JPH0922012A - 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 and a small variation in color hue due to a luminance inversion at a halftone color and usable for various purposes such as the accomplishment of a large-sized screen and the observation by plural users. SOLUTION: The device is composed of a light source 3, a light transmission body 2 provided with at least one incident plane and one going plane which are placed opposite to the light source 3, and a liquid crystal display element 5 arranged on the light transmission body 2. And the outgoing plane of the light transmission body 2 is composed of a rugged surface 4 where a projecting part and a flat part are alternately arranged so as to be parallel to the light source 3, the projection part is composed of two opposed rise-up planes 9 and 10, at least the rise-up plane 9 positioned far away from the light source 3 is provided with an inclined angle α of 50 deg. to 70 deg. against the flat part 11.

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 excellent directivity for emitting light in the normal direction of the emission surface of peak light, 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 narrow, 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 having at least one entrance surface and an exit surface facing the light source, and the exit surface of the light guide is formed parallel to the light source. The convex portions and the flat portions are alternately arranged, and the convex portions are composed of two rising surfaces facing each other, and at least the rising surface located on the side distant from the light source with respect to the flat portion. It has a tilt angle of 50 to 70 °. Further, the liquid crystal display device of the present invention comprises a light guide body having at least one entrance surface and an exit surface facing each other, and a liquid crystal display element arranged on the light guide body, and the exit surface of the light guide body. Is composed of a concave-convex surface in which convex portions and flat portions formed in parallel with the light source are alternately arranged, the convex portions are composed of two rising surfaces facing each other, and the rising surface is located at least away from the light source. Has an inclination angle of 50 to 70 ° with respect to the flat portion.

[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 an incident surface and one surface substantially orthogonal to this as an emission surface 4, and the emission surface 4 is alternately formed with a convex portion 8 and a flat portion 11 formed in parallel with the light source. It is composed of an uneven surface formed on. Also, this convex portion 8
2, the two rising surfaces 9 and 10 facing each other are provided, and the rising surface 9 located at least on the side away from the light source has an inclination angle (α of 50 to 70 ° with respect to the flat portion 11). ) Has. These rising surfaces 9, 10
May be a flat surface or a curved surface having a predetermined curvature,
When the curved surface is used, the angular distribution of the outgoing light beam can be increased to some extent. In the light guide 2 of the present invention, when a light beam propagating in the light guide 2 is incident on the convex portion 8, the emitted light is reflected by the rising surfaces 9 and 10 and the directivity is normal to the emission surface. Will be emitted. In the present invention, by using the light guide 2 formed of the emission surface 4 having such a specific uneven surface, it is possible to make the emission light from the backlight into pseudo parallel light with a narrow distribution angle. It is possible to use an emitted light beam in which the directivity of the peak light is in the direction normal to the emission surface. Preferably, the inclination angle (α) of the rising surface 9 located on the side away from the light source forming the convex portion 8 is in the range of 55 to 65 ° with respect to the flat portion 11.

The convex portion 8 formed on the emission surface of the light guide 2 is
The flat surface portion 12 rising from the flat portion 11 and the outwardly convex curved surface portion 13 formed continuously with the flat surface portion 12 can further narrow the distribution angle of the peak light of the light emitted from the backlight. This is preferable in that the directivity of the outgoing light beam can be made more normal to the outgoing surface.
In this case, the inclination angle (β) of the flat portion 12 with respect to the flat portion 11 is in the range of β ≦ α, and α-β ≦ 1 to 5 in consideration of productivity such as die-cutting property at the time of molding the convex portion 8. It is preferable to set the angle to about °. Further, it is preferable that the radius of curvature (R) of the curved surface portion 13 formed continuously with the flat surface portion 12 is in the range of 0.1 to 2 mm in order to further narrow the distribution angle of the light rays emitted from the backlight. . Further, when the length of the bottom portion (a) of the convex portion 8 is 1, the height (b) of the flat portion 12 that constitutes the rising surface 10 on the light source side is 1 to 2
The range is preferably, and more preferably 1.2.
１．５1.5. The width (c) and height (d) of the convex portion 8 and the width (a) of the flat portion 11 are not particularly limited, but the width (c) is preferably 0.05 to 1.5 m.
m, the height (d) is 0.07 to 2 mm, and the width (a) of the flat portion 11 is 0.05 to 1.5 mm.

In the present invention, the half-width of the angular distribution of the outgoing light beam 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 2 is preferably within the range of 15 ° with respect to the normal line direction of the outgoing surface, and more preferably within the range of 10 °.

The concavo-convex surface formed on the emission surface 4 of 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 may be formed by extrusion molding or injection molding. They may be processed and formed at the same time when the body 2 is manufactured. Alternatively, they may be integrally formed by using heat or a photocurable resin or the like. In the method of integrally forming the convex portion 8 on the emission surface of the light guide 2 using heat or a photocurable resin, the light guide 2
It is also possible to manufacture the convex portions 8 having different refractive indexes. Further, the convex portion 8 is formed by the 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 concavo-convex sheet on which is formed may be integrated with the light guide 2 by a method such as adhesion or fusion.

When the convex portion 8 is formed by using the active energy ray-curable resin, the active energy ray-curable resin liquid is poured into a mold having a predetermined uneven pattern, and the light guide 2 or the transparent film is formed. Overlap. Then, active energy rays such as ultraviolet rays and electron beams are irradiated through the light guide 2 to polymerize and cure the active energy ray-curable resin liquid,
It can be manufactured by peeling from the mold. Examples of the active energy ray curable resin forming the convex portion 8 include polyfunctional (meth) acrylic compounds, vinyl compounds,
(Meth) acrylic acid esters, allyl compounds, metal salts of (meth) acrylic acid and the like can be used.

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. On the back surface of the light guide 2, a reflective layer 7 is formed by metal vapor deposition or the like to form a reflective surface.

As the synthetic resin constituting the light guide 2, various highly transparent synthetic resins such as methacrylic resin, acrylic resin, polycarbonate resin and vinyl chloride resin are used, and extrusion molding and injection molding are carried out. It can be manufactured by a usual molding method such as. In particular, methacrylic resin is excellent in light transmittance, heat resistance, mechanical properties, and moldability, and is most suitable 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 includes a liquid crystal display element 5 and a backlight unit composed of the light source 3 and the light guide 2 having the above-mentioned configuration. By using the light guide 2 composed of the emission surface 4 having the specific uneven surface as described above, the light beam emitted from the light guide 2 has a small angular distribution when passing through the liquid crystal display element 5. Since the light becomes parallel light and the influence of the tilt direction of the liquid crystal molecules can be minimized, it is possible to obtain a liquid crystal display device in which there is little change in the color tone due to the contrast or brightness inversion of the intermediate color depending on the viewing angle. The liquid crystal display element 5 is not particularly limited, and is an active matrix driving TFT type liquid crystal display element or a simple matrix driving ST.
Any of N-type liquid crystal display elements 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 way, 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, by using the light guide 2 composed of the emission surface having a specific uneven surface, the influence of the tilt direction of the liquid crystal molecules can be minimized when passing through the liquid crystal display element 5 by the pseudo-parallel light having a small angle distribution. 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 and the brightness reversal of the intermediate color depending on the viewing angle.
A liquid crystal display device having a wide viewing angle can be provided.

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.

[0020]

The present invention will be described below in detail with reference to examples. Inverter the cold cathode tube of the measuring light guide luminosity (TDK Corp. CXA-
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 By injection molding of an acrylic resin, as shown in FIG. 2, one surface has a rising surface 9 having an inclination angle (α) of 60 °, and an inclination angle (β) of 58 °. A raised portion 10 having a width of 1 mm and a flat portion 11 having a width of 1 mm and two rising surfaces having a flat surface 12 having a length of 1.33 mm and a curved surface 13 having a radius of curvature of 1.33 mm. ,
A light guide body having an uneven surface formed in parallel with the light source and alternately arranged was produced. A PET film with silver vapor deposition is adhered to and pasted on the two 90 mm end faces of the obtained light guide, and a PET film with silver vapor deposition is taped to the opposite surface of the concavo-convex surface or the matte surface to provide a reflective surface. Was formed. Cold cathode tubes (KC13 manufactured by Matsushita Electric Industrial Co., Ltd.) were made of silver-deposited PET film on two 100 mm end faces of an acrylic plate.
0T4E72, 4mmφ × 130mm)
It was installed as a light source lamp and used as a backlight. The light source lamp was installed on the end surface of the light guide so that the rising surface with the inclination angle of 58 ° was on the light source side.

A liquid crystal display device was assembled by mounting a TFT type liquid crystal display element on the emission 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 ray was in the direction of 10 ° with respect to the normal direction of the outgoing surface, and the full width at half maximum of the outgoing ray was ± 15 °. 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 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, 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 a mat shape was printed by screen printing on one surface of the plate 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. On the other hand, 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.

[0027]

EFFECTS OF THE INVENTION According to the present invention, by forming a large number of convex portions having a specific shape on the exit surface of the light guide member, the angular distribution of outgoing rays can be narrowed without using parts such as a prism sheet.
It is possible to provide a backlight which has excellent directivity in which peak light is emitted in the direction normal to the emission surface, and which can achieve simplification and compactness of the structure. Further, by using such a backlight, by further mounting the lenticular lens sheet on the liquid crystal display element,
It has a wide viewing angle and has no change in contrast depending on the viewing angle and no change in color tone due to brightness inversion in intermediate colors, and can be used for various applications such as an increase in screen size and observation 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]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 2 ... Light guide 3 ... Light source 4 ... Emitting surface (uneven surface) 5 ... Liquid crystal display element 6 ... Lenticular lens sheet 7 ... Reflection layer 8 ... Convex part 9, 10 ... Rising surface 11 ... Flat part 12 ... Flat part 13 ... Curved part

Claims (3)

[Claims] 1. A light source, and a light guide body having at least one incident surface and an emission surface facing the light source,
The light-emitting surface of the light guide is composed of an uneven surface in which convex portions and flat portions formed in parallel with the light source are alternately arranged, and the convex portions are composed of two rising surfaces facing each other, and at least from the light source. A backlight characterized in that a rising surface located on a distant side has an inclination angle of 50 to 70 ° with respect to a flat portion. 2. A light source, a light guide having at least one entrance surface and an exit surface facing the light source, and a liquid crystal display element disposed on the light guide, wherein the light exits from the light guide. A convex surface and a flat surface formed in parallel with the light source are formed of an uneven surface, and the convex portion is formed of two rising surfaces facing each other, and the rising surface is located at least away from the light source. A liquid crystal display device, wherein the surface has an inclination angle of 50 to 70 ° with respect to the flat portion. 3. The liquid crystal display device according to claim 2, 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.