JP5189899B2 - Optical compensation film, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to an optical compensation film and a polarizing plate useful as a member of a liquid crystal display device, and a liquid crystal display device.

Various optical compensation films for compensating the viewing angle of a liquid crystal display device have been proposed. These optical compensation films contribute to the improvement of viewing angle characteristics by compensating for the birefringence of the liquid crystal cell. However, the viewing angle characteristic of the liquid crystal display device is that the transmission axes of the pair of polarizing plates arranged in the liquid crystal display device are shifted from the orthogonal arrangement when observed from an oblique direction, so-called viewing angle characteristics of the polarizing plate. Is also greatly affected. The viewing angle characteristics of the polarizing plate cause a color shift that occurs when the liquid crystal display device of any mode is observed from an oblique direction during black display.
Patent Document 1 discloses a wide viewing angle polarized light in which a retardation film satisfying a predetermined optical characteristic is laminated as a polarizing film that prevents light leakage when viewed from an oblique direction of the polarizing film and the leakage light is not colored. A film has been proposed.
JP 2002-221622 A

An object of the present invention is to provide an optical compensation film that contributes to reducing color shift that occurs in an oblique direction during black display of a liquid crystal display device.
Another object of the present invention is to provide a polarizing plate in which light leakage and color shift caused by deviation from the orthogonal arrangement of the transmission axes are reduced.
It is another object of the present invention to provide a liquid crystal display device in which a color shift that occurs in an oblique direction during black display is reduced.

Means for solving the above-mentioned problems are as follows.
[1] It has an optically anisotropic layer and at least one optically isotropic layer adjacent to the optically anisotropic layer and having a refractive index different from the average refractive index of the optically anisotropic layer. An optical compensation film characterized by
[2] The optical compensation film according to [1], wherein a refractive index of the optically isotropic layer is lower than an average refractive index of the optically anisotropic layer.
[3] The optical compensation film according to [1], wherein a refractive index of the optically isotropic layer is higher than an average refractive index of the optically anisotropic layer.
[4] Any one of [1] to [3], wherein a difference between a refractive index of the optically isotropic layer and an average refractive index of the optically anisotropic layer is 0.05 or more. Optical compensation film.
[5] The optical compensation film according to any one of [1] to [4], wherein a refractive index of the optically isotropic layer has wavelength dispersion.
[6] The refractive index of the optically isotropic layer and the average refractive index of the optically anisotropic layer are | n1 (450) −n2 (450) | ≧ 0.05 [1] Optical compensation film of any one of [5]:
Here, n1 (λ) and n2 (λ) are the average refractive indices at the wavelength λ [nm] of the optical isotropic layer and the optical anisotropic layer, respectively.
[7] The optical compensation film according to any one of [1] to [6], wherein at least one of the optically isotropic layers is provided on a front surface or a back surface.
[8] The optical compensation film according to any one of [1] to [7], comprising at least one optical isotropic layer on both the front surface and the back surface.
[9] A polarizing plate comprising a polarizer and an optically isotropic layer adjacent to the polarizer and having a refractive index different from the average refractive index of the polarizer.
[10] A polarizing plate having at least a polarizer and the optical compensation film of any one of [1] to [8].
[11] A liquid crystal display device comprising the optical compensation film of any one of [1] to [8].
[12] A liquid crystal display device comprising at least one laminated structure in which an optically isotropic layer having a refractive index n1 and an optically anisotropic layer having an average refractive index n2 (where n1 ≠ n2) are adjacent to each other.
[13] The liquid crystal display device according to [12], further comprising an optically anisotropic layer or an optically isotropic layer having an average refractive index n3 (where n1 ≠ n3) adjacent to the optically isotropic layer. .
[14] The liquid crystal display device according to [12] or [13], wherein the laminated structure is provided between a liquid crystal cell and a polarizer.
[15] The liquid crystal display device according to [12] or [13], wherein the laminated structure is provided in a liquid crystal cell, and the optically anisotropic layer is a color filter layer.
[16] A color filter having at least first and second colored layers having hues different from each other, wherein the optical isotropic layer is disposed in a region corresponding to the first colored layer, and the second colored layer is provided in the second colored layer. The liquid crystal display device according to any one of [12] to [13], wherein the optically isotropic layer is not disposed in a corresponding region.
[17] An RGB color filter is provided, the optical isotropic layer is disposed in a region corresponding to the B layer of the RGB color filter, and satisfies the following relational expressions: [12] to [16] ] Liquid crystal display device:
| N1_b-n_g | ≧ 0.05 and | n1_b-n_r | ≧ 0.05
Here, n1_b is a refractive index at a wavelength of 450 nm of the optical isotropic layer disposed in a region corresponding to the B layer, n_g and n_r are average refractive indexes of the G layer and the R layer, respectively. The refractive index of the colored layer is a refractive index at a wavelength at which the transmittance is maximum.

ADVANTAGE OF THE INVENTION According to this invention, the optical compensation film which contributes to reducing the color shift which arises in the diagonal direction at the time of black display of a liquid crystal display device can be provided.
In addition, according to the present invention, it is possible to provide a polarizing plate in which light leakage and color shift caused by deviation from the orthogonal arrangement of the transmission axes are reduced.
Further, according to the present invention, it is possible to provide a liquid crystal display device in which color shift that occurs in an oblique direction during black display is reduced.

Hereinafter, the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
[Optical compensation film]
The optical compensation film of the present invention has an optically anisotropic layer, and an optically isotropic layer adjacent to the optically anisotropic layer and having a refractive index different from the average refractive index of the optically anisotropic layer. It is characterized by that. The light incident on the optically anisotropic layer has a phase difference, but the phase difference varies depending on the wavelength of the incident light, so that the polarization state varies. In the present invention, the difference in refractive index at the interface between the optically anisotropic layer and the optically isotropic layer is used to adjust the polarization state of the incident light, and as a result, the color shift (color) of the polarized light emitted in the oblique direction. The taste is reduced. The optical compensation film of the present invention is particularly excellent in reducing reddish color shift that is easily recognized by human vision. By using the optical compensation film of the present invention, the color shift that occurs in an oblique direction during black display can be reduced in any mode of the liquid crystal display device. The effect of the present invention can be obtained by forming an optically isotropic layer that satisfies the above conditions on the surface of various existing optical compensation films.

The refractive index difference between the optically anisotropic layer and the optically isotropic layer is preferably 0.05 or more, and more preferably 0.1 or more. Since the effect of the present invention is obtained as the difference in refractive index increases, there is no upper limit in terms of the effect, but considering that it can be realized with existing materials, the difference in refractive index is 0.5 or less. For the optically anisotropic layer, the “refractive index” refers to the average refractive index.
The refractive index of the optically isotropic layer may be higher or lower than the refractive index of the optically anisotropic layer, but in order to obtain the effect without affecting display performance. The refractive index of the optically isotropic layer is preferably lower than the refractive index of the optically anisotropic layer. Considering a mode that can be realized by existing materials, a preferable mode is that the optically isotropic layer has a low refractive index of about 1.0 to 1.4, and the optically anisotropic layer has a low refractive index. This is a high refractive index mode having a refractive index of about 1.45 to 1.6. In a more preferred embodiment, the refractive index of the optical isotropic layer is about 1.2 to 1.3, and the refractive index of the optical anisotropic layer is about 1.48 to 1.55. .

  The refractive index of the optically isotropic layer may have wavelength dispersion. If the optically isotropic refractive index has wavelength dispersion, the incident polarization state can be adjusted for each wavelength, so that the color shift can be further reduced.

  The conventional retardation film compensation mainly adjusts the incident polarization state at the green wavelength from the viewpoint of luminance reduction, so the color shift is blue, red, or a magenta color that is a mixed color thereof. There are many cases. From this and the optical principle of polarization adjustment by providing the optically isotropic layer, the color shift can be reduced by providing a refractive index difference only for light having a wavelength corresponding to blue. That is, when the refractive index of the optically isotropic layer exhibits wavelength dispersion in the visible light region and / or when the refractive index of the optically anisotropic layer exhibits wavelength dispersion in the visible light region, the optical isotropic property The difference | n1-n2 | between the refractive index n1 of the layer and the refractive index n2 of the optically anisotropic layer may also exhibit so-called wavelength dispersion that varies depending on the wavelength. In order to obtain the effects of the present invention, the difference between the refractive index n1 (450) of the optical isotropic layer and the refractive index n2 (450) of the optically anisotropic layer at least at a wavelength of 450 nm | n1 (450) −n2 ( 450) | is preferably 0.05 or more, and more preferably 0.1 or more.

  The optical compensation film of the present invention preferably has the optical isotropic layer as the outermost layer. When bonded to another member (which may be optically anisotropic or optically isotropic), the refractive index difference that can adjust the polarization state of incident light is also between the member and the member. This is preferable because a certain interface is formed. The optical compensation film of the present invention may have two or more optically isotropic layers, for example, the optically isotropic layer is disposed on both the front and back surfaces of the optically anisotropic layer. May be. Two or more optically anisotropic layers may be provided, and in that case, the optically isotropic layer may be disposed between the optically anisotropic layers.

1A and 1B are schematic cross-sectional views of examples of the optical compensation film of the present invention. However, the relative relationship of the thickness of each layer in the figure does not necessarily reflect the actual relative relationship. The same applies to the other drawings.
An optical compensation film 22 shown in FIG. 1A has an optically anisotropic layer 10 made of a birefringent polymer film or the like, and an optically isotropic layer 12 on the surface thereof. The optical compensation film 22 ′ shown in FIG. 1B has the optical isotropic layer 12 on both the front surface and the back surface of the optical anisotropic layer 10. The optical compensation films 22 and 22 ′ shown in FIGS. 1A and 1B can adjust the polarization state of incident light by the difference in refractive index at the interface between the optical anisotropic layer 10 and the optical isotropic layer 12. is there. In addition, when these optical compensation films are incorporated into a liquid crystal display device, the polarization state of incident light can be adjusted by bonding to the surface of another member having a refractive index different from that of the optical isotropic layer 12 It is possible to further form an interface having a difference in refractive index.

Hereinafter, various materials and manufacturing methods used for manufacturing the optical compensation film of the present invention will be described.
(Optical isotropic layer)
In the present invention, there are no limitations on the material of the optically isotropic layer and the method for producing the same. The material can be selected according to the desired refractive index.
・ Low refractive index optical isotropic layer (refractive index of about 1.4 or less)
It is preferable that the optically isotropic layer is formed as a layer having a relatively low refractive index and has a difference from the average refractive index of the optically anisotropic layer. Although the low refractive index layer can be formed using various low refractive index materials, it is an optically isotropic layer and does not cause opacity or coloring that affects display performance. For this, it is preferable to use the following materials that are used for forming the low refractive index layer of the antireflection film.

  An example of a low refractive index optically isotropic layer is a metal oxide thin film. The metal oxide thin film can be formed using, for example, a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method, and more specifically, a vacuum vapor deposition method or a sputtering method which is a kind of physical vapor deposition method. Can be formed.

  Another example of the low refractive index optical isotropic layer is a low refractive index layer containing microvoids. In the low refractive index layer of this example, the refractive index of the layer is made close to the refractive index of air 1.00 by forming microvoids. Microvoids are formed between and / or within the fine particles contained in the layer. The low refractive index layer containing microvoids can be formed by applying a dispersion of organic fine particles, inorganic fine particles, or composite fine particles thereof to the surface and drying. The materials and methods used for forming the low refractive index layer in this example are described in detail in, for example, JP-A Nos. 9-222502, 9-288201, and 11-6902. Reference can be made in the fabrication of the optically isotropic layer.

  In addition, as the low refractive index isotropic layer, a coating layer containing a fluorine-containing compound as a main component can be used. Examples of the fluorine-containing compound include a fluorine-containing polymer, a fluorine-containing surfactant, a fluorine-containing ether, and a fluorine-containing silane compound. More specifically, JP-A-9-222503 [0018]-[0026], JP-A-11-38202 [0019]-[0030], JP-A-2001-40284 [0027]-[0028], Examples thereof include fluorine-containing compounds described in JP-A No. 2000-284102 [0036] to [0052]. As the fluorine-containing polymer, a copolymer comprising a repeating structural unit containing a fluorine atom, a repeating structural unit containing a crosslinkable or polymerizable functional group, and a repeating structural unit composed of other substituents is preferable. The crosslinkable or polymerizable functional group is preferably a radical polymerizable group or a cationic polymerizable group. The low refractive index isotropic layer can be formed using a silicone compound together with the fluoropolymer. The silicone compound is a compound having a polysiloxane structure, preferably containing a curable functional group or a polymerizable functional group in the polymer chain and having a crosslinked structure in the film. For example, reactive silicones such as commercially available silaplane (manufactured by Chisso Corporation), compounds containing silanol groups at both ends of the polysiloxane structure described in JP-A-11-258403, and the like can be mentioned. The low refractive index isotropic layer of this example can be formed by preparing the above material as a coating solution, and coating and drying the surface of the optically anisotropic layer. When the fluorine-containing polymer has a crosslinking or polymerizable group, the crosslinking or polymerization reaction is preferably carried out by light irradiation or heating at the same time as or after the application of the coating solution. In addition, the coating solution may contain a polymerization initiator, a sensitizer, and the like. The production method of the low refractive index isotropic layer and other agents used in this example are described in the above-mentioned publications, and can be referred to in the production of the low refractive index optical isotropic layer.

  Further, as another example of the low-refractive-index optically isotropic layer, a sol-gel cured film in which a silane coupling agent and a specific fluorine-containing hydrocarbon group-containing silane coupling agent are cured by a condensation reaction in the presence of a catalyst. Is also preferable. For example, polyfluoroalkyl group-containing silane compounds or partially hydrolyzed condensates thereof (compounds described in JP-A-58-142958, JP-A-58-147483, JP-A-58-147484, etc.), JP-A-9-157582 Perfluoroalkyl group-containing silane coupling agents described in Japanese Patent Publication No. JP-A-2000-117902, and silyl compounds containing a poly "perfluoroalkyl ether" group which is a fluorine-containing long chain group (JP 2000-117902 A, JP 2001-48590 A, And the like described in JP-A-2002-53804). Moreover, the film | membrane formed by hardening the composition containing the hydrolysis partial condensate of organosilane described in Unexamined-Japanese-Patent No. 2001-40284 is also preferable. These materials cure to build a network structure, thereby resulting in a low refractive index in the formed layer. The low refractive index layer in this example can be formed, for example, by preparing a sol solution containing the above components, applying the sol solution to the surface, and drying by heating. In order to accelerate the curing reaction, energy rays may be irradiated.

・ High refractive index optical isotropic layer (refractive index of about 1.7 or more)
The optical isotropic layer may be formed as a layer having a relatively high refractive index, and may have a difference from the average refractive index of the optically anisotropic layer. For example, it is effective when the optically anisotropic layer has a relatively low refractive index. The high-refractive index layer can be formed using a high-refractive index material, but in order to make it an optically isotropic layer and not to cause opacity and coloring that affect display performance. Is preferably made of the following materials that are used for forming the high refractive index layer of the antireflection film.

  As an example of the optically isotropic layer having a high refractive index, a curable film containing at least high-refractive-index inorganic compound fine particles and a matrix binder can be given. Regarding the material and the forming method used for forming this curable film, JP-A Nos. 11-295503, 11-153703, 2000-9908, and 2001-272502, No. 2001-166104, JP-A-11-153703, US Pat. No. 6,210,858, JP-A-2001-315242, JP-A-2001-31871, JP-A-2001-296401, etc. There is an explanation and can be referred to in the formation of the high refractive index optical isotropic layer.

  Other examples of the optically isotropic layer having a high refractive index include colloidal metal oxides obtained from hydrolyzed condensates of metal alkoxides and curable films obtained from compositions containing metal alkoxides. The material used for the formation of the curable film and the method thereof are described in detail in, for example, JP-A-2001-293818, and can be referred to in the formation of the high refractive index optical isotropic layer. it can.

  In the optical compensation film of the present invention, the optical isotropic layer may be an adhesive layer. The adhesive layer is advantageous when, for example, bonding with another member.

  There is no particular limitation on the thickness of the optically isotropic layer. In order to meet the demand for thinning, the thinner the thickness, the better. For example, when an optical isotropic layer is formed by coating, an optical isotropic layer of about 1.0 to 2.0 μm can be formed. However, it is not limited to this range.

  The optical isotropic layer is preferably not subjected to a treatment such as stretching that causes optical anisotropy during the manufacturing process, and therefore the optical isotropic layer is exemplified above. As described above, a layer formed by applying a predetermined material directly to the surface of the optically anisotropic layer is preferable. Coating is performed by various methods such as a dip coating method, an air knife coating method, a curtain coating method, a roller coating method, a wire bar coating method, a gravure coating, a micro gravure method and an extrusion coating method (US Pat. No. 2,681,294). It can be carried out. Of course, if an optical isotropic layer satisfying the above conditions can be obtained, an optical isotropic film may be separately produced and affixed to the surface of the optical anisotropic layer.

In the present invention, the refractive index of the optical isotropic layer may have wavelength dispersion. That is, the refractive index may be different depending on the wavelength of incident light. The refractive index of a general substance has a higher dispersion curve (forward dispersion characteristic) as the wavelength becomes shorter. In addition, a mixture in which materials having different refractive indexes are mixed may exhibit reverse dispersion characteristics such that the shorter the wave, the lower the refractive index. The wavelength dispersion of the refractive index of such a mixture is shown by Maxwell, G., JC, Colors in metal glasses and metal films,
Philos. Trans. R. Soc. London, Sect. A, Vol. 3, 385-420 (1904); and DAGBruggeman, Ann. Phys. (Leipzig), Vol. 24, 636-665 (1935) It can be predicted by the described calculation formula.

(Optically anisotropic layer)
About the optically anisotropic layer which the optical compensation film of this invention has, there is no restriction | limiting about the material, a structure, etc. at all. Various optical compensation films used for optical compensation of liquid crystal display devices of various modes can be used as the optically anisotropic layer as they are. Specifically, as the optically anisotropic layer, a birefringent polymer film, a multilayer body of a birefringent polymer film, a cured film of a liquid crystal composition, a multilayer body of the liquid crystal cured film, and the liquid crystal cured film and a polymer Any of a laminate with a film can be used.
For example, for an optical compensation film used in various modes of liquid crystal display devices, by forming an optically isotropic layer having a low refractive index on the surface of the optical compensation film, the optical compensation ability of the optical compensation film can be increased. The color shift that occurs in the oblique direction can be reduced without any loss.

  Examples of birefringent films include cellulose esters (eg, triacetyl cellulose, diacetyl cellulose, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, nitrocellulose), polyamides, polycarbonates, polyesters (eg, polyethylene terephthalate, polyethylene naphthalate, Poly-1,4-cyclohexanedimethylene terephthalate, polyethylene-1,2-diphenoxyethane-4,4′-dicarboxylate, polybutylene terephthalate), polystyrene (eg, syndiotactic polystyrene), polyolefin (eg, polypropylene) , Polyethylene, polymethylpentene), polysulfone, polyethersulfone, polyarylate, polyetherimide, polymethylmethacrylate And films such as silicate and polyether ketone.

  Moreover, there is no restriction | limiting also about the liquid crystal used for formation of a liquid crystal cured film. Either a rod-like liquid crystal or a disk-like liquid crystal may be used.

[Polarizer]
The present invention relates to a polarizing plate having a polarizer and the optical compensation film of the present invention. The example of the polarizing plate of this invention is shown to Fig.2 (a) and (b). The polarizing plates of FIGS. 2A and 2B have a polarizer 20 and a protective film 22 on one surface. It is preferable to have a protective film also on the other surface. The protective film 22 is an embodiment of the optical compensation film of the present invention shown in FIG. 1B, and has an optically anisotropic layer 10 and an optically isotropic layer 12. In FIG. The surface of the anisotropic layer 12 is disposed in contact with the surface of the polarizer 20, and the surface of the optically anisotropic layer 10 is disposed in contact with the surface of the polarizer 20 in FIG. . In the polarizing plates of FIGS. 2A and 2B, the polarization state of incident light is adjusted by the refractive index difference at the interface between the optically anisotropic layer 10 and the optically isotropic layer 12. In addition, in the polarizing plate of FIG. 2A, when the polarizer 20 and the optically isotropic layer 12 have different refractive indexes, the polarization state of incident light is adjusted by the difference in refractive index at the interface. .

  The present invention also relates to a polarizing plate having a polarizer and an optically isotropic layer adjacent to the polarizer and having a refractive index different from the average refractive index of the polarizer. Polarized light that has a certain degree of refractive index and forms an interface with an optically isotropic layer having a different refractive index on the surface of the polarizer to adjust the polarization state in the same manner as described above, and to emit light in an oblique direction. The color shift can be reduced. A protective film or retardation film may be further disposed on the optically isotropic layer formed on the surface of the polarizer. Furthermore, a protective film or the like may be disposed on the surface on which the optically isotropic layer is not disposed. When incorporating the polarizing plate of this embodiment into a liquid crystal display device, it is preferable to dispose the optically isotropic layer between the liquid crystal cell and the polarizer from the viewpoint of obtaining a higher effect.

(Polarizer)
As the polarizer of the polarizing plate of the present invention, any of an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film can be used. The iodine polarizing film and the dye polarizing film are generally produced using a polyvinyl alcohol film.

(Second protective film)
The polarizing plate of the present invention preferably has a second protective film (22 in FIG. 2) other than the optical compensation film of the present invention. The second protective film is bonded to the other surface of the polarizer that is not bonded to the optical compensation film of the present invention. There is no restriction | limiting in particular about the material of a said 2nd protective film, Any may be a cellulose acylate film, a polycarbonate film, a norbornene-type film, etc.

[Liquid Crystal Display]
The present invention includes a liquid crystal display device comprising at least one laminated structure in which an optically isotropic layer having a refractive index n1 and an optically anisotropic layer having an average refractive index n2 (where n1 ≠ n2) are adjacent to each other. Also related. The laminated structure can be incorporated into the liquid crystal display device by using the optical compensation film and the polarizing plate of the present invention.
In FIG. 3, the cross-sectional schematic diagram of an example of the liquid crystal display device of this invention is shown.
The liquid crystal display device shown in FIG. 3 includes a liquid crystal cell LC and a pair of polarizing plates PL1 and PL2 arranged therebetween. The polarizing plates PL1 and PL2 are polarizing plates of the present invention, and have an optical compensation film 22 ′ of the present invention shown in FIG. 1B as a protective film disposed on the liquid crystal cell side of the polarizer 20. Usually, a protective film is also disposed on the outer surface of the polarizer 20, but this is omitted in FIG. The optical compensation film 22 ′ used as a protective film has an optically anisotropic layer 10 and optically isotropic layers 12a and 12b on both the front and back surfaces, and the surface of the optically isotropic layer 12a is Are bonded to the surface of the polarizer 20. The other optically anisotropic layer 12b is bonded to the surface of the substrate 24 of the liquid crystal cell LC. In the liquid crystal display device shown in FIG. 3, the polarization state of the incident light is adjusted by the refractive index difference at the interface between the optically anisotropic layer 10 and the optically isotropic layers 12a and 12b, and the polarizer 20 and the optical isotropic When the refractive index of the optical layer 12 is different from each other, and when the refractive index of the substrate 24 and the optically isotropic layer 12 are different from each other, the polarization state of the incident light is also adjusted by the difference in refractive index between the interfaces. As a result, a color shift, particularly reddish, that occurs in an oblique direction during black display is reduced.

FIG. 4 is a schematic cross-sectional view of another example of the liquid crystal display device of the present invention.
The liquid crystal display device shown in FIG. 4 includes a liquid crystal cell LC and a pair of polarizing plates PL1 ′ and PL2 ′ disposed therebetween. The polarizing plate PL1 ′ is the polarizing plate of the present invention, and has the optical compensation film 22 of the present invention shown in FIG. 1 (a) as a protective film disposed on the liquid crystal cell side of the polarizer 20. Usually, a protective film is also disposed on the outer surface of the polarizer 20, but this is omitted in FIG. The optical compensation film 22 of the present invention used as a protective film has an optically anisotropic layer 10 and an optically isotropic layer 12 on the surface, and the surface of the optically isotropic layer 12 is a liquid crystal cell. It is bonded to the surface of the substrate 24. In the liquid crystal display device shown in FIG. 3, the polarization state of incident light is adjusted by the refractive index difference at the interface between the optically anisotropic layer 10 and the optically isotropic layer 12, and the substrate 24 and the optically isotropic layer 12 are adjusted. When the refractive indexes are different from each other, the polarization state of the incident light is adjusted also by the difference in refractive index at the interface. As a result, the color shift that occurs in the oblique direction during black display is reduced.

  The polarizing plate PL2 'is a polarizing plate having the optically anisotropic layer 10 as a protective film disposed on the liquid crystal cell side of the polarizer 20, and no optical isotropic layer exists. In the example shown in FIG. 4, an optically isotropic layer having a refractive index n1 and an optically anisotropic layer having an average refractive index n2 (where n1 ≠ n2) are adjacent only between the liquid crystal cell and one polarizer. It is embodiment which has the laminated structure to do. Also in this example, the effect of the present invention can be obtained as in the embodiment shown in FIG.

  Conventionally, it is preferable that the retardation of an optically anisotropic layer used for optical compensation exhibits ideal wavelength dispersion in optical compensation. In order to obtain an effect substantially equivalent to that of the optically anisotropic layer having ideal wavelength dispersion, it is preferable to dispose an optically isotropic layer on the colored layer of a specific color of the color filter. Then, it is preferable to arrange an optically isotropic layer in a region corresponding to the blue layer. Thereby, the color shift occurring in the oblique direction can be reduced. This effect can be obtained by placing an optically isotropic layer in contact with the color filter. Further, it can be obtained even if the optically isotropic layer is not in contact with the color filter. That is, the optical isotropic layer may be disposed inside or outside the liquid crystal cell, and in the aspect disposed inside, the optical isotropic layer is the same as the substrate on which the color filter is formed. Even if it arrange | positions on the inner surface of a board | substrate, you may arrange | position on the inner surface of the other board | substrate.

FIG. 5 shows a schematic cross-sectional view of an example of the liquid crystal display device of the present invention having an RGB color filter.
The liquid crystal display device shown in FIG. 5 includes a liquid crystal cell LC and a pair of polarizing plates PL1 ″ and PL2 ′ disposed therebetween. A red color is formed on the inner surface of the display surface side substrate 24 of the liquid crystal cell LC. An RGB color filter 27 having an (R) layer, a green (G) layer, and a blue (B) layer is disposed and configured to be capable of color display. The polarizing plate PL1 ″ is a polarizing plate of the present invention. As a protective film disposed on the liquid crystal cell side of the polarizer 20, the optical compensation film 22 "of the present invention is provided. Usually, a protective film is also disposed on the outer surface of the polarizer 20, but is omitted in FIG. The optical compensation film 22 ″ used as a protective film has an optically anisotropic layer 10 and an optically isotropic layer 12 ″ on the surface thereof, and the surface of the optically isotropic layer 12 ″ is a liquid crystal cell. The substrate 24 is bonded to the surface. In the liquid crystal display device shown in FIG. 3, the polarization state of incident light is adjusted by the refractive index difference at the interface between the optically anisotropic layer 10 and the optically isotropic layer 12 ″, and the substrate 24 and the optically isotropic layer are adjusted. When the refractive indexes of 12 ″ are different from each other, the polarization state of the incident light is adjusted by the difference in the refractive index at the interface. As a result, the color shift that occurs obliquely during black display is reduced. The polarizing plate PL2 ′ is a polarizing plate having the optical anisotropic layer 10 as a protective film disposed on the liquid crystal cell side of the polarizer 20, and there is no optical isotropic layer. In the example shown in FIG. 5, an optically isotropic layer having a refractive index n1 and an optically anisotropic layer having an average refractive index n2 (where n1 ≠ n2) are adjacent only between the liquid crystal cell and one polarizer. It is embodiment which has the laminated structure to do. Also in this example, the effect of the present invention can be obtained as in the example shown in FIG.

  In the optical compensation film 22 ″ used in the liquid crystal display device of FIG. 5, the optically isotropic layer 12 ″ is not disposed in contact with the entire surface of the optically anisotropic layer 10; It is arranged only in a region corresponding to 27 blue layers B. In the embodiment shown in FIG. 5, as in the embodiment shown in FIG. 4, the polarization state of incident light is adjusted by the refractive index difference at the interface between the optically anisotropic layer 10 and the optically isotropic layer 12 ″, As a result, the color shift that occurs in the oblique direction during black display is reduced.In the embodiment shown in FIG. 5, the optical isotropic layer is disposed only in the region corresponding to the blue layer. The effect of the present invention can also be obtained by providing a refractive index difference only for light having a wavelength corresponding to blue, so that the optical isotropic layer is uniformly formed as in the embodiment shown in FIG. The effect of reducing the color shift in the oblique direction can be obtained.

In the present invention, a laminated structure in which an optically isotropic layer having a refractive index n1 and an optically anisotropic layer having an average refractive index n2 (where n1 ≠ n2) are adjacent may be disposed in a liquid crystal cell. In one example of this embodiment, the color filter layer can function as an optically anisotropic layer. Depending on the material, the color filter layer may exhibit an optically anisotropic layer. Therefore, the laminated structure can be incorporated in the liquid crystal cell by forming an optically isotropic layer adjacent to the color filter layer. it can. The optical isotropic layer may be disposed on the entire surface of the color filter layer, or may be disposed only in part, such as the optical isotropic layer 12 ″ shown in FIG. In the aspect using the filter layer, if the optical isotropic layer is disposed at least on the B layer, the effect of the present invention can be obtained even if the optical isotropic layer is not disposed on the R layer and the G layer. Can do.
In the aspect of the present invention, a laminated structure in which an optically isotropic layer having a refractive index n1 and an optically anisotropic layer having an average refractive index n2 (where n1 ≠ n2) are adjacent is disposed in a liquid crystal cell. The function as an optically anisotropic layer is not limited to the color filter. For example, in an embodiment in which the optical isotropic layer is in contact with the liquid crystal layer in the liquid crystal cell, the liquid crystal layer will function as the optically anisotropic layer. That is, the optically isotropic layer does not need to be disposed in contact with the color filter layer, and is disposed on the inner surface of the counter substrate of the substrate on which the color filter is formed, out of the pair of substrates of the liquid crystal cell. Even if it is an aspect, the effect of this invention can be acquired.

In the present invention, an aspect in which the optical isotropic layer is disposed in a region corresponding to the B layer of the RGB color filter (an aspect in which the optical isotropic layer is disposed in the cell and an aspect in which the optical isotropic layer is disposed outside the cell) In other words, the refractive index n1_b of the optical isotropic layer preferably satisfies the following relational expressions with the respective refractive indexes n_r and n_g of the R layer and the G layer.
| N1_b-n_g | ≧ 0.05 and | n1_b-n_r | ≧ 0.05
Here, n1_b is a refractive index at a wavelength of 450 nm of the optical isotropic layer disposed in a region corresponding to the blue layer, n_g and n_r are average refractive indexes of the green layer and the red layer, respectively. The refractive index of the colored layer is a refractive index at a wavelength at which the transmittance is maximum.
If the above relational expression is satisfied, only blue polarized light can be adjusted, and as a result, the color shift in the oblique direction is reduced, which is preferable.

  According to another aspect of the present invention, there is provided at least one interface between an optically isotropic layer having a refractive index n1 and a layer having an average refractive index n2 (where n1 ≠ n2), and a polarizer and a liquid crystal cell. It is a liquid crystal display device characterized by including in between. The layer having an average refractive index n2 may be a polarizer or a liquid cell substrate. Moreover, the optically anisotropic layer arrange | positioned between a polarizer and a liquid crystal cell may be sufficient.

  The present invention can be applied to various modes, a TN (Twisted Nematic) mode, a VA (Vertically aligned) mode, an OCB (Optically Compensated Bend) mode, an IPS (In-phase switching) mode, or an ECB (Electrically controlled liquid crystal display). This has the effect of reducing the color shift that occurs in the direction.

Hereinafter, the effects of the present invention will be described more specifically with reference to examples. However, Example 2, Example 4, and Example 6 are reference examples.
[Example 1]
The effect of the present invention was confirmed for the liquid crystal display device having the configuration shown in FIG. Specifically, u ′ and v ′ representing the color in all directions of the polar angle 60 ° and the in-plane azimuth angle 0 ° to 360 ° of the display surface during black display were calculated. It can be said that the color shift is reduced as u ′ and v ′ are constant regardless of the azimuth. U ′ is a chromaticity recognized as reddish, and v ′ is a chromaticity recognized as bluish. The refractive index of the optical isotropic layers 12a and 12b was 1.2. The material used was a fluorine compound. The average refractive index of the optically anisotropic layer 10 was 1.5. The material used was a triacetyl cellulose film.
As a comparative example, a liquid crystal display device having a configuration excluding all of the four optically isotropic layers 12a and 12b in FIG. 3 also has an in-plane azimuth angle of 0 ° to 360 ° on the display surface during black display. U ′ and v ′ in the direction were calculated. The results are shown in the graph of FIG.

  From the results shown in the graph of FIG. 6, when comparing the u ′ and v ′ curves of the example and the comparative example, the amplitude of each curve depending on the azimuth is smaller in the example, and Δu ′ and Δv in all directions. I can understand that 'can be reduced. In particular, for u ′ that is easily recognized by human vision, u′max−u′min in the comparative example was 0.112, whereas the example was 0.073, and redness was reduced. I can understand that. Note that u′max and u′min are the maximum u ′ and the minimum u ′ of 0 to 360 degrees, respectively.

[Example 2]
In the same configuration as in Example 1, the refractive index of the optically isotropic layers 12a and 12b was 2.0. The material used was a curable film containing zirconia fine particles and a matrix binder. The average refractive index of the optically anisotropic layer 10 was 1.5.
As a comparative example, a liquid crystal display device having a configuration excluding all of the four optically isotropic layers 12a and 12b in FIG. 3 also has an in-plane azimuth angle of 0 ° to 360 ° on the display surface during black display. U ′ and v ′ in the direction were calculated. The results are shown in the graph of FIG.

  From the results shown in the graph of FIG. 7, when comparing the u ′ and v ′ curves of the example and the comparative example, the amplitude of each curve depending on the azimuth is smaller in the example, and Δu ′ and Δv in all directions. I can understand that 'can be reduced. In particular, for u ′ that is easily recognized by human vision, u′max−u′min of the comparative example was 0.112, whereas the example was 0.108, and redness was reduced. I can understand that.

[Example 3]
The effect of the present invention was confirmed for the liquid crystal display device having the configuration shown in FIG. Specifically, Δu′v ′ = {(u ′) from u′v ′ representing the color in all directions of the in-plane azimuth angle of 0 ° to 360 ° at the polar angle of 60 degrees on the display surface during black display. max−u′min) ² + (v′max−v′min) ² } was calculated. Here, u′max (v′max) and u′min (v′min) are the maximum and minimum u ′ (v ′) of 0 to 360 degrees, respectively. It can be said that the color shift is reduced as u ′ and v ′ are constant regardless of the azimuth, that is, as Δu′v ′ is closer to 0.
Here, the refractive index of the optical isotropic layer 12 was set to 1.2. The average refractive index of the optically anisotropic layer 10 was 1.5.
As a comparative example, Δu′v ′ was also calculated for a liquid crystal display device having a configuration excluding the two optical isotropic layers 12 in FIG. As a result, Δu′v ′ of the comparative example was 0.07, whereas the example was 0.059, and it can be understood that the color shift was reduced.

[Example 4]
In the same configuration as in Example 3, the refractive index of the optical isotropic layer 12 was set to 2.0. The average refractive index of the optically anisotropic layer 10 was 1.5, and Δu′v ′ was calculated.
As a comparative example, Δu′v ′ was also calculated for a liquid crystal display device having a configuration excluding the two optical isotropic layers 12 in FIG. As a result, Δu′v ′ of the comparative example was 0.07, whereas the example was 0.059, and it can be understood that the color shift was reduced.

[Example 5]
The effect of the present invention was confirmed for the liquid crystal display device having the configuration shown in FIG. The refractive index of the optical isotropic layer 12 disposed in contact with the optical anisotropic layer 10 in the region corresponding to the blue layer of the color filter was set to 1.2. The average refractive index of the optically anisotropic layer 10 was 1.5. The refractive indexes n_r and n_g of the R layer and the G layer of the color filter are both 1.5, and satisfy | n1_b−n_g | ≧ 0.05 and | n1_b−n_r | ≧ 0.05. It was.
As a comparative example, Δu′v ′ was also calculated for a liquid crystal display device having a configuration excluding the two optical isotropic layers 12 in FIG. As a result, Δu′v ′ of the comparative example was 0.07, whereas the example was 0.056, and it can be understood that the color shift was reduced.

[Example 6]
In the same configuration as in Example 5, the refractive index of the optical isotropic layer 12 was set to 2.0. The average refractive index of the optically anisotropic layer 10 was 1.5. The refractive indexes n_r and n_g of the R layer and the G layer of the color filter are both 1.5, and satisfy | n1_b−n_g | ≧ 0.05 and | n1_b−n_r | ≧ 0.05. It was.
As a comparative example, Δu′v ′ was also calculated for a liquid crystal display device having a configuration excluding the two optical isotropic layers 12 in FIG. As a result, Δu′v ′ of the comparative example was 0.07, whereas the example was 0.056, and it can be understood that the color shift was reduced.

It is a cross-sectional schematic diagram of two examples of the optical compensation film of this invention. It is a cross-sectional schematic diagram of an example of the polarizing plate of this invention. It is a cross-sectional schematic diagram of an example of the liquid crystal display device of this invention. It is a cross-sectional schematic diagram of the other example of the liquid crystal display device of this invention. It is a cross-sectional schematic diagram of the other example of the liquid crystal display device of this invention. It is a graph which shows u 'and v' with respect to the azimuth of an Example and a comparative example. It is a graph which shows u 'and v' with respect to the azimuth of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical anisotropic layer 12, 12a, 12b, 12 "Optical isotropic layer 20 Polarizer 22, 22 ', 22" Optical compensation film of this invention (In FIG.3, 4,5, it is a protective film of a polarizer. As well)
24 Cell substrate 26 Liquid crystal layer 27 Color filter LC Liquid crystal cell PL1, PL1 ′, PL1 ″, PL2, PL2 ′ Polarizing plate

Claims (9)

An optically anisotropic layer and at least one optically isotropic layer adjacent to the optically anisotropic layer and having an average refractive index lower than the average refractive index of the optically anisotropic layer,
The refractive index of the optical isotropic layer is 1.0 to 1.4, the refractive index of the optical anisotropic layer is 1.45 to 1.60, and the refractive index of the optical isotropic layer is wavelength dispersion. Optical compensation film. The refractive index of the optically isotropic layer and the average refractive index of the optically anisotropic layer are | n1 (450) −n2 (450) | ≧ 0.05. Optical compensation film:
Here, n1 (λ) and n2 (λ) are the average refractive indices at the wavelength λ [nm] of the optical isotropic layer and the optical anisotropic layer, respectively. The optical compensation film according to claim 1, wherein the optical compensation film has at least one optical isotropic layer on a front surface or a back surface. The optical compensation film according to claim 1, comprising at least one optical isotropic layer on both the front surface and the back surface. The optical compensation film according to any one of claims 1 to 4, wherein the refractive index of the optical isotropic layer is 1.0 to 1.3. The optical according to any one of claims 1 to 5, wherein the optically isotropic layer is a metal oxide thin film, a low refractive index layer containing microvoids, or a coating layer containing a fluorine-containing compound as a main component. Compensation film. The polarizing plate which has a polarizer and the optical compensation film of any one of Claims 1-4 at least. A liquid crystal display device comprising an optical compensation film of any one of claims 1-7. A liquid crystal display device comprising the optical compensation film according to any one of claims 1 to 7 between a liquid crystal cell and a polarizer.

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