JPH03103822A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To decrease the visual angle dependency by combining the crossing angles of optical axes of two kinds of phase difference plates in which codes of refractive index anisotropy are different to 45 deg.-90 deg.. CONSTITUTION:When an angle of torsion of a liquid crystal molecule is the left spiral of 240 deg., and orthogonal axes X, Y for dividing it into two equal parts are determined, an angle theta1 made by an optical axis of a negative phase difference plate 103 against the X axis, and an angle theta2 made by an optical axis of a positive phase difference plate 102 against the X axis are set as 30 deg. and 60 deg., respectively. Also, an angle P1 made by a polarization axis of the upper polarizing plate 101 against the X axis, and an angle P2 made by a polarization axis of the lower polarizing plate against the X axis are set to 75 deg. and 15 deg., respectively. In such a state, the direction of a large refractive index, and that of a small refractive index come to be combined with the large direction and the small direction, respectively, and as for a phase difference, it becomes the same as that which is added. Also, from the viewpoint of the visual angle dependency, in the direction in which one phase difference increases, the other becomes the combination in which the phase difference decreases, therefore, an optical biaxial ratio, and an absolute value of each phase difference quantity are set so that its value becomes near '0', and the variation quantity of the phase difference is negated to each other and becomes small. In such a way, the visual angle dependency of the phase difference plate can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention performs correction using a retardation plate as a means of color correction to change the coloration due to the birefringence of an STN type crystal display device to black and white display. The present invention relates to liquid crystal display devices.

[Conventional technology]

Conventionally, STN type liquid crystal display devices have been known as display devices that enable large-capacity display by increasing the twist angle of liquid crystal molecules between a pair of electrode substrates to increase the steepness of changes in transmittance in response to changes in applied voltage. , coloring of the display due to its birefringence is known as a drawback.

Such liquid crystal display devices cannot display black and white,
Therefore, color display in combination with color filters was not possible.

Therefore, as a method for creating a black-and-white display, the OMI method is used, in which a display close to a black-and-white display can be obtained by setting the product in-d of the refractive index anisotropy Jn of the liquid crystal and the thickness d of the liquid crystal layer to a small value of around 0.6 μm. is proposed.

However, the display is dark and bluish, with low contrast and poor clarity.

Another method is a two-layer method that uses two liquid crystal panels and performs color correction on one panel, which provides good black-and-white display and high contrast. (Unexamined Japanese Patent Publication No. 6
2-54226) However, the use of two liquid crystal panels increases the weight, and the cost also increases by one panel.

Also,. A retardation plate method has been proposed that uses the same principle as the two-layer method described above to perform color correction using the amount of retardation of a retardation plate having refractive index anisotropy instead of a liquid crystal panel. The display quality has good black and white display and contrast. In addition, the retardation plate can be manufactured in the form of a film (3) and has good mass productivity, making it thin, lightweight, and low cost.

However, a uniaxial retardation plate that is easy to manufacture has viewing angle dependence in that the amount of retardation changes greatly depending on the viewing angle (viewing angle). This has the disadvantage that the display, color tone, and contrast are highly dependent on the viewing angle.

[Problem to be solved by the invention]

An object of the present invention is to eliminate the drawback that color tone and contrast are highly dependent on viewing angle in color correction using a retardation plate.

[Means to solve the problem]

In order to achieve the above object, in the present invention, color correction is performed by combining two types of retardation plates having different signs of refractive index anisotropy such that their optical axes intersect at an angle of 45° to 90°.

[Effect]

A uniaxial retardation plate having optical anisotropy is generally uniaxial because it can be easily manufactured by unidirectional stretching or the like. A uniaxial retardation plate that also has positive refractive index anisotropy (4) has a large refractive index ne in a direction parallel to the optical axis direction, and a refractive index n0 in a direction perpendicular to the optical axis direction of 0.
Refractive index anisotropy Jn(n,-no) smaller than 8
It is something that has. The thickness of this retardation plate as a whole is d
With respect to the perpendicular direction, a phase difference Jn-d occurs in a direction parallel to the optical axis and in a direction perpendicular to the optical axis. Moreover, this phase difference In-
When d is observed from a direction in which the angle θ is changed with respect to the vertical direction, the actual thickness becomes d/cos θ.

Furthermore, when observed from a direction in which the angle θ is changed toward the optical axis, the observed actual an becomes smaller, and the actual phase difference value becomes smaller, which is larger than the rate of increase in the actual thickness. Become. In this way, it has viewing angle dependence that shows a different phase difference depending on the viewing angle direction. Since the viewing angle dependence of this retardation plate is greater than the viewing angle dependence of an STN type liquid crystal panel, a liquid crystal display device using a retardation plate reflects the viewing angle characteristics of the retardation plate.

Furthermore, a biaxial retardation plate can also be manufactured by bidirectional stretching or the like. Biaxial retardation plates with positive refractive index anisotropy have viewing angle dependence that is greater than that of uniaxial retardation plates. ．． Therefore, it is difficult to use a liquid crystal display device using only one of these because the viewing angle characteristics become large. Moreover, this increases the rate of change in the amount of substantial phase difference observed in the direction when the angle θ is changed with respect to the vertical direction, which is the thickness direction d. This is the phase difference Jn-
This means that even if the value of d is small, the absolute value of the amount of change in the amount of substantial phase difference due to the dependence on the angle θ can be increased.

Furthermore, some of these uniaxial and biaxial retardation plates have negative refractive index anisotropy. This is the refractive index n in the optical axis direction
The value of the refractive index no in the perpendicular direction is larger than that of 6, and the other properties are similar to those of the positive one.

Therefore, if we combine materials with positive and negative optical refractive index anisotropy with uniaxial or biaxial properties so that their optical axes are orthogonal to each other, the direction in which the refractive index is large is the direction in which the refractive index is large,
The smaller direction is combined with the smaller direction, and the phase difference is the same as being added. In addition, in terms of viewing angle dependence, from the above-mentioned characteristics, the combination is such that when the phase difference increases in one direction, the phase difference decreases in the other direction, so the biaxial ratio is adjusted so that the value is close to O. , and the absolute value of each phase difference amount is set, and the amount of change in the phase difference cancels each other out and becomes extremely small.

In this way, the viewing angle dependence of the retardation plate can be made very small, so even if a monochrome display is performed in combination with an STN liquid crystal panel, the contrast and color tone of the display can be displayed with a small viewing angle dependence, that is, a display with a wide viewing angle. It can be realized.

〔Example〕

Embodiments according to the present invention will be described below with reference to the drawings.

FIG. 1 is a structural diagram showing an embodiment of the present invention.

In the example, a left helix with a twist angle of 240°,
Product Jn-d of refractive index anisotropy Jn of liquid crystal and thickness d of liquid crystal layer
The value of is 9 5 Q nmOSTN type liquid crystal panel 104
A biaxial negative retardation plate 106 having a negative refractive index anisotropy, an I4In-d value of 100 nm, and a viewing angle dependence equivalent to a uniaxial 530 nm is placed on the upper surface, and It has uniaxial positive refractive index anisotropy, and the value of In-d is 5.
A positive retardation plate 102 of 3Q nm is laminated. An upper polarizing plate 101 and a lower polarizing plate 105 are provided to sandwich them from the outside. A reflecting plate 106 is provided on the lower surface of the lower polarizing plate 105.

FIG. 2 shows a positive retardation plate 102 in an embodiment of the present invention.
, the optical axis direction of the negative retardation plate 106, the upper polarizing plate 101,
FIG. 3 is an explanatory diagram showing the polarization axis of the lower polarizing plate 105 and the arrangement of liquid crystal molecules. The twist angle of the liquid crystal molecules is a left helix of 240 degrees, and if the orthogonal axes XY are set to divide this into two equal parts, then the angle θ1 between the optical axis of the negative retardation plate 106 and the X axis is 30'.
The angle θ, which the optical axis of the positive retardation plate 102 makes with the X axis, is 6
It is set to 0°. Also, the polarization axis of the upper polarizing plate 101 is
The angle P1 formed with the axis is 75 degrees, and the angle P2 formed between the polarization axis of the lower polarizing plate and the X axis is 15 degrees.

Due to the above-mentioned precautions, the embodiment has a reflective positive type STN type liquid crystal display with good black and white display. In addition, regarding the viewing angle characteristics, we confirmed that negative and positive images can be well recognized at 45 degrees in all directions without being reversed.Also, we have confirmed that the display is good with very little change in color tone. It has been confirmed.

In this embodiment, a reflective positive type is used, but it can be easily determined that similar effects can be obtained with a transmissive type or a negative type.

Further, as for the material of the negative retardation plate 106, a stretched acrylic film was used, but the same effect can be obtained using a material capable of having negative refractive index anisotropy such as styrene. .

In addition, as for the material of the positive retardation plate 102, a stretched polycarbonate film was used, but the same effect can be obtained using a material that can have positive refractive index anisotropy, such as polyvinyl alcohol. .

Furthermore, although this embodiment uses l positive and l negative retardation plates, it is clear that the same effect can be obtained by combining a plurality of each.

Further, it is clear that the same effect can be obtained even when the arrangement is arranged on the upper surface, the lower surface, or both surfaces.

In addition, in this example, the optical axes of the positive and negative retardation plates are orthogonal, but it is clear that the effect can be obtained in the range of 45° to 90°, although the effect is different, and depending on the angle setting, the liquid crystal It can be easily inferred that even the viewing angle dependence of the panel can be corrected.

〔Effect of the invention〕

As explained above, the present invention is applicable to the conventional retardation plate type ST.
Like the N-type black and white liquid crystal display device, a bright and good black and white display can be obtained, and a liquid crystal display device that is thin, lightweight, and low cost and has improved visibility at a wide viewing angle can be realized.

[Brief explanation of drawings]

FIG. 1 is a composition diagram showing an embodiment according to the present invention, and FIG. 2 is an explanatory diagram showing angle settings of a retardation plate and a polarizing plate according to an embodiment according to the present invention. 101... Upper polarizing plate, 102... Positive retardation plate, 106... Negative retardation plate, 104... Liquid crystal panel, 105... ...Lower polarizing plate, 106...Reflector.

Claims (1)

[Claims] (1) Has positive dielectric anisotropy and has a twist angle of 180° to 3
A liquid crystal panel consisting of a nematic liquid crystal layer having a 00° twisted structure, a pair of electrode substrates that sandwich this liquid crystal layer, a pair of polarizing plates placed on both sides of this liquid crystal panel, and a liquid crystal panel between the pair of polarizing plates. In a liquid crystal display device comprising a retardation plate for color correction arranged, the retardation plate has a first retardation plate having uniaxial or biaxial positive refractive index anisotropy.
and a second retardation plate having uniaxial or biaxial negative refractive index anisotropy, and the optical axes of the respective retardation plates are at an angle of 45° to 90° with respect to each other. A liquid crystal display device characterized in that the display devices are arranged so as to intersect at an angle of. (2) A claim characterized in that the first retardation plate has biaxial positive refractive index anisotropy, and the second retardation plate has uniaxial negative refractive index anisotropy. Item 1. The liquid crystal display device according to item 1. (3) A claim characterized in that the first retardation plate has biaxial positive refractive index anisotropy, and the second retardation plate has biaxial negative refractive index anisotropy. Item 1. The liquid crystal display device according to item 1.