JP3315810B2 - Liquid crystal display - Google Patents

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 in which a backlight including a plurality of fluorescent tubes is arranged below a liquid crystal display element, and more particularly to a technique for making the brightness of the backlight uniform. About.

[0002]

2. Description of the Related Art In a liquid crystal display device, for example, two transparent glass substrates are overlapped at a predetermined interval so that the surfaces on which a pixel electrode made of a transparent conductive film and an alignment film are laminated face each other. A liquid crystal display element (liquid crystal display panel) comprising a substrate which is attached to the periphery of the substrate and a liquid crystal is sealed between the two substrates by a sealing material provided around the edge between the substrates, and a polarizing plate is further provided outside the both substrates; It is arranged below the liquid crystal display element and includes a backlight for supplying light to the liquid crystal display element, a circuit board for driving the liquid crystal display element, and the like.

[0003] A backlight is, for example, a substantially rectangular parallelepiped made of a transparent acrylic or other synthetic resin plate for guiding light emitted from a light source to a direction away from the light source and uniformly irradiating the entire liquid crystal display element with the light. A light guide plate, a fluorescent tube which is a light source disposed in the vicinity of the side surface of the light guide plate along the side surface in parallel with the side surface, and covering the fluorescent tube over substantially the entire length thereof; A lamp reflection cover that returns the light to the light guide plate so as not to leak outside, a diffusion sheet that is placed on the light guide plate and diffuses light from the light guide plate, and a light reflection plate that is placed below the light guide plate and is placed under the light guide plate And a reflection sheet for reflecting the light toward the liquid crystal display element. In addition, the light that enters the light guide plate from the fluorescent tube is guided while totally reflecting inside the light guide plate. However, in order to emit light from the upper surface of the light guide plate by diffuse reflection, a plurality of light beams are provided on the bottom surface of the light guide plate. White dot pattern by diffusion printing and holes, grooves,
The projections are regularly arranged and formed. In addition, a plurality of fluorescent tubes arranged in parallel with each other via a diffusion plate below the liquid crystal display device, and a reflector plate disposed below the fluorescent tube and reflecting light from the fluorescent tube toward the liquid crystal display device There is also a so-called direct-type backlight composed of

[0004] Such a conventional liquid crystal display device is disclosed in, for example, Japanese Patent Publication No. 60-19474 and Japanese Utility Model Laid-Open No. 4-22780.
No., published in Japanese Unexamined Patent Publication No.

FIG. 14A is a top view showing a conventional backlight, and FIG. 14B is a side view as seen from the direction of arrow A in FIG.

Reference numeral 37 denotes a light guide plate made of an acrylic plate disposed below a liquid crystal display device (not shown; see FIG. 3); 36, a cold cathode fluorescent tube as a light source; 2, driving means for lighting the fluorescent tube 36; For example, the inverter 1 is a line schematically showing light emission from the fluorescent tube 36, and the longer the brightness, the higher the brightness, and the shorter the brightness, the lower the brightness. In this figure, the fluorescent tube 36 is covered over substantially the entire length, and the light of the fluorescent tube 36 is transmitted to the light guide plate 3.
7, a lamp reflection cover, a diffusion sheet disposed on the upper surface of the light guide plate 37 for diffusing the light from the light guide plate 37, and a diffusion sheet disposed on the lower surface of the light guide plate 37 to transmit the light from the light guide plate 37 toward the liquid crystal display element. Reflecting sheet for reflecting light and light guide plate 37
The dot pattern for light diffusion and the like provided on the bottom surface of are not shown.

In order to increase the brightness, this backlight has a length in which a total of four fluorescent tubes 36 are provided along the two long sides facing each other of the light guide plate 37 and in parallel with the two sides. This is an example of a four-sided edge light type backlight. The two fluorescent tubes 36 are arranged in the thickness direction of the light guide plate 37 as shown in FIG. 14B. However, in FIG. Are not shown as such for clarity. One end of each pair of fluorescent tubes 36 is directly electrically connected to another inverter 2, and the other end of each pair of fluorescent tubes 36 is electrically connected to each other. This other end is referred to as a ground side.

[0008]

In the conventional backlight shown in FIG. 14, a pair of fluorescent tubes 36 connected in parallel is connected directly to the inverter 2 at one end. Because of the close electrical connection, high voltage,
Brightness is high. On the other hand, the other side of the ground, which is electrically connected to the other side, has a low voltage and low brightness because the electrical connection to the inverter 2 is far. That is, in the conventional backlight, as shown in FIG. 14 (a), the lead wires of the fluorescent tubes 36 are drawn out in the same direction, and two sets of the two fluorescent tubes 36 are electrically connected to each other. Are arranged on the same side (right side in the figure). Therefore, as is clear from the line 1 indicating the light emission of the fluorescent tube 36, the high-luminance side and the low-luminance side of the four fluorescent tubes 36 arranged on the upper and lower sides of the figure overlap each other, and the right side of the light guide plate 37 Is bright,
The left side becomes dark, and a difference in brightness occurs between the right side and the left side. This difference in brightness is particularly noticeable when the backlight is turned on at a low temperature, and also when the liquid crystal display device is driven shortly.

An object of the present invention is to provide a liquid crystal display device having a backlight capable of reducing a difference in luminance of the backlight.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention has the features described in the claims.
Configuration. That is, the liquid crystal display device according to claim 1.
Is a first fluorescent tube connected to the first lighting drive circuit
A second fluorescent tube connected to the second lighting drive circuit;
A liquid crystal display device having a backlight having
The second fluorescent light from the high-luminance side end of the first fluorescent tube
The first fluorescent light is longer than the distance to the high-luminance side end of the tube.
Low brightness of the second fluorescent tube from the high brightness side end of the tube
The distance to the side end is shorter. Ma
The liquid crystal display device according to claim 2 is a liquid crystal display device according to claim 1.
In the display device, the backlight is a direct-type backlight.
It is characterized by being a lite. Claim 3
The liquid crystal display device according to claim 1,
The backlight has a light guide plate, and the first fluorescent light
The tube is arranged on a first side of the light guide plate, and
The second fluorescent tube is a first fluorescent tube facing the first side of the light guide plate.
It is characterized by being arranged on the side of the second side. In addition,
The liquid crystal display device according to claim 4, wherein the first lighting drive circuit
Connected to the first fluorescent tube to be connected and the second lighting drive circuit
Direct type backlight having a second fluorescent tube connected
A liquid crystal display device having the first lighting drive.
The high-voltage end of the first fluorescent tube connected to the circuit
The second fluorescent lamp connected to the second lighting drive circuit.
The first fluorescent lamp is longer than the distance to the high-voltage end of the light tube.
The low voltage of the second fluorescent tube is connected to the high voltage side end of the light tube.
It is characterized in that the distance to the end on the compression side is shorter. Ma
The liquid crystal display device according to claim 5, wherein the first driving for lighting is performed.
A first fluorescent tube connected to the circuit, and a second lighting drive
Liquid crystal having a second fluorescent tube connected to a path and a light guide plate
A display device, wherein the first fluorescent tube is a light guide plate of the first type.
And the second fluorescent tube is disposed on the side of the light guide plate.
It is arranged on a second side opposite to the first side.
The first lighting circuit connected to the first lighting drive circuit.
The second lighting drive circuit from the high voltage side end of the fluorescent tube;
To the high voltage side end of the second fluorescent tube connected to
The distance between the end of the first fluorescent tube on the high voltage side and the distance
The distance from the low voltage side end of the second fluorescent tube to
It is characterized by being short. A liquid crystal display according to claim 6.
The device is provided with a light guide plate and a first long side of the light guide plate.
A first fluorescent tube, and the first long side of the light guide plate.
And a second fluorescent tube provided on a second long side facing the second fluorescent lamp.
Liquid crystal display device, wherein the first fluorescent tube has a high-luminance side.
From the end of the second fluorescent tube to the end on the high brightness side of the second fluorescent tube.
From the end of the first fluorescent tube on the high luminance side,
The distance to the lower luminance side end of the second fluorescent tube is shorter.
It is characterized by that. A liquid crystal display device according to claim 7.
7. The liquid crystal display device according to claim 6, wherein
And the second fluorescent tube are located on the short side of the light guide plate.
Connected to the lighting drive circuit provided in the
Sign. The liquid crystal display device according to claim 8 is a liquid crystal display device.
Of two opposing side surfaces of the light guide plate arranged below the display element
In the vicinity, each along the side surface and substantially parallel to the side surface,
A bag in which three fluorescent tubes are arranged in the light guide plate in the thickness direction.
In a liquid crystal display device having a light, the pair of two
Each one end of the fluorescent tube to a different or common
Connected directly to the inverter, each of the fluorescent tubes in each set
The other ends are electrically connected to each other, and
Characterized in that one end side is arranged alternately with respect to the light guide plate.
And In the liquid crystal display device according to the ninth aspect, a high voltage
A first fluorescent tube having a first end and a low-voltage end;
A first fluorescent tube connected to the low-voltage-side end of the first fluorescent tube
2 fluorescent tubes, a high-voltage end and a low-voltage end.
A third fluorescent tube, and the low voltage side of the third fluorescent tube
And a fourth fluorescent tube connected to an end of the backlight.
A liquid crystal display device having a
The high voltage of the third fluorescent tube from the end on the high voltage side
The height of the first fluorescent tube is greater than the distance to the side end.
From the end on the voltage side to the end on the low voltage side of the third fluorescent tube
The distance to the part is shorter. Also, billing
A liquid crystal display according to claim 10 is a liquid crystal display according to claim 9.
In the apparatus, the backlight is a direct-type backlight.
It is a light. Claim 11
A liquid crystal display device according to claim 9,
The backlight has a light guide plate, and the first fluorescent light
The tube and the second fluorescent tube are arranged on a first side of the light guide plate.
And the third fluorescent tube and the fourth fluorescent tube
Is on a second side of the light guide plate opposite to the first side.
It is characterized by being arranged. Claim 12
The liquid crystal display device has a high-voltage end and a low-voltage end.
Fluorescent tube, second fluorescent tube and third fluorescent tube having
And a fourth fluorescent tube, wherein the liquid crystal display device comprises:
The third fluorescent light from the high voltage side end of the first fluorescent tube
The distance to the high voltage end of the tube is less than the first
From the end of the fluorescent tube on the high voltage side to the front of the third fluorescent tube
The distance to the end on the low voltage side is shorter, and the second
The end of the high voltage side of the light tube from the end of the fourth fluorescent tube
The distance of the second fluorescent tube is longer than the distance to the end on the high voltage side.
The low voltage of the fourth fluorescent tube from the end on the high voltage side
The distance to the side end is shorter than the distance to the end of the first fluorescent tube.
The high voltage side of the second fluorescent tube from the high voltage side end;
Than the distance to the end of the first fluorescent tube.
From the pressure side end to the low voltage side end of the second fluorescent tube
Is longer than the high voltage of the third fluorescent tube.
Side end to the high voltage side end of the fourth fluorescent tube.
The higher voltage end of the third fluorescent tube than the distance at
From the section to the end of the fourth fluorescent tube on the low voltage side.
It is characterized in that the separation is longer. Claim 13
Is a liquid crystal display device according to claim 12.
And the end on the high voltage side of the first fluorescent tube and the second fluorescent lamp.
The same lighting drive as the high voltage end of the two fluorescent tubes
A high voltage of the third fluorescent tube connected to a circuit;
And the end of the fourth fluorescent tube on the high voltage side
It is connected to a common lighting drive circuit.
You. The liquid crystal display device according to the fourteenth aspect is the first aspect.
14. The liquid crystal display device according to item 2 or 13, wherein
The light is a direct backlight.
I do. Further, the liquid crystal display device according to claim 15 has
14. The liquid crystal display device according to item 12 or 13, wherein
The light has a light guide plate, the first fluorescent tube and the second fluorescent tube.
The fluorescent tube is disposed on the first side of the light guide plate.
The third fluorescent tube and the fourth fluorescent tube are connected to the light guide.
Being disposed on a second side of the plate opposite to the first side.
It is characterized by being.

[0011]

[0012]

[0013]

[0014]

According to the present invention, the high-luminance side (or low-luminance side) of a plurality of fluorescent tubes which are close to the lighting driving means are alternately arranged, so that the high-luminance side and the low-luminance side are alternately arranged. Are superimposed, the luminance difference of the backlight is reduced, and the luminance can be made uniform.

[0015]

FIG. 1A is a top view showing a backlight according to an embodiment of the present invention, and FIG. 1B is a side view seen from the direction of arrow A in FIG.

Reference numeral 37 denotes a light guide plate made of an acrylic plate disposed below a liquid crystal display element (not shown; see FIG. 3); 36, a cold cathode fluorescent tube as a light source; 2, driving means for lighting the fluorescent tube 36; For example, the inverter 1 is a line schematically showing light emission from the fluorescent tube 36, and the longer the brightness, the higher the brightness, and the shorter the brightness, the lower the brightness. In this figure, the fluorescent tube 36 is covered over substantially the entire length, and the light of the fluorescent tube 36 is transmitted to the light guide plate 3.
7, a lamp reflection cover, a diffusion sheet disposed on the upper surface of the light guide plate 37 for diffusing the light from the light guide plate 37, and a diffusion sheet disposed on the lower surface of the light guide plate 37 to transmit the light from the light guide plate 37 toward the liquid crystal display element. Reflecting sheet for reflecting light and light guide plate 37
The dot pattern for light diffusion and the like provided on the bottom surface of are not shown.

This backlight has a long-side four-lamp type edge in which two fluorescent tubes are provided along the two long sides facing each other of the light guide plate 37 in order to increase the brightness. It is an example of a light type backlight. In addition, two 1
As shown in FIG. 1B, the set of fluorescent tubes 36 is
7 are arranged in the thickness direction of FIG.
Here, the features of the present invention are not shown so as to make them easy to understand. One end of each pair of fluorescent tubes 36 is directly electrically connected to another inverter 2, and the other end of each pair of fluorescent tubes 36 is electrically connected to each other. This other end is referred to as a ground side.

The pair of fluorescent tubes 36 connected in parallel in the backlight of this embodiment shown in FIG.
One end directly connected to the inverter 2 is close to the electrical connection to the inverter 2 and therefore has a high voltage and a high luminance. On the other hand, the other side of the ground, which is electrically connected to the other side, has a low voltage and low brightness because the electrical connection to the inverter 2 is far. For this reason, in the backlight of this embodiment, as shown in FIG. 1A, the lead wires of the fluorescent tubes 36 are drawn out in different directions in the left and right directions in the figure, and the two sets of fluorescent tubes 36 are electrically connected. The two inverters 2 are arranged on the left and right sides different from each other (right and left reversed). Therefore, the high brightness side of the fluorescent tube 36 arranged above is arranged on the right side, and the high brightness side of the fluorescent tube 36 arranged below is arranged on the left side. (That is, the fluorescent tube 3 disposed above
6 is disposed on the left side, and the low luminance side of the fluorescent tube 36 disposed below is disposed on the right side. )For this reason,
As is clear from the line 1 indicating the light emission of the fluorescent tube 36, the high-luminance side and the low-luminance side of the fluorescent tube 36 overlap each other, the luminance difference of the light guide plate 37 is reduced, and the luminance can be made uniform.

In the above embodiment, four fluorescent tubes 36 are used.
The case where two inverters 2 for lighting are provided is shown.
As shown in FIG. 2, by providing one common inverter 2 and connecting the lead wires of the fluorescent tubes 36 as shown, the same operation and effect as the embodiment of FIG. 1 can be obtained.

FIG. 3 is an exploded perspective view of an active matrix type color liquid crystal display module using the thin film transistor having the backlight shown in FIG. 1 as a switching element.

FIG. 4 shows a liquid crystal display element 62, a driving circuit for driving the liquid crystal display element 62, and a liquid crystal display module 63 of a simple matrix type to which the present invention can be applied in which light sources are compactly integrated. It is an exploded perspective view. The IC 34 for driving the liquid crystal display element 62 is mounted on a frame-shaped printed circuit board 35 provided with 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 a window of a frame 42 made of plastic mold, a metal frame 41 is superimposed on the window, and its claws 43 are formed in the frame 42. The frame 41 is fixed to the frame-shaped body 42 by folding it into the cut 44.

The cold cathode fluorescent tubes 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 tubes 36, metal A reflection plate 38 formed by applying a white paint to the plate and a milky white diffusion plate 39 for diffusing light from the light guide plate 37 are fitted into the window of the frame 42 from the back side in the order shown in FIG. An inverter power supply circuit (not shown) for lighting the cold cathode fluorescent tube 36 is provided with a concave portion (not shown; a concave portion 45 of the reflection plate 38) provided on the right back of the frame 42.
It is in the position facing. ). Diffusion plate 39,
The light guide plate 37, the cold cathode fluorescent tube 36, and the reflection plate 38 are fixed by bending a tongue piece 46 provided on the reflection plate 38 into a small opening 47 provided on the frame 42.

Also in this module 63, although not shown, the two inverters for lighting the fluorescent tubes 36 of the long-side two-light type edge light type backlight are reversed left and right with respect to each other. By arranging the high-luminance side and the low-luminance side to overlap, the luminance difference of the light guide plate 37 is reduced, and the luminance can be made uniform.

FIG. 5 is a block diagram of a laptop computer using the liquid crystal display module 63 as a display unit, and FIG. 6 is a diagram showing a state in which the liquid crystal display module 63 is mounted on a laptop computer 64. In this laptop personal computer 64, the microprocessor 49
The liquid crystal display module 63 is driven by the liquid crystal driving semiconductor IC 34 via the control LSI 48 based on the result calculated in the above.

FIG. 7 shows an arrangement direction (eg, rubbing direction) of liquid crystal molecules, a twist direction of liquid crystal molecules, a polarizing plate when the liquid crystal display element 62 of the liquid crystal display device to which the present invention can be applied is viewed from above. Polarization axis (or absorption axis)
FIG. 8 is a perspective view of a main part of the liquid crystal display element 62.

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

In FIG. 8, in order to align liquid crystal molecules in a twisted helical structure between the two upper and lower electrode substrates 11 and 12 sandwiching the liquid crystal layer 50, a transparent upper layer made of, for example, glass is used. A method of rubbing the surfaces of the alignment films 21 and 22 made of, for example, an organic polymer resin made of polyimide on the lower electrode substrates 11 and 12 in contact with the liquid crystal in one direction with a cloth, for example, is called a rubbing method. ing. The rubbing direction at this time, that is, the rubbing direction, the rubbing direction 6 for the upper electrode substrate 11, and the rubbing direction 7 for the lower electrode substrate 12 are the alignment directions of the liquid crystal molecules. The two upper and lower electrode substrates 1 thus oriented are treated.
The _first and second electrode substrates 11 and 12 are notched for injecting a liquid crystal, with the gaps d1 therebetween so that the rubbing directions 6 and 7 intersect each other at approximately 180 degrees to 360 degrees. When a nematic liquid crystal having a positive dielectric anisotropy and a predetermined amount of an optical rotatory substance is sealed in the gap between them, a liquid crystal molecule is adhered. Has a helical molecular arrangement with a twist angle θ in the figure between the electrode substrates. 31 and 32 are, for example, indium oxide or ITO, respectively.
(Indium Tin Oxide) transparent upper and lower electrodes. A member that provides a birefringence effect above the upper electrode substrate 11 of the liquid crystal cell 60 configured as described above (hereinafter, referred to as a birefringent member. Fujimura et al., "Phase Difference Film for STN-LCD", Magazine Electronic Materials, 1991, Feb. Monthly Pages 37-41)
The upper and lower polarizing plates 15 and 16 are provided with the member 40 and the liquid crystal cell 60 interposed therebetween.

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 °, and is preferably 200 ° to 300 °. From the practical viewpoint of avoiding the state in which 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 acts to make the response of the liquid crystal molecules to the voltage more sensitive and 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, and more preferably in the range of 0.6 μm to 0.9 μm.

The birefringent member 40 functions to modulate the polarization state of the light transmitted through the liquid crystal cell 60, and converts the liquid crystal cell 60, which could only display in a colored state, into a monochrome 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 a range of 0.7 μm.

Further, since the liquid crystal display element 62 utilizes elliptically polarized light due to birefringence, the axes of the polarizing plates 15 and 16 and the optical axis thereof when a 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 twelve liquid crystal alignment directions 6 and 7 is extremely important.

The operation and effect of the above relationship will be described with reference to FIG. FIG. 7 shows the axis of the polarizing plate and the optical axis of the uniaxial transparent birefringent member when the liquid crystal display device having the configuration of FIG. 8 is viewed from above.
FIG. 3 shows a relationship between a liquid crystal molecular axis arrangement direction of an electrode substrate of a liquid crystal cell.

In FIG. 8, 5 is the optical axis of the uniaxial transparent birefringent member 40, 6 is the liquid crystal molecular axis arrangement direction 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 polarizer 15, 9 is the absorption axis or polarization axis of the lower polarizer 16, and the angle α is uniaxial birefringence with the liquid crystal alignment direction 6 of the upper electrode substrate 11. The angle between the optical axis 5 of the member 40 and the angle β is the angle between the absorption axis or the polarization axis 8 of the upper polarizer 15 and the optical axis 5 of the uniaxial transparent birefringent member 40, and the angle γ is the lower polarizer 16 Between the absorption axis or polarization axis 9 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 is defined. In FIG. 12, a description will be given by taking an example of an intersection angle between the optical axis 5 of the birefringent member 40 and the liquid crystal alignment direction 6 of the upper electrode substrate. The intersection angle between the optical axis 5 and the liquid crystal alignment direction 6 as shown in FIG. 12, but can be represented by phi ₁ and phi _2, in the present specification employs the corners of the smaller of the phi _1, phi _2. That is, in FIG. 12A, 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 the optical axis 5 and the liquid crystal alignment direction 6 φ _1> φ ₂ so phi ₂ in FIG. 12 (b) I do. Of course φ ₁
= In the case of φ ₂ may be adopted either.

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

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

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

In FIG. 8, 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 replaced.
And may be arranged between them. This case corresponds to a case where the entire configuration in FIG. 8 is inverted.

FIG. 9 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 degrees was used. Here, the liquid crystal layer thickness d (μm) and the helical pitch p (μ
The ratio d / p of m) was 0.67. Alignment films 21, 22
Used was formed of a polyimide resin film and rubbed. The tilt angle (pretilt angle) at which the alignment film subjected to the rubbing treatment causes the liquid crystal molecules in contact with the alignment film to be tilt-aligned with respect to the substrate surface is 4 degrees. 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 having a structure in which the liquid crystal molecules are twisted 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 reduced. When the voltage is lower than the threshold value, light opacity, that is, black, and when the voltage exceeds a certain threshold value, light transmission, that is, white black and white display can be realized. Also, the axis of the lower polarizing plate 16 is set at 50 degrees from the above position.
When rotated by 90 degrees from the degree, white when the voltage applied to the liquid crystal layer 50 was equal to or less than the threshold value, and black when the voltage was equal to or more than the threshold value, black and black was displayed in reverse.

FIG. 10 shows a change in contrast during time-division driving at 1/200 duty when the angle α is changed in the configuration of FIG. When the angle α is around 90 degrees, the contrast is extremely high, but the contrast decreases as the angle α deviates from this angle. In addition, when the angle α is small, both the lighted part and the non-lighted part become bluish, and when the angle α is large, the non-lighted part becomes purple and the lighted part becomes yellow. The results are almost the same for the angles β and γ. However, in the case of the angle γ, when the image is rotated from 50 degrees to nearly 90 degrees, a black-and-white display is reversed.

FIG. 11 is a diagram showing another specific example such as the twist angle θ. 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
The difference is that Δn ₁ · d ₁ is about 0.65 μm to 0.75 μm. Δn ₂ · d ₂ of the parallel alignment liquid crystal layer used as the uniaxial transparent birefringent member 40 is about 0.58 μm, which is the same as in the above specific example. The thickness d ₁ (μm) of the liquid crystal layer and the helical pitch p of the nematic liquid crystal material to which the optical rotatory substance is added
(μm) 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 same monochrome display as in the first specific example was realized. As in the first specific example, it is possible to perform the reverse black and white display by rotating the position of the axis of the lower polarizing plate by 50 to 90 degrees from the above value. The tendency of the angles α, β, and γ to shift is almost the same as in the first specific example.

In each of the above embodiments, the uniaxial transparent birefringent member 40 is a parallel alignment liquid crystal cell having no twist of liquid crystal molecules, 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 due to the angle. This twisted liquid crystal layer is formed by sandwiching the liquid crystal between substrates in which the alignment processing directions of a pair of alignment-processed transparent substrates cross a predetermined twist angle, similarly to the liquid crystal layer 50 described above. You. In this case, the direction of the bisecting angle between the two alignment processing directions sandwiching the twisted structure of the liquid crystal molecules may be treated as the optical axis of the birefringent member. Further, a transparent polymer film may be used as the birefringent member 40 (in this case, a uniaxially stretched one is preferable). In this case, as the polymer film, PET (polyethylene terephthalate), an acrylic resin film, and polycarbonate are effective.

In the above embodiment, the single birefringent member is used. In FIG. 8, in addition to the birefringent member 40, another birefringent member is provided between the lower electrode substrate 12 and the lower polarizing plate 16. Refraction members can also be inserted. In this case, Δn ₂ · d ₂ of these birefringent members may be readjusted.

However, as shown in FIG.
Red, green and blue color filters 33R, 33G, 3
3B, by providing the light-shielding film 33D between the filters, multi-color display becomes possible. FIG. 10 shows the relationship among the arrangement direction of the liquid crystal molecules, the twist direction of the liquid crystal molecules, the direction of the axis of the polarizing plate, and the optical axis of the birefringent member in the specific example.

In FIG. 13, each filter 33
On the R, 33G, 33B and the light shielding film 33D, a smooth layer 23 made of an insulator is formed to reduce the influence of these irregularities, and then an upper electrode 31 and an alignment film 21 are formed.

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

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the gist of the present invention. . For example, it goes without saying that the present invention can be applied to a simple matrix type liquid crystal display device and an active matrix type liquid crystal display device using a thin film transistor or the like as a switching element. In the above-described embodiment shown in FIGS. 1 and 2, an example of a long-side four-light type edge light type backlight in which two fluorescent tubes 36 are provided on each of two side surfaces of the light guide plate 37, that is, four in total. However, the present invention relates to a long-side two-light type edge light type backlight in which one fluorescent tube is provided on each of two sides of a light guide plate, and two fluorescent tubes are provided on one side of the light guide plate. In the backlight arranged in the thickness direction of the light guide plate, the effect of the present invention is more remarkable when the fluorescent tube is arranged on the long side of the light guide plate in the above embodiment, but the light guide plate 37
The present invention can be similarly applied to a backlight in which a fluorescent tube 36 is arranged on the short side of the liquid crystal display device, and a direct-type backlight in which a plurality of fluorescent tubes are arranged below a liquid crystal display element via a diffusion plate. The effect of equalizing the luminance difference can be obtained.

[0049]

As described above, according to the present invention,
By alternately arranging the high luminance side or the low luminance side of a plurality of fluorescent tubes, the high luminance side and the low luminance side overlap,
The difference in luminance of the backlight can be reduced, the luminance can be made uniform, and the display quality can be improved.

[Brief description of the drawings]

FIG. 1A is a top view showing a backlight according to an embodiment of the present invention, and FIG. 1B is a side view seen from the direction of arrow A in FIG.

FIG. 2A is a top view showing a backlight according to another embodiment of the present invention, and FIG. 2B is a side view seen from the direction of arrow A in FIG.

FIG. 3 is an exploded perspective view of the active matrix type color liquid crystal display module having the backlight shown in FIG. 1;

FIG. 4 is an exploded perspective view of an example of a simple matrix type liquid crystal display module to which the present invention can be applied.

FIG. 5 is a block diagram of an example of a laptop personal computer.

FIG. 6 is a perspective view of an example of a laptop personal computer.

FIG. 7 shows an example of the relationship among the arrangement direction of liquid crystal molecules, the twist direction of liquid crystal molecules, the direction of the axis of a polarizing plate, and the optical axis of a birefringent member in a simple matrix type liquid crystal display device to which the present invention can be applied. FIG.

FIG. 8 is an exploded perspective view of a main part of an example of a liquid crystal display element.

FIG. 9 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 another example of a liquid crystal display device.

FIG. 10 is a graph showing contrast and transmitted light color-intersection angle α characteristics of the example of FIG. 7 of the liquid crystal display element.

FIG. 11 is an explanatory view showing the relationship among the alignment direction of liquid crystal molecules, the twist direction of liquid crystal molecules, the direction of the axis of a polarizing plate, and the optical axis of a birefringent member in a liquid crystal display element of yet another example.

FIG. 12 is a diagram for explaining how to measure intersection angles α, β, and γ.

FIG. 13 is a partially cutaway perspective view of an example of an upper electrode substrate portion of a liquid crystal display element.

FIG. 14A is a top view showing a conventional backlight, and FIG. 14B is a side view seen from the direction of arrow A in FIG.

[Explanation of symbols]

Reference numeral 1 denotes a line indicating light emission of the fluorescent tube, 2 denotes an inverter, 36 denotes a fluorescent tube, and 37 denotes a light guide plate.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masumi Nagaseki 3300 Hayano, Mobara-shi, Chiba Examiner, Electronic Device Division, Hitachi, Ltd. Keiji Iguchi (56) References JP-A-5-72530 (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/13357 F21V 8/00

Claims (15)

(57) [Claims] 1. A liquid crystal display device having a backlight having a first fluorescent tube connected to a first lighting drive circuit and a second fluorescent tube connected to a second lighting drive circuit. An end portion of the first fluorescent tube on the high brightness side, which is longer than a distance from a high brightness side end portion of the first fluorescent tube to a high brightness side end portion of the second fluorescent tube. A liquid crystal display device, wherein a distance from the second fluorescent tube to an end on the low luminance side of the second fluorescent tube is shorter. 2. The liquid crystal display device according to claim 1, wherein the backlight is a direct type backlight. 3. The backlight has a light guide plate, the first fluorescent tube is disposed on a first side of the light guide plate, and the second fluorescent tube is disposed on the first side of the light guide plate. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is arranged on a second side opposite to the first side. 4. A direct-type backlight having a first fluorescent tube connected to a first lighting driving circuit and a second fluorescent tube connected to a second lighting driving circuit. A liquid crystal display device, comprising: a second fluorescent lamp connected to the second lighting drive circuit from a high-voltage side end of the first fluorescent tube connected to the first lighting drive circuit. The distance from the high voltage side end of the first fluorescent tube to the low voltage side end of the second fluorescent tube is shorter than the distance to the high voltage side end of the tube. A liquid crystal display device characterized by the above-mentioned. 5. A liquid crystal display device comprising a first fluorescent tube connected to a first lighting driving circuit, a second fluorescent tube connected to a second lighting driving circuit, and a light guide plate. Wherein the first fluorescent tube is disposed on a first side of the light guide plate, and the second fluorescent tube is disposed on a second side of the light guide plate opposite to the first side. And a second fluorescent tube connected to the second lighting drive circuit from a high-voltage end of the first fluorescent tube connected to the first lighting drive circuit. The distance from the high voltage side end of the first fluorescent tube to the low voltage side end of the second fluorescent tube is shorter than the distance to the high voltage side end. Liquid crystal display device. 6. A light guide plate, a first fluorescent tube provided on a first long side of the light guide plate, and a second long side of the light guide plate facing the first long side. A liquid crystal display device having a second fluorescent tube provided, wherein a distance from a high-luminance side end of the first fluorescent tube to a high-luminance side end of the second fluorescent tube is greater than a distance from the high-luminance side end of the first fluorescent tube. A liquid crystal display device, wherein a distance from the high-luminance side end of the first fluorescent tube to the low-luminance side end of the second fluorescent tube is shorter. 7. The light-emitting drive circuit according to claim 6, wherein the first fluorescent tube and the second fluorescent tube are connected to a driving circuit provided on a short side of the light guide plate. The liquid crystal display device as described in the above. 8. A light guide plate provided with two fluorescent tubes near and in parallel with the side surfaces of the light guide plate disposed below the liquid crystal display element, respectively, in the vicinity of the two opposite side surfaces of the light guide plate. In a liquid crystal display device having a backlight arrayed in two directions, one end of each pair of the fluorescent tubes is electrically connected directly to another or common inverter, respectively, and each set of the fluorescent tubes is connected. A liquid crystal display device, wherein the other ends are electrically connected to each other, and the one end sides of each set are alternately arranged with respect to the light guide plate. 9. A first fluorescent tube having a high voltage side end and a low voltage side end, and a second fluorescent lamp connected to the low voltage side end of the first fluorescent tube. A third fluorescent tube having a tube, a high voltage side end and a low voltage side end, and a fourth fluorescent tube connected to the low voltage side end of the third fluorescent tube; A liquid crystal display device having a backlight having: a distance from the high voltage side end of the first fluorescent tube to the high voltage side end of the third fluorescent tube, A liquid crystal display device, wherein a distance from the high voltage side end of the first fluorescent tube to the low voltage side end of the third fluorescent tube is shorter. 10. The liquid crystal display device according to claim 9, wherein said backlight is a direct type backlight. 11. The backlight has a light guide plate, the first fluorescent tube and the second fluorescent tube are arranged on a first side of the light guide plate, and the third fluorescent tube 10. The liquid crystal display device according to claim 9, wherein the tube and the fourth fluorescent tube are arranged on a second side of the light guide plate opposite to the first side. 12. A first fluorescent lamp, a second fluorescent lamp, a third fluorescent lamp and a fourth fluorescent lamp having an end on the high voltage side and an end on the low voltage side.
A fluorescent tube, wherein the distance from the end of the first fluorescent tube on the high voltage side to the end of the third fluorescent tube on the high voltage side is greater than the distance from the end of the third fluorescent tube on the high voltage side. The distance from the high voltage side end of the first fluorescent tube to the low voltage side end of the third fluorescent tube is shorter, and the distance from the high voltage side end of the second fluorescent tube is The distance from the high voltage side end of the second fluorescent tube to the low voltage side end of the fourth fluorescent tube is longer than the distance of the fourth fluorescent tube to the high voltage side end. Is shorter than the distance from the high voltage side end of the first fluorescent tube to the high voltage side end of the second fluorescent tube. The distance from the end on the high voltage side to the end on the low voltage side of the second fluorescent tube is longer, and the distance from the end on the high voltage side of the third fluorescent tube to the fourth end Of the distance from the high voltage side end of the third fluorescent tube to the low voltage side end of the fourth fluorescent tube, rather than the distance to the high voltage side end of the fluorescent tube. A liquid crystal display device characterized by being longer. 13. The high voltage side end of the first fluorescent tube and the high voltage side end of the second fluorescent tube are connected to a common lighting drive circuit. 13. The high voltage side end of the third fluorescent tube and the high voltage side end of the fourth fluorescent tube are connected to a common lighting drive circuit. Liquid crystal display. 14. The liquid crystal display device according to claim 12, wherein the backlight is a direct type backlight. 15. The backlight according to claim 1, wherein the backlight has a light guide plate, the first fluorescent tube and the second fluorescent tube are arranged on a first side of the light guide plate, and 14. The liquid crystal display device according to claim 12, wherein the tube and the fourth fluorescent tube are arranged on a second side of the light guide plate opposite to the first side.