CN102460286B - Transmission type liquid crystal display device and diffuser - Google Patents

Abstract

The present invention relates to a transmissive liquid crystal display device, which at least has: a backlight source; a light control unit for controlling the directionality of light emitted from the above-mentioned backlight source; a transmissive liquid crystal cell; A light-diffusing layer of a substance and a colorant, wherein the transmissive liquid crystal cell and the light-diffusing layer are sequentially arranged on the side closer to the above-mentioned light control unit.

Description

Transmissive liquid crystal display device and light diffusion plate

technical field

The invention relates to a transmissive liquid crystal display device and a light diffusion plate.

Background technique

A transmissive liquid crystal display device is widely used as a representative flat panel display due to its advantages of thinness, light weight, and low power consumption. In particular, they are widely used as televisions, monitors of personal computers, display screens for vehicles, and mobile phones. Since the liquid crystal itself is a device that does not emit light, it can be roughly classified into three types: a transmissive type, a transflective type, and a reflective type, depending on how light is irradiated from a light source. Under conditions such as weak external light, high image quality can be achieved by a transmissive method that can stably irradiate light of appropriate intensity from a backlight. Therefore, transmissive liquid crystal display devices are mainly used in applications requiring high image quality, such as televisions and personal computer monitors.

Regarding the molecular arrangement of liquid crystals, there are TN mode, VA mode, IPS mode, OCB mode, and the like. These modes have viewing angle dependence due to their respective optical characteristics. Therefore, even if it is designed to have good image quality such as contrast and color in the normal direction (front direction) of the liquid crystal panel, the image quality will deteriorate in the oblique direction. In order to solve this problem, a method using a viewing angle compensation film as shown in FIG. 10 and a method using a light diffusion layer as shown in FIG. 11 have been proposed.

In the method of using the viewing angle compensation film, for example, as shown in FIG.

In the method of using the viewing angle compensation film, a part of the light passes obliquely through the liquid crystal layer in the liquid crystal panel because a backlight that diverges light toward a wide angle is used. Therefore, in order to compensate the phase difference between light passing through the liquid crystal layer in the normal direction and light passing through the liquid crystal layer obliquely, the viewing angle compensation film 3 is used. Most of the currently commercially available liquid crystal display devices use a viewing angle compensation film.

10 shows the case where two viewing angle compensation films are used, but only one or three or more viewing angle compensation films may be used. In addition, the transparent protective film may also function as a viewing angle compensation film.

The field angle compensation film is generally more expensive than other optical films due to the high degree of birefringence control required. In addition, the phase difference between the light passing through the liquid crystal layer in the normal direction and the light passing obliquely through the liquid crystal layer generally depends on the wavelength. Therefore, it is necessary to adjust the viewing angle compensation film so that it has a wavelength dispersion suitable for the birefringence of the liquid crystal layer used, but since the wavelength dispersion of birefringence is an inherent property of the material, it is not easy to obtain ideal characteristics. field angle compensation film.

On the other hand, in the method of using a light-diffusing layer, for example, as shown in FIG. 11 , the light emitted from the backlight source 1 and passing through the light guide plate 6 passes through the liquid crystal panel 4 and the light-diffusing layer 5 in sequence substantially along the normal direction, and then passes through the liquid crystal. display panel.

In the method of using the light diffusion layer, since most of the light passes through the liquid crystal layer in the liquid crystal panel in the normal direction after being combined with the highly directional backlight, it is also possible not to provide a visual barrier for compensating the phase difference of the light. A field angle compensation film, and since the light passing through the liquid crystal layer is diffused to a wide angle under the action of the light diffusion layer 5, a wide viewing angle can be realized.

In addition, for the light diffusion layer, for example, a light diffusion layer in which transparent fine particles are spread between a polarizing plate and a glass substrate and gaps between the fine particles are filled with a transparent filler has been proposed (for example, see Patent Document 1).

Furthermore, a method of using a light-diffusing film in which a scattering substance is dispersed in a transparent resin is proposed as a protective film of a polarizing plate (for example, see Patent Document 2.). Patent Document 2 describes a flat scattering material as a scattering material dispersed in a transparent resin.

However, the method using a light-diffusing layer has a problem of lowering contrast due to external light, and is hardly used.

Moreover, the method of using a viewing angle compensation film and a light-diffusion layer together is also proposed (for example, refer patent document 3). This patent document 3 describes a method of improving the viewing angle in OCB mode by using a viewing angle compensating sheet mainly composed of a liquid crystal compound and a light diffusing layer in combination, and using a cellulose acetate film having optical anisotropy in combination with a light diffusing layer. layer, a way to improve the field of view in VA mode.

However, the above-mentioned problems in the light-diffusing layer have not been solved yet.

prior art literature

patent documents

Patent Document 1: Specification of Japanese Patent No. 3517975

Patent Document 2: Specification of Japanese Patent No. 3822102

Patent Document 3: Specification of Japanese Patent No. 4054670

Contents of the invention

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a transmissive liquid crystal display device and a light diffusing plate in which reduction in contrast due to external light is suppressed while achieving a wide viewing angle.

The invention of claim 1 is a transmissive liquid crystal display device comprising at least:

backlight source;

a light control unit for controlling the directionality of light emitted from the above-mentioned backlight light source;

transmissive liquid crystal cell; and

a light-diffusing layer comprising a light-transmitting polymer, a scattering substance and a colorant,

The above-mentioned transmissive liquid crystal cell and the above-mentioned light-diffusing layer are sequentially arranged on the side close to the above-mentioned light control unit,

The above-mentioned light-diffusing layer is added with the above-mentioned coloring agent in order to adjust the internal absorbance at the main wavelength of light emitted from the above-mentioned backlight source, and the above-mentioned light-diffusing layer has a single-layer structure containing a light-transmitting polymer, a scattering substance, and a coloring agent, or It is a laminate of a scattering layer formed by dispersing the scattering substance in the above-mentioned light-transmitting polymer and a colored layer containing the above-mentioned light-transmitting polymer and the above-mentioned coloring agent arranged adjacently in order on the side close to the above-mentioned light control unit, The said light-transmitting polymer and coloring agent exist between the visual confirmation side surface of the said light-diffusion layer, and the said scattering material.

The invention according to claim 2 is the transmissive liquid crystal display device according to claim 1, wherein the light-diffusing layer has an internal absorbance of 0.014 or more at a main wavelength of light emitted from the backlight light source.

The invention of claim 3 is the transmissive liquid crystal display device according to claim 1 or 2, wherein the light-diffusing layer has an internal absorbance of 0.020 or more at a main wavelength of light emitted from the backlight light source.

The invention of claim 4 is the transmissive liquid crystal display device according to any one of claims 1 to 3, wherein the light diffusion layer has an internal absorbance of 0.028 to 0.062 at a main wavelength of light emitted from the backlight source.

The invention of claim 5 is the transmissive liquid crystal display device according to any one of claims 1 to 4, wherein the concentration of the scattering substance in the light-diffusing layer is in the liquid crystal cell in the thickness direction of the light-diffusing layer. side high.

The invention of claim 6 is the transmissive liquid crystal display device according to any one of claims 1 to 5, wherein the light-diffusing layer is a scattering layer formed by dispersing the light-scattering substance in the light-transmitting polymer. A laminate of a colored layer comprising the above-mentioned light-transmitting polymer and the above-mentioned colorant.

The invention of claim 7 relates to a light diffusion plate provided on a side farthest from a light control unit for controlling directivity of light emitted from a backlight light source in a transmissive liquid crystal display device,

The light diffusion plate contains a light-transmitting polymer, a scattering substance and a colorant,

the colorant is added to the light diffusion plate in order to adjust internal absorbance at a main wavelength of light emitted from the backlight light source,

The light diffusion plate is a single-layer structure containing a light-transmitting polymer, a scattering substance, and a colorant, or it is arranged adjacent to each other on the side close to the light control unit and dispersed in the light-transmitting polymer. A laminate of a scattering layer formed of the above-mentioned scattering substance and a colored layer containing the above-mentioned light-transmitting polymer and the above-mentioned colorant,

The light-transmitting polymer and the colorant are present between the visually recognizable side surface of the light-diffusing plate and the scattering material.

According to the present invention, it is possible to provide a transmissive liquid crystal display device and a light-diffusing plate in which a decrease in contrast due to external light is suppressed while realizing a wide viewing angle.

Description of drawings

FIG. 1 is a schematic cross-sectional view of a light-diffusing layer according to a first embodiment.

Fig. 2 is a diagram illustrating the action and function of the light-diffusing layer according to the present invention.

Fig. 3 is a schematic cross-sectional view of a light-diffusing layer according to a second embodiment.

Fig. 4 is a schematic cross-sectional view of a light-diffusing layer according to a third embodiment.

Fig. 5 is a schematic cross-sectional view of a light-diffusing layer according to a fourth embodiment.

Fig. 6 is a schematic cross-sectional view of a light-diffusing layer in another embodiment.

Fig. 7 is a schematic cross-sectional view showing an example of the structure of the transmissive liquid crystal display device of the present invention.

8 is an internal absorbance spectrum of samples 11 to 14 in Example 1. FIG.

9 is an internal transmittance spectrum of samples 11 to 14 in Example 1. FIG.

FIG. 10 is a diagram illustrating the passage of light in a liquid crystal display using a conventional viewing angle compensation film.

FIG. 11 is a diagram illustrating a passage of light in a liquid crystal display using a general light-diffusing layer.

12 is photographs showing the influence of external light when using a conventional light diffusion layer, (A) is a photograph taken without external light, and (B) is a photograph taken with external light.

Detailed ways

The transmissive liquid crystal display device of the present invention has at least: a backlight source; a light control unit for controlling the directivity of light emitted from the above-mentioned backlight source; a transmissive liquid crystal cell; A light-diffusing layer of an agent, wherein the transmissive liquid crystal cell and the light-diffusing layer are sequentially arranged on the side closer to the light control unit. In addition, the above-mentioned light-diffusing layer is a single-layer structure containing a light-transmitting polymer, a scattering substance, and a colorant, or is arranged adjacently in order on the side close to the above-mentioned light control unit in the above-mentioned light-transmitting polymer to disperse the above-mentioned scattering. A laminate of a scattering layer formed of a substance and a colored layer containing the above-mentioned light-transmitting polymer and the above-mentioned colorant. And the said translucent polymer and coloring agent exist between the visually-recognizable side surface of the said light-diffusion layer, and the said scattering material.

Generally, in order to reduce the color shift caused by the viewing angle of the liquid crystal display, a viewing angle compensation film as shown in FIG. 10 can be used. It is necessary to impart appropriate birefringence and wavelength dispersion to this viewing angle compensation film. However, the wavelength dispersion of birefringence is an inherent property of materials, and it is not easy to obtain a polymer with ideal wavelength dispersion.

Therefore, in this invention, the method of using the light-diffusion layer shown in FIG. 11, that is, the method of using the backlight with high directivity together with a light-diffusion layer is adopted. By adopting this method, the color shift of the viewing angle caused by light passing at a large angle with respect to the normal direction (0°) of the liquid crystal panel is reduced, and the method of using the viewing angle compensation film is eliminated. Existing problems, and can achieve a wide field of view.

Since the light-diffusing layer of the present invention contains a scattering material, it diffuses backlight with strong directivity and realizes a wide viewing angle. In addition, since the light-diffusing layer of the present invention contains a colorant such as a pigment, it has a function of absorbing incident external light. A (transparent) protective layer on the viewer side, or providing the light-diffusing layer on the outside of the transparent protective layer can suppress a decrease in contrast.

Here, in order to demonstrate the function and action of this invention, the actual situation of the liquid crystal display using the conventional light-diffusion layer is demonstrated first.

Figure 12 is a photograph of a liquid crystal display (right half) with a PMMA polymer film (light diffusion layer) doped with alumina microparticles on the front and a liquid crystal display without this film (left half) photo.

Here, Fig. 12(A) is shooting in a state where the room is darkened so that the external light does not reach the liquid crystal display. On the other hand, Fig. 12(B) is turning on the fluorescent lamp located in the Shooting with bright light shining on the LCD monitor.

Comparing Fig. 12(A) and Fig. 12(B), it can be seen that when the liquid crystal display is provided with a light-diffusing layer and irradiated with external light, whitening occurs and contrast decreases (right side of Fig. 12(B) ). Compared with the case of FIG. 12(A) where no external light is irradiated, the reason why whitening occurs and the contrast decreases in FIG. 12(B) irradiated with external light is that after the external light enters the light-diffusing layer and scatters, the The light returns to the outside (observer side) of the light diffusion layer again.

A liquid crystal display using a conventional light-diffusing layer has a problem of a decrease in contrast due to penetration of external light.

Under the above circumstances, the inventors of the present invention have found that the light-diffusing layer obtained by adding a colorant such as a scattering substance for diffusing light and a pigment for absorbing light to a light-transmitting polymer can substantially maintain an image. While suppressing whitening caused by external light, it diffuses the light from the backlight to a wide angle. The first embodiment as such a light-diffusing layer is shown in FIG. 1 .

In FIG. 1 , in the light diffusion layer 10 , the scattering material 12 is dispersed in the light-transmitting polymer 14 , and it is more preferable that the scattering material 12 is uniformly distributed in the light-transmitting polymer 14 . In addition, the translucent polymer 14 contains a colorant (not shown) such as a pigment. That is, the said translucent polymer and coloring agent exist between the visual confirmation side surface of the said light-diffusion layer, and the said scattering material.

Here, by making the light-diffusion layer 10 contain a coloring agent, the backlight by the external light which causes whitening can be weakened, and the reason is presumed as follows. However, the present invention is not limited by such assumptions.

As shown by the solid-line arrows in FIG. 2 , among the light from the backlight, the light that reaches the viewer's eyes is light that is scattered approximately once to several times and passes through the light-diffusing layer 10 . On the other hand, among the external light, the light reaching the eyes of the observer is the light that enters the light-diffusing layer 10 and is repeatedly scattered by the scattering material 12 to reach the observer's side. Therefore, external light travels a longer distance in the light diffusing layer 10 than light from the backlight (see dotted arrow in FIG. 2 ).

Here, when the colorant is contained in the light-diffusing layer 10 , the colorant gradually absorbs the external light having a long travel distance, and can reduce the return light caused by the external light causing whitening.

The configuration of the light-diffusing layer is not limited to the configuration shown in FIG. 1 as long as the above basic principle is considered. FIG. 3 is given as a second embodiment of the light-diffusing layer.

In FIG. 3 , the scattering substances 12 are respectively on the side close to the liquid crystal layer in the thickness direction of the light diffusion layer 10 . The scattering materials 12 may be arranged at appropriate intervals, may be in contact with each other, and may also be arranged irregularly.

In addition, FIG. 4 is given as a third embodiment of the light-diffusing layer.

In FIG. 4 , the scattering materials 12 are arranged in the thickness direction of the light diffusion layer to form multiple layers. The scattering substances 12 do not have to be in a regular layered shape. In FIGS. 1 to 4, the light-diffusing layer has a single-layer structure containing a light-transmitting polymer, a scattering substance, and a colorant.

Furthermore, FIG. 5 is shown as 4th Embodiment of a light-diffusion layer.

In FIG. 5 , a colored layer 18 including a light-transmitting polymer 14 and a colorant is provided on the outside (observer side) of the scattering layer 16 including the light-transmitting polymer 14 and the scattering substance 12 . The scattering layer 16 may not contain a colorant, but may contain a colorant. In FIG. 5 , the light diffusion layer is a scattering layer 16 formed by dispersing the above-mentioned scattering substance in the above-mentioned light-transmitting polymer, which is adjacent to the side close to the light control unit in sequence, and a layer containing the above-mentioned light-transmitting polymer and the above-mentioned colored layer. A laminate of the coloring layer 18 of the agent.

As can be seen from the travel paths of the backlight and the external light shown in FIG. 2, by forming the light-diffusing layer with the configuration shown in FIG. 3, FIG. 4, and FIG. Travel longer distances, thereby prioritizing dimming of ambient light. In particular, the light-diffusing layer of the configuration shown in FIG. 5 can effectively reduce external light.

In addition, the scattering layer 16 shown in FIG. 5 may be distributed on the side closer to the film thickness direction as shown in FIGS. 3 and 4 .

Antireflection or antiglare treatment can also be performed on the outside of the light diffusion layer 10 using known techniques. In addition, as shown in FIG. 6 , antiglare particles 20 may be introduced into the light diffusion layer 10 .

Hereinafter, the components which comprise a light-diffusion layer are demonstrated.

Various organic pigments are preferable as the colorant, but organic pigments and inorganic pigments can also be used as long as they are finely divided to such an extent that the image resolution is not significantly deteriorated and the dispersion state is good. Specifically, known organic and inorganic pigments such as carbon black, anthraquinone-based compounds, perylene-based compounds, didiazo-based compounds, phthalocyanine-based compounds, isoindoline-based compounds, and dioxazine-based compounds can be used. The type of organic colorant is not particularly limited.

As the coloring agent, one kind of coloring agent may be used alone, or a plurality of coloring agents may be used in combination. Ideally, the spectrum of internal absorbance obtained by using one or a combination of a plurality of light absorbing agents has substantially the same value over the entire wavelength range of visible light (about 380 nm to about 750 nm).

As a backlight source for liquid crystal displays, cold cathode tubes or LEDs are often used, and generally have light intensity peaks at three main wavelengths corresponding to red (R), green (G), and blue (B). Therefore, the light absorption of the pigment added in the present invention may not necessarily be the same absorbance (transmittance) over the entire wavelength range of visible light as described above, but after adjusting the appropriate balance of absorbance at the three main wavelengths of the backlight light absorption.

It is preferable to adjust so that the difference of each internal absorbance of a light-diffusion layer is as small as possible at the main wavelength of the light emitted from a backlight light source from a viewpoint of displaying favorable white. For example, when using a cold-cathode tube with three main wavelengths as a light source, it is preferable to adjust the difference between the internal absorbances of the light-diffusing layer at wavelengths of about 435 nm, about 545 nm, and about 615 nm to be as small as possible.

Specifically, the difference in the internal absorbance of the light diffusion layer at the main wavelength of light emitted from the backlight source is preferably 0.05 or less, more preferably 0.02 or less, and even more preferably 0.01 or less.

Here, the main wavelengths of light emitted from the backlight light source, for example, refer to three wavelengths of about 435 nm, about 545 nm, and about 615 nm in general cold cathode tubes. In addition, light sources whose main wavelengths are other than the three wavelengths are sometimes used as backlights. For example, there are four-wavelength backlights in which magenta is added to the three wavelengths of blue, green, and red. Therefore, at this time, these four wavelengths are set as the main wavelengths. In addition, in the case of an LED, it may have a main wavelength different from that of the above-mentioned general cold-cathode tube.

In addition, the main wavelength of the light emitted from the backlight light source does not undergo a large shift after passing through the light control unit for controlling its directivity, and the light diffusion layer can be adjusted according to the main wavelength of the light passing through the light control unit. internal absorbance.

In addition, the color filter provided on the liquid crystal cell and the resin in each layer sometimes cause attenuation of light of a specific wavelength or a peak wavelength shift. At this time, it is also possible to adjust the internal absorbance of the light-diffusing layer according to the main wavelength of the light about to enter the light-diffusing layer in consideration of the spectrum of the light about to enter the light-diffusing layer.

Table 1 shows the internal absorbance and transmittance of an example of the light-scattering layer of the present invention in which the internal absorbance is adjusted according to the main wavelength of a general cold cathode tube.

[Table 1]

As shown in Table 1, it is preferable to adjust the main wavelength of the light emitted from the backlight light source used as the light source so that the difference in the internal absorbance of the light diffusion layer at the main wavelength becomes small.

On the other hand, from the viewpoint of improving brightness, it is preferable that the light from the backlight is not absorbed by the colorant in the light-diffusing layer 10 as much as possible, and passes through the light-diffusing layer to reach the viewer. Therefore, it is preferable to adjust the content of the colorant in the light-diffusing layer 10 so that the absorbance range can suppress the loss of the light from a backlight, reducing the return light by external light.

Therefore, from the objective of the present invention of weakening the external light and suppressing the weakening of the light from the backlight, it is preferable to adjust the internal absorbance of the light-diffusing layer at the main wavelength of the light emitted from the backlight to 0.014 or more, more preferably 0.020 or more. , and more preferably 0.028 or more. If the front brightness is further considered, it is preferable to adjust the internal absorbance of the light-diffusing layer to the range of 0.014 to 0.095 at the main wavelength of light emitted from the backlight source, more preferably 0.014 to 0.088, and even more preferably 0.020 to 0.088. The range is more preferably in the range of 0.028 to 0.088, still more preferably in the range of 0.028 to 0.062.

The light-transmitting polymer 14 and the scattering material 12 in the light-diffusing layer are preferably selected appropriately so that the combination of the respective refractive indices and the size of the scattering material 12 become appropriate values. Through these adjustments, the light from the backlight is diffused by the scattering material 12 to achieve a wide viewing angle, and efficiently passes through the light diffusion layer to exhibit high brightness. Furthermore, by these adjustments, blurring of an image due to the provision of a light-diffusing layer can be suppressed.

Specifically, as the light-transmitting polymer 14 used for the light-diffusing layer, cellulose derivatives represented by triacetyl cellulose, acrylic polymers represented by polymethyl methacrylate, polycarbonate Various translucent polymers such as cycloolefin polymers and norbornene-based polymers are represented, but are not limited to these polymers. In addition, the translucent polymer 14 used for the light diffusion layer may be a homopolymer or a copolymer, or a mixture of polymers may be used. In addition, these polymers may be high-purity polymers containing almost no other additives, or may contain various additives such as plasticizers. In addition, the light-transmitting polymer 14 may be an adhesive polymer.

The refractive index of the light-transmitting polymer 14 is appropriately selected depending on the combination with the added scattering substance 12 and the like, so it cannot be determined uniformly, but generally, it is preferably 1.33 to 1.65, and more preferably 1.45 to 1.60. For example, triacetyl cellulose has a refractive index of 1.48, and polymethyl methacrylate has a refractive index of 1.49.

Translucent particles are preferable as the scattering substance 12 . Specifically, alumina particles, siloxane polymer particles, melamine-formaldehyde condensate particles, benzoguanamine-formaldehyde condensate particles, benzoguanamine-melamine-formaldehyde condensate particles, titanium oxide particles, silica particles, etc. can be used. , but not limited to these particles.

The average particle size of the scattering material 12 is appropriately selected depending on the combination with the above-mentioned light-transmitting polymer 14, etc., so it cannot be determined uniformly, but it is generally preferably 0.05 μm to 25 μm, more preferably 0.1 μm to 20 μm, and even more preferably 0.05 μm to 20 μm. 0.8μm～18μm.

The refractive index of the scattering material is also appropriately selected depending on the combination of the above-mentioned light-transmitting polymers and the like, so it cannot be determined uniformly, but generally, it is preferably 1.40 to 2.75, and more preferably 1.43 to 1.9. Furthermore, the difference between the refractive index of the scattering material 12 and the refractive index of the translucent polymer 14 is preferably 0.02 to 1.25, and more preferably 0.03 to 0.30. From the viewpoint of the light diffusion effect, the refractive index difference in the above range is preferable.

The content of the scattering material 12 relative to the light-transmitting polymer 14 is appropriately adjusted according to the type of the light-transmitting polymer 14 and the type and size of the scattering material 12. Therefore, it cannot be determined uniformly, but generally, it is preferably 0.1% by mass to 50% by mass. %, more preferably 0.5% by mass to 15% by mass.

As described above, the light-diffusing layer of the present invention has a function of diffusing light and a function of absorbing light.

For the light diffusion function, in the configuration of the transmissive liquid crystal display device described later (see FIG. 7 ), the brightness of the backlight before entering the liquid crystal panel (corresponding to before entering the transparent protective layer 26 in FIG. 7 ) can be compared. The angle distribution and the angle distribution of the luminance after the light from the backlight is diffused by the liquid crystal panel were evaluated.

More simply, evaluation can be performed by measuring the haze (Haze, haze value) of a film-like sample formed by adding a scattering substance to a light-transmitting polymer.

In order to diffuse the highly directional light from the edge light backlight in the light diffusion layer to obtain a sufficient viewing angle, a haze of more than 40% is generally required. However, the desired haze depends on the degree of divergence of the light from the backlight and the degree of divergence of the light desired after passing through the light diffusing layer.

For example, if it is necessary to obtain a brightness angle distribution of the degree of divergence of a general LCD TV from the light of a backlight with a very strong directivity and a full width at half maximum of the brightness angle distribution of about 30° or less, the haze is preferably 70% or more. , more preferably 80% or more.

In addition, when using a highly directional backlight with a full width at half maximum of the luminance angular distribution of about 30° or less, the internal absorbance of the light-diffusing layer at the main wavelength of light emitted from the backlight light source is preferably adjusted to 0.028 or more, more preferably It is in the range of 0.028 to 0.088, more preferably in the range of 0.028 to 0.062, and the internal absorbance is preferably in the range of 0.055 to 0.062 from the viewpoint of displaying good black and maintaining high front brightness.

On the other hand, if a backlight with low directivity is used, sufficient diffusion can be achieved even with a light-diffusing layer with low haze. For example, in the case of a backlight with a half maximum width of luminance angular distribution greater than 30° and less than or equal to about 50° and having moderate directivity, the haze is preferably 60% or more, more preferably 70% or more.

In addition, in the case of using a backlight with a full width at half maximum of the luminance angular distribution greater than 30° and less than or equal to about 50°, and having a moderate degree of directivity, the light diffusion layer has a main wavelength of light emitted from the backlight source. The internal absorbance is preferably adjusted to 0.020 or more, more preferably in the range of 0.020 to 0.095, and even more preferably in the range of 0.020 to 0.068. From the viewpoint of displaying good black and maintaining high front brightness, the internal absorbance is in the range of 0.029 to 0.068. ideal.

As mentioned above, depending on the directionality of the light from the backlight to be used, the ranges of the more suitable haze value and internal absorbance are somewhat different, but from the viewpoint of suppressing whitening of the screen, in the case of light with any direction , as long as the internal absorbance of the light-diffusing layer is adjusted to 0.014 or more, the effect can be exerted, and this point can also be shown in the examples described later.

The function of absorbing light can be evaluated by measuring absorbance (or transmittance) with a commercially available measuring device. A film-like sample obtained by adding a light absorbing agent to a light-transmitting polymer was used for the measurement. In this case, the influence of the surface reflection of the sample is subtracted by measuring the baseline using a comparative film-like sample to which no light absorbing agent has been added. The absorbance inside the film thus obtained was defined as internal absorbance. The attenuation and transmittance were obtained from the internal absorbance. They are defined as internal attenuation (%) and internal transmittance (%), respectively. The internal attenuation and internal transmission add up to 100%.

Finally, a light-diffusing layer appropriately designed based on the above-mentioned evaluation results was provided on a transmissive liquid crystal display device configured as shown in FIG. 7 , and its effect was evaluated.

As a method for producing the light-diffusing layer 10, for example, a method of preparing a coating solution containing the light-transmitting polymer 14, the scattering substance 12, a colorant, and a solvent, etc. This coating liquid is coated on the outermost layer of the liquid crystal cell such as the transparent protective layer 26 .

Next, a transmissive liquid crystal display device will be described.

The transmissive liquid crystal display device of the present invention has at least: a backlight source; a light control unit for controlling the directionality of light emitted from the above-mentioned backlight source; a transmissive liquid crystal cell; and a light diffusion layer containing a translucent polymer substance, scattering substance and coloring agent, the above-mentioned transmissive liquid crystal cell and the above-mentioned light diffusion layer are sequentially arranged on the side close to the above-mentioned light control unit.

An example of the specific configuration of the transmissive liquid crystal display device of the present invention will be described with reference to FIG. 7 .

In Fig. 7, the light emitted from the backlight source 22 passes through the light guide plate 24 to become directional light, and the light passes through the transparent protective layer 26, polarizing film 28, transparent protective layer 26, glass substrate 30, liquid crystal layer 32, color filter 34 . The glass substrate 30 , the transparent protective layer 26 , the polarizing film 28 , and the transparent protective layer 26 are diffused in the light diffusion layer 10 .

In the transmissive liquid crystal display device of FIG. 7, as the liquid crystal cell of the present invention, a transparent protective layer 26, a polarizing film 28, a transparent protective layer 26, a glass substrate 30, a liquid crystal layer 32, a color filter 34, A liquid crystal cell obtained by a glass substrate 30 , a transparent protective layer 26 , a polarizing film 28 and the transparent protective layer 26 . However, it is not limited to such a configuration, as long as it has at least the liquid crystal layer 32 , the number of sheets used for each component can be appropriately selected, and components other than these components may be added.

For example, the transparent protective layer 26 adjacent to the light-diffusing layer 10 described in FIG. 7 and the light-diffusing layer 10 may be combined together, and the light-diffusing layer may be used as the protective layer. When the transparent protective layer 26 and the light-diffusing layer 10 are combined to design the light-diffusing layer also as a protective layer, the light-emitting layer can be formed by a known film-making method such as a solution casting film-making method or a melt-extrusion method. The diffusion layer is formed into a film, and it is produced by affixing it to the polarizing film 28 by a known method.

In addition, the scattering substance 12 and a colorant may be added to an adhesive layer (not shown) for bonding the polarizing film 28 and the outer transparent protective layer 26 together, and this adhesive layer may be used as a light diffusion layer. An adhesive polymer is contained in this adhesive layer, and this adhesive polymer is used as a light-transmitting polymer.

The light-diffusing layer 10 included in the transmissive liquid crystal display device of the present invention only needs to contain a light-transmitting polymer, a scattering substance, and a colorant, and may be the light-diffusing layer of the first embodiment shown in FIG. 1 , or the light-diffusing layer shown in FIG. The light-diffusing layer of the second embodiment, the light-diffusing layer of the third embodiment shown in FIG. 4 , the light-diffusing layer of the fourth embodiment shown in FIG. Any light-diffusing layer of the diffusing layer.

As the backlight light source 22, cold-cathode tubes are preferable, but not limited thereto, and hot-cathode tubes, LEDs, and the like can also be used. For LEDs, either white LEDs can be used, or red, green, and blue LEDs can be mixed to form white.

In addition, a laser such as a laser diode can be used as a backlight light source. In particular, lasers that emit polarized light are suitable for the transmissive liquid crystal display device of the present invention because they can achieve high efficiency. Laser diodes, like LEDs, can mix several colors of light to create white.

A known light guide plate can be used as the light guide plate 24 .

In addition, in the transmissive liquid crystal display device of FIG. 7, the backlight light source 22 and the light guide plate 24 are attached as a light source part, but other components may be further attached. For example, a prism sheet for improving brightness, a diffusion plate with a prism structure, and a reflective polarizing film with a light recycling function ( For example, 3M's DBEF, etc.) and so on. Although description is omitted in FIG. 7 , members such as reflective sheets and lamp reflectors may of course be arranged around the light guide plate.

In addition, in the transmissive liquid crystal display device of FIG. 7, although the light with directionality is formed by the light guide plate 24, the directionality of light may be controlled by means other than the light guide plate. For example, as shown in Figure 10, it is also possible to arrange the cold cathode tubes at appropriate intervals, then place the diffuser plate 2, and arrange a film with a light-gathering function on the diffuser plate 2 to replace the light guide plate, or use a diffuser plate In place of the light guide plate, the diffuser plate is equipped with a light-collecting function by microfabrication itself. In addition, when an element that emits more directional light, such as an LED or LD, is used instead of a cold cathode tube, it is also possible to use a diffuser sheet or a diffuser plate to reduce the directivity of light emitted from these elements. In addition, light guiding members, light collecting members, and light reflecting members already used in lighting applications can be appropriately combined with these elements to adjust the angular distribution of luminance to an appropriate level.

A known transmissive liquid crystal cell can be applied as the transmissive liquid crystal cell (liquid crystal layer) 32 . In addition, known elements can be appropriately applied to the transparent protective layer 26 , the polarizing film 28 , the glass substrate 30 , and the color filter 34 used in the transmissive liquid crystal display device of the present invention. Moreover, the transmissive liquid crystal display device of this invention can also use a viewing angle compensation film together with the light-diffusion layer which concerns on this invention.

A transmissive liquid crystal display device using the light diffusion layer according to the present invention can realize a wide viewing angle without using a viewing angle compensation film. And the transmissive liquid crystal display device using the light-diffusion layer which concerns on this invention can suppress the fall of contrast.

In order to diverge the light with strong directionality in the light-diffusing layer to obtain a sufficient viewing angle, it is generally necessary to make the light-diffusing layer contain more scattering substances to increase the haze. As a result of containing a large amount of scattering substances in the light-diffusing layer, the whitening of external light as shown in FIG. 12 is remarkable, and it is difficult to freely use a backlight with strong directivity in the conventional light-diffusing layer.

However, if the light-diffusing layer of the present invention is used, even when a backlight with strong directivity is used, it is possible to sufficiently realize a wide viewing angle while suppressing whitening.

Example

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[Example 1]

<Production of light diffusion layer>

The single-layer light-diffusing layer shown in FIG. 1 was produced by the method shown below.

Add triacetyl cellulose to dichloromethane, dissolve it, and stir evenly to prepare a polymer solution. This solution was applied on a stainless steel substrate with a smooth surface, and the solvent was evaporated to form a transparent protective layer with a thickness of about 50 μm.

On the other hand, polymethyl methacrylate, red, blue, and yellow organic pigments were added to methylene chloride, and alumina fine particles (average particle diameter: 1.1 μm) were added and stirred uniformly to prepare a dispersion.

In addition, red, blue, and yellow organic dyes were added at concentrations (mass %) in the following Table 2 with respect to the polymethyl methacrylate. Furthermore, 10 parts by mass of alumina fine particles were added to 100 parts by mass of polymethyl methacrylate.

The concentration of dichloromethane is appropriately adjusted so that the above-mentioned dispersion liquid can obtain a light-diffusing layer with a target thickness and be easy to coat. This dispersion liquid was applied on the said transparent protective layer, and the light-diffusion layers 11-14 with a thickness of about 30 micrometers were obtained.

<Measurement of internal absorbance, internal attenuation and internal transmittance>

A film (sample for measurement) having a composition in which only alumina fine particles were removed from the light-diffusing layer of the above-mentioned composition was prepared and used for measuring internal absorbance, internal attenuation, and internal transmittance.

In preparation of the measurement sample, first, polymethyl methacrylate, red, blue and yellow organic pigments were added to dichloromethane, and a solution was prepared after uniform stirring. This solution was applied on a stainless steel substrate with a smooth surface, and the solvent was mostly volatilized, thereby preparing measurement samples 11 to 14 with a thickness of about 30 μm. In addition, the samples 11-14 for a measurement correspond to the said light-diffusion layers 11-14, respectively.

The internal absorbance, internal attenuation, and internal transmittance of the films of measurement samples 11 to 14 were measured using a commercially available spectrophotometer.

The internal absorbance here refers to the absorbance of a film formed by adding a light-absorbing substance to a light-transmitting polymer without adding a scattering substance such as alumina particles. Its meaning is the absorbance generated by the light absorption inside the film, excluding the reflection of the film surface.

The internal attenuation rate is the attenuation rate (%) converted from the internal absorbance.

In addition, the internal transmittance is a value calculated by the following formula.

[Internal transmittance]=100(%)-[Internal attenuation rate]

In addition, a polymer film having a composition in which alumina fine particles and an organic dye were removed from the above-mentioned composition was produced. Using the value measured using this film as a reference (baseline), the measurement of the above-mentioned film is carried out to obtain the internal absorbance, internal attenuation, and internal transmittance after deducting the loss due to surface reflection. The results are listed in Table 2.

[Table 2]

In addition, FIG. 8 shows the internal absorbance spectra of the above-mentioned measurement samples 11 to 14, and FIG. 9 shows the internal transmittance spectra of the above-mentioned measurement samples 11 to 14.

<Evaluation of Haze>

In order to evaluate the haze (haze value) of the light-diffusing layer, a polymer film (sample for haze measurement) in which only alumina fine particles (average particle diameter: 1.1 μm) was added at the same concentration was produced without adding an organic dye.

In preparation of the sample for haze measurement, first, polymethyl methacrylate and alumina fine particles were added to methylene chloride, and the mixture was uniformly stirred to prepare a dispersion liquid. 10 parts by mass of alumina fine particles were added to 100 parts by mass of polymethyl methacrylate. This dispersion liquid was applied on a stainless steel substrate with a smooth surface, and the solvent was mostly volatilized to obtain a haze measurement sample with a thickness of about 30 μm.

The sample for haze measurement was measured with a haze meter (Nippon Denshoku Industries Co., Ltd., NDH2000), and the haze was about 91%.

<Comments on the whitening of the screen>

The said light-diffusion layers 11-14 were provided on the transmissive liquid crystal display element of the structure of FIG. 7, and it evaluated. The VA type is used for the liquid crystal panel, and cold cathode tubes with main wavelengths of about 435nm, about 545nm and about 615nm are used as the backlight light source. Then, a fluorescent lamp was irradiated obliquely at 45 degrees from the front of the screen to obtain an illumination intensity of about 100 lx, which is a general active level, and the whitening of the screen was evaluated. The screen is displayed in black during evaluation.

As a result, the higher the internal absorbance of the sample, the lower the degree of whitening. As long as the internal absorbance is 0.014, it is practical. When it is 0.028 or more, almost no whitening is observed. In particular, samples 13 and 14, which have an internal absorbance of 0.055 or more, exhibit good black.

<Measurement of luminance angular distribution>

For the transmissive liquid crystal display element used for the evaluation of the above-mentioned whitening of the screen, the front luminance and luminance angular distribution were measured using a luminance meter (TOPCON, BM-7FAST, Ltd.). The measurement is performed after the screen is displayed in white.

The full width at half maximum of the angular distribution of the luminance of the backlight before entering the liquid crystal panel (corresponding to before entering the transparent protective layer 26 in FIG. 7 ) is about 30 degrees. Light from the backlight passes through the liquid crystal panel and is diffused in the front light-diffusing layer. As a result, the full width at half maximum becomes about 70 degrees in any of the light-diffusing layers 11 to 14 .

For comparison, front luminance and luminance angular distribution were also measured for a conventional liquid crystal panel provided with a viewing angle compensation film. The conventional liquid crystal panel provided with this viewing angle compensation film is a commercially available liquid crystal display, does not have a light-diffusion layer, and does not have the layer which added the coloring agent like this invention either.

For the screen of a conventional liquid crystal panel equipped with a viewing angle compensation film, the full width at half maximum of the luminance angular distribution is about 70 degrees. From the above results, it can be confirmed that although a backlight with strong directivity is used, the The degree of angular distribution of brightness necessary for an adequate field of view.

In addition, substantially the same characteristics were obtained for the luminance angular distribution in the vertical direction. Furthermore, regarding the front luminance, as shown in Table 3, the higher the addition concentration of the organic dye, the lower the front luminance. As long as the internal absorbance at the main wavelength of the light emitted from the backlight source is 0.062 or less, frontal luminance and luminance angular distribution can be obtained on the same level as the screen of a conventional liquid crystal panel equipped with a viewing angle compensation film.

[table 3]

As can be seen from the above, by forming a light-diffusing layer having an internal absorbance in the range of about 0.062 or less at the main wavelength of light emitted from the backlight source, it is possible to obtain a conventional film having a viewing angle compensation film similar to that shown in FIG. 10 . Liquid crystal displays with the same degree of frontal brightness and angular distribution of brightness as the screen of the liquid crystal panel. In particular, a light-diffusing layer having an internal absorbance in the range of 0.028 to 0.062 at the main wavelength of light emitted from the backlight source obtained favorable characteristics.

These liquid crystal displays hardly suffer from image blur caused by the light-diffusing layer. Furthermore, although it is a structure which does not use a viewing angle compensation film, the viewing angle substantially equivalent to the screen of the conventional liquid crystal panel equipped with a viewing angle compensation film shown in FIG. 10 was obtained.

[Example 2]

<Production of light diffusion layer>

The single-layer light-diffusing layers 21 to 24 shown in FIG. 4 were produced by the method shown below.

First, it carried out similarly to Example 1, and prepared the transparent protective layer.

On the other hand, the same polymethyl methacrylate as in Example 1, red, blue and yellow organic pigments were added to methylene chloride, and melamine-formaldehyde condensate fine particles (average particle diameter: 1.3 μm) were added and stirred. After uniformity, a dispersion is prepared.

In addition, red, blue, and yellow organic dyes were added at the concentrations (mass %) of Table 4 below with respect to the polymethyl methacrylate. Furthermore, 5 parts by mass of melamine-formaldehyde condensate fine particles were added to 100 parts by mass of polymethyl methacrylate.

The concentration of dichloromethane is appropriately adjusted so that the above-mentioned dispersion liquid can obtain a light-diffusing layer with a target thickness and be easy to apply. This dispersion liquid was applied on the above-mentioned transparent protective layer to obtain a light-diffusing layer with a thickness of about 30 μm.

The cross-section of the obtained light-diffusing layer was observed with a transmission electron microscope, and it was confirmed that the added light-transmitting fine particles (melamine-formaldehyde condensate fine particles) existed on one side of the light-diffusing layer as shown in FIG. 4 .

<Measurement of internal absorbance, internal attenuation and internal transmittance>

Films (measurement samples 21 to 24) having a composition in which only melamine-formaldehyde condensate fine particles were removed from the light-diffusing layer having the above-mentioned composition were prepared for measurement of internal absorbance, internal attenuation, and internal transmittance. The preparation method of the measurement samples 21-24 refers to the preparation method of the measurement samples 11-14 in Example 1. The internal absorbance, internal attenuation, and internal transmittance of these films were measured using a commercially available spectrophotometer.

In addition, a polymer film having a composition in which melamine-formaldehyde condensate fine particles and an organic dye were removed from the above-mentioned composition was produced. Using the value measured using this film as a reference (baseline), the above-mentioned film measurement is performed to obtain the internal absorbance, internal attenuation, and internal transmittance after deducting the loss due to surface reflection. The results are listed in Table 4.

[Table 4]

<Evaluation of Haze>

In order to evaluate the haze of the light-diffusing layer, a polymer film (for haze measurement) with a film thickness of about 30 μm was prepared by adding only melamine-formaldehyde condensate particles (average particle size: 1.3 μm) at the same concentration without adding organic pigments. sample). For the preparation method of the sample for haze measurement, refer to the preparation method of the sample for haze measurement in Example 1.

The prepared sample for haze measurement was measured using a haze meter (Nippon Denshoku Industries Co., Ltd., NDH2000), and the haze was about 94%.

<Comments on the whitening of the screen>

The above-mentioned light-diffusion layers 21-24 were provided on the transmissive liquid crystal display element of the structure of FIG. 7, and the evaluation of a light-diffusion layer was performed. The VA type is used for the liquid crystal panel, and cold cathode tubes with main wavelengths of about 435 nm, about 545 nm, and about 615 nm are used as the backlight. In addition, fluorescent lamps were irradiated obliquely at 45 degrees from the front of the screen to form an illuminance of about 100 lx, which is a general active level, and the degree of whitening of the screen was evaluated. The screen is displayed in black during evaluation.

As a result, the higher the internal absorbance of the sample, the lower the degree of whitening. The internal absorbance at the main wavelength of light emitted from the backlight source is 0.014 for practical use, and when it is 0.028 or more, almost no whitening is observed. In particular, the internal absorbance at the main wavelength of light emitted from the backlight source is 0.055. The above sample 23 and sample 24 showed good black.

<Measurement of luminance angular distribution>

For the transmissive liquid crystal display element used for the evaluation of the above-mentioned whitening of the screen, the front luminance and luminance angular distribution were measured using a luminance meter (TOPCON, BM-7FAST, Ltd.). Make the screen display in white and perform the measurement.

The full width at half maximum of the angular distribution of the luminance of the backlight before entering the liquid crystal panel (corresponding to before entering the transparent protective layer 26 in FIG. 7 ) is about 30 degrees. Light from the backlight passes through the liquid crystal panel and is diffused in the front light-diffusing layer. As a result, the full width at half maximum becomes about 70 degrees in any of the light-scattering layers 21 to 24 .

For the screen of a conventional liquid crystal panel equipped with a viewing angle compensation film, the full width at half maximum of its luminance angle distribution is about 70 degrees. From the above results, it can be confirmed that although a backlight with strong directionality is used, sufficient The degree of angular distribution of brightness necessary for the field of view.

In addition, substantially the same characteristics were obtained for the luminance angular distribution in the vertical direction. Furthermore, regarding the front brightness, as shown in Table 5, the higher the addition concentration of the organic dye, the lower the front brightness. As long as the internal absorbance at the main wavelength of the light emitted from the backlight source is 0.062 or less, frontal luminance and luminance angular distribution can be obtained on the same level as the screen of a conventional liquid crystal panel equipped with a viewing angle compensation film.

[table 5]

[Example 3]

The laminated light-diffusing layer shown in FIG. 5 is produced by the method shown below, that is, the light-diffusing layer in which the colored layer 18 is laminated on the outside (on the observer's side) of the scattering layer 16 on the light-transmitting layer 16. The colored layer 18 is formed by adding a colorant to a light-transmitting polymer. Triacetyl cellulose was selected as the light-transmitting polymer.

<Production of light diffusion layer>

First, triacetyl cellulose was dissolved in methylene chloride, and alumina fine particles (average particle diameter: 1.1 μm) were further added and stirred uniformly to prepare Dispersion-1. 10 parts by mass of alumina fine particles were added to 100 parts by mass of triacetylcellulose. The concentration of dichloromethane was adjusted appropriately so that the dispersion liquid-1 could obtain the target film thickness and be easy to coat.

On the other hand, triacetyl cellulose and red, blue, and yellow organic pigments were dissolved in methylene chloride and stirred uniformly to prepare solution-1. Red, blue, and yellow organic dyes were added at concentrations (mass %) in Table 6 below relative to triacetyl cellulose. Adjust the concentration of dichloromethane appropriately so that solution-1 can obtain the target film thickness and is easy to coat.

The above-mentioned dispersion liquid-1 was coated on the transparent protective layer prepared by the same method as in Example 1 to obtain a scattering layer 16 having a thickness of about 30 μm. Furthermore, the said solution-1 was apply|coated on the scattering layer 16, the colored layer 18 with a thickness of about 30 micrometers was formed, and the light-diffusion layers 31-34 were obtained.

<Measurement of internal absorbance, internal attenuation and internal transmittance>

Films having the same composition as the colored layer 18 (measurement samples 31 to 34) were produced to measure internal absorbance, internal attenuation, and internal transmittance. The preparation method of the measurement samples 31-34 refers to the preparation method of the measurement samples 11-14 in Example 1. The film thickness was about 30 μm. The internal absorbance, internal attenuation, and internal transmittance of these films were measured using a commercially available spectrophotometer.

In addition, a film containing only a polymer without adding a dye was produced. Using the value measured using this film as a reference (baseline), the measurement of the above-mentioned film was carried out to obtain the internal absorbance and internal transmittance after deducting the loss due to surface reflection. The results are listed in Table 6.

[Table 6]

<Evaluation of Haze>

In order to evaluate the haze of the light-diffusing layer, a film having the same composition as the scattering layer 16 in Example 3 above (sample for haze measurement) was prepared. For the preparation method of the sample for haze measurement, refer to the preparation method of the sample for haze measurement in Example 1.

The prepared sample for haze measurement was measured using a haze meter (Nippon Denshoku Industries Co., Ltd., NDH2000), and the haze was about 92%.

<Comments on the whitening of the screen>

The above-mentioned light-scattering layers 31 to 34 were provided on the transmissive liquid crystal display element having the configuration of FIG. 7 , and the evaluation of the light-diffusing layer was performed. A VA-type liquid crystal panel was used for the liquid crystal panel, and cold cathode tubes having main wavelengths of about 435 nm, about 545 nm, and about 615 nm were used as backlights. Then, a fluorescent lamp was irradiated obliquely at 45 degrees from the front of the screen to obtain an illumination intensity of about 100 lx, which is a general active level, and the whitening of the screen was evaluated. The screen is displayed in black during evaluation.

As a result, the higher the internal absorbance of the sample, the lower the degree of whitening. The internal absorbance at the main wavelength of the light emitted from the backlight source is 0.014 for practical use, and when it is 0.029 or more, almost no whitening is observed. In particular, the internal absorbance at the main wavelength of the light emitted from the backlight source is 0.056. The above samples 33 and 34 exhibited good black color.

<Measurement of luminance angular distribution>

For the transmissive liquid crystal display element used for the evaluation of the above-mentioned whitening of the screen, the front luminance and the angular distribution of the luminance in the horizontal direction were measured using a luminance meter (TOPCON, BM-7FAST, Ltd.). The measurement was performed after the screen was displayed in white. The full width at half maximum of the angular distribution of the luminance of the used backlight before entering the liquid crystal panel (corresponding to before entering the transparent protective layer 26 in FIG. 7 ) was about 30 degrees. Light from the backlight passes through the liquid crystal panel and is diffused in the front light-diffusing layer. As a result, the full width at half maximum becomes about 70 degrees in either light-diffusing layer.

For the screen of a conventional liquid crystal panel equipped with a viewing angle compensation film, the full width at half maximum of the luminance angular distribution is about 70 degrees, and it has been confirmed that a sufficient viewing angle can be obtained despite the use of a highly directional backlight. The degree of angular distribution of brightness required.

Regarding the front brightness, as shown in Table 7, the higher the concentration of the organic pigment added, the lower the front brightness. As long as the internal absorbance at the main wavelength of light emitted from the backlight source is 0.062 or less, the front luminance and luminance angular distribution can be obtained at a level equal to or higher than that of a conventional liquid crystal panel equipped with a viewing angle compensation film.

[Table 7]

From the above, it can be seen from Examples 1 to 3 that, despite the configuration without using the viewing angle compensation film, a visual field substantially equivalent to the screen of the conventional liquid crystal panel equipped with the viewing angle compensation film shown in FIG. 10 is obtained. horn.

In addition, it can be seen from Examples 1 to 3 that by forming a light-diffusing layer whose internal absorbance corresponds to a range of about 0.062 or less at the main wavelength of light emitted from the backlight light source, it is possible to obtain a light-diffusing layer that can satisfactorily reduce whitening and have a A liquid crystal display having front luminance and luminance angle distribution level equal to or higher than that of a conventional liquid crystal panel equipped with a viewing angle compensation film shown in FIG. 10 . In particular, good characteristics were obtained when the internal absorbance at the main wavelength of light emitted from the backlight was in the range of 0.028 to 0.062.

Moreover, in the liquid crystal display provided with the light-diffusion layer of Examples 1-3, the image blur by a light-diffusion layer hardly produced|generated.

Moreover, conventionally, no coloring agent is added to the light-diffusion layer of a transmissive liquid crystal display device. This is because the use of colorants to prevent the decrease in contrast due to external light was not thought of at first, and there was a concern that the colorants would absorb light from the backlight and cause a significant decrease in brightness, so there was no reason to actively add colorants. However, as shown by the results of Examples 1 to 3, even if a colorant is added, brightness equivalent to or higher than that of conventional liquid crystal display devices can be exhibited, and a decrease in contrast due to external light can be suppressed.

[Example 4]

<Production of light diffusion layer>

The light-diffusion layers 41-45 were produced by the method shown below.

First, it carried out similarly to Example 1, and prepared the transparent protective layer.

On the other hand, polymethyl methacrylate, red, blue, and yellow organic pigments were added to ethyl acetate, C.I. Pigment Red 48:3 (Sanyo Pigment Co., Ltd.), C.I. Pigment Blue (Pigment Blue) 15:1 (copper compound) (Sanyo Pigment Co., Ltd.), C.I. Pigment Yellow (PigmentYellow) 14 (Sanyo Pigment Co., Ltd.), and further add alumina particles (average particle size 1.1μm), and stir well A dispersion is prepared.

Here, red, blue, and yellow organic pigments were added at the concentrations (mass %) of Table 8 below with respect to polymethyl methacrylate. Furthermore, 5 parts by mass of alumina fine particles were added to 100 parts by mass of polymethyl methacrylate.

The concentration of ethyl acetate is appropriately adjusted so that the above-mentioned dispersion liquid can obtain a light-diffusing layer with a target thickness and be easy to apply. This dispersion liquid was applied on the above-mentioned transparent protective layer to obtain light-diffusing layers 41 to 45 having a thickness of about 30 μm.

<Measurement of internal absorbance, internal attenuation and internal transmittance>

Films (measurement samples 41 to 45) having the composition in which only the alumina fine particles were removed from the light-diffusing layer of the above-mentioned composition were prepared for measurement of internal absorbance, internal attenuation, and internal transmittance. The preparation method of the measurement samples 41-45 refers to the preparation method of the measurement samples 11-14 in Example 1. The internal absorbance, internal attenuation, and internal transmittance of these films were measured using a commercially available spectrophotometer.

In addition, a polymer film having a composition in which alumina fine particles and an organic dye were removed from the above-mentioned composition was produced. Using the value measured using this film as a reference (baseline), the above-mentioned film measurement was carried out to obtain the internal absorbance, internal attenuation, and internal transmittance after deducting the loss due to surface reflection. The results are listed in Table 8.

[Table 8]

<Evaluation of Haze>

In order to evaluate the haze of the light-diffusing layer, a polymer film (sample for haze measurement) having a film thickness of about 30 μm was prepared by adding only alumina fine particles (average particle diameter: 1.1 μm) at the same concentration without adding an organic dye. For the preparation method of the sample for haze measurement, refer to the preparation method of the sample for haze measurement in Example 1.

The prepared sample for haze measurement was measured using a haze meter (Nippon Denshoku Industries Co., Ltd., NDH2000), and the haze was about 77%.

<Comments on the whitening of the screen>

The above-mentioned light-scattering layers 41 to 45 were provided on the transmissive liquid crystal display element of the structure of FIG. 7, and the evaluation of the light-diffusion layer was performed. An IPS type liquid crystal panel was used for the liquid crystal panel, and cold cathode tubes having main wavelengths of about 435 nm, about 545 nm, and about 615 nm were used as backlights. Then, a fluorescent lamp was irradiated obliquely at 45 degrees from the front of the screen to obtain an illumination intensity of about 100 lx, which is a general active level, and the whitening of the screen was evaluated. The screen is displayed in black during evaluation.

As a result, the higher the internal absorbance of the sample, the lower the degree of whitening. The internal absorbance at the main wavelength of the light emitted from the backlight source is practically as long as it is 0.014, and when it is 0.020 or more, almost no whitening is observed. In particular, the internal absorbance at the main wavelength of the light emitted from the backlight source is Samples 43 to 45 of 0.029 or more showed good black.

<Measurement of luminance angular distribution>

About the transmissive liquid crystal display element used for the evaluation of said whitening of a screen, it carried out similarly to Example 1, and measured the luminance angular distribution. In addition, in the samples 41 and 42 for the measurement of the brightness angle distribution as the light diffusion layer used for the measurement of the brightness angle distribution, the organic pigment in the amount shown in the sample 43 of the above-mentioned Table 8 was added, and with respect to 100 parts by mass of polymethylmethacrylate 5 parts by mass or 10 parts by mass of alumina fine particles were added to methyl acrylate.

The full width at half maximum of the luminance angular distribution of the backlight used before entering the liquid crystal panel (corresponding to before entering the transparent protective layer 26 in FIG. 7 ) is about 47 degrees. Light from this backlight passed through the liquid crystal panel and was diffused in the front light-diffusing layer. As a result, as shown in Table 9, the full width at half maximum was about 70 degrees or more in any light-diffusing layer.

[Table 9]

The full width at half maximum of the luminance angular distribution of the screen of a conventional liquid crystal panel equipped with a viewing angle compensation film is about 70 degrees. From this, it can be confirmed that when a backlight with a full width at half maximum of the luminance angular distribution of 47 degrees is used, The sample 41 for measuring the angular distribution of luminance has a degree of angular distribution of luminance necessary for obtaining a sufficient viewing angle.

As can be seen from Example 4, when a backlight having a full width at half maximum of the luminance angular distribution of about 47 degrees is used, the internal absorbance corresponding to a range of about 0.020 or more at the main wavelength of light emitted from the backlight light source is formed by light diffusion. layer, whitening can be well reduced, and the viewing angle is sufficiently divergent, and the full width at half maximum of the luminance becomes about 70 degrees or more. In particular, good characteristics are obtained when the internal absorbance at the main wavelength of light emitted from the backlight is in the range of 0.029 or more.

Moreover, in the liquid crystal display which has the light-diffusion layer of Example 4, the image blur by a light-diffusion layer hardly arises.

[Example 5]

<Preparation of a light-diffusing layer that doubles as a protective layer>

The light-diffusion layer 51 which also serves as a protective layer was produced by the method shown below.

Add the same polymethyl methacrylate and red, blue, and yellow organic pigments as in Example 4 to ethyl acetate, and further add alumina particles (average particle size: 1.1 μm), and stir to prepare a dispersion .

In addition, 20 parts by mass of alumina fine particles were added to 100 parts by mass of polymethyl methacrylate. Also, as red, blue, and yellow organic pigments, C.I. Pigment Red 48:3 (Sanyo Pigment Co., Ltd.) and C.I. Pigment Blue 15:1 (copper compound) (Sanyo Pigment Co., Ltd.), C.I. Pigment Yellow (Pigment Yellow) 14 (Sanyo Pigment Co., Ltd.). 0.392 mass parts of red organic pigments, 0.072 mass parts of blue organic pigments, and 0.120 mass parts of yellow organic pigments were added with respect to 100 mass parts of polymethyl methacrylates.

This dispersion liquid was applied on a stainless steel substrate with a smooth surface, and the solvent was roughly dried to prepare a film-like sample. The obtained film-like sample was pulverized and dried under reduced pressure. Mix the obtained sample with 3 times the amount of polymethyl methacrylate particles, mix it with a twin-screw extruder at 230°C, extrude it into a film with a single-screw extruder at 270°C, and roll it with a roll Pick. The light-diffusion layer 51 which also serves as a protective layer is manufactured as mentioned above.

The light-diffusing layer 51 serving as a protective layer in Example 5 has the same organic dye concentration and the addition amount of alumina fine particles as the light-diffusing layer 42 in Example 4, so it is considered that the same performance as that of the light-diffusing layer 42 in Example 4 can be exerted. Effect.

[Example 6]

<Preparation of a light-diffusing layer that doubles as an adhesive layer>

The light-diffusion layer 61 which also serves as an adhesive layer was produced by the method shown below.

Dissolve an acrylic polymer with a weight-average molecular weight of about 100,000 in ethyl acetate and adjust the copolymer The concentration of the solution is about 30% by mass. To the above-mentioned acrylic polymer solution, 4 parts by mass of CORONATE L manufactured by Nippon Polyurethane Co., Ltd. and additives (KBM403, Shin-Etsu Chemical Co., Ltd. Co., Ltd.) 0.5 parts by mass, 5 parts by mass of alumina fine particles (average particle diameter: 1.1 μm), and red, blue, and yellow organic pigments to prepare a binder solution.

As red, blue, and yellow organic pigments, C.I. Pigment Red 48:3 (Sanyo Pigment Co., Ltd.) and C.I. Pigment Blue 15:1 (copper compound) (Sanyo Pigment Co., Ltd.) were used, respectively. Club), C.I. Pigment Yellow (Pigment Yellow) 14 (Sanyo Pigment Co., Ltd.). Moreover, 0.098 mass parts, 0.018 mass parts, and 0.030 mass parts of red, blue, and yellow organic pigments were added with respect to 100 mass parts of said copolymers, respectively.

Add a solvent (ethyl acetate) for viscosity adjustment, and apply this adhesive solution on a release film (polyethylene terephthalate substrate: Diafoil MRF38, manufactured by Mitsubishi Chemical Polyester) and make it dry to a thickness of 25 μm, and then dry in a hot air circulation oven to form an adhesive layer containing scattering substances and colorants. The polarizing film 28 and the outer transparent protective layer 26 are bonded together using this adhesive layer.

The light-diffusing layer 61 serving as an adhesive layer in Example 6 has the same organic dye concentration and the addition amount of alumina fine particles as the light-diffusing layer 42 in Example 4, so it is considered that the light-diffusing layer 42 in Example 4 can exhibit Same effect.

The entire disclosure of Japanese Patent Application No. 2009-138442 filed on June 9, 2009 is incorporated herein by reference.

All documents, patent applications, and technical standards described in this specification are incorporated by reference to the same extent as when each document, patent application, and technical standard is specifically and individually stated to be incorporated by reference.

Claims (6)

1. A transmissive liquid crystal display device, which at least has: backlight source; a light control unit for controlling the directionality of light emitted from the backlight light source; transmissive liquid crystal cell; and a light-diffusing layer comprising a light-transmitting polymer, a scattering substance and a colorant, The transmissive liquid crystal cell and the light diffusion layer are sequentially arranged on a side close to the light control unit, The colorant is added to the light-diffusing layer in order to adjust the internal absorbance at the main wavelength of the light emitted from the backlight, and the light-diffusing layer is a single composition containing a light-transmitting polymer, a scattering material, and a colorant. A layer structure, or a scattering layer formed by dispersing the scattering substance in the light-transmitting polymer adjacent to the side close to the light control unit in sequence and containing the light-transmitting polymer and the A laminate of a colored layer of a colorant, wherein the light-transmitting polymer and the colorant are present between the visually visible side surface of the light-diffusing layer and the scattering material. 2. The transmissive liquid crystal display device according to claim 1, wherein the internal absorbance of the light diffusion layer at a main wavelength of light emitted from the backlight light source is 0.014 or more. 3. The transmissive liquid crystal display device according to claim 1 or 2, wherein the light-diffusing layer has an internal absorbance of 0.020 or more at a main wavelength of light emitted from the backlight light source. 4. The transmissive liquid crystal display device according to claim 1 or 2, wherein the internal absorbance of the light diffusion layer at a main wavelength of light emitted from the backlight source is 0.028˜0.062. 5. The transmissive liquid crystal display device according to claim 1 or 2, wherein the content concentration of the scattering substance in the light-diffusing layer is higher on the side of the liquid crystal cell in the film thickness direction of the light-diffusing layer. 6. A light diffusion plate disposed on a side farthest from a light control unit for controlling the directivity of light emitted from a backlight light source in a transmissive liquid crystal display device, The light diffusion plate contains a light-transmitting polymer, a scattering substance and a colorant, the colorant is added to the light diffusion plate in order to adjust internal absorbance at a main wavelength of light emitted from the backlight light source, The light diffusion plate is a single-layer structure containing a light-transmitting polymer, a scattering substance, and a colorant, or it is arranged adjacent to each other on the side close to the light control unit and dispersed in the light-transmitting polymer. A laminate of a scattering layer formed of the above-mentioned scattering substance and a colored layer containing the above-mentioned light-transmitting polymer and the above-mentioned colorant, The light-transmitting polymer and the colorant are present between the visually recognizable side surface of the light-diffusing plate and the scattering material.