JP2008122918A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film suitably used as a viewing angle compensation film for an in-plane-switching (IPS) liquid crystal display, having a wide range of feasible optical characteristics, wherein the optical characteristics can be readily adjusted. <P>SOLUTION: The retardation film has an optical anisotropic layer that contains the optical anisotropy material that shows the wavelength dependence on the retardation of a positive distribution type, wherein the retardation film includes an optically anisotropic film, where a relation of nx<SB>1</SB>>ny<SB>1</SB>is satisfied, between a refractive index nx<SB>1</SB>in a direction of a slow axis in an in-plane direction and a refractive index ny<SB>1</SB>in a direction of a fast axis in the in-plane direction; and a liquid crystal material, that is formed on the optically anisotropic film and forms homeotropic alignment. An Nz factor (Nz) and in-plane retardation (Re) lie within the range of -0.5<Nz<0.5 and 50 nm<Re<170 nm, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a retardation film suitably used for an IPS liquid crystal display device.

  The liquid crystal display device has features such as power saving, light weight, thinness, and the like, and has rapidly spread in recent years in place of the conventional CRT display. As a general liquid crystal display device, as shown in FIG. 6, a liquid crystal display device having an incident side polarizing plate 102 </ b> A, an outgoing side polarizing plate 102 </ b> B, and a liquid crystal cell 101 can be exemplified. The polarizing plates 102A and 102B are configured to selectively transmit only linearly polarized light having a vibration surface in a predetermined vibration direction, and crossed Nicols so that the vibration directions are perpendicular to each other. It is arranged to face each other. The liquid crystal cell 101 includes a large number of cells corresponding to the pixels, and is disposed between the polarizing plates 102A and 102B.

  As such a liquid crystal display device, those using various driving methods are known depending on the arrangement form of the liquid crystal material used in the liquid crystal cell. The main ones of liquid crystal display devices that are popular today are classified into TN, STN, MVA, IPS, OCB, and the like. In particular, today, those having the MVA and IPS driving methods have come into widespread use.

  On the other hand, the liquid crystal display device has a problem of viewing angle dependency due to the refractive index anisotropy of the liquid crystal cell and the polarizing plate as a specific problem. This problem of viewing angle dependency is a problem that the color and contrast of an image that is visually recognized change when the liquid crystal display device is viewed from the front and when viewed from an oblique direction. Such a problem of viewing angle characteristics has become more serious as the liquid crystal display device has recently been enlarged.

Various techniques have been developed so far to improve the viewing angle dependency problem. As a typical method, there is a method using a retardation film. In this method using a retardation film, a retardation film 103 having predetermined optical characteristics is disposed between the liquid crystal cell 101 and the polarizing plates 102A and 102B as shown in FIG. It is a way to improve the problem. Since such a method can improve the viewing angle dependency problem only by incorporating the retardation film 103 in the liquid crystal display device, it can be easily obtained as a liquid crystal display device having excellent viewing angle characteristics. It has been widely used.
Here, as the retardation film, for example, a film having a structure in which a retardation layer containing a regularly arranged liquid crystal material is formed on a transparent substrate or a film made of a stretched film is generally known. It has been.

  Further, in recent years, a method in which the retardation film and the polarizing plate are not separately disposed as illustrated in FIG. 7, but a method in which the retardation film is also used as a polarizing plate protective film constituting the polarizing plate has become mainstream. It is coming. That is, as illustrated in FIG. 8, a general liquid crystal display device has a configuration in which polarizing plates 102 </ b> A and 102 </ b> B are disposed on both sides of the liquid crystal cell 101. The polarizer 111 is sandwiched between two polarizing plate protective films 112a and 112b (FIG. 8A) (here, for convenience of explanation, a polarizing plate disposed on the liquid crystal cell 101 side) The protective film 112a is referred to as “inner polarizing plate protective film”, and the other polarizing plate protective film 112b is referred to as “outer polarizing plate protective film”. When the viewing angle characteristic of the liquid crystal display device is improved using the retardation film 103, as illustrated in FIG. 8B, the inner polarizing plate of the two polarizing plate protective films 112a and 112b. The use of polarizing plates 102A ′ and 102B ′ in which the retardation film 103 is used as the protective film 112a has become the mainstream in recent years.

Here, as a polarizing plate protective film used for the said polarizing plate, what consists of a cellulose derivative represented by the cellulose triacetate and what consists of cycloolefin type resin represented by the norbornene-type resin are known. Since the said cellulose derivative is excellent in water permeability, it has the advantage that the water | moisture content contained in the polarizer in the manufacturing process of a polarizing plate can be volatilized through a film. However, on the other hand, there is a disadvantage that the dimensional change due to moisture absorption and the change in optical characteristics are relatively large in a high temperature and high humidity atmosphere. Furthermore, the polarizing plate protective film made of a cellulose derivative has a poor gas barrier property. For this reason, when the polarizing plate protective film which consists of a cellulose derivative is used on both sides, there exists a problem that durability of the optical characteristic of a polarizing plate will fall.
On the other hand, since the cycloolefin-based resin is a hydrophobic resin, it has an advantage that a dimensional change due to moisture absorption and a change in optical characteristics are relatively small in a high-temperature and high-humidity atmosphere. However, on the other hand, it has a drawback that moisture contained in the polarizer in the production process of the polarizing plate cannot be volatilized through the film. For this reason, when the polarizing plate protective film which consists of a cycloolefin type resin is used for both sides, there exists a problem that a polarizing characteristic will fall with time.
For this reason, as the polarizing plate, a polarizing plate protective film made of a cellulose derivative is used as the inner polarizing plate protective film, and a polarizing plate protective film made of a cycloolefin resin is used as the outer polarizing plate protective film. Thus, the advantages of both can be combined and the disadvantages of both can be offset, so that a polarizing plate with excellent durability can be obtained (for example, Patent Document 1).
Therefore, it is considered that the retardation film preferably uses a substrate made of a cellulose derivative.

  By the way, the retardation of the retardation film depends on the driving method of the liquid crystal display device that is the object of improving the viewing angle characteristics, and in particular, the IPS (In-Plane Switching) type liquid crystal. For the display device, it is desirable to use a retardation film having a property as a positive C plate and a property as an A plate and having a predetermined retardation. In this regard, Patent Documents 2 to 5 describe a polarizing plate-integrated optical compensation film in which a film having a property as a positive C plate, a film having a property as an A plate, and a polarizing film are laminated. A polarizing plate-integrated optical compensation film is disclosed in which either the film having the property as the positive C plate or the film having the property as the A plate is made of cellulose propionate. . Such a polarizing plate-integrated optical compensation film is desirable in that a film made of a cellulose derivative is used. However, since the optical properties of the film having the property as the positive C plate and the film having the property as the A plate are both adjusted by including an optical property developing agent in the film, There is a problem that it is difficult to realize optical characteristics. In addition, since there is a limit to the amount of the optical property-expressing agent that can be contained in the film, in the polarizing plate-integrated optical compensation film having the above configuration, the range of optical properties that can be realized is narrow. There was a problem of becoming. Furthermore, since the optical property developing agent usually exhibits hydrophobicity, when such an optical property developing agent is included in the film, the film is bonded to a polarizing film made of a hydrophilic resin such as polyvinyl alcohol. There was also a problem that the adhesion decreased.

  Therefore, it can be suitably used as a viewing angle compensation film for IPS liquid crystal display devices in the past, has a wide range of realizable optical properties, has excellent adhesion to polarizers, and has optical properties. It was difficult to obtain a retardation film that can be easily adjusted.

Japanese Patent No. 3132122 JP 2006-71963 A JP 2006-71964 A JP 2006-71965 A JP 2006-71966 A

  The present invention has been made in view of such problems, and is a retardation film suitably used as a viewing angle compensation film of an IPS liquid crystal display device, and has a wide range of realizable optical characteristics. It is an object of the present invention to provide a retardation film that has excellent adhesion to a polarizer and can easily adjust optical properties.

In order to solve the above problems, the present invention provides a transparent substrate comprising a cellulose derivative, a cellulose derivative formed on the transparent substrate, and constituting the transparent substrate, and the wavelength dependence of retardation is a positive dispersion type. Between the refractive index nx ₁ in the slow axis direction in the in-plane direction and the refractive index ny ₁ in the fast axis direction in the in-plane direction. And an optically anisotropic film satisfying a relationship of nx ₁ > ny ₁ and a liquid crystal material formed on the optically anisotropic film and having homeotropic alignment, and are orthogonal to each other in the in-plane direction. A retardation film having a refractive index nx ₂ , ny _{2 in} any x, y direction and a retardation layer in which a relationship of nx ₂ ≦ ny ₂ <nz ₂ is established between a refractive index nz _{2 in} the thickness direction So Nz factor (Nz) is in the range of −0.5 <Nz <0.5, and in-plane retardation (Re) is in the range of 50 nm <Re <170 nm. A phase difference film is provided.

According to the present invention, the optically anisotropic film has a configuration in which an optically anisotropic layer containing an optically anisotropic material is laminated on a transparent substrate made of a cellulose derivative. When the retardation layer contains a liquid crystal material in which homeotropic alignment is formed, for example, by changing the thickness of the optically anisotropic layer or the retardation layer, the optical characteristics of the retardation film as a whole Can be easily adjusted within a predetermined range. The optically anisotropic material contained in the optically anisotropic layer and the liquid crystal material contained in the retardation layer both exhibit excellent refractive index anisotropy. Therefore, it is possible to realize a wide range of optical characteristics.
In addition, according to the present invention, it is possible to express desired optical characteristics without including a hydrophobic compound in the transparent substrate, so that the adhesion of the transparent substrate to the hydrophilic polarizer is impaired. There is no. For this reason, according to this invention, the retardation film excellent in adhesiveness with a polarizer can be obtained.
Furthermore, the retardation film of the present invention is excellent in the viewing angle compensation function of the IPS liquid crystal display device because the Nz factor and the in-plane retardation are within the above ranges.
Therefore, according to the present invention, the retardation film is suitably used as a viewing angle compensation film for an IPS liquid crystal display device, and has a wide range of realizable optical characteristics and has optical characteristics. A retardation film that is easy to adjust can be obtained.

In the present invention, the in-plane retardation (Re ¹ ) of the optically anisotropic film is in the range of 50 nm <Re ¹ <170 nm, and the Nz factor (Nz ¹ ) is 1.0 <Nz <3. Is preferably in the range of 0.0.
In the present invention, the retardation in the thickness direction (Rth ² ) of the retardation layer is preferably in the range of −270 nm <Rth ² <−50 nm. Since the optical properties of the optically anisotropic film and the retardation layer are within the above ranges, the retardation film of the present invention can be made more excellent in the viewing angle compensation function of the IPS liquid crystal display device. It is.

  Furthermore, in the present invention, the cellulose derivative is preferably triacetyl cellulose. Since triacetyl cellulose is excellent in optical isotropy, the use of triacetyl cellulose as the cellulose derivative has advantages such as easy design of optical properties of the retardation film of the present invention. is there.

  In the retardation film of the present invention, the Nz factor (Nz) may be in the range of −0.5 <Nz <0.3.

  Further, in the retardation film of the present invention, the retardation layer may be formed on the optically anisotropic layer of the optically anisotropic film.

  The present invention is a retardation film suitably used as a viewing angle compensation film of an IPS liquid crystal display device, and has a wide range of optical characteristics that can be realized, excellent adhesion to a polarizer, and adjustment of optical characteristics. The effect that the retardation film which is easy to provide can be provided.

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

The retardation film of the present invention includes a transparent substrate made of a cellulose derivative, an optical derivative formed on the transparent substrate and constituting the transparent substrate, and an optical difference in which the wavelength dependence of retardation exhibits a positive dispersion type. having an optically anisotropic layer containing a isotropic material, the refractive index nx ₁ of the slow axis direction in the plane direction, between the refractive index ny ₁ in fast axis direction in the plane direction, nx ₁ An optically anisotropic film satisfying a relationship of> ny ₁ and any x which is formed on the optically anisotropic film and has a homeotropic alignment and which is orthogonal to each other in the in-plane direction, a retardation layer in which a relationship of nx ₂ ≦ ny ₂ <nz ₂ is established between the refractive indices nx ₂ and ny _{2 in the} y direction and the refractive index nz _{2 in} the thickness direction, and an Nz factor ( z) is in the range of -0.5 <Nz <0.5, and in which in-plane retardation (Re) is being in the range of 50nm <Re <170nm.

Such a retardation film of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an example of the retardation film of the present invention. As illustrated in FIG. 1, a retardation film 10 of the present invention includes an optically anisotropic film 1 having a transparent substrate 1a made of a cellulose derivative and an optically anisotropic layer 1b formed on the transparent substrate 1a. And the retardation layer 2 formed on the optically anisotropic layer 1b of the optically anisotropic film 1, and the Nz factor (Nz) of the entire retardation film 10 is -0.5 <Nz. <0.5, and in-plane retardation (Re) is in the range of 50 nm <Re <170 nm.
Here, the optically anisotropic film 1 is composed of a cellulose derivative constituting the transparent substrate 1a in the optically anisotropic layer 1b, and an optically anisotropic material in which the wavelength dependency of retardation is a positive dispersion type. Nx ₁ between the refractive index nx ₁ in the slow axis direction in the in-plane direction and the refractive index ny ₁ in the fast axis direction in the in-plane direction as the entire optically anisotropic film _1. The optical characteristics satisfying the relationship of> ny ₁ are provided.
The retardation layer 2 includes a liquid crystal material in which homeotropic alignment is formed, and the retardation layer 2 as a whole has a refractive index nx ₂ in any x and y directions orthogonal to each other in the in-plane direction. It has optical characteristics in which a relationship of nx ₂ ≦ ny ₂ <nz ₂ is established between ny ₂ and the refractive index nz ₂ in the thickness direction.

  Here, in FIG. 1, the example in which the retardation layer is formed on the optically anisotropic layer provided in the optically anisotropic film has been described. However, the above description is an example, and the retardation of the present invention is described. The configuration of the film is not limited to that illustrated in FIG. Therefore, the retardation film of the present invention may be one in which the retardation layer is formed on a transparent substrate of the optically anisotropic film.

According to the present invention, the optically anisotropic film has a configuration in which an optically anisotropic layer containing an optically anisotropic material is laminated on a transparent substrate made of a cellulose derivative. When the retardation layer contains a liquid crystal material in which homeotropic alignment is formed, for example, by changing the thickness of the optically anisotropic layer or the retardation layer, the optical characteristics of the retardation film as a whole Can be easily adjusted within a predetermined range. The optically anisotropic material contained in the optically anisotropic layer and the liquid crystal material contained in the retardation layer both exhibit excellent refractive index anisotropy. Therefore, it is possible to realize a wide range of optical characteristics.
In addition, according to the present invention, it is possible to express desired optical characteristics without including a hydrophobic compound in the transparent substrate, so that the adhesion of the transparent substrate to the hydrophilic polarizer is impaired. There is no. For this reason, according to this invention, the retardation film excellent in adhesiveness with a polarizer can be obtained.
Furthermore, the retardation film of the present invention is excellent in the viewing angle compensation function of the IPS liquid crystal display device because the Nz factor and the in-plane retardation are within the above ranges.

  Further, according to the present invention, when the retardation film of the present invention is used as an inner polarizing plate protective film, the optically anisotropic film having a transparent substrate made of a cellulose derivative is used. Since a polarizing plate protective film made of a cycloolefin-based resin can be used as the outer polarizing plate protective film, a polarizing plate having excellent durability can be obtained.

  Therefore, according to the present invention, the retardation film is suitably used as a viewing angle compensation film for an IPS liquid crystal display device, and has a wide range of optical characteristics that can be realized. It is possible to obtain a retardation film that is excellent in properties and easy to adjust optical properties.

The Nz factor (Nz) is a parameter indicating the shape of the refractive index ellipsoid included in the retardation film of the present invention, and is represented by the following equation.
Nz = {(Rth ¹ + Rth ² ) / (Re ¹ + Re ² )} + 0.5
Here, Rth ¹ and Rth ² represent the retardation (Rth) in the thickness direction of the optically anisotropic film and the retardation layer used in the present invention, respectively.
The Re ¹ and Re ² represent the in-plane retardation (Re) of the optically anisotropic film and the retardation layer used in the present invention, respectively.

In the above formula, Rth ¹ and Re ¹ are nx _{1 as} the refractive index in the slow axis direction in the in-plane direction of the optically anisotropic film used in the present invention, and ny _{1 as} the refractive index in the fast axis direction in the in-plane direction. When the refractive index in the thickness direction is nz ₁ and the thickness is d ₁ , they are respectively represented by the following formulae.
Rth ¹ = {((nx ₁ + ny ₁ ) / 2) −nz ₁ } × d ₁
Re ¹ = (nx ₁ −ny ₁ ) × d ₁

In the above formula, Rth ² and Re ² represent the refractive indices in arbitrary x and y directions orthogonal to each other in the in-plane direction of the optically anisotropic film used in the present invention, respectively nx ₂ , ny ₂ , and thickness direction. When the refractive index is nz ₂ and the thickness is d ₂ , these are respectively expressed by the following formulas.
Rth ² = {((nx ₂ + ny ₂ ) / 2) −nz ₂ } × d ₂
Re ² = (nx ₂ −ny ₂ ) × d ₂

Further, in the present invention, the optically anisotropic layer includes an optically anisotropic material whose retardation value has a wavelength dependency of a positive dispersion type. In the present invention, the “positive dispersion type” means a wavelength of 450 nm. The ratio of the in-plane retardation (Re ₄₅₀ ) at 550 nm to the in-plane retardation (Re ₅₅₀ ) at a wavelength of 550 nm (Re ₄₅₀ / Re ₅₅₀ ) (hereinafter sometimes simply referred to as “Re ratio”) is 1. It means a large wavelength-dependent type.

  In the present invention, the wavelength-dependent type with the Re ratio smaller than 1 is called “reverse dispersion type”, and the wavelength-dependent type with the Re ratio of 1 is called “flat type”.

  The in-plane retardation and the retardation in the thickness direction in the present invention mean values for a wavelength of 550 nm unless a wavelength is specified.

The retardation film of the present invention has at least the optically anisotropic film and a retardation layer.
Hereinafter, each structure used for the retardation film of the present invention will be described in detail.

1. Optically anisotropic film First, the optically anisotropic film used in the present invention will be described. The optically anisotropic film used in the present invention is a transparent substrate made of a cellulose derivative, and the cellulose derivative that is formed on the transparent substrate and constitutes the transparent substrate, and the wavelength dependence of retardation is a positive dispersion type. Between the refractive index nx ₁ in the slow axis direction in the in-plane direction and the refractive index ny ₁ in the fast axis direction in the in-plane direction. In addition, the relationship of nx ₁ > ny ₁ is established.
Hereinafter, such an optically anisotropic film will be described in detail.

(1) Optically anisotropic layer First, the optically anisotropic layer used for this invention is demonstrated. The optically anisotropic layer used in the present invention is formed on a transparent substrate, which will be described later, and is composed of a cellulose derivative constituting the transparent substrate, and an optically anisotropic material in which the wavelength dependency of retardation exhibits a positive dispersion type. It contains.

a. Optically anisotropic material The optically anisotropic material used in the present invention is not particularly limited as long as the wavelength dependency of retardation is a positive dispersion type, and the use of the retardation film of the present invention According to the above, it is possible to appropriately select and use a film capable of imparting a desired retardation to the retardation film of the present invention. Among them, the optically anisotropic material used in the present invention is preferably one having the Re ratio in the range of 1 to 2.

Here, the Re ratio of the optically anisotropic material is such that an alignment film such as polyimide is formed, and a layer made of the optically anisotropic material is formed on an isotropic substrate such as a glass substrate subjected to the alignment treatment. It can be calculated by measuring Re (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and Re (Re ₅₅₀ ) at a wavelength of 550 nm.

As the optically anisotropic material used in the present invention, it is preferable to use a rod-shaped compound among those having the Re ratio within the above range. Since the rod-shaped compound can exhibit excellent retardation by being regularly arranged, it is easy to impart desired retardation to the optically anisotropic film by using such a rod-shaped compound. Because.
Here, the “rod-like compound” in the present invention means a compound in which the main skeleton of the molecular structure is rod-like.

As the rod-shaped compound used in the present invention, a compound having a relatively small molecular weight is preferable. More specifically, a compound having a molecular weight in the range of 200 to 1200 is preferable, and a compound having a molecular weight in the range of 400 to 1000 is particularly preferably used. The reason is as follows. That is, the optically anisotropic layer used in the present invention contains the optically anisotropic material and a cellulose derivative constituting the transparent substrate described later, but has a relatively small molecular weight as the rod-shaped compound. This is because in the optically anisotropic layer, the rod-like compound can be easily mixed with the cellulose derivative, and adhesion between the transparent substrate and the optically anisotropic layer can be improved.
In addition, when using the material which has a polymerizable functional group as said rod-shaped compound, the molecular weight of the said rod-shaped compound shall show the molecular weight of the monomer before superposition | polymerization.

  Moreover, it is preferable that the rod-shaped compound used for this invention is a liquid crystalline material which shows liquid crystallinity. This is because the liquid crystalline material has a property of regularly arranging, and thus has a large birefringence Δn (nx−ny) and easily imparts a desired phase difference.

  As the liquid crystalline material, any material exhibiting any liquid crystal phase such as a nematic phase, a cholesteric phase, and a smectic phase can be suitably used. In particular, in the present invention, it is preferable to use a liquid crystalline material exhibiting a nematic phase. This is because a liquid crystalline material exhibiting a nematic phase is easily arranged regularly as compared with liquid crystalline materials exhibiting other liquid crystal phases.

  Further, as the liquid crystalline material exhibiting the nematic phase, it is preferable to use a material having spacers at both ends of the mesogen. This is because the liquid crystalline material having spacers at both ends of the mesogen is excellent in flexibility, and by using such a liquid crystalline material, the optically anisotropic film used in the present invention can be made excellent in transparency.

Furthermore, as the rod-shaped compound used in the present invention, those having a polymerizable functional group in the molecule are preferably used, and among them, those having a polymerizable functional group capable of three-dimensional crosslinking are more preferably used. Since the rod-shaped compound has a polymerizable functional group, the rod-shaped compound can be polymerized and fixed. Therefore, an optically anisotropic layer that has excellent alignment stability and is less likely to change over time in retardation. Because it can be obtained.
In the present invention, the rod-shaped compound having the polymerizable functional group may be mixed with the rod-shaped compound having no polymerizable functional group.
The “three-dimensional cross-linking” means that liquid crystal molecules are polymerized three-dimensionally to form a network (network) structure.

  Examples of the polymerizable functional group include polymerizable functional groups that are polymerized by the action of ionizing radiation such as ultraviolet rays and electron beams, or heat. Representative examples of these polymerizable functional groups include radically polymerizable functional groups or cationic polymerizable functional groups. Further, representative examples of radically polymerizable functional groups include functional groups having at least one addition-polymerizable ethylenically unsaturated double bond, and specific examples include vinyl groups having or not having substituents, An acrylate group (generic name including an acryloyl group, a methacryloyl group, an acryloyloxy group, and a methacryloyloxy group) and the like can be given. Moreover, an epoxy group etc. are mentioned as a specific example of the said cation polymerizable functional group. In addition, examples of the polymerizable functional group include an isocyanate group and an unsaturated triple bond. Among these, from the viewpoint of the process, a functional group having an ethylenically unsaturated double bond is preferably used.

Furthermore, the rod-like compound is a liquid crystalline material exhibiting liquid crystallinity, and the one having the polymerizable functional group at the terminal is particularly preferable. By using such a liquid crystal material, for example, they can be polymerized three-dimensionally to form a network structure, so that they have alignment stability and excellent optical properties. This is because an optically anisotropic layer can be formed.
In the present invention, even when a liquid crystalline material having a polymerizable functional group at one end is used, the alignment can be stabilized by crosslinking with other molecules.

  Specific examples of the rod-like compound used in the present invention include compounds represented by the following formulas (1) to (6).

  Here, the liquid crystalline materials represented by the chemical formulas (1), (2), (5) and (6) are disclosed in DJ Broer et al., Makromol. Chem. 190, 3201-3215 (1989), or DJ Broer et al., Makromol. Chem. 190, 2250 (1989), or can be prepared similarly. The preparation of liquid crystalline materials represented by the chemical formulas (3) and (4) is disclosed in DE 195,04,224.

Specific examples of the nematic liquid crystalline material having an acrylate group at the terminal include those represented by the following chemical formulas (7) to (17).

  In addition, the liquid crystalline material used for this invention may be only 1 type, or 2 or more types. For example, when the liquid crystalline material is a mixture of a liquid crystalline material having one or more polymerizable functional groups at both ends and a liquid crystalline material having one or more polymerizable functional groups at one end, This is preferable because the polymerization density (crosslinking density) and optical characteristics can be arbitrarily adjusted by adjusting the blending ratio.

b. Next, a cellulose derivative contained in the optically anisotropic layer used in the present invention will be described. The cellulose derivative used for this invention is a cellulose derivative which comprises the transparent substrate mentioned later. In the present invention, an optically anisotropic film having excellent adhesion between the transparent substrate and the optically anisotropic layer can be obtained by containing such a cellulose derivative in the optically anisotropic layer.

  The amount of the cellulose derivative contained in the optically anisotropic layer in the present invention is such that the adhesiveness between the transparent substrate and the optically anisotropic layer is within a desired range in the optically anisotropic film used in the present invention. If it is in the range which can do, it will not specifically limit. Especially in this invention, it is preferable that content of the said cellulose derivative exists in the range of 1 mass%-50 mass%, and it is especially preferable that it exists in the range of 5 mass%-30 mass%.

  The cellulose derivative contained in the optically anisotropic layer is the same as that described as the cellulose derivative constituting the transparent substrate in the section “(2) Transparent substrate” described later. Description is omitted.

c. Optically anisotropic layer The optically anisotropic layer used in the present invention may contain other compounds in addition to the optically anisotropic material and the cellulose derivative. Examples of such other compounds include silicon leveling agents such as polydimethylsiloxane, methylphenylsiloxane, and organically modified siloxane; linear polymers such as polyalkyl acrylate and polyalkyl vinyl ether; fluorine surfactants; Surfactants such as hydrocarbon surfactants; fluorine leveling agents such as tetrafluoroethylene; photopolymerization initiators and the like can be mentioned.
Especially in this invention, when using the rod-shaped compound which has a polymerizable functional group which superposes | polymerizes by light irradiation as said optically anisotropic material, it is preferable that a photoinitiator is included as said other compound.

  Examples of the photopolymerization initiator used in the present invention include benzophenone, methyl o-benzoylbenzoate, 4,4-bis (dimethylamine) benzophenone, 4,4-bis (diethylamine) benzophenone, α-amino acetophenone, 4,4-dichlorobenzophenone, 4-benzoyl-4-methyldiphenyl ketone, dibenzyl ketone, fluorenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpro Piophenone, p-tert-butyldichloroacetophenone, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthioxanthone, benzyldimethyl ketal, benzylmethoxyethyla Tar, benzoin methyl ether, benzoin butyl ether, anthraquinone, 2-tert-butylanthraquinone, 2-amylanthraquinone, β-chloroanthraquinone, anthrone, benzanthrone, dibenzsuberon, methyleneanthrone, 4-azidobenzylacetophenone, 2,6-bis ( p-azidobenzylidene) cyclohexane, 2,6-bis (p-azidobenzylidene) -4-methylcyclohexanone, 2-phenyl-1,2-butadion-2- (o-methoxycarbonyl) oxime, 1-phenyl-propanedione 2- (o-ethoxycarbonyl) oxime, 1,3-diphenyl-propanetrione-2- (o-ethoxycarbonyl) oxime, 1-phenyl-3-ethoxy-propanetrione-2- (o- Nzoyl) oxime, Michler's ketone, 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone , Naphthalene sulfonyl chloride, quinoline sulfonyl chloride, n-phenylthioacridone, 4,4-azobisisobutyronitrile, diphenyl disulfide, benzthiazole disulfide, triphenylphosphine, camphorquinone, Adeca N1717, carbon tetrabromide And a combination of a photoreductive dye such as tribromophenylsulfone, benzoin peroxide, eosin, and methylene blue with a reducing agent such as ascorbic acid and triethanolamine.

  In the present invention, these photopolymerization initiators may be used alone or in combination of two or more.

  In the present invention, when the photopolymerization initiator is used, it is preferable to use a photopolymerization initiation assistant in combination. Examples of the photopolymerization initiation aid that can be used in the present invention include tertiary amines such as triethanolamine and methyldiethanolamine, and benzoic acid derivatives such as 2-dimethylaminoethylbenzoic acid and ethyl 4-dimethylamidebenzoate. Although it can illustrate, it is not restricted to these.

  When the optically anisotropic layer used in the present invention contains the photopolymerization initiator, the content is not particularly limited as long as the optically anisotropic material can be polymerized in a desired time, Usually, it is preferably in the range of 1 to 10 parts by weight, particularly preferably in the range of 3 to 6 parts by weight with respect to 100 parts by weight of the rod-shaped compound.

  Furthermore, the compounds as shown below can be added to the optically anisotropic layer used in the present invention within the range not impairing the object of the present invention. Examples of compounds that can be added include polyester (meth) acrylate obtained by reacting (meth) acrylic acid with a polyester prepolymer obtained by condensing polyhydric alcohol and monobasic acid or polybasic acid; A polyurethane (meth) acrylate obtained by reacting a compound having two isocyanate groups with each other and then reacting the reaction product with (meth) acrylic acid; bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak Type epoxy resins, polycarboxylic acid polyglycidyl esters, polyol polyglycidyl ethers, aliphatic or cycloaliphatic epoxy resins, amino group epoxy resins, triphenolmethane type epoxy resins, dihydroxybenzene type epoxy resins and the like (meta Acu Photopolymerizable compounds such as epoxy (meth) acrylate obtained by reacting Le acid; photopolymerizable liquid crystal compound having an acryl group or methacryl group and the like. By containing such a compound, the mechanical strength of the optically anisotropic layer used in the present invention may be improved and stability may be improved.

  As the thickness of the optically anisotropic layer used in the present invention, the optical property of the optically anisotropic film used in the present invention is a desired value depending on the type of the optically anisotropic material and the transparent substrate described later. If it is in the range which can be made, it will not specifically limit. Especially in this invention, it is preferable to exist in the range of 0.5 micrometer-20 micrometers.

(2) Transparent substrate Next, the transparent substrate used for the optically anisotropic film in this invention is demonstrated. The transparent substrate used in the present invention is made of a cellulose derivative.

  The cellulose derivative constituting the transparent substrate used in the present invention has a desired water permeability and is contained in the polarizer in the polarizing plate production process when the retardation film of the present invention is used as a polarizing plate protective film. It is not particularly limited as long as it can permeate moisture and can suppress a decrease in polarization characteristics over time to a desired level. Among these, in the present invention, it is preferable to use cellulose esters as the cellulose derivative, and among the cellulose esters, it is preferable to use cellulose acylates. This is because cellulose acylates are advantageous in terms of availability because they are widely used industrially.

  As said cellulose acylates, C2-C4 lower fatty acid ester is preferable. The lower fatty acid ester may include only a single lower fatty acid ester such as cellulose acetate, and may include a plurality of fatty acid esters such as cellulose acetate butyrate and cellulose acetate propionate. There may be.

  In the present invention, among the above lower fatty acid esters, cellulose acetate can be particularly preferably used. As the cellulose acetate, it is most preferable to use triacetyl cellulose having an average acetylation degree of 57.5 to 62.5% (substitution degree: 2.6 to 3.0). Since triacetyl cellulose has a molecular structure having a relatively bulky side chain, by using a transparent substrate made of such triacetyl cellulose, the adhesion between the transparent substrate and the optically anisotropic layer is further improved. It is because it can improve.

  Here, the degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation can be determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). In addition, the acetylation degree of the triacetyl cellulose which comprises a triacetyl cellulose film can be calculated | required by said method, after removing impurities, such as a plasticizer contained in a film.

The transparency of the transparent substrate used in the present invention may be arbitrarily determined according to the transparency required for the retardation film of the present invention, but it is usually preferable that the transmittance in the visible light region is 80% or more. 90% or more is more preferable.
Here, the transmittance of the transparent substrate can be measured by JIS K7361-1 (Testing method for total light transmittance of plastic-transparent material).

  Moreover, the thickness of the transparent substrate used for this invention will not be specifically limited if it is in the range in which required self-supporting property is obtained according to the use etc. of the retardation film of this invention. In particular, in the present invention, it is preferably in the range of 10 μm to 188 μm, particularly preferably in the range of 20 μm to 125 μm, and more preferably in the range of 30 μm to 80 μm. This is because if the thickness of the transparent substrate is thinner than the above range, the necessary self-supporting property may not be imparted to the retardation film of the present invention. Further, if the thickness is thicker than the above range, for example, when cutting the retardation film of the present invention, processing waste may increase or the cutting blade may be worn quickly.

  Further, the in-plane retardation of the transparent substrate used in the present invention is not particularly limited as long as it is within a range in which a desired retardation can be imparted to the retardation film of the present invention, and the retardation film of the present invention. It can be arbitrarily adjusted according to the application and the specific embodiment of the optically anisotropic film used in the present invention. Among these, the transparent substrate used in the present invention preferably has an in-plane retardation at a wavelength of 550 nm in the range of 0 nm to 50 nm.

  Here, the wavelength dependence of the in-plane retardation of the transparent substrate used in the present invention may be any of a reverse dispersion type, a normal dispersion type, and a flat dispersion type.

  The transparent substrate used in the present invention preferably has a thickness direction retardation at a wavelength of 550 nm in the range of 0 nm to 100 nm.

In addition, the structure of the transparent substrate used for this invention is not restricted to the structure which consists of a single layer, You may have the structure by which the several layer was laminated | stacked.
Moreover, when it has the structure by which the several layer was laminated | stacked, the layer of the same composition may be laminated | stacked, and the several layer which has a different composition may be laminated | stacked.

(3) Optically anisotropic film The optically anisotropic film used in the present invention has a refractive index nx ₁ in the slow axis direction in the in-plane direction and a refractive index ny ₁ in the fast axis direction in the in-plane direction. In the meantime, the relationship of nx ₁ > ny ₁ is established. Therefore, the optically anisotropic film used in the present invention has properties as a so-called A plate or B plate.
Here, as a mode in which the relationship of nx ₁ > ny ₁ is established, nx ₁ > ny ₁ > nz ₁ , nx ₁ > nz ₁ > ny ₁ , nx ₁ > ny ₁ = nz ₁ , and nz ₁ > A mode in which the relationship of nx ₁ > ny ₁ is established can be given. As the optically anisotropic film used in the present invention, any film satisfying any of these relationships can be preferably used.

The Re ¹ of the optically anisotropic film used in the present invention is not particularly limited as long as the Nz factor and in-plane retardation of the retardation film of the present invention are within the range specified by the present invention. And can be appropriately adjusted according to the use of the retardation film of the present invention. In particular, in the present invention, Re ^{1 of the} optically anisotropic film is preferably within a range of 50 nm <Re ¹ <170 nm, and particularly preferably within a range of 70 nm <Re ¹ <150 nm. This is because, when Re ¹ is within such a range, the retardation film of the present invention can be made more excellent in the viewing angle compensation function of the IPS liquid crystal display device.

Further, the wavelength dependence of Re ¹ of the optically anisotropic film used in the present invention may be any of a reverse dispersion type, a normal dispersion type, and a flat dispersion type.

Further, the Nz factor (Nz ¹ ) of the optically anisotropic film used in the present invention is not particularly limited as long as the Nz factor of the retardation film of the present invention is within the range specified by the present invention. is not. In particular, in the present invention, the Nz factor (Nz ¹ ) of the optically anisotropic film is preferably in the range of 1.0 to 3.0, particularly in the range of 1.0 to 2.0. Is preferred. This is because, when the Nz factor (Nz ¹ ) is within such a range, the retardation film of the present invention can be made more excellent in the viewing angle compensation function of the IPS liquid crystal display device.
Incidentally, Nz factor of the optically anisotropic film (Nz ¹⁾ is, _nx 1, ny ₁ described above, and, with nz _1, is represented by the following formula.
Nz ¹ = (Rth ¹ / Re ¹ ) +0.5
The Nz factor can be obtained from Rth ¹ and Re ¹ obtained by the method described above by the parallel Nicol rotation method using, for example, KOBRA-WR manufactured by Oji Scientific Instruments.

The optically anisotropic film used in the present invention has a structure formed so that the optically anisotropic layer is in close contact with the transparent substrate. The degree of adhesion between the optically anisotropic layer and the transparent substrate at this time is particularly within the range in which the mechanical properties of the optically anisotropic layer can be controlled by the mechanical properties of the transparent substrate. It is not limited. In particular, in the present invention, it is preferable that the degree of adhesion is within the range of 20/100 to 100/100 as a result of evaluation by the crosscut method.
The above-mentioned “cross-cut method” refers to Japanese Industrial Standards JISK5600-5-6 “General paint test method—Part 5: Mechanical properties of coating film—Section 6: Evaluation according to adhesion (cross-cut method) In this method, a 1 mm square cut is put in a grid pattern on the coated surface side, an adhesive tape (manufactured by Nichiban Co., Cellotape (registered trademark)) is applied, the tape is then peeled off, and the number remaining in 100 1 mm square pieces The adhesion is evaluated by counting.
Moreover, the evaluation result by the said cross-cut method represents the number which remained among the checkered-like evaluation site | parts of 100 places, for example, said "20/100" does not peel among 100 evaluation site | parts. This means that there are 20 remaining portions, and the above “100/100” means that 100 out of 100 evaluation portions remain without peeling.

  In the optically anisotropic film used in the present invention, the transparent substrate and the optically anisotropic layer are laminated as an independent layer of the transparent substrate and the optically anisotropic layer. It may be a laminated mode, or there is no clear interface between the transparent substrate and the optically anisotropic layer, and the content of the optically anisotropic material continuously changes between the two. In this way, the layers may be laminated.

  The aspect in which the transparent substrate and the optically anisotropic layer are laminated in the optically anisotropic film used in the present invention will be described with reference to the drawings. FIG. 2 is a schematic view showing an example of an aspect in which the transparent substrate and the optically anisotropic layer are laminated in the optically anisotropic film used in the present invention. As illustrated in FIG. 2, the optically anisotropic film 1, 1 ′ used in the present invention may be an embodiment in which the transparent substrate 1 a and the optically anisotropic layer 1 b are laminated as independent layers. Well (FIG. 2 (a)), or there is no clear interface between the transparent substrate 1a and the optically anisotropic layer 1b ′, and the content of the optically anisotropic material is continuous between the two. The layers may be stacked so as to change (FIG. 2B).

2. Next, the retardation layer used in the present invention will be described. The retardation layer used in the present invention contains a liquid crystal material in which homeotropic alignment is formed, and has refractive indexes nx ₂ and ny ₂ in arbitrary x and y directions orthogonal to each other in the in-plane direction, and a refractive index in the thickness direction. The relationship of nx ₂ ≦ ny ₂ <nz ₂ is established between nz ₂ and nz ₂ .
Hereinafter, the retardation layer used in the present invention will be described.

(1) Liquid Crystal Material First, the liquid crystal material used in the present invention will be described. The liquid crystal material used in the present invention is a homeotropic liquid crystal material that can form homeotropic alignment and can impart a phase difference that satisfies the above relationship to nx ₂ , ny ₂ , and nz _2. There is no particular limitation as long as it is present. Among these, the homeotropic liquid crystal material used in the present invention preferably has a polymerizable functional group. This is because by using such a homeotropic liquid crystal material, they can be polymerized with each other via a polymerizable functional group, so that the mechanical strength of the retardation layer used in the present invention can be improved. In addition, the alignment stability of the homeotropic liquid crystal material in the retardation layer can be improved.

As the polymerizable functional group, various polymerizable functional groups that are polymerized by the action of ionizing radiation such as ultraviolet rays and electron beams, or heat can be used. Typical examples of these polymerizable functional groups include radical polymerizable functional groups or cationic polymerizable functional groups.
Representative examples of the radical polymerizable functional group include a functional group having at least one addition-polymerizable ethylenically unsaturated double bond, and specific examples include a vinyl group having or not having a substituent, An acrylate group (generic name including an acryloyl group, a methacryloyl group, an acryloyloxy group, and a methacryloyloxy group), and the like.
Moreover, an epoxy group etc. are mentioned as a specific example of the said cation polymerizable functional group.
Examples of other polymerizable functional groups that can be used in the present invention include an isocyanate group and an unsaturated triple bond.
In particular, in the invention, among these polymerizable functional groups, a functional group having an ethylenically unsaturated double bond is preferably used from the viewpoint of the process.

  The homeotropic liquid crystal material used in the present invention may have a plurality of the above polymerizable functional groups, or may have only one.

  The homeotropic liquid crystal material that can be used in the present invention includes a homeotropic alignment property (first homeotropic liquid crystal material) that can form a homeotropic alignment without using a vertical alignment film, and a homeotropic liquid crystal material alone. Although a tropic alignment cannot be formed, a material that can form a homeotropic alignment by using a vertical alignment film (second homeotropic liquid crystal material) can be used. In the present invention, not only the first homeotropic liquid crystal material but also the second homeotropic liquid crystal material can be suitably used.

In the present invention, when the second homeotropic liquid crystal material is used, in order to homeotropically align the homeotropic liquid crystal material in the retardation layer, the optically anisotropic film and the retardation layer described above are usually used. A method is used in which an alignment layer having an alignment regulating force for homeotropic alignment of the liquid crystal material is used, or an alignment control compound having a function of homeotropic alignment of the liquid crystal material in the retardation layer. The orientation control compound is described in, for example, JP-A-10-319408.
In addition, a transfer method in which a retardation layer in which the second homeotropic liquid crystal material is homeotropically oriented is separately formed on another substrate such as a glass substrate, and is then peeled and laminated on the optically anisotropic film. Can also be used. In such a transfer method, a method for forming a retardation layer on the other substrate is disclosed in, for example, JP-A No. 2003-177242.

  As the first homeotropic liquid crystal material, any homeotropic alignment can be formed without using a vertical alignment film, and any desired retardation can be imparted to the retardation layer used in the present invention. It is not particularly limited. Examples of the first homeotropic liquid crystal material include a monomer unit containing a liquid crystalline fragment side chain having positive refractive index anisotropy and a monomer unit containing a non-liquid crystalline fragment side chain. Liquid crystal such as a side chain type liquid crystal polymer containing, a side chain type liquid crystal polymer containing a monomer unit containing the liquid crystalline fragment side chain and a monomer unit containing a liquid crystalline fragment side chain having an alicyclic ring structure Mention may be made of polymers. Examples of such a liquid crystal polymer include compounds described in JP-A No. 2003-121853, JP-A No. 2002-174725, and JP-A No. 2005-70098.

  On the other hand, as the second homeotropic liquid crystal material, a homeotropic alignment can be formed by using a vertical alignment film or the like, and a desired retardation can be imparted to the retardation layer used in the present invention. If it is, it will not specifically limit. Among these, in the present invention, a nematic liquid crystal material exhibiting a nematic phase is preferably used.

  Specific examples of the second homeotropic liquid crystal material used in the present invention include, for example, compounds described in JP-T-10-508882 and JP-A-2003-287623. . In particular, in the present invention, compounds represented by the above formulas (1) to (17) can be suitably used as the second homeotropic liquid crystal material.

  Examples of the second homeotropic liquid crystal material used in the present invention include compounds described in JP-A-10-319408. In particular, in the present invention, a compound represented by the following chemical formula can be preferably used.

In the above formula, x is 1 to 12, Z is a 1,4-phenylene group or 1,4-cyclohexylene group, R ¹ is halogen or cyano, or has 1 to 12 carbon atoms. An alkyl group or an alkoxy group, and L is H, halogen or CN, or an alkyl group, an alkoxy group or an acyl group having 1 to 7 carbon atoms.

  In addition, when a compound having a polymerizable functional group is used as the homeotropic liquid crystal material, the homeotropic liquid crystal material contained in the retardation layer used in the present invention is polymerized via the polymerizable functional group. It becomes a thing.

  The homeotropic liquid crystal material used in the present invention may be one type or two or more types. When two or more kinds of liquid crystal materials are used, the first homeotropic liquid crystal material and the second homeotropic liquid crystal material may be mixed and used.

(2) Other compounds The retardation layer used in the present invention may contain other compounds other than the liquid crystal material. Such other compounds are not particularly limited as long as they do not impair the alignment state of the liquid crystal material in the retardation layer or the optical properties of the retardation layer, and the retardation film of the present invention. It can be appropriately selected and used depending on the purpose of use. Among these, examples of the other compound suitably used in the present invention include an alignment control compound that assists in forming homeotropic alignment of the liquid crystal material. By using such an alignment control compound, there is an advantage that the homeotropic liquid crystal material of the second aspect can be used. Further, even when the homeotropic liquid crystal material of the first aspect is used, there is an advantage that the regularity of homeotropic alignment can be improved by using such an alignment control compound.

  The alignment control compound is not particularly limited as long as a desired homeotropic alignment regulating force can be imparted to the retardation layer used in the present invention. Among these, as the alignment control compound used in the present invention, a surfactant can be preferably used. In the retardation layer, the surfactant is unevenly distributed at the air interface and can be arranged with the specific direction of the molecule directed toward the retardation layer, so that the homeotropic alignment regulating force is easily imparted to the retardation layer. Because it can.

  Examples of the surfactant used in the present invention include sulfonate surfactants, and fluorinated sulfonate surfactants are particularly preferably used.

  Specific examples of the fluorinated sulfonate surfactant include trade names FC-4430 and FC-4432 (both manufactured by 3M Company).

  Moreover, as said other compound used for this invention, a polymerization initiator, a polymerization inhibitor, a plasticizer, surfactant, a silane coupling agent etc. can be mentioned, for example.

  Moreover, the compounds as shown below can be added to the retardation layer used in the present invention within a range not impairing the object of the present invention. Examples of compounds that can be added include polyester (meth) acrylate obtained by reacting (meth) acrylic acid with a polyester prepolymer obtained by condensing polyhydric alcohol and monobasic acid or polybasic acid; A polyurethane (meth) acrylate obtained by reacting a compound having two isocyanate groups with each other and then reacting the reaction product with (meth) acrylic acid; bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak Type epoxy resins, polycarboxylic acid polyglycidyl esters, polyol polyglycidyl ethers, aliphatic or cycloaliphatic epoxy resins, amino group epoxy resins, triphenolmethane type epoxy resins, dihydroxybenzene type epoxy resins and the like (meta Acu Photopolymerizable compounds such as epoxy (meth) acrylate obtained by reacting Le acid; photopolymerizable liquid crystal compound having an acryl group or methacryl group and the like.

(3) Retardation layer The retardation layer used in the present invention is provided between the refractive indices nx ₂ and ny ₂ in arbitrary x and y directions orthogonal to each other in the in-plane direction and the refractive index nz _{2 in the} thickness direction. The relationship of nx ₂ ≦ ny ₂ <nz ₂ is established. Therefore, the retardation layer used in the present invention has a property as a so-called positive C plate.

The retardation in the thickness direction of the retardation layer (Rth ² ) used in the present invention is not particularly limited as long as the Nz factor of the retardation film of the present invention is within the range specified by the present invention. Absent. In particular, in the present invention, the Rth ² is preferably in the range of −270 nm to −50 nm. This is because when Rth ² is within the above range, the retardation film of the present invention can be made more excellent in the viewing angle compensation function of the IPS liquid crystal display device.
Here, Rth ² can be measured by a parallel Nicol rotation method using, for example, KOBRA-WR manufactured by Oji Scientific Instruments.

  The thickness of the retardation layer in the present invention is not particularly limited as long as it is within a range in which desired optical characteristics can be imparted to the retardation layer, depending on the type of the liquid crystal material, etc., but within the range of 0.5 μm to 10 μm. It is preferable that it is within a range of 0.5 μm to 5 μm, particularly preferably within a range of 1 μm to 3 μm.

  In addition, although the retardation layer in the present invention is formed on the optically anisotropic film, in the present invention, as an aspect in which the retardation layer is formed on the optically anisotropic film, The aspect formed in the optically anisotropic layer of the said optically anisotropic film may be sufficient, or the aspect formed on the transparent substrate of the said optically anisotropic film may be sufficient.

3. Retardation Film The retardation film of the present invention has an Nz factor (Nz) in the range of −0.5 <Nz <0.5, and an in-plane retardation (Re) of 50 nm <Re <170 nm. It is characterized by being within the range.
In the retardation film of the present invention, the Nz factor (Nz) may be in the range of −0.5 <Nz <0.3.

  The Nz factor (Nz) of the retardation film of the present invention is not particularly limited as long as it is within the above range, and may be appropriately adjusted according to the specific application of the retardation film of the present invention. Especially in this invention, it is preferable that the said Nz factor (Nz) exists in the range of 0.0-0.5. This is because when the Nz factor (Nz) is within the above range, the retardation film of the present invention can be made more excellent in the viewing angle compensation function of the IPS liquid crystal display device.

  Further, the in-plane retardation (Re) of the retardation film of the present invention is not particularly limited as long as it is within the above range, and may be appropriately adjusted according to the specific application of the retardation film of the present invention. Good. In particular, in the present invention, the in-plane retardation (Re) is preferably in the range of 70 nm <Re <150 nm.

  The form of the retardation film of the present invention is not particularly limited, and may be, for example, a sheet shape that matches the screen size of a liquid crystal display device using the retardation film of the present invention, or a long shape. There may be.

4). Use of Retardation Film The retardation film of the present invention can be used as a viewing angle compensation film, an elliptically polarizing plate, a brightness enhancement film and the like used in a liquid crystal display device. In particular, it can be suitably used as a viewing angle compensation film for an IPS liquid crystal display device.

  When the retardation film of the present invention is used as a viewing angle compensation film for a liquid crystal display device, the retardation film of the present invention can be used alone, and the retardation film of the present invention and other optical functions can be used. It is also possible to use it laminated with a film. Furthermore, it is also possible to directly laminate another retardation layer on the surface opposite to the side on which the retardation layer is formed of the optically anisotropic film used for the retardation film of the present invention.

  As an example of laminating and using the retardation film of the present invention and another optical functional film, for example, by laminating a liquid crystal layer containing cholesteric aligned liquid crystal molecules on the retardation film of the present invention, Examples of use as a brightness enhancement film for liquid crystal display devices can be given.

  Moreover, the retardation film of this invention can be used also for the use as a polarizing plate by bonding together with a polarizer. That is, the polarizing plate is usually composed of a polarizer and a polarizing plate protective film formed on both surfaces thereof. In the present invention, for example, as one polarizing plate protective film, the retardation of the present invention is used. By using a film, it can be used as a polarizing plate having a viewing angle compensation function of a liquid crystal display device.

5. Next, a method for producing the retardation film of the present invention will be described. The method for producing the retardation film of the present invention is not particularly limited as long as it can produce the retardation film having the above-described configuration. As such a method, the following three methods can be illustrated, for example.
The first method uses a transparent substrate made of a cellulose derivative, and an optically anisotropic film is formed by coating an optically anisotropic layer-forming coating solution containing an optically anisotropic material on the transparent substrate. An optically anisotropic film production step to be produced, a drawing step for drawing the optically anisotropic film produced by the optically anisotropic film production step, and an optical difference of the optically anisotropic film drawn by the drawing step. A retardation layer forming step of forming a retardation layer on the optically anisotropic layer by coating a retardation layer-forming coating liquid containing the liquid crystal material on the anisotropic layer. It is.
The second method uses an optically anisotropic film by applying a coating liquid for forming an optically anisotropic layer containing the optically anisotropic material onto the transparent substrate, using a transparent substrate made of a cellulose derivative. An optically anisotropic film production process for producing an optically anisotropic film prepared by the optically anisotropic film production process and a retardation layer-forming coating containing the liquid crystal material on the optically anisotropic layer of the optically anisotropic film produced by the optically anisotropic film production process. A retardation layer forming step of forming a retardation layer on the optically anisotropic layer by applying a working solution; and a stretching step of stretching the laminate of the optically anisotropic film and the retardation layer; It is the method which has.
The third method is to use an optically anisotropic film by coating an optically anisotropic layer-forming coating solution containing the optically anisotropic material on the transparent substrate, using a transparent substrate made of a cellulose derivative. Containing the liquid crystal material on a substrate provided with a vertical alignment film, a step of stretching the optical anisotropic film produced by the optical anisotropic film production step, and an optically anisotropic film production step. A retardation layer forming step in which only the retardation layer is adhered to the optically anisotropic layer of the optically anisotropic film via an adhesive after the retardation layer is formed.
The retardation film of the present invention can be produced by any of the above methods. Among them, according to the first method, the optically anisotropic film of the first aspect can be more easily obtained. The used retardation film can be obtained.

  Here, in the description of the first method to the third method, the example in which the retardation layer is formed on the optical anisotropic film provided in the optical anisotropic film has been described. From the method to the third method, a retardation layer may be formed on the transparent substrate of the optically anisotropic film.

In addition, as an apparatus and a processing method used for the stretching process, basically the same apparatus as that used for the stretching process of a normal synthetic resin film is used. In view of the retardation value, the film may be stretched under appropriate conditions.
For stretching, either uniaxial stretching treatment or biaxial stretching treatment may be performed. The biaxial stretching process may be an unbalanced biaxial stretching process. In unbalanced biaxial stretching, a polymer film is stretched at a certain ratio in a certain direction, and stretched at a larger ratio in a direction perpendicular thereto. The bi-directional stretching process may be performed simultaneously.
Further, the stretching treatment is not particularly limited. For example, it can be appropriately performed by an arbitrary stretching method such as a roll stretching method, a long gap stretching method, a tenter stretching method, and a tubular stretching method. In the stretching treatment, the polymer film is preferably heated to, for example, a glass transition temperature or higher and a melting temperature (or melting temperature) or lower. In particular, in the present invention, it is preferable to use a tenter stretching method because it can be bonded to a polarizing member made of a hydrophilic resin such as PVA by Roll to Roll.
Furthermore, the draw ratio of the drawing treatment is appropriately determined depending on the retardation value to be obtained, and is not particularly limited. From the point of making the retardation value uniform at each point in the in-plane direction of the film, it is preferably in the range of 1.03 to 2 times.
In addition, since a method generally used for producing a retardation film for a liquid crystal display device can be used as a specific method for performing each step in each of the above methods, detailed description thereof is omitted here. To do.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Next, the present invention will be described more specifically by showing examples.
1. Example 1
(1) Production of optically anisotropic film An optically anisotropic material represented by the following formula (I) is dissolved in cyclohexanone in an amount of 20% by weight, and is made of a TAC film (manufactured by Fuji Film Co., Ltd., trade name: TF80UL). The surface of the substrate was coated by bar coating so that the coating amount after drying was 2.5 g / m ² .
Subsequently, after removing the solvent by heating at 50 ° C. for 4 minutes, the optically anisotropic material was fixed by irradiating the coated surface with ultraviolet rays.
Next, the film was stretched in the in-plane direction while being heated at 160 ° C. so that the stretching ratio was 1.15 times using a stretching experiment apparatus to prepare an optically anisotropic film. At this time, Re ^{1 of the} optical anisotropic film was 110 nm and Nz ¹ was 1.50.

2. Preparation of retardation film Liquid crystal mixture of 50% by mass of side chain polymer represented by the following formula (A) and 50% by mass of polymerizable liquid crystal represented by the following formula (B), photopolymerization initiator (Ciba Specialty) Chemicals, Irgacure 907, 5% by mass with respect to the liquid crystal mixture) is dissolved in a toluene solution to a solid content of 20% by mass, and a leveling agent is added to obtain a coating solution for forming a retardation layer. Obtained. After coating the retardation layer forming coating solution on the optically anisotropic layer, the coating layer is dried at 100 ° C. for 1 minute and cooled to room temperature as it is, so that the liquid crystal mixture is homeotropically aligned, and the retardation layer. Got. Furthermore, it was cured with 100 mJ / cm ² of UV to prepare a retardation film. At this time, the film thickness was adjusted so that Rth ² = −155 nm of the retardation layer.

2. Example 2
A retardation film was produced in the same manner as in Example 1 except that the film thickness was adjusted so that Rth ² of the retardation layer was −145 nm.

3. Example 3
A retardation film was produced in the same manner as in Example 1 except that the film thickness was adjusted so that Rth ² of the retardation layer was −135 nm.

4). Example 4
An optically anisotropic film was produced in the same manner as in Example 1 except that the coating amount after drying of the optically anisotropic material was 2.8 g / m ² . At this time, Re ¹ = 115 nm of the optically anisotropic film and Nz ¹ = 1.6. In addition, a retardation layer having homeotropic alignment as in Example 1 was prepared. At this time, the film thickness was adjusted so that Rth ² = −185 nm of the retardation layer.

5. Example 5
(1) Production of optically anisotropic film An optically anisotropic material prepared by mixing 1: 1 a polymerizable liquid crystal material represented by the following formulas (II) and (III) is dissolved in cyclohexanone to obtain a TAC film. The transparent substrate surface (made by Fuji Film Co., Ltd., trade name: TF80UL) was coated with a bar coating so that the coating amount after drying was 3.0 g / m ² . Subsequently, after removing the solvent by heating at 50 ° C. for 4 minutes, the optically anisotropic material was fixed by irradiating the coated surface with ultraviolet rays.
Next, the film was stretched in the in-plane direction while being heated at 160 ° C. so that the stretching ratio was 1.15 times using a stretching experiment apparatus to prepare an optically anisotropic film. At this time, Re ¹ = 90 nm of the optically anisotropic film and Nz ¹ = 2.0.

(2) Production of retardation film Optically anisotropic material containing a liquid crystal material represented by the following formulas (C), (D), and (E), a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, Irgacure 907) , 5 mass% with respect to the optically anisotropic material) was dissolved in a toluene solution so as to have a solid content of 20 mass%, and a leveling agent was further added to obtain a coating solution for forming a retardation layer. Next, the retardation layer forming coating solution is applied onto a glass substrate on which a vertical alignment film is formed, dried at 60 ° C. for 2 minutes, homeotropic aligned, and cured with UV of 100 mJ / cm ^2. It was. At this time, the film thickness was adjusted so that Rth ² = −195 nm of the retardation layer.
Next, the retardation layer was peeled from the glass substrate, and bonded to the optically anisotropic layer of the optically anisotropic film described in Example 5 via an adhesive to produce a retardation film.

6). Example 6
An optically anisotropic film was produced in the same manner as in Example 5 except that the coating amount after drying of the optically anisotropic material was 3.3 g / m ² . At this time, Re ¹ = 80 nm of the optically anisotropic film and Nz ¹ = 2.5. In addition, a retardation layer having homeotropic alignment was prepared in the same manner as in Example 5. At this time, the film thickness was adjusted so that Rth ² = −225 nm of the retardation layer.

7). Example 7
An optically anisotropic film was produced in the same manner as in Example 5 except that the coating amount after drying of the optically anisotropic material was 3.6 g / m ² . At this time, Re ^{1 of the} optical anisotropic film was 75 nm, and Nz ¹ was 2.9. In addition, a retardation layer having homeotropic alignment was prepared in the same manner as in Example 5. At this time, the film thickness was adjusted so that Rth ² = −245 nm of the retardation layer.

8). Example 8
A retardation film was produced in the same manner as in Example 1 except that the film thickness was adjusted so that Rth ² of the retardation layer was −125 nm.

9. Example 9
A retardation film was produced in the same manner as in Example 1 except that the film thickness was adjusted so that Rth ² of the retardation layer was −115 nm.

10. Example 10
A retardation layer was formed by the same method as in Example 1 on the side of the optically anisotropic film produced in Example 1 on which the optically anisotropic layer was not formed. At this time, the film thickness was adjusted so that Rth ² = −130 nm of the retardation layer.

11. Comparative Example 1
A retardation film was produced in the same manner as in Example 7 except that the film thickness was adjusted so that Rth ² of the retardation layer was −260 nm.

12 Comparative Example 2
A retardation film was produced in the same manner as in Example 7 except that the film thickness was adjusted so that Rth ² of the retardation layer was −270 nm.

13. Comparative Example 3
An optically anisotropic film was produced in the same manner as in Example 5 except that the coating amount after drying of the optically anisotropic material was 1.5 g / m ² . At this time, Re ¹ = 40 nm of the optically anisotropic film and Nz ¹ = 2.0. In addition, a retardation layer having homeotropic alignment was prepared in the same manner as in Example 5. At this time, the film thickness was adjusted so that Rth ^{2 of the} retardation layer was −70 nm.

14 Comparative Example 4
A retardation film was produced in the same manner as in Comparative Example 5 except that the film thickness was adjusted so that Rth ² of the retardation layer was −80 nm.

15. Comparative Example 5
An optically anisotropic film was produced in the same manner as in Example 1 except that the coating amount after drying of the optically anisotropic material was 4.0 g / m ² . At this time, Re ¹ = 180 nm of the optical anisotropic film, and Nz ¹ = 2.0. In addition, a retardation layer having homeotropic alignment as in Example 1 was prepared. At this time, the film thickness was adjusted so that Rth ² = −370 nm of the retardation layer.

16. Comparative Example 6
A retardation film was produced in the same manner as in Example 1 except that the film thickness was adjusted so that Rth ² of the retardation layer was −105 nm.

17. Evaluation In-plane retardation Re ¹ and Nz ^{1 of} the optically anisotropic film produced in the above Examples and Comparative Examples, thickness direction retardation Rth ^{2 of} the retardation layer, and Nz factor were evaluated for the retardation film. Each in-plane retardation, thickness direction retardation, and Nz ¹ were measured using an automatic birefringence measuring apparatus KOBRA. The Nz factor of the retardation film was calculated by the above formula.
For leakage light evaluation, a liquid crystal display device was prepared according to the following procedure, and leakage light in the 60 ° left oblique direction of the manufactured liquid crystal display device was measured using EZ contrast (manufactured by Eldim).

(1) Production of Polarizing Plate As shown in FIG. 3, saponified TAC film 22 (manufactured by Fuji Photo Film Co., Ltd., trade name: TF80UL) is already applied to one surface of polarizing film 23 made of polyvinyl alcohol. The surface opposite to the retardation layer 21 b of the retardation film 21 saponified on one surface is set so that the slow axis of the optically anisotropic film 21 a is orthogonal to the absorption axis of the polarizing film 23. The TAC film 22 and the retardation film 21 were bonded using a polyvinyl alcohol-based adhesive.

(2) Fabrication of IPS cell Next, as shown in FIG. 4, electrodes are placed on a glass substrate so that the distance between the electrodes is 20 μm, a polyimide alignment film is provided thereon, and a rubbing treatment is performed. went. A polyimide alignment film was provided on one surface of another glass substrate, and similarly rubbed. Two glass substrates are laminated and bonded so that the alignment films face each other, the cell gap d is 3.5 μm, and the rubbing directions of the two glass substrates are parallel to each other. A nematic liquid crystal composition having a property (Δn) of 0.0885 and a dielectric anisotropy (Δε) of 4.5 was enclosed. The value of Δn · d of the liquid crystal layer was 310 nm.
In FIG. 4, 31 is a liquid crystal element pixel region, 32 is a pixel electrode, 33 is a display electrode, 34 is a bending direction, 35a and 35b are liquid crystal directors during black display, and 36a and 36b are liquid crystals during white display. Represents a director.

(4) Production of Liquid Crystal Display Device A liquid crystal display device was produced with a layer structure as shown in FIG. Here, in FIG. 5, 40 is the slow axis direction when the liquid crystal in the IPS cell is black, 41 is the IPS cell, 42 is the slow axis of the optical anisotropic film, 43 is the retardation film, and 44 is the polarizing film. The absorption axis, 45 is a polarizing film, 37a is a TAC film, 38 is an absorption axis of the polarizing film, 39 is a polarizing film, 37b is an isotropic film (Re≈0 nm, Rth <10 nm), and 46 is a TAC film.

  The evaluation results are shown in Table 1. As shown in Table 1, Examples 1 to 10 had less leakage light and good viewing angle characteristics, but Comparative Examples 1 to 6 had more leakage light, and the viewing angle characteristics compared to Examples 1 to 10. Was significantly reduced.

  Furthermore, the contrast ratio of the manufactured liquid crystal display device and color shift vision in the dark and bright places were evaluated by the following methods.

・ Measurement method of contrast ratio of liquid crystal display device A white image and a black image are displayed on the liquid crystal display device in a dark room, and the product name “EZContrast160” manufactured by ELDIM Co., Ltd. The Y value of the XYZ color system on the display screen (˜360 °) was measured. Then, the contrast ratio “Yw / Yb” in all directions is calculated from the Y value (Yw) in the white image and the Y value (Yb) in the black image, and a contrast contour (contour) diagram is obtained in monochrome shades. Painted. The polar angle of 80 ° represents a direction inclined at an angle of 80 ° when the front direction of the display screen is 0 °.

-Visual evaluation of color shift in dark and bright places Display a black image on a liquid crystal display device in dark and bright places, and how the black image looks from a polar angle of 60 ° and an azimuth angle of 45 ° Visual evaluation was performed. Here, the azimuth angle of 45 ° represents an angle 45 ° direction when the polarizing plate absorption axis on the observer side is 0 ° and the polarizing plate absorption axis on the backlight side is 90 °. The bright place is about 200 lux when a fluorescent lamp is turned on in a general home.

  The evaluation results are shown in Table 2 below.

It is the schematic which shows an example of the retardation film of this invention. It is the schematic which shows the other example of the retardation film of this invention. It is the schematic which shows an example of the polarizing plate using the retardation film of this invention. It is the schematic which shows an example of the IPS cell produced using the retardation film of this invention. It is the schematic which shows an example of the liquid crystal display device produced using the retardation film of this invention. It is the schematic which illustrates typically a part of common liquid crystal display device. It is the schematic which illustrates typically a part of liquid crystal display device with which the phase difference film was used. It is the schematic which shows an example of the usage condition of a phase difference film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1 ', 21 ... Optically anisotropic film 1a, 21a ... Transparent substrate 1b, 21b ... Optically anisotropic layer 2 ... Phase difference layer 10 ... Phase difference film 31 ... Liquid crystal element pixel area 32 ... Pixel electrode 33 ... Display Electrode 34 ... rubbing direction 35a, 35b ... liquid crystal director 36a, 36b during black display ... liquid crystal director 37a, 46 during white display TAC film 38, 44 ... absorption axis 39, 45 of polarizing film ... polarizing film 37b ... Isotropic film 40... IPS cell liquid crystal in black display slow axis direction 41... IPS cell 42... Optically anisotropic film slow axis 43 .. retardation film 101... Liquid crystal cell 102A, 102B, 102A ', 102B '... Polarizing plate 103 ... Retardation film 111 ... Polarizer 112, 112a, 112b ... Polarizing plate protective film

Claims (6)

A transparent substrate comprising a cellulose derivative, an optical derivative containing a cellulose derivative formed on the transparent substrate and constituting the transparent substrate, and an optically anisotropic material in which the wavelength dependence of retardation exhibits a positive dispersion type. A relationship of nx ₁ > ny ₁ is established between the refractive index nx ₁ in the slow axis direction in the in-plane direction and the refractive index ny ₁ in the fast axis direction in the in-plane direction. An optically anisotropic film;
A liquid crystal material formed on the optically anisotropic film and containing homeotropic alignment is contained, and the refractive indexes nx ₂ and ny ₂ in arbitrary x and y directions orthogonal to each other in the in-plane direction, and the thickness direction A retardation film having a relationship of nx ₂ ≦ ny ₂ <nz ₂ between the refractive index nz ₂ and a retardation film,
The Nz factor (Nz) is in the range of −0.5 <Nz <0.5, and the in-plane retardation (Re) is in the range of 50 nm <Re <170 nm. Phase difference film. The in-plane retardation (Re ¹ ) of the optically anisotropic film is in the range of 50 nm <Re ¹ <170 nm, and the Nz factor (Nz ¹ ) is in the range of 1.0 <Nz <3.0. The retardation film according to claim 1, wherein the retardation film is provided. The thickness direction retardation of the retardation layer (Rth ^2), characterized in that it is in the range of -270nm ^<Rth 2 ^<-50nm, the retardation film according to claim 1 or claim 2.   The retardation film according to any one of claims 1 to 3, wherein the cellulose derivative is triacetylcellulose.   The retardation film according to any one of claims 1 to 4, wherein the Nz factor (Nz) is in a range of -0.5 <Nz <0.3.   The retardation film according to any one of claims 1 to 6, wherein the retardation layer is formed on the optically anisotropic layer of the optically anisotropic film. .

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