanyl methacrylate, and isobornyl methacrylate, and Examples include units derived from acrylate monomers such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate. Among these, a methyl methacrylate unit is preferable. These (meth) acrylic acid ester monomer units may be one kind or a combination of two or more kinds.

The copolymer used for the film B is a vinyl monomer unit other than an aromatic vinyl monomer unit, a (meth) acrylic acid ester monomer unit, and an unsaturated dicarboxylic anhydride monomer unit. It may be included within a range not inhibiting the effect, and is preferably 5% by mass or less. Other vinyl monomer units include vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, vinyl carboxylic acid monomers such as acrylic acid and methacrylic acid, N-methylmaleimide, N-ethylmaleimide, N- Derived from various monomers such as N-alkylmaleimide monomers such as butylmaleimide and N-cyclohexylmaleimide, N-arylmaleimide monomers such as N-phenylmaleimide, N-methylphenylmaleimide and N-chlorophenylmaleimide The unit to do is mentioned. Other vinyl monomer units may contain two or more kinds.

The preferred content of the aromatic vinyl monomer unit is 50 to 90% by mass, and more preferably 60 to 85% by mass. If the aromatic vinyl monomer unit is 50% by mass or more, the retardation can be improved, so that the thickness of the film can be reduced, and when performing film forming by melt extrusion, an optical compensation film is used. A suitable and beautiful film can be obtained, and if it is 60% by mass or more, the retardation can be further improved to reduce the thickness of the film, and when performing film forming processing by melt extrusion It is particularly preferable because a more beautiful film suitable for an optical compensation film can be obtained. If the aromatic vinyl monomer unit is 90% by mass or less, heat resistance or film strength is improved, and if the aromatic vinyl monomer unit is 85% by mass or less, heat resistance or film strength is further increased. Since it improves, it is especially preferable.

The content of unsaturated dicarboxylic acid anhydride monomer units is preferably 5 to 25% by mass, more preferably 8 to 20% by mass. If the unsaturated dicarboxylic acid anhydride monomer unit is 5% by mass or more, the heat resistance is improved, and if it is 8% by mass or more, the heat resistance is further improved, which is particularly preferable. If the unsaturated dicarboxylic acid anhydride monomer unit is 25% by mass or less, the film strength is improved, and a beautiful film suitable for an optical compensation film can be obtained when film forming by melt extrusion is performed. The amount of 20% by mass or less is particularly preferable because the film strength is further improved and a more beautiful film suitable for an optical compensation film can be obtained when film forming by melt extrusion is performed.

The preferred content of the (meth) acrylic acid ester monomer unit is 5 to 45% by mass, more preferably 7 to 32% by mass. If the (meth) acrylic acid ester monomer unit is 5% by mass or more, transparency and film strength are improved, and if it is 7% by mass or more, transparency and film strength are further improved, which is particularly preferable. . If the (meth) acrylic acid ester monomer unit is 45% by mass or less, the retardation development property is improved, so that the thickness of the film can be reduced and the film forming process by melt extrusion is optical. A beautiful film suitable for a compensation film can be obtained, and is preferably 32% by mass or less. Since the retardation development is further improved, the thickness of the film can be further reduced, and the film is formed by melt extrusion. In particular, a more beautiful film suitable for an optical compensation film can be obtained, which is particularly preferable.

The copolymer used for the film B preferably has a weight average molecular weight (Mw) of 1 to 250,000. A weight average molecular weight (Mw) of 120,000 or more is preferable because the film strength is improved. A weight average molecular weight (Mw) of 250,000 or less is preferable because a beautiful film suitable for an optical compensation film can be obtained when film forming by melt extrusion is performed. The weight average molecular weight (Mw) is a value in terms of polystyrene measured by gel permeation chromatography (GPC), and is a value measured under the measurement conditions described below.
Device name: SYSTEM-21 Shodex (manufactured by Showa Denko)
Column: 3 series PL gel MIXED-B Temperature: 40 ° C
Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2% by mass
Calibration curve: Prepared using standard polystyrene (PS) (manufactured by PL).

The production method of the film B is not particularly limited. For example, after forming an unstretched film by a melt extrusion method, a solution cast method, or the like, the unstretched film is uniaxially formed by a roll stretching method, a tenter stretching method, or the like. Or it can produce by extending | stretching biaxially.

The manufacturing method of the copolymer used for the film B is demonstrated.
The polymerization mode is not particularly limited and can be produced by a known method such as solution polymerization or bulk polymerization, but solution polymerization is more preferable. The solvent used in the solution polymerization is preferably non-polymerizable from the viewpoint that a by-product is difficult to produce and that there are few adverse effects. The type of the solvent is not particularly limited. For example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, ethers such as tetrahydrofuran, 1,4-dioxane, toluene, ethylbenzene, xylene, chlorobenzene Aromatic hydrocarbons, etc. are mentioned, but methyl ethyl ketone and methyl isobutyl ketone are preferred from the viewpoint of the solubility of the monomer and copolymer and the ease of solvent recovery. The amount of the solvent added is preferably 10 to 100 parts by mass, and more preferably 30 to 80 parts by mass with respect to 100 parts by mass of the copolymer to be obtained. If it is 10 parts by mass or more, it is suitable for controlling the reaction rate and the polymerization solution viscosity, and if it is 100 parts by mass or less, it is suitable for obtaining a preferable weight average molecular weight (Mw).

The polymerization process may be any of a batch polymerization method, a semi-batch polymerization method, and a continuous polymerization method, but the batch polymerization method is suitable for obtaining a desired molecular weight range and transparency.

The polymerization method is not particularly limited, but is preferably a radical polymerization method from the viewpoint that it can be produced with high productivity by a simple process. The polymerization initiator is not particularly limited. For example, dibenzoyl peroxide, t-butylperoxybenzoate, 1,1-bis (t-butylperoxy) -2-methylcyclohexane, t-butylperoxy Known organic compounds such as isopropyl monocarbonate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyacetate, dicumyl peroxide, ethyl-3,3-di- (t-butylperoxy) butyrate Known azo compounds such as peroxides, azobisisobutyronitrile, azobiscyclohexanecarbonitrile, azobismethylpropionitrile, azobismethylbutyronitrile, and the like can be used. Two or more of these polymerization initiators can be used in combination. Of these, organic peroxides having a 10-hour half-life temperature of 70 to 110 ° C. are preferably used.

Since the aromatic vinyl monomer and unsaturated dicarboxylic acid anhydride monomer have strong alternating copolymerization, it corresponds to the polymerization rate of the aromatic vinyl monomer and the (meth) acrylate monomer. Thus, a method in which the unsaturated dicarboxylic acid anhydride monomer is continuously added and the addition flow rate is appropriately adjusted in accordance with the polymerization rate is suitable. It is preferable to control the polymerization rate while appropriately adjusting the polymerization temperature, the polymerization time, and the addition amount of the polymerization initiator because the composition distribution of the copolymer can be reduced more precisely.

Furthermore, regarding a method for obtaining a copolymer having a preferred weight average molecular weight (Mw) range, in addition to adjustment of polymerization temperature, polymerization time, and polymerization initiator addition amount, solvent addition amount and chain transfer agent addition amount Can be adjusted. The chain transfer agent is not particularly limited. For example, a known chain transfer agent such as n-dodecyl mercaptan, t-dodecyl mercaptan or 2,4-diphenyl-4-methyl-1-pentene is used. Can do.

After the polymerization is completed, the polymerization solution is optionally provided with a heat resistant stabilizer such as a hindered phenol compound, a lactone compound, a phosphorus compound, a sulfur compound, a light resistant stabilizer such as a hindered amine compound, a benzotriazole compound, Additives such as lubricants, plasticizers, colorants, antistatic agents and mineral oils may be added. The addition amount is preferably less than 0.2 parts by mass with respect to 100 parts by mass of all monomer units. These additives may be used alone or in combination of two or more.

There is no limitation in particular about the method of collect | recovering a copolymer from a polymerization liquid, A well-known devolatilization technique can be used. For example, a method of continuously feeding the polymerization liquid to a twin-screw devolatilizing extruder using a gear pump and devolatilizing a polymerization solvent, an unreacted monomer and the like can be mentioned. The devolatilizing component including the polymerization solvent, unreacted monomer, etc. is condensed and recovered using a condenser, etc., and the polymerization solvent can be reused by purifying the condensate in a distillation tower. .

Since the film B used for the optical compensation film of the present invention is laminated with the film A to perform optical compensation, it is preferably a positive C plate or a negative A plate in designing optical compensation. The positive C plate is a film satisfying the following (formula 10), and the negative A plate is a film satisfying the following (formula 11).
(Formula 10) nx = ny <nz
(Formula 11) ny <nz = nx

There is no limitation in particular about the extending | stretching method of an unstretched film, It can select according to desired optical compensation, and it extends | stretches uniaxially or biaxially. When producing a positive C plate, for example, it is biaxially stretched, preferably simultaneously biaxially stretched. The draw ratio is adjusted according to the target retardation value, and is 1.05 to 5 times, more preferably 1.1 to 4 times, and still more preferably 1.5 to 3 times in the vertical and horizontal directions, respectively. This stretching may be performed in a single stage or in multiple stages. When producing a negative A plate, for example, it is uniaxially stretched, preferably free end uniaxially stretched. The draw ratio is adjusted according to the target retardation value, and is 1.05 to 5 times, more preferably 1.1 to 4 times, and still more preferably 1.5 to 3 times in the vertical and horizontal directions, respectively. This stretching may be performed in a single stage or in multiple stages.

In the case where the film B is a positive C plate, between the polarizing plates arranged with the absorption axes orthogonal to each other, the film A is arranged adjacent to each other with the slow axis orthogonal to the absorption axis of one polarizing plate. When the films B are laminated adjacent to each other, an optical compensation film having a high contrast ratio with an oblique viewing angle can be produced. The contrast ratio at an incident angle of 60 ° is preferably 100: 1 or more, more preferably 300: 1 or more, still more preferably 900: 1 or more, and particularly preferably 1000: 1 or more. The contrast ratio represents the difference in brightness of the liquid crystal display device, and the higher the contrast ratio, the clearer the image quality.

FIG. 1 shows the combined structure when film B is a positive C plate.

When the film B is a positive C plate, a high contrast ratio can be obtained by adjusting the balance between the in-plane retardation of the film A and the film B and the retardation in the thickness direction according to the Nz coefficient of the film A. it can.

When film B is a positive C plate and film A is in the range of (Equation 12) below, film A satisfies (Equation 13) and (Equation 14), and film B is (Equation 15), and It is preferable to satisfy (Expression 16) in order to obtain a high contrast ratio.
(Formula 12) 0.8 ≦ Nz ≦ 1.2
(Formula 13) 120 nm ≦ Re (550) ≦ 170 nm
(Formula 14) 55 nm ≦ Rth (550) ≦ 90 nm
(Formula 15) Re (550) = 0
(Expression 16) −120 nm ≦ Rth (550) ≦ −70 nm

Furthermore, it is more preferable that the film B satisfies the following (formula 16 ′) in order to obtain a high contrast ratio.
(Formula 16 ′) −110 nm ≦ Rth (550) ≦ −90 nm

When film B is a positive C plate and film A is in the range of (Equation 17) below, film A satisfies (Equation 18) and (Equation 19), and film B is (Equation 20), And satisfying (Equation 21) is preferable for obtaining a high contrast ratio.
(Formula 17) 0.6 ≦ Nz ≦ 0.8
(Formula 18) 170 nm ≦ Re (550) ≦ 230 nm
(Formula 19) 15 nm ≦ Rth (550) ≦ 55 nm
(Equation 20) Re (550) = 0
(Formula 21) −70 nm ≦ Rth (550) ≦ −20 nm

When the film B is a positive C plate, the Nz coefficient of the film A is preferably 0.6 ≦ Nz ≦ 1.2 as described above, but 0.6 ≦ Nz ≦ 0.8. More preferred. When the Nz coefficient of the film A is 0.6 ≦ Nz ≦ 0.8, a higher contrast ratio can be obtained because the Nz coefficient is small.

In the case where the film B is a negative A plate, between the polarizing plates arranged with the absorption axes orthogonal to each other, the film B is arranged adjacent to each other with the slow axis orthogonal to the absorption axis of one polarizing plate. An optical compensation film having a high contrast ratio at an oblique viewing angle when the film A is laminated with the slow axes orthogonal to each other can be produced. The contrast ratio at an incident angle of 60 ° is preferably 100: 1 or more, more preferably 300: 1 or more.

Even when the film B is a negative A plate, a high contrast ratio is obtained by adjusting the balance between the in-plane retardation of the film A and the film B and the retardation in the thickness direction according to the Nz coefficient of the film A. Can do.

FIG. 2 shows the combined structure when the film B is a negative A plate.

When film B is a negative A plate, film A satisfies the following (formula 22) and (formula 23), and film B satisfies (formula 24) and (formula 25) to obtain a high contrast ratio. More preferred.
(Formula 22) 70 nm ≦ Re (550) ≦ 120 nm
(Formula 23) 30 nm ≦ Rth (550) ≦ 60 nm
(Formula 24) 70 nm ≦ Re (550) ≦ 120 nm
(Formula 25) −60 nm ≦ Rth (550) ≦ −30 nm

When the film B is a negative A plate, the contrast ratio is improved particularly when the difference in absolute value of the retardation in the thickness direction between the film A and the film B is small. Regarding the absolute value | RthA | of the retardation in the thickness direction of the film A and the absolute value | RthB | of the retardation in the thickness direction of the film B, it is more preferable to satisfy the following (formula 26).
(Formula 26) −10 nm ≦ | ARth | − | RthB | ≦ 10 nm

By using the positive C plate and the negative A plate as described above as the film B, it is possible to provide an optical compensation film having a high contrast ratio. Furthermore, since a particularly high contrast ratio can be obtained by combining the positive C plate with the film A, it is more preferable to use the positive C plate.

The film of the present invention has a high contrast ratio at a viewing angle in an oblique direction, and can be suitably used as an optical compensation film for a liquid crystal display device.

Examples are given below to illustrate the present invention in more detail. However, the present invention is not limited to these examples.

Production of copolymer used for film B <Production example of copolymer (B-1)>
20% maleic anhydride solution dissolved in methyl isobutyl ketone so that maleic anhydride has a concentration of 20% by mass and methyl so that t-butylperoxy-2-ethylhexanoate becomes 2% by mass. A 2% t-butyl peroxy-2-ethylhexanoate solution diluted in isobutyl ketone was prepared in advance and used for the polymerization.
A 120 liter autoclave equipped with a stirrer was charged with 2 kg of a 20% maleic anhydride solution, 24 kg of styrene, 12 kg of methyl methacrylate, 30 g of t-dodecyl mercaptan, and 2 kg of methyl isobutyl ketone, and the gas phase part was filled with nitrogen gas. After the replacement, the temperature was raised to 87 ° C. over 40 minutes with stirring. While maintaining 87 ° C. after the temperature rise, a 20% maleic anhydride solution was added at a rate of 1.5 kg / hour, and a 2% t-butylperoxy-2-ethylhexanoate solution was added at a rate of 375 g / hour, respectively. The addition continued continuously over 8 hours. Thereafter, the addition of the 2% t-butylperoxy-2-ethylhexanoate solution was stopped, and 30 g of t-butylperoxyisopropyl monocarbonate was added. The 20% maleic anhydride solution was heated to 120 ° C. over 4 hours at a temperature rising rate of 8.25 ° C./hour, while maintaining the addition rate of 1.5 kg / hour. The addition of the 20% maleic anhydride solution was stopped when the amount of addition reached 18 kg. After the temperature increase, the polymerization was terminated by maintaining 120 ° C. for 1 hour. The polymerization solution is continuously fed to a twin-screw devolatilizing extruder using a gear pump, and methyl isobutyl ketone and a small amount of unreacted monomer are devolatilized, and extruded into a strand to cut it. A polymer (B-1) was obtained. The obtained copolymer (B-1) was subjected to composition analysis by the C-13 NMR method, and the weight average molecular weight (Mw) was measured by a GPC apparatus. Further, using an injection molding machine (IS-50EPN manufactured by Toshiba Machine Co., Ltd.), a mirror surface plate having a length of 90 mm, a width of 55 mm, and a thickness of 2 mm was injection molded under molding conditions of a cylinder temperature of 230 ° C. and a mold temperature of 40 ° C. to ASTM D1003. In accordance with this standard, a haze of 2 mm thickness was measured using a haze meter (NDH-1001DP type manufactured by Nippon Denshoku Industries Co., Ltd.). As a result of the compositional analysis, they were 59.8% by mass of styrene monomer units, 29.8% by mass of methyl methacrylate monomer units, and 10.4% by mass of maleic anhydride monomer units. The polymerization average molecular weight (Mw) was 18,000 g / mol, and the haze was 0.4%.

[Example 1]
Using a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide to a 40mmφ single screw extruder, gear pump, polymer filter “Dena filter, mesh opening 5μm” (manufactured by Nagase Sangyo Co., Ltd.) A non-stretched film having a thickness of 70 μm was formed using a film-forming machine equipped with a 300 mm-wide single-layer T-die and a take-up winder “touch roll flexible type” (manufactured by Plastics Engineering Laboratory). The obtained unstretched film was cut into a 100 mm square, and the length was increased by 2.0 times in the longitudinal direction using a biaxial stretching apparatus (X61-S manufactured by Toyo Seiki Co., Ltd.) at a temperature of 155 ° C. and a stretching speed of 2 mm / s. A free end uniaxially stretched film (a-1) was obtained. As a result of measuring the birefringence of the film (a-1) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 128 nm, Re (550) = 146 nm, Re (650) = 150 nm, Rth (550) = 73 nm The film thickness was 50 μm, and the Nz coefficient was 1.00.
An unstretched film having a thickness of 170 μm was formed using the copolymer (B-1) in the same manner as the film (a-1) by a film casting machine. The obtained unstretched film was cut into a square of 100 mm each, and it was 2.0 times in the longitudinal direction at a temperature of 129 ° C. and a stretching speed of 2 mm / s using a biaxial stretching apparatus (X61-S manufactured by Toyo Seiki Co., Ltd.) A film (b-1) which was simultaneously biaxially stretched 2.0 times in the transverse direction was obtained. The film (b-1) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 93 nm, and film thickness was 42 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
The film (a-1) and the film (b-1) are arranged between polarizing plates arranged in the configuration shown in FIG. 1 with the polarization axes orthogonal to each other, and an incident angle of 60 degrees using a contrast measuring machine (Conoscope manufactured by Autronic Melchers). As a result of measuring the contrast ratio, the contrast ratio was 945: 1. The results are shown in Table 1.

[Example 2]
Stretching was carried out in the same manner as the film (b-1) except that the thickness of the unstretched film was 144 μm using the copolymer (B-1) to obtain a film (b-2). The birefringence of the film (b-2) was measured with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 79 nm, and the film thickness was 36 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
The result of measuring the contrast ratio at an incident angle of 60 degrees with a contrast measuring machine by arranging the film (a-1) and the film (b-2) between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. The contrast ratio was 507: 1. The results are shown in Table 1.

[Example 3]
Stretching was carried out in the same manner as the film (b-1) except that the thickness of the unstretched film was changed to 212 μm using the copolymer (B-1) to obtain a film (b-3). The birefringence of the film (b-3) was measured with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 116 nm, and the film thickness was 53 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-1) and film (b-3) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 335: 1. The results are shown in Table 1.

[Example 4]
Stretching was carried out in the same manner as the film (b-1) except that the thickness of the unstretched film was changed to 108 μm using the copolymer (B-1) to obtain a film (b-4). The film (b-4) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 60 nm, and film thickness was 27 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-1) and film (b-4) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 179: 1. The results are shown in Table 1.

[Example 5]
Stretching was carried out in the same manner as the film (b-1) except that the unstretched film thickness was changed to 252 μm using the copolymer (B-1) to obtain a film (b-5). The film (b-5) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) =-139 nm, and film thickness 63 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-1) and film (b-5) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 108: 1. The results are shown in Table 1.

[Example 6]
The film was stretched in the same manner as the film (a-1) except that a 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide copolymer was used to make the unstretched film thickness 77 μm. A film (a-2) was obtained. As a result of measuring the birefringence of the film (a-2) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 141 nm, Re (550) = 160 nm, Re (650) = 165 nm, Rth (550) = 80 nm The film thickness was 55 μm and the Nz coefficient was 1.00.
Film (a-2) and film (b-1) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 539: 1. The results are shown in Table 1.

[Example 7]
Stretching was carried out in the same manner as the film (a-1) except that the unstretched film thickness was changed to 60 μm using a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. A film (a-3) was obtained. As a result of measuring the birefringence of the film (a-3) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 109 nm, Re (550) = 124 nm, Re (650) = 128 nm, Rth (550) = 62 nm The film thickness was 43 μm and the Nz coefficient was 1.00.
Film (a-3) and film (b-1) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration shown in FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 320: 1. The results are shown in Table 1.

[Example 8]
Stretching was carried out in the same manner as the film (a-1) except that the unstretched film thickness was 84 μm using a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. A film (a-4) was obtained. As a result of measuring the birefringence of the film (a-4) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 153 nm, Re (550) = 174 nm, Re (650) = 179 nm, Rth (550) = 87 nm The film thickness was 60 μm and the Nz coefficient was 1.00.
Film (a-4) and film (b-1) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 222: 1. The results are shown in Table 1.

[Example 9]
Stretching was carried out in the same manner as the film (a-1) except that the unstretched film thickness was 91 μm using a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. A film (a-5) was obtained. As a result of measuring the birefringence of the film (a-5) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 165 nm, Re (550) = 188 nm, Re (650) = 194 nm, Rth (550) = 94 nm The film thickness was 65 μm and the Nz coefficient was 1.00.
Film (a-5) and film (b-1) are arranged between polarizing plates arranged in the configuration of FIG. 1 with the polarization axes orthogonal to each other, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 112: 1. The results are shown in Table 1.

[Example 10]
A copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide is dissolved in methylene chloride and applied directly onto a shrinkable film (PP uniaxially stretched film) using a wire bar. A coating film was formed. Further, it was dried at 60 ° C. for 5 minutes to produce a laminate of the shrinkable film and a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. Next, using a biaxial stretching apparatus (X61-S manufactured by Toyo Seiki Co., Ltd.), the laminate is shrunk 0.8 times at 150 ° C., and at the same time, the stretching speed is 2 mm / s in the direction perpendicular to the shrinkage direction of the laminate. The film was stretched 2.0 times under the following conditions. Subsequently, the shrinkable film was peeled off to obtain a film (a-6). As a result of measuring the birefringence of the film (a-6) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 153 nm, Re (550) = 174 nm, Re (650) = 179 nm, Rth (550) = 43 nm The film thickness was 60 μm, and the Nz coefficient was 0.75.
Stretching was carried out in the same manner as the film (b-1) except that the unstretched film thickness was changed to 120 μm using the copolymer (B-1) to obtain a film (b-6). The film (b-6) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 65 nm, and the film thickness was 30 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-6) and film (b-6) are arranged between polarizing plates arranged in the configuration of FIG. 1 with the polarization axes orthogonal to each other, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 1020: 1. The results are shown in Table 1.

[Example 11]
A copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide is dissolved in methylene chloride and applied directly onto a shrinkable film (PP uniaxially stretched film) using a wire bar. A coating film was formed. Further, it was dried at 60 ° C. for 5 minutes to produce a laminate of the shrinkable film and a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. Next, using a biaxial stretching apparatus (X61-S manufactured by Toyo Seiki Co., Ltd.), the laminate is shrunk 0.7 times at 150 ° C., and at the same time, the stretching speed is 2 mm / s in the direction perpendicular to the shrinkage direction of the laminate. The film was stretched 2.0 times under the following conditions. Subsequently, the shrinkable film was peeled off to obtain a film (a-7). As a result of measuring the birefringence of the film (a-7) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 183 nm, Re (550) = 208 nm, Re (650) = 214 nm, Rth (550) = 21 nm The film thickness was 72 μm, and the Nz coefficient was 0.60.
Stretching was carried out in the same manner as the film (b-1) except that the unstretched film thickness was changed to 76 μm using the copolymer (B-1) to obtain a film (b-7). The film (b-7) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 42 nm, and film thickness was 19 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-7) and film (b-7) are arranged between polarizing plates arranged in the configuration of FIG. 1 with the polarization axes orthogonal to each other, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 1135: 1. The results are shown in Table 1.

[Example 12]
Stretching was carried out in the same manner as the film (b-1) except that the thickness of the unstretched film was changed to 20 μm using the copolymer (B-1) to obtain a film (b-8). The birefringence of the film (b-8) was measured with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) =-11 nm, and the film thickness was 5 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-7) and film (b-8) are arranged between polarizing plates arranged in the configuration of FIG. 1 with the polarization axes orthogonal to each other, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 202: 1. The results are shown in Table 1.

[Example 13]
A copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide is dissolved in methylene chloride and applied directly onto a shrinkable film (PP uniaxially stretched film) using a wire bar. A coating film was formed. Further, it was dried at 60 ° C. for 5 minutes to produce a laminate of the shrinkable film and a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. Next, using a biaxial stretching apparatus (X61-S manufactured by Toyo Seiki Co., Ltd.), the laminate is shrunk 0.7 times at 150 ° C., and at the same time, the stretching speed is 2 mm / s in the direction perpendicular to the shrinkage direction of the laminate. The film was stretched 2.0 times under the following conditions. Subsequently, the shrinkable film was peeled off to obtain a film (a-8). As a result of measuring the birefringence of the film (a-8) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 245 nm, Re (550) = 278 nm, Re (650) = 286 nm, Rth (550) = 28 nm The film thickness was 97 μm, and the Nz coefficient was 0.60.
Film (a-8) and film (b-7) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration shown in FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 110: 1. The results are shown in Table 1.

[Example 14]
Stretching was carried out in the same manner as the film (a-1) except that the unstretched film thickness was 47 μm using a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. A film (a-9) was obtained. As a result of measuring the birefringence of the film (a-9) with a birefringence measuring device KOBRA-WR, Re (450) = 84 nm, Re (550) = 96 nm, Re (650) = 99 nm, Rth (550) = 48 nm The film thickness was 33 μm and the Nz coefficient was 1.00.
Using the copolymer (B-1), the film was stretched in the same manner as the film (a-1) except that the unstretched film thickness was 33 μm and the temperature was 130 ° C. to obtain a film (b-9). The birefringence of the film (b-9) was measured with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 96 nm, Rth (550) = − 48 nm, and the film thickness was 23 μm. Further, the refractive index was ny <nz = nx and was a negative A plate.
The result of measuring the contrast ratio at an incident angle of 60 degrees with a contrast measuring device by arranging the film (a-9) and the film (b-9) between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. The contrast ratio was 869: 1. The results are shown in Table 1.

[Example 15]
Using the copolymer (B-1), the film was stretched in the same manner as the film (a-1) except that the unstretched film thickness was 47 μm and the temperature was 130 ° C. to obtain a film (b-10). The film (b-10) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 136 nm, Rth (550) = − 68 nm, and the film thickness was 32 μm. Further, the refractive index was ny <nz = nx and was a negative A plate.
The result of measuring the contrast ratio at an incident angle of 60 degrees with a contrast measuring machine by placing the film (a-9) and the film (b-10) between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. The contrast ratio was 124: 1. The results are shown in Table 1.

[Example 16]
Stretching was carried out in the same manner as the film (a-1) except that the unstretched film thickness was 25 μm using a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. A film (a-10) was obtained. As a result of measuring the birefringence of the film (a-10) with the birefringence measuring apparatus KOBRA-WR, Re (450) = 46 nm, Re (550) = 52 nm, Re (650) = 54 nm, Rth (550) = 26 nm The film thickness was 18 μm and the Nz coefficient was 1.00.
The result of measuring the contrast ratio at an incident angle of 60 degrees with a contrast measuring machine by arranging the film (a-10) and the film (b-9) between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. The contrast ratio was 102: 1. The results are shown in Table 1.

[Comparative Example 1]
Stretching was performed in the same manner as the film (b-1) except that the unstretched film thickness was changed to 312 μm using the copolymer (B-1) to obtain a film (b-11). The film (b-11) was measured for birefringence with a birefringence measurement apparatus KOBRA-WR. As a result, Re (550) = 0 nm, Rth (550) = − 160 nm, and the film thickness was 78 μm. The refractive index was a positive C plate with a relationship of nx = ny <nz.
Film (a-1) and film (b-11) are arranged between polarizing plates arranged in the configuration of FIG. 1 with the polarization axes orthogonal to each other, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 100: 1 or less. The results are shown in Table 1.

[Comparative Example 2]
Stretching was carried out in the same manner as the film (a-1), except that a 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide copolymer was used and the unstretched film thickness was changed to 105 μm. A film (a-11) was obtained. As a result of measuring the birefringence of the film (a-11) with a birefringence measuring apparatus KOBRA-WR, Re (450) = 192 nm, Re (550) = 218 nm, Re (650) = 225 nm, Rth (550) = 109 nm The film thickness was 75 μm and the Nz coefficient was 1.00.
The result of measuring the contrast ratio at an incident angle of 60 degrees with a contrast measuring device by placing the film (a-11) and the film (b-1) between the polarizing plates arranged in the configuration of FIG. The contrast ratio was 100: 1 or less. The results are shown in Table 1.

[Comparative Example 3]
A copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide is dissolved in methylene chloride and applied directly onto a shrinkable film (PP uniaxially stretched film) using a wire bar. A coating film was formed. Further, it was dried at 60 ° C. for 5 minutes to produce a laminate of the shrinkable film and a copolymer of 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene and isosorbide. Next, using a biaxial stretching apparatus (X61-S manufactured by Toyo Seiki Co., Ltd.), the laminate is shrunk 0.7 times at 150 ° C., and at the same time, the stretching speed is 2 mm / s in the direction perpendicular to the shrinkage direction of the laminate. The film was stretched 2.0 times under the following conditions. Subsequently, the shrinkable film was peeled off to obtain a film (a-12). As a result of measuring the birefringence of the film (a-12) with the birefringence measuring apparatus KOBRA-WR, Re (450) = 255 nm, Re (550) = 290 nm, Re (650) = 299 nm, Rth (550) = 29 nm The film thickness was 100 μm, and the Nz coefficient was 0.6.
Film (a-12) and film (b-7) are arranged between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. 1, and the contrast ratio at an incident angle of 60 degrees is measured with a contrast measuring device. The contrast ratio was 100: 1 or less. The results are shown in Table 1.

[Comparative Example 4]
Using the copolymer (B-1), the film was stretched in the same manner as the film (a-1) except that the unstretched film thickness was 52 μm and the temperature was 130 ° C. to obtain a film (b-12). The film (b-12) was measured for birefringence with a birefringence measuring apparatus KOBRA-WR. As a result, Re (550) = 154 nm, Rth (550) = − 77 nm, and film thickness was 37 μm. Further, the refractive index was ny <nz = nx and was a negative A plate.
The result of measuring the contrast ratio at an incident angle of 60 degrees with a contrast measuring machine by arranging the film (a-9) and the film (b-12) between polarizing plates arranged with the polarization axes orthogonal to each other in the configuration of FIG. The contrast ratio was 100: 1 or less. The results are shown in Table 1.

By using the optical compensation film of the present invention, it is possible to produce an optical compensation film having characteristics that improve the viewing angle of a liquid crystal device, that is, characteristics of a high contrast ratio at a wide viewing angle.

ADVANTAGE OF THE INVENTION According to this invention, the optical compensation film for providing the liquid crystal display device which is excellent in a viewing angle characteristic and has a high contrast ratio also in the diagonal direction can be provided.

Claims

A film A satisfying (Formula 1) to (Formula 3) and a film B satisfying (Formula 4) and (Formula 5) are laminated, and the film B is composed of an aromatic vinyl monomer unit and an unsaturated dicarboxylic acid. It is a copolymer consisting of an acid anhydride monomer unit and a (meth) acrylic acid ester monomer unit,
Re (450), Re (550) and Re (650) are in-plane retardations at wavelengths of 450 nm, 550 nm and 650 nm, Rth (550) is a thickness direction retardation at a wavelength of 550 nm,
When the refractive index in the slow axis direction of the film is nx, the refractive index in the fast axis direction of the film is ny, the refractive index in the thickness direction of the film is nz, and the film thickness is d, the in-plane retardation Re is In (Expression 6), the thickness direction retardation Rth is a value defined by (Expression 7).
(Formula 1) Re (450) <Re (550) <Re (650)
(Formula 2) 25 nm ≦ Re (550) ≦ 280 nm
(Formula 3) 12 nm ≦ Rth (550) ≦ 95 nm
(Formula 4) 0 nm ≦ Re (550) ≦ 140 nm
(Formula 5) −140 nm ≦ Rth (550) ≦ 0 nm
(Expression 6) Re = (nx−ny) × d
(Expression 7) Rth = {(nx + ny) ÷ 2-nz} × d
2. The optical compensation film according to claim 1, wherein the Nz coefficient of the film A satisfies (Equation 8), and the Nz coefficient is a value defined by (Equation 9).
(Formula 8) 0.6 ≦ Nz ≦ 1.2
(Formula 9) Nz = (nx−nz) / (nx−ny)
The optical compensation film according to claim 1, wherein the film B is a positive C plate, and the positive C plate is a film satisfying (Equation 10).
(Formula 10) nx = ny <nz
The optical compensation film according to claim 1, wherein the film B is a negative A plate, and the negative A plate is a film satisfying (Equation 11).
(Formula 11) ny <nz = nx
4. The optical compensation according to claim 3, wherein the film A satisfies (Equation 12), (Equation 13), and (Equation 14), and the film B satisfies (Equation 15) and (Equation 16). the film.
(Formula 12) 0.8 ≦ Nz ≦ 1.2
(Formula 13) 120 nm ≦ Re (550) ≦ 170 nm
(Formula 14) 55 nm ≦ Rth (550) ≦ 90 nm
(Formula 15) Re (550) = 0
(Expression 16) −120 nm ≦ Rth (550) ≦ −70 nm
4. The optical compensation according to claim 3, wherein the film A satisfies (Equation 17), (Equation 18), and (Equation 19), and the film B satisfies (Equation 20) and (Equation 21). the film.
(Formula 17) 0.6 ≦ Nz ≦ 0.8
(Formula 18) 170 nm ≦ Re (550) ≦ 230 nm
(Formula 19) 15 nm ≦ Rth (550) ≦ 55 nm
(Equation 20) Re (550) = 0
(Formula 21) −70 nm ≦ Rth (550) ≦ −20 nm
The optical compensation film according to claim 4, wherein the film A satisfies (Formula 22) and (Formula 23), and the film B satisfies (Formula 24) and (Formula 25).
(Formula 22) 70 nm ≦ Re (550) ≦ 120 nm
(Formula 23) 30 nm ≦ Rth (550) ≦ 60 nm
(Formula 24) 70 nm ≦ Re (550) ≦ 120 nm
(Formula 25) −60 nm ≦ Rth (550) ≦ −30 nm
A liquid crystal display device using the optical compensation film according to any one of claims 1 to 7.