JPH0534676A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the light which leaks to the outside from the part of a clearance between the inside end part of a display window and the outside end part of the upper polarizing plate without adding a special manufacturing process by specifying the lower polarizing plate. CONSTITUTION:A backlight 67, the lower polarizing plate 16, a liquid crystal cell 60, and the upper polarizing plate 15 are superposed and placed successively, and by a frame 41 provided with a display window 65 on the upper polarizing plate l5 side, each member of them is held. Also, dimensions of the lower polarizing plate 16 are set to the same as that of the dimensions lower electrode substrate 12, and light for going to the display window 65 from the backlight 67 through a clearance (g) between the inside end part of the display window 65 and the outside end part of the upper polarizing plate 15 is shielded by the lower light shielding plate 16. In such a way, light which leaks from the clearance (g) can be reduced without adding a special manufacturing process such as sticking of an adhesive tape, etc. Light transmittivity of the lower polarizing plate 16 is about 40-45%, and by this lower polarizing plate 16, light from the backlight 67 is eliminated by about 60%, and the leakage quantity of light can be reduced to half or below of the conventional one.

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, and more particularly to a field effect liquid crystal display device having excellent time-division driving characteristics and capable of black and white and multicolor display.

[0002]

2. Description of the Related Art A conventional twisted nematic type liquid crystal display device has a 90 ° twisted helix structure formed by a nematic liquid crystal having a positive dielectric anisotropy between two electrode substrates. A pair of polarizing plates is arranged outside the electrode substrate so that the polarization axis (or absorption axis) thereof is orthogonal or parallel to the axis of the liquid crystal molecules adjacent to the electrode substrate (Japanese Patent Publication No. 51- 13666
Publication).

In such a liquid crystal display device having a twist angle of 90 °, there are problems in the steepness γ of the change in the transmittance of the liquid crystal layer with respect to the voltage applied to the liquid crystal layer and in the viewing angle characteristics. The practical limit was 64 for the number of electrodes). However, in order to cope with recent demands for improving image quality and increasing the amount of display information for liquid crystal display elements, the twist angle α of liquid crystal molecules sandwiched between a pair of polarizing plates is set to be larger than 180 °, and the voltage applied to this liquid crystal layer is increased. Applied physics by TJ Schaefer and J. Nailing to improve the time-division drive characteristics and increase the number of time-divisions by adopting a configuration that detects changes in the birefringence effect of the liquid crystal layer due to
Letter 45, No. 10, 1021, 1984 "Ann Hailey
Multiplexer "(Applied Physics Letter, T.J.
Scheffer, J. Nehring: “A new, highly multiplexabl
e liquid crystal display ”), and a super twisted birefringence effect (SBE) liquid crystal display device has been proposed.

In the conventional liquid crystal display module 63, for example, as shown in FIG. 12, upper and lower two upper electrode substrates 11 and lower electrode substrate 1 are arranged so that the surfaces provided with electrodes face each other.
Liquid crystal cell 6 made by stacking 2 and sealing liquid crystal between them
0, a printed circuit board 35 on which an LSI is mounted to drive the liquid crystal, a conductive rubber 66 and a thermocompression conductive rubber (not shown here) for electrically connecting the liquid crystal cell 60 and the printed circuit board 35, and Frame 41 with window 65
And a backlight 67 including a cold cathode fluorescent lamp and a light guide body. The printed circuit board 35, the backlight 67, and the liquid crystal cell 60 are sequentially stacked and arranged.
The frame 41 holds each of these members. The upper polarizing plate 15 and the lower polarizing plate 1 are provided on the upper and lower surfaces of the liquid crystal cell 60.
6 is attached.

[0005]

The frame 41 and the upper polarizing plate 15 are not shown in the drawing, but the frame 41 and the upper polarizing plate 1 are not shown.
In some cases, the thickness of the overlapping portion of 0.3 to 0.5 mm becomes a problem as the liquid crystal display module becomes thinner in recent years.
2, between the inner end of the display window 65 of the frame 41 and the outer end of the upper polarizing plate 15, for example, 0.5 to 1.0 mm.
The gap g is provided so that they do not overlap.

However, in such a structure, since the light of the backlight 67 leaks from the gap g to the outside, there is a problem that the visibility is deteriorated. In order to prevent this, for example, a method of attaching an adhesive tape to the gap to shield the light is conceivable, but the productivity is poor and the manufacturing cost increases.

An object of the present invention is to provide a liquid crystal display device capable of reducing the leaked light without adding a special manufacturing process.

[0008]

In order to achieve the above object, a liquid crystal display device of the present invention comprises a backlight, a lower polarizing plate, a liquid crystal cell, and an upper polarizing plate, which are sequentially stacked. In a liquid crystal display device in which each of these members is held by a frame provided with a display window on the upper polarizing plate side, from the backlight in the gap between the inner end portion of the display window and the outer end portion of the upper polarizing plate. Light directed to the display window is shielded by the lower polarizing plate.

The present inventors have paid attention to the lower polarizing plate attached to the liquid crystal cell. The size of the lower polarizing plate is usually the same as that of the upper polarizing plate, but the size of this lower polarizing plate is increased,
The light of the backlight was blocked.

[0010]

In the liquid crystal display device of the present invention, since the light directed from the backlight to the display window in the gap between the inner end of the display window and the outer end of the upper polarizing plate is shielded by the lower polarizing plate, The light leaked from the gap between the inner end of the display window and the outer end of the upper polarizing plate can be reduced without adding a special manufacturing process. The light transmittance of the polarizing plate is 40 to 45%, and the amount of light leakage can be reduced to less than half that of conventional ones. It should be noted that increasing the size of the lower polarizing plate and attaching it to the liquid crystal cell does not cause any inconvenience in the manufacturing process.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the liquid crystal display module of the present invention.

11 is an upper electrode substrate, 12 is a lower electrode substrate, 1
5 is an upper polarizing plate, 16 is a lower polarizing plate, 35 is a printed circuit board,
41 is a frame, 60 is a liquid crystal cell, 63 is a liquid crystal display module, 65 is a display window, 66 is a conductive rubber, 67 is a backlight, g is the inner end of the display window 65 of the frame 41 and the outer end of the upper polarizing plate 15. It is a gap with the club. ..

In this embodiment, the size of the lower polarizing plate 16 is larger than that of the conventional one, and is the same as that of the lower electrode substrate 12 in this case, and the gap between the inner end portion of the display window 65 and the outer end portion of the upper polarizing plate 15 is set. Light from the backlight 67 toward the display window 65 in g is shielded by the lower polarizing plate 16. As a result, it is possible to reduce the light leaked from the gap g without adding a special manufacturing process such as attaching an adhesive tape. The light transmittance of the lower polarizing plate 16 is about 40 to 45%, and the light from the backlight 67 is about 60 by this lower polarizing plate 16.
%, The amount of light leakage can be reduced to less than half that of the conventional one. It should be noted that increasing the size of the lower polarizing plate 16 and attaching it to the lower electrode plate 12 of the liquid crystal cell 60 does not cause any inconvenience in the manufacturing process.

FIG. 2 shows an arrangement direction (for example, rubbing direction) of liquid crystal molecules on an electrode substrate when the liquid crystal display device 62 according to the present invention is viewed from above, a twisting direction of liquid crystal molecules, and a polarization axis (or absorption) of a polarizing plate. The (axial) direction and the optical axis direction of the member that brings about the birefringence effect are shown, and FIG. 3 is a perspective view of a main part of the liquid crystal display device 62 according to the present invention.

Twisting direction 10 of liquid crystal molecules and twist angle θ
Is 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 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. 3, 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, 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 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, that is, a so-called rubbing method is adopted. 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 subjected to the orientation treatment in this manner
1 and 12 are opposed to each other with a gap d ₁ so that the rubbing directions 6 and 7 intersect each other at approximately 180 ° to 360 °, and two electrode substrates 11 and 12 are notched for injecting liquid crystal. When a nematic liquid crystal having a positive dielectric anisotropy and having a predetermined amount of an optical rotatory substance is enclosed in the gap by sealing with a frame-shaped sealant 52 having a portion 51,
The liquid crystal molecules have 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 that produces 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., "ST
N-LCD retardation film ", magazine electronic material 1991
February issue, pages 37-41) 40, and upper and lower polarizing plates 15 and 16 with the member 40 and the liquid crystal cell 60 sandwiched 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 °, but is preferably 200 ° to 300 °, but lighting in the vicinity of the threshold of the transmittance-applied voltage curve From a 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 degrees 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 the light passing through the liquid crystal cell 60, and converts what could be colored display by the liquid crystal cell 60 alone 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 device 62 according to the present invention utilizes the elliptically polarized light due to the birefringence, the polarizing plate 15,
When the uniaxial transparent birefringent plate is used as the birefringent member 40, the relationship between the 16 axes and the liquid crystal alignment directions 6 and 7 of the electrode substrates 11 and 12 of the liquid crystal cell 60 is extremely important. ..

The operation and effect of the above relationship will be described with reference to FIG. FIG. 2 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. 3 is viewed from above.
3 shows the relationship between the alignment directions of liquid crystal molecular axes of an electrode substrate of a liquid crystal cell.

In FIG. 3, 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 between 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. 7, 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 is shown in FIG.
As shown in FIG. ₂ , it can be represented by φ ₁ and φ ₂ , but in the present specification, the smaller corner of φ ₁ and φ ₂ is adopted. That is, since φ ₁ <φ ₂ in FIG. 7A, φ ₁ is the intersection angle α between the optical axis 5 and the liquid crystal alignment direction 6,
Since φ ₁ > φ ₂ in FIG. 7B, φ ₂ is defined as an intersection angle α between the optical axis 5 and the liquid crystal alignment direction 6. Of course, either one may be adopted when φ ₁ = φ ₂ .

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

The angle α is preferably 50 to 90 degrees, more preferably 70 to 90 degrees, the angle β is preferably 20 to 70 degrees, more preferably 30 to 60 degrees, 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 ° to 360 °, the above angle is satisfied regardless of whether the twist direction 10 is clockwise or counterclockwise. α, β, and γ may be in the above range.

In FIG. 3, the birefringent member 40 is arranged 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 arranged between and. This case corresponds to the case where the entire configuration of FIG. 3 is inverted.

Example 1 The basic structure is the same as that shown in FIGS.
In FIG. 4, 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 ratio d / p of the thickness d (μm) of the liquid crystal layer and the helical pitch p (μm) of the liquid crystal material added with the optical rotatory substance was set to 0.67. The alignment films 21 and 22 were formed of a polyimide resin film and used after being rubbed. The alignment film that has been subjected to this rubbing treatment tilts the liquid crystal molecules in contact with the alignment film with respect to the substrate surface with a tilt angle (p
The retilt angle) is 4 degrees. The uniaxial transparent birefringent member 4
Δn ₂ · d ₂ of 0 is about 0.6 μm. On the other hand, Δn ₁ · d ₁ of the liquid crystal layer 50 having a structure in which the liquid crystal molecules are twisted by 240 degrees 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, light non-transmission, that is, black, 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. 5 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 in the vicinity of the angle α of 90 °, it decreased as the angle deviated. Moreover, when the angle α becomes small, both the lit part and the non-lit part become bluish, and when the angle α becomes large, the non-lit part becomes purple and the lit part becomes 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.

Example 2 The basic structure is the same as that of Example 1. However, the liquid crystal layer 50
The twist angle of the liquid crystal molecule is 260 degrees, and Δn ₁ · d ₁ is about 0.
The difference is that the thickness is 65 μm to 0.75 μm. Δ of the parallel alignment liquid crystal layer used as the uniaxial transparent birefringent member 40
n ₂ · d ₂ is about 0.58 μm as in the first embodiment. The ratio of the thickness d ₁ (μm) of the liquid crystal layer to the helical pitch p (μm) of the nematic liquid crystal material to which the optically active substance is added is d / p =
It was set to 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 monochrome display similar to that of the first embodiment can be realized. It is also similar to the first embodiment in that the reverse black and white display is possible by rotating the position of the axis of the lower polarizing plate from the above value by 50 to 90 degrees. The tendency with respect to the deviation of the angles α, β, and γ is almost the same as that of the first embodiment.

In each of the above embodiments, a parallel alignment liquid crystal cell having no twist of liquid crystal molecules was used as the uniaxial transparent birefringent member 40, but rather 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 a 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 direction 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 embodiment, in addition to the birefringent member 40 in FIG. 3, 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.

Example 3 The basic structure is the same as that of Example 1. However, as shown in FIG. 8, the red, green, and blue color filters 3 are provided on the upper electrode substrate 11.
By providing the light shielding film 33D between the filters 3R, 33G, 33B and the respective filters, multicolor display is possible.

In FIG. 8, each filter 33
A smoothing layer 23 made of an insulating material is formed on the R, 33G, 33B, and the light shielding film 33D to reduce the influence of these irregularities, and then an upper electrode 31 and an alignment film 21 are formed.

Embodiment 4 A liquid crystal display module 62 in which a liquid crystal display device 62 according to Embodiment 3, a drive circuit for driving the liquid crystal display device 62, and a light source are compactly integrated.

FIG. 9 shows an exploded perspective view thereof.
The IC 34 that drives the liquid crystal display device 62 is mounted on a frame-shaped printed circuit board 35 that has a window for fitting the liquid crystal display device 62 in the center. The printed circuit board 35 in which the liquid crystal display device 62 is fitted is fitted in the window portion of the frame-shaped body 42 formed by plastic molding, the metal frame 41 is superposed on this, and the claws 43 are formed on the frame-shaped body 42. The frame 41 is fixed to the frame-like body 42 by bending it into the notch 44.

A cold cathode fluorescent lamp 36 arranged at the upper and lower ends of the liquid crystal display device 62, a light guide 37 made of an acrylic plate for uniformly irradiating the liquid crystal display cell 60 with light from the cold cathode fluorescent lamp 36, A reflecting plate 38 formed by applying white paint to a metal plate, and a milky white diffusing plate 39 for diffusing light from the light guide 37 are fitted into the window portion from the back side of the frame-shaped body 42 in the order of FIG. Be done. An inverter power supply circuit (not shown) for lighting the cold cathode fluorescent lamp 36 is provided with a recess (not shown) provided on the back side of the right side of the frame-shaped body 42. The recess 45 of the reflector 38 is provided.
It is in a position opposite to. ). Diffusion plate 39,
The light guide 37, the cold cathode fluorescent lamp 36, and the reflector 38 are fixed by bending a tongue piece 46 provided on the reflector 38 into a small opening 47 provided on the frame-shaped body 42.

Embodiment 5 The liquid crystal display module 63 according to Embodiment 4 is used in the display section of a laptop personal computer.

FIG. 10 shows the block diagram, and FIG. 11 shows the block diagram mounted on the laptop personal computer 64.
The result calculated by the microprocessor 49 is to drive the liquid crystal display module 63 by the drive IC 34 via the control LSI 48.

[0042]

As described above, according to the liquid crystal display device of the present invention, the light leaked to the outside in the gap between the inner end portion of the display window and the outer end portion of the upper polarizing plate is conventionally special. The number of manufacturing steps can be reduced without adding, and the visibility can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a liquid crystal display module of the present invention.

FIG. 2 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 a polarizing plate axis, and an optical axis of a birefringent member in a first embodiment of a liquid crystal display device according to the present invention. Is.

FIG. 3 is an exploded perspective view of essential parts of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 4 is an explanatory diagram showing a relationship among a twisting direction of liquid crystal molecules, a direction of an axis of a deflecting plate, and an optical axis of a birefringent member in a second embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a graph showing the contrast and transmitted light color-crossing angle α characteristics of the first embodiment of the liquid crystal display device according to the present invention.

FIG. 6 is an explanatory view 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 deflection plate, and an optical axis of a birefringent member in a third embodiment of the liquid crystal display device according to the present invention. Is.

FIG. 7 is a diagram for explaining how to measure intersection angles α, β, and γ.

FIG. 8 is a partially cutaway perspective view of an upper electrode substrate portion of an embodiment of the liquid crystal display device according to the present invention.

FIG. 9 is an exploded perspective view of a liquid crystal display module according to the present invention.

FIG. 10 is a block diagram of an embodiment of a laptop personal computer according to the present invention.

FIG. 11 is a perspective view of an embodiment of a laptop computer according to the present invention.

FIG. 12 is a cross-sectional view of an example of a conventional liquid crystal display module.

[Explanation of symbols]

11 ... Upper electrode substrate, 12 ... Lower electrode substrate, 15 ... Upper polarizing plate, 16 ... Lower polarizing plate, 35 ... Printed circuit board, 41 ... Frame, 60 ... Liquid crystal cell, 63 ... Liquid crystal display module, 6
5 ... Display window, 66 ... Conductive rubber, 67 ... Backlight, g
... A portion (gap) between the inner edge of the display window and the outer edge of the upper polarizing plate.

Claims (1)

Claim: What is claimed is: 1. A backlight, a lower polarizing plate, a liquid crystal cell, and an upper polarizing plate are sequentially stacked and arranged, and a frame provided with a display window on the upper polarizing plate side is used for these components. In a liquid crystal display device holding each member, light directed from the backlight to the display window in the gap between the inner end of the display window and the outer end of the upper polarizing plate is blocked by the lower polarizing plate. A liquid crystal display device characterized by the above.