JPH024220A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To obtain a sufficient contrast ratio and a light shielding property by providing a layer having an anisotropy of a refractive index with one layer or more on the inside of a pair of polarizing plates. CONSTITUTION:A light beam from a light source passes through a polarizer 62 is made into linearly polarized light, and also, elliptically polarized light by a refractive index anisotropy of a liquid crystal in a liquid crystal panel 63. Since such a refractive index anisotropy is different in accordance with wavelength, the elliptically polarized light which comes out is different in degree, therefore, a phase correcting plate 64 is placed so that each wavelength light returns to roughly linearly polarized light. When an analyzer of 65 is installed in the direction vertical to this polarization direction, it comes to scarcely allow a light beam to pass through and goes to black. When a voltage is applied to the liquid crystal panel 63, since the balance for compensating the elliptically polarized light is broken, the light beam which cannot be compensated leaks from the analyzer, and the display is executed thereby. In such a way, the light shielding property of a dark state ascends, the contrast ratio can be increased, and a liquid crystal device having a high picture quality is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to electro-optical devices using liquid crystals used in systems such as computer terminals, image display devices, and shutters, particularly electro-optical devices using ferroelectric liquid crystals. This invention relates to a liquid crystal device with improved display characteristics.

[Summary of the Invention] The present invention relates to a liquid crystal device, and more specifically, a ferroelectric liquid crystal device having a pair of parallel substrates and an arrangement of molecules forming a plurality of layers perpendicular to the planes of the pair of parallel substrates. and a pair of polarizing plates on the outside of the parallel substrates, the liquid crystal display is The transmission spectrum of the device is made neutral in the visible light range,
The aim is to improve image quality by making the background color closer to white and the display color closer to black.

[Prior Art] C1 is a type of display device that uses the refractive index anisotropy of ferroelectric liquid crystal molecules to control transmitted light in combination with a polarizing element.
ark and Lagerwall (Japanese Unexamined Patent Publication No. 107218/1983, U.S. Patent No. 4367).
924 specification, etc.). This ferroelectric liquid crystal generally has a chiral smectic C phase (SmC) in a specific temperature range.
), and in this state, it has two optically stable states in response to an applied electric field, and has the property (bistability) of maintaining that state when no electric field is applied,
It is expected that it will be widely used as a display device.

By the way, as a method for aligning ferroelectric liquid crystal, a method using a uniaxial alignment process such as a rubbing process or an oblique evaporation process is known.

However, when the above-mentioned alignment control film was applied to control the alignment of a ferroelectric liquid crystal with a non-helical structure exhibiting bistability published by C1a rk et al., the following problems were encountered.

[Problem to be solved by the invention] FIG. 5 shows a cross-sectional view of a conventional liquid crystal device. 51a.

sib is a transparent substrate, 52a, 52b are transparent conductive films, 53
a.

53b is a uniaxial alignment film, 54 is a liquid crystal molecular layer, 55 is a tilt angle, 58 is a light source, 59a is a polarizer, 59b is an analyzer, 5
A and 5B are sealants.

Here, since the tilt angle of the ferroelectric liquid crystal with a non-helical structure obtained by alignment using a conventional alignment control film is small, the liquid crystal molecules are not aligned parallel to the transparent substrate, and the liquid crystal molecule layer is
It becomes "kunoji".

Therefore, even if the transmission axes of the polarizing plates 51a and 51b in FIG. 5 are set so that the contrast ratio is maximized, a sufficient contrast ratio and light shielding property cannot be obtained, resulting in a decrease in visibility.

[Means for Solving the Problems] In order to solve the above problems, the present invention has a pair of parallel substrates and an arrangement of molecules forming a plurality of Jt'J perpendicular to the plane of the parallel substrates. In a liquid crystal device that has a ferroelectric liquid crystal and a pair of polarizing plates on the outside of parallel substrates, there is one or more layers with anisotropy of refractive index on the inside of the pair of polarizing plates. It is characterized by being determined.

[Function] FIG. 6 is a diagram explaining the function based on the operating principle of a liquid crystal device having a phase correction plate, in which 61 is a light source, 62 is a polarizer, and 6
3 is a liquid crystal panel to which a liquid crystal driving voltage is applied, 64 is a phase compensation plate, and 65 is an analyzer. The directions of the transmission axes of the polarizer and analyzer are determined to maximize the contrast ratio.

The light from the light source passes through 62 polarizers and becomes linearly polarized.
It becomes elliptically polarized light due to the refractive index anisotropy of the liquid crystal in the liquid crystal panel No. 3. Since this refractive index anisotropy differs depending on the wavelength, the degree of elliptically polarized light that emerges differs, but a phase correction plate 64 is placed so that each wavelength of light returns to approximately linearly polarized light. If one analyzer 65 is installed in a direction perpendicular to this polarization direction, almost no light will pass through, resulting in a black color.

When a voltage is applied to the liquid crystal panel 63, the balance of elliptical polarization compensation is disrupted, so that light that cannot be compensated leaks from the analyzer, thereby producing a display.

[Examples] The details of the present invention will be described below based on illustrated examples.

Figure 1 shows a liquid crystal device according to the present invention.
lb is a transparent substrate made of glass, plastic, etc. for sandwiching liquid crystal molecules, and has transparent electrode layers 12a and 12b on the surface,
Furthermore, uniaxial alignment film layers 13a and 13b are provided in which thin films of polyimide, Teflon, or the like are formed by printing, dipping, vapor deposition, etc., and then subjected to alignment treatment. Substrate 11a
and llb have their alignment film layers facing each other, so that the ferroelectric liquid crystal molecules 14 are uniaxially aligned. A liquid crystal driving voltage is applied to the transparent electrode layers 12a and 12b. Reference numeral 17 denotes a phase compensator, which has one or more laminated layers having anisotropy in refractive index. 18 is a light source, 19a is a polarizer, 19
b is an analyzer. LA and 1B are sealings for sealing liquid crystal molecules.

Here, specific examples and measurement results of the liquid crystal device according to the present invention will be described.

FIG. 2 is a diagram showing the optical axis directions in the liquid crystal device shown in FIG. The maximum direction of refractive index in the layer 24 is the direction of the liquid crystal molecule layer of the ferroelectric liquid crystal. 25 is the angle from the lower polarizing plate transmission axis direction to the liquid crystal molecule layer direction (hereinafter abbreviated as [I]), 26 is the angle from the lower polarizing plate transmission axis direction to the maximum direction of refractive index in the layer having refractive index anisotropy angle (hereinafter abbreviated as [D]), 2
7 is an angle (hereinafter abbreviated as [H]) from the lower polarizing plate transmission axis direction to the upper polarizing plate transmission axis direction.

In the measurement, a polycarbonate uniaxially stretched film was used as a layer having refractive index anisotropy.

The direction of the angle is ``10 J'' clockwise.

A pyrimidine-based composition was used for the ferroelectric liquid crystal. The product of the thickness (d) of the liquid crystal layer in the normal direction to the transparent substrate and the refractive index anisotropy (Δn) of the ferroelectric liquid crystal composition is Δn X d
=0.25 μm.

Further, the retardation of the uniaxially stretched film of the phase correction plate is 0.14 μIn.

(Embodiment 1) Here, an example will be shown where the background is in a dark state, that is, in negative mode.

[I] = 90', [D] = O', [H] = 35@.

FIG. 3 shows the transmission spectrum of the liquid crystal device according to the present invention when a voltage is applied, and when a driving waveform of 1/400 duty is applied. 31 is 32 when the bright state voltage is applied.
is the spectrum when a dark state voltage is applied.

Furthermore, FIG. 4 shows the transmission spectrum of a conventional ferroelectric liquid crystal device. The transmission axes of the upper and lower polarizing plates were arranged so that the spectra of the embodiment shown in FIG. 3 and when a voltage in the bright state was applied were approximately the same. 41 is a spectrum when a bright state voltage is applied, and 42 is a spectrum when a dark state voltage is applied.

Table 1 shows the transmittance (550 nm) when the dark state voltage shown in FIGS. 3 and 4 is applied.

As is clear from Table 1, the light shielding property at 550 nm is
It can be seen that this has increased compared to conventional liquid crystal devices.

(Embodiment 2) Here, an example will be shown where the background is in a bright state, that is, in positive mode.

[I] = 35° [D] , 110@[H] = 100
It is 0.

The same effect as in this case (Example 1) was obtained.

In the example, measurements were taken with a light source placed on the back of the liquid crystal device as shown in Figure 1, but if a reflector is used in place of the light source, it can be used as a reflective liquid crystal display device. I can do it.

(Example 1) and (Example 2) show the results when the angle is fixed, but the same effect can be obtained by shifting the angles [I], [D], and [H] by -30'' to +30', respectively. is obtained.

In addition, the results are shown when the Δnd of the liquid crystal panel and stretched film is fixed, but the Δnd is -0.1 to +0.1 (μm
), the same effect can be obtained by changing Δnd between the liquid crystal panel and the stretched film to an optimal value.

In the examples, a pyrimidine-based composition was used as the ferroelectric liquid crystal, but other systems may also be used to improve the Δn of the liquid crystal panel and stretched film.
d. A similar effect can be obtained by changing the optical axis direction to an optimum value.

(Example 3) Using the same liquid crystal device configuration as in the above example, the effects of layers having different refractive index anisotropy made of different materials were investigated. As a result, the film's ∆
Similar effects were obtained when nd was the same as in the previous example.

[Effects of the Invention] As explained above, according to the present invention, a ferroelectric liquid crystal having a pair of parallel substrates and an arrangement of molecules forming a plurality of layers perpendicular to the planes of the parallel substrates. In a liquid crystal device, a layer with anisotropy of refractive index is provided on the inside of the pair of polarizing plates.
By having more than one layer, the light-shielding property in the dark state is improved, the contrast ratio can be increased, and a liquid crystal device with high image quality can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a liquid crystal device according to an embodiment of the present invention, FIG. 2 is a diagram showing the optical axis direction in a liquid crystal device according to an embodiment of the present invention, and FIG. 3 is a diagram showing transmission of the liquid crystal device according to an embodiment of the present invention. Spectrum diagram, Figure 4 is a transmission spectrum diagram of a conventional liquid crystal device, Figure 5 is a transmission spectrum diagram of a conventional liquid crystal device.
This figure is a block diagram of a conventional liquid crystal device, and FIG. 6 is a diagram illustrating the operating principle of a liquid crystal device having a liquid crystal correction plate. 11a, llb...Transparent substrate 12a
, 12b......Transparent electrode layer 13a,
13b...Alignment film 14...
......Liquid crystal molecules 17......Layer 18 having anisotropy of refractive index...Light source 19a... ...Polarizer 19b ...
......Analyzer IA, IB...
...Sealing for encapsulating liquid crystal molecules Applicant: Seiko Electronics Co., Ltd.

Claims (1)

[Claims] a pair of parallel substrates, and a ferroelectric liquid crystal having a molecular arrangement forming a plurality of layers perpendicular to the planes of the pair of parallel substrates, and a pair of polarized light beams arranged outside the parallel substrates. 1. A liquid crystal device comprising a plate, the liquid crystal device comprising one or more layers having anisotropy of refractive index inside the pair of polarizing plates.