JP2009086260A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film suitably used as a view angle compensation film for IPS (in-plane switching) type liquid crystal display device, which can be suitably used also as a polarizing plate protective film. <P>SOLUTION: The retardation film includes a transparent substrate formed of a cellulose derivative, and an optical anisotropic layer formed on the transparent substrate, containing a bar-like compound having refractive index anisotropy, and satisfying the relation of nx<SP>1</SP>>ny<SP>1</SP>≥nz<SP>1</SP>among refractive index nx<SP>1</SP>in a slow axial direction x, refractive index ny<SP>1</SP>in an in-plane fast axial direction, and refractive index nz<SP>1</SP>in a thickness direction z in a plane. The retardation film has flexibility of ≤16 mm. <P>COPYRIGHT: (C)2009,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. 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 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, VA, IPS, OCB, and the like. In particular, today, those having the MVA and IPS drive systems 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 the method using this retardation film, the 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.

  In recent years, the method of using the retardation film as the polarizing plate protective film constituting the polarizing plate has become the mainstream, not the method of separately arranging the retardation film and the polarizing plate as illustrated in FIG. It is coming. That is, as illustrated in FIG. 6, 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. 6A) (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. 6B, the inner polarizing plate of the two polarizing plate protective films 112a and 112b. The use of polarizing plates 102A ′ and 102B ′ using the retardation film 103 as the protective film 112a has become the mainstream in recent years.

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 display. It is common technical knowledge to use a retardation film having a property as a positive C plate and a retardation film having a property as a positive A plate in the apparatus (for example, Patent Document 1).
Conventionally, as the retardation film having the property as the positive A plate, a film obtained by uniaxially stretching a film made of a cycloolefin polymer has been mainly used. Such a retardation film is disclosed in Patent Document 2, for example.
However, as described above, in recent years, it has become common to use a retardation film as a polarizing plate protective film, and the retardation film made of the cycloolefin-based polymer has poor adhesion to a polarizer. There was a problem. For this reason, in order to use the retardation film composed of the cycloolefin polymer as a polarizing plate protective film, it is essential to use a polarizer and another layer having adhesiveness with the cycloolefin polymer in combination. Therefore, it is not always desirable as a retardation film that can be used as a polarizing plate protective film.

JP 2002-296424 A JP 2002-174725 A

  The present invention has been made in view of such problems, and is a retardation film that is suitably used as a viewing angle compensation film for an IPS liquid crystal display device, and is also suitable for use as a polarizing plate protective film. Another object of the present invention is to provide a retardation film.

In order to solve the above-mentioned problems, the present invention includes a transparent substrate made of a cellulose derivative, a rod-shaped compound formed on the transparent substrate and having refractive index anisotropy, and an in-plane slow axis direction x refraction. rate nx ^1, the refractive index ny ¹ in fast axis direction, a phase difference film having an optically anisotropic layer relationship ^{nx 1>} ny 1 ≧ nz 1 between the refractive index nz ¹ in the thickness direction z is satisfied There,
A retardation film characterized by having a flexibility of 16 mm or less is provided.

According to the present invention, the transparent substrate is made of a cellulose derivative, and the optically anisotropic layer has a refractive index nx ¹ in the in-plane slow axis direction x and a refractive index in the fast axis direction. By using a material having a property of so-called optically A plate or B plate in which a relationship of nx ¹ > ny ¹ ≧ nz ¹ is established between ny ¹ and the refractive index nz ^{1 in} the thickness direction z. A retardation film that is suitably used as a viewing angle compensation film for an IPS liquid crystal display device and has excellent adhesion to a polarizer can be obtained.
In addition, since the retardation film of the present invention is excellent in punching workability because the bending rate is in the above range, a polarizing plate is produced using the retardation film of the present invention as a polarizing plate protective film. The production efficiency can be improved.
Therefore, according to the present invention, a retardation film that is suitably used as a viewing angle compensation film for an IPS liquid crystal display device and that is suitable for use as a polarizing plate protective film is obtained. be able to.

  The retardation film of the present invention preferably has an Nz factor in the range of 1.0 to 3.0. This is because the retardation film of the present invention can be made more suitable as an optical compensation film used in an IPS liquid crystal display device.

In the retardation film of the present invention, the liquid crystal material having homeotropic alignment formed on the transparent substrate or the optically anisotropic layer is contained, and in any x and y directions orthogonal to each other in the in-plane direction. It is preferable that a retardation layer satisfying a relationship of nx ² ≦ ny ² <nz ² is formed between the refractive indexes nx ² and ny ² and the refractive index nz ^{2 in} the thickness direction. This is because the viewing angle characteristics of the IPS liquid crystal display device can be improved by using only the retardation film of the present invention.

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

  The retardation film of the present invention can be suitably used as a viewing angle compensation film for an IPS liquid crystal display device, and can also be advantageously used as a polarizing plate protective film.

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

As described above, the retardation film of the present invention contains a transparent substrate made of a cellulose derivative, a rod-shaped compound having a refractive index anisotropy formed on the transparent substrate, and has an in-plane slow axis direction x. refractive index nx ^1, the refractive index ny ¹ in fast axis direction, those having an optical anisotropic layer relationship ^{nx 1>} ny 1 ≧ nz 1 is established between the refractive index nz ¹ in the thickness direction z Thus, the flexibility is 16 mm or less.

Such a retardation film of the present invention will be described with reference to the drawings. FIG. 1 is a schematic perspective 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 a transparent substrate 1 made of a cellulose derivative and a rod-shaped compound A formed on the transparent substrate 1 and having refractive index anisotropy. Optical anisotropy in which a relationship of nx ¹ > ny ¹ ≧ nz ¹ is established among the refractive index nx ¹ in the slow axis direction x, the refractive index ny ^{1 in the} fast axis direction, and the refractive index nz ^{1 in} the thickness direction z. And the conductive layer 2.
In such an example, the retardation film 10 of the present invention is characterized in that the flexibility of the retardation film 10 as a whole is 16 mm or less.

According to the present invention, the transparent substrate is made of a cellulose derivative, and the optically anisotropic layer has a refractive index nx ¹ in the in-plane slow axis direction x and a refractive index in the fast axis direction. By using a material having a property of so-called optically A plate or B plate in which a relationship of nx ¹ > ny ¹ ≧ nz ¹ is established between ny ¹ and the refractive index nz ^{1 in} the thickness direction z. A retardation film that is suitably used as a viewing angle compensation film for an IPS liquid crystal display device and has excellent adhesion to a polarizer can be obtained.
In addition, since the retardation film of the present invention is excellent in punching workability because the bending rate is in the above range, a polarizing plate is produced using the retardation film of the present invention as a polarizing plate protective film. The production efficiency can be improved.
Therefore, according to the present invention, a retardation film that is suitably used as a viewing angle compensation film for an IPS liquid crystal display device and that is suitable for use as a polarizing plate protective film is obtained. be able to.

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

1. Transparent substrate First, the transparent substrate used for this invention is demonstrated. The transparent substrate used in the present invention is made of a cellulose derivative. Since the retardation film of the present invention is made of such a cellulose derivative as a transparent substrate, it has excellent adhesion to the polarizer and has flexibility within the range specified by the present invention. It becomes possible.
Hereinafter, such a transparent substrate will be described in detail.

  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 (testing method for cellulose acetate, etc.). 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.

2. Optically anisotropic layer Next, the optically anisotropic layer used in the present invention will be described. The optically anisotropic layer used in the present invention is formed on the transparent substrate, contains a rod-shaped compound having refractive index anisotropy, and further has a refractive index nx ¹ in the in-plane slow axis direction x, A relationship of nx ¹ > ny ¹ ≧ nz ¹ is established between the refractive index ny ^{1 in} the axial direction and the refractive index nz ^{1 in} the thickness direction z. Since the retardation film of the present invention uses such an optically anisotropic layer, even if the transparent substrate is made of a cellulose derivative, an optically positive A plate or It can be made to have properties as a B plate.
Hereinafter, such an optically anisotropic layer will be described in detail.

(1) Rod-shaped compound The rod-shaped compound used for this invention is demonstrated. The rod-shaped compound used in the present invention has a refractive index anisotropy in the molecule, and is contained in the optical anisotropic layer in a predetermined manner, whereby the above-mentioned nx ¹ > ny is contained in the optical anisotropic layer. ^The optical characteristic is not particularly limited as long as the optical characteristic that satisfies the relationship ¹ ≧ nz ¹ can be imparted. Among them, the rod-shaped compound used in the present invention preferably has a retardation wavelength dependency of a positive dispersion type, and particularly preferably has a Re ratio in the range of 1 to 2.
Here, the Re ratio of the rod-shaped compound is such that an alignment film such as polyimide is formed, a layer composed of the rod-shaped compound is formed on an isotropic substrate such as a glass substrate subjected to alignment treatment, and the Re ratio at a wavelength of 450 nm is obtained. It can be calculated by measuring (Re ₄₅₀ ) and Re (Re ₅₅₀ ) at a wavelength of 550 nm.

  In addition, the rod-shaped compound used in the present invention preferably has a structure in which a polymerizable functional group and a mesogenic group are bonded via an alkyl chain. A typical example of a compound having such a structure is a polymerizable liquid crystal compound.

  Examples of the polymerizable liquid crystal compound used in the present invention include a polyfunctional polymerizable liquid crystal compound having a plurality of polymerizable functional groups and a monofunctional polymerizable liquid crystal compound having a single polymerizable functional group. In the present invention, any of the polyfunctional polymerizable liquid crystal compound and the monofunctional polymerizable liquid crystal compound can be suitably used. In particular, in the present invention, it is preferable to use the monofunctional polymerizable liquid crystal compound. The monofunctional polymerizable liquid crystal compound has a higher degree of freedom of the mesogenic group than the polyfunctional polymerizable liquid crystal compound, and in the case of performing a stretching treatment after polymerization, a crosslinking point that restricts and inhibits the reorientation of molecules. Since the density of the polymer is low and the orientation of the molecule (the electric dipole efficiency vector) becomes easy, by using such a monofunctional polymerizable liquid crystal compound, the optically anisotropic layer can be made to exhibit more optical anisotropy. It is because it can be made excellent.

The polymerizable liquid crystal compound is one in which the mesogenic group and the polymerizable functional group are bonded by an alkyl chain, and the number of carbon atoms constituting the alkyl chain is preferably 4 or more. It is preferably within the range of 12, and particularly preferably within the range of 6 to 10. When the number of carbon atoms is within the above range, the mesogenic group provided in the polymerizable liquid crystal compound can have a higher degree of freedom in molecular orientation. It is because it can improve further.
In the present invention, the “number of carbon atoms constituting the alkyl chain” means the number of carbon atoms constituting the main chain portion of the alkyl group that binds the polymerizable functional group and the mesogenic group. . Therefore, for example, when the alkyl group is a branched chain having a side chain, the number of carbon atoms constituting the side chain is not included in the “number of carbon atoms constituting the alkyl chain”.

  The alkyl chain used in the present invention is not particularly limited as long as the carbon number is within the above range. Therefore, the alkyl chain used in the present invention may be a straight chain having no side chain or a branched chain having a side chain. Moreover, the saturated alkyl chain which consists only of a saturated bond may be sufficient, or the unsaturated alkyl chain which has an unsaturated bond may be sufficient. Furthermore, it may have a structure in which an arbitrary functional group is bonded to a hydrocarbon chain.

  Moreover, when using the said polyfunctional polymerizable liquid crystal compound in this invention, all the carbon number which comprises the alkyl chain couple | bonded with each polymeric functional group may be the same, or may differ.

The mesogenic group used in the polymerizable liquid crystal compound is not particularly limited as long as it can give a predetermined optical anisotropy to the optically anisotropic layer by arranging regularly. In particular, in the present invention, those having a rod-like structure as the mesogenic group are usually used. This is because mesogenic groups having a rod-like structure can easily exhibit optical anisotropy by being regularly arranged.
Here, the “rod-like structure” means a compound in which the main skeleton of the structure of the mesogen group is a rod-like structure.

  Further, the mesogenic group used in the present invention is preferably a liquid crystalline compound among the mesogenic groups having the rod-like structure. This is because by using a mesogenic group exhibiting liquid crystallinity, it becomes easy to impart desired optical anisotropy to the optically anisotropic film used in the present invention.

  When using what has liquid crystallinity as said mesogenic group, the kind of liquid crystal phase which the said mesogenic group shows is not specifically limited. Examples of such a liquid crystal phase include a nematic phase, a cholesteric phase, and a smectic phase. In the present invention, any mesogenic group exhibiting any of these liquid crystal phases can be preferably used, but among them, a mesogenic group exhibiting a nematic phase is preferably used. This is because mesogenic groups exhibiting a nematic phase can be easily arranged regularly as compared with mesogenic groups exhibiting other liquid crystal phases.

  Specific examples of such a mesogenic group include those in which two or more ring structures represented by the following formulas (1) to (11) are connected directly or via a bonding group.

Here, any hydrogen in the ring structures of the above formulas (1) to (11) has halogen, —CN, —CF ₃ , —CF ₂ H, —NO ₂ , or 1 to 7 carbon atoms. It may be replaced with alkyl. In the alkyl having 1 to 7 carbon atoms, arbitrary —CH ₂ — may be replaced by —O—, —CH═CH— or —C≡C—, and arbitrary hydrogen may be replaced by halogen. May be.

  The linking group is not particularly limited as long as it can bond the ring structure at a predetermined distance. Examples of such a linking group include those represented by the following formulas (12) to (23).

  The polymerizable functional group used in the polymerizable liquid crystal compound is not particularly limited as long as it can be polymerized by performing a desired polymerization treatment, depending on the method for producing the retardation film of the present invention. Can be appropriately selected and used. Examples of such polymerizable functional groups 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) can be given. Moreover, an epoxy group etc. can be mentioned as a specific example of the said cation polymerizable functional group. In addition, examples of the polymerizable functional group used in the present invention include an isocyanate group and an unsaturated triple bond. In the present invention, among these polymerizable functional groups, a functional group having an ethylenically unsaturated double bond is preferably used from the viewpoint of the process.

  When the polyfunctional polymerizable liquid crystal compound is used as the polymerizable liquid crystal compound used in the present invention, all the polymerizable functional groups used in the polyfunctional polymerizable liquid crystal compound may be the same or different. It may be.

The polymerizable liquid crystal compound used in the present invention is preferably a compound having a relatively small molecular weight. 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 preferable. The reason is as follows. That is, the optically anisotropic layer used in the present invention contains the rod-shaped compound and a cellulose derivative constituting the transparent substrate described later, but a compound having a relatively small molecular weight as the polymerizable liquid crystal compound. When used, the polymerizable liquid crystal compound is easily mixed with the cellulose derivative in the optically anisotropic layer. For this reason, it is because the haze of the said optically anisotropic layer can be made smaller by using the polymeric liquid crystal compound whose molecular weight is in the said range.
The molecular weight of the polymerizable liquid crystal compound means a molecular weight in a monomer state before polymerization.

  Specific examples of the polymerizable liquid crystal compound used in the present invention include compounds represented by the following formula.

  Here, the polymerizable liquid crystal compounds represented by the above formulas (I), (IV) and (V) are, for example, DJBroer et al., Makromol Chem. 190, 3201-3215 (1989) or DJBroer et al., Makromol Chem. It can be prepared according to the method disclosed in .190,2250 (1989) or by a method similar thereto. In addition, the polymerizable liquid crystal compounds represented by the chemical formulas (II) and (III) can be prepared by the method disclosed in DE195, 04, 224, for example.

  Moreover, as an example of the polymeric liquid crystal compound used for this invention, the compound represented by a following formula can be illustrated, for example.

  The polymerizable liquid crystal compound used in the present invention may be only one type or two or more types. When two or more kinds of polymerizable liquid crystal compounds are used, the polymerizable liquid crystal compound may be selected only from the monofunctional polymerizable liquid crystal compound, or may be selected only from the polyfunctional polymerizable liquid crystal compound. Or you may select from both the said monofunctional polymerizable liquid crystal compound and the said polyfunctional polymerizable liquid crystal compound. In particular, in the present invention, it is preferable to select at least the monofunctional polymerizable liquid crystal compound. This is because the monofunctional polymerizable liquid crystal compound is excellent in optical anisotropy as described above.

(2) Arrangement form of rod-shaped compound As an embodiment in which the rod-shaped compound is contained in the optically anisotropic layer, the refractive index nx ¹ in the in-plane slow axis direction x, There is no particular limitation as long as it is an aspect capable of providing an optical characteristic in which a relationship of nx ¹ > ny ¹ ≧ nz ¹ is established between the refractive index ny ^{1 in} the phase axis direction and the refractive index nz ^{1 in} the thickness direction z. In particular, in the present invention, it is preferable that the rod-like compound forms an irregular random homogeneous orientation in the optically anisotropic layer. This is because it becomes easy to impart the above-described optical characteristics to the optically anisotropic layer.
Here, the irregular random homogeneous orientation represents one aspect of the arrangement state of the rod-like compounds, and is a novel arrangement aspect that can achieve the optical characteristics described above using the rod-like compounds.
Hereinafter, such irregular random homogeneous orientation will be described in detail.

The irregular random homogeneous orientation has at least the following three characteristics. That is, the anomalous random homogeneous orientation in the present invention is
First, when the optically anisotropic layer is viewed from the direction perpendicular to the surface of the optically anisotropic layer, the arrangement direction of the rod-shaped compounds has anisotropy (hereinafter simply referred to as “anisotropic”). ),
Second, the size of the domain formed by the rod-shaped compound in the optically anisotropic layer is smaller than the wavelength in the visible light region (hereinafter sometimes simply referred to as “dispersibility”);
Thirdly, the rod-like compound molecules in the optically anisotropic layer are present on a plane parallel to the surface of the optically anisotropic layer (in the example of FIG. 1, a plane parallel to the xy plane) (hereinafter simply “ Sometimes referred to as “in-plane orientation”),
At least.

  Next, the irregular random homogeneous orientation in the present invention will be described with reference to the drawings. 2A is a front view of the retardation film of the present invention from the direction perpendicular to the surface (xy plane) of the optically anisotropic layer represented by Z in FIG. 1 described above (xy plane). It is the schematic in the case. 2B and 2C are cross-sectional views taken along line X-X 'in FIG.

First, “anisotropy” possessed by the irregular random homogeneous orientation in the present invention will be described with reference to FIG. As shown in FIG. 2A, the “anisotropic” is an optically anisotropic layer when the retardation film 10 of the present invention is viewed from the direction perpendicular to the surface of the optically anisotropic layer 2. 2 shows that rod-shaped compounds A are arranged in one direction on average.
That is, when the probability distribution function (probability density function) of each rod-like compound molecule oriented in each direction in the xy plane (surface of the optically anisotropic layer) is obtained, the probability distribution function is expressed in a specific direction (FIG. 2). In this example, the distribution is such that it has a peak (average orientation direction) in the x direction and has a predetermined dispersion (variation width in the orientation direction) in the orientation direction. Furthermore, in other words, the orientation direction of the major axis of the rod-like compound molecule is not that all the molecules are aligned in parallel, but that is not completely messy. An example of this is shown in FIG.
Here, in the present invention, in order to explain the arrangement direction of the rod-shaped compound A, the molecular major axis direction (hereinafter referred to as a molecular axis) represented by a in FIG. . Therefore, the fact that the rod-shaped compounds are arranged in one direction means that the molecular axis a of the rod-shaped compound A contained in the optically anisotropic layer is oriented in one direction on average.
As described above, the “anisotropy” in the present invention does not require that the rod-like compounds are completely arranged in one direction, and the arrangement directions of the rod-like compounds are arranged in one direction on average. It is sufficient that the optical anisotropic layer is provided with desired optical biaxiality. The degree of such anisotropy will be described later.

  Next, the “dispersibility” possessed by the irregular random homogeneous orientation in the present invention will be described with reference to FIG. As shown in FIG. 2A, the above “dispersibility” means that when the rod-shaped compound A forms the domain b in the optically anisotropic layer 2, the size of the domain b is larger than the wavelength in the visible light region. Is also small. In the present invention, the smaller the size of the domain b is, the more preferable, and the state where the rod-like compound is dispersed in a single molecule is the most preferable.

Next, the “in-plane orientation” possessed by the irregular random homogeneous orientation in the present invention will be described with reference to FIG. As shown in FIG. 2B, the above-mentioned “in-plane orientation” indicates that the rod-shaped compound A in the optically anisotropic layer 2 has a molecular axis “a” in the normal direction Z of the optically anisotropic layer 2 (see FIG. 1). It is oriented so as to be substantially perpendicular to the z direction in FIG. 1 (substantially parallel to the xy plane in FIG. 1). The “in-plane orientation” in the present invention is such that the molecular axes a of all rod-like compounds A in the optically anisotropic layer 2 are substantially in the normal direction Z as shown in FIG. For example, as shown in FIG. 2 (c), a rod-shaped compound A whose molecular axis a ′ is not perpendicular to the normal direction Z is formed in the optically anisotropic layer 2 as shown in FIG. Even if it exists, the case where the average direction of the molecular axis a of the rod-shaped compound A existing in the optically anisotropic layer 2 is substantially perpendicular to the normal direction Z is included.
That is, in FIG. 2, even if the molecular axis direction of each rod-like compound molecule has a distribution, the molecular axis direction averaged over all the molecules of the rod-like compound exists substantially in the xy plane.

  As described above, the irregular random homogeneous orientation in the present invention is characterized by exhibiting the above-mentioned “anisotropy”, “dispersibility” and “in-plane orientation”, but the rod-shaped compound forms an irregular random homogeneous orientation. This can be confirmed by the following method.

First, a method for confirming “anisotropy” possessed by the irregular random homogeneous orientation in the present invention will be described. The “anisotropy” can be confirmed by evaluating the in-plane retardation of the optically anisotropic layer (hereinafter sometimes simply referred to as “Re ¹ ”).

The fact that the rod-shaped compound has the above “anisotropy” means that the in-plane retardation (Re ¹ ) value of the optically anisotropic layer indicates that the optically anisotropic layer exhibits optical biaxiality. Can be confirmed by being within a possible range. In particular, in the present invention, the in-plane retardation (Re ¹ ) of the optically anisotropic layer is preferably in the range of 5 nm to 300 nm, and more preferably in the range of 10 nm to 200 nm. It is particularly preferable that the thickness is in the range of 40 nm to 150 nm.
Here, Re ¹ is a value represented by the equation Re = (nx ¹ −ny ¹ ) × d ^{1 based on} nx ¹ , ny ¹ and the thickness d ¹ (nm) of the optically anisotropic layer. is there.

The in-plane retardation (Re ¹ ) of the optically anisotropic layer is obtained, for example, by subtracting the in-plane retardation of the layer other than the optically anisotropic layer from the in-plane retardation (Re) of the retardation film. be able to. That is, in-plane retardation measurement was performed on the entire retardation film and the optically anisotropic layer excised from the retardation film, and the surface of the optically anisotropic layer was obtained by subtracting the latter measured value from the former measured value. Internal retardation can be obtained. In-plane retardation can be measured by, for example, the parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

When the rod-shaped compound having a rod-shaped main skeleton to which two or more benzene rings are bonded is used, the “anisotropy” refers to the in-plane direction of the optically anisotropic layer. This can also be confirmed by measuring the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ). Namely, the Raman peak intensity ratio in the in-plane slow axis direction of the optically anisotropic layer in the present invention ^{(1605cm -1} / ^2942cm -1) is, fast axis direction Raman peak intensity ratio of the plane (1605 cm ^-1 / 2942 cm ⁻¹ ), it can be confirmed that the above “anisotropy” is provided. In particular, in the present invention, the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ) in the slow axis direction in the plane of the optically anisotropic layer is the Raman peak intensity ratio (1605 cm) in the fast axis direction in the plane. preferably ^-1 / ^{2942cm -1)} is 1.1 times or more, preferably in particular 1.15 times or more, preferably further in the range of 1.20 ～3.00 times.

Here, the "Raman peak intensity ratio ^{(1605cm -1} / 2942cm -1)" means the ratio of the in the Raman spectrum (spectral light intensity of the spectral light intensity / wave number 2942cm ^-1 in wavenumber 1605 cm ^-1) To do.

Here, the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ) in the present invention is obtained by using, for example, a laser Raman spectrophotometer (JASCO: NRS-3000) and the linearly polarized electric field vibration surface is optically different. Injecting measurement light so that it coincides with the slow axis direction and the fast axis direction in the plane of the isotropic layer, the Raman spectrum for each of the fast axis direction in the plane and the fast axis direction in the plane Can be obtained by evaluating the peak intensity of 1605 cm ⁻¹ (C—H bond-derived peak) and the peak intensity of 2942 cm ⁻¹ (benzene ring-derived peak). The conditions for measuring a Raman spectrum using the laser Raman spectrophotometer are an exposure time of 15 seconds, an integration count of 8 times, and an excitation wavelength of 532.11 nm.

  Next, a method for confirming “dispersibility” of the irregular random homogeneous orientation in the present invention will be described. The “dispersibility” can be confirmed by the fact that the haze value of the optically anisotropic layer is within the range indicating that the domain size of the rod-shaped compound is not more than the wavelength in the visible light region. Among them, in the present invention, the haze value of the optically anisotropic layer is preferably in the range of 0% to 5%, particularly preferably in the range of 0% to 1%, and more preferably 0% to It is preferable to be within the range of 0.5%.

  Here, the haze value of the optically anisotropic layer can be obtained, for example, by subtracting the haze value of a layer other than the optically anisotropic layer from the haze value of the retardation film. That is, the haze value of the optically anisotropic layer is determined by measuring the haze value of the whole retardation film and the optically anisotropic layer cut from the retardation film, and subtracting the latter haze value from the former haze value. Can be requested. As the haze value, a value measured according to JIS K7105 is used.

  The size of the domain in the present invention is less than or equal to the wavelength of visible light, but the specific size is preferably 380 nm or less, more preferably 350 nm or less, particularly 200 nm or less. Preferably there is. In the present invention, since the rod-shaped compound is preferably monomolecularly dispersed, the lower limit value of the domain size is the size of a single molecule of the rod-shaped compound. The size of such a domain can be evaluated by observing the optically anisotropic layer with a polarizing microscope, AFM, SEM, or TEM.

Next, a method for confirming “in-plane orientation” possessed by the irregular random homogeneous orientation in the present invention will be described. The above “in-plane orientation” means that the in-plane retardation (Re ¹ ) of the optically anisotropic layer constituting the retardation film of the present invention is in the above-described range, and the optically anisotropic layer in the present invention. Can be confirmed by having a retardation in the thickness direction (hereinafter sometimes simply referred to as “Rth ¹ ”) that can exhibit optical biaxiality. In particular, Rth ¹ of the optically anisotropic layer in the present invention is preferably in the range of 50 nm to 400 nm, more preferably in the range of 75 nm to 200 nm, and particularly in the range of 75 nm to 150 nm. It is preferable.
Here, the Rth ¹ is a value represented by the formula Rth ¹ = {(nx ¹ + ny ¹ ) / 2−nz ¹ } × d ^{1 by} the nx ¹ , ny ¹ , nz ¹ , and d ^1. is there.
The Rth ¹ value in the present invention indicates the absolute value of the value represented by the above formula.

For the retardation in the thickness direction (Rth ¹ ) of the optically anisotropic layer, for example, the retardation in the thickness direction indicated by the layers other than the optically anisotropic layer is subtracted from the retardation (Rth) in the thickness direction of the retardation film. Can be obtained. That is, the retardation film in the thickness direction was measured for the whole retardation film and the optically anisotropic layer cut out from the retardation film, and the optically anisotropic layer was obtained by subtracting the latter measured value from the former measured value. The retardation in the thickness direction can be obtained. The retardation in the thickness direction can be measured, for example, by the parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

When the rod-shaped compound having a rod-shaped main skeleton to which two or more benzene rings are bonded is used, the “in-plane orientation” is the thickness direction of the optically anisotropic layer. This can also be confirmed by measuring the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ). That is, the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ) in the direction perpendicular to the thickness direction in the cut surface in the thickness direction of the optically anisotropic layer is the Raman peak intensity ratio in the direction parallel to the thickness direction. By being larger than (1605 cm ⁻¹ / 2942 cm ⁻¹ ), it can be confirmed that the above “in-plane orientation” is provided. In particular, in the present invention, the Raman peak intensity ratio in the direction perpendicular to the thickness direction in a cross section in the thickness direction of the optically anisotropic layer ^{(1605cm -1} / ^2942cm -1) is parallel to the thickness direction direction Is preferably 1.1 times or more of the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ), particularly preferably 1.50 times or more, and more preferably in the range of 1.20 times to 3.00 times. It is preferable to be within.

Here, the "Raman peak intensity ratio ^{(1605cm -1} / 2942cm -1)" means the ratio of the in the Raman spectrum (spectral light intensity of the spectral light intensity / wave number 2942cm ^-1 in wavenumber 1605 cm ^-1) To do.

Here, the Raman peak intensity ratio (1605 cm ⁻¹ / 2942 cm ⁻¹ ) in the present invention is obtained by using, for example, a laser Raman spectrophotometer (JASCO: NRS-3000) and the linearly polarized electric field vibration surface is optically different. The measurement light is incident on the cut surface in the thickness direction of the anisotropic layer so as to coincide with the parallel direction and the vertical direction with respect to the thickness direction, whereby the parallel direction and the vertical direction with respect to the thickness direction in the thickness direction cut surface After measuring the Raman spectrum for each of the above, the peak intensity of 1605 cm ⁻¹ (C—H bond-derived peak) and the peak intensity of 2942 cm ⁻¹ (benzene ring-derived peak) can be determined. The conditions for measuring a Raman spectrum using the laser Raman spectrophotometer are an exposure time of 15 seconds, an integration count of 8 times, and an excitation wavelength of 532.11 nm.
The Raman peak intensity ratio of the optically anisotropic layer can be determined by, for example, preparing a slice by cutting a retardation film in the thickness direction and then measuring a Raman spectrum of only a portion corresponding to the optically anisotropic layer. It can be determined by measuring.

(3) Other compounds The optically anisotropic layer in the invention may contain other compounds in addition to the rod-shaped compound. Such other compounds are not particularly limited as long as they do not impair the optical properties of the optically anisotropic layer. As said other compound in this invention, the polymeric material generally used for a hard-coat agent can be mentioned, for example.

  Examples of the polymerizable material include polyester (meth) acrylates obtained by reacting (meth) acrylic acid with polyester prepolymers obtained by condensing polyhydric alcohols with monobasic acids or polybasic acids; Polyurethane (meth) acrylate obtained by reacting a compound having a polyol group and 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, novolac type epoxy resin, polycarboxylic acid polyglycidyl ester, polyol polyglycidyl ether, aliphatic or cycloaliphatic epoxy resin, amino group epoxy resin, triphenolmethane type epoxy resin, dihydroxybenzene type epoxy resin and the like , (Meta) It may be mentioned a photopolymerizable liquid crystal compound having an acryl group or a methacryl group or the like; photopolymerizable compounds such as epoxy (meth) acrylates obtained by reacting an acrylic acid.

  In the present invention, when the optically anisotropic layer is directly formed on the transparent substrate, the optically anisotropic layer preferably contains a cellulose derivative constituting the transparent substrate. Thereby, in the retardation film of the present invention, the adhesion between the transparent substrate and the optically anisotropic layer can be improved.

(4) Optically anisotropic layer It is preferable that the optically anisotropic layer in this invention is directly formed on the transparent substrate mentioned later. This is because the optically anisotropic layer is directly formed on the transparent substrate, whereby the retardation film of the present invention can be excellent in adhesion between the optically anisotropic layer and the transparent substrate.
Thus, it is understood that the adhesion mechanism between the two is improved by the direct formation of the optically anisotropic layer on the transparent substrate due to the following mechanism. That is, when the optically anisotropic layer is directly formed on the transparent substrate, rod-like molecules contained in the optically anisotropic layer penetrate into the transparent substrate from the surface of the transparent substrate, or the optically anisotropic layer Depending on the solvent used in forming the transparent substrate, the surface of the transparent substrate can be dissolved and the rod-shaped compound and the transparent substrate can be mixed, so that there is a clear interface at the bonded portion between the transparent substrate and the optically anisotropic layer. It does not exist, and both are “mixed”. For this reason, it is considered that the adhesion is remarkably improved as compared with the adhesion by the conventional interface interaction.

  The thickness of the optically anisotropic 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 optically anisotropic layer according to the kind of the rod-shaped compound. In particular, in the present invention, the thickness of the optically anisotropic layer is preferably in the range of 0.5 μm to 10 μm, more preferably in the range of 0.5 μm to 5 μm, particularly in the range of 1 μm to 3 μm. It is preferable to be within. If the thickness of the optically anisotropic layer is larger than the above range, “in-plane orientation”, which is one of the characteristics of irregular random homogeneous orientation, is impaired, and the desired optical characteristics may not be obtained. Because. On the other hand, if the thickness is smaller than the above range, the target optical characteristics may not be obtained depending on the kind of the rod-shaped compound.

3. Other Configurations The retardation film of the present invention has at least the transparent substrate and the optically anisotropic layer, but may have other configurations as necessary. In particular, in the present invention, as such another configuration, any liquid crystal material having homeotropic alignment formed on the transparent substrate or the optically anisotropic layer is included, and any arbitrary orthogonal to each other in the in-plane direction. It is preferable that a retardation layer satisfying a relationship of nx ² ≦ ny ² <nz ² is formed between the refractive indexes nx ² and ny ^{2 in the} x and y directions and the refractive index nz ^{2 in} the thickness direction. This is because the viewing angle characteristics of the IPS liquid crystal display device can be improved by using only the retardation film of the present invention.

The case where such a retardation layer is used in the retardation film of the present invention will be described with reference to the drawings. FIG. 3 is a schematic cross-sectional view showing an example in which a retardation layer is used in the retardation film of the present invention. As illustrated in FIG. 3, the retardation film 10 of the present invention contains a liquid crystal material in which homeotropic alignment is formed on the transparent substrate 1, and has arbitrary x and y directions orthogonal to each other in the in-plane direction. The retardation layer 3 in which a relationship of nx ² ≦ ny ² <nz ² is established between the refractive indexes nx ² and ny ² and the refractive index nz ^{2 in} the thickness direction may be formed.

Here, in FIG. 3, the example in which the retardation layer is formed on the transparent substrate has been described as an embodiment in which the retardation layer is used in the retardation film of the present invention. The aspect in which the retardation layer is used is not limited to this, and an aspect in which the retardation layer is formed on the optically anisotropic layer may be used.
Hereinafter, the retardation layer used in the present invention will be described in detail.

(1) Liquid crystal material First, the liquid crystal material will be described. The liquid crystal material is not particularly limited as long as it 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. It is not something. 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 can be given.
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 present 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 case where the second homeotropic liquid crystal material is used in the present invention, in order to align the homeotropic liquid crystal material in the retardation layer, the alignment usually has an alignment regulating force for homeotropic alignment of the liquid crystal material. A method using an alignment control compound having a function of using a layer or a homeotropic alignment of the liquid crystal material in the retardation layer is used. The orientation control compound is described in, for example, JP-A-10-319408.
In addition, 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 then peeled off and laminated on the transparent substrate or the optically anisotropic layer. A transfer method 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. .

  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.

4). Retardation film The retardation film of the present invention is characterized by having a flexibility of 16 mm or less. Since the retardation film of the present invention can be made excellent in punching workability when the flexibility is in the above range, the retardation film of the present invention is used as a polarizing plate protective film to produce a polarizing plate. The production efficiency can be improved.
The flexibility of the retardation film of the present invention is not particularly limited as long as it is within the above range, but is preferably in the range of 2 mm to 16 mm, and preferably in the range of 2 mm to 10 mm. Further preferred. This is because, when the flexibility is in the above range, the punching processability and the like can be further improved, so that the retardation film of the present invention can be made suitable for further use as a polarizing plate protective film.

  Here, the bendability is determined by the mandrel method described in JIS-K5600-5-1 (a film sample is wound around a metal cylinder of 2 to 32 mm, and the coating film is cracked or cracked. It shall mean the value measured by the method of determining the minimum diameter of a cylinder that begins to enter.

  The optical properties of the retardation film of the present invention are appropriately determined by adjusting the optical properties of the optical anisotropic layer or using the retardation layer according to the use of the retardation film of the present invention. It can be adjusted. Among them, the retardation film of the present invention preferably has an Nz factor in the range of 1.0 to 3.0, more preferably in the range of 1.0 to 2.5, and 1.0 to More preferably, it is within the range of 2.0. This is because when the Nz factor is within the above range, the retardation film of the present invention can be suitably used as a viewing angle compensation film for an IPS liquid crystal display device.

Here, the Nz factor (Nz) is a parameter indicating the shape of the refractive index ellipsoid provided in the retardation film of the present invention, and is represented by the following equation.
Nz = (nx−nz) / (nx−ny))
Here, nx, ny, and nz respectively represent the refractive index (nx) in the slow axis direction, the refractive index (ny) in the fast axis direction, and the refractive index (nz) in the thickness direction in the plane of the retardation film. Is.

Further, the in-plane retardation (Re) and the thickness direction retardation (Rth) of the retardation film of the present invention are not particularly limited, and are appropriately adjusted according to the use of the retardation film of the present invention. It is something that can be done. In particular, the in-plane retardation (Re) of the retardation film of the present invention is preferably in the range of 5 nm to 300 nm, more preferably in the range of 10 nm to 200 nm, and in the range of 40 nm to 150 nm. More preferably it is. Further, the retardation (Rth) in the thickness direction of the retardation film is preferably in the range of 50 nm to 400 nm, more preferably in the range of 75 nm to 200 nm, and in the range of 75 nm to 150 nm. Further preferred.
Here, unless otherwise specified, Re and Rth mean values measured by entering measurement light having a wavelength of 550 nm in a direction parallel to the thickness direction. Such Re and Rth can be measured by, for example, a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

  The haze value of the retardation film of the present invention is preferably in the range of 0% to 5.0%, more preferably in the range of 0% to 3.0%, and 0% to 1 More preferably, it is in the range of 0.0%. Here, as the haze value, a value measured in accordance with JIS K7105 is used.

  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.

5). 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.

  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.

6). 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 forms an optically anisotropic layer by coating an optically anisotropic layer forming coating solution containing the rod-shaped compound on the transparent substrate. A step of forming a retardation film having a configuration in which an optically anisotropic layer is laminated on the transparent substrate, a step of stretching the retardation film, and a retardation film stretched by the stretching step. A step of forming a retardation layer on the optically anisotropic layer by applying a coating solution for forming a retardation layer containing the liquid crystal material on the optically anisotropic layer or the transparent substrate; It is a method to have.
In the second method, an optically anisotropic layer is formed by coating an optically anisotropic layer-forming coating solution containing the rod-shaped compound on the transparent substrate. A step of forming a retardation film having a configuration in which an anisotropic layer is laminated, and a coating for forming a retardation layer containing the liquid crystal material on an optically anisotropic layer or a transparent substrate of the retardation film It is a method having a step of forming a retardation layer on the optically anisotropic layer by applying a liquid and a step of stretching the retardation film on which the retardation layer is formed.
In the third method, an optically anisotropic layer is formed by coating an optically anisotropic layer-forming coating solution containing the rod-shaped compound on the transparent substrate, thereby forming an optically anisotropic layer on the transparent substrate. A step of forming a retardation film having a structure in which an anisotropic layer is laminated, a step of stretching the retardation film, and a retardation layer containing the liquid crystal material are formed on a substrate having a vertical alignment film. Then, the step of adhering only the retardation layer on the optically anisotropic layer or the transparent substrate via an adhesive.

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
The photopolymerizable nematic liquid crystals (A) and (B) represented by the following formulas were mixed at a weight ratio of 1: 1, dissolved in cyclohexanone at 20% by weight, and a TAC film (trade name, manufactured by Fuji Film Co., Ltd.). : TF80UL) coated on the surface of the transparent substrate by bar coating so that the coating amount after drying is 2.5 g / m ² , heated at 50 ° C. for 4 minutes to remove the solvent, and then the coated surface Were irradiated with 100 mJ / cm ² of ultraviolet rays to fix the photopolymerizable liquid crystal and form an optically anisotropic layer.

  Next, the transparent substrate on which the optically anisotropic layer is formed is uniaxially stretched in the in-plane direction while being heated at 160 ° C. so that the stretch ratio is 1.2 times by a stretching experiment apparatus, and for an IPS retardation film. A substrate was prepared. At this time, the IPS retardation film substrate had Re = 100 nm and Rth = 100 nm.

2. Example 2
A liquid crystal mixture of 50% by mass of a side chain polymer represented by the following formula (C) and 50% by mass of a photopolymerizable liquid crystal represented by the following formula (D), a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, Irgacure 907, 5 mass% with respect to the photopolymerizable compound) was dissolved in a cyclohexanone solution so as to have a solid content of 20%, and a leveling agent was further added to obtain a coating solution for forming a retardation layer. The surface on which the optically anisotropic layer of the IPS retardation film substrate described in Example 1 was prepared as the retardation layer forming coating liquid was bar-coated on the surface of the transparent substrate opposite to the surface. The coating amount after drying is 2.0 g / m ² , the solvent is removed by heating at 40 ° C. for 2 minutes, and then the coating surface is irradiated with ultraviolet rays at 100 mJ / cm ^2, so that the homeo A retardation layer was formed by fixing a tropic liquid crystal material. The retardation film had Re = 100 nm and Rth = −20 nm.

3. Comparative Example 1
An acrylic transparent substrate (acrylonitrile / styrene copolymer) is uniaxially stretched in the in-plane direction while being heated at 100 ° C. so as to have a draw ratio of 2.0 times by a stretching experiment apparatus, and is a base for an IPS retardation film. A material was prepared. At this time, the IPS retardation film base material had Re = -50 nm and Rth = -110 nm.

4). Comparative Example 2
The acrylic transparent base material (PMMA) was uniaxially stretched in the in-plane direction while being heated at 100 ° C. so that the stretch ratio was 2.0 times by a stretching experiment apparatus, thereby preparing a base material for an IPS retardation film. At this time, the IPS retardation film substrate had Re = −25 nm and Rth = −25 nm.

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 the other example of 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 ... Transparent substrate 2 ... Optically anisotropic layer 3 ... Phase difference layer 10 ... Phase difference film 101 ... Liquid crystal cell 102A, 102B, 102A ', 102B' ... Polarizing plate 103 ... Phase difference film 111 ... Polarizer 112a, 112b ... Polarizing plate protective film

Claims (4)

A transparent substrate made of a cellulose derivative and a rod-shaped compound formed on the transparent substrate and having refractive index anisotropy, an in-plane slow axis direction x refractive index nx ¹ , a fast axis direction refractive index ny ^1, a retardation film having an optical anisotropic layer relationship ^{nx 1>} ny 1 ≧ nz 1 between the refractive index nz ¹ in the thickness direction z is satisfied,
A retardation film having a flexibility of 16 mm or less.   The retardation film according to claim 1, wherein the Nz factor is in the range of 1.0 to 3.0. A liquid crystal material in which homeotropic alignment is formed on the transparent substrate or the optically anisotropic layer, and refractive indexes nx ² and ny ² in arbitrary x and y directions orthogonal to each other in the in-plane direction, and thickness The retardation film according to claim 1, wherein a retardation layer satisfying a relationship of nx ² ≦ ny ² <nz ² is formed between the refractive index nz ^{2 in the} direction. .   The retardation film according to any one of claims 1 to 3, wherein the cellulose derivative is triacetylcellulose.

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