JPH11326890A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize light from a light source and to control the decrease of a contrast due to external light in a liquid crystal display. SOLUTION: Unpolarized light from a light source device 12 is made incident on a liquid crystal cell 16 via a circularly polarized light separating layer 14. The liquid crystal cell 16 varies the retardation value corresponding to the application of an electric field and essentially shifts the phase of the light from π/2 to -π/2 or from -π/2 to π/2, modulating the circularly polarized incident light into a linearly polarized light, making the resulting light incident on the dichroic linearly polarizing layer 18 on the surface and making only the component which coincides with its polarizing transmission axis exit outwards. The dichroic linearly polarizing layer 18 transmits 50% of the incident external light and absorbs the remainder.

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 using a polarization separation layer that transmits one polarized light component and reflects the other polarized light component, and a liquid crystal cell whose retardation value changes by an electric field. .

[0002]

2. Description of the Related Art A liquid crystal display device modulates polarized light obtained by transmitting light through a polarizing plate by a liquid crystal layer. For example, as shown in FIG. The display device 1 causes the light emitted from the light source device 2 to enter a dichroic linear polarizing plate 3 of a light absorption type, and causes the linearly polarized light obtained here to enter a liquid crystal cell 4.

In this liquid crystal display device 1, the liquid crystal cell 4
The polarized light that has entered and passed through is modulated by applying a voltage to the electrodes provided in the liquid crystal cell 4 and changing the liquid crystal layer in the cell with an electric field, or modulated without an electric field. Instead, the light is emitted from the liquid crystal cell 4 and only the polarized light in a specific direction is transmitted by the light-absorbing dichroic linear polarizing plate 5 disposed outside the liquid crystal cell 4.

[0004] The dichroic linear polarizing plate 3 of the light absorption type,
Numeral 5 transmits polarized light in the transmission axis direction and absorbs most of the polarized light in the direction perpendicular to the transmission axis. Therefore, about 50% of the light (non-polarized light) emitted from the light source device 2 is emitted. 2
The light is absorbed by the chromatic linearly polarizing plate 3, so that the light use efficiency of the liquid crystal display device 1 as a whole is lowered.
It was necessary to make the light enter the chromatic linear polarizing plate 3.

However, when the light emission amount of the light source device 2 is increased as described above, not only power consumption is increased, but also the heat generation amount of the light source device 2 is increased, which adversely affects the liquid crystal in the liquid crystal cell 4. The problem arises.

On the other hand, for example, Japanese Patent Application Laid-Open No. 4-502
As disclosed in JP-A-524-524 and JP-A-6-130424, the use of a cholesteric liquid crystal layer to transmit or reflect unpolarized light from a light source to circularly polarized light in the right or left turning direction. The circularly polarized light in one of the directions of rotation that has been separated and transmitted by the cholesteric liquid crystal layer is incident on the liquid crystal cell, and the reflected circularly polarizing plate in the other direction of rotation is reflected by the reflector, and the direction of rotation is reversed. There has been proposed a liquid crystal display device that transmits light and improves light use efficiency.

Further, as disclosed in Japanese Patent Publication No. 9-506985, unpolarized light from a light source is separated into two linearly polarized lights by transmission or reflection using a stretched multilayer film, and one of the transmitted ones is transmitted. Linearly polarized light is incident on the liquid crystal cell, and the reflected, linearly polarized light in the direction orthogonal to the above is changed in the polarization direction by a reflector, and then guided again to the stretched multilayer film so as to improve the light use efficiency. A liquid crystal display device has been proposed.

[0008] The liquid crystal layer in the liquid crystal display device disclosed in JP-A-4-502524 and JP-A-6-130424 has a light phase of π (λ / 2) when no electric field is applied. ) Or π / 2 (λ / 4) so that the phase of light is not shifted when an electric field is applied. Light emitted from this liquid crystal layer is a circularly polarizing plate disposed outside. , Where the light is transmitted or reflected depending on the degree of polarization of the incident light.

In the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 9-506985, one of the linearly polarized lights transmitted through the stretched multilayer film is incident on a liquid crystal cell. There is no disclosure of retardation.

[0010]

SUMMARY OF THE INVENTION The above-mentioned Japanese translation of PCT application No. Hei 4-502
The liquid crystal display devices disclosed in Japanese Patent Application Publication No. 524 and Japanese Patent Application Laid-Open No. Hei 6-130424 have extreme deterioration in the visibility of the liquid crystal display and a significant decrease in contrast due to the following reasons, and display quality is insufficient. There was a problem that it is.

That is, in the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 4-502524, a circularly polarizing plate disposed outside a liquid crystal layer and directly visible from the outside is formed of a low-pitch cholesteric coating film having wavelength selective reflection. As a result, about 50% of the external light incident on the circularly polarizing plate is reflected, which directly enters the observer's eyes, and extremely deteriorates the visibility.

Similarly, in the liquid crystal display device described in JP-A-6-130424, the color selection layer directly visible from the outside is a circular polarizer made of, for example, cholesteric liquid crystal. About 50 of external light
% Is directly reflected, and visibility is extremely reduced.

The present invention has been made in view of the above-mentioned conventional problems, and has a simple structure without a decrease in visibility and a significant decrease in contrast due to external light. In the case of a display device, the use efficiency of light can be significantly improved, and in the case of a reflection type liquid crystal display device, a liquid crystal display device which has high contrast and can perform colorization using birefringence by a liquid crystal layer. The purpose is to provide.

[0014]

According to the present invention, a light source and a circularly polarized light component of one of right and left turning directions of light emitted from the light source are transmitted. It comprises a circularly polarized light separating layer for reflecting the other circularly polarized light component, a liquid crystal layer, and an electrode for applying an electric field to the liquid crystal layer. The electric field is applied to the liquid crystal layer from the electrode to reduce the retardation value of the liquid crystal. And thereby the phase of the circularly polarized light transmitted through the circularly polarized light separating layer and incident is substantially from -π / 2 to π / 2.
A liquid crystal cell having a shifting function, disposed on the opposite side of the liquid crystal cell from the circularly polarized light separating layer, transmits one of the linearly polarized light components of the linearly polarized light incident from the liquid crystal cell,
A light absorption type 2 that absorbs a linear polarization component in a direction orthogonal to this.
The above object is achieved by a liquid crystal display device comprising a chromatic linearly polarizing layer.

According to a second aspect of the present invention, a light source includes:
It includes a linearly polarized light separating layer that transmits one linearly polarized light component of the light emitted from the light source and reflects a linearly polarized light component in a direction orthogonal to the linearly polarized light component, a liquid crystal layer, and an electrode that applies an electric field to the liquid crystal layer. An electric field is applied to the liquid crystal layer from the electrode to change the retardation value of the liquid crystal, whereby the phase of the linearly polarized light transmitted through the linearly polarized light separating layer and incident is substantially -π / A liquid crystal cell having a function of shifting by 2 to π / 2, and one of rightward and leftward turning directions of circularly polarized light incident from the liquid crystal cell, which is disposed on the liquid crystal cell on the side opposite to the linearly polarized light separating layer. The above object is achieved by a liquid crystal display device comprising: a light absorption type dichroic circularly polarizing layer that transmits a circularly polarized light component and reflects and absorbs the other circularly polarized light component.

According to a third aspect of the present invention, there is provided a light-absorbing dichroic linear line which transmits one linearly polarized light component of external light and absorbs a linearly polarized light component in a direction orthogonal thereto. A polarizing layer; a liquid crystal layer; and an electrode for applying an electric field to the liquid crystal layer. The electric field is applied to the liquid crystal layer from the electrode to change the retardation value of the liquid crystal, thereby obtaining the liquid crystal layer.
A liquid crystal cell having a function of substantially shifting the phase of linearly polarized light transmitted through the chromatic linearly polarizing layer and incident thereon by -π / 2 to π / 2, and opposite to the dichroic linearly polarizing layer of the liquid crystal cell A circularly-polarized light separating layer, which is disposed on the side and transmits one circularly-polarized light component in the right or left turning direction of the circularly-polarized light incident from the liquid crystal cell and reflects the other circularly-polarized light component; The above object is achieved by a liquid crystal display device comprising: an absorption layer that absorbs circularly polarized light transmitted through the layer.

Further, the circularly polarized light separating layer may be constituted by an optical rotation selecting layer composed of a cholesteric liquid crystal layer.

Further, the linearly polarized light separating layer has a planar multilayer structure in which three or more birefringent films are laminated, and has a vibration direction perpendicular to each other in the plane of each layer.
Of the two lights, the difference in refractive index between layers adjacent in the thickness direction with respect to one light may be different from the difference in refractive index between layers adjacent in the thickness direction with respect to the other light.

The circularly polarized light separating layer is formed by laminating a retardation layer having a retardation value for substantially shifting the phase of transmitted light by π / 2 and a birefringent film into three or more layers. Of two lights having vibration directions perpendicular to each other in the plane of each layer, a difference in refractive index between layers adjacent to each other in the thickness direction for one light, and a difference between the layers adjacent to each other in the thickness direction for the other light. And a planar multilayer structure having a different refractive index difference, and linearly polarized light transmitted and / or reflected by the planar multilayer structure may be converted into circularly polarized light.

Further, the linearly polarized light separating layer comprises a phase difference having a retardation value for substantially shifting the phase of transmitted light by π / 2, and an optical rotation selecting layer composed of a cholesteric liquid crystal layer. Circularly polarized light transmitted and / or reflected by the layer may be converted to linearly polarized light.

Further, in the liquid crystal cell, the liquid crystal layer is sandwiched between two substrates, the electrodes are arranged on the two substrates with the layer liquid crystal interposed therebetween, and a voltage is applied to the electrodes. In this case, the angle of the liquid crystal molecules in the layer liquid crystal with respect to the substrate surface changes, and the retardation value of the liquid crystal may be changed.

According to the present invention, a dichroic polarizing plate of a light absorption type is used for a notation surface which is visually recognized from the outside,
A change in the retardation value of the liquid crystal layer is selected in accordance with the dichroic polarizing plate, thereby preventing a significant decrease in contrast and deterioration in visibility due to external light without lowering light use efficiency. In addition, by using the birefringence of the liquid crystal layer, a color liquid crystal display device having good contrast can be obtained.

[0023]

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

As shown in FIG. 1, a liquid crystal display device 10 according to a first embodiment of the present invention has a light source 12 that emits unpolarized light, and a light source 12 that emits unpolarized light. A circularly polarized light separating layer 14 that transmits one (elliptical) circularly polarized light component and reflects the other (elliptically polarized light) component in the right or left turning direction, and changes the retardation value of the liquid crystal by applying an electric field. A liquid crystal cell 16 having a function of substantially shifting the phase of the circularly polarized light transmitted through the circularly polarized light separating layer 14 and incident thereon by -π / 2 to π / 2, and the circularly polarized light separation of the liquid crystal cell 16 A light-absorbing dichroic linearly polarizing layer 18 disposed on the side opposite to the layer 14 and receiving the linearly polarized light transmitted through the liquid crystal cell 16.

In FIGS. 1 and 5 to 8, “← →”,
“•” indicates an electric field vibration vector of linearly polarized light, “← →” indicates an in-plane direction (parallel), and “•” indicates a direction perpendicular to the paper plane. R and L show right circularly polarized light and left circularly polarized light.

A reflection layer 12A is formed on the back surface (the lower surface in FIG. 1) of the light source device 12. Reflective layer 12
A reflects the polarized light component emitted from the light source device 12 and reflected by the polarized light separating layer 14 in the direction of the circularly polarized light separating layer 14 again, inverting the phase of the circularly polarized light component at this time, and transmitting through the circularly polarized light separating layer 14. As a result, the light utilization rate is improved.

The circularly polarized light separating layer 14 is composed of, for example, a cholesteric liquid crystal layer.
The chromatic linear polarization layer 18 transmits polarized light in the transmission axis direction,
It absorbs most of the polarized light in the direction perpendicular to the transmission axis. By immersing a PVA (polyvinyl alcohol) film in a potassium iodide-iodine aqueous solution, and then stretching the PVA film in one direction in a boric acid aqueous solution, And a dichroic polarizing material such as a so-called iodine-based polarizing plate in which iodine molecules absorbed in the PVA film are arranged in one direction and a protective film is laminated, or a dye-based polarizing plate.

As shown in FIG. 2, the liquid crystal cell 16 includes a liquid crystal layer 22 sandwiched between two substrates 20A and 20B.
And a pair of pixel electrodes 24A and 24B arranged on the lower surface of the upper substrate 20A and the upper surface of the lower substrate 20B in FIG. 2 and sandwiching the liquid crystal layer 22 in the thickness direction. .

The liquid crystal layer 22 in the liquid crystal cell 16 is
An electric field is applied from the pixel electrodes 24A and 24B to change the retardation value of the liquid crystal, thereby changing the phase of the circularly polarized light transmitted through the circularly polarized light separating layer 14 to substantially −π / 2 to −2. It is adjusted to have a function of shifting by π / 2.

This adjustment can be performed with various known liquid crystals by controlling the birefringence and the thickness of the liquid crystal layer 22.

Such a liquid crystal is ECB (Electrikally
Controlled Briefringence (DAP) is known as the Deformation of vertical Aligned Phase
s) mode, HAN (Hybrid Aligned Nematic) mode
Mode, STN (Super Twisted Nematic) mode, SBE
(Super Twisted Briefringence Effect) SSFLC
(Surface Stabilized Ferroelectric Liquid Crystal
) Mode, OCB (Optically Compensated Bend) mode, VAN (Vertically-aligned nematic) mode, and the like.

The OCB mode usually has a structure in which a bend-aligned liquid crystal cell and a biaxial retardation plate are sandwiched between light absorption type dichroic linear polarizers whose light absorption axes are orthogonal to each other. In the above, only the bend-aligned liquid crystal cell is described.

The VAN mode usually has a configuration in which a VAN array cell vertically sandwiching an Nn (nematic) liquid crystal is sandwiched between light-absorbing dichroic linear polarizers whose light absorption axes are orthogonal to each other. In the present invention, it refers only to a VAN-aligned liquid crystal cell.

The same applies to other modes.

The expression ECB is often used as a color display system utilizing birefringence, but in the present invention, it is a mode in which the value of the birefringence of the liquid crystal layer changes. Used.

The “substantially shift by −π / 2 to π / 2” means that the phase is substantially changed by the liquid crystal layer 22 itself, or a phase difference layer different from the liquid crystal cell 16 is formed. Between the liquid crystal cell 16 and the dichroic circularly polarizing layer 18 circle, and / or
Alternatively, it is formed between the liquid crystal cell 16 and the circularly polarized light separating layer 14 to substantially change the phase of light transmitted therethrough by the interaction between the liquid crystal layer 22 and the retardation layer from −π / 2 to π / 2. It means to shift.

For example, the retardation value of the liquid crystal layer 22 itself is changed from 0 to π so that the liquid crystal layer 22 is between the dichroic circularly polarizing layer 18 and / or the circularly polarized light separating layer 14 side. And the phase shift of light transmitted therethrough is substantially shifted by -π / 2 to π / 2 by interaction with a phase difference having a retardation value of substantially π / 2.

The interaction means the fast axis or retard axis of the retardation layer whose retardation value is substantially π / 2 with respect to the fast axis or slow axis when the retardation value of the liquid crystal layer shows π. The action that occurs when the slow axes are orthogonalized, for example, 0-π / 2 = -π / 2, π-π / 2 = π /
2, it can be calculated.

It is needless to say that the use of a liquid crystal cell having an action of shifting the phase substantially by π / 2 to -π / 2 also falls within the scope of the present invention.

When the phase of the circularly polarized light is shifted by π / 2, the light becomes linearly polarized light, and when the phase of the circularly polarized light is shifted by −π / 2, the light becomes linearly polarized light in a direction orthogonal to the above. The phase of the linearly polarized light is π /
When the light is shifted by two, the light becomes circularly polarized light, and when the light is shifted by -π / 2, the light becomes circularly polarized light having a turning direction opposite to the above.

The shift will be described with reference to the Poincare sphere in FIG. The Poincare sphere is used to describe the polarization and to examine how the shape of the polarization changes when the phase changes. In FIG. 3, both the upper and lower poles of the sphere are left circles, respectively. Polarized light and right-handed circularly polarized light are shown. Points on the equator indicate linearly polarized light, and the other points indicate elliptically polarized light.

An arbitrary point H on the equator indicates horizontal polarization, and a point V on the equator opposite to the diameter passing through the point H indicates vertical polarization. Polarizations perpendicular to each other will be represented by points at one end of a diameter, and generally assume that the radius of the sphere is 1, but may be proportional to the intensity of the light beam.

An arbitrary point P on the surface of a Poincare sphere having a unit radius is represented by a longitude 2λ and a latitude 2ω. However, -180 ° <2λ <180 °, -90 ° <
2ω <90 °.

The longitude is positive when measured clockwise from point H, and the latitude is positive when measured downward from the equator, that is, when measured toward the pole representing right-handed circularly polarized light. Therefore, the coordinates of the point P in FIG. 3 are positive.

An arbitrary point P represents perfect elliptically polarized light having an azimuthal angle λ of the ellipse and an ellipticity of tan | ω |. Further, whether the point P is counterclockwise or clockwise is determined depending on whether the point P is in the upper hemisphere or the lower hemisphere. In summary, the following equations (1) and (2) hold for the cross-sectional view of the elliptically polarized light represented by the point P.

Α = λ (1) b / a = tan | ω | (2)

The cross section of monochromatic light is generally elliptical,
This ellipse can be represented using the symbols shown in FIG. The angle α between the semi-major axis and the X axis is called the azimuth angle of the sectional view, and 90 ° ≧ α ≧ −90 °. Ratio of two half axes b
/ A is called ellipticity, and if tan ^-1 b / a = β, 90 °
≧ β ≧ −90 °.

The direction of polarization is clockwise if 2ω is positive, and counterclockwise if 2ω is negative. Thus, each point on the Poincare sphere represents a different polarization shape. That is, one polarization shape can be represented by one point on the Poincare sphere.

Accordingly, for example, if the counterclockwise perfect circularly polarized light of the point of the upper pole of the Poincare sphere is shifted in the positive direction by π / 2 at the azimuth λ = 0, the point H on the equator in the Poincare sphere becomes To reach. That is, the circularly polarized light becomes horizontal linearly polarized light by being shifted by π / 2. Similarly, if it is shifted by π in the π-positive direction, it reaches the lower pole and becomes clockwise perfect circularly polarized light.

Further, when the clockwise complete circularly polarized light at the lower pole position of the Poincare sphere is shifted by π / 2 at the azimuth λ = 0, it reaches the point V on the equator and becomes π-shifted as vertical linearly polarized light. Then, the light reaches the upper pole and becomes fully circularly polarized counterclockwise. When the shift amount is not π / 2 or π, the light is elliptically polarized light.

As described above, the circularly polarized light separating layer 14 is composed of, for example, a cholesteric liquid crystal layer. The cholesteric liquid crystal layer generally exhibits an optical rotation selection characteristic that separates an optical rotation component in one direction and an optical rotation component in the opposite direction based on a physical molecular arrangement, but the cholesteric liquid crystal layer has a helical axis in a planar arrangement. The incident light is a right-handed rotation light and a left-handed rotation light.
The light is split into two circularly polarized lights, one is transmitted and the other is reflected.

This phenomenon is known as circular dichroism.
When the optical rotation direction of the circularly polarized light is appropriately selected with respect to the incident light, the circularly polarized light having the same optical rotation direction as the helical axis direction of the cholesteric liquid crystal is selectively scattered and reflected.

The maximum optical rotation scattering in this case is expressed by the following (3)
It occurs at the wavelength λ0 in the equation.

Λ 0 = nav · p (3)

Here, p is a helical pitch, and nav is an average refractive index in a plane orthogonal to the helical axis.

At this time, the wavelength bandwidth Δλ of the reflected light is
It is expressed by the following equation (4).

Δλ = Δn · p (4)

Here, Δn = n (‖) -n (perpendicular), where n (‖) is the maximum refractive index in a plane perpendicular to the helical axis, and n (perpendicular) is in a plane parallel to the helical axis. Is the maximum refractive index.

As a method for widening the wavelength bandwidth Δλ, a method of changing the helical pitch (for example,
US Pat. No. 5,691,789), several cholesteric liquid crystal layers having different p are stacked (for example, see Japanese Patent Application Laid-Open No. 9-30467).
0) and the like.

It is also known that the wavelength λφ of the selectively scattered light of the light obliquely incident on the helical axis of the planar arrangement shifts to a shorter wavelength side than λ0.

As a material of the cholesteric liquid crystal, an optically active 2-methylbutyl group, 2-methylbutoxy group or 4-methylhexyl group is bonded to a terminal group of a nematic liquid crystal compound such as a Schiff base, an azo type, an ester type or a biphenyl type. Preferred are chiral nematic liquid crystal compounds.

In general, a polymer liquid crystal is a polymer in which a mesogen group exhibiting a liquid crystal is introduced into a main chain, a side chain, or positions of a main chain and a side chain. A polymer cholesteric liquid crystal also has, for example, a cholesteryl group. It can be obtained by introduction into the side chain.

The polarization separation effect of the cholesteric liquid crystal is such that one circularly polarized light component (clockwise or counterclockwise) is transmitted by the cholesteric liquid crystal and the other circularly polarized light component is reflected. Upon reflection, right (left) circularly polarized light is reflected as right (left) circularly polarized light.

The light source device 12 is, for example, a transparent thin film white surface light source made of thin film electroluminescence sandwiched between transparent resin sheets having transparent electrodes, and is made of, for example, a metal thin film as described above. Reflective layer 12A
Is provided on the back.

The light source device 12 may be, for example, a so-called edge light type white surface light source in which a linear light source is disposed on a light guide plate.

In the liquid crystal display device 10 described above,
In the non-polarized light emitted from the light source device 12, only the circularly polarized light component in one of the turning directions of the light, for example, only the left-handed circularly polarized light component L as shown in FIG. To reach the liquid crystal cell 16.

The other right-handed circularly polarized light component R is reflected by the circularly polarized light separation layer 14, and its phase is reversed when reflected by the reflection layer 12 A of the light source device 12 or by the light diffusion plate in the optical path. Alternatively, the light is in a non-polarized state, and the left-handed circularly polarized light L transmitted through the circularly polarized light separating layer 14 increases and enters the liquid crystal cell 16.

By applying a voltage to the liquid crystal layer 22 in the liquid crystal cell 16 from the pixel electrodes 24A and 24B, the retardation value of the liquid crystal is changed, whereby the circularly polarized light passing through the liquid crystal cell 16 is applied with an electric field. Shifts the phase substantially by -π / 2 to π / 2.

Therefore, as described above, the circularly polarized light incident on the liquid crystal cell 16 becomes linearly polarized light when its phase is shifted by π / 2, and becomes orthogonally polarized when it is shifted by -π / 2. Out of the liquid crystal cell 16 as linearly polarized light.

If the polarization transmission axis of the dichroic linear polarizing layer 18 is made coincident with one of the two deflection directions, the electric field applied to the liquid crystal layer 22 is controlled to thereby control the dichroic linear polarizing layer 18. You can adjust the amount of light transmitted through
A liquid crystal display function can be provided. Also, of course, gradation display can be performed.

This will be described with reference to the Poincare sphere shown in FIG. 3. By shifting from the upper pole point of the Poincare sphere to a point H on the equator at an azimuth λ = 0 by 0 to π / 2, Circularly polarized light becomes left-handed elliptically polarized light → horizontal linearly polarized light, and is shifted from 0 to −π / 2 to point V on the equator to become left-handed elliptically polarized light → vertical linearly polarized light.

Accordingly, when the shift amount is in the range of 0 to π / 2, the larger the shift amount, the larger the amount of light transmitted through the dichroic linear polarizing layer 18, and in the range of 0 to -π / 2, the shift amount is large. The darker the image becomes, the darker the display finally becomes as shown in FIG.

Since the dichroic linear polarizing layer 18 is composed of a dichroic polarizing plate of a light absorption type, external light (non-polarized light) is incident on the surface of the dichroic linear polarizing layer 18. Also, since 50% of the light is absorbed and the remaining 50% is transmitted, and there is almost no reflection component, a decrease in the contrast of the screen of the liquid crystal display device 10 can be significantly suppressed.

Since the birefringence of the liquid crystal layer 22 is utilized, it is possible to provide a color liquid crystal display function without using a separate color filter.

Next, a liquid crystal display device 30 according to a second embodiment of the present invention shown in FIG. 6 will be described.

In FIG. 6, the same parts as those in the liquid crystal display device 10 shown in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and the description will be omitted.

The liquid crystal display device 30 includes the light source device 12
Of the light emitted from the light source device 12, for example, a linearly polarized light separating layer 32 that transmits a linearly polarized light component in the plane of the paper (hereinafter referred to as horizontal) and reflects a linearly polarized light component in a direction orthogonal to this. , A liquid crystal cell 16 and the liquid crystal cell 16
And a light-absorbing dichroic circularly polarizing layer 34 for receiving polarized light transmitted therethrough.

The linearly polarized light separating layer 32 has a planar multilayer structure in which three or more birefringent films are laminated, and has a vibration direction perpendicular to each other in the plane of each layer.
Of the two lights, the difference in the refractive index between the layers adjacent in the thickness direction for one light is different from the difference in the refractive index between the layers adjacent in the thickness direction for the other light, The light is transmitted and the other light is reflected.

The film having birefringence as described above is disclosed in, for example, JP-A-3-75705, and
As disclosed in Japanese Patent Application Laid-Open No. 06837 and the like, in-plane birefringence (refractive index anisotropy) of polycarbonate resin, polyester resin (for example, crystalline naphthalenedicarboxylic acid polyester), polyvinyl alcohol resin, cellulose acetate resin, and the like. ) Can be obtained by a method such as stretching.

For example, adjacent birefringent layers (films)
Has a refractive index of substantially n for a light beam oscillating in the X-axis direction.
x, and the refractive index difference Δnx (= | nx−nx |) between adjacent layers in the X-axis direction is substantially zero.

On the other hand, for example, among the three birefringent layers, the refractive indices of the first layer and the third layer with respect to the light oscillating in the Y-axis direction are both ny ₁ and the refractive index of the second layer in the same direction is the same. Assuming that the refractive index is ny ₂ (≠ ny ₁ ), the refractive index Δny between adjacent layers in the Y-axis direction is not substantially zero.

The reflection of light oscillating in the direction with a large refractive index difference (Y-axis direction) is greater than the reflection of light oscillating in the direction with a small refractive index difference (X-axis direction). Light transmission is greater than light transmission in the Y-axis direction.

For the light oscillating in the X-axis direction, even if the linearly polarized light separating layer 32 has a planar multilayer structure, the refractive index is substantially the same. Only a slight surface reflection occurs at two points, the surface and the exit surface.

On the other hand, for the light oscillating in the Y-axis direction, the refractive index in the planar multilayer structure is different between the respective layers. Surface (interface) reflection occurs between the layers, and the greater the number of birefringent layers, the greater the number of times of reflection of light vibrating in the Y-axis direction.

The dichroic circularly polarizing layer 34 is the same as the dichroic linear polarizing layer 18 in the liquid crystal display device 10 shown in FIG.
The λ / 4 retardation layer (plate) 35 is placed on the liquid crystal cell 16 side such that linearly polarized light is incident at an angle of 45 degrees with respect to the slow axis or fast axis direction in the plane of the λ / 4 retardation layer 35. It is formed by a method such as lamination on the right, transmits one of the right or left-handed circularly polarized light components of the incident light, and almost absorbs the other.

The λ / 4 retardation layer (plate) 35 is
Any function that shifts the phase of light by λ / 4 is sufficient, and it may be formed from a liquid crystal material or an inorganic material.
Stretching a film made of a polymer such as CAB, PS, PMMA, norbornene resin (stretching ratio of 1.3 to 4 times)
It is preferable to use a stretched film obtained from the viewpoint of mass productivity.

Further, in order to obtain a broadband λ / 4 retarder that shifts the phase of light λ / 1 over the entire wavelength band of visible light, a λ / 4 retarder and a λ / 2 retarder are required. It is preferable to arrange the λ / 2 phase difference plate on the polarizing plate side by crossing the fast axis or the slow axis at an angle of 60 ° ± 10 °. At that time, the relationship between the transmission axis of the polarizing plate and the fast axis or slow axis of the λ / 2 phase difference plate is such that the amount of transmitted circularly polarized light incident on the λ / 4 phase difference plate is maximized, or It is appropriately adjusted so that the amount of transmitted circularly polarized light that is opposite to the circularly polarized light is minimized.

In the liquid crystal display device 30, the unpolarized light from the light source device 12 is transmitted through the linearly polarized light separating layer 32 by a horizontal linearly polarized light component, and is reflected by the linearly polarized light component in a direction orthogonal to the horizontal direction.

The reflected linearly polarized light component is
The phase is disturbed by being reflected in the reflection layer 12A or in the light source device (for example, by the light diffusion function), and the component transmitted through the linearly polarized light separating layer 32 increases.

The linearly polarized light transmitted through the linearly polarized light separating layer 32 enters the liquid crystal cell 16 and its phase is shifted by an electric field applied thereto.

By applying a voltage to the liquid crystal layer 22 in the liquid crystal cell 16 from the pixel electrodes 24A and 24B,
The retardation value of the liquid crystal is changed, so that the phase of the linearly polarized light passing through the liquid crystal cell 16 is substantially shifted by -π / 2 to π / 2 by applying an electric field.

As described above, when the phase of the linearly polarized light incident on the liquid crystal cell 16 is shifted by π / 2, it becomes circularly polarized light, and when the phase of the linearly polarized light is shifted by −π / 2, the light rotates in the opposite direction. The light is emitted from the liquid crystal cell 16 as circularly polarized light in the direction.

This will be described with reference to the Poincare sphere of FIG. 3. From the point H on the equator of the Poincare sphere, the azimuth λ =
By being shifted from 0 to π / 2 at 0, the horizontal linearly polarized light becomes clockwise elliptically polarized light → clockwise circularly polarized light R. Therefore, the larger the shift amount is, the larger the light amount transmitted through the dichroic circularly polarizing layer 34 is. When the point H is shifted from the point H by 0 to π, the image becomes darker in accordance with the shift amount. When the point H is −π / 2, the display becomes dark as shown in FIG.

If the polarization transmission axis of the dichroic circularly polarizing layer 34 is set to be clockwise in one of the two rotation directions,
By controlling the electric field applied to the liquid crystal layer 22, 2
The amount of light transmitted through the chromatic circularly polarizing layer 18 can be adjusted, a liquid crystal display function can be provided, and gradation display is possible.

This is expressed by the following equation (5).

I = I ₀ sin ² 2θ sin ² (πdΔn (V) / λ) (5)

Here, I is the intensity of light transmitted through the dichroic linear polarizing layer 34, I ₀ is the intensity of incident light, θ is the angle between the incident polarization direction and the vibration direction of normal light in the liquid crystal cell, Δn
(V) and d indicate the birefringence of the liquid crystal and the cell thickness at the applied voltage V, respectively, and λ indicates the wavelength of the incident light. Note that the counterclockwise circularly polarized light L that does not pass through the dichroic circularly polarized light layer 34 is absorbed thereby.

In the liquid crystal display device 30,
Even when external light that is unpolarized light is incident on the chromatic circularly polarizing layer 34, 50% of the light is absorbed, so that a decrease in screen contrast due to reflection can be suppressed.

Next, a liquid crystal display device 40 according to a third embodiment of the present invention shown in FIG. 8 will be described.

In FIG. 8, the same parts as those in the liquid crystal display device 10 shown in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and the description will be omitted.

The liquid crystal display device 40 of FIG. 8 is a reflection type of the liquid crystal display device 10 of FIG. 1, and has a light absorbing layer 36 instead of the light source device 12 of FIG.

Since the other structure is the same as that of the liquid crystal display device 10 of FIG. 1, the description will be omitted by giving the same reference numerals to the same parts.

Here, the light absorption layer 36 is made of, for example, black paper, a resin plate, a film, a thin film, or the like whose surface is matted to prevent reflection.

In the reflection type liquid crystal display device 40, external light (non-polarized light) is incident on the dichroic linearly polarized light layer 18 and horizontal linearly polarized light only in the direction coinciding with the set transmission axis. Enters the liquid crystal cell 16. Since the other linearly polarized light component of the external light is absorbed by the dichroic linearly polarizing layer 18, the reflected light does not lower the contrast of the screen.

The phase of the horizontal linearly polarized light incident on the liquid crystal layer 22 is shifted by the electric field applied to the liquid crystal layer existing here.

That is, the liquid crystal layer 22 in the liquid crystal cell 16
In addition, when a voltage is applied from the pixel electrodes 24A and 24B, the retardation value of the liquid crystal is changed. As a result, the phase of the linearly polarized light passing through the liquid crystal cell 16 is substantially -π / It is shifted by 2 to π / 2.

As described above, the linearly polarized light that has entered the liquid crystal cell 16 becomes circularly polarized light when its phase is shifted by π / 2, and rotates in the opposite direction when it is shifted by −π / 2. The light is emitted from the liquid crystal cell 16 as circularly polarized light in the direction.

The circularly polarized light emitted from the liquid crystal cell 16 is a circularly polarized light component in one of the turning directions of the light, for example, as shown in FIG.
As shown in (2), only the counterclockwise circularly polarized light component L passes through the circularly polarized light separation layer 14 and reaches the light absorption layer 36.

The other right-handed circularly polarized light component R is reflected by the circularly polarized light separation layer 14 and directly enters the liquid crystal cell 16 without reversing the phase.

Since the voltage is applied to the pixel electrodes 24A and 24B to the liquid crystal layer 22 in the liquid crystal cell 16 as described above, the circularly polarized light passing through the liquid crystal cell 16 due to the change in the retardation value of the liquid crystal is: The phase is substantially shifted by -π / 2 to π / 2 by application of the electric field.

Therefore, as described above, the circularly polarized light incident on the liquid crystal cell 16 becomes a linearly polarized light when the phase is shifted by π / 2, and becomes a direction orthogonal to the above when the phase is shifted by −π / 2. Out of the liquid crystal cell 16 as linearly polarized light.

Since the polarization transmission axis of the dichroic linear polarization layer 18 coincides with one of the two deflection directions as described above, the inclination of the polarization axis of the linearly polarized light emitted from the liquid crystal cell 16 varies. Accordingly, the light passes through the dichroic linear polarizing layer 18 to become display light. Therefore, by controlling the electric field applied to the liquid crystal layer 22, the amount of light transmitted through the dichroic linear polarizing layer 18 can be adjusted, and a liquid crystal display function can be provided. Also, of course, gradation display can be performed.

In the first and second examples of each of the above embodiments, the light source device 12 is a transparent thin-film white surface made of thin-film electroluminescence or the like sandwiched between transparent resin sheets having transparent electrodes. The light source is provided with a reflective layer 12A made of, for example, a metal thin film on the back surface. However, the present invention is not limited to this, and the light source light incident from the side end surface of the light guide plate may be used as a light guide plate. The light may be emitted from one surface. In this case, a reflective layer made of a metal thin film or the like is provided on the other surface of the light guide plate, but white PET (polyethylene terephthalate) may be used.

A phase difference layer having a retardation value for substantially shifting the phase of transmitted light by π / 2 is laminated on the circularly polarized light separating layer or the linearly polarized light separating layer. Alternatively, it may have the same function as the circularly polarized light separating layer.

When a voltage is not applied from the pixel electrode to the liquid crystal layer of the liquid crystal cell, the phase of light passing through the liquid crystal cell is substantially shifted by π / 2. May not substantially shift the phase of the light passing therethrough.

[0116]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a liquid crystal display device 10 shown in FIG. 1, a cholesteric liquid crystal layer is used as a circularly polarized light separating layer 14, a retardation value is changed by applying a voltage, and the phase of light is substantially -π / 2 to π. The liquid crystal cell 16 and the dichroic linearly polarizing layer 18 that shift by a factor of 2 were laminated.

When an electric field was applied to the liquid crystal cell 16 to change the retardation value of the liquid crystal, no significant reduction in contrast due to external light was observed, and the light use efficiency was improved. The same applies to the reflection type liquid crystal display device 40 of FIG.

The liquid crystal display device 30 shown in FIG. 5 uses a stretched multilayer layer as the linearly polarized light separating layer 32, and further includes a liquid crystal cell 16 similar to the above, and a light absorption type dichroic circularly polarizing layer 3.
As a result, as in the case described above, there was no significant decrease in contrast due to external light, and the light use efficiency was improved.

[0119]

According to the present invention, as described above, the light utilization efficiency can be greatly improved, there is no significant decrease in contrast due to external light, and the birefringence of the liquid crystal layer can be utilized. Display has an excellent effect that a display state with good contrast can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded schematic sectional view showing a main part of a liquid crystal display device according to a first example of an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a liquid crystal cell in the liquid crystal display device.

FIG. 3 is a diagram showing a Poincare sphere for explaining a polarization state of light.

FIG. 4 is a schematic sectional view showing a state of dark display in the liquid crystal display device of FIG. 1;

FIG. 5 is a diagram showing a symbol for describing elliptically polarized light and a cross section of elliptically polarized light.

FIG. 6 is an exploded schematic cross-sectional view showing a main part of a liquid crystal display device according to a second example of the embodiment of the present invention.

FIG. 7 is a diagram showing a state of dark display in the liquid crystal display device.
Cross section similar to

FIG. 8 is an exploded schematic cross-sectional view showing a main part of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 9 is a sectional view similar to FIG. 1, showing a conventional liquid crystal display device;

[Explanation of symbols]

 10, 30, 40: Liquid crystal display device 12: Light source device 12A: Reflective layer 14: Circularly polarized light separating layer 16: Liquid crystal cell 18: Dichroic linearly polarizing layer 20A, 20B: Substrate 22: Liquid crystal layer 24A, 24B: Pixel electrode 32: linearly polarized light separating layer 34: dichroic circularly polarizing layer 36: light absorbing layer

Claims (8)

[Claims] 1. A light source, a circularly polarized light separating layer that transmits one circularly polarized light component in the right or left turning direction of light emitted from the light source and reflects the other circularly polarized light component, and a liquid crystal. A liquid crystal layer, and an electrode for applying an electric field to the liquid crystal layer. The electric field is applied to the liquid crystal layer from the electrode to change the retardation value of the liquid crystal. The phase of the circularly polarized light is substantially -π /
A liquid crystal cell having a function of shifting by 2 to π / 2; and a liquid crystal cell disposed on a side of the liquid crystal cell opposite to the circularly polarized light separating layer and transmitting one linearly polarized light component of linearly polarized light incident from the liquid crystal cell; A liquid crystal display device comprising: a light absorption type dichroic linear polarization layer that absorbs a linear polarization component in a direction orthogonal to the above. 2. A light source, a linearly polarized light separating layer that transmits one linearly polarized light component of light emitted from the light source and reflects a linearly polarized light component in a direction perpendicular to the light, a liquid crystal layer, and the liquid crystal layer And an electrode for applying an electric field to the liquid crystal layer to change the retardation value of the liquid crystal by applying an electric field from the electrode to thereby change the retardation value of the linearly polarized light transmitted through the linearly polarized light separating layer. The phase is substantially -π / 2 to π /
A liquid crystal cell having a two-shift function, and one circularly polarized light component of the right or left rotation direction of the circularly polarized light incident from the liquid crystal cell, which is disposed on the opposite side of the liquid crystal cell from the linearly polarized light separating layer. And a light absorption type dichroic circularly polarizing layer that transmits light and reflects and absorbs the other circularly polarized light component. 3. A light-absorbing dichroic linearly polarizing layer that transmits one linearly polarized light component of external light and absorbs a linearly polarized light component in a direction orthogonal thereto, a liquid crystal layer, and the liquid crystal layer. And an electrode for applying an electric field to the liquid crystal layer to change the retardation value of the liquid crystal by applying an electric field from the electrode to the liquid crystal layer. A liquid crystal cell having a function of substantially shifting the phase of light by -π / 2 to π / 2; and a circularly polarized light which is disposed on the liquid crystal cell on the side opposite to the dichroic linear polarizing layer and is incident from the liquid crystal cell. A circularly polarized light separating layer that transmits one circularly polarized light component in the right or left turning direction and reflects the other circularly polarized light component, and an absorbing layer that absorbs circularly polarized light transmitted through the circularly polarized light separating layer, A liquid crystal display device comprising: 4. A liquid crystal display device according to claim 1, wherein said circularly polarized light separating layer is constituted by an optical rotation selecting layer comprising a cholesteric liquid crystal layer. 5. The linearly polarized light separating layer according to claim 2, wherein the linearly polarized light separating layer has a planar multilayer structure in which three or more birefringent films are laminated, and has a vibration direction perpendicular to each other in the plane of each layer. The difference in the refractive index between the layers adjacent to each other in the thickness direction with respect to one of the two lights is different from the difference in the refractive index between the layers adjacent to each other in the thickness direction with respect to the other light. Liquid crystal display device. 6. The method according to claim 1, wherein the circularly polarized light separating layer comprises a retardation layer having a retardation value for substantially shifting the phase of transmitted light by π / 2, and a birefringent film. Of two lights having vibration directions perpendicular to each other in the plane of each layer, the difference in the refractive index between adjacent layers in the thickness direction for one light, and the thickness for the other light. And a planar multilayer structure in which the difference in the refractive index between adjacent layers in the vertical direction is different from each other, so that linearly polarized light transmitted and / or reflected by the planar multilayer structure is converted into circularly polarized light. A liquid crystal display device characterized in that: 7. A linearly polarized light separating layer according to claim 2, wherein said linearly polarized light separating layer comprises a phase difference having a retardation value for substantially shifting the phase of transmitted light by π / 2, and an optical rotation selecting layer comprising a cholesteric liquid crystal layer. A liquid crystal display device wherein circularly polarized light transmitted and / or reflected by the cholesteric liquid crystal layer is converted into linearly polarized light. 8. The liquid crystal cell according to claim 1, wherein the liquid crystal layer is sandwiched between two substrates, and the electrodes are arranged on the two substrates with the layer liquid crystal interposed therebetween. A mode in which the angle of the liquid crystal molecules in the layer liquid crystal with respect to the substrate surface changes when a voltage is applied to the electrode;
Thus, a retardation value of the liquid crystal is changed.