JP2898501B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display using an optical retardation element for improving a viewing angle characteristic, and more particularly to a TN (Twisted Nematic) liquid crystal display.

[0002]

2. Description of the Related Art A display device using a nematic liquid crystal is
It is widely used for numerical segment type display such as digital clocks and electronic desk calculators. At present, TFT (Thin
An active drive type TN type liquid crystal display device in which an active element such as a Film Transistor (thin film transistor) is formed, and a color filter layer of red, green, blue or the like is provided as a color display means, and a twist angle of liquid crystal molecules is 90 °. A multiplex drive type STN (Super Twisted Nematic) liquid crystal display device having a twist angle of 90 ° or more has been put to practical use.

The TN type liquid crystal display device has a normally black mode in which a pair of polarizers are arranged so that their polarization directions are parallel to each other, and black display is performed in a state where no voltage is applied to a liquid crystal layer (off state). There is a normally white mode in which the polarization directions are arranged so as to be orthogonal to each other and a white display is performed in an off state. From the viewpoint of display characteristics such as display contrast, color reproducibility and viewing angle dependence of the display, the latter is preferred. Is normally used. In addition, one example is to dispose an optical retardation compensator to improve the viewing angle characteristics, or to dispose a compensation cell in which liquid crystal molecules are twisted 16.25 times.
992 SID 22.3.

On the other hand, the STN type liquid crystal display device utilizes a sharp steepness of a transmittance-applied voltage characteristic due to a twist angle of 90 ° or more, and the display device has a unique coloring. Exists. For this reason, an optical phase difference compensating plate is provided to perform monochrome display. Such a display system uses a so-called DSTN (Double layered) using a liquid crystal cell having a twist angle in a direction opposite to that of the display liquid crystal cell.
(STN) display method and film-added liquid crystal display method using a film having optical anisotropy. The latter film-added liquid crystal display method is often used from the viewpoint of lightness and low cost.

[0005]

In the TN type liquid crystal display device, when the observer observes from a direction inclined with respect to the normal direction of the display surface, the contrast changes according to the inclination angle, that is, the so-called viewing angle dependence. There is a problem of having a property. This occurs because the liquid crystal molecules have a refractive index anisotropy, and the liquid crystal molecules have a tilt, that is, a pretilt angle with respect to the substrate surface on which the electrodes are formed. In particular, FIG.
When the image is tilted in the direction of the normal viewing angle shown in (1), the image is colored at a certain angle or more (hereinafter, referred to as “coloring phenomenon”), and black and white are reversed (hereinafter, referred to as “reversal phenomenon”). Further, when the lens is inclined in the opposite viewing direction, the contrast is sharply reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device using an optical phase difference element, which eliminates viewing angle dependence and improves display quality.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a pair of polarizers and a liquid crystal element disposed between the pair of polarizers, wherein liquid crystal molecules are twisted by approximately 90 ° between the pair of light transmitting substrates. A liquid crystal element in which a nematic liquid crystal layer is interposed, and a transparent electrode and an alignment film are respectively formed in this order on the liquid crystal layer side surface of the translucent substrate, and at least the liquid crystal element and the polarizing plate are arranged between the liquid crystal element and the polarizing plate. A liquid crystal display device comprising one optical phase difference element, wherein the optical phase difference element is helically twisted between a pair of light-transmitting substrates each having a transparent electrode and an alignment film formed on opposing surfaces. An optical retardation element in which a liquid crystal layer that is nematically aligned and whose helical axis is inclined with respect to the normal direction of the surface of the transparent substrate is interposed, or the liquid crystalline polymer has a glass transition point Helically twisted nematic orientation at the following temperatures And an optical phase difference element whose helical axis is fixed to be inclined with respect to the normal direction of the surface, wherein the alignment processing direction of an alignment film on the optical phase difference element side of the liquid crystal element and the optical position A liquid crystal display device characterized in that the liquid crystal display device is arranged so that the direction of inclination of the phase difference element with respect to the normal direction of the helical axis is opposite to the direction of inclination.

The present invention also relates to a liquid crystal element disposed between a pair of polarizing plates and a pair of polarizing plates, wherein a nematic liquid crystal layer in which liquid crystal molecules are twisted by approximately 90 ° is interposed between the pair of light transmitting substrates. And a liquid crystal element in which a transparent electrode and an alignment film are formed in this order on the liquid crystal layer side surface of the translucent substrate, and a liquid crystal element and one of a pair of polarizing plates. A liquid crystal display device comprising: two optical retardation elements disposed between the optical retardation element;
A pair of light-transmitting substrates having a transparent electrode and an alignment film formed on opposite surfaces are twisted in a helical manner in a nematic orientation, and the helical axis is inclined with respect to a normal direction of the surface of the light-transmitting substrate. Liquid crystal layer is interposed, or the liquid crystalline polymer is twisted nematically in a helical shape at a temperature below the glass transition point, and the helical axis is oriented in the normal direction of the surface. An optical phase difference element that is fixed in an inclined manner with respect to the liquid crystal element, the orientation direction of the alignment film on the optical phase difference element side of the liquid crystal element, and the normal to the spiral axis of the optical phase difference element on the liquid crystal element side. The liquid crystal element is disposed so that the inclination direction is opposite to the direction, the orientation direction of the alignment film on the side opposite to the optical phase difference element of the liquid crystal element, and the spiral axis of the optical phase difference element on the polarizing plate side. Make sure that the direction of inclination relative to the line direction is the same A liquid crystal display device characterized by being arranged.

Further, according to the present invention, the optical phase difference element includes:
Average refractive index n of liquid crystal layer or liquid crystal polymer and helical pitch p
N · p ≦ 360 nm or n · p ≧ 7
It is characterized in that it is selected to be 80 nm. Still further, in the present invention, the optical retardation element includes a product Δn1 · d1 of a refractive index anisotropy Δn1 of a liquid crystal layer or a liquid crystal polymer and a thickness d1.
Is selected in the range of 100 nm to 200 nm.

[0010]

According to the present invention, in the optical phase difference element, a transparent electrode and an alignment film are respectively formed on the surface of a pair of translucent substrates in this order, and the surfaces are opposed to each other and a liquid crystal layer is interposed. . The liquid crystal layer is spirally twisted and nematic between the substrates, and has a helical axis inclined with respect to a normal direction of the substrate surface. This inclination is realized, for example, by applying an appropriate voltage between the electrodes. Therefore, the retardation value of the optical phase difference element is not symmetric about the normal direction of the surface of the light transmitting substrate. In the optical retardation element, the liquid crystalline polymer is spirally twisted and nematically oriented at a temperature equal to or lower than its glass transition point, and the helical axis is fixed to be inclined with respect to the normal direction of the surface. Therefore, the retardation value of the optical phase difference element is not symmetric about the surface normal direction. In the liquid crystal display device of the present invention, at least one optical retardation element is disposed between the liquid crystal element disposed between a pair of polarizing plates and the polarizing plate. In the liquid crystal element, a transparent electrode and an alignment film are respectively formed in this order on surfaces of a pair of translucent substrates, and the surfaces are further opposed to each other,
Further, a liquid crystal layer in which liquid crystal molecules are twisted by approximately 90 ° and nematically aligned is interposed between the substrates. Further, the liquid crystal element is arranged such that the alignment processing direction of the alignment film on the optical phase difference element side of the liquid crystal element and the direction of inclination with respect to the normal direction of the helical axis of the optical phase difference element are opposite to each other. Light incident from one polarizing plate side of such a liquid crystal display device becomes linearly polarized light by the polarizing plate, and when this light passes through the liquid crystal layer, normal light and extraordinary light are generated due to its birefringence,
In addition, elliptically polarized light corresponding to the phase difference is generated. Since the elliptically polarized light is converted into linearly polarized light by the phase difference element having a helically twisted nematic orientation, coloring caused by the elliptically polarized light is eliminated. Further, since the retardation value of the optical phase difference element is not symmetrical with respect to the normal direction of the surface as an axis, there is no coloring phenomenon or inversion phenomenon when the viewing angle is inclined in the normal viewing direction of the liquid crystal display device. In addition, it is possible to improve the viewing angle characteristics in the opposite viewing angle direction. Further, when at least one optical phase difference element is provided, it is possible to improve the viewing angle characteristics in the normal viewing angle direction and the opposite viewing angle direction.

According to the invention, in the liquid crystal display device, two optical retardation elements are disposed between the liquid crystal element disposed between a pair of polarizing plates and the polarizing plate. The liquid crystal element is
Same as described above. Further, the liquid crystal device is disposed such that the alignment processing direction of the alignment film on the optical phase difference element side of the liquid crystal element and the tilt direction with respect to the normal direction of the helical axis of the optical phase difference element on the liquid crystal element side are opposite to each other, The liquid crystal element is disposed such that the alignment direction of the alignment film on the side opposite to the optical retardation element and the direction of inclination of the optical axis of the optical retardation element on the polarizing plate side with respect to the normal direction are the same. You. Light incident from one polarizing plate side of such a liquid crystal display device becomes linearly polarized light by the polarizing plate, and when this light passes through the liquid crystal layer, normal light and extraordinary light are generated due to the birefringence thereof, and Elliptically polarized light corresponding to the phase difference is generated. Since the elliptically polarized light is converted into linearly polarized light by the phase difference element having a helically twisted nematic orientation, coloring caused by the elliptically polarized light is eliminated. Further, since the retardation value of the optical phase difference element is not symmetrical with respect to the normal direction of the surface as an axis, there is no coloring phenomenon or inversion phenomenon when the viewing angle is inclined in the normal viewing direction of the liquid crystal display device. In addition, it is possible to improve the viewing angle characteristics in the opposite viewing angle direction. Further, when two optical phase difference elements are provided, it is possible to improve the viewing angle characteristics not only in the normal viewing angle direction and the opposite viewing angle direction but also in all directions.

According to the present invention, the optical retardation element may be configured such that a product n · p of an average refractive index n of a liquid crystal layer or a liquid crystal polymer and a helical pitch p is n · p ≦ 360 nm or n · p ≧
By selecting 780 nm, selective reflection in the visible light range does not occur, and the coloring phenomenon can be prevented.

According to the present invention, in the optical retardation element, the product Δn1 · d1 of the refractive index anisotropy Δn1 of the liquid crystal layer or the liquid crystal polymer and the thickness d1 is selected in the range of 100 nm to 200 nm. , The liquid crystal display device of the TN mode can fall within the range of a general retardation value required, and the balance between the contrast ratio and the brightness between the normal viewing angle direction and the opposite viewing angle direction can be kept high.

[0014]

FIG. 1 is a sectional view showing the structure of an optical phase difference element 3 according to one embodiment of the present invention. Optical phase difference element 3
Are transparent substrates 6 and 7, transparent electrodes 8 and 9, alignment film 10,
11, a liquid crystal layer 12, and a sealing member 13. The substrates 6 and 7 are realized by, for example, glass, a liquid crystal layer 12 is interposed between the substrates 6 and 7, and further bonded by a sealing member 13 realized by, for example, a synthetic resin. Transparent electrodes 8, 9 and alignment films 10, 11 are formed in this order on the surfaces 6a, 7a of the substrates 6, 7 on the liquid crystal layer 12 side. The transparent electrodes 8 and 9 are made of, for example, ITO.
(Indium Tin Oxide) and is formed on the entire surfaces 6a and 7a of the substrates 6 and 7. The alignment films 10 and 11 are
For example, the alignment films 10 and 1 are realized by a polyimide resin.
The liquid crystal molecules 12a of the liquid crystal layer 12 are aligned on the surface of No. 1;
Rubbing treatment is performed so that the pretilt angle becomes 5 °.

The liquid crystal layer 12 is realized by a nematic liquid crystal, and liquid crystal molecules 12a of the liquid crystal layer 12 are spirally twisted between the substrates 6 and 7. That is, the rubbing treatment is performed so that the product n · p of the average refractive index n and the helical pitch p of the liquid crystal layer 12 becomes 354 nm. The refractive index anisotropy Δn1 of the liquid crystal layer 12 is set to 0.04, and the layer thickness d1 is set to 4 μm. That is, the spiral shaft 22
The product Δ of the difference Δn1 between the principal refractive index in the direction perpendicular to the axis and the principal refractive index in the direction parallel to the helical axis 22 and the layer thickness d1.
n1 · d1 is set to 160 nm.

The liquid crystal molecules 1 of such an optical retardation element 3
The helical axis 22a of the liquid crystal molecule 12a is formed so as to be inclined by an inclination angle θ in the direction of the arrow A with respect to the normal direction 23 of the surface of the element 3 (hereinafter, the helical axis 22 of the liquid crystal molecule 12a is (A direction inclined with respect to the normal direction 23 is referred to as an inclination direction.) The tilt angle θ is adjusted by applying an appropriate voltage to the element 3. The inclination angle θ is 10
The angle is appropriately determined in the range of 45 ° to 45 °, and if the inclination angle θ is outside the above range, inconveniences such as occurrence of a reversal phenomenon occur, which is not preferable.

FIG. 2 is a sectional view showing the structure of a liquid crystal display device 1 using the optical retardation element 3 according to one embodiment of the present invention. The liquid crystal display device 1 includes a liquid crystal element 2, the optical retardation element 3, and first and second polarizing plates 4 and 5. The liquid crystal element 2 includes first and second polarizers 4,
5, and the optical retardation element 3 is disposed between the first polarizing plate 4 and the liquid crystal element 2. Liquid crystal element 2
Is configured to include transparent substrates 14 and 15, transparent electrodes 16 and 17, alignment films 18 and 19, a liquid crystal layer 20, and a sealing member 21.

The substrates 14 and 15 are made of, for example, glass, and a liquid crystal layer 20 is interposed between the two substrates 14 and 15 and bonded together by a sealing member 21 made of, for example, a synthetic resin. Liquid crystal layer 20 side surface 1 of substrates 14 and 15
4a and 15a have transparent electrodes 16, 17 and alignment films 18,
19 are formed in this order. Transparent electrode 16,
17 is realized by, for example, ITO, and alignment films 18 and 19 are provided.
Is realized by, for example, a polyimide resin. The transparent electrode 16 on the substrate 14 side is formed on the entire surface, and the transparent electrode 17 on the substrate 15 side is, for example, a TFT (Thin Fil) (not shown).
m Transistor).

On the surfaces of the alignment films 18 and 19, a liquid crystal layer 20 is provided.
For example, a rubbing process is performed in the direction shown in FIG. 3 to align the liquid crystal molecules 20a. That is, the alignment processing direction 18a of the alignment film 18 is formed so as to be 45 ° counterclockwise with respect to the left-right direction in the figure, and the alignment processing direction 19a of the alignment film 19 is 45 ° clockwise. It is formed so that it becomes. Therefore, the alignment directions 18a and 19a are orthogonal to each other, and the liquid crystal molecules 20a of the liquid crystal layer 20 are twisted by approximately 90 ° between the substrates 14 and 15. The liquid crystal layer 20 is realized by a nematic liquid crystal, and has a refractive index anisotropy Δn2 of 0.08. The thickness d2 of the liquid crystal layer 20 is 4.5 μm.

FIG. 4 is a perspective view showing the positional relationship of the liquid crystal display device 1. As shown in FIG. The transmission axis 4a of the first polarizing plate 4 is disposed so as to be orthogonal to the alignment processing direction 18a of the alignment film 18 of the liquid crystal element 2, and the transmission axis 5a of the second polarizing plate 5 is
Are arranged so as to be orthogonal to the alignment processing direction 19a. The tilt direction A of the optical retardation element 3 is arranged so as to be opposite to the alignment processing direction 18a of the alignment film 18. At this time, the alignment processing directions of the alignment films 10 and 11 of the optical phase difference element 3 are arranged in an arbitrary direction. Therefore, the liquid crystal display device 1 is of a so-called normally white display type in which light is transmitted and white display is performed when a voltage is applied.

FIG. 5 is a sectional view showing an optical phase difference element 24 as a comparative example corresponding to the optical phase difference element 3 of the above embodiment. The optical retardation element 24 is configured in substantially the same manner as the element 3 except that the optical phase difference element 24 does not include the transparent electrodes 8 and 9 and
The helical axis 22a is substantially parallel to the normal direction 23 of the surface of the element 24. The product n · p of the average refractive index n of the liquid crystal layer 12 and the helical pitch p is 354 nm
It is said. The refractive index anisotropy Δn1 of the liquid crystal layer 12 is set to 0.04, and the layer thickness d1 is set to 4 μm. That is, the main refractive index perpendicular to the helical axis 22 and the helical axis 2
2, the difference between the principal refractive index in the parallel direction and the layer thickness d1.
Is 160 nm.

FIG. 6 is a perspective view showing the positional relationship of a liquid crystal display device 25 as a comparative example corresponding to the liquid crystal display device 1 of the above embodiment. The liquid crystal display device 25 includes an optical retardation element 24 instead of the optical retardation element 3,
The configuration is the same as that of the liquid crystal display device 1. The direction 26 of the main refractive index in the surface of the optical phase difference element 24, that is, the direction 26 of the average refractive index n is the alignment processing direction 1
8a.

Next, the result of evaluating the viewing angle dependence using the liquid crystal display devices 1 and 25 will be described. FIG.
FIG. 1 is a perspective view schematically showing a measurement system of a viewing angle dependency. In the liquid crystal display devices 1 and 25, each constituent member, that is, the first
The second polarizers 4, 5, the optical retardation elements 3, 24, and the liquid crystal element 2 are arranged in parallel with each other. The plane 27 in the figure is a plane parallel to the constituent members. This plane 27 is placed on the reference plane xy of the rectangular coordinate system x, y, z, and z
A light receiving element 29 having a fixed three-dimensional light receiving angle is disposed at a position at a predetermined distance from the coordinate origin in the direction of an angle す な わ ち from the axis, that is, the normal direction 23. Next, monochromatic light having a wavelength of 550 nm is incident on the plane 27 from the side opposite to the side on which the light receiving elements 29 are arranged. The output of the light receiving element 29 is amplified to a predetermined level by an amplifier 30 and recorded by recording means 31 such as a waveform memory or a recorder.

FIGS. 8 and 9 are graphs showing the applied voltage-transmittance characteristics measured in the measurement system. FIG.
Is a measurement result of the liquid crystal display device 1 based on the present invention,
FIG. 9 shows a measurement result of the liquid crystal display device 25 as a comparative example. The curves L1 and L4 in the figure show the results obtained by measuring the devices 1 and 25 directly above, that is, from the position of the angle ψ = 0 °, and the curves L2 and L5 represent the positions where the angle ψ = 30 ° is inclined in the normal viewing direction. Are shown, and curves L3, L6
Shows the results measured from the position inclined at an angle ψ = 30 ° in the anti-viewing angle direction.

From the measurement result of the device 25 shown in the curve L5 inclined in the normal viewing direction, the phenomenon that the transmittance increases again when a high voltage is applied is confirmed, but the measurement of the device 1 shown in the curve L2 is performed. The results do not confirm the above phenomenon. For this reason, in the device 1, the inversion phenomenon unlike the related art does not occur, and the contrast is improved. Further, since the transmittance of the curve L3 when a high voltage is applied is lower than that of the curve L6, the contrast of the device 1 in the anti-viewing angle direction is improved. Furthermore, in the device 1, since the transmittance of the curve L1 and the transmittance of the curve L2 when a low voltage is applied are close to each other, a change in characteristics when viewed from directly above and when viewed from a direction inclined toward the normal viewing angle is reduced. Is done.

FIG. 10 is a sectional view showing the structure of a liquid crystal display device 32 according to another embodiment of the present invention. The liquid crystal display device 32 is configured in substantially the same manner as the liquid crystal display device 1, but is characterized in that two optical retardation elements 3 are arranged. The optical retardation elements 3a and 3b are formed in the same manner as the optical retardation element 3 of the liquid crystal display device 1, respectively. The element 3a is disposed on the liquid crystal element 2 side, and the element 3b is disposed on the first polarizing plate 4 side. Is done.

FIG. 11 is a perspective view showing the positional relationship of the liquid crystal display device 32. As shown in FIG. The tilt direction B of the optical phase difference element 3a is arranged so as to be opposite to the alignment processing direction 18a of the alignment film 18, and the tilt direction C of the optical phase difference element 3b is the same as the alignment processing direction 19a of the alignment film 19. It is arranged so that it becomes. As described above, the liquid crystal display device 32 is, similarly to the liquid crystal display device 1, a so-called normally white display system in which light is transmitted and white display is performed when no voltage is applied.

FIG. 12 is a perspective view showing the positional relationship of a liquid crystal display device 33 as a comparative example corresponding to the liquid crystal display device 32 of the above embodiment. The liquid crystal display device 33 has substantially the same configuration as the liquid crystal display device 32 except that two optical retardation elements 3a and 3b
4. Optical phase difference elements 24a, 24
4b are formed in the same manner as the optical retardation element 24 of the liquid crystal display device 25 described above, and the element 24a is disposed on the liquid crystal element 2 side, and the element 24b is disposed on the first polarizing plate 4 side. The direction 34 of the average refractive index n of the element 24a is arranged so as to be parallel to the alignment processing direction 18a of the alignment film 18 of the liquid crystal element 2, and the direction 35 of the average refractive index n of the element 24b is aligned with the alignment direction of the alignment film 19. It is arranged so as to be parallel to the processing direction 19a.

FIGS. 13 and 14 are graphs showing the applied voltage-transmittance characteristics measured by arranging the liquid crystal display devices 32 and 33 in the above-described measuring system. FIG. 13 shows a measurement result of the liquid crystal display device 32 based on the present invention, and FIG. 14 shows a measurement result of the liquid crystal display device 33 which is a comparative example. Curves L7 and L10 in the figure have an angle ψ = 0 ° and curves L8 and L1
1 is an angle ψ = 30 ° (normal viewing angle direction), and curves L9, L
12 shows the result when the angle ψ = 30 ° (opposite viewing angle direction). Since this measurement result has the same tendency as the above-described measurement result, the reversal phenomenon is also eliminated in the liquid crystal display device 32, the characteristics in the anti-viewing angle direction are improved, and the characteristics are more correct when viewed from directly above. Changes in characteristics when viewed from a direction inclined in the viewing angle direction are reduced. Further, in the liquid crystal display device 32, compared with the liquid crystal display device 1 using one optical retardation element 3 which can improve the characteristics in only one direction, the total number of the optical retardation elements 3 is two. Since the characteristics in the direction can be improved, the viewing angle characteristics can be further improved.

In this embodiment, the product n · p of the average refractive index n and the helical pitch p of the optical phase difference element 3 is set to 354 nm.
Examples below m or 780 nm also belong to the scope of the present invention. For example, the product n · p is 784
Even in the case of nm, the same effect as in the present embodiment was obtained. If the product n · p is outside the above range, selective reflection occurs in the visible light range, which causes a coloring phenomenon, which is not preferable.

In this embodiment, the difference Δn1 between the main refractive index in the direction perpendicular to the helical axis 22 and the main refractive index in the direction parallel to the helical axis 22.
And the product Δn1 · d1 of the layer thickness d1 is set to 160 nm, but the product is not limited to this, and is 100 nm to 2 nm.
It is appropriately determined in the range of 00 nm. If the product is outside the above range, it is not preferable because it is out of the range of the general retardation value required by the TN mode liquid crystal display device, and the contrast ratio and the brightness between the normal viewing angle direction and the opposite viewing angle direction are not preferable. It is not preferable because the balance is deteriorated.

Further, in this embodiment, an example in which the optical retardation element 3 having the liquid crystal layer 12 interposed between the substrates 6 and 7 has been described, but instead of the element 3, a liquid crystal realized by, for example, polyester or polycarbonate is used. An example in which a conductive polymer film is inserted also belongs to the scope of the present invention. For example, the product n · p of the average refractive index n and the helical pitch p of the film is 348 nm, and the film thickness is 3.5 μm.
m, the product of the difference between the principal refractive index in the direction perpendicular to the helical axis direction and the principal refractive index in the parallel direction and the film thickness, and 140 nm, and the inclination angle θ of the helical axis being 20 °. The same effect as the example was obtained. Further, even when the product n · p was set to 780 nm in the film, the same effect as in the present example was obtained.

Further, in this embodiment, an example in which one or two optical retardation elements are arranged between the liquid crystal element 2 and the first polarizing plate 4 has been described. An example in which one or more sheets are disposed between the second polarizing plate 5 and the second polarizing plate 5 also belongs to the scope of the present invention.

On the other hand, in the comparative example, the product n · p of the average refractive index n of the optical phase difference element 24 and the helical pitch p is 354 nm.
However, the same result was obtained when the product was 784 nm. Similar results were obtained when the film was used instead of the element 24. At this time, the inclination angle θ of the spiral axis of the film was 0 °. Further, similar results were obtained when the product n · p was set to 780 nm in the film.

[0035]

As described above, according to the present invention, in the optical phase difference element, the liquid crystal layer interposed between the substrates is spirally twisted and nematically oriented, and the helical axis is in the direction normal to the substrate surface. , The retardation value of the optical phase difference element is not symmetric about the normal direction. Further, in the optical retardation element, the liquid crystal polymer is spirally twisted and nematically oriented, and its helical axis is inclined with respect to the normal direction of the surface. It is not symmetric about the line direction. In a liquid crystal display device, at least one optical retardation element is disposed between the polarizers and the liquid crystal element, so that elliptically polarized light obtained by passing through the liquid crystal layer can be converted to linearly polarized light. Disappears. Further, since the retardation value of the optical phase difference element is not symmetrical with respect to the normal direction of the surface as an axis, it is possible to eliminate the phase difference corresponding to the viewing angle in the normal viewing angle direction and the opposite viewing angle direction. For this reason, the contrast can be improved without the inversion phenomenon. Further, the viewing angle characteristics in the anti-viewing angle direction are improved, so that the contrast is improved and the display quality is significantly improved.

Further, according to the present invention, in the liquid crystal display device,
Since the two optical retardation elements are arranged between the polarizer and the liquid crystal element, elliptically polarized light obtained by passing through the liquid crystal layer can be converted to linearly polarized light, and the display is not colored. Further, since the retardation value of the optical phase difference element is not symmetrical with respect to the normal direction of the surface as an axis, it is possible to eliminate the phase difference corresponding to the viewing angle in the normal viewing angle direction and the opposite viewing angle direction. Therefore, it is possible to improve the contrast without the inversion phenomenon. Further, the viewing angle characteristics in the anti-viewing angle direction are improved, so that the contrast is improved and the display quality is significantly improved. When two optical retardation elements are provided, the viewing angle characteristics in all directions can be improved in addition to the normal viewing angle direction and the opposite viewing angle direction.

According to the invention, in the optical retardation element, the product n · p of the average refractive index n of the liquid crystal layer or the liquid crystal polymer and the helical pitch p is n · p ≦ 360 nm or n · p.
Since p ≧ 780 nm, selective reflection in the visible light range does not occur, and the coloring phenomenon can be prevented. According to the invention, in the optical retardation element, the product Δn1 · d1 of the refractive index anisotropy Δn1 of the liquid crystal layer or the liquid crystal polymer and the thickness d1 is selected in the range of 100 nm to 200 nm. The liquid crystal display device falls within the range of a general retardation value required by the liquid crystal display device, and can maintain a high contrast ratio and a high balance of brightness between the normal viewing angle direction and the opposite viewing angle direction.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of an optical phase difference element 3 according to an embodiment of the present invention.

FIG. 2 is an optical phase difference element 3 according to an embodiment of the present invention.
FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device 1 using a liquid crystal display.

FIG. 3 is a plan view showing an alignment processing direction of alignment films 18 and 19;

FIG. 4 is a perspective view showing a positional relationship of the liquid crystal display device 1.

FIG. 5 is a cross-sectional view showing an optical phase difference element 24 as a comparative example corresponding to the optical phase difference element 3.

FIG. 6 is a perspective view showing a positional relationship of a liquid crystal display device 25 as a comparative example corresponding to the liquid crystal display device 1.

FIG. 7 is a perspective view schematically showing a measurement system of a viewing angle dependency.

FIG. 8 is a graph showing an applied voltage-transmittance characteristic of the liquid crystal display device 1.

FIG. 9 is a graph showing an applied voltage-transmittance characteristic of the liquid crystal display device 25.

FIG. 10 is a cross-sectional view illustrating a configuration of a liquid crystal display device 32 according to one embodiment of the present invention.

FIG. 11 is a perspective view showing a positional relationship of the liquid crystal display device 32.

FIG. 12 is a perspective view showing a positional relationship of a liquid crystal display device 33 which is a comparative example corresponding to the liquid crystal display device 32.

FIG. 13 is a graph showing an applied voltage-transmittance characteristic of the liquid crystal display device 32.

FIG. 14 is a graph showing an applied voltage-transmittance characteristic of the liquid crystal display device 33.

[Explanation of symbols]

 1,32 liquid crystal display device 2 liquid crystal element 3 optical phase difference element 4 first polarizing plate 5 second polarizing plate 6,7,14,15 translucent substrate 8,9,16,17 transparent electrode 10,11,18, 19 Alignment film 12, 20 Liquid crystal layer 22 Spiral axis 23 Normal direction

Claims (4)

(57) [Claims] 1. A liquid crystal element disposed between a pair of polarizing plates and a pair of polarizing plates, wherein a nematic liquid crystal layer in which liquid crystal molecules are twisted by approximately 90 ° is interposed between the pair of light transmitting substrates, and A liquid crystal element in which a transparent electrode and an alignment film are respectively formed in this order on the liquid crystal layer side surface of the translucent substrate; and at least one liquid crystal element disposed between the liquid crystal element and the polarizing plate.
A liquid crystal display device comprising two optical phase difference elements, wherein the optical phase difference element is spirally twisted nematic between a pair of translucent substrates each having a transparent electrode and an alignment film formed on opposing surfaces. Is an optical retardation element in which a liquid crystal layer is interposed and whose helical axis is inclined with respect to the normal direction of the surface of the translucent substrate, or the liquid crystal polymer has a glass transition point or less. An optical phase difference element in which the liquid crystal element is twisted and nematically helically twisted at a temperature of, and the helical axis of the liquid crystal element is fixed to be inclined with respect to the normal direction of the surface. A liquid crystal display device, wherein the orientation direction of the film and the tilt direction with respect to the normal direction of the helical axis of the optical phase difference element are arranged in opposite directions. 2. A pair of polarizing plates, and a liquid crystal element disposed between the pair of polarizing plates, wherein a nematic liquid crystal layer in which liquid crystal molecules are twisted by approximately 90 ° is interposed between the pair of translucent substrates, and A liquid crystal element in which a transparent electrode and an alignment film are respectively formed in this order on the liquid crystal layer side surface of the light-transmitting substrate, and disposed between the liquid crystal element and one of the pair of polarizing plates. A liquid crystal display device comprising two optical retardation elements, wherein the optical retardation element has a spiral shape between a pair of light-transmitting substrates each having a transparent electrode and an alignment film formed on opposing surfaces. Is an optical phase difference element in which a liquid crystal layer is interposed in a twisted nematic orientation, and a helical axis thereof is inclined with respect to a normal direction of the surface of the transparent substrate, or a liquid crystalline polymer is made of glass. Spirally twisted nematic orientation at temperatures below the transition point An optical phase difference element whose helical axis is fixed to be inclined with respect to the direction of the normal to the surface; and an alignment treatment direction of an alignment film on the optical phase difference element side of the liquid crystal element; The liquid crystal element is disposed such that the inclination direction with respect to the normal direction of the helical axis of the optical retardation element is opposite to the optical phase difference element. A liquid crystal display device, wherein the liquid crystal display device is arranged such that an inclination direction with respect to a normal direction of a helical axis of the optical phase difference element on the plate side is the same as the inclination direction. 3. The optical retardation element comprises a product n · p of an average refractive index n of a liquid crystal layer or a liquid crystal polymer and a helical pitch p.
3. The liquid crystal display device according to claim 1, wherein n is set to n · p ≦ 360 nm or n · p ≧ 780 nm. 4. The optical retardation element has a product Δn1 of a refractive index anisotropy Δn1 of a liquid crystal layer or a liquid crystal polymer and a thickness d1.
4. The liquid crystal display device according to claim 1, wherein d1 is selected from a range of 100 nm to 200 nm. 5.