JPH09101413A - Polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

(57) [Summary] [Structure] Contains a plurality of dyes selected to transmit the emission wavelength of a cold cathode fluorescent tube used for illuminating a liquid crystal panel and absorb external light of a wavelength other than that wavelength. A polarizing plate having a hard coat layer on its surface is arranged in the visible light path system of the liquid crystal display device. [Effect] Since the brightness of the displayed image is little attenuated and the external light reflected by the display device of the liquid crystal display device is largely attenuated, it is possible to provide a display device which has a high contrast and is easy to see even in a bright place. it can. No increase in the number of parts such as filters, and high mechanical reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate having an antiglare property and a liquid crystal display device having improved visibility by using the polarizing plate.

[0002]

2. Description of the Related Art When a display device such as a liquid crystal display device is used in a bright place where sunlight is incident,
The contrast decreases and the image becomes difficult to see. This is because external light such as sunlight is reflected by a display element such as a liquid crystal panel and enters the eyes together with the displayed image.

A device for reducing this reflected light has been conventionally devised. An example is shown below.

(1) Sharp Technical Report No. 54 (November 1992) pp. 39-42 discloses a technique of providing an antireflection film on a front protective plate in order to prevent reflection on the surface of a display device.

On the other hand, (2) Japanese Patent Application Laid-Open No. 3-116021 discloses a liquid crystal display device in which a colored glass arranged on the display surface side of a display device absorbs and attenuates reflected light having a wavelength of 500 to 600 nm. ing. Also, (3)
Japanese Patent Application Laid-Open No. 4-194803 discloses a filter including an absorption film formed on a transparent plastic substrate.

In the liquid crystal display device, the structure in which the front surface protection plate is arranged on the front surface of the liquid crystal panel is changed to the structure in which the polarizing plate of the liquid crystal panel is directly exposed to the outside. This is to prevent external light from being reflected on the front surface protection plate and to prevent display brightness from being reduced due to surface reflection. Therefore, a hard coat layer has been provided on the surface of the polarizing plate in order to prevent scratching.

[0007]

However, the antireflection film (1) is very expensive and can attenuate the reflected light on the surface of the display device, but it is reflected inside the display device. There is a problem that the incoming light cannot be attenuated.

The filter of (2) is colored glass, and generally contains rare earths such as neodymium. A plastic filter containing a rare earth compound has been devised, but it has a problem that it is more expensive than a transparent resin such as acrylic. On the other hand, in the filter of (3) above,
Since the inorganic film containing neodymium is directly formed on the transparent plastic substrate, there is a problem that the adhesion is weak.
This is because the rare earth compound has a small absorption coefficient and cannot be made thin when dispersed.

The present invention solves such a problem and is an inexpensive polarizing plate which attenuates light in an unnecessary wavelength region and which has a stable film structure and high mechanical reliability. It is an object of the present invention to provide a liquid crystal display device that attenuates reflected light from the display device and that has improved contrast and has excellent visibility.

[0010]

The first polarizing plate of the present invention is characterized in that a hard coat layer for absorbing light in a specific wavelength region is formed on the surface of the polarizing plate.

The second polarizing plate of the present invention is characterized in that a hard coat layer for absorbing light in a specific wavelength region is formed on the surface of the polarizing plate, and an antireflection layer is further laminated thereon.

The third polarizing plate of the present invention is characterized in that a hard coat layer which absorbs light in a specific wavelength region and has an antiglare effect due to surface irregular reflection is formed on the surface of the polarizing plate. .

The liquid crystal display device of the present invention is characterized in that the first to third polarizing plates are arranged in a visible light path system of the display device.

[0014]

In order to impart the function of absorbing light in a specific wavelength range to the hard coat layer on the surface of the polarizing plate, the hard coat agent to be coated has an unnecessary wavelength range other than the wavelength related to the display of the display device. It is necessary to include a component that absorbs light. This component has a high absorption coefficient and is preferably a dye that dissolves in the hard coat agent. In order to attenuate light in a plurality of wavelength regions, a plurality of dyes are contained in a preferable ratio. Further, if an antireflection layer is laminated or an antiglare effect due to surface irregular reflection is applied so that reflection and reflection of external light on the surface of the polarizing plate do not reduce the visibility of display, the visibility is further improved. Since the polarizing plate of the present invention is structurally the same as a polarizing plate with a hard coat layer, it has the same reliability as a polarizing plate available on the market.

The polarizing plate of the present invention, which absorbs light in a wavelength region other than the wavelength used for display in a liquid crystal display device, is provided in the optical path from the light source of the display device to the eye of the person who is watching the display device. When the display color is arranged, the display color passes through the polarizing plate and enters the eye, while the light other than the display color is absorbed by the polarizing plate.
In particular, when this polarizing plate is arranged on the outermost surface of the liquid crystal display device, external light reflected inside the liquid crystal display device passes through the polarizing plate twice before entering the eye, and therefore is absorbed by a square. The effect is great. Further, since the liquid crystal display device of the present invention is provided with the antireflection film, reflection on the display surface can be suppressed, so that an image with high contrast can be viewed. Further, since the liquid crystal display device of the present invention is provided with the antiglare function film, it is possible to suppress the reflection of external light on the display surface, so that an image that is easy to see can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

(Example 1) A first example of the polarizing plate of the present invention will be described.

FIG. 1 shows a cross section of the polarizing plate. The polarizing layer 10 made of polyvinyl alcohol containing iodine as a basic structure is provided with a transparent film of triacetyl cellulose (hereinafter referred to as T
It is sandwiched by 11).

An acrylic hard coat layer 12 having a thickness of 3 μm is formed on the surface of the TAC film. This hard coat layer contained 1% by weight of an azo dye, and its transmittance curve is shown in FIG. As can be seen from FIG. 7, it mainly absorbs light of 570 to 600 nm. This wavelength range is a wavelength range in which the human eye has a relatively high luminous sensitivity, and the reflected light gives a glare to the viewer.

The hard coat layer is not limited to an acrylic type, but a thermosetting resin cannot be used because of the durability of the polarizing plate, and it must be a photocuring resin.

(Embodiment 2) A first embodiment of the display device of the present invention will be described.

FIG. 5 shows a sectional view of the structure of the liquid crystal display device according to this embodiment. It is composed of the polarizing plate 50, the liquid crystal panel 51, the ordinary polarizing plate 52, and the backlight 53 described in the first embodiment. The liquid crystal panel is composed of liquid crystal sandwiched between glass substrates, transparent electrodes, color filters, etc., and the backlight is a cold cathode fluorescent tube, a light guide plate, a reflection plate,
It is composed of a diffusion plate. The polarizing plate is attached to the glass substrate of the liquid crystal panel via the adhesive 54,
The hard coat layer, which is a constituent element of the polarizing plate 50 and absorbs light in a specific wavelength region, is arranged so as to come to the outermost surface.

The structure of the liquid crystal panel and the backlight is not limited to the structure of this embodiment.

Light 55 from the backlight is the liquid crystal panel 5
The light used for the illumination of No. 1 and transmitted through the polarizing plate 52 and the liquid crystal panel 51 further passes through the polarizing plate 50 and enters the eyes of a person who is watching the display device.

On the other hand, external light 56 such as sunlight is partially reflected on the surface of the polarizing plate 50, and the rest passes through the polarizing plate 50, and then at the interface of the liquid crystal panel 51, the polarizing plate 52, the backlight 53 and the like. The light is reflected and again enters the eye through the polarizing plate 50.

In FIG. 8, the emission spectrum 80 of the cold cathode fluorescent lamp used for the backlight and the transmittance curve 70 of the polarizing plate 50 are shown in an overlapping manner. The left vertical axis in the figure shows the transmittance of the polarizing plate, and the right vertical axis shows the intensity of the emission spectrum of the cold cathode fluorescent tube.

As can be seen from this figure, the light of the emission wavelength of the cold cathode fluorescent tube, that is, the backlight is slightly absorbed, but since it is attenuated only once by this polarizing plate 50, most of it is a polarizing plate. It penetrates and enters the eye. Therefore,
There is little attenuation of the brightness of the image displayed on the LCD panel.

On the other hand, since the external light 56 reflected inside the liquid crystal display device passes through the polarizing plate twice before entering the eye, it is absorbed by the square of the transmittance 570.
Light in the wavelength region of up to 600 nm is greatly attenuated. A transmittance curve 81 for reflected light passing through the polarizing plate twice is also shown in FIG. This curve is the square of the transmittance value represented by the transmittance curve 70.

As described above, the polarizing plate of the present invention can greatly attenuate the reflected light from the inside of the display device without darkening the display image, so that a display device with a high contrast and easy to see even in a bright place can be obtained. Could be configured. In addition, an excellent liquid crystal display device was achieved in which the number of parts such as a cover glass and a filter was not increased, the cost was low, and effective light attenuation due to surface reflection was small.

Example 3 A second example of the polarizing plate of the present invention will be described.

Although the basic structure is the same as that of the first embodiment,
As shown in FIG. 2, an antireflection layer 20 composed of a multilayer film is formed on the surface of the hard coat layer, and the reflectance is reduced in a wide wavelength range of visible light. An antireflection film made of an inorganic material such as SiO ₂ does not have good adhesion to the TAC film, but has good adhesion to the hard coat layer 12.
The hard coat layer 12 has both a function as a light absorbing layer and a function as an adhesion improving layer. The antireflection film may be a single layer film instead of a multilayer film depending on the application. What is different from Example 1 is the dye contained in the hard coat layer 12, and in this example, 0.5 wt% of an azo dye and 0.8 wt% of a polymethine dye are contained. The polymethine dye mainly absorbs light having a wavelength of 500 nm to 530 nm.

The transmittance curve of the polarizing plate of this example is shown by the curve 90 in FIG. In FIG. 9, the emission spectrum 80 of the cold cathode fluorescent lamp used in the liquid crystal display device described in the second embodiment is also drawn.

The polarizing plate containing only the azo dye described in Example 1 only absorbed light having a wavelength of 570 to 600 nm, but by adding the polymethine dye, absorption by two kinds of dyes was performed. And the absorption of light having a wavelength of 500 to 530 nm is also largely absorbed. Further, since the surface is provided with the antireflection layer, the reflection on the surface of the polarizing plate could be suppressed to be small.

Example 4 Second Example of Liquid Crystal Display Device of the Present Invention
An example will be described.

The structure of the display device is the same as that of the liquid crystal display device described in the second embodiment, but the polarizing plate described in the third embodiment is used as the front polarizing plate 50. Also, the rear polarizing plate 5
2 has a hard coat layer containing the dye described in Example 3, but has an antireflection layer 2 composed of a multilayer film on the surface.
A polarizing plate in which 0 was not formed was used.

In the liquid crystal display device having the polarizing plate containing only the azo dye in the hard coat layer as described in Example 2,
Of the external light reflected inside the liquid crystal display device, mainly 57
Although it could only absorb light in the wavelength range of 0 to 600 nm, in a liquid crystal display device having a polarizing plate containing an azo dye and a polymethine dye in a hard coat layer as in this embodiment, the inside of the liquid crystal display device is 50 of the external light reflected by
Light in the wavelength range of 0 to 530 nm and 570 to 600 nm can be largely absorbed. Moreover, as can be seen from FIG. 9, there is little attenuation of light of the emission wavelength of the cold cathode fluorescent tube.

The external light 36 reflected on the surface of the polarizing plate, that is, the surface of the liquid crystal display device is reduced by the antireflection film.

Therefore, also in the display device of this embodiment,
By including the polarizing plate of Example 3, the reflected light on the surface of the display device is reduced, and the reflected light not related to the display or the reflected light from the inside of the display device is greatly attenuated without darkening the display image. Because you can
It was possible to construct a display device that has high contrast and is easy to see even in bright places.

(Example 5) A third example of the polarizing plate of the present invention will be described.

The structure is a sectional view as shown in FIG. 3, and in this embodiment, a 5 μm thick acrylic hard coat layer 30 containing silica fine particles is formed on the surface of the TAC film. This is aimed at the anti-glare effect due to surface irregular reflection, and can prevent the reflection of external light. Glossiness and haze can be adjusted by changing the particle size and density of the silica particles. Further, the hard coat layer contains 1% by weight of a quinone dye, and the transmittance curve is shown in FIG. As can be seen from FIG. 10, it mainly absorbs light of 520 to 580 nm. This wavelength region is a wavelength region in which the human eye has a relatively high luminosity factor, which causes glare.

Example 6 Third Example of Liquid Crystal Display Device of the Present Invention
An example will be described.

FIG. 6 shows a sectional view of the structure of the liquid crystal display device according to this embodiment. The polarizing plate 50, the phase difference compensating plate 60, the liquid crystal panel 51, the normal polarizing plate 52 described in the fifth embodiment,
It is composed of a reflector 61. The positional relationship of the liquid crystal panel, the phase difference compensating plate, the reflecting plate, etc. is not limited to the configuration of this embodiment.

External light 62 such as sunlight and indoor light passes through the front polarizing plate 50, and then the phase difference compensating plate 60 and the liquid crystal panel 5
1. The light passes through the rear polarizing plate 52, is reflected by the reflecting plate 61, and again passes through the polarizing plate, the liquid crystal panel, the phase difference compensating plate, and the polarizing plate, and then enters the eyes of a person who is watching the display device. Of course, even the light reflected at the interface inside the liquid crystal display device will eventually reach the front polarizing plate 50.
Through the eyes of the person watching the display. A polarizing plate in which silica particles are simply contained in the hard coat layer can prevent external light from being reflected due to surface irregular reflection, but the display is blurred and the contrast is lowered.
Since the liquid crystal display device absorbs light in a wavelength range in which the human eye has a relatively high luminosity factor, the phenomenon that the surface is glaring and white blurring does not occur.

As described above, the polarizing plate of the present invention can provide an antiglare effect without lowering the display contrast, and thus a display device which is easy to see even in a bright place can be constructed. . In addition, an excellent liquid crystal display device was achieved in which the number of parts such as a cover glass and a filter was not increased, the cost was low, and effective light attenuation due to surface reflection was small.

(Embodiment 7) A fourth embodiment of the polarizing plate of the present invention will be described.

The structure has a cross section as shown in FIG. 4, and in this embodiment, an acrylic hard coat layer 40 having a thickness of 3 μm is formed on the surface of the TAC film, which is provided with an uneven shape by transfer. This is aimed at the anti-glare effect due to surface irregular reflection, and can prevent the reflection of external light. Glossiness and cloudiness can be adjusted by the size and density of the unevenness. Furthermore, an antireflection layer 13 composed of a multilayer film is formed on the surface of the hard coat layer, and the reflectance is reduced in a wide wavelength range of visible light. The hard coat layer contains 0.5% by weight of an azo dye and 0.8% by weight of a polymethine dye.

The transmittance curve of the polarizing plate of this example is as shown by the curve 90 in FIG. 9 as in Example 3. In FIG. 9, the emission spectrum 80 of the cold cathode fluorescent lamp used in the liquid crystal display device described in the second embodiment is also drawn. In addition to the function of absorbing light of wavelengths other than the emission spectrum, it has a well-balanced antireflection function and external light reflection prevention function.

[0048]

Since the polarizing plate of the present invention is composed of a hard coating agent containing a plurality of appropriately selected dyes, the polarizing plate of the present invention has a simple structure and can absorb light in a desired wavelength region. Have. In addition, since it is inexpensive, has high mechanical reliability, and has the same film structure as the conventional product, it can be immediately replaced with the existing polarizing plate.

Further, the liquid crystal display device of the present invention is provided with the polarizing plate in the optical path from the light source to the eye. Such a display device has an effect that the brightness of the displayed image is little attenuated and the external light reflected by the display device is greatly attenuated, so that the contrast is high and easy to see even in a bright place.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a polarizing plate according to Example 1 of the present invention.

FIG. 2 is a cross-sectional view showing the structure of a polarizing plate according to Example 3 of the present invention.

FIG. 3 is a sectional view showing the structure of a polarizing plate according to Example 5 of the present invention.

FIG. 4 is a sectional view showing the structure of a polarizing plate according to Example 7 of the present invention.

FIG. 5 is a sectional view showing a configuration of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing a configuration of a liquid crystal display device according to a sixth embodiment of the present invention.

FIG. 7 is a diagram showing spectral characteristics of a polarizing plate in Example 1 of the present invention.

FIG. 8 is a diagram showing spectral characteristics of a polarizing plate used in Example 2 of the present invention and an emission spectrum of a cold cathode fluorescent tube used in a liquid crystal display device.

FIG. 9 is a diagram showing the spectral characteristics of the polarizing plate of Example 3 of the present invention and the emission spectrum of a cold cathode fluorescent tube used in a liquid crystal display device.

FIG. 10 is a diagram showing a spectral characteristic of a polarizing plate in Example 7 of the present invention.

[Explanation of symbols]

 10 Polarizing Layer 11 TAC Film 12 Hard Coat Layer Containing Dye 20 Antireflection Layer 30 Hard Coat Layer Containing Dye and Fine Particles 40 Hard Coat Layer Containing Dye and Surface Roughness 50 Front Polarizing Plate 51 Liquid Crystal Panel 52 Rear Polarizing Plate 53 Backlight 54 Adhesive 55 Light from Backlight 56 External Light 60 Phase Difference Compensation Plate 61 Reflector 70 Curve showing spectral characteristics of polarizing plate 80 Curve showing emission spectrum of cold cathode fluorescent tube 81 Reflection of polarizing plate Curve showing spectral characteristics 90 Curve showing spectral characteristics of polarizing plate 100 Curve showing spectral characteristics of polarizing plate

Claims (7)

[Claims] 1. A polarizing plate having a hard coat layer for absorbing light in a specific wavelength region formed on the surface of the polarizing plate. 2. The polarizing plate according to claim 1, wherein the hard coat layer is a photocurable resin layer containing a single dye or a plurality of dyes. 3. A polarizing plate characterized in that a hard coat layer that absorbs light in a specific wavelength region is formed on the surface of the polarizing plate, and an antireflection layer is further laminated thereon. 4. A polarizing plate having a hard coat layer formed on the surface of the polarizing plate, which absorbs light in a specific wavelength region and has an antiglare effect due to surface irregular reflection. 5. The polarizing plate according to claim 4, wherein the hard coat layer is a photocurable resin layer containing a single or a plurality of dyes and fine particles. 6. The polarizing plate according to claim 4, wherein the hard coat layer is a photo-curable resin layer containing a single dye or a plurality of dyes, and the surface thereof has an uneven shape. 7. The polarizing plate according to claim 1,
A liquid crystal display device, wherein the liquid crystal display device is arranged in a visible light path system of the display device.