JPH08240719A - Liquid crystal display - Google Patents

Abstract

PURPOSE: To improve the luminance of a light transmission body and to decrease consumption of electric power for a back light by dispersing a gas phase in a solid phase to obtain a diffusion pattern. CONSTITUTION: A diffusion pattern 1 of many dots formed on the bottom of a light transmission body 37 is obtd. by dispersing a gas phase such as an air layer 3 in a solid phase comprising a resin 2. The diffusion dot pattern 1 of this structure has less absorption of light and a smaller outgoing angle of light compared to a conventional pattern comprising dispersion of a pigment such as titanium oxide or spherical hollow glass beads in a resin. Therefore, the loss of light due to a diffusion pattern can be decreased and the use efficiency of light can be improved. Thereby, the luminance of the light transmission body can be increased by about 30%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device provided with a so-called edge light type backlight in which a light source is arranged along an end face of a light guide located below a liquid crystal display element.

[0002]

2. Description of the Related Art In a liquid crystal display device, for example, two transparent glass substrates are superposed on each other with a predetermined gap so that the surfaces on which a display pixel electrode made of a transparent conductive film and an alignment film are laminated are opposed to each other. , Both substrates are bonded by a frame-shaped sealing material near the peripheral portion between the two substrates, and liquid crystal is sealed inside the sealing material between the two substrates from a liquid crystal sealing port provided in a part of the sealing material. , A liquid crystal display element (ie, a liquid crystal display panel, LCD: liquid crystal display (Liquid crystal display) that is sealed and further provided with a polarizing plate on the outside of both substrates.
d Crystal Display)), a backlight arranged below the liquid crystal display element to supply light to the liquid crystal display element, a liquid crystal drive circuit board arranged outside the outer periphery of the liquid crystal display element, and each of these members. And a frame-shaped body which is a molded product for holding, and a metal frame in which each of these members is housed and a display window is opened.

The backlight is, for example, a light guide body made of a synthetic resin plate such as transparent acrylic resin for guiding the light emitted from the light source away from the light source and uniformly irradiating the light on the entire liquid crystal display element. , End face of light guide (ie, side face)
A fluorescent tube which is a light source disposed in the vicinity along the end surface and in parallel with the end surface; and a lamp reflection sheet which covers the fluorescent tube over substantially the entire length thereof and has a substantially U-shaped cross section and whose inner surface is white or silver. A diffusion sheet disposed above the light guide and diffusing light from the light guide, and disposed below the light guide,
And a reflection sheet that reflects the light from the light guide toward the liquid crystal display element.

Further, the light entering the light guide from the fluorescent tube is guided while being totally reflected in the light guide, but is diffused and reflected to be emitted from the upper surface of the light guide, so that the light is guided to the bottom surface of the light guide. Has a plurality of light-diffusing dot patterns printed with white ink, and convex portions and concave portions integrally formed on the bottom surface of the light guide body are regularly arranged.

Incidentally, such a conventional liquid crystal display device is
For example, Japanese Patent Publication No. 60-19474 and Japanese Utility Model Publication No. 4-22
No. 780.

[0006]

A conventional diffusion pattern printed on the bottom surface of a light guide is a resin (resin) as a base material.
Among them, a mixture of a pigment such as titanium oxide as a light scattering agent or a spherical hollow bead made of an inorganic substance such as SiO ₂ glass as a light scattering agent was used. However, since such a light scattering agent such as a pigment or glass beads has a large light absorption and a large light emission angle, there is a problem that the light loss is large and the light utilization efficiency is low.

An object of the present invention is to have a diffusion pattern with low light loss and high light utilization efficiency, and therefore, the brightness of the light guide can be improved and the power consumption of the backlight can be reduced. An object is to provide a liquid crystal display device.

[0008]

In order to achieve the above object, the present invention provides a light guide disposed below a liquid crystal display device,
A light source such as a fluorescent tube disposed near at least one end face of the light guide and along the end face, and a diffusing means (diffusing sheet or diffusing plate) disposed above the light guide below the liquid crystal display element.
In a liquid crystal display device having a reflection means (a reflection sheet and a reflection plate) arranged under the light guide body, and a diffusion pattern having a diffusion action provided on the lower surface of the light guide body, the diffusion pattern is It is characterized in that a gas phase is dispersed in a solid phase.

Further, the solid phase is a resin.

Further, the resin is made to contain a foaming agent, or a foaming agent is applied on or under the resin so that the resin is foamed by heating or the like to disperse a gas phase in the resin. And

Further, the solid phase is the light guide. That is, a diffusion pattern is formed on the bottom surface of the light guide body integrally with the light guide body, and the gas is dispersed therein.

Further, the diffusion pattern is characterized in that a resin which is a base material of the diffusion pattern contains plastic beads in which gas is contained.

The shape of the plastic beads is
For example, it is characterized by being spherical.

The refractive index of the resin is substantially the same as or smaller than the refractive index of the light guide.

Further, at least one of the resin and the plastic beads is colorless and transparent.

The plastic beads containing a low boiling point liquid are heated to vaporize the liquid, and the gas is enclosed in the plastic beads.

Further, the diffusion pattern is dot-shaped.

Further, the dots are arranged in a plurality of straight lines parallel or perpendicular to the long axis direction of the fluorescent tube.

Further, at least one prism sheet is arranged between the diffusion sheet and the liquid crystal display element.

[0020]

In the present invention, as the diffusion pattern provided on the bottom surface of the light guide, the gas phase is dispersed in the solid phase, or the resin which is the base material thereof contains the plastic beads in which the gas is enclosed. Let Since the diffusion pattern having such a configuration has a small light absorption and a small light emission angle,
The light loss can be reduced, and the light utilization efficiency can be improved. As a result, the brightness of the light guide can be improved and the power consumption of the backlight can be reduced.

[0021]

EXAMPLE FIG. 3 is a side view of a backlight arranged below a liquid crystal display element to which the present invention is applicable. In the drawings described below, components having the same function are designated by the same reference numeral, and repeated description thereof will be omitted.

Reference numeral 62 is a liquid crystal display element, 77 is a backlight for supplying light to the liquid crystal display element 62, 37 is a light guide disposed under the liquid crystal display element 62, 65 is a light incident end face of the light guide 37, and 36 is a light guide end face. Is a fluorescent tube which is a light source arranged in the vicinity of the light incident end surface 65 of the light guide 37 along the light incident end surface 65 and in parallel with the light incident end surface 65, and 66 covers the fluorescent tube 36 over substantially the entire length thereof and has a cross section. The lamp reflection sheet is substantially U-shaped, and its inner surface is white or silver, 39 is a diffusion sheet disposed above the light guide 37 under the liquid crystal display element 62, and 38 is disposed below the light guide 37. The reflection sheet 1 is provided on the bottom surface of the light guide body 37, and a plurality of diffusion dot patterns that cause the light guided while being totally reflected inside the light guide body 37 to exit from the upper surface of the light guide body 37 (see FIG. 5). ), 72, 73 are a diffusion sheet 39 and a liquid crystal display, respectively. A prism sheet disposed between the element 62 (lens film), 67 a lamp reflection sheet 6
6 is an end portion of 6, 6 is a double-sided tape for adhering the end portion 67 of the lamp reflection sheet 66 to the upper surface of the light guide 37, 68, 69, 7
Reference numeral 0 denotes an adhesive layer, a base material layer, and an adhesive layer that respectively configure the double-sided tape 71, 74 denotes an end surface facing the light incident end surface 65, and 7
5 is a reflective tape provided on the end face 74, and 76 is a reflective tape 7.
5 is an adhesive layer that adheres 5 to the end surface 74.

The diffusion sheet 39 and the reflection sheet 38 are not adhered to the light guide 37. Lamp reflection sheet 66
The end portion 67 is attached to the upper surface of the light guide body 37 with the double-sided tape 71. The other end portion 78 of the lamp reflection sheet 66 is located below the reflection sheet 38, but is not bonded and is held and held by a frame or the like although not shown. Although the prism sheets 72 and 73 and the liquid crystal display element 62 are shown in a floating state in FIG. 3, the prism sheets 72 and 73 are placed on the diffusion sheet 39 in an overlapping manner and are not adhered. A liquid crystal display element 62 is placed on top. On the inner surface of the lamp reflection sheet 66, that is, the surface on the fluorescent tube 36 side, light is guided by the light guide 37.
It is formed in white or silver so as to be reflected toward the light incident end face 65 side. Further, although not shown, a reflection tape similar to the reflection tape 75 is also adhered to the two end faces of the light guide 37 which are perpendicular to the light incident end face 65.

FIG. 4 is a side view of another backlight to which the present invention can be applied.

In the backlight 77 shown in FIG. 3, the light guide 37 has a flat plate shape (a rectangular parallelepiped shape).
In FIG. 1, a backlight 77 using a light guide 37 having a wedge shape (that is, a trapezoidal cross section) is shown in order to reduce the weight and the thickness of the liquid crystal display module. Other configurations are the same as those of the backlight shown in FIG. The prism sheets 72 and 73 and the liquid crystal display element 62 are not shown in FIG.

FIG. 5 is a perspective view of yet another backlight to which the present invention can be applied to show a diffusion pattern.

The shape of the diffusion pattern 1 of the backlight 77 is a round dot, and as the distance from the fluorescent tube 36 increases, the dot diameter of the diffusion pattern 1 gradually increases to increase the diffuse reflection characteristic and move away from the light source. The decrease in the amount of light due to this is corrected, and the surface brightness of the light guide 37 is made uniform. Here, the pitches of the diffusion patterns 1 are all the same.

As described above, in the light guide body, the amount of light incident from the light source into the light guide body decreases and becomes darker as the distance from the light source increases, so that the decrease in the light amount is corrected and the surface brightness of the light guide body is corrected. In order to make the light uniform, the diffuse reflection characteristic of the light guide is designed to increase as the distance from the light source increases. Further, the correction amount of the irregular reflection characteristic must be increased as the distance from the light source to the light guide becomes longer (that is, as the length of the light guide becomes longer) or as the light guide becomes thinner. .

Example 1 FIG. 1 is a sectional view of a diffusion pattern according to Example 1 of the present invention (for example, showing a section of one diffusion dot pattern corresponding to the AA cutting line in FIG. 5).

37 is a light guide made of an acrylic plate, and 1 is a diffusion dot pattern provided on the bottom surface of the light guide 37 (see FIG. 3,
4 and 5), 2 is a base resin (resin) that is a base material of the diffusion dot pattern 1, and 3 is an air layer (air bubble).

As the resin 2, when the light guide 37 is made of acrylic, a colorless and transparent resin such as an acrylate UV resin such as a urethane acrylate oligomer (medium molecule) can be used. The acrylic resin forming the light guide 37 has a refractive index of about 1.49, and the resin 2 whose refractive index is substantially the same as or smaller than that of the light guide 37 is used. The reason for this will be described later. The refractive index of the gas in the air layer 3 is 1.

The thickness t of the diffusion dot pattern 1 is about 15
Is about 40 μm.

A method of forming such a diffusion dot pattern 1 is performed as follows, for example. That is, a resin containing a foaming agent is applied or screen-printed, or a foaming agent is applied by contacting the top or bottom of the resin coated or screen-printed, and then foamed by heating etc. To form the air layer 3.

In the present embodiment, a large number of diffusion dot patterns 1 formed on the bottom surface of the light guide 37 as shown in FIG.
1, a gas phase, for example, an air layer 3 was dispersed in a solid phase composed of the resin 2 as shown in FIG. The diffusion dot pattern 1 having such a configuration is
Compared to a mixture of a pigment such as titanium oxide or a spherical hollow glass bead as a light scattering agent, light absorption is small and a light emission angle is small. Therefore, the light loss due to the diffusion pattern can be reduced, and the light utilization efficiency can be improved. As a result, the brightness of the light guide body could be improved by about 30%, and the power consumption of the backlight could be reduced. The reason for this will be described later.

Embodiment 2 FIG. 2 is a sectional view similar to FIG. 1 of a diffusion pattern of Embodiment 2 of the present invention.

Reference numeral 2 is a base resin (resin) which is a base material of a large number of diffusion dot patterns 1 (see FIGS. 3, 4 and 5) provided on the bottom surface of a light guide 37 made of acrylic, and 4 is a resin 2.
Spherical hollow plastic beads mixed in a number of 3
Is an air layer enclosed in the center of the plastic beads 4.

As the resin 2, when the light guide 37 is made of acrylic, an acrylate UV resin such as a urethane acrylate oligomer (medium molecule) having a refractive index substantially equal to or smaller than that of acrylic is used. A colorless and transparent resin can be used. In addition, the hollow plastic beads 4 have almost the same refractive index as acrylic,
Polymethylmethacrylate (PMMA) of less than that,
A colorless transparent bead made of polyacrylonitrile (PAN), polymethylacetoacrylate (PMAA), or the like can be used.

The thickness t of the diffusion dot pattern 1 is about 15
The diameter of the hollow plastic beads 4 is about 5 to 15 μm, which enables screen printing.

The method of forming such a diffusion dot pattern 1 is performed as follows, for example. That is, for example, a large number of the plastic beads containing a low-boiling liquid filler such as alcohol or liquefied butane gas are well mixed in the base resin, and the bead-mixed resin is screen-printed on the bottom surface of the light guide 37. Or apply. Next, by heating to vaporize the liquid contained in the beads, a diffusion dot pattern 1 made of a resin containing beads in which gas is enclosed can be formed in the center.

In this embodiment, a large number of diffused dot patterns 1 formed on the bottom surface of the light guide 37 as shown in FIG.
As shown in FIG. 2, the resin 2 was formed by mixing a large number of plastic beads 4 having an air layer 3 enclosed therein. Compared with the above-mentioned conventional dot pattern, the diffusion dot pattern 1 having such a configuration has less light absorption and a smaller light emission angle as in the case of the above-described first embodiment, so that the light loss due to the diffusion pattern is reduced. Therefore, the light utilization efficiency can be improved. As a result, the brightness of the light guide body could be improved by about 30%, and the power consumption of the backlight could be reduced. The reason for this will be described below.

That is, since the conventional pigment has a light-absorbing property in itself, the existing pigments have a limit in reducing the light loss due to light absorption in any structure. In addition, the light absorption by the glass material itself is small in the hollow glass beads, but the light scattering (reflection) at the outer interface of each bead and the light scattering at the inner interface thereof are intricately entangled with each other, resulting in repeated diffuse reflection within each bead. Light loss occurs. However, if the hollow glass beads are included in a transparent material having a refractive index almost equal to that of glass, the same effect as that of the present invention is produced, but the refractive index of glass is generally high, and This is not possible with such a base resin.

In the present invention, since a plurality of hollow plastic beads are contained in the base resin having the same refractive index as that of the hollow plastic beads, the reflection at the outer interface of the hollow plastic beads is prevented. Almost disappeared, and only reflection at the inner interface of the hollow plastic beads having a small diameter, which is efficient in light dispersion (diffusion), can be obtained. That is, in a backlight device such as a liquid crystal display panel that requires uniform light of a predetermined brightness for a display unit of a certain size, how much brightness of light from a cold cathode fluorescent tube can be obtained by printing dots of a light guide. Is uniform and isotropically diffused so that there is no unevenness.
The point lies in the light diffusivity of each dot (in the case of a circular dot, the diameter contributes), the ease of calculating the dot density according to the distance from the cold cathode fluorescent tube (light source), and the like. Therefore, according to the present invention, while maintaining the light diffusivity in each dot, and the ease of calculation of the dot density according to the distance from the light source, each of which cannot be eliminated by conventional pigments or hollow glass beads. The light loss can be reduced without causing any disadvantage.

The refractive index of the resin is set to be substantially the same as or lower than the refractive index of the light guide, so that the light from the light source passing through the light guide is entirely contained in the hollow plastic. This is because it does not prevent the user from going to, and it is desirable that they are approximately the same. Therefore, the relationship of the refractive index is as follows, and it is more preferable that the equal signs are obtained.

Refractive index of light guide ≧ refractive index of resin≈refractive index of hollow plastic beads The gas in the hollow plastic beads has the lowest refractive index.

As described above, in the reflection layer (diffusion layer) using the resin and the hollow plastic beads, it is easy to calculate the directing direction of the light (light flux direction) due to its structure, which affects the product specifications. It serves as an accurate index for designing other optical members (particularly, a prism sheet etc.), and improves the light utilization efficiency as compared with the conventional one.

In the first embodiment, the resin 2 is not used as the base material of the diffusion dot pattern 1, and when the light guide 37 is molded, it is integrated with the bottom surface of the light guide 37.
It is also possible to form a diffusion dot pattern composed of convex portions as indicated by reference numeral 2 and disperse the gas therein. In addition, in the second embodiment, the shape of the plastic beads 4 is not necessarily spherical. Further, in Examples 1 and 2 described above, even if another gas such as nitrogen, oxygen, or carbon dioxide is used instead of the air in the air layer 3, the same effect can be obtained because the refractive index does not change to 1. To be Further, the diffusion pattern does not necessarily have to be a round dot or a dot pattern, and it is possible to use patterns of various shapes.

Hereinafter, a simple matrix type liquid crystal display device to which the present invention shown in FIGS. 1 and 2 as Embodiments 1 and 2 can be applied will be described.

FIG. 6 shows an arrangement direction of liquid crystal molecules on the electrode substrate (for example, a rubbing direction), a twisting direction of liquid crystal molecules, and a polarizing plate when the liquid crystal display element 62 of the liquid crystal display device to which the present invention is applied is viewed from above. Polarization axis (or absorption axis) of
Direction and the optical axis direction of the member that brings about the birefringence effect, and FIG. 7 is a perspective view of a main part of the liquid crystal display element 62.

Twisting direction 10 of liquid crystal molecules and twist angle θ
Is a rubbing direction 6 of the alignment film 21 on the upper electrode substrate 11, a rubbing direction 7 of the alignment film 22 on the lower electrode substrate 12, and a positive dielectric anisotropy sandwiched between the upper electrode substrate 11 and the lower electrode substrate 12. It is defined by the type and amount of the optical rotatory substance added to the nematic liquid crystal layer 50 having the property.

In FIG. 7, in order to align the liquid crystal molecules between the two upper and lower electrode substrates 11 and 12 sandwiching the liquid crystal layer 50 so as to form a twisted spiral structure, for example, a transparent upper layer made of glass is used. The rubbing method, which is a method of rubbing the surfaces of the alignment films 21 and 22 made of an organic polymer resin made of polyimide, for example, in contact with the liquid crystal on the lower electrode substrates 11 and 12 with a cloth in one direction, is used. ing. The rubbing direction at this time, that is, the rubbing direction, the rubbing direction 6 in the upper electrode substrate 11, and the rubbing direction 7 in the lower electrode substrate 12 are the alignment directions of the liquid crystal molecules. The two upper and lower electrode substrates 1 that have been oriented in this way
1 and 12 are made to face each other with a gap d ₁ so that the rubbing directions 6 and 7 intersect each other at approximately 180 to 360 degrees, and the two electrode substrates 11 and 12 are notched for injecting liquid crystal. Portion, that is, a nematic liquid crystal having a positive dielectric anisotropy adhered by a frame-shaped sealing material 52 having a cutout portion (liquid crystal sealing port) 51 and having a predetermined amount of an optically active substance added thereto. When encapsulated, the liquid crystal molecules form a helical molecular arrangement with a twist angle θ in the figure between the electrode substrates. Reference numerals 31 and 32 are transparent upper and lower electrodes made of, for example, indium oxide or ITO (Indium Tin Oxide). A member for producing a birefringence effect on the upper electrode substrate 11 of the liquid crystal cell 60 thus configured (hereinafter referred to as a birefringence member. Fujimura et al., "STN-LCD retardation film", magazine electronic material 1991 2 Monthly issue No. 3
(See page 7-41) 40, and this member 4
0 and the liquid crystal cell 60 are sandwiched between the upper and lower polarizing plates 15 and 16
Is provided.

The twist angle θ of the liquid crystal molecules in the liquid crystal 50 can take a value in the range of 180 ° to 360 °, preferably 200 ° to 300 °, but the transmittance-applied voltage curve is turned on in the vicinity of the threshold value. From the practical viewpoint of avoiding the phenomenon that the state becomes an orientation that scatters light and maintaining excellent time division characteristics, the range of 230 to 270 degrees is more preferable. This condition basically makes the response of the liquid crystal molecules to the voltage more sensitive and acts to realize excellent time division characteristics. In order to obtain excellent display quality and the refractive index anisotropy [Delta] n ₁ of the liquid crystal layer 50 a product [Delta] n ₁ of the thickness d ₁
-D ₁ is preferably set in the range of 0.5 μm to 1.0 μm, more preferably 0.6 μm to 0.9 μm.

The birefringent member 40 acts so as to modulate the polarization state of light passing through the liquid crystal cell 60, and converts what could only be colored display by the liquid crystal cell 60 into black and white display. Thus the birefringent member 40 refractive index anisotropy [Delta] n ₂ and is extremely important product [Delta] n ₂ · d ₂ of a thickness d _2, preferably 0.8μm from 0.4 .mu.m, more preferably 0.5μm To 0.7 μm.

Further, since the liquid crystal display element 62 uses the elliptically polarized light due to the birefringence, the axes of the polarizing plates 15 and 16 and the optical axis thereof when the uniaxial transparent birefringent plate is used as the birefringent member 40. And the electrode substrate 11 of the liquid crystal cell 60,
The relationship between the liquid crystal alignment directions 12 and 6 is extremely important.

The operation and effect of the above relationship will be described with reference to FIG. FIG. 6 shows an axis of a polarizing plate, an optical axis of a uniaxial transparent birefringent member when the liquid crystal display device having the configuration of FIG. 7 is viewed from above,
3 shows the relationship between the alignment directions of liquid crystal molecule axes of an electrode substrate of a liquid crystal cell.

In FIG. 7, 5 is the optical axis of the uniaxial transparent birefringent member 40, 6 is the alignment direction of the liquid crystal molecules of the birefringent member 40 and the upper electrode substrate 11 adjacent thereto, and 7 is the lower electrode substrate 12. The liquid crystal alignment direction, 8 is the absorption axis or polarization axis of the upper polarization plate 15, 9 is the absorption axis or polarization axis of the lower polarization plate 16, and the angle α is uniaxial birefringence with the liquid crystal alignment direction 6 of the upper electrode substrate 11. The angle β formed by the optical axis 5 of the member 40 is the angle formed by the absorption axis or polarization axis 8 of the upper polarizing plate 15 and the optical axis 5 of the uniaxial transparent birefringent member 40, and the angle γ is the lower polarizing plate 16. Is the angle between the absorption axis or polarization axis 9 of the liquid crystal and the liquid crystal alignment direction 7 of the lower electrode substrate 12.

Here, how to measure the angles α, β, and γ in this specification will be defined. In FIG. 11, the intersection angle between the optical axis 5 of the birefringent member 40 and the liquid crystal alignment direction 6 of the upper electrode substrate will be described as an example. The intersection angle between the optical axis 5 and the liquid crystal alignment direction 6 can be represented by φ ₁ and φ ₂ , as shown in FIG. 11, but in this specification, the smaller angle of φ ₁ and φ ₂ is adopted. That is, in FIG. 11A, φ ₁ <φ ₂
Since it is, the phi ₁ and the crossing angle α between the optical axis 5 and the liquid crystal alignment direction 6, and the intersection angle α between φ _1> φ ₂ So the optical axis 5 of phi ₂ liquid crystal alignment direction 6 in FIG. 11 (b) To do. Of course φ ₁
In the case of = φ ₂ , either one may be adopted.

In the liquid crystal display device, the angles α, β and γ are extremely important.

The angle α is preferably 50 ° to 90 °, more preferably 70 ° to 90 °, the angle β is preferably 20 ° to 70 °, more preferably 30 ° to 60 °, and the angle γ is preferably. It is desirable to set each to 0 to 70 degrees, and more preferably to 0 to 50 degrees.

If the twist angle θ of the liquid crystal layer 50 of the liquid crystal cell 60 is in the range of 180 degrees to 360 degrees, the above angle is satisfied regardless of whether the twist direction 10 is clockwise or counterclockwise. α, β, and γ may be within the above range.

In FIG. 7, the birefringent member 40 is disposed between the upper polarizing plate 15 and the upper electrode substrate 11, but instead of this position, the lower electrode substrate 12 and the lower polarizing plate 16 are provided.
It may be disposed between and. This case corresponds to the case where the entire configuration of FIG. 7 is inverted.

FIG. 8 is a diagram showing a specific example of the twist angle θ and the like. As shown in the figure, the twist angle θ of the liquid crystal molecules is 240 degrees, and as the uniaxial transparent birefringent member 40, a liquid crystal cell having a parallel orientation (homogeneous orientation), that is, a twist angle of 0 degree was used. Here, the thickness d (μm) of the liquid crystal layer and the helical pitch p (μ of the liquid crystal material added with the optical rotatory substance)
The ratio d / p of m) was set to 0.67. Alignment films 21 and 22
Was used, which was formed of a polyimide resin film and rubbed. The tilt angle (pretilt angle) at which the alignment film subjected to the rubbing process causes the liquid crystal molecules in contact with the alignment film to be tilted with respect to the substrate surface is 4 degrees. The Δn ₂ · d ₂ of the uniaxial transparent birefringent member 40 is about 0.6 μm. On the other hand, Δn ₁ · of the liquid crystal layer 50 in which the liquid crystal molecules are twisted by 240 degrees
d ₁ is about 0.8 μm.

At this time, by setting the angle α to about 90 degrees, the angle β to about 30 degrees, and the angle γ to about 30 degrees, the voltage applied to the liquid crystal layer 50 via the upper and lower electrodes 31 and 32 is increased. When the voltage is below the threshold value, light non-transmission, that is, black display, and when the voltage exceeds a certain threshold, light transmission, that is, white and black display is realized. In addition, the axis of the lower polarizing plate 16 is 50
When rotated 90 degrees from 90 degrees, white display was realized when the voltage applied to the liquid crystal layer 50 was below the threshold value, and black when the voltage was above the threshold value, which was the reverse of the above.

FIG. 9 shows a change in contrast during time-division driving at 1/200 duty when the angle α is changed in the configuration of FIG. Although the contrast was extremely high when the angle α was in the vicinity of 90 degrees, the contrast decreased as the angle deviated. Moreover, when the angle α is small, both the lighting part and the non-lighting part are bluish, and when the angle α is large, the non-lighting part is purple and the lighting part is yellow, and in any case black and white display is impossible. Similar results are obtained for the angle β and the angle γ, but in the case of the angle γ, as described above, when the image is rotated from 50 degrees to 90 degrees, the black and white display is reversed.

FIG. 8 is a diagram showing another specific example of the twist angle θ and the like. The basic structure is the same as the specific example shown in FIG.
However, the twist angle of the liquid crystal molecules of the liquid crystal layer 50 is 260 degrees,
The difference is that Δn ₁ · d ₁ is about 0.65 μm to 0.75 μm. The Δn ₂ · d ₂ of the parallel alignment liquid crystal layer used as the uniaxial transparent birefringent member 40 is about 0.5, which is the same as that in the above-mentioned specific example.
It is 8 μm. The thickness d ₁ (μm) of the liquid crystal layer and the helical pitch p (μm) of the nematic liquid crystal material added with the optically active substance.
And the ratio was set to d / p = 0.72.

At this time, by setting the angle α to about 100 degrees, the angle β to about 35 degrees, and the angle γ to about 15 degrees, the black and white display similar to the first specific example was realized. Also, the reverse black-and-white display is possible by rotating the position of the axis of the lower polarizing plate by 50 to 90 degrees from the above value, which is similar to the first specific example. The tendency with respect to the deviations of the angles α, β, and γ is almost the same as in the first specific example.

In each of the specific examples described above, a parallel alignment liquid crystal cell having no twist of liquid crystal molecules is used as the uniaxial transparent birefringent member 40, but a liquid crystal layer in which liquid crystal molecules are twisted by about 20 to 60 degrees is used. There is less color change depending on the angle. Like the above-mentioned liquid crystal layer 50, this twisted liquid crystal layer is formed by sandwiching liquid crystal between a pair of transparent substrates that have been subjected to the alignment treatment so that the alignment treatment directions intersect a predetermined twist angle. It In this case, the bisected angle of the two orientation treatment directions sandwiching the twisted structure of the liquid crystal molecules may be treated as the optical axis of the birefringent member. A transparent polymer film may be used as the birefringent member 40 (uniaxially stretched film is preferable at this time). In this case, PET (polyethylene terephthalate), acrylic resin film and polycarbonate are effective as the polymer film.

Further, although the single birefringent member is used in the above-mentioned specific example, in addition to the birefringent member 40 in FIG. 7, another birefringent member is provided between the lower electrode substrate 12 and the lower polarizing plate 16. It is also possible to insert a bending member. In this case, Δn ₂ · d ₂ of these birefringent members should be readjusted.

However, as shown in FIG. 12, the upper electrode substrate 1
Red, green, and blue color filters 33R, 33G, 3 on top of 1
By providing the light shielding film 33D between the filters 3B and the respective filters, multicolor display is possible. FIG. 10 shows the relationship among the alignment direction of the liquid crystal molecules, the twisting direction of the liquid crystal molecules, the axis direction of the polarizing plate, and the optical axis of the birefringent member in the above specific example.

In FIG. 12, each filter 33
On the R, 33G, 33B and the light shielding film 33D, a smoothing film 23 made of an insulating material is formed on the light shielding film 33D, and an upper electrode 31 and an alignment film 21 are formed on the smoothing film 23.

FIG. 13 is an exploded perspective view showing a liquid crystal display element 62, a drive circuit for driving the liquid crystal display element 62, and a liquid crystal display module 63 in which a light source is integrated compactly. IC 34 for driving the liquid crystal display element 62
Is mounted on a frame-shaped printed circuit board 35 having a window for fitting the liquid crystal display element 62 in the center. The printed circuit board 35 in which the liquid crystal display element 62 is fitted is fitted in the window portion of the frame-like body 42 formed by plastic molding,
The metal frame 41 is superposed on this, and the claw 43 is bent into the notch 44 formed in the frame-shaped body 42 to fix the frame 41 to the frame-shaped body 42.

A cold cathode fluorescent tube 36 arranged at the upper and lower ends of the liquid crystal display element 62, a light guide plate 37 made of an acrylic plate for uniformly irradiating the liquid crystal display cell 60 with light from the cold cathode fluorescent tube 36, a metal A reflecting plate 38 formed by applying white paint to the plate, and a diffusing plate 39 made of milk-white polycarbonate or the like for diffusing light from the light guide plate 37 are arranged in the order of FIG. Fit in. An inverter power supply circuit (not shown) for lighting the cold cathode fluorescent tube 36 is located at a position (not shown) provided on the back side of the right side of the frame-shaped body 42 and facing the recess 45 of the reflection plate 38. .). As for the diffusion plate 39, the light guide plate 37, the cold cathode fluorescent tube 36, and the reflection plate 38, the tongue piece 46 provided on the reflection plate 38 is provided with the edge 47 provided on the frame-shaped body 42.
It is fixed by bending it inside.

Although not shown in this figure, the loss of light due to the diffusion pattern on the bottom surface of the light guide 37 is reduced by applying Examples 1 and 2 as shown in FIGS. Since the light utilization efficiency can be improved, the brightness of the light guide can be improved, and the power consumption of the backlight can be reduced.

FIG. 14 is a block diagram of a laptop personal computer using the liquid crystal display module 63 for the display portion, and FIG. 15 is a diagram showing a state in which the liquid crystal display module 63 is mounted on the laptop personal computer 64. In this laptop personal computer 64, the microprocessor 4
The result calculated in 9 is transferred to the liquid crystal display module 63 by the liquid crystal driving semiconductor IC 34 via the control LSI 48.
Is to drive.

As described above, according to the above specific example, it is possible to realize a field effect liquid crystal display device having excellent time-division driving characteristics and capable of monochrome and multicolor display.

Next, an active matrix type liquid crystal display device to which the present invention shown in FIGS. 1 and 2 as Embodiments 1 and 2 can be applied will be described.

FIG. 16 is an exploded perspective view showing each component of the liquid crystal display module MDL.

SHD is a shield case made of a metal plate (also called a metal frame), WD is a display window and INS1.
3 to 3 are insulating sheets, PCBs 1 to 3 are circuit boards (PCB1
Is the drain side circuit board, PCB2 is the gate side circuit board,
PCB3 is an interface circuit board), JN is a joiner that electrically connects the circuit boards PCB1 to PCB3, T
CP1, TCP2 are tape carrier packages, PNL
Is a liquid crystal display panel, GC is a rubber cushion, ILS is a light-shielding spacer, PRS is a prism sheet, SPS is a diffusion sheet, GLB is a light guide plate, RFS is a reflection sheet, and MCA is a lower case (molded case) formed by integral molding. , LP is a fluorescent tube, LPC is a lamp cable, and GB is a rubber bush that supports the fluorescent tube LP, and the liquid crystal display module MDL is assembled by stacking the members in a vertical arrangement relationship as shown in the figure.

The module MDL includes a lower case MCA,
The shield case SHD has two types of storage / holding members. Insulation sheets INS1-3, circuit boards PCB1-3,
By combining the metal shield case SHD, which houses and fixes the liquid crystal display panel PNL, and the lower case MCA, which houses the backlight BL composed of the fluorescent tube LP, the light guide plate GLB, the prism sheet PRS, etc., the module MDL is assembled. Can be assembled.

Although not shown in the figure, by applying Examples 1 and 2 as shown in FIGS. 1 and 2, the light loss due to the diffusion pattern on the bottom surface of the light guide 37 is reduced. Since the light utilization efficiency can be improved, the brightness of the light guide can be improved, and the power consumption of the backlight can be reduced.

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and it is needless to say that various modifications can be made without departing from the scope of the invention. .

[0081]

As described above, according to the present invention,
Since the light loss due to the diffusion pattern on the bottom surface of the light guide of the backlight can be reduced and the light utilization efficiency can be improved, the brightness of the light guide can be improved and the power consumption of the backlight can be reduced. can do.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a diffusion pattern according to a first embodiment of the present invention (showing a cross section of one diffusion dot pattern corresponding to the AA cutting line in FIG. 5).

FIG. 2 is a sectional view similar to FIG. 1 of a diffusion pattern according to a second embodiment of the present invention.

FIG. 3 is a side view of a backlight arranged below a liquid crystal display device to which the present invention is applicable.

FIG. 4 is a side view of another backlight to which the present invention can be applied.

FIG. 5 is a perspective view of still another backlight to which the present invention can be applied.

FIG. 6 shows an example of a relationship among an alignment direction of liquid crystal molecules, a twisting direction of liquid crystal molecules, a direction of a polarizing plate axis, and an optical axis of a birefringent member in a simple matrix type liquid crystal display device to which the present invention is applicable. FIG.

FIG. 7 is an exploded perspective view of an essential part of an example of a liquid crystal display element.

FIG. 8 is an explanatory diagram showing a relationship among a twist direction of liquid crystal molecules, a direction of an axis of a polarizing plate, and an optical axis of a birefringent member in a liquid crystal display element of another example.

9 is a graph showing contrast and transmitted light color-crossing angle α characteristics for the example of FIG. 6 of the liquid crystal display device.

FIG. 10 is an explanatory diagram showing a relationship among an alignment direction of liquid crystal molecules, a twisting direction of liquid crystal molecules, a direction of an axis of a polarizing plate, and an optical axis of a birefringent member in a liquid crystal display element of still another example.

FIG. 11 is a diagram for explaining how to measure intersection angles α, β, and γ.

FIG. 12 is a partially cutaway perspective view of an example of an upper electrode substrate portion of a color liquid crystal display element.

FIG. 13 is an exploded perspective view of an example of a liquid crystal display module.

FIG. 14 is a block diagram of an example of a laptop personal computer.

FIG. 15 is a perspective view of an example of a laptop computer.

FIG. 16 is an exploded perspective view of an active matrix type liquid crystal display module to which the present invention is applicable.

[Explanation of symbols]

1 ... Diffusion dot pattern, 2 ... Base resin, 3 ... Air layer, 4 ... Plastic beads, 37 ... Light guide.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshio Hirayama 3350 Hayano, Mobara-shi, Chiba Hitachi Electric Devices Co., Ltd.

Claims (12)

[Claims] 1. A light guide disposed below a liquid crystal display device, a light source disposed near at least one end face of the light guide along the end face, and a light guide disposed below the liquid crystal display device. In a liquid crystal display device having a diffusing means arranged above, a reflecting means arranged under the light guide, and a diffusing pattern having a diffusing action provided on a lower surface of the light guide, the diffusing pattern is a solid state. A liquid crystal display device comprising a gas phase dispersed in a phase. 2. The liquid crystal display device according to claim 1, wherein the solid phase is a resin. 3. A resin containing a foaming agent, or after applying a foaming agent in contact with the resin, foaming the resin to disperse the gas phase in the resin.
The described liquid crystal display device. 4. The liquid crystal display device according to claim 1, wherein the solid phase is the light guide. 5. A light guide arranged below the liquid crystal display element, a light source arranged near at least one end face of the light guide along the end surface, and a light guide of the light guide below the liquid crystal display element. In a liquid crystal display device having a diffusing means arranged above, a reflecting means arranged under the light guide, and a diffusing pattern having a diffusing action provided on the lower surface of the light guide, the diffusing pattern is A liquid crystal display device comprising a resin, which is a base material, and plastic beads in which a gas is enclosed. 6. The liquid crystal display device according to claim 5, wherein the plastic beads have a spherical shape. 7. The liquid crystal display device according to claim 1, wherein a refractive index of the resin is substantially the same as or smaller than a refractive index of the light guide. 8. The liquid crystal display device according to claim 1, wherein at least one of the resin and the plastic beads is colorless and transparent. 9. The liquid crystal display device according to claim 5, wherein the plastic beads containing a liquid having a low boiling point are heated to vaporize the liquid, and the gas is enclosed in the plastic beads. 10. The liquid crystal display device according to claim 1, wherein the diffusion pattern has a dot shape. 11. The liquid crystal display device according to claim 10, wherein the dots are arranged in a plurality of straight lines that are parallel or perpendicular to the long axis direction of the fluorescent tube. 12. The liquid crystal display device according to claim 1, wherein at least one prism sheet is arranged between the diffusion sheet and the liquid crystal display element.