KR20150034631A - Polarizing plate, image display device, and improvement method of photopic contrast in image display device - Google Patents

Abstract

The purpose of the present invention is to provide a polarization plate and an image display device which can guarantee a visibility in a crossed Nicols state when an observer recognizes a display image at a liquid crystal display device over polarization sunglasses, improves the transmittance in a parallel Nicols state which is frequently observed compared to a case that an optical transmissive film having birefringence on the surface is arranged to make the fast axis with respect to a direction of absorption axis of a polarizer, and improves photopic contrast when the image display device is observed with naked eye (the polarization sunglasses are not equipped). According to an embodiment of the present invention, a polarization plate (10) includes: a polarizer (11) and an optical transmissive film (12) which is installed on a surface of the observer and has birefringence on the surface. The polarizer (11) is arranged to make a direction of the absorption axis (11A) of the polarizer be aligned to the horizontal direction, and the optical transmissive film (12) is arranged to make an angle α of the fast axis with respect to the absorption axis (11A) be at least 5 and at most 40.

Description

TECHNICAL FIELD [0001] The present invention relates to a polarizing plate, an image display device, and an image display device, and more particularly to a polarizing plate, an image display device, and an image display device,

The present invention relates to a method of improving a spot contrast in a polarizing plate, an image display apparatus, and an image display apparatus.

In a liquid crystal display device, a polarizing plate (upper (upper) polarizing plate) is usually disposed on the image display surface side of the liquid crystal cell. The polarizing plate is generally composed of a polarizer such as a polyvinyl alcohol film which is stretched by iodine or the like and a protective film bonded to one surface of the polarizer and for protecting the polarizer.

Conventionally, as a protective film, a film containing a cellulose ester represented by triacetylcellulose has been used. This is because cellulose ester is excellent in transparency and optical isotropy and has appropriate water permeability and is based on the advantage that moisture remaining in a polarizer can be dried through a cellulose ester film when a polarizing plate is produced will be.

However, since the cellulose ester has an excessively high moisture permeability, there has been a problem that when the humidity resistance test is performed, the transmittance is increased and the polarization degree is lowered due to soil color. To solve this problem, a polarizing plate using a cycloolefin resin as a protective film has been proposed (see JP-A-6-51117). In addition, for the purpose of improving the durability, it is desired to use a universal film which is inexpensive as compared with the cellulose ester film and is easily available in the market or can be produced by a simple method, as a protective film. For example, As an alternative to the film, an attempt has been made to use a polyester film such as polyethylene terephthalate (see, for example, Japanese Patent Laid-Open No. 2007-279243).

Incidentally, a liquid crystal display device such as a notebook type personal computer may be used not only indoors but also outdoors. When the observer visually observes the display image of the liquid crystal display device over the polarizing sunglasses, the observer may attach the polarizing sunglass to the observer by the angle formed between the absorption axis of the polarizing plate and the absorption axis of the polarizing sunglass, The displayed image becomes difficult to appear dark, and the visibility may be lowered. Here, the " visibility " in the present specification is used as an index indicating whether or not a display image is less likely to be seen depending on an observation angle when an observer visually displays a display image over polarized sunglasses.

In order to solve this problem, it has been proposed to dispose a lambda / 4 retardation film on the observer side of the upper polarizing plate so that the angle of the polarizing plate in the fast axis direction with respect to the polarizer absorption axis direction is 45 degrees (for example, Japanese Patent Application Laid-Open No. 2009-122454).

In addition, it has been proposed to arrange the polyethylene terephthalate film having retardation of 3000 to 30000 nm so that the angle formed by the slow axis of the polyethylene terephthalate film and the absorption axis of the polarizing plate is 45 degrees (see, for example, Japanese Patent Laid-Open Publication No. 2011-107198 Reference).

Japanese Patent Laid-Open No. 6-51117 Japanese Patent Laid-Open No. 2007-279243 Japanese Patent Application Laid-Open No. 2009-122454 Japanese Patent Application Laid-Open No. 2011-107198

In an image display device usable indoors and outdoors, when the observer visually observes the display image of the liquid crystal display device beyond the polarized sunglasses, not only the good visibility is ensured regardless of the viewing angle, It is desired to improve the spot contrast when observed with naked eyes (no polarized sunglasses). Here, when a polarizing plate provided with a protective film containing various materials is used for an image display device, when a protective film for a polarizing plate including a polyester film, typically polyethylene terephthalate, is used, It has been found that the contrast is improved to the extent that the contrast can be perceived with the naked eye. With respect to this point, the inventors of the present invention have conducted intensive researches, and it has been found that there is a correlation between the fast axis of the protective film relating to the birefringence that the polyester film usually has and the improvement of the spot contrast of the image display device. More specifically, it has been found that the direction of the fast axis of the protective film in a state of being embedded in the image display device can have a great influence on the spot contrast of the image display device.

P polarized light and S polarized light are present as light polarization components, and P-polarized light has a Brewster angle at which the reflectance is 0%, so that when the light is reflected, the P polarized light decreases and, as a result, the S polarized light increases. Therefore, if the S polarized light can be absorbed by the polarized sunglasses, the reflected light can be cut. For this reason, usually, the absorption axis of polarized sunglasses exists in the left and right directions. Therefore, when the observer wears the polarizing sunglasses and the absorption axis direction of the gastight polarizing plate such as the VA mode or the IPS mode is horizontal (the attitude in which the absorption axis direction of the polarizing sunglasses becomes almost horizontal) The polarized light sunglasses and the upper polarizer are in a state of parallel Nicole. The present inventors have made intensive researches on the light transmittance when the polarizing sunglasses and the polarizing plate are in the state of the parallel Nicol, and it has been found that the direction of the fast axis of the protective film has a great influence on the light transmittance.

The present invention is based on this finding of the inventors of the present invention. It is an object of the present invention to provide a liquid crystal display device capable of improving the visibility in the cross-Nicol state to some extent when the observer visually observes a display image of the liquid crystal display device beyond polarized sunglasses, Transmissive film having a birefringent property so as to have an angle of 45 degrees with respect to the surface of the image display device, the light transmittance in the state of the parallel Nicol is often observed frequently, and the image display device is visually observed State), and to provide a polarizing plate and an image display apparatus which can improve the contrast of a spot.

According to one aspect of the present invention, there is provided a polarizing plate comprising a polarizer and a light-transmissive film having birefringence in a plane provided on the observer side surface of the polarizer, And a direction in which the refractive index in the plane of the light-transmissive film is largest is referred to as a ground axis direction and a direction orthogonal to the ground axis direction in the plane is referred to as a leading axis direction, And the light-transmitting film is disposed such that the angle of the fast axis direction with respect to the axial direction is 5 degrees or more and 40 degrees or less.

According to another aspect of the present invention, there is provided an image display apparatus including the polarizing plate, wherein the polarizing plate is disposed such that an absorption axis direction of the polarizing plate is parallel to a horizontal direction.

According to another aspect of the present invention, there is provided an image display device characterized in that the polarizing plate is arranged in the image display device so that the absorption axis direction of the polarizer in the polarizing plate is along the horizontal direction. Method is provided.

According to the polarizing plate of one embodiment of the present invention, a light transmitting film having birefringence is used, a polarizer is disposed such that the absorption axis direction of the polarizer is along the horizontal direction, and the light transmitting film Transparent film is disposed so that the angle in the fast axis direction is 5 degrees or more and 40 degrees or less. Therefore, when the observer visually observes the display image of the liquid crystal display device beyond the polarizing sunglasses, the polarizer Transmittance in the state of parallel nichols, which is often observed frequently, can be improved as compared with the case where a light-transmitting film having birefringence is arranged in the plane so that the angle in the fast axis direction with respect to the absorption axis direction of the image It is possible to improve the spot contrast when the display device is observed with the naked eye (polarized sunglasses not mounted).

According to another aspect of the image display apparatus of the present invention, the polarizer is arranged such that the absorption axis direction of the polarizer is along the horizontal direction, and the angle of the light transmitting film in the fast axis direction with respect to the absorption axis direction of the polarizer is not less than 5 When the observer visually observes the display image of the liquid crystal display device beyond the polarizing sunglasses, the viewing angle of the polarizer in the fast axis direction with respect to the absorption axis direction of the polarizer is maintained Transmittance in the state of parallel Nicol, which is often observed frequently, can be improved as compared with the case where a light-transmitting film having birefringence is arranged in the plane so that the angle is 45 degrees, and the image display device can be visually observed ) Can be improved.

According to the method for improving the spot contrast in the image display apparatus of another embodiment of the present invention, the polarizer is disposed such that the absorption axis direction of the polarizer is along the horizontal direction, Transmissive film is disposed so that the angle of the polarizer is in a range of 5 to 40 degrees so that when the observer visually observes the display image of the liquid crystal display device beyond the polarized sunglasses, The transmittance in the state of parallel nichols, which is often observed frequently, can be improved as compared with the case where the light-transmitting film having birefringence is arranged in the plane so that the angle in the fast axis direction with respect to the axial direction is 45 degrees, Can be improved in the case of observing with a naked eye (no polarized sunglasses).

1 is a longitudinal sectional view of a polarizing plate according to an embodiment.
2 is a diagram showing the arrangement relationship of the polarizing plate and the polarizing sunglasses according to the embodiment and the polarization state of the light transmitted through the polarizing plate.
3 is a schematic configuration diagram of a liquid crystal display, which is an example of an image display apparatus according to the embodiment.

Hereinafter, a polarizing plate according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a longitudinal sectional view of a polarizing plate according to the present embodiment, Fig. 2 is a diagram showing the arrangement relationship of the polarizing plate and the polarizing sunglasses according to the present embodiment and the polarization state of light transmitted through the polarizing plate. In this specification, terms such as "film", "sheet", "plate" and the like are based on difference in designation and are not distinguished from each other. Thus, for example, the term " film " is a concept including a member which may also be referred to as a sheet or a plate. As one specific example, the "light-transmitting film" also includes a member called a "light-transmitting sheet" or a "light-transmitting plate".

In the present specification, the "weight average molecular weight" is a value obtained by dissolving in a solvent such as tetrahydrofuran (THF) and converting it into polystyrene by a conventionally known gel permeation chromatography (GPC) method.

&Quot; Polarizer "

1, the polarizing plate 10 includes a polarizer 11, a light-transmissive film 12 provided on the observer-side surface of the polarizer 11, and a polarizer 11 of the light-transmissive film 12 And a functional layer (13) provided on a surface opposite to the surface on which the optical element is mounted. The polarizing plate of the present invention may be provided with a polarizer and a light-transmitting film, and may not have a functional layer.

<Polarizer>

The polarizer 11 has an absorption axis, but the polarizer 11 is arranged such that the absorption axis direction 11A of the polarizer 11 follows the horizontal direction, as shown in Fig. Means that the absorption axis direction of the polarizer is within a range of less than +/- 10 DEG with respect to the horizontal direction. It is preferable that the polarizer 11 is arranged such that the absorption axis direction 11A of the polarizer 11 is within a range of less than +/- 5 degrees with respect to the horizontal direction.

Examples of the polarizer 11 include a polyvinyl alcohol film, a polyvinyl formal film, a polyvinyl acetal film, and an ethylene-vinyl acetate copolymerization system saponified film which are dyed and stretched by iodine or the like.

&Lt; Transparent film &

The light-transmissive film 12 functions as a protective film for protecting the polarizer 11.

The light-transmissive film 12 has birefringence in the plane. In determining whether or not the light-transmitting film has birefringence in the surface, it is assumed that Δn (Δn = n _x -n _y ) ≥0.0005 at the refractive index of 550 nm has birefringence, It is assumed that? N < 0.0005 does not have birefringence. The birefringence index can be measured by using KOBRA-WR manufactured by Oji Keisoku Co., Ltd., and setting the measurement angle to 0 ° and the measurement wavelength to 552.1 nm. At this time, the film thickness and the average refractive index are required for the calculation of the birefringence. The film thickness can be measured using, for example, a Digimatic Micrometer (manufactured by Mitsutoyo Corporation) or an electric micrometer (manufactured by Anritsu). The average refractive index can be measured using an Abbe's refractometer or an ellipsometer.

DELTA n of TD80UL-M (manufactured by Fuji Photo Film Co., Ltd.) containing triacetylcellulose and ZF16-100 (manufactured by Nippon Zeon Co., Ltd.) containing a cycloolefin polymer, which is generally known as an isotropic material, is 0.0000375, 0.00005, and it was judged that it is not birefringent (isotropic).

As another method for measuring the birefringence, two polarizing plates are used to obtain the orientation axis direction (principal axis direction) of the light-transmitting base material, and two axis refractive indices (n _x , n _y ) Or a black vinyl tape (for example, Yamato Vinyl Tape No. 200-38-21 38 mm wide) is attached to the back surface, and then a spectrophotometer (V7100 type, Automatic Absolute Reflectance Ratio Polarizing measurement: S-polarized light, and the 5-degree reflectance was measured when the slow axis was made parallel to the S polarized light and when the fast axis was made parallel, (N _x , n _y ) of each wavelength of the slow axis and the fast axis can be calculated from the refractive index (1).

R (%) = (1-n) ² / (1 + n) ² ... Equation (1)

The retardation value of the light-transmitting film 12 is not particularly limited as long as it is not zero. The term &quot; retardation &quot; refers to the refractive index n _{x in} the slow axis direction in the plane of the light-transmitting film, the refractive index n _{y in} the fast axis direction in the plane of the light-transmitting film, and the thickness d of the light- Is expressed by the following formula (2).

Retardation (Re) = (n _x , n _y ) x d Equation (2)

The retardation value is preferably 80 to 150 nm or 3000 nm or more as retardation value with respect to light having a wavelength of 550 nm. If the retardation value is less than 80 nm, the viewer may not be able to secure sufficiently the visibility when viewing the display image of the display device over the polarized sunglasses. In addition, when the retardation value is more than 150 nm and less than 3000 nm, an interference color is observed, and a chromatic color different from that of an actual display image may be seen. It is particularly preferable that the retardation value is not less than 3000 nm from 80 nm to 150 nm from the viewpoint that the film thickness precision is unnecessary. Specifically, for example, when a material having Δn of 0.1 is used and the retardation value is 80 nm to 150 nm, it is necessary to fabricate the material having a thickness d of 0.8 μm to 1.5 μm (with a gap of 0.7 μm or less), but when the retardation value is 3000 nm , It is sufficient if the thickness d is 30 占 퐉 or more.

The retardation can be measured by KOBRA-WR manufactured by Oji Keisei Co., Ltd. (measurement angle of 0 DEG, measurement wavelength of 589.3 nm). The refractive index (n _x , n _y ) of the slow axis and the fast axis of the light-transmitting film was measured by Abbe's refractometer (NAR-4T manufactured by Atago Co., Ltd.) and the light transmissive film thickness d Manufactured by REITS Co., Ltd.), and the unit is converted into nm. Then, the retardation can be obtained by the equation (2) using the refractive index (n _x , n _y ) and the thickness d obtained. As described above, the retardation is obtained by measuring the reflectance at 5 degrees in the case where the slow axis is made parallel to the S polarized light and the fast axis is made parallel, and n _x and n _y are obtained from the above formula (1) , The difference between the obtained n _x and n _y , and the thickness of the light-transmitting film.

The direction in which the refractive index in the plane of the light transmitting film 12 is largest is referred to as the slow axis direction 12A and the direction orthogonal to the slow axis direction 12A in this plane is referred to as the fast axis direction 12B 2, the angle? Of the fast axis direction 12B of the light transmitting film 12 with respect to the absorption axis direction 11A of the polarizer 11 is 5 degrees or more 40 degrees or less. Therefore, the fast axis direction 12B of the light-transmitting film 12 is positioned with respect to the absorption axis direction 11A of the polarizer 11. The angle alpha of the fast axis direction 12B of the light transmitting film 12 with respect to the absorption axis direction 11A of the polarizer 11 is preferably not less than 10 degrees from the viewpoint of ensuring the visibility as polarized sunglasses, 35 degrees or less, and more preferably 15 degrees or more and 30 degrees or less.

A light-transmitting film 12 is difference between the refractive index n _y in the light-transmitting film 12 slow axis direction (12A), the refractive index n _x and a slow axis direction (12A) and in a direction orthogonal to the fast axis direction (12B) of the △ n is preferably not less than 0.01 and not more than 0.30. When the refractive index difference DELTA n is less than 0.01, the difference in reflectance when the slow axis and the fast axis are set in the horizontal direction becomes small, and the effect of improving the spot contrast obtained is small. On the other hand, when the refractive index difference DELTA n is more than 0.30, it is necessary to excessively increase the draw ratio, so that tearing, fracture, etc. are apt to occur and practical utility as an industrial material may be remarkably lowered. Preferably, the lower limit of the refractive index difference DELTA n is 0.05, more preferably 0.07. The preferred upper limit of the refractive index difference DELTA n is 0.27. When the refractive index difference DELTA n exceeds 0.27, the durability of the light-transmitting film in the heat and humidity resistance test may be deteriorated depending on the kind of the light-transmitting film. From the viewpoint of ensuring excellent durability in the heat and humidity resistance test, a more preferable upper limit of the refractive index difference DELTA n is 0.25.

The light-transmissive film 12 is not particularly limited as long as it is a light-transmissive film having birefringence in the surface. Examples of such a light-transmitting film include a polyester film, a polycarbonate film, a cycloolefin polymer film, and an acrylic film. Of these, a polyester film and a polycarbonate film are preferable from the viewpoint that the expression of the refractive index difference DELTA n is large and the effect of improving the spot contrast is easily obtained. In addition, even a cellulose ester film can be used as long as it is a cellulose ester film which is stretched to have birefringence in its surface.

Examples of the polyester film include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylene dimethylene terephthalate), polyethylene naphthalate (polyethylene-2,6-naphthalate, , 4-naphthalate, polyethylene-1,5-naphthalate, polyethylene-2,7-naphthalate, polyethylene-2,3-naphthalate).

The polyester used in the polyester film may be a copolymer of the above-mentioned polyesters, and the polyester may be used as a main component (for example, 80 mol% or more) and a small proportion (for example, 20 mol% or less) It may be blended with other kinds of resins.

As the polyester, polyethylene terephthalate (PET) or polyethylene-2,6-naphthalate (PEN) is particularly preferable because it has good balance of mechanical properties and optical properties. Particularly, it is preferable to include polyethylene terephthalate. Polyethylene terephthalate has high versatility, is easy to obtain, and can increase birefringence.

Examples of the polycarbonate film include aromatic polycarbonate films based on bisphenols (such as bisphenol A), aliphatic polycarbonate films such as diethylene glycol bisaryl carbonate, and the like.

As the cycloolefin polymer film, for example, a film containing a polymer such as a norbornene monomer and a monocyclic cycloolefin monomer can be mentioned.

Examples of the acrylic film include a poly (meth) acrylate film, a poly (meth) acrylate film and a methyl (meth) acrylate-butyl (meth) acrylate film.

Examples of the cellulose ester film include a cellulose triacetate film and a cellulose diacetate film. The cellulose ester film is excellent in light transmittance, and among the cellulose acylate films, triacetylcellulose film (TAC film) is preferable. The triacetylcellulose film is a light-transmissive film capable of setting an average light transmittance of 50% or more in a visible light region of 380 to 780 nm. The average light transmittance of the triacetylcellulose film is preferably 70% or more, and more preferably 85% or more.

As the triacetylcellulose film, in addition to pure triacetylcellulose, a fatty acid which forms an ester with cellulose such as cellulose acetate propionate and cellulose acetate butyrate may be used in combination with components other than acetic acid. If necessary, other cellulose lower fatty acid esters such as diacetyl cellulose or various additives such as plasticizers, ultraviolet absorbers, lubricants and the like may be added to these triacetylcellulose.

The thickness of the light-transmissive film 12 is preferably in the range of 5 占 퐉 to 300 占 퐉. If it is less than 5 占 퐉, the anisotropy of the mechanical properties becomes remarkable, and rupture and breakage are likely to occur, and practical utility as an industrial material may be remarkably lowered. On the other hand, if it exceeds 300 탆, the light-transmitting film is very rigid, and the elasticity specific to the polymer film is lowered, and practical utility as an industrial material is lowered. A more preferable lower limit of the thickness of the light-transmitting film is 10 占 퐉, a more preferable upper limit is 200 占 퐉, and a more preferable upper limit is 150 占 퐉.

The transmittance of the light-transmissive film 12 in the visible light region is preferably 80% or more, more preferably 84% or more. The transmittance can be measured by JIS K7361-1 (total light transmittance test method of plastic-transparent material).

The light-transmitting film may be subjected to surface treatment such as saponification treatment, glow discharge treatment, corona discharge treatment, ultraviolet (UV) treatment and flame treatment within the range not deviating from the object of the present invention.

The light-transmitting film 12 may be longitudinally uniaxial stretching, tenter stretching, sequential or simultaneous biaxial stretching. Among them, tilt stretching is preferably performed so that the orientation direction of the molecules is not parallel to the traveling direction and the width direction of the light-transmitting film. Since the roll-shaped polarizer is manufactured while its stretching process is controlled with extremely high accuracy, an absorption axis exists along the longitudinal direction except for a special case. Therefore, the light-transmitting film and the polarizer, which are obliquely stretched by the roll- By bonding, a polarizing plate having an angle formed by the absorption axis direction of the polarizer and the fast axis direction of the light transmissive film other than parallel and orthogonal can be formed.

<Functional layer>

The functional layer 13 is provided on the surface of the light-transmissive film 12 opposite to the surface on which the polarizer 11 is provided as described above. The functional layer 13 is a layer which is intended to exhibit a certain function. Specifically, the functional layer 13 is a layer which exhibits one or more functions such as hard coatability, antistatic property, antireflection property, antistatic property, . The refractive index of the functional layer 13 in the direction parallel to the fast axis direction 12B of the light transmissive film 12 is lower than the refractive index of the fast axis direction 12B of the light transmissive film 12. When a functional layer whose refractive index in a direction parallel to the slow axis direction of the light-transmitting film is higher than the refractive index in the slow axis direction of the light-transmitting film is used, the light- Is arranged to follow the horizontal direction.

Further, one or more other functional layers may be provided on the side of the functional layer 13 opposite to the side on which the light-transmissive film 12 is provided. As another functional layer, a layer exhibiting one or more functions such as hard coatability, antifogging property, antireflection property, antistatic property or antifouling property can be exemplified as the functional layer 13 described above.

(Hard coat layer)

The hard coat layer is a layer exhibiting hard coatability, and specifically has a hardness of "H" or higher at a pencil hardness test (4.9 N load) prescribed by JIS K5600-5-4 (1999).

The thickness of the hard coat layer is preferably 1.0 占 퐉 or more and 10.0 占 퐉 or less. When the thickness of the hard coat layer is within this range, desired hardness can be obtained. In addition, the hard coat layer can be made thinner, and the hard coat layer can be prevented from being broken or curling. The thickness of the hard coat layer can be determined by observing the cross section of the hard coat layer with a transmission electron microscope (TEM, STEM) (magnification preferably 10,000 times or more). Specifically, an image of a transmission electron microscope is used to measure the film thicknesses of three first transparent layers in one image, and this is divided into five images, and an average value of the measured film thicknesses is calculated. The lower limit of the thickness of the hard coat layer is more preferably 1.5 탆 or more, and the upper limit is more preferably 7.0 탆 or less, and the thickness of the hard coat layer is more preferably 2.0 탆 or more and 5.0 탆 or less.

The hard coating layer comprises, for example, at least a binder resin. The binder resin is obtained by polymerizing (crosslinking) a photopolymerizable compound by light irradiation. The photopolymerizable compound has at least one photopolymerizable functional group. In the present specification, the "photopolymerizable functional group" is a functional group capable of undergoing polymerization reaction by light irradiation. Examples of the photopolymerizable functional group include ethylenic double bonds such as (meth) acryloyl group, vinyl group and allyl group. The term "(meth) acryloyl group" is meant to include both of "acryloyl group" and "methacryloyl group". Examples of the light to be irradiated when the photopolymerizable compound is polymerized include visible light and ionizing radiation such as ultraviolet rays, X-rays, electron beams, alpha rays, beta rays and gamma rays.

Examples of the photopolymerizable compound include a photopolymerizable monomer, a photopolymerizable oligomer or a photopolymerizable polymer, and they can be suitably adjusted and used. As the photopolymerizable compound, a combination of a photopolymerizable monomer and a photopolymerizable oligomer or a photopolymerizable polymer is preferable.

Photopolymerizable monomer

The photopolymerizable monomer has a weight average molecular weight of less than 1,000. As the photopolymerizable monomer, a polyfunctional monomer having two photopolymerizable functional groups (i.e., bifunctional) or more is preferable. In the present specification, the "weight average molecular weight" is a value obtained by dissolving it in a solvent such as tetrahydrofuran (THF) and converting it into polystyrene by a conventionally known gel permeation chromatography (GPC) method.

Examples of the bifunctional or higher functional monomer include trimethylolpropane tri (meth) acrylate, tripropylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, dipropylene glycol di (meth) (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol tetra (Meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, tripentaerythritol octa (Meth) acrylate, isocyanuric acid tri (meth) acrylate, diisocyanuric acid di (meth) acrylate, polyester tri (meth) (Meth) acrylate, isobornyl di (meth) acrylate, dicyclopentyl (meth) acrylate, diglycerol tetra (meth) acrylate, (Meth) acrylate, tricyclodecane di (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, and those modified with PO and EO.

Among these, from the viewpoint of obtaining a hard coat layer having a high hardness, it is preferable to use at least one selected from the group consisting of pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPPA) and the like are preferable.

Photopolymerization Oligomer

The photopolymerizable oligomer has a weight average molecular weight of 1000 or more and less than 10,000.

The photopolymerizable oligomer is preferably a bifunctional or higher polyfunctional oligomer. Examples of the polyfunctional oligomer include polyester (meth) acrylate, urethane (meth) acrylate, polyester urethane (meth) acrylate, polyether (meth) acrylate, polyol , Isocyanurate (meth) acrylate, and epoxy (meth) acrylate.

Photopolymerization  polymer

The photopolymerizable polymer preferably has a weight average molecular weight of 10000 or more, and preferably has a weight average molecular weight of 10000 or more and 80000 or less, more preferably 10000 or more and 40000 or less. When the weight-average molecular weight exceeds 80000, the viscosity of the coating film is lowered, resulting in deterioration of coating applicability and the appearance of the resulting optical film may be deteriorated. Examples of the polyfunctional polymer include urethane (meth) acrylate, isocyanurate (meth) acrylate, polyester urethane (meth) acrylate and epoxy (meth) acrylate.

The hard coat layer may be further added with a solvent-drying resin (such as a thermoplastic resin), or a thermosetting resin, if necessary, which is a film-forming resin by simply drying the solvent added for coating and particularly for adjusting the solid content.

When a solvent drying type resin is added, coating defects on the coating surface of the coating liquid can be effectively prevented when the hard coating layer is formed. The solvent-drying resin is not particularly limited, and a thermoplastic resin can be generally used. Examples of the thermoplastic resin include a styrene resin, a (meth) acrylic resin, a vinyl acetate resin, a vinyl ether resin, a halogen-containing resin, an alicyclic olefin resin, a polycarbonate resin, Amide-based resins, cellulose derivatives, silicone-based resins, and rubber or elastomer.

The thermoplastic resin is preferably amorphous and soluble in an organic solvent (in particular, a common solvent capable of dissolving a plurality of polymers or curable compounds). Particularly, styrene resins, (meth) acrylic resins, alicyclic olefin resins, polyester resins, cellulose derivatives (such as cellulose esters) and the like are preferable from the viewpoint of transparency and weatherability.

The thermosetting resin to be added to the hard coat layer is not particularly limited, and examples thereof include phenol resin, urea resin, diallyl phthalate resin, melamine resin, guanamine resin, unsaturated polyester resin, polyurethane resin, epoxy resin, aminoalkyd resin , Melamine-co-condensed resins, silicon resins, polysiloxane resins, and the like.

The hard coating layer can be formed by applying a composition for a hard coating layer containing the photopolymerizable compound to a light transmitting film, drying the coated composition, and then irradiating light to the composition for a hard coat layer in the form of a coating film such as ultraviolet light, ).

In addition to the photopolymerizable compound, the thermoplastic resin, thermosetting resin, solvent, and polymerization initiator may be added to the composition for the hard coat layer, if necessary. The composition for the hard coat layer may contain conventionally known dispersants, surfactants, antistatic agents, silane coupling agents, thickeners, coloring agents, and the like depending on the purpose of increasing the hardness of the hard coat layer, suppressing the curing shrinkage and controlling the refractive index. A leveling agent, a flame retardant, an ultraviolet absorber, an adhesion-imparting agent, a polymerization inhibitor, an antioxidant, a surface modifier, and a lubricant may be added.

Examples of the method for applying the composition for the hard coat layer include known coating methods such as spin coating, dipping, spraying, slide coating, bar coating, roll coating, gravure coating and die coating.

When ultraviolet rays are used as the light for curing the hard coat layer composition, ultraviolet rays emitted from ultrahigh pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arc, xenon arc, metal halide lamps, or the like can be used. As the wavelength of ultraviolet rays, a wavelength range of 190 to 380 nm can be used. Specific examples of the electron beam source include various types of electron beam accelerators such as a Cocross Walton type, a Bandegraft type, a resonant transformer type, an insulating core transformer type, or a linear type, a dinamic type, and a high frequency type.

(Antiglare layer)

The antiglare layer is a layer exhibiting antireflection properties. The surface of the antiglare layer is an uneven surface. By making the surface of the antiglare layer an uneven surface, it is possible to diffuse and reflect external light. The &quot; surface of the antiglare layer &quot; means a surface opposite to the side (back surface) of the antiglare layer on the side of the light transmitting film. The antiglare layer can be formed by containing organic fine particles or inorganic fine particles for forming an uneven surface in the composition for the hard coat layer.

(Antistatic layer)

The antistatic layer is a layer exhibiting antistatic properties. The antistatic layer can be formed by containing an antistatic agent in the composition for the hard coat layer. As the antistatic agent, conventionally known antistatic agents can be used. For example, cationic antistatic agents such as quaternary ammonium salts, fine particles such as tin-doped indium oxide (ITO), and conductive polymers can be used. When the antistatic agent is used, the content thereof is preferably 1 to 30% by mass based on the total mass of the total solid content.

(Stratum corneum)

The antifouling layer is a layer that exhibits antifouling properties. Specifically, dirt (fingerprints, water or oil ink, pencil, etc.) is hardly adhered to the outermost surface of the image display device or is easily wiped It is the layer that plays the role of being able. Further, by forming the antifouling layer, the antifouling property and the scratch resistance of the liquid crystal display device can be improved. The antifouling layer can be formed, for example, by a composition comprising a antifouling agent and a resin.

The antifouling agent is mainly intended to prevent contamination of the outermost surface of the image display apparatus, and it is also possible to give scratch resistance to the liquid crystal display apparatus. Examples of the antifouling agent include a fluorine-based compound, a silicon-based compound, and a mixed compound thereof. More specifically, a silane coupling agent having a fluoroalkyl group such as 2-perfluorooctylethyltriaminosilane, and the like can be used. In particular, those having an amino group can be preferably used.

It is preferable that the antifouling layer is formed so as to be the outermost surface. The antifouling layer can be replaced, for example, by imparting an antifouling property to the hard coat layer itself.

It is preferable that a low refractive index layer is formed on the hard coat layer or the antiglare layer.

(Low refractive index layer)

The low refractive index layer is for reducing the reflectance of light (for example, fluorescent light, natural light, etc.) from the outside when the light is reflected from the surface of the polarizing plate. The low refractive index layer has a lower refractive index than the hard coating layer or the antiglare layer. Specifically, for example, the low refractive index layer preferably has a refractive index of 1.45 or less, and more preferably has a refractive index of 1.42 or less.

The thickness of the low refractive index layer is not limited, but may be appropriately set within a range of usually about 30 nm to 1 mu m. The thickness of the low refractive index layer can be obtained by observing the cross section of the low refractive index layer with a transmission electron microscope (TEM, STEM) (magnification preferably being 10,000 times or more). Specifically, by using an image of a transmission electron microscope, film thicknesses of three first low refractive index layers in one image are measured, and these are divided into five images, and an average value of the measured film thicknesses is calculated. The thickness d _A (nm) of the low refractive index layer preferably satisfies the following formula (3).

_{d A = mλ / (4n A} ) ... (3)

In the above formula, n _A represents a refractive index of the low refractive index layer, m represents a positive odd number, preferably 1, and? Is a wavelength, preferably a value in a range of 480 nm to 580 nm.

The low refractive index layer preferably satisfies the following formula (4) from the viewpoint of lowering the reflectance.

_{120 <n A d A <145} ... (4)

Although the low refractive index layer is effective in a single layer, it is also possible to provide two or more low refractive index layers for the purpose of adjusting a lower minimum reflectance or a higher minimum reflectance. When two or more low refractive index layers are provided, it is preferable to provide a difference in the refractive index and the thickness of each low refractive index layer.

The low refractive index layer is preferably 1) a resin containing low refractive index particles such as silica or magnesium fluoride, 2) a fluorine resin as a low refractive index resin, 3) a fluorine resin containing silica or magnesium fluoride, 4) A thin film of a low refractive index material such as magnesium, or the like. For the resin other than the fluororesin, the same resin as the binder resin constituting the hard coat layer described above can be used.

The silica is preferably a hollow silica fine particle, and such a hollow silica fine particle can be produced by, for example, the manufacturing method described in the embodiment of Japanese Patent Application Laid-Open No. 2005-099778.

<Improvement of Spot Contrast by Polarizing Plate>

The polarizing plate 10 includes the polarizer 11 arranged so that the absorption axis direction 11A of the polarizer 11 is along the horizontal direction and the polarizer 11 disposed along the absorption axis direction 11A of the polarizer 11, Transmitting film 12 arranged so that the angle alpha of the fast axis direction 12B of the light-transmitting film 12 is not less than 5 degrees and not more than 40 degrees. The present inventors confirmed that by using this polarizing plate 10 as a polarizing plate positioned on the observer side of the display apparatus, that is, a so-called top polarizing plate, the contrast of the spot can be effectively increased to such an extent that the degree of improvement can be detected with the naked eye. The detailed reason for this phenomenon is unclear, but the following may be considered as a factor. However, the present invention is not limited to the following estimation.

First, the spot contrast is calculated as {(luminance of white display + reflection of external light) / (luminance of black display + reflection of external light)}, and the higher the obtained contrast value, the better the contrast.

Therefore, if the reflection of external light on the surface of the light-transmissive film 12 can be reduced, the contrast of the spot can be improved. On the other hand, each layer included in the polarizing plate is expected to exhibit various functions, and the refractive index setting of each layer determined by the material used for each layer and the material is naturally restricted. As a result, a refractive index difference inevitably occurs between the light-transmissive film 12 and the functional layer 13, except for a special case. Further, unlike the illustrated embodiment, it is assumed that a layer such as the functional layer 13 is not provided on the observer side of the light-transmissive film 12, but even in this case, the refractive index interface, Permeable film 12, as shown in Fig. This difference in refractive index causes reflection of external light at the interface between the light-transmissive film 12 and the functional layer 13, which is one factor of lowering the spot contrast of the display device.

On the other hand, there exist P polarized light and S polarized light as polarization components of light that can enter the display device and cause a spot contrast. The reflectance of the P-polarized light is lower than that of the S-polarized light, and the P-polarized light has a Brewster angle at which the reflectance is 0%. As a result, polarized light component (S polarized light) that oscillates in the horizontal direction is inevitably included in the light incident on the image display surface of the image display device after being reflected by the bottom surface or the ceiling surface. In view of the above, even if the average refractive index determined depending on the material to be used differs between the light-transmitting film 12 and the functional layer 13, the in-plane refractive index along the horizontal direction of the light- It is possible to effectively prevent reflection of external light between the light-transmissive film 12 and the functional layer 13, which causes a reduction in spot contrast, as long as it is close to the in-plane refractive index along the horizontal direction of the functional layer 13. [

Therefore, in the polarizing plate 10 of the present embodiment, the difference in average refractive index between the light-transmissive film 12 and the functional layer 13, which can inevitably arise from the constraint of material selection, By using the film 12 and further imparting a birefringence even to the light-transmissive film 12 including a material normally treated with optical isotropy, light that dominates the reflectivity of the polarized light component oscillating in the horizontal direction The refractive index difference between the transmissive film 12 and the functional layer 13 in the horizontal direction is slightly reduced.

More specifically, since the average refractive index of the light-transmitting film 12 is generally higher than the average refractive index of the functional layer 13, the refractive index in the fast axis direction 12B Transmissive film 12 and the functional layer 13 in the horizontal direction is made within a range of 5 degrees or more and 40 degrees or less with respect to the absorption axis direction 11A of the polarizer 11 to reduce the difference in refractive index between the light- . By thus setting the fast axis direction 12B of the light transmitting film 12 included in the polarizing plate 10 to be in the range of 5 degrees or more and 40 degrees or less with respect to the absorption axis direction 11A of the polarizer 11, Transmitting film 12 and the functional layer 13 while allowing a refractive index difference to be generated between the film 12 and the functional layer 13 at an average index of refraction to secure a degree of freedom in selecting a material used for the light- ) And the functional layer 13 in the horizontal direction and reduces the contrast of the spot when observing the image display device with the naked eye (no polarized sunglasses) The reflection of the polarization component oscillating in the horizontal direction at the interface between the light-transmissive film 12 and the functional layer 13 is effectively reduced. As compared with the case of arranging the light transmitting film so that the angle in the fast axis direction with respect to the absorption axis direction of the polarizer is 45 degrees, the fast axis 12B with respect to the absorption axis direction 11A of the polarizer 11, The refractive index difference in the horizontal direction at the interface between the light-transmissive film 12 and the functional layer 13 can be further reduced by arranging the light-transmissive film 12 so that the angle of the light- It is possible to more effectively reduce the reflection of the polarization component oscillating in the horizontal direction at the interface between the light transmitting film 12 and the functional layer 13. When the functional layer 13 is not present, the light-transmitting base material 12 is in contact with the air, so that the fast axis direction 12B, which is the lowest refractive index among the in-plane refractive indexes of the light- The difference in the refractive index between the air can be reduced by setting the range of 5 degrees or more and 40 degrees or less with respect to the absorption axis direction 11A of the optical fiber 11. As a result, similarly to the above, reflection of the polarized light component oscillating in the horizontal direction, which is a main cause of lowering the spot contrast, can be effectively reduced.

Further, it is possible to reduce the reflection of the polarized light component (S polarized light) oscillating in the horizontal direction with a large incident ratio on the image display surface in the light transmissive film 12. As a result, Permeable film 12, as shown in Fig. Usually, the polarized light component that vibrates in the horizontal direction transmitted through the light-transmissive film is absorbed in the image display apparatus or becomes stray light and returns to the observer side. The stray light returned to the observer side produces a brightness distribution different from that of the display image, which is one of the factors for reducing the spot contrast. In this respect, in the present embodiment, since the polarizer 11 is disposed so that the absorption axis direction 11A of the polarizer 11 is along the horizontal direction, the polarizing element 11 vibrates in the horizontal direction transmitted through the light- Can be absorbed by the polarizer (11). This makes it possible to reduce the quantity of light of the polarized light component oscillating in the horizontal direction that returns to the observer's side after passing through the light-transmissive film 12, thereby effectively preventing the generation of stray light and effectively preventing the image display apparatus from being visually perceived In the state of mounting), it is possible to improve the spot contrast.

According to the present embodiment, as compared with the case where the light transmitting film is disposed so that the angle of the polarizer in the fast axis direction with respect to the absorption axis direction is 45 degrees, the light transmitting film 12 vibrates in the horizontal direction on the surface of the light transmitting film 12 The reflection of the polarized light component (S polarized light) can be reduced, so that the spot contrast can be effectively improved as compared with arranging the light transmitting film so that the angle in the fast axis direction with respect to the absorption axis direction of the polarizer is 45 degrees. Further, stray light returning to the observer side can be absorbed by the polarizer as a polarized light component (S polarized light) that vibrates in the horizontal direction transmitted through the light-transmitting film, so deterioration of image quality can be suppressed and further improvement in spot contrast can be achieved have.

2, since the absorption axis direction 11A of the polarizer 11 is in the horizontal direction, linearly polarized light in a direction parallel to the transmission axis orthogonal to the absorption axis is transmitted through the polarizer 11 . The linearly polarized light transmitted through the polarizer 11 changes its polarization state by the birefringence of the light-transmissive film 12 to become elliptically polarized light and is emitted from the light-transmissive film 12 in this elliptically polarized state. Then, the elliptically polarized light is emitted from the polarizing plate 10 through the functional layer 13 while maintaining the elliptically polarized light.

On the other hand, as described above, the observer wears the polarizing sunglasses and the absorption axis of the polarizer, such as the VA mode or the IPS mode, is set at an attitude (a direction in which the absorption axis direction of the polarizing sunglasses is substantially horizontal) The direction of the absorption axis 14A of the polarizing sunglasses 14 and the absorption of the polarizer 11 of the polarizing plate 10 are set so as to be equal to each other as shown in Fig. The axial direction 11A is in a state of parallel Nicol, but when the observer tilts in the lateral direction or when the observer is lying down, the polarized sunglasses and the polarizing plate are not in a state of parallel Nicol. Particularly, when the observer visually observes the display image in a state in which the absorption axis of the polarizing sunglasses is almost in the vertical direction, the polarizing sunglasses and the polarizing plate are in crossed-Nicol state.

The transmitted light intensity observed under Cross Nicol is represented by the following equation (5) when the angle formed by the absorption axis of the polarizer (the direction of the linearly polarized light) and the slow axis of the light-transmitting film having birefringence in the plane is defined as? .

^{_{I = I o · sin 2 (}} 2θ) · sin 2 (π · Re / λ) ... Equation (5)

In the formula (5), I is the intensity of light transmitted through the crossed-Nicol, I _o is the intensity of light incident on the light-transmitting film having a birefringence in the plane, λ is the wavelength of light, Re is the retardation of the transparent film.

When the light-transmissive film 12 is not provided, sin ² (2?) In the formula (5) becomes 0, and since the light does not transmit through the polarizing sunglasses, the visibility deteriorates. On the other hand, in the present embodiment, since the light-transmissive film 12 is provided, sin ² (2?) In the formula (5) takes a value larger than zero. Thus, even if the polarizing sunglasses and the polarizing plate are in a state of crossed-Nicol, visibility can be secured to some extent.

Further, in the case where the polarizing sunglasses and the polarizing plate are in a state of parallel Nicol, there is a case where a? / 4 retardation film having birefringence is arranged in the plane so that the angle of the polarizer in the fast axis direction with respect to the absorption axis direction is 45 degrees Transmissive film having birefringence is arranged in the plane so that the angle of the fast axis direction with respect to the absorption axis direction of the polarizer is not less than 5 degrees and not more than 40 degrees as compared with the case where the light- Retardation film was arranged such that the angle of the direction of the fast axis with respect to the absorption axis direction of the polarizer was 45 degrees in the case where the light transmitting film having birefringence was arranged so that the angle was 5 degrees or more and 40 degrees or less The transmittance is higher than the case. This is because of the following reasons. When the lambda / 4 retardation film is arranged so that the angle of the fast axis with respect to the absorption axis direction of the polarizer is 45 degrees, the linearly polarized light passing through the transmission axis of the polarizer is changed into the circularly polarized light. The state of the circularly polarized light is such that the state of the linearly polarized light that can pass through the transmission axis of the polarizer and the linearly polarized light (linearly polarized light that is absorbed by the absorption axis of the polarizer) oscillating in the direction perpendicular to the oscillation direction of the linearly polarized light It means the same state as half the state. Thus, even in an ideal state without reflection or absorption, when the absorption axis of the polarizing sunglasses and the absorption axis of the polarizing plate are in the state of parallel Nicol, the transmittance becomes half. In contrast, when a light transmitting film having birefringence is arranged in the plane so that the angle of the fast axis with respect to the absorption axis direction of the polarizer is not less than 5 degrees and not more than 40 degrees, the linearly polarized light having passed through the transmission axis of the polarizer, The polarization state is changed. The state of this elliptically polarized light is such that the linearly polarized light component that can pass through the transmission axis of the polarizer is larger than the linearly polarized light component (linearly polarized light absorbed by the absorption axis of the polarizer) oscillating in a direction perpendicular to the oscillation direction of the linearly polarized light It means the same state as existing state. Therefore, when the absorption axis of the polarizing sunglasses and the absorption axis of the polarizing plate are in the state of parallel Nicol, the transmittance is not reduced to half or less, and the angle of the fast axis direction with respect to the absorption axis direction of the polarizer is 45 deg. The transmittance is higher than that in the case where the four-phase difference film is disposed. In the present embodiment, since the light transmitting film 12 is disposed so that the angle of the fast axis direction 12B with respect to the absorption axis direction 11A of the polarizer 11 is 5 degrees or more and 40 degrees or less, The transmittance is higher than that in the case where the? / 4 phase difference film is arranged so that the angle in the fast axis direction with respect to the direction is 45 degrees.

&Quot; Improvement method of spot contrast in image display device and image display device &quot;

The polarizing plate 10 can be incorporated in an image display apparatus. Examples of the image display device include a liquid crystal display (LCD), a cathode ray tube display (CRT), a plasma display (PDP), a light emitting device display (ELD), a field emission display (FED), a touch panel, Paper and the like. 3 is a schematic configuration diagram of a liquid crystal display, which is an example of an image display apparatus incorporating an optical film according to the present embodiment.

The image display apparatus 20 shown in Fig. 3 is a liquid crystal display. The image display device 20 includes a backlight unit 30 and a liquid crystal panel 40 having a polarizing plate 10 disposed closer to the observer than the backlight unit 30. [

The backlight unit 30 preferably includes a white light emitting diode (white LED) as a backlight source. The white LED is a device that emits white light by combining a phosphor or a light emitting diode that emits blue light or ultraviolet light using a phosphor compound, that is, a compound semiconductor. Among them, a white light emitting diode including a light emitting element comprising a combination of a blue light emitting diode using a compound semiconductor and a yttrium aluminum garnet yellow phosphor has a continuous and broad emission spectrum, which is effective for improvement of spot contrast And is also suitable as the backlight light source in the present invention. In addition, since the white LED having a small power consumption can be widely used, it is possible to exhibit the effect of energy saving.

3 includes a protective film 41 such as a triacetylcellulose film (TAC film), a polarizer 42, a retardation film 43, and a protective film 41 from the backlight unit 30 side toward the viewer side. The adhesive layer 44, the liquid crystal cell 45, the adhesive layer 46, the retardation film 47, and the polarizing plate 10 are stacked in this order. In the liquid crystal cell 45, a liquid crystal layer, an alignment layer, an electrode layer, a color filter, and the like are arranged between two glass substrates.

The polarizing plate 10 is disposed in the image display device 20 so that the absorption axis direction 11A of the polarizer 11 follows the horizontal direction. The light transmitting film 12 of the polarizing plate 10 is arranged such that the angle alpha of the fast axis direction 12B of the light transmitting film 12 with respect to the absorption axis of the polarizer 11 is 5 degrees or more and 40 degrees or less Needless to say, there is.

The image display device 20 is preferably a VA mode or IPS mode liquid crystal display device. The VA (Vertical Alignment) mode is an operation mode in which the liquid crystal molecules are oriented so as to be perpendicular to the substrate of the liquid crystal cell when no voltage is applied, and the dark display is indicated by dropping the liquid crystal molecules by the application of a voltage. The IPS (In-Plane Switching) mode is a mode in which the liquid crystal is rotated in the plane of the substrate by the electric field in the horizontal direction applied to the interdigital electrode pairs provided on one substrate of the liquid crystal cell to perform display.

The reason why the image display apparatus is preferably a VA mode or an IPS mode is that in the VA mode or the IPS mode, the absorption axis of the polarizer provided on the observer side of the liquid crystal cell follows the horizontal direction.

The image display apparatus may be an organic electroluminescence display (organic EL display) provided with an absorption axis of the polarizer in the horizontal direction. In this case, the polarizer, the? / 4 retarder, and the organic EL element may be laminated in this order on the observer side. As an image display method of an organic EL display, a color filter system in which a white display is obtained by passing a color filter through a color filter, a color filter system in which a blue display is used, and a part of the emitted light is passed through a color conversion layer A color conversion system, a three-color system using a red, green, and blue light-emitting layers, and a system using a color filter in combination with the three-color system. The material of the light emitting layer may be either low molecular weight or high molecular weight.

[Example]

In order to explain the present invention in detail, the following description will be made by way of examples, but the present invention is not limited to this description.

<Spot Contrast>

Hereinafter, the spot contrast was evaluated in each of the polarizers obtained in the examples and the comparative examples, but the spot contrast was evaluated as follows. The polarizing plate relating to Examples and Comparative Examples was replaced with a polarizing plate provided on the observer side of a liquid crystal monitor (FLATORON IPS226V (manufactured by LG Electronics Japan)) so that the absorption axis direction of the polarizer was in the horizontal direction. (P-3132, manufactured by LINTEC CO., LTD.) So as to be on the side of the liquid crystal panel, and the black display was applied from a place spaced about 50 to 60 cm from the black display liquid crystal monitor at a peripheral illuminance of 400 lux 15 persons were observed with the naked eye (no polarized sunglasses), and evaluated according to the following criteria. The evaluation was carried out for each of the polarizing plates formed using the same material, and the polarizing plate provided with the light transmitting film at an angle of 45 degrees with respect to the absorption axis direction of the polarizing film in the fast axis direction.

A: It was blacker than the reference, and the appearance and the spot contrast were excellent.

B: It was blacker than the reference, and the appearance and the spot contrast were excellent.

C: A little better than the reference, but the spot contrast was excellent.

D: Equivalent to the reference or the contrast of the spot has dropped.

Spot contrast: CR = LW / LB

Spot White Luminance (LW): Luminance when a display device is displayed in white at a spot with external light (peripheral illuminance of 400 lux)

Spot Black Luminance (LB): Brightness when the display device is displayed in black at a spot with ambient light (ambient illuminance 400 lux)

&Lt; Reflectivity &

Hereinafter, in each of the polarizing plates obtained in Examples and Comparative Examples, the reflectance was measured, but the reflectance was measured as follows. (V7100 type, automatic absolute reflectance measurement unit VAR-7010 manufactured by Nippon Bunko Co., Ltd.) after attaching a black vinyl tape (Yamato vinyl tape No. 200-38-21 38 mm width) to the side opposite to the light transmitting film side of the polarizing plate, Was used to measure the 5-degree reflectance in the case where the absorption axis of the polarizer was set parallel to the S-polarized light.

<Evaluation of visibility>

Each of the polarizing plates obtained in Examples and Comparative Examples was evaluated for visibility, but evaluation of visibility was performed as follows. The polarizing plate relating to the examples and comparative examples was used in such a manner that the TD80UL-M side of the polarizing plate, which will be described later, was placed in the liquid crystal display (FLATORON IPS226V (manufactured by LG Electronics Japan)) instead of the polarizer provided on the observer side, (P-3132, manufactured by Lintec Co., Ltd.) so as to be on the panel side. In a dark place, the liquid crystal display device is turned to a white display, and the angle between the absorption axis of the polarizing sunglasses and the absorption axis of the polarizer is rotated from 0 ° (parallel Nicol) to 90 ° (cross Nicol) Respectively.

A: The display image could be viewed at any angle (polarized sunglasses corresponded).

B: The visibility was slightly lowered depending on the angle, but it was a level at which there was no problem in actual use.

C: Although the visibility was lowered depending on the angle, the display image could be recognized.

D: There was an angle at which the displayed image could not be viewed depending on the angle (polarized sunglasses were not supported).

&Lt; Light transmittance in the state of parallel Nicol &

In each of the polarizers obtained in Examples and Comparative Examples, the light transmittance in a state of parallel Nicol was measured as follows. The polarizing plate relating to Examples and Comparative Examples was replaced with a polarizing plate provided on the observer side of a liquid crystal monitor (FLATORON IPS226V (manufactured by LG Electronics Japan)) so that the absorption axis direction of the polarizer was in the horizontal direction. (Parallel Nicole) at an angle formed by the absorption axis direction of the polarizing sunglasses and the absorption axis direction of the polarizing plate. Was measured with a luminance meter BM-5A (Topcon Corporation). The transmittance was expressed by the transmittance of the polarizing plate provided on both sides of the polarizer, that is, TD80UL-M described later, as 100%.

<Overall evaluation>

A comprehensive evaluation was conducted based on the following criteria.

◎: Over B evaluation in spot contrast evaluation and visibility evaluation.

○: C evaluation or more in spotlight contrast evaluation and visibility evaluation.

X: D evaluation in spot contrast evaluation and visibility evaluation.

&Lt; Example 1 >

(Fabrication of light-transmissive film)

The polyethylene terephthalate material was melted at 290 占 폚, extruded into a sheet form through a film-forming die, adhered on a rotating quenching drum cooled by water cooling, and cooled to produce an unstretched film. The unoriented film was preheated at 120 ° C for 1 minute with a biaxial stretching tester (manufactured by Toyo Seiki), and then uniaxially stretched 4.0 times at 120 ° C to obtain a light-transmitting film having birefringence in the surface . The refractive index n _x of the light-transmitting film at a wavelength of 550 nm was 1.701 and n _y = 1.6015, and Δn = 0.0995. The film thickness of the light-transmitting film was 75 占 퐉, and Re = 7500 nm.

(Production of polarizing plate)

A polyvinyl alcohol film having an average degree of polymerization of about 2400, a degree of saponification of 99.9 mol% or more and a thickness of 75 탆 was immersed in pure water at 30 캜 and then immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.02 / Lt; / RTI &gt; Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 12/5/100 at 56.5 ° C. Subsequently, the substrate was washed with pure water at 8 占 폚 and dried at 65 占 폚 to obtain a polarizer in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was carried out mainly by iodine dyeing and boric acid treatment, and the total draw ratio was 5.3 times.

An active energy ray curable adhesive containing an alicyclic epoxy compound was placed on one side of the obtained polarizer and bonded together so that the angle formed by the absorption axis of the polarizer and the fast axis of the light transmitting film was 5 degrees. Subsequently, an active energy ray-curable adhesive of TD80UL-M (manufactured by Fuji Film Co., Ltd.), which is an isotropic film, containing no alicyclic epoxy compound was bonded and bonded to the side opposite to the side where the light-transmitting film of the polarizer was laminated , A polarizing plate relating to Example 1 was produced.

&Lt; Example 2 >

A polarizing plate relating to Example 2 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 10 degrees.

&Lt; Example 3 >

A polarizing plate relating to Example 3 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 15 degrees.

<Example 4>

A polarizing plate relating to Example 4 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 30 degrees.

&Lt; Example 5 >

A polarizing plate relating to Example 5 was produced in the same manner as in Example 1 except that the angle formed by the absorption axis of the polarizer and the fast axis of the light transmitting film was 35 degrees.

&Lt; Example 6 >

A polarizing plate relating to Example 6 was produced in the same manner as in Example 1 except that the angle formed between the absorption axis of the polarizer and the fast axis of the light transmitting film was 40 degrees.

&Lt; Comparative Example 1 &

A polarizing plate relating to Comparative Example 1 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was zero.

&Lt; Comparative Example 2 &

A polarizing plate relating to Comparative Example 2 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 45 degrees.

&Lt; Comparative Example 3 &

A polarizing plate relating to Comparative Example 3 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 60 degrees.

&Lt; Comparative Example 4 &

A polarizing plate relating to Comparative Example 4 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 75 degrees.

&Lt; Comparative Example 5 &

A polarizing plate relating to Comparative Example 5 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 90 degrees.

&Lt; Example 7 >

A composition for a hard coat layer obtained by dissolving 30 mass% of pentaerythritol triacrylate (PETA) in a solvent of methyl isobutyl ketone (MIBK) and adding 5 mass% of a photopolymerization initiator (Irgacure 184, manufactured by BASF) , And applied by a bar coater so as to have a thickness of 5 mu m after drying, to form a coating film on the light-transmissive film produced in Example 1. Subsequently, the formed coating film was heated at 70 占 폚 for 1 minute to remove the solvent, and the coated surface was irradiated with ultraviolet rays to fix it, thereby obtaining a light-transmitting film with a hard coat layer having a hard coat layer having a refractive index of 1.53.

The polarizing element was bonded to the surface opposite to the side of the hard coat layer side of the light transmitting film so that the angle formed by the absorption axis of the polarizer and the fast axis of the hard coat layer-attached light transmitting film was 15 degrees. , A polarizing plate relating to Example 7 was produced.

&Lt; Example 8 >

A polarizing plate relating to Example 8 was produced in the same manner as in Example 7 except that the angle formed by the absorption axis of the polarizer and the fast axis of the hard coat layer-attached light-transmitting film was 30 degrees.

&Lt; Comparative Example 6 >

A polarizing plate relating to Comparative Example 6 was produced in the same manner as in Example 7 except that the angle between the absorption axis of the polarizer and the fast axis of the hard-coating layer-attached light-transmitting film was zero.

&Lt; Comparative Example 7 &

A polarizing plate relating to Comparative Example 7 was produced in the same manner as in Example 7 except that the angle between the absorption axis of the polarizer and the fast axis of the hard-coating layer-attached light-transmitting film was 45 degrees.

&Lt; Comparative Example 8 >

A polarizing plate relating to Comparative Example 8 was produced in the same manner as in Example 7 except that the angle formed by the absorption axis of the polarizer and the fast axis of the hard coat layer-attached light-transmitting film was 60 degrees.

&Lt; Comparative Example 9 &

A polarizing plate relating to Comparative Example 9 was produced in the same manner as in Example 7 except that the angle formed by the absorption axis of the polarizer and the fast axis of the hard coat layer-attached light-transmitting film was 90 degrees.

&Lt; Example 9 >

A light-transmitting film having birefringence in a plane was produced in the same manner as in Example 1 except that the film thickness of the unstretched film was adjusted and the uniaxial stretching at a temperature of 120 占 폚 was fixed at 3.0 times. Refractive index n _x = 1.6922 and n _y = 1.6123 at a wavelength of 550 nm of this light-transmitting film, and? N = 0.0799. The film thickness of the light-transmitting film was 36 占 퐉, and Re = 2900 nm.

The polarizing plate relating to Example 9 was produced in the same manner as in Example 1 except that the light transmitting film was used and the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 15 degrees.

&Lt; Example 10 >

A polarizing plate relating to Example 10 was produced in the same manner as in Example 9 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 30 degrees.

&Lt; Comparative Example 10 &

A polarizing plate relating to Comparative Example 10 was produced in the same manner as in Example 9 except that the angle formed by the absorption axis of the polarizer and the fast axis of the light transmitting film was zero.

&Lt; Comparative Example 11 &

A polarizing plate relating to Comparative Example 11 was produced in the same manner as in Example 9 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 45 degrees.

&Lt; Comparative Example 12 >

A polarizing plate relating to Comparative Example 12 was produced in the same manner as in Example 9 except that the angle formed between the absorption axis of the polarizer and the fast axis of the light transmitting film was 60 degrees.

&Lt; Comparative Example 13 &

A polarizing plate relating to Comparative Example 13 was produced in the same manner as in Example 9 except that the angle formed between the absorption axis of the polarizer and the fast axis of the light transmitting film was 90 degrees.

&Lt; Example 11 >

Cellulose acetate propionate (CAP504-0.2, manufactured by Eastman Chemical Co., Ltd.) was dissolved in methylene chloride so as to have a solid concentration of 15%, and then plied and dried on glass to obtain an unstretched film. The unstretched film was uniaxially stretched 1.5 times at 160 캜 at a free end with a biaxial stretching tester (manufactured by Toyo Seiki) to prepare a light-transmitting film having birefringence in the surface. Refractive index n _x = 1.4845 and n _y = 1.4835 at a wavelength of 550 nm of the light-transmitting film, and? N = 0.001. The film thickness of the light-transmitting film was 138 m, and Re = 138 nm.

Using this light-transmitting film, the polarizing plate relating to Example 11 was produced in the same manner as in Example 1 except that the angle between the absorption axis of the polarizer and the fast axis of the light-transmitting film was 15 degrees.

&Lt; Example 12 >

A polarizing plate relating to Example 12 was produced in the same manner as in Example 11 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 30 degrees.

&Lt; Comparative Example 14 >

A polarizing plate relating to Comparative Example 14 was produced in the same manner as in Example 11 except that the angle formed by the absorption axis of the polarizer and the fast axis of the light transmitting film was zero.

&Lt; Comparative Example 15 &

A polarizing plate relating to Comparative Example 15 was produced in the same manner as in Example 11 except that the angle formed between the absorption axis of the polarizer and the fast axis of the light transmitting film was 45 degrees.

&Lt; Comparative Example 16 >

A polarizing plate relating to Comparative Example 16 was produced in the same manner as in Example 11 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 60 degrees.

&Lt; Comparative Example 17 >

A polarizing plate relating to Comparative Example 17 was produced in the same manner as in Example 11 except that the angle between the absorption axis of the polarizer and the fast axis of the light transmitting film was 90 degrees.

The results are shown in Table 1 below.

As shown in Table 1, in Comparative Example 1, the contrast of the spot was superior to that of Comparative Example 2, and the light transmittance in the parallel Nicol state was higher than that of Comparative Example 2, but the visibility was not ensured. In Comparative Examples 3 and 4, the light transmittance in the parallel Nicol state was higher and the visibility was also secured to some extent, but the contrast of the spot was equal to or lower than that of Comparative Example 2. In Comparative Example 5, the light transmittance in the parallel Nicol state was higher than that in Comparative Example 2, but the spot contrast was equal to or lower than that of Comparative Example 2, and the visibility was not ensured. On the other hand, in Examples 1 to 6, the contrast of the spot was better than that of Comparative Example 2, and the light transmittance in the state of parallel Nicol was higher than that of Comparative Example 2. In addition, visibility was secured to some extent.

Further, as shown in Table 1, in Comparative Example 6, the contrast of the spot was superior to that of Comparative Example 7, and the light transmittance in the parallel Nicol state was higher than that of Comparative Example 7, but the visibility was not ensured. In Comparative Example 8, the light transmittance in the parallel Nicol state was higher and the visibility was also secured to some extent, but the contrast of the spot was equal to or lower than that of Comparative Example 7. In Comparative Example 9, the light transmittance in the parallel Nicol state was higher than that in Comparative Example 7, but the spot contrast was equal to or lower than that of Comparative Example 7, and the visibility was not ensured. On the other hand, in Examples 7 and 8, the contrast of the spot was superior to that of Comparative Example 7 which is the reference, and the light transmittance in the state of parallel Nicol was higher than that of Comparative Example 7. In addition, visibility was secured to some extent.

Further, as shown in Table 1, in Comparative Example 10, the contrast of the spot was superior to that of Comparative Example 11, and the light transmittance in the state of parallel Nicol was higher than that of Comparative Example 11, but the visibility was not ensured. In Comparative Example 12, the light transmittance in the parallel Nicol state was higher and the visibility was also secured to some extent, but the contrast of the spot was equal to or lower than that of Comparative Example 11. In Comparative Example 13, the light transmittance in the parallel Nicol state was higher than that in Comparative Example 11, but the spot contrast was equal to or lower than that of Comparative Example 11, and the visibility was not ensured. On the other hand, in Examples 9 and 10, the contrast of the spot was superior to that of Comparative Example 11, which was the reference, and the light transmittance in the state of parallel Nicol was higher than that of Comparative Example 11. In addition, visibility was secured to some extent.

As shown in Table 1, in Comparative Example 14, the contrast of the spot was superior to that of Comparative Example 15, and the light transmittance in the parallel Nicol state was higher than that of Comparative Example 11, but the visibility was not ensured. In Comparative Example 16, the light transmittance in the parallel Nicol state was higher and the visibility was also secured to some extent, but the contrast of the spot was equal to or lower than that of Comparative Example 15.

In Comparative Example 17, the light transmittance in the parallel Nicol state was higher than that in Comparative Example 15, but the contrast of the spot was equal to or lower than that of Comparative Example 15, and the visibility was not ensured. On the other hand, in Examples 11 and 12, the contrast of the spot was superior to that of Comparative Example 15 which is a reference, and the light transmittance in the state of parallel Nicol was higher than that of Comparative Example 15. In addition, visibility was secured to some extent.

In the above embodiment, when the angle of the fast axis of the light transmitting film with respect to the absorption axis of the polarizer is in the positive direction, that is, when the polarizing plate is viewed from the front, the left side of the fast axis of the light transmitting film is positioned above the absorption axis of the polarizer However, even in a polarizing plate in which the right-handed axis of the light-transmitting film with respect to the absorption axis of the polarizer is in the negative direction, that is, when the polarizing plate is viewed from the front, Evaluation and measurement similar to those described above were carried out, and the same results as those of the above-mentioned examples were obtained.

10: polarizer
11: Polarizer
11A: absorption axis direction
12: light transmissive film
12A: Direction of the ground axis
12B:
13: Functional layer
14: polarized sunglasses
14A: absorption axis direction
20: Image display device

Claims (9)

A polarizing plate comprising a polarizer and a light-transmissive film having birefringence in a plane provided on the observer side surface of the polarizer,
The polarizer is arranged such that the absorption axis direction of the polarizer is along the horizontal direction,
Wherein a direction in which a refractive index in a plane of the light transmissive film is largest is referred to as a ground axle direction and a direction orthogonal to the ground axle direction in the plane is a leading axis direction, Wherein the light-transmitting film is disposed such that the angle in the axial direction is 5 degrees or more and 40 degrees or less. The polarizing plate according to claim 1, wherein the light-transmissive film is a polyester film. The optical film according to claim 1, wherein a refractive index in a direction which is formed on a surface of the light-transmissive film opposite to the surface on which the polarizer is formed and which is parallel to the fast axis direction of the light- Further comprising a functional layer having a refractive index lower than a refractive index in a fast axis direction of the transparent film. The polarizing plate according to claim 3, wherein the functional layer is a hard coating layer or an antiglare layer. An image display apparatus comprising the polarizing plate according to claim 1, wherein the polarizing plate is arranged so that an absorption axis direction of the polarizer is along a horizontal direction. The image display apparatus according to claim 5, wherein the image display apparatus is a VA mode or IPS mode liquid crystal display apparatus. The image display apparatus according to claim 5, further comprising a light emitting diode as a light source. The image display apparatus according to claim 5, wherein the image display apparatus further comprises a? / 4 retardation plate and the polarizing plate is arranged closer to an observer than the? / 4 retardation plate. A method of improving a spot contrast in an image display apparatus, wherein the polarizing plate according to claim 1 is disposed in an image display apparatus such that an absorption axis direction of the polarizer in the polarizing plate is along a horizontal direction.

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