JPH0922011A - Back light and liquid crystal display device using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device having a wide visual field angle with a small variation in contrast due to a visual angle, a small hue variation due to a luminance inversion at a halftone color and usable for various purposes such as the accomplishment of the large-sized screen and the observation by plural users. SOLUTION: This device is provided with a light source 3, a light transmission body 2 provided with at least one light incident plane and one light outgoing plane which are confronted with the light source 3 and with specified prism trains 4 composed of two prism planes on the rear side opposite to the light outgoing plane so as to be parallel to the light incident plant, a liquid crystal display element 5 arranged on the light transmission body 2, and a lenticular lens sheet 6 arranged on the liquid crystal display element 5 and with many lenticular lenses arranged in parallel at least on one side thereof, and composed of two prism planes arranged on the rear side opposite to the light outgoing plane.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a notebook computer,
The present invention relates to a liquid crystal display device used in a portable liquid crystal TV or the like, and more specifically, it has a narrow distribution angle of emitted light rays, has an excellent directivity in which peak light is emitted in a direction normal to an emission surface, and has a structure. The present invention relates to a backlight which can be simplified and made compact, and a liquid crystal display device which is excellent in directivity, has a wide viewing angle, has a good contrast, and has no inversion of luminance of intermediate colors.

[0002]

2. Description of the Related Art In recent years, color liquid crystal display devices have been widely used in various fields as a portable notebook personal computer, a portable liquid crystal TV using a color liquid crystal panel, a video integrated liquid crystal TV, and the like. In addition, with the increase in information processing volume, diversification of needs, multimedia support, etc.,
Larger screens and higher definition of liquid crystal display devices are being actively pursued. The liquid crystal display device basically includes a backlight unit and a liquid crystal display element unit. As the backlight part, there are a direct type in which a light source is provided directly below the liquid crystal display element and an edge light type in which a light source is provided on the side surface of the light guide body.The edge light type has been widely used due to the compactness of the liquid crystal display device. There is. The edge light system is a backlight system in which a light source is arranged on the side surface of a plate-shaped light guide so that the entire surface of the light guide is illuminated.

The liquid crystal display element portion is roughly classified into a thin film transistor driven thin film transistor type (TFT) and a spar twisted nematic type (STN) according to its driving method. In the TFT type liquid crystal display element, a liquid crystal is twisted by 90 ° and sealed between a TFT substrate on which a thin film transistor is formed and which functions as an electrical switch and a color filter substrate which is provided with a color filter and plays a role of coloring. It has a different structure. Further, a polarizing plate is placed in front of and behind the substrate, and when the light polarized by the polarizing plate enters the liquid crystal layer, the light is reflected along the liquid crystal molecules by 9
It is rotated by 0 ° and the axis of the polarizing plate on the output side is rotated by 90 ° so that light is transmitted and emitted. On the other hand, when the switch of the TFT substrate is turned on, the liquid crystal molecules rise, the light incident on the liquid crystal layer cannot rotate, and cannot pass through the polarizing plate on the emission side. In this way, image information corresponding to the switch state of the TFT substrate is displayed. It is said that such a TFT type liquid crystal display device is capable of high-speed switching and is suitable for displaying halftone colors corresponding to full color.

[0004]

However, in such a liquid crystal display device, the image quality greatly changes depending on the viewing angle, and, for example, the contrast and brightness change depending on the viewing angle of the screen, or the halftone color. However, there is a problem that a normal image cannot be obtained due to the inversion of the luminous intensity and the change in color tone. This is because in the TFT type liquid crystal display element, the liquid crystal molecules are not completely raised in the display of a halftone color, and the light seen in the tilted direction of the liquid crystal molecules passes through the liquid crystal molecules at an angle close to vertical. This is because the probability that the light will be rotated increases, and the amount of light that passes through the polarizing plate will increase, resulting in a whitish display. Further, when viewed from the direction in which the liquid crystal molecules are not tilted, the light passing through the liquid crystal layer is less affected by the liquid crystal molecules, and the light does not rotate, resulting in a dark display. Such a problem has become more serious due to the demand for a larger screen size of the liquid crystal display device and the observation by a plurality of people due to the expansion of applications.

Further, since such a color liquid crystal display device is driven by a battery, the power consumption of the liquid crystal display device is an obstacle for extending the battery drive time. Above all, the power consumption of the backlight used in liquid crystal display devices is large, and it is important to keep this power consumption as low as possible in order to extend the battery drive time and increase the practical value of the above products. ing. However, if the light intensity of the backlight is reduced by suppressing the power consumption of the backlight, it is not preferable because the liquid crystal display becomes difficult to see.

It is desirable to improve the optical efficiency of the backlight in order to reduce power consumption without sacrificing the brightness of the backlight. As a means for achieving this, there has been proposed a backlight in which a prism sheet having a large number of prism rows such as a prism row and a lenticular row formed on one surface is placed on the exit surface side of a light guide. In such a backlight, a prism sheet is used to improve the luminous intensity of the backlight, but the use of the prism sheet complicates the structure of the backlight unit and is an obstacle to downsizing in terms of thickness. .

Therefore, according to the present invention, the distribution angle of the outgoing light beam is narrow and the outgoing surface of the peak light (the light beam having the highest luminous intensity in the luminous intensity distribution of the outgoing light beam) is output without using parts such as a prism sheet. With excellent directivity that emits in the normal direction of, and with excellent directivity that can maximize the luminous intensity in the front, while providing a backlight that can achieve simplification and compactness of the structure, An object of the present invention is to provide a liquid crystal display device having a wide viewing angle, good contrast, little luminance reversal in intermediate colors, a large screen size, and various applications such as observation by a plurality of people.

[0008]

SUMMARY OF THE INVENTION The inventors of the present invention have realized that a light guide having a specific structure is used.
The distribution angle of the emitted light of the backlight is small, and it has excellent directivity to emit in the normal direction of the emission surface of the peak light, and it is found that it has excellent directivity that can maximize the luminous intensity in the front, The change in the contrast and color tone of the screen depending on the viewing direction in the conventional liquid crystal display device has a wide angular distribution of the light emitted from the backlight unit, and the influence of the tilt direction of the liquid crystal molecules caused by entering the liquid crystal display element from various directions. The light incident on the liquid crystal display element is made into pseudo-parallel light with a narrow angle distribution, and the light is diffused after passing through the liquid crystal display element, so that the contrast depending on the viewing angle and the brightness reversal in the intermediate color The inventors have found that a liquid crystal display device having a wide viewing angle with little change in color tone due to the above can be obtained, and have accomplished the present invention.

That is, the backlight of the present invention comprises a light source and a light guide body having at least one light incident surface and a light exit surface facing the light source, and the light guide surface faces the light exit surface of the light guide body. A large number of prism rows composed of two prism surfaces are formed on the back surface in parallel with the light incident surface, and one surface (first prism surface) forming the prism row is located at 35 to 55 ° with respect to the light emitting surface. It has a tilt angle, and the other surface (second prism surface) has a tilt angle of 80 to 100 ° with respect to the light exit surface. Further, the liquid crystal display device of the present invention includes a light source, a light guide having at least one light incident surface and a light exit surface facing the light source, and a liquid crystal display element arranged on the light guide. One surface (first prism surface) forming a prism row, in which a large number of prism rows composed of two prism surfaces are formed in parallel with the light incident surface on the back surface facing the light exit surface of the light guide body Has an inclination angle of 35 to 55 ° with respect to the light emitting surface, and the other surface (second prism surface) has an inclination angle of 80 to 100 ° with respect to the light emitting surface. Is.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The backlight of the present invention comprises a light source 3 and a light guide 2 as shown in FIG.
The light guide 2 has at least one side surface as a light incident surface, one surface substantially orthogonal to this side as a light emitting surface, and a large number of prism rows 4 are formed on the back surface facing the light emitting surface in parallel with the light incident surface. ing. As shown in FIG. 2, the prism array 4 has a first inclination angle (α) of 35 to 55 ° with respect to the light exit surface.
Prism surface 8 and a second prism surface 9 having an inclination angle (β) of 80 to 100 ° with respect to the light exit surface. This is because by setting the inclination angles of the first and second prism surfaces in the above ranges, respectively, the peak light of the emitted light beam becomes a light beam in the direction normal to the light emission surface, and the angle of the emitted light beam becomes This is because the distribution can be narrowed. Preferably, the inclination angle (α) of the first prism surface 8 is in the range of 40 to 50 °, and the inclination angle (β) of the second prism surface 9 is in the range of 85 to 95 °. Further, in the present invention, it is preferable that the second prism surface 9 is located on the light source side in one prism row 4.
This is because when the first prism surface 8 is arranged on the light source side,
This is because the peak light of the emitted light beam tends to shift with respect to the normal direction of the light emission surface, or the angular distribution of the emitted light beam tends to widen.

In the present invention, the half-width of the angular distribution of the outgoing light rays emitted from the light guide 2 (in the direction perpendicular to the light source 3) is preferably 40 ° or less, more preferably 2
It is 0 ° or less. If this half-value width exceeds 40 °, the contrast in the liquid crystal display device tends to deteriorate and gradation inversion tends to occur. Further, the peak light of the outgoing light rays emitted from the light guide body 2 is preferably within a range of 10 ° with respect to the normal direction of the light emitting surface, and more preferably within a range of 5 °. The pitch of the formed prism rows 4 can be appropriately selected within a processable range, but is preferably in the range of 10 to 500 μm, and more preferably in the range of 30 to 300 μm.
When the light intensity distribution on the light emitting surface is uneven due to the shape of the light guide body 2 or the like, the pitch of the prism rows 4 is partially or continuously changed to change the light intensity distribution on the light emitting surface. Uniformity can be achieved. Further, the prism surface may be a flat surface or a curved surface having a predetermined curvature, and in the case of a curved surface, the angular distribution of the outgoing light beam can be somewhat increased.

The prism array 4 formed on the light guide 2 may be formed by processing the back surface of the light guide 2 by a hot press method or the like, or the light guide 2 may be formed by extrusion molding or injection molding. They may be processed and formed at the same time during manufacturing. Alternatively, they may be integrally formed by using heat or a photocurable resin or the like.
In the method of integrally forming the prism array 4 on the back surface of the light guide 2 using heat or a photocurable resin, it is possible to manufacture the light guide 2 and the prism array 4 having different refractive indexes. Further, the prism row 4 is made of an active energy ray curable resin on a transparent substrate such as a transparent film or sheet made of polyester resin, acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylimide resin or the like. The formed prism sheet may be integrated with the light guide 2 by a method such as adhesion or fusion.

When the prism array 4 is formed by using the active energy ray-curable resin, the active energy ray-curable resin liquid is injected into a mold having a predetermined prism pattern, and the light guide 2 or the transparent film is formed. Overlap. Then, it can be manufactured by irradiating an active energy ray such as an ultraviolet ray or an electron beam through the light guide 2, polymerizing and curing the active energy ray-curable resin liquid, and peeling it from the mold. As the active energy ray-curable resin forming the prism array 4, use should be made of polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylic acid esters, allyl compounds, metal salts of (meth) acrylic acid, etc. You can

The light guide 2 may have various shapes such as a plate shape, a wedge shape, and a boat shape, and is made of a synthetic resin having a high light transmittance. In order to effectively introduce light from the light source 3 to the light guide body 2, it is preferable that the light incident surfaces of the light source 3 and the light guide body 2 are covered with a case or film coated with a reflecting agent on the inside. A reflection layer 7 is formed on the back surface of the light guide 2 by metal vapor deposition or the like to form a reflection surface, if necessary. As the synthetic resin forming the light guide 2, various highly transparent synthetic resins such as methacrylic resin, acrylic resin, polycarbonate resin, vinyl chloride resin, etc. are used, and are usually used for extrusion molding, injection molding and the like. It can be manufactured by the molding method. In particular, methacrylic resin
It has excellent light transmittance, heat resistance, mechanical properties, and moldability, and is optimal as a light guide material. Such a methacrylic resin is a resin containing methyl methacrylate as a main component, and methyl methacrylate is preferably 80% by weight or more.

As shown in FIG. 1, the liquid crystal display device 1 of the present invention comprises a liquid crystal display element 5 and a backlight portion composed of a light source 3 and a light guide 2 having the above-mentioned configuration. By using the light guide 2 as described above, a light beam emitted from the light guide 2 becomes pseudo parallel light having a small angle distribution when passing through the liquid crystal display element 5, and the influence of the tilt direction of liquid crystal molecules is minimized. Therefore, it is possible to obtain a liquid crystal display device in which there is little change in the color tone due to the contrast and the brightness inversion of the intermediate color depending on the viewing angle. The liquid crystal display element 5 is not particularly limited, and either an active matrix driving TFT type liquid crystal display element or a simple matrix driving STN type liquid crystal display element can be used. Further, in the TFT type liquid crystal display element, the element and various active elements such as polysilicon, amorphous silicon and metal insulator metal can be used.

Further, as shown in FIG. 3, a lenticular lens sheet 6 in which a large number of lenticular lenses are formed in parallel on at least one surface of a liquid crystal display element 5.
May be placed. By mounting the lenticular lens sheet 6 on the liquid crystal display element 5 in this manner, the pseudo-parallel light that has passed through the liquid crystal display element 5 enters the lenticular lens sheet 6, and the incident light is once focused on the focal point of the lenticular lens. Since the light is diffused later, the viewing angle of the liquid crystal display device can be widened. That is, the light guide 2 having the specific prism row 4 on the back surface facing the emission surface minimizes the influence of the tilt direction of the liquid crystal molecules by the pseudo-parallel light having a small angular distribution when passing through the liquid crystal display element 5. Since the light is diffused by the lenticular lens sheet 6 after passing through the liquid crystal display element 5, there is little change in the color tone due to the contrast or brightness inversion of the intermediate color depending on the viewing angle, and a liquid crystal display device with a wide viewing angle is provided. it can.

The lenticular lens sheet 6 placed on the liquid crystal display element 5 is a member having a function of widening a viewing angle by diffusing light transmitted through the liquid crystal display element 5. The lenticular lens sheet 6 is formed by forming a large number of lenticular lenses having a semicylindrical shape, a semielliptic shape, or a shape similar to these in parallel on at least one surface, and has a thickness of about 0.1 to 10 mm, The lens pitch is preferably about 10 to 800 μm. Further, the lenticular lens sheet 6 is preferably manufactured using a material having a high visible light transmittance, and examples thereof include an acrylic resin, a polycarbonate resin, a vinyl chloride resin, and an active energy ray curable resin. In the present invention, if necessary, additives such as an antioxidant, an ultraviolet absorber, an anti-yellowing agent, a bluing agent, a pigment and a diffusing agent may be added to the lenticular lens sheet 6. The lenticular lens sheet 6 can be manufactured by a usual molding method such as extrusion molding, injection molding, or a method using an active energy ray curable resin.

[0018]

The present invention will be described below in detail with reference to examples. Measurement of luminous intensity Inverter (CXA-made by TDK) in the cold cathode tube of the light guide.
M10L) to connect to a DC power supply, and apply DC 12 V to light up. The liquid crystal display device was placed on a measuring table, and the center of the liquid crystal display device was adjusted to rotate on a rotation axis parallel to the cold cathode tube axis. Then, a black paper having a 3 mmφ pinhole was fixed on the light guide so that the pinhole was located at the center of the light guide, and a measurement circle was measured using a luminance meter (Minolta nt-1 °). Was adjusted to be 8 to 9 mm.
After aging time of the cold cathode fluorescent lamp for 30 minutes or more, while rotating the rotating shaft from 80 ° to -80 ° at 5 ° intervals,
The angular distribution of the luminous intensity of the emitted light was measured.

Example 1 100 mm × 90 mm × 100 mm × 90 mm × a plurality of parallel prism rows each having a prism surface having an inclination angle of 45 ° and a prism surface having an inclination angle of 90 ° on one surface by injection molding of an acrylic resin. A 4 mm light guide was made.
The two 90-mm end faces of the light guide obtained were silver-deposited on P.
An ET film was adhesively processed and attached, and a PET film on which silver was vapor-deposited was taped to the surface opposite to the matte surface to form a reflective surface. Cold cathode tubes (KC130T4E72, 4 mmφ × 130 m, made by Matsushita Electric Industrial Co., Ltd.) made of silver-deposited PET film on two 100 mm end faces of an acrylic plate.
m) was wound and installed as a light source lamp to provide a backlight. The light source lamp was installed on the end surface of the light guide so that the prism surface of the light guide having the inclination angle of 90 ° was on the light source side.

A liquid crystal display device was assembled by mounting a TFT type liquid crystal display element on the light emitting surface of the obtained light guide. The obtained liquid crystal display device was used to measure the angular distribution of the luminous intensity of the emitted light. The results are shown in FIG. 4 as a luminous intensity ratio when the luminous intensity of the maximum peak is 1. Further, the peak light of the outgoing light ray is in the direction of 0 ° with respect to the normal direction of the light outgoing surface,
The full width at half maximum of the emitted light beam was 13 °. Furthermore, even when observed from an oblique direction of about 30 °, almost no change in contrast, color tone, brightness, etc. was observed.

Example 2 On a TFT type liquid crystal display element of the liquid crystal display device used in Example 1, an acrylic resin plate having a thickness of 2 mm and a pitch of 0.2.
A lenticular lens sheet having a 2 mm lenticular lens formed thereon was placed. The obtained liquid crystal display device was used to measure the angular distribution of the luminous intensity of the emitted light. The result is shown in FIG. 5 as a luminous intensity ratio when the maximum peak luminous intensity is 1.
It was shown to. Further, the peak light of the outgoing light ray is in the direction of 0 ° with respect to the normal line direction of the light outgoing surface, and the half value width of the outgoing light ray is 6
It was 0 ° or more. Furthermore, even when observed from an oblique direction of about 30 °, almost no change in contrast, color tone, brightness, etc. was observed.

Comparative Example 1 A transparent acrylic resin plate (Acrylite 001 manufactured by Mitsubishi Rayon Co., Ltd.) having a size of 100 mm × 90 mm × 4 mm was prepared, and one surface of the transparent acrylic resin plate was printed with a matte shape to prepare a light guide. A PET film having silver vapor-deposited on the two end faces of 90 mm of the obtained light guide was adhered by adhesion processing, and PE vapor-deposited with silver was formed on the surface opposite to the matte surface.
The T film was taped to form a reflective surface. Cold cathode tubes (KC130T4E7 manufactured by Matsushita Electric Industrial Co., Ltd.) were made of silver-deposited PET film on two 100 mm end faces of an acrylic plate.
(2, 4 mmφ × 130 mm) was wound and installed as a light source lamp to provide a backlight.

An acrylic ultraviolet curable resin solution was poured into a mold having a prism pattern with a prism apex angle of 90 ° and a pitch of 50 μm, and a PET film having a thickness of 150 μm was overlaid with a roll. Then, 570 mJ of ultraviolet ray was irradiated through the PET film to polymerize and cure the acrylic ultraviolet ray curable resin, and peeled from the mold to obtain a prism sheet having a refractive index of 1.59 and an apex angle of 90 °.

On the light emitting surface of the obtained light guide, an apex angle of 90
A liquid crystal display device was obtained by placing the prism sheet of 3 ° so that the prism array was on the light guide side. On the light emitting surface of the obtained light guide, a prism sheet having an apex angle of 90 ° is placed so that the prism array is on the light guide side, and further a TFT type liquid crystal display element is placed to form a liquid crystal display device. Assembled The obtained liquid crystal display device was used to measure the angular distribution of the luminous intensity of the emitted light. The results are shown in FIG. 6 as a luminous intensity ratio when the luminous intensity of the maximum peak is 1. Further, the peak light of the outgoing light ray was in the direction of 10 ° with respect to the normal direction of the light outgoing surface, and the full width at half maximum of the outgoing light ray was 35 °. Furthermore, even when observed from an oblique direction of about 30 °, almost no change in contrast, color tone, brightness, etc. was observed.

Comparative Example 2 On the TFT type liquid crystal display element of the liquid crystal display device used in Example 1, an acrylic resin plate having a thickness of 2 mm and a pitch of 0.2.
A lenticular lens sheet having a 2 mm lenticular lens formed thereon was placed. The obtained liquid crystal display device was used to measure the angular distribution of the luminous intensity of the emitted light. The result is shown in FIG. 7 as a luminous intensity ratio when the maximum peak luminous intensity is 1.
It was shown to. Further, the peak light of the outgoing light ray was in the direction of 10 ° with respect to the normal direction of the light outgoing surface, and the half width of the outgoing light ray was 60 ° or more. Furthermore, when observed from an oblique direction of about 30 °, changes in contrast, color tone, brightness, etc. were observed.

[0026]

According to the present invention, by forming a large number of specific prism rows on the back surface of the light guide, the distribution angle of the emitted light beam is narrow and the emission surface of the peak light is eliminated without using parts such as a prism sheet. It is possible to provide a backlight having excellent directivity that emits in the direction of the normal line and capable of simplifying and compacting the structure. In addition, by using such a backlight and further mounting a lenticular lens sheet on the liquid crystal display element, the viewing angle is wide, and there is no change in contrast depending on the viewing angle or change in color tone due to brightness reversal in intermediate colors. It can be used for various purposes such as increasing the screen size and observing by multiple people.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration example of a liquid crystal display device of the present invention.

FIG. 2 is a partial cross-sectional view showing a light guide according to the present invention.

FIG. 3 is a perspective view showing another configuration example of the liquid crystal display device of the present invention.

FIG. 4 is a graph showing an emission light distribution of the liquid crystal display device of Example 1.

FIG. 5 is a graph showing an emission light distribution of the liquid crystal display device of Example 2.

FIG. 6 is a graph showing an emission light distribution of the liquid crystal display device of Comparative Example 1.

FIG. 7 is a graph showing an emission light distribution of the liquid crystal display device of Comparative Example 2.

[Explanation of symbols]

 1 ... Liquid crystal display device 2 ... Light guide 3 ... Light source 4 ... Prism row 5 ... Liquid crystal display element 6 ... Lenticular lens sheet 7 ... Reflection layer 8 ... First prism surface 9 ・ ・ ・ Second prism surface

Claims (5)

[Claims] 1. A light guide and a light guide having at least one light incident surface facing the light source and a light exit surface substantially orthogonal to the light entrance surface, the back surface of the light guide facing the light exit surface. A large number of prism rows composed of two prism surfaces are formed in parallel to the light incident surface, and one surface (first prism surface) of the prism rows is 35 to 35 with respect to the light emitting surface.
Has an inclination angle of 55 °, the other surface (second prism surface)
Has a tilt angle of 80 to 100 with respect to the light emitting surface. 2. The backlight according to claim 1, wherein a second prism surface forming a prism row formed on the back surface of the light guide is located on the light source side in the prism row. 3. A light source, a light guide having at least one light incident surface facing the light source and a light exit surface substantially orthogonal thereto, and a liquid crystal display element disposed on the light guide. A large number of prism rows composed of two prism surfaces are formed in parallel with the light incident surface on the back surface of the light guide opposite to the light exit surface, and one surface (first
Prism surface) has an inclination angle of 35 to 55 ° with respect to the light emitting surface, and the other surface (second prism surface) has an inclination angle of 80 to 100 ° with respect to the light emitting surface. Characteristic liquid crystal display device. 4. The liquid crystal display device according to claim 3, wherein a second prism surface forming a prism row formed on the back surface of the light guide is located on the light source side in the prism row. 5. The liquid crystal display device according to claim 3, wherein a lenticular lens sheet having a large number of lenticular lenses formed in parallel on at least one surface thereof is placed on the liquid crystal display element.