JP2007304444A - Retardation film and method of manufacturing retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film which shows wavelength dependence of a reverse distribution type having smaller retardation value at a short wavelength side than that at a long wavelength side and which is excellent in industrial productivity. <P>SOLUTION: The retardation film comprises: a transparent substrate which is made of a resin material and in which Y denoting a ratio (Re<SB>450</SB>/Re<SB>550</SB>) of a retardation value at 450 nm wavelength (Re<SB>450</SB>) to a retardation value at 550 nm wavelength (Re<SB>550</SB>) is less than 1; and an optical anisotropic layer which is formed on the transparent substrate and contains the resin material and an optical anisotropic material with X of ≥1, wherein X denotes a ratio (Re<SB>450</SB>/Re<SB>550</SB>) of a retardation value at 450 nm wavelength (Re<SB>450</SB>) to a retardation value at 550 nm wavelength (Re<SB>550</SB>). Further in the retardation film, a relation: nx>ny≥nz is satisfied between a refractive index (nx) of a phase lagging axis direction in an in-plane direction, a refractive index (ny) of a phase advancing axis direction in the in-plane direction and a refractive index (nz) of a thickness direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a retardation film used for a viewing angle compensation film or the like of a liquid crystal display device and a method for producing the same.

Since the liquid crystal display device has features such as power saving, light weight, thinness, etc., the conventional C
Instead of RT display, it has been rapidly spreading in recent years. As a general liquid crystal display device, as shown in FIG. 4, 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 104 can be exemplified. The polarizing plates 102A and 102B are configured to selectively transmit only linearly polarized light (schematically illustrated by arrows in the figure) having a vibration surface in a predetermined vibration direction. They are arranged to face each other in a crossed Nicol state so as to have a right angle relationship with each other. The liquid crystal cell 104 includes a large number of cells corresponding to the pixels, and is disposed between the polarizing plates 102A and 102B.

Here, in such a liquid crystal display device 100, the liquid crystal cell 104 has a VA (Vertical Alignment) method in which nematic liquid crystal having negative dielectric anisotropy is sealed (in the drawing, a liquid crystal director is schematically shown by a dotted line). As an example, the linearly polarized light transmitted through the incident-side polarizing plate 102A is phase-shifted when passing through the non-driven cell portion of the liquid crystal cell 104. And is blocked by the output-side polarizing plate 102B. On the other hand, when the liquid crystal cell 104 is transmitted through the portion of the driven cell, the linearly polarized light is phase-shifted, and an amount of light corresponding to the amount of the phase shift is transmitted through the polarizing plate 102B on the emission side. Emitted. Thus, a desired image can be displayed on the exit side polarizing plate 102B side by appropriately controlling the driving voltage of the liquid crystal cell 104 for each cell. The liquid crystal display device 100 is not limited to the above-described light transmission and blocking modes, and light emitted from the non-driven cell portion of the liquid crystal cell 104 is emitted from the polarizing plate on the emission side. There has also been devised a liquid crystal display device configured so that light emitted from the portion of the cell in the driving state is blocked by the polarizing plate 102B on the emission side while being emitted through 102B.

  On the other hand, the liquid crystal display device has the advantages as described above, but there is a problem of viewing angle dependency as a unique problem. The problem of viewing angle dependency is a problem that the color and contrast of a visually recognized image change between 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 is becoming more and more important as the liquid crystal display device has recently been enlarged.

  In order to improve such a problem of viewing angle dependency, various techniques have been developed so far, and a representative method is a method using a retardation film. The method using the retardation film improves the viewing angle problem by disposing the retardation film 30 having predetermined optical characteristics between the liquid crystal cell 104 and the polarizing plate 102B as shown in FIG. It is a method to do. Since this method can improve the problem of the viewing angle dependency only by incorporating the retardation film 30 in the liquid crystal display device, it has been widely used as a method for easily obtaining a liquid crystal display device having excellent viewing angle characteristics. .

As the retardation film, as shown in FIG. 5, an alignment film 42 is provided on an arbitrary transparent substrate 41, and an optically anisotropic layer 43 having liquid crystal molecules is further formed on the alignment film 42. In general, the film 43 has a configuration in which the liquid crystal molecules are aligned by the alignment regulating force of the film 43 to develop a desired refractive index anisotropy. As such a phase difference film, for example, as disclosed in Patent Document 1 or Patent Document 2, an optically anisotropic layer having a cholesteric regular molecular structure (an optically anisotropic layer exhibiting birefringence) A retardation film is disclosed in which is formed on a substrate having an alignment film. Patent Document 3 discloses a retardation film in which an optically anisotropic layer (an optically anisotropic layer exhibiting birefringence) made of a discotic compound is formed on a substrate having an alignment film.
The retardation film using such liquid crystal molecules has the advantage that the refractive index anisotropy can be arbitrarily adjusted by changing the alignment form of the liquid crystal molecules, and the liquid crystal molecules generally have an intrinsic birefringence index. Therefore, it has an advantage that it easily develops the refractive index anisotropy, so that it is excellent in industrial practicality.

By the way, the retardation film exhibits refractive index anisotropy, thereby canceling out the phase difference generated in the liquid crystal cell and improving the viewing angle dependency problem of the liquid crystal display device. For this reason, in the conventional retardation film, it has been strictly required that the retardation value be within a specific range so that the retardation can be appropriately canceled out.
However, in recent years, not only the retardation value at a specific wavelength is within a predetermined range but also the wavelength dependency of the retardation value is required to exhibit a specific behavior.
In particular, in a biaxial film having two optical axes and a uniaxial film having one optical axis in the in-plane direction, the retardation value is smaller on the short wavelength side than on the long wavelength side, so-called reverse. It is ideal to have a dispersion-type wavelength dependency.

However, the liquid crystal molecules that have been conventionally used generally have a retardation value larger on the short wavelength side than on the long wavelength side, that is, so-called positive dispersion type wavelength dependence. It was difficult to obtain a reverse dispersion retardation film by using it.
In addition, liquid crystal molecules exhibiting reverse dispersibility are being developed at the laboratory level, but they are in mass production and are far from being industrially practical.

  For this reason, it is difficult to obtain a retardation film that uses liquid crystal molecules and has a retardation value that is a positive dispersion type wavelength dependency and excellent in industrial productivity. there were.

JP-A-3-67219 JP-A-4-322223 Japanese Patent Laid-Open No. 10-312166

  The present invention has been made in view of the above problems, and has a retardation value that is smaller on the short wavelength side than on the long wavelength side, and exhibits reverse dispersion-type wavelength dependence, and is excellent in industrial productivity. The main object is to provide a retardation film.

In order to solve the above problems, the present invention is made of a resin material, and is represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. The ratio between the transparent substrate in which Y is Y <1, and the resin material and the retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is formed on the transparent substrate. An optically anisotropic layer containing an optically anisotropic material in which X represented by (Re ₄₅₀ / Re ₅₅₀ ) is X ≧ 1, and a refractive index nx in the slow axis direction in the in-plane direction; A retardation film in which a relationship of nx> ny ≧ nz is established between the refractive index ny in the fast axis direction in the in-plane direction and the refractive index nz in the thickness direction. Z represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is such that Z <1. A retardation film is provided.

According to the present invention, the optically anisotropic layer containing the optically anisotropic material in which X is X ≧ 1, the transparent substrate in which Y is Y <1, and the Z is Z <1. Thus, a retardation film having an inverse dispersion type wavelength dependency in which the retardation value is smaller on the short wavelength side than on the long wavelength side as a whole can be obtained.
In the present invention, the retardation film of the present invention is industrially produced by using an optically anisotropic material in which X is X ≧ 1, which is widely used industrially, as the optically anisotropic material. It can be made excellent.
For this reason, according to the present invention, a retardation film having a retardation value that is smaller on the short wavelength side than on the long wavelength side and having a reverse dispersion type wavelength dependency and excellent in industrial productivity is obtained. be able to.

  In the present invention, the optically anisotropic material is preferably a rod-like compound. Since the rod-shaped compound can exhibit excellent retardation by being regularly arranged, it is easy to impart desired retardation to the retardation film of the present invention by using such a rod-shaped compound. Because.

  In the present invention, the above Z is preferably in the range of 0.6 to 1.0. This is because when the Z is in such a range, the retardation film of the present invention can be suitably used as a viewing angle compensation film for a liquid crystal display device.

In the present invention, the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is preferably in the range of 0 nm <Re ₅₅₀ <300 nm. This is because the retardation value (Re ₅₅₀ ) within such a range can also make the retardation film of the present invention suitable as a viewing angle compensation film for a liquid crystal display device.

  Furthermore, in the present invention, the resin material is preferably a cellulose derivative. This is because the cellulose derivative is excellent in optical isotropy, and the use of such a cellulose derivative makes it easy to design the optical characteristics of the retardation film of the present invention.

In order to solve the above problems, the present invention is made of a resin material and has a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. Using a transparent substrate in which Y is represented as Y <1, the ratio (Re ₄₅₀ / Re ₅₅₀ ) of the retardation value at a wavelength of 450 nm (Re ₄₅₀ ) and the retardation value at a wavelength of 550 nm (Re ₅₅₀ ) is represented. By coating an optically anisotropic material in which X is X ≧ 1 and an optically anisotropic layer forming coating solution containing a solvent capable of dissolving the resin material on the transparent substrate, An optically anisotropic layer forming step for producing an optical laminated body in which an optically anisotropic layer is formed on the transparent substrate, and the optical laminated body in an in-plane direction. Stretching so that a relationship of nx> ny ≧ nz is established among the refractive index nx in the slow axis direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction. Z represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is Z <1 A method for producing a phase difference film, wherein the optical anisotropic layer forming step comprises a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation at a wavelength of 550 nm. The optically anisotropic layer is formed so that W represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) to a value (Re ₅₅₀ ) satisfies W <1. A method for producing a retardation film is provided.

  According to the present invention, the optically anisotropic layer forming step forms the optically anisotropic layer such that the W of the optical laminate has W <1, so that the Y is Even when a transparent substrate where Y <1 is used and an optically anisotropic material where X is X ≧ 1 is used, the retardation value as a whole is smaller on the short wavelength side than on the long wavelength side. A retardation film exhibiting reverse dispersion type wavelength dependency can be obtained.

  The present invention has an effect of providing a retardation film having a reverse dispersion type wavelength dependency in which the retardation value is smaller on the short wavelength side than on the long wavelength side.

The present invention relates to a retardation film and a method for producing a retardation film.
Hereinafter, the retardation film of the present invention and the method for producing the retardation film will be described in order.

In the present invention, the wavelength dependence of the retardation value may be referred to as “wavelength dispersion”. At this time, the type of chromatic dispersion in which the retardation value is larger on the short wavelength side than on the long wavelength side (that is, the retardation value is a decreasing function of the wavelength) is referred to as “normal dispersion”. A type of chromatic dispersion in which the short wavelength side is smaller than the long wavelength side (that is, the retardation value is an increase function of the wavelength) may be referred to as “reverse dispersion”.
Further, in the present invention, the ratio of the retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm to the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm (Re ₄₅₀ / Re ₅₅₀ ) is larger than 1 at a wavelength of ₄₅₀ nm to 550 nm. The chromatic dispersion means normal dispersion, and conversely that the ratio (Re ₄₅₀ / Re ₅₅₀ ) is smaller than 1 means that chromatic dispersion at wavelengths of 450 nm to 550 nm is reverse dispersion.
Re represents the refractive index in the slow axis direction in the in-plane direction of each material layer as nx, the refractive index in the fast axis direction in the in-plane direction as ny, and the refractive index in the thickness direction as nz. Sometimes, Re = (nx−ny) × d. Re ₅₅₀ means the Re value at a wavelength of 550 nm.

A. Retardation Film First, the retardation film of the present invention will be described. The retardation film of the present invention is made of a resin material and is represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) between a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. There transparent and the substrate is Y <1, is formed on the transparent substrate, the retardation value in the resin material and a wavelength 450nm and _{(Re 450),} the ratio _{(Re 450} the retardation value at a wavelength of 550 nm _{(Re 550)} / Re ₅₅₀ ), an optically anisotropic layer containing an optically anisotropic material in which X is X ≧ 1, and a refractive index nx in the slow axis direction in the in-plane direction, and in-plane A retardation film in which a relationship of nx> ny ≧ nz is established between the refractive index ny in the fast axis direction in the direction and the refractive index nz in the thickness direction. Z represented by the ratio (Re ₄₅₀ / Re ₅₅₀ ) of the retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is characterized by Z <1. Is.

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, the retardation film 10 of the present invention is made of a resin material, and the Y is formed on the transparent substrate 1 where Y is Y <1, and constitutes the transparent substrate 1. And an optically anisotropic layer 2 containing an optically anisotropic material where X ≧ 1.
In such an example, in the retardation film 10 of the present invention, the optically anisotropic layer 2 and the transparent substrate 1 are laminated so that the Z of the retardation film 10 satisfies Z <1. It is characterized by.

According to the present invention, the optically anisotropic layer containing the optically anisotropic material in which X is X ≧ 1, the transparent substrate in which Y is Y <1, and the Z is Z <1. Thus, a retardation film having an inverse dispersion type wavelength dependency in which the retardation value is smaller on the short wavelength side than on the long wavelength side as a whole can be obtained.
In the present invention, the retardation film of the present invention is industrially produced by using an optically anisotropic material in which X is X ≧ 1, which is widely used industrially, as the optically anisotropic material. It can be made excellent.
For this reason, according to the present invention, a retardation film having a retardation value that is smaller on the short wavelength side than on the long wavelength side and having a reverse dispersion type wavelength dependency and excellent in industrial productivity is obtained. be able to.

Conventionally, a retardation film used for a viewing angle compensation film for liquid crystal display, etc., which has a structure that exhibits retardation by utilizing the alignment of liquid crystal molecules, is usually wavelength dispersion of the liquid crystal molecules Since it is normal dispersion, it was difficult to obtain a retardation film in which chromatic dispersion is reverse dispersion.
In this regard, in the present invention, even when the optical anisotropic material in which X is X ≧ 1 is used for the optical anisotropic layer, the Y is Y <1 as the transparent substrate. And the retardation value is smaller on the short wavelength side than on the long wavelength side by laminating the optically anisotropic layer and the transparent substrate so that Z is Z <1. It is possible to obtain a retardation film exhibiting reverse dispersion type wavelength dependency.

The retardation film of the present invention includes at least the substrate and the optically anisotropic layer, and may have other configurations as necessary.
Hereafter, each structure used for the retardation film of this invention is demonstrated in order.

1. Optically anisotropic layer First, the optically anisotropic layer used in the present invention will be described. The optically anisotropic layer used in the present invention comprises a resin material constituting a transparent substrate, which will be described later, and a ratio (Re ₄₅₀ ) between a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. ₄₅₀ / Re ₅₅₀ ) and an optically anisotropic material in which X is X ≧ 1, and has a function of imparting a desired retardation to the retardation film of the present invention. .

(1) Optically anisotropic material The optically anisotropic material contained in the optically anisotropic layer used for this invention is demonstrated. The optically anisotropic material used in the present invention is not particularly limited as long as X is X ≧ 1, and depending on the use of the retardation film of the present invention, the level of the present invention is not limited. Those capable of imparting a desired retardation to the retardation film can be appropriately selected and used. Especially, it is preferable that said X is in the range of 1-2 for the optically anisotropic material used for this invention. In particular, in order to take advantage of the reverse dispersion characteristics of the substrate, it is preferable that X is as close to 1 as possible.

Here, X is formed on an isotropic base material such as a glass substrate on which an alignment film such as polyimide is formed and subjected to an alignment treatment, and a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation at a wavelength of 550 nm. It can be calculated by measuring the value (Re ₅₅₀ ).
The retardation (Re) is defined as Re = (nx−), which is determined by the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the thickness d. ny) × d. The slow axis direction means a direction having the largest refractive index in the in-plane direction, and the fast axis direction means a direction perpendicular to the slow axis direction in the in-plane direction.
The retardation can be measured by, for example, a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

As the optically anisotropic material used in the present invention, it is preferable to use a rod-like compound among those in which X is 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 retardation film of the present invention by using such a rod-shaped compound. Because.
Here, the “rod-shaped compound” in the present invention refers to a compound in which the main skeleton of the molecular structure is rod-shaped.

As the rod-shaped compound used in the present invention, a compound having a relatively small molecular weight is preferably used. 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 800 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 resin material constituting the transparent substrate described later, but the compound having a relatively small molecular weight as the rod-shaped compound. This is because the rod-like compound can be easily mixed with the resin material in the optically anisotropic layer.
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.

  In addition, the rod-like compound used in the present invention is preferably a liquid crystalline material exhibiting liquid crystallinity. This is because the liquid crystalline material has a property of being regularly arranged, and thus by using such a liquid crystalline material, it is easy to impart desired retardation to the retardation film of the present invention.

The liquid crystalline material used in the present invention is not particularly limited as long as a desired retardation can be imparted to the retardation film of the present invention. Examples of such a liquid crystalline material include materials exhibiting a liquid crystal phase such as a nematic phase, a cholesteric phase, and a smectic phase.
In the present invention, any material exhibiting any of these liquid crystal phases can be suitably used, but it is particularly 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.

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

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 in the present invention is a liquid crystalline material exhibiting liquid crystallinity and particularly preferably has a polymerizable functional group at the terminal. By using such a liquid crystal material, for example, they can be polymerized three-dimensionally to form a network structure, so that they have column 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 the present invention, the rod-shaped compound may be used alone or in combination of two or more. For example, when the rod-shaped compound is used by mixing 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, The polymerization density (crosslink density) and the optical characteristics can be arbitrarily adjusted by adjusting the ratio, which is preferable.

(2) Resin Material Next, the resin material contained in the optically anisotropic layer in the present invention will be described. The resin material used for this invention is the same as the resin material which comprises the transparent substrate mentioned later.
In the present invention, by containing such a resin material in the optically anisotropic layer, the refractive index nx in the slow axis direction in the in-plane direction and the refractive index ny in the fast axis direction in the in-plane direction A retardation film in which a relationship of nx> ny ≧ nz is established between the refractive index nz in the thickness direction can be easily obtained.

In the present invention, by containing such a resin material in the optically anisotropic layer, the refractive index nx in the slow axis direction in the in-plane direction and the refractive index ny in the fast axis direction in the in-plane direction The reason why a retardation film satisfying the relationship of nx> ny ≧ nz with respect to the refractive index nz in the thickness direction can be easily obtained is as follows.
That is, in order to obtain a retardation film that generally satisfies the relationship of nx> ny ≧ nz, it is necessary to regularly arrange optically anisotropic materials having optical anisotropy using an alignment film or the like. However, since the retardation film of the present invention usually has a structure in which an optically anisotropic layer is directly formed on a transparent substrate described later, the alignment film is rarely used.
However, since the optically anisotropic layer contains the resin material, the optically anisotropic layer can be subjected to an orientation treatment such as stretching. Therefore, the orientation film is not used. As a result, the optically anisotropic material can be arranged. As a result, it is easy to obtain a retardation film having a refractive index having the above relationship.

  Here, since the resin material used in the present invention will be described in detail in the section of “2. Transparent substrate” described later, description thereof is omitted here.

(3) Other compounds The optically anisotropic layer used in the present invention may contain other compounds in addition to the optically anisotropic material and the resin material. Such other compounds are not particularly limited as long as the above-described Z of the retardation film of the present invention can be maintained at Z <1. Accordingly, a compound having an arbitrary function can be used.

Examples of the other compounds used in the present invention include silicon leveling agents such as polydimethylsiloxane, methylphenylsiloxane, and organically modified siloxane; linear polymers such as polyalkyl acrylate and polyalkyl vinyl ether; fluorine-based interfaces Surfactants such as activators and hydrocarbon surfactants; fluorine leveling agents such as tetrafluoroethylene; photopolymerization initiators and the like.
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 this invention, these photoinitiators can be used 1 type or in combination of 2 or more types.

  The content of the photopolymerization initiator is not particularly limited as long as the rod-shaped compound can be polymerized in a desired time, but usually 1 to 10 parts by weight with respect to 100 parts by weight of the rod-shaped compound. Is preferably within the range of 3 parts by weight to 6 parts by weight.

  When the photopolymerization initiator is used, a photopolymerization initiation assistant can be used in combination. Examples of such photopolymerization initiation assistants include tertiary amines such as triethanolamine and methyldiethanolamine, and benzoic acid derivatives such as ethyl 2-dimethylaminoethylbenzoate and ethyl 4-dimethylamidebenzoate. Yes, but not limited to these.

  Furthermore, the following compounds can be added to the optical anisotropy 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 the stability may be improved.

(4) Optically anisotropic layer The thickness of the optically anisotropic layer used in the present invention is desired for the retardation film of the present invention depending on the optically anisotropic material and the type of transparent substrate described later. There is no particular limitation as long as the retardation can be imparted and the Z of the retardation film of the present invention is within a range where Z <1. In particular, the thickness of the optically anisotropic layer in the present invention is usually preferably in the range of 0.5 μm to 20 μm. This is because if the thickness is larger than the above range, the Z of the retardation film of the present invention may not be Z <1 depending on the type of the optically anisotropic material. Moreover, it is because it will become difficult to provide desired retardation to the retardation film of this invention when it is thinner than the said range.

2. Transparent substrate Next, the transparent substrate used in the present invention will be described. The transparent substrate used in the present invention is made of a resin material, and is represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) between a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. Y is Y <1.
In addition, the transparent substrate of the present invention has a function of setting the Z of the retardation film of the present invention to Z <1 when Y is Y <1.

The transparent substrate used in the present invention is not particularly limited as long as Y is Y <1. In particular, in the present invention, the above Y is preferably in the range of 0.3 to 1, and particularly preferably in the range of 0.5 to 0.9. When Y is in the above range, the retardation film of the present invention can be obtained by the ratio of the retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm (Re ₄₅₀ / Re _550). This is because it is easy to make Z represented by Z) such that Z <1.

Further, the retardation value of the transparent substrate used in the present invention is not particularly limited as long as Y is within a range where Y <1. Especially in this invention, it is preferable that the retardation value in 550 nm exists in the range of 0 nm-50 nm.
Here, Y can be calculated, for example, by measuring retardation values at wavelengths of 450 nm and 550 nm by the parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

The transparent substrate used in the present invention preferably has a retardation in the thickness direction (Rth) at a wavelength of 550 nm in the range of 0 nm to 100 nm.
Here, the retardation in the thickness direction (Rth) is the in-plane slow axis direction refractive index Nx, the in-plane fast axis direction refractive index Ny, the thickness direction refractive index Nz, and the transparent substrate. The thickness d (nm) is a value represented by the formula Rth = {(nx + ny) / 2−nz} × d. The value of retardation (Rth) in the thickness direction in the present invention can be measured by, for example, KOBRA-WR manufactured by Oji Scientific Instruments.

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).

Further, the thickness of the transparent substrate used in the present invention is not particularly limited as long as necessary self-supporting properties can be obtained according to the use of the retardation film of the present 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, when the thickness is larger than the above range, for example, when cutting the retardation film of the present invention, there is a case where processing waste increases or wear of the cutting blade is accelerated.

Examples of the resin material constituting such a transparent substrate include cellulose derivatives, polymethyl methacrylate, polyvinyl alcohol, polyimide, polyarylate, polyethylene terephthalate, polysulfone, polyethersulfone, amorphous polyolefin, modified acrylic polymer, polystyrene, and epoxy. Resins, polycarbonates, polyesters and the like can be mentioned.
In particular, in the present invention, it is preferable to use a cellulose derivative as the resin material. This is because the cellulose derivative is excellent in optical isotropy, and thus the use of such a cellulose derivative facilitates the design of the optical characteristics of the retardation film of the present invention.

  As the cellulose derivative, cellulose esters are preferably used, and among the cellulose esters, cellulose acylates are preferably used. 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, adhesion between the transparent substrate and the above optically anisotropic layer can be improved. It is because it can improve more.
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 constituting the triacetyl cellulose film can be determined by the above method after removing impurities such as a plasticizer contained in the film.

The configuration of the transparent substrate in the present invention is not limited to a configuration composed of a single layer, and may have a configuration in which a plurality of layers are laminated.
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.

In addition, the transparent substrate used in the present invention may be subjected to a stretching treatment. Between the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction by using the transparent substrate after being subjected to stretching treatment In addition, it is easy to obtain a retardation film that satisfies the relationship of nx> ny ≧ nz.
Here, the stretching process may be a uniaxial stretching process or a biaxial stretching process.

3. Other Configurations The retardation film of the present invention may have other configurations in addition to the optically anisotropic layer and the transparent substrate. Such other configurations are not particularly limited as long as a desired function can be imparted to the retardation film of the present invention in accordance with the use of the retardation film of the present invention.
Examples of such other configurations include a hard coat layer, an overcoat layer, an AG layer, and an AR layer.

4). Retardation film The retardation film of the present invention has a refractive index nx in the slow axis direction in the in-plane direction, a refractive index ny in the fast axis direction in the in-plane direction, and a refractive index nz in the thickness direction. The relationship of nx> ny ≧ nz is established, and Z is represented by the ratio (Re ₄₅₀ / Re ₅₅₀ ) of the retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. In which Z <1.

  The Z in the retardation film of the present invention is not particularly limited as long as it is within the range of Z <1. Especially in this invention, it is preferable that said Z exists in the range of 0.6-1.0, and it is especially preferable that it exists in the range of 0.7-0.95. This is because when the Z is in such a range, the retardation film of the present invention can be suitably used as a viewing angle compensation film for a liquid crystal display device.

  In the retardation film of the present invention, the relationship between the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction is nx> ny = It can be divided into a uniaxial retardation film having a refractive index of nz and a biaxial retardation film having a refractive index relationship of nx> ny> nz.

When the retardation film of the present invention is the uniaxial retardation film, the retardation (Re) at a wavelength of 550 nm is preferably in the range of 0 nm <Re ₅₅₀ <300 nm.
The thickness direction retardation (Rth) at a wavelength of 550 nm is preferably in the range of 0 nm to 150 nm. This is because, when the retardation (Re) and the retardation in the thickness direction (Rth) are within the above ranges, the retardation film of the present invention can be made suitable as a viewing angle compensation film for a liquid crystal display device.

On the other hand, when the retardation film of the present invention is the biaxial retardation film, the retardation (Re) at a wavelength of 550 nm is preferably in the range of 0 nm <Re ₅₅₀ <300 nm.
The thickness direction retardation (Rth) at a wavelength of 550 nm is preferably in the range of 0 nm to 300 nm. This is because, when the retardation (Re) and the retardation in the thickness direction (Rth) are within the above ranges, the retardation film of the present invention can be made suitable as a viewing angle compensation film for a liquid crystal display device.

  The retardation film of the present invention has a configuration in which the optically anisotropic layer is formed on the transparent substrate. In the present invention, the transparent substrate and the optically anisotropic layer are laminated. The embodiment may be an embodiment in which the transparent substrate and the optically anisotropic layer are laminated as independent layers, or a clear interface between the transparent substrate and the optically anisotropic layer. There may be a mode in which the optically anisotropic material is laminated so that the content of the optically anisotropic material continuously changes between the two.

  An embodiment in which the transparent substrate and the optically anisotropic layer are laminated 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 retardation film of the present invention. As illustrated in FIG. 2, the manipulating film 10 according to the present invention may have a mode in which the transparent substrate 1 and the optically anisotropic layer 2 are laminated as independent layers (FIG. 2A). ) Or there is no clear interface between the transparent substrate 1 and the optically anisotropic layer 2 ′, and the layers are laminated so that the content of the optically anisotropic material continuously changes between the two. An aspect may be sufficient (FIG.2 (b)).

  As a form of the retardation film of this invention, it can be set as a desired form according to the use etc. of the retardation film of this invention. Therefore, for example, it may be formed in a long shape and wound up in a roll shape, or may be in a sheet shape cut into a predetermined size.

5). Use of Retardation Film The retardation film of the present invention can be used as an optical compensator, an elliptically polarizing plate, a brightness enhancement plate and the like used in a liquid crystal display device.

  When the retardation film of the present invention is used as an optical compensator 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 has other optical functions. It is also possible to use it laminated with a film.

  As an example of laminating and using the retardation film of the present invention and another optical functional film, for example, a VA optical compensation film having a configuration in which the retardation film of the present invention is laminated with a negative C plate, and An IPS optical compensation film having a configuration in which the retardation film of the invention is laminated with a positive C plate can be used.

  In addition, the retardation film of the present invention is obtained by laminating a positive C plate and a liquid crystal layer containing cholesteric aligned liquid crystal molecules in this order on the retardation film of the present invention. It can also be used as an enhancement film.

  Furthermore, the retardation film of the present invention can be used for a polarizing plate by being bonded to 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, a polarizing plate having a viewing angle compensation function of a liquid crystal display device can be obtained.

  Although it does not specifically limit as said polarizer, For example, a dye type polarizer using a dichroic dye, a dichroic dye, a polyene type polarizer, etc. can be used. In general, iodine-based polarizers and dye-based polarizers are manufactured using polyvinyl alcohol.

6). Production method of retardation film The production method of 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 manufacturing method, the method demonstrated in the term of the "B. manufacturing method of retardation film" mentioned later, for example can be used.

B. Next, the retardation film of the present invention will be described. The method for producing a retardation film of the present invention comprises a resin material, and is represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) between a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. Using a transparent substrate in which Y is Y <1, the ratio of the retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm to the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is represented by Re ₄₅₀ / Re _550. By coating an optically anisotropic material in which X is X ≧ 1 and an optically anisotropic layer forming coating solution containing a solvent capable of dissolving the resin material on the transparent substrate, An optically anisotropic layer forming step of producing an optical layered body in which an optically anisotropic layer is formed on a transparent substrate, and the optical layered body are delayed in an in-plane direction. A stretching step of stretching so that a relationship of nx> ny ≧ nz is established among the refractive index nx in the phase axis direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction. A phase difference in which Z expressed by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is Z <1 A film is manufactured, and the optical anisotropic layer forming step is a ratio of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm of the optical laminate to a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm ( The optically anisotropic layer is formed so that W represented by Re ₄₅₀ / Re ₅₅₀ ) satisfies W <1.

Such a method for producing a retardation film of the present invention will be described with reference to the drawings. FIG. 3 is a schematic view showing an example of a method for producing a retardation film according to the present invention. As illustrated in FIG. 3, the method for producing a retardation film of the present invention uses a transparent substrate made of a resin material, wherein Y is Y <1 (FIG. 3A), and X is X ≧ 1. By applying on the transparent substrate 1 a coating liquid for forming an optically anisotropic layer, which contains an optically anisotropic material and a solvent capable of dissolving the resin material constituting the transparent substrate 1. An optically anisotropic layer forming step of forming the optical laminated body 20 in which the optically anisotropic layer 2 ″ is formed on the transparent substrate 1 (FIG. 3B), and the optical laminated body 20 A relationship of nx> ny ≧ nz is established among the refractive index nx in the slow axis direction in the inward direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction. It has a configuration in which the optically anisotropic layer 2 is laminated on the transparent substrate 1 by the stretching step (FIG. 3C) for stretching. It is intended to produce a retardation film 10 (FIG. 3 (d)).
In such an example, in the method for producing a retardation film of the present invention, the optical anisotropic layer forming step (FIG. 3B) is performed so that the optical laminated body 20 has W and W <1. The optically anisotropic layer 2 is formed on the transparent substrate 1, and the Z of the produced retardation film is Z <1.

According to the present invention, the optically anisotropic layer forming step includes a ratio (Re ₄₅₀ / R) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. Re ₅₅₀ ) is used to form the optically anisotropic layer so that W is W <1, so that the transparent substrate in which Y is Y <1 is used, and the X is Even when an optically anisotropic material with X ≧ 1 is used, a retardation film having a reverse dispersion type wavelength dependency in which the retardation value as a whole is smaller on the short wavelength side than on the long wavelength side is obtained. Can do.

The method for producing a retardation film of the present invention includes at least the optically anisotropic layer forming step and the stretching step.
Hereinafter, each process which comprises the manufacturing method of the retardation film of this invention is demonstrated in order.

1. Optically anisotropic layer forming step First, the optically anisotropic layer forming step used in the present invention will be described. This step is made of a resin material, uses a transparent substrate where Y is Y <1, and contains an optically anisotropic material where X is X ≧ 1 and a solvent capable of dissolving the resin material. A step of producing an optical layered body in which an optically anisotropic layer is formed on the transparent substrate by coating a coating liquid for forming an optical layer on the transparent substrate, The optically anisotropic layer is formed so that W is W <1.
Hereinafter, such an optically anisotropic layer forming step will be described.

(1) Optically anisotropic layer-forming coating solution First, the optically anisotropic layer-forming coating solution used in this step will be described. The coating liquid for forming an optically anisotropic layer used in this step contains an optically anisotropic material in which X is X ≧ 1, and a solvent capable of dissolving the optically anisotropic material and the resin material. Is.

a. Solvent The solvent used in this step is particularly limited as long as it can dissolve a resin material constituting the substrate described later and can dissolve the optically anisotropic material at a desired concentration. is not. Examples of such solvents include hydrocarbon solvents such as benzene and hexane; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and methylcyclohexanone; ether solvents such as tetrahydrofuran and 1,2-dimethoxyethane: chloroform And alkyl halide solvents such as dichloromethane; ester solvents such as methyl acetate, butyl acetate and propylene glycol monomethyl ether acetate; amide solvents such as N, N-dimethylformamide, and sulfoxide solvents such as dimethyl sulfoxide. Can do.
Of these, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and methyl cyclohexanone are preferably used in this step.

  In this step, when a transparent substrate made of a cellulose derivative is used, it is preferable to use cyclohexanone or methylcyclohexanone as the solvent.

  The solvent used in this step may be a single solvent or a mixed solvent of a plurality of solvents.

b. Optically anisotropic material Next, the optically anisotropic material used in this step will be described. As an optically anisotropic material used in the present invention, X represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. If it is X> = 1, it will not specifically limit, According to the use etc. of the phase difference film manufactured by this invention, it can select suitably and can be used. Such an optically anisotropic material is the same as that described in the above section “A. Retardation film”, and thus description thereof is omitted here.

c. Other compounds The coating liquid for forming an optically anisotropic layer used in this step contains other compounds than the above solvent and the above optically anisotropic material as long as the object of the present invention is not impaired. It may be a thing. As such another compound, a compound having a desired function can be used according to the use of the retardation film produced according to the present invention. Such other compounds are the same as those described as “other compounds” used in the optically anisotropic layer in the section “A. Retardation film” above, and thus the description thereof is omitted here. To do.

(2) Optically anisotropic layer-forming coating solution The content of the optically anisotropic material contained in the optically anisotropic layer-forming coating solution used in this step is the optically anisotropic layer in this step. Depending on the coating amount when applying the coating liquid for forming the isotropic layer on the substrate described later, the optical layered body in which W is W <1 can be produced in this step. It is not limited. Especially in this process, it is preferable that content of the said optically anisotropic material contained in the said coating liquid for optically anisotropic layer formation exists in the range of 5 mass%-80 mass%, especially It is preferably within the range of 10% by mass to 40% by mass.

(3) Transparent substrate Next, the transparent substrate used for this process is demonstrated. The transparent substrate used in the present invention is made of a resin material, and is represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) between a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. Y is Y <1.

  Here, since the transparent substrate used in this step is the same as that described in the section “A. Retardation film”, description thereof is omitted here.

(4) Method for forming optically anisotropic layer Next, in this step, the optically anisotropic layer is formed on the transparent substrate by coating the optically anisotropic layer forming coating solution on the transparent substrate. And forming an optical laminate in which W expressed by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is W <1. A manufacturing method will be described.

  In this step, as a method of coating the optically anisotropic layer forming coating solution on the transparent substrate, a predetermined amount of the optically anisotropic layer forming coating solution can be applied on the transparent substrate. The method is not particularly limited. As such a coating method, for example, gravure coating method, reverse coating method, knife coating method, dip coating method, spray coating method, air knife coating method, spin coating method, roll coating method, printing method, immersion pulling method , Curtain coating method, die coating method, casting method, bar coating method, extrusion coating method, E-type coating method, and the like.

In this step, the retardation value at a wavelength of 450 nm of the optical laminate (Re ₄₅₀ ) is usually adjusted by adjusting the coating amount of the coating liquid for forming an optically anisotropic layer onto the transparent substrate. Then, the optically anisotropic layer is formed such that W represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) to a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is W <1. For this reason, the coating amount of the coating liquid for forming an optically anisotropic layer on the transparent substrate is the type and content of the optically anisotropic material used in the coating liquid for forming an optically anisotropic layer. According to the value of Y of the transparent substrate and the like, the W may be appropriately adjusted so that W <1.

  The drying method of the coating film for forming the optically anisotropic layer may be a commonly used drying method such as a heat drying method, a reduced pressure drying method, or a gap drying method. In addition, the drying method in this step is not limited to a single method, and a plurality of drying methods may be employed, for example, by sequentially changing the drying method according to the amount of solvent remaining in the coating film. .

  When a polymerizable material is used as the optically anisotropic material, the polymerizable material is polymerized after the coating film of the optically anisotropic layer forming coating liquid is dried in this step. At this time, the method for polymerizing the polymerizable material may be arbitrarily determined according to the type of the polymerizable functional group of the polymerizable material. In particular, in this step, a method of curing by irradiation with actinic radiation is preferable.

  The actinic radiation is not particularly limited as long as it is a radiation capable of polymerizing the polymerizable material. Usually, ultraviolet light or visible light is used from the viewpoint of the ease of the apparatus. Among them, it is preferable to use irradiation light having a wavelength of 150 to 500 nm, preferably 250 to 450 nm, and more preferably 300 to 400 nm.

  As the light source of this irradiation light, low pressure mercury lamp (sterilization lamp, fluorescent chemical lamp, black light), high pressure discharge lamp (high pressure mercury lamp, metal halide lamp), short arc discharge lamp (super high pressure mercury lamp, xenon lamp, mercury xenon) Lamp). Among these, use of a metal halide lamp, a xenon lamp, a high-pressure mercury lamp, etc. is recommended. The irradiation intensity can be appropriately adjusted according to the content of the photopolymerization initiator.

  In addition, in this process, since the solvent which can melt | dissolve the resin material which comprises the said transparent substrate is used for the said coating liquid for optically anisotropic layer formation, the said coating liquid for optically anisotropic layer formation When this is coated on the transparent substrate, a part of the transparent substrate is dissolved. For this reason, the optically anisotropic layer formed by this process usually contains the optically anisotropic material and the resin material.

(5) Optical laminated body Next, the optical laminated body produced in this process is demonstrated. The optical laminate produced in this step has a configuration in which the optically anisotropic layer is laminated on the transparent substrate, and has a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a letter at a wavelength of 550 nm. W represented by the ratio (Re ₄₅₀ / Re ₅₅₀ ) to the foundation value (Re ₅₅₀ ) is W <1.

The W of the optical laminate produced in this step is not particularly limited as long as it is within the range of W <1, and can be appropriately adjusted according to the use of the retardation film produced according to the present invention. good. Especially in this process, it is preferable that said W exists in the range of 0.5-0.99, and it is preferable that it exists in the range of 0.6-0.9 especially.
This is because when the W is in such a range, the retardation film produced in the present invention can be made suitable for use as a viewing angle compensation film for a liquid crystal display device.
Here, in this step, the W is set to a predetermined value by adjusting the coating amount when the optically anisotropic layer forming coating solution is applied onto the transparent substrate as described above. Can be controlled.
The above W can be calculated, for example, by measuring retardation values at wavelengths of 450 nm and 550 nm by the parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

2. Stretching process Next, the stretching process used in the present invention will be described. In this step, the optical layered body produced in the optical anisotropic layer forming step is obtained by measuring the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the thickness. It is a process of extending | stretching so that the relationship of nx>ny> = nz may be materialized with the refractive index nz of a direction.

  In this step, the optical layered body is stretched by a refractive index nx in the slow axis direction in the in-plane direction, a refractive index ny in the fast axis direction in the in-plane direction, and a refractive index nz in the thickness direction. There is no particular limitation as long as it can be stretched so that the relationship of nx> ny ≧ nz is established. As such an aspect, an aspect (first aspect) in which the optical laminate is stretched so that a relationship of nx> ny = nz is established between nx, ny, and nz by uniaxially stretching the optical layered body. And an aspect (second aspect) in which the optical layered body is stretched so that a relationship of nx> ny> nz is established between nx, ny, and nz by biaxially stretching the optical layered body. it can.

  The method for stretching the optical laminate in the first aspect and the second aspect is not particularly limited as long as the optical laminate can be stretched to a desired stretch ratio. Examples of such a method include a roll stretching method, a long gap stretching method, a tenter stretching method, and a tubular stretching method.

  In this step, the optical laminate is usually stretched in a heated state, but the heating temperature at this time is particularly limited as long as the optical laminate can be stretched at a desired magnification. Not. In particular, in the present invention, it is usually not lower than the glass transition temperature and not higher than the melting point temperature.

As the retardation of the optical laminate stretched according to the first aspect, the retardation value (Re) at a wavelength of 550 nm is preferably in the range of 0 nm <Re ₅₅₀ <300 nm. Further, the thickness direction retardation (Rth) at a wavelength of 550 nm is preferably in the range of 0 nm to 150 nm. When the retardation (Re) and the retardation in the thickness direction (Rth) are within the above ranges, the retardation film produced according to the present invention is a uniaxial film suitable as a viewing angle compensation film for a liquid crystal display device. Because it can be done.

On the other hand, as the retardation of the optical layered body stretched by the second aspect, the retardation value at a wavelength of 550 nm is preferably in the range of 0 nm <Re ₅₅₀ <300 nm. Further, the thickness direction retardation (Rth) at a wavelength of 550 nm is preferably in the range of 0 nm to 300 nm. Since the retardation (Re) and the retardation in the thickness direction (Rth) are within the above ranges, the retardation film produced according to the present invention is suitable as a viewing angle compensation film for a liquid crystal display device. Because it can be.

3. Method for Producing Retardation Film The method for producing a phase difference film of the present invention may have other steps in addition to the optically anisotropic layer and the stretching step. As such other processes, those capable of producing a phase difference film having a desired function according to the present invention can be appropriately selected and used according to the use of the phase difference film produced according to the present invention.

  In addition, the mode in which the retardation film of the present invention is implemented is not particularly limited as long as the optically anisotropic layer forming step and the stretching step are performed. As such an embodiment, for example, an optically anisotropic layer and the stretching step may be continuously performed by a Roll to Roll process using a long transparent substrate. Alternatively, the optically anisotropic layer forming step and the stretching step may be performed while using a transparent substrate that has been processed into a sheet of a predetermined size and sequentially moving the transparent substrate.

4). Retardation Film The retardation film produced according to the present invention has a transparent substrate, an optically anisotropic layer formed on the transparent substrate and containing the resin material and the optically anisotropic material, and has a wavelength. Z represented by the ratio (Re ₄₅₀ / Re ₅₅₀ ) of the retardation value (Re ₄₅₀ ) at ₄₅₀ nm and the retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is Z <1. Especially, as for the phase difference film manufactured by this invention, it is preferable that said Z exists in the range of 0.6-1.0, and it is preferable that it exists in the range of 0.7-0.95 especially. This is because, when Z is in such a range, the retardation film produced according to the present invention can be suitably used as a viewing angle compensation film for a liquid crystal display device.

  Here, the phase difference film manufactured according to the present invention is the same as that described in the above section “A. Phase difference film”, and therefore the description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the technical idea described in the claims of the present invention has substantially the same configuration and exhibits the same function and effect regardless of the case. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to examples.

1. Example 1
(1) Optically anisotropic layer forming step A photopolymerizable liquid crystal compound (X = 1.2) represented by the following formula (1) is used as a refractive index anisotropic material, and this is 20% by mass in cyclohexanone. TAC film (manufactured by Fuji Photo Film Co., Ltd., trade name: TF80UL: Y = 0.68) by bar coating on the substrate surface so that the coating amount after drying is 1.0 g / m ² Coated.
Subsequently, the solvent was dried and removed by heating at 90 ° C. for 4 minutes, and the photopolymerizable liquid crystal compound was fixed by irradiating the coated surface with ultraviolet rays to prepare an optical laminate. At this time, W of the optical laminated body was W = 0.75.

(2) Stretching Step The optical layered body was heated on a hot plate at 120 ° C. for 5 minutes, and uniaxially stretched so that the stretch ratio was 1.20 times, thereby producing a retardation film. At this time, the relationship between the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction was nx>ny> nz.

(3) Evaluation The retardation (Re) and retardation in the thickness direction (Rth) at a wavelength of 550 nm of the produced retardation film were 21.4 nm and 77 nm, respectively, and Z was Z = 0.76.

2. Example 2
(1) Optically anisotropic layer forming step The photopolymerizable liquid crystal compound (X = 1.2) represented by the above formula (1) is used as a refractive index anisotropic material, and this is 20% by mass in cyclohexanone. TAC film (manufactured by Konica Minolta, trade name: KC4UYW: Y = 0.86) coated on the substrate surface by bar coating so that the coating amount after drying is 1.0 g / m ² Worked.
Subsequently, the solvent was dried and removed by heating at 90 ° C. for 4 minutes, and the photopolymerizable liquid crystal compound was fixed by irradiating the coated surface with ultraviolet rays to prepare an optical laminate. At this time, W of the optical laminated body was W = 0.90.

(2) Stretching process The optical layered body was heated on a hot plate at 120 ° C. for 3 minutes, and uniaxially stretched so that the stretching ratio was 1.20 times, thereby producing a retardation film. At this time, the relationship between the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction was nx>ny> nz.

(3) Evaluation The retardation (Re) and the retardation in the thickness direction (Rth) at a wavelength of 550 nm of the prepared retardation film were 22.3 nm and 51 nm, respectively, and Z was Z = 0.92.

3. Comparative Example (1) Optically anisotropic layer forming step The photopolymerizable liquid crystal compound (X = 1.2) represented by the above formula (1) was used as a refractive index anisotropic material, and this was added to cyclohexanone in an amount of 20% by mass. TAC film (manufactured by Konica Minolta, trade name: KC4UYW: Y = 0.86) by bar coating on the substrate surface so that the coating amount after drying is 4.0 g / m ² Coated.
Subsequently, the solvent was dried and removed by heating at 90 ° C. for 4 minutes, and the photopolymerizable liquid crystal compound was fixed by irradiating the coated surface with ultraviolet rays to prepare an optical laminate. At this time, W of the optical laminated body was W = 1.1.

(2) Stretching process The optical layered body was heated on a hot plate at 120 ° C. for 3 minutes, and uniaxially stretched so that the stretching ratio was 1.20 times, thereby producing a retardation film. At this time, the relationship between the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction was nx>ny> nz.

(3) Evaluation The retardation (Re) and the retardation in the thickness direction (Rth) at a wavelength of 550 nm of the produced retardation film were 20.5 nm and 180 nm, respectively, and Z was Z = 1.2.

It is the schematic which shows an example of the phase difference film of this invention. It is the schematic which shows the other example of the phase difference film of this invention. It is the schematic which shows an example of the manufacturing method of the phase difference film of this invention. It is the schematic which shows an example of the conventional liquid crystal display device. It is the schematic which shows an example of the conventional phase difference film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2, 2 ', 2''... Optically anisotropic layer 10, 10' ... Phase difference film 20 ... Optical laminated body 30 ... Phase difference film 41 ... Base material 42 ... Orientation film 43 ... Optical anisotropy Layer 100 ... Liquid crystal display device 102A, 102B ... Polarizing plate 104 ... Liquid crystal cell

Claims (6)

A transparent substrate made of a resin material and represented by a ratio Y (re ₄₅₀ / re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. When,
X formed on the transparent substrate and represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of the resin material and a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm An optically anisotropic layer containing an optically anisotropic material with X ≧ 1, and
The relationship of nx> ny ≧ nz is established among the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction. A phase difference film,
Z represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value at a wavelength of 450 nm (Re ₄₅₀ ) and a retardation value at a wavelength of 550 nm (Re ₅₅₀ ) is Z <1, Retardation film.   The retardation film according to claim 1, wherein the optically anisotropic material is a rod-shaped compound.   The retardation film according to claim 1, wherein Z is in a range of 0.6 to 1.0. The retardation film according to claim 1, wherein a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is in a range of 0 nm <Re ₅₅₀ <300 nm.   The retardation film according to any one of claims 1 to 4, wherein the resin material is a cellulose derivative. A transparent substrate made of a resin material and represented by a ratio Y (re ₄₅₀ / re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm. Use
An optically anisotropic material in which X represented by a ratio of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm (Re ₄₅₀ / Re ₅₅₀ ) is X ≧ 1, and An optically anisotropic layer is formed on the transparent substrate by coating a coating liquid for forming an optically anisotropic layer containing a solvent capable of dissolving the resin material on the transparent substrate. An optically anisotropic layer forming step for producing a laminate;
Nx> ny ≧ nz between the refractive index nx in the slow axis direction in the in-plane direction, the refractive index ny in the fast axis direction in the in-plane direction, and the refractive index nz in the thickness direction. Stretching step so that the relationship of
Producing a retardation film in which Z represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm is Z <1; A method for producing a retardation film, comprising:
The optical anisotropic layer forming step is represented by a ratio (Re ₄₅₀ / Re ₅₅₀ ) of a retardation value (Re ₄₅₀ ) at a wavelength of ₄₅₀ nm and a retardation value (Re ₅₅₀ ) at a wavelength of 550 nm of the optical laminate. The method for producing a retardation film is characterized in that the optically anisotropic layer is formed such that W satisfies W <1.

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