JPH03226713A - Liquid crystal display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device that performs negative type display and has a light shielding film formed thereon.

[Prior Art] Conventionally, liquid crystal display devices used for displaying automobile instruments or clocks, etc., often employ a negative type display in which bright characters, figures, etc. are displayed on a dark display surface.

In negative type liquid crystal display devices, no voltage is applied to the liquid crystal layer in the background area other than the display area, so the liquid crystal molecules are twisted, and light travels along this twisted axis, changing the polarization axis of the pair of polarizing films. By arranging them in parallel, light does not pass through the background area. However, in the background area of a normal negative-type liquid crystal display device, as the light twists through the liquid crystal layer, the degree of polarization decreases, so a certain amount of light of a certain color passes through, resulting in insufficient contrast. There was a problem.

In order to solve this problem, we formed a light-shielding film on the background area other than the display area, and also polarized the light so that it passes through without applying voltage to the liquid crystal, as in the case of normal positive type liquid crystal display devices. Negative display devices have been proposed in which a film is disposed. This display device applies a voltage below a threshold voltage at which liquid crystal molecules rise to a predetermined display pattern portion (hereinafter referred to as a light-transmitting segment) of the display portion to transmit light, and displays a display pattern other than the predetermined display pattern. A liquid crystal display device has been proposed in which a voltage equal to or higher than a threshold voltage is applied to the light-shielding segment (hereinafter referred to as a light-shielding segment) to block light and perform a negative type display. (Japanese Patent Application Laid-open No. 162227/1982) In this display device, the light-shielding segment portion stands up against the substrate of the liquid crystal molecules, so the direction perpendicular to the substrate is the optical axis direction of the liquid crystal molecules, and when viewed from this direction. Insofar as liquid crystal molecules do not exhibit birefringence. Therefore, since the same degree of light shielding as when the polarizing plates are laminated with their polarization axes perpendicular to each other can be obtained, it is possible to obtain an extremely high contrast ratio of 1000 or more.

However, when the light-shielding segment portion of this display device is viewed from an oblique direction, light leaks due to the birefringence of liquid crystal molecules, resulting in insufficient light-shielding of the light-shielding segment portion.

This light leakage increases as the angle becomes lower in a particular direction, and the contrast ratio decreases, resulting in poor visibility (
Become. Further, the brightness of the background portion and the light-shielding segment portion is greatly different, and the difference in brightness between the light-shielding segment portion and the light-transmitting segment portion is small, so there is a problem that there is a risk of misunderstanding the displayed content.

For this reason, the present inventors have proposed using a uniaxial birefringent plate having a small principal refractive index in the direction perpendicular to the surface to eliminate this drawback (Japanese Patent Laid-Open No. 63-239421).

[Problems to be Solved by the Invention] By using the uniaxial birefringent plate as described above, a wide viewing angle can be obtained.

However, there is a problem in that it is difficult to obtain a uniform uniaxial birefringent plate having such characteristics, and it is difficult to apply it to mass production.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a nematic liquid crystal layer sandwiched between substrates provided with electrodes,
A light-shielding film is provided in areas other than those corresponding to the display pattern, and a pair of polarizing films are placed on both sides of the liquid crystal cell so that the polarization axis of the polarizing film passes through the non-voltage area, and the desired display pattern is created. In a negative-type liquid crystal display device in which a voltage higher than that for excitation of the nematic liquid crystal is applied to the electrodes of display pattern parts other than the above, two uniaxial birefringent plates are provided at least on one side between the polarizing film and the nematic liquid crystal layer. and a nematic liquid crystal layer is sandwiched between substrates provided with electrodes, and a light-shielding film is provided in areas other than those corresponding to the display pattern. A pair of polarizing films are arranged on both sides of the liquid crystal cell so that the polarizing axis of the polarizing film is aligned with the polarizing axis of the polarizing film so that light is transmitted through the non-voltage area. In a negative-type liquid crystal display device in which a voltage higher than the voltage that excites A liquid crystal display device characterized in that nxs ny and a principal refractive index n2 in the vertical direction are arranged so as to satisfy the relationship n)+"F ny>nz, and in these liquid crystal display devices, Product Δn1・d of refractive index anisotropy Δn1 and substrate gap d1
When N birefringent plates (natural number N22) are used for l, the refractive index anisotropy Δn2 of each birefringent plate and its thickness d
The value of the product Δn2d2 with 2 is 0.2×Δn1d1<Δn2
d2・N<3. Provided are a liquid crystal display device characterized in that OXΔnl 'di, and a liquid crystal display device characterized in that a liquid crystal obtained by adding a dichroic dye to a nematic liquid crystal is used in the liquid crystal display device. It is something to do.

The present invention will be explained with reference to the drawings.

FIG. 1 shows a cross-sectional view of a basic example of a negative-tone twisted nematic liquid crystal display device of the present invention.

In FIG. 1, IA is a substrate, 2A is an electrode formed thereon, and an alignment film 3A is further formed thereon. On the other hand, on the other substrate IB, an electrode 2B is formed, a light shielding film 4 is formed on a portion other than the display pattern, and an alignment film 3B is formed thereon. These two substrates are arranged so that their electrode surfaces face each other, their peripheries are sealed with a sealing material 5, and nematic liquid crystal is injected inside to form a liquid crystal layer 6 to form a liquid crystal cell.

A pair of polarizing films 7A and 7B are arranged on both sides of this liquid crystal cell, and the polarizing axis is set so that light is blocked at the part to which a voltage is applied, as in the case of a normal positive type liquid crystal display element. It is being done.

Furthermore, two uniaxial birefringent plates 8A and 8B are arranged between the polarizing film 7A and the liquid crystal cell so that their optical axes are substantially perpendicular to each other.

The intersection angle of the orientation control direction of the alignment film is usually set to 90°, but if necessary, it may be twisted by about 60° to 120°.
However, the twist of liquid crystal molecules is not 90° but 270"
or 450°.

The crossing angle of the polarization axes of the polarizing film is usually 90° in order to block light when a voltage is applied, that is, when the liquid crystal molecules are standing up. In order to improve visibility, if necessary, the figurines may be slightly shifted from this and placed so that the optical axes of the figurines appear to be perpendicular to each other.

The uniaxial birefringent plate used in the present invention has a high principal refractive index ny in a specific in-plane direction (for purposes of explanation, this direction is referred to as the X direction),
Even within the plane, the principal refractive index ny in the direction perpendicular to it (for purposes of explanation this direction is referred to as the is almost the same as the in-plane lower principal refractive index ny. The optical axis of this -axial birefringent plate is in the X direction showing a high principal refractive index n8.

In the present invention, two such -axial birefringence plates are used,
They are used by stacking them so that their optical axes are substantially orthogonal. Specifically, two uniaxial birefringent plates are stacked and arranged between one polarizing film and a liquid crystal cell. Alternatively, a total of four sheets may be arranged, two on each side of the liquid crystal cell. Note that the number may be further increased, such as four on one side of the liquid crystal cell.

In the present invention, since each uniaxial birefringent plate has an optical axis in the in-plane direction, its principal refractive index is nx>ny→n2,
Since the two uniaxial birefringent plates are arranged so that their optical axes are substantially orthogonal, the overall principal refractive index is substantially uniform in the in-plane direction, and the relationship n-F ny>ny holds.

In a liquid crystal display device using a normal nematic liquid crystal, since the liquid crystal has positive optical anisotropy, these two uniaxial birefringent plates are used to cancel this.

Therefore, for the product Δnl d+ of the refractive index anisotropy Δn1 of the liquid crystal and the substrate gap d1, the product Δn2 of the refractive index anisotropy Δn2 of these plurality of uniaxial birefringent plates and their thickness d2
- It is preferable to set the value of d2 within a specific range. That is,
When the number of birefringent plates used is N (N22 is a natural number), Δn1・dl of the liquid crystal cell and Δn2・d of each birefringent plate
It is preferable to set the relationship with 2 as follows in order to cancel out the birefringence of the liquid crystal and obtain a liquid crystal display device with a wide viewing angle.

0.2XΔn+・d+ <Δnz'd2'N < 3.
OXΔn,・d.

Specifically, when two birefringent plates are stacked on one side and used, N=2, so Δn2·d2 is 0.
It is preferable that 1×Δn+−d, to 1.5×Δn,−d. When two birefringent plates are stacked on each side, N=4, so Δn2・d2 is 0.
．． 05XΔn+-d+ ~0.75xΔn.

- It is preferable to set it as d.

As this -axial birefringent plate, any transparent plate that is uniaxial and exhibits birefringence (ny>ny'+=ny) with an optical axis in the plane can be used, such as a plastic film, an inorganic crystal material plate, etc. etc. are available.

In addition, the value of Δn1・dl of the liquid crystal layer is 0.3 to 0.7μ
It is preferable that it be within a range of about m. When Δn1・dl becomes less than 0.3 μm, the transmittance of the transmission segment expressed by the following formula (1) decreases, causing coloring or darkening (
It happens.

Note that U=2Δn·°d·λ: Wavelength of light Further, if Δn1·dl exceeds 0.7 μm, the angular dependence of the contrast ratio decreases, so it is preferably set to 0.7 μm or less.

Orientation control methods include films of organic polymers such as polyimide, polyamide, polyvinyl alcohol, SiO□,
A method of rubbing a film of an inorganic material such as TiO□ or Al2O, or an oblique evaporation method of SiO or the like may be used.

The light shielding film of the present invention may be provided on the inner surface of the liquid crystal cell, or
It may be provided on the outer surface, and its light transmittance is 0.02 to 1.0.
It is said to be about %. However, it is preferable to form a light-shielding film on the inner surface of the liquid crystal cell to prevent misalignment between the display pattern and the light-shielding film when viewed from an oblique direction.

This light-shielding film is formed on the background portion of the display, and usually only needs to be formed on one substrate. Of course, it may be formed separately on both substrates, but forming it on one substrate requires fewer steps (higher productivity).

This light-shielding film is formed by depositing or plating a metallic light-shielding film such as aluminum, nickel, or chromium through a transparent electrode and an insulating film, or by printing a light-shielding ink such as carbon paste. It is sufficient if it is formed.

The sealing material is a normal sealing material such as epoxy resin or silicone resin (normally, an opening is formed in a part of the sealing material, and after forming a cell, liquid crystal is injected through the opening, and the liquid crystal is injected through the opening. All you have to do is seal it.

Soup Sususu Wave Enn 1. Deke: Ordinary standing and rivet crystals are fine, but to prevent the formation of a spiral structure with reverse rotation,
It is usually preferable to add a small amount of chiral substance.

In addition, a color filter layer may be formed on the inner or outer surface of the substrate, a polarizing film substrate may be used as the substrate, a touch switch, an ultraviolet cut filter, or a non-reflection filter may be laminated on the outer surface of the substrate. The technique applied to ordinary liquid crystal display elements may be applied within a range that does not impair the effects of the invention.

Although the present invention is a negative type display as a whole, voltage is applied to the electrodes in the same way as a positive type display.

That is, in the light-transmitting segment of the display portion that transmits light, a voltage lower than the threshold voltage at which liquid crystal molecules rise is applied, and in the light-blocking segment, a voltage higher than the threshold voltage is applied. As for the method of applying the voltage, each segment may be driven individually, or a multi-handed brake driving method may be used to drive a plurality of segments 8-1.

Usually, an illumination means is provided behind the polarizing film on the back surface, but a reflective plate may be provided behind the polarizing film and display may be performed using light from the front.

The present invention can also be applied to a device that uses light from both the back and the front by installing an illumination means and a semi-transparent and semi-reflecting plate.

Furthermore, by adding a negative or positive dichroic dye to the liquid crystal, an even higher contrast ratio can be obtained over a wider viewing angle. Additionally, this dichroic dye may be used to compensate for the color temperature of the illumination means.

[Function] Before explaining the role of the optical element in the present invention, the reason why light leaks and the contrast ratio decreases when viewed from a low angle in the light-shielding segment portion in the conventional example will be explained.

As shown in FIG. 2(a), the Z axis is in the direction perpendicular to the substrate, and the polarization axes 9A and 9B of the two polarizing films are in the X direction,
direction). When a sufficient electric field is applied, liquid crystal molecules are oriented approximately in the Z-axis direction. The transmittance of light when the light travels through this liquid crystal at the angle shown in FIG. 2(b) is calculated. If the refractive index of the liquid crystal is nl in the direction of the molecular axis and na (ne>no) in the direction perpendicular to the molecular axis, its birefringence Δn, 2. △sty", no'n.

(..・3, .・θ and.,・.8・θ)・・−〇・
(2) becomes. The retardation caused by this birefringence is expressed by setting the thickness of the liquid crystal layer as dl, and the transmittance in this case is I = sin22ψ・sin'' (α/2).θ
= 0°, it does not exhibit birefringence, but Δnavy increases according to Transmittance increases.

225°, 315” becomes most obvious.

To eliminate this birefringence, add a phase difference that cancels out the phase in equation (3). Two laminated uniaxial birefringent plates in the present invention are used as a phase plate that provides this phase difference.

That is, by arranging two uniaxial birefringent plates so that their optical axes are substantially perpendicular to each other at least on one side between the polarizing film and the liquid crystal layer, a liquid crystal display device with a wide viewing angle can be easily produced. Obtainable.

[Example] The configuration of the comparative example in which only the uniaxial birefringent plates 8A and 8B were removed in FIG.
I-2978-0004 As a polarizing film, “G” manufactured by Nitto Denko Corporation
−1220DuJ, the cell gap is 5.5μm, so Δ
n, d+=0.484 cm.

A light shielding film was formed on the inner surface of the cell and printed with carbon ink to have a thickness of about 2 μm and a light transmittance of about 0.3%. Also,
The driving voltage was AC12V. In this element, the angles at which the contrast ratio was 200 or more were up to 26" from the center in the viewing angle direction, 10 degrees in the opposite viewing angle direction, and up to about 17 degrees in the left and right directions. The transmittance of the light-shielding segment portion increases, degrading the display quality and causing a risk of misreading the displayed content.

Example 1 Using a liquid crystal cell similar to that of the comparative example, two uniaxial birefringent plates were superimposed between the polarizing film on one side and the liquid crystal cell so that their optical axes were orthogonal to each other, and one light The axes were arranged parallel to a line bisecting the alignment control direction of the pair of alignment films.

Each Δn2・d2 of this -axial birefringent plate is 0.30μ
It was m.

When this liquid crystal cell was driven with AC12V, the angle at which the contrast ratio was 200 or more was 2 in the viewing angle direction from the center.
The viewing angle widened to 9 degrees, 13 degrees in the opposite viewing angle direction, and about 29 degrees in the left and right directions, and the visibility was significantly improved compared to the comparative example.

Example 2 Using the same liquid crystal cell as in the comparative example, two uniaxial birefringent plates were placed between each polarizing film and the liquid crystal cell so that their optical axes were perpendicular to each other, and one of the optical axes was The pair of alignment films were arranged parallel to a line dividing the alignment control direction into two equal parts.

Each Δn2・d2 of this -axial birefringent plate is 0.15μ
It was m.

When this liquid crystal cell was driven with AC12V, the angle at which the contrast ratio was 200 or more was 2 in the viewing angle direction from the center.
The viewing angle widened to 9 degrees, 13 degrees in the opposite viewing angle direction, and about 30 degrees in the left and right directions, and the visibility was significantly improved compared to the comparative example.

[Effects of the Invention] In the present invention, the optical retardation caused by the birefringence exhibited by the liquid crystal layer is suppressed by using two easily available uniaxial birefringent plates so that their optical axes are substantially orthogonal to each other. By stacking them and arranging them, it becomes possible to cancel out the
Display with extremely high contrast ratio can be obtained over a wide angle range.

In particular, uniaxial birefringent plates with a high principal refractive index in one direction in the plane, which have been mass-produced in the past, can be used in combination, so uniaxial birefringent plates with good uniformity can be easily obtained, and even large areas can be used. It is easy to mass-produce liquid crystal display devices with good uniformity.

Further, since the display colors are positive-type driven, there is an effect that angle changes are small, and it is possible to display a wide variety of colors on -1 display panels. This allows display with extremely good visibility over a wide angular range.

Furthermore, the present invention exhibits good visibility not only in transmissive displays but also in reflective displays, so it can be used even in places where outside light is sufficiently bright, and visibility is good even when the brightness of the background illumination is lowered. Therefore, there is an effect that the display device can be made smaller.

In addition, various other applications are possible within a range that does not impair the effects of the present invention.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a basic example of the invention. FIG. 2 is a perspective view illustrating the invention in detail. Substrate: lA%IB Electrode: 2A, 2B Alignment film: 3A, 3B Light shielding film = 4 Seal material = 5 Liquid crystal layer 26 Polarizing film: 7A, 7B - Axial birefringence plate = 8A, 8B Polarization axis: 9A, 9B No. figure No. figure

Claims (4)

[Claims] (1) A nematic liquid crystal layer is sandwiched between substrates provided with electrodes, and a light-shielding film is provided in areas other than those corresponding to the display pattern.
A pair of polarizing films is arranged on both sides of the liquid crystal cell so that light passes through the polarizing axis of the polarizing film in the part where no voltage is applied, and the nematic liquid crystal is excited at the electrodes in the display pattern part other than the desired display pattern. In a negative type liquid crystal display device to which the above voltage is applied, two uniaxial birefringent plates are arranged at least on one side between the polarizing film and the nematic liquid crystal layer so that their optical axes are substantially orthogonal to each other. A liquid crystal display device featuring: (2) A nematic liquid crystal layer is sandwiched between substrates provided with electrodes, and a light-shielding film is provided in areas other than those corresponding to the display pattern.
A pair of polarizing films is arranged on both sides of the liquid crystal cell so that light passes through the polarizing axis of the polarizing film in the part where no voltage is applied, and the nematic liquid crystal is excited at the electrodes in the display pattern part other than the desired display pattern. In a negative type liquid crystal display device to which the above voltage is applied, two uniaxial birefringent plates are provided at least on one side between the polarizing film and the nematic liquid crystal layer, and the combined in-plane principal refractive index n_x, n_y and a principal refractive index n_z in the vertical direction satisfy the relationship n_x≒n_y>n_z. (3) In the liquid crystal display device according to claim 1 or 2,
Product Δ of refractive index anisotropy Δn_1 of liquid crystal and substrate gap d_1
When using N birefringent plates (N≧2 natural number) for n_1・d_1, the refractive index anisotropy Δn_ of each birefringent plate is
2 and its thickness d_2, the value of the product Δn_2・d_2 is 0.
2×Δn_1・d_1<Δn_2・d_2・N<3.0
A liquid crystal display device characterized in that ×Δn_1·d_1. (4) The liquid crystal display device according to claim 1, 2 or 3, characterized in that a liquid crystal obtained by adding a dichroic dye to a nematic liquid crystal is used.