JP2594219B2 - LCD 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 in which liquid crystal molecules have a helical structure. More specifically, the present invention relates to a liquid crystal display in which liquid crystal molecules are aligned so as to have a large helical twist angle and to be driven stably and at high speed.

[0002]

2. Description of the Related Art Conventionally, there is a liquid crystal display having a helical structure in which liquid crystal molecules are twisted by 90 degrees in order to drive a liquid crystal by an electric field effect (Japanese Patent Publication No. 51-13666). But 9
A display having a 0-degree twist orientation has a large visual dependency and is not suitable for high time-division driving. For example, in a matrix display, as the number of time divisions increases, the display contrast decreases. However, with 1/100 duty driving, the display contrast becomes 3 to 5, reaching the limit of reading the display contents. Further, the display contrast is limited to observation from a specific direction, and the margin in the observation direction is only about 20 degrees with respect to a perpendicular to the display surface. This means that they are not suitable for large-screen display, especially for dot matrix display with high pixel density.

Therefore, the twist angle of the liquid crystal was reexamined, and was disclosed in Japanese Patent Application Laid-Open Nos.
No. 7020, the twist angle of the liquid crystal is 160 to 360.
Research and proposals have been made on a display mode in which a practical contrast can be obtained even in a high time-division drive with a duty ratio of 1/100 to 1/200.

[0004]

However, a problem that must be solved in this display mode is that the liquid crystal molecules are stably aligned. In this display mode, the quality of the stable alignment of the liquid crystal molecules can be regarded as the domain countermeasure and the tilt angle control, and the two cannot be considered separately. As the alignment reproducibility, the tilt angle control mainly affects the high-speed response.

[0005] Among them, the measure against the domain refers to the non-uniformity of the orientation due to an increase in the torsion angle, and the initial orientation when the panel is formed and the original orientation when the voltage is applied and then removed. There is an orientation reproducibility of whether to return to or not. For example, even if the dextrorotatory alignment of the liquid crystal molecules is forced, the levorotatory alignment or the alignment with a different twist angle or the like occurs partially. The domain is observed as a non-uniform display color or a local difference in response speed during driving, and the display quality is significantly reduced. On the other hand, the countermeasure against the tilt angle is that if the angle between the liquid crystal molecules and the substrate surface (tilt angle) is not large, the response will be slow or the display color will be uneven, and the polymer alignment film used for 90 ° twist alignment will be used. In this display mode, the tilt angle is 0 to 3 degrees. In this display mode, the tilt angle is 5 degrees or more, preferably 10 to 3 degrees.
It is said that 0 degrees is necessary.

[0006] Regarding these points, in the above-mentioned prior art, the stability of the orientation is obtained by using an orientation film obtained by obliquely depositing an inorganic substance on a substrate. However, since the orientation angle has an important factor in the orientation film, a uniform orientation film has a limited area, for example, a flat plate of at most about 10 cm, unless a special vacuum evaporation apparatus is used. However, on the other hand, a large display is suitable for such a high time-division driving, and therefore, an alignment film by a vapor deposition method which has low productivity and requires a special device is not suitable. Further, it is well known that a liquid crystal display uses a linear polymer alignment film. However, in this display mode in which the twist angle of liquid crystal molecules is large and a wide area is provided, not only is there no guarantee of stable alignment, but also a polymer alignment film. Has been considered to be unsuitable for this display mode because the tilt angle is usually 3 degrees or less.

Further, this display mode is essentially a reflection type, and the above-mentioned prior art discloses a reflection type in which light passes through the analyzer and the polarizer twice each. As a result, the brightness of the screen is determined, and as a result, the contrast is affected. When the image becomes dim, the display is not observed.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a substrate having an alignment film for homogeneously aligning liquid crystal molecules, a liquid crystal in contact with the alignment film of the substrate, and a liquid crystal when no electric field is applied. In a liquid crystal display comprising a nematic liquid crystal in which molecules are helically twisted and held at a predetermined angle and a polarizer disposed outside a layer of the liquid crystal, the alignment film aligns the liquid crystal molecules homogeneously. fluoroalkyl chain side chain such treatment to have a predetermined tilt angle to the liquid crystal molecules with are subjected _{(C n H m F 2n +} 1-m:
n is a natural number, m is 0 or a natural number of 2n or less), and the liquid crystal has a predetermined twist angle of 180 ° or more and 360 ° or less when no liquid crystal molecules are in an electric field. Are arranged on both sides of the liquid crystal layer so as to have a predetermined angle with respect to the alignment direction of the alignment film whose polarization axes are close to each other so as to have high contrast to transmitted light.

[0009]

This facilitates the production of an alignment film at a predetermined tilt angle, and the fluoroalkyl side chain of the linear polymer coating is capable of causing a large twisted liquid crystal molecule when at least a weak electric field is applied (high time division driving). (For example, when non-selection is selected), the tilt angle is increased, and when a strong electric field is applied by selecting the polarization axis (when high time division driving is selected), the operation peculiar to the display mode in which the twist angle of the liquid crystal molecules is large is transmitted. Perform as type display.

[0010]

FIG. 1 is a cross-sectional view of a liquid crystal display according to an embodiment of the present invention. Reference numeral 1 denotes a substrate disposed oppositely, and a transparent electrode 11 for applying an electric field to the liquid crystal, Has an alignment film 12 for performing a homogeneous alignment. Numeral 2 denotes a liquid crystal sandwiched between the substrates 1 arranged in parallel, which is composed of a nematic liquid crystal exhibiting a nematic phase.
It has a helical structure with a predetermined angle such that it has a twist angle of less than or equal to degrees, and has a chiral nematic display mode. Reference numeral 3 denotes a sealant for filling and holding the liquid crystal between the substrates 1 and forming a liquid crystal container so as to stably accommodate the liquid crystal molecules over a wide area, and is disposed around the inner surface of the substrate. Reference numeral 4 denotes a polarizing plate disposed outside each of the substrates 1 so as to be positioned on both outer sides of the layer of the liquid crystal 2. The polarizing plate may be provided by imparting a polarizing action to the substrate 1 itself. .

[0011] In such a configuration, as described later, fluoroalkyl chain side chain so as to have a predetermined tilt angle to the liquid crystal molecules homogeneously aligned in the alignment film _{12 (C n H m F 2n} + 1 _-m : n is a natural number, m is 0 or 2n
A coating of a linear polymer having the following natural number) is used.
As the sealant 3, an organic polymer such as an epoxy resin is used so that a liquid crystal container can be formed without giving a high-temperature impact to the alignment film 12. The liquid crystal 2 is filled with a liquid crystal 2 containing a liquid crystal molecule having at least one polar group of, for example, a cyano group, a nitro group, and an ester bond. It is preferable to make it easy to have a tilt angle below. At this time, the liquid crystal 2 has a thickness of, for example, 7 μm and Δn is about 0.12, and a helical structure is easily formed by a rotatory material.
It is more preferable to include liquid crystal molecules in which the volume occupied by the molecules is increased by the rotation of the bond between carbon atoms. The polarizing plates 4 are arranged on both outer sides of the liquid crystal layer 2 so that the polarization axis has a predetermined angle with the orientation direction of the liquid crystal molecules so as to have a high contrast with respect to transmitted light.

The alignment film 12 is disclosed in Japanese Patent Application Laid-Open No. 55-1635.
No. 13, JP-A-58-91430, JP-A-58-91430
Examples of application to the present invention will be described based on the alignment agents listed in JP-A-104129. However, depending on how these alignment agents are used, as described later in detail, they become homeotropic alignment, and the purpose of the present invention is to increase the torsion angle by the homogeneous alignment and use the birefringence effect of the liquid crystal. The display mode is no longer available and must be considered.

Example (A-1): The structure shown in FIG. 2 in which one hydrogen atom of ε-caprolactam is substituted with CF ₃ as one of fluoroalkyl groups, and the ring-opening of ε-caprolactam at various ratios. Polymerization resulted in an average molecular weight of approximately 10,000 atomic units. This was dissolved in N-methyl-2-pyrrolidone to give an 8% solution. Then, the solution was applied and dried on a soda glass substrate having an underlayer and an electrode film to form a film of about 1000 Å. The coating was rubbed in one direction with a cotton cloth to obtain an alignment film 12. Then, the gap is adjusted so that the layer thickness of the liquid crystal 2 becomes 10 μm to form a liquid crystal display, and a liquid crystal ZLI manufactured by Merck is formed.
1840 (nematic phase) was charged. At this time, the rubbing directions of the substrate 1 are arranged so as to be opposite to each other for the purpose of analyzing the characteristics, and aiming at the minimum angle of the twist angle of 180 degrees. The relationship between the CF ₃ substitution ratio and the tilt angle of the liquid crystal molecules (measured by a magnetic field method) is shown in FIG. 3, and the substitution for setting the tilt angle suitable for this display mode to 5 degrees or more and 40 degrees or less is performed. Caprolactam is more than 20% 60
% Or less. It was difficult to control the tilt angle in a delicate range such as 1 degree unit or 0.5 degree unit.
Control of 5 degree increments (e.g. 15 degrees plus or minus 2 degrees, etc.) made sure that can be controlled with a mixed amount of a substituted caprolactam (substitution ratio of -CF _3).

Example (A-2): In the above (A-1), the substitution ratio of the fluoroalkyl chain is 50%, and -CnF _{2n + 1}
Was changed sequentially to form a similar liquid crystal cell. The results are shown in FIG. 4. The tilt angle was increased by increasing n. In order to set the tilt angle between 5 degrees and 40 degrees, n may be 1 or 2. And since this fluoroalkyl chain has the strongest effect on the volume exclusion effect, which is one of the factors in the orientation, -CnH containing hydrogen is used.
F _2n can also be used. In this case, n corresponding to the tilt angle could be selected from 1, 2, and 3.

Example (A-3): (A-1) (A-2)
Were reclassified based on the molar ratio of substituted caprolactam, and continuous electricity was supplied. FIG. 5 shows 15V _0-F , 100μ
It shows the total area of defective orientations (domains) generated within an effective display area of 180 × 220 mm after a positive / negative alternating pulse of 30 Hz and 30 Hz is applied for 100 hours at room temperature.
It has been shown that the stability of the monodomain is related by the amount of fluoroalkyl chain per unit atom, but this is related to the liquid crystal molecules described later,
It should be recognized that one or more fluoroalkyl chains are required per 5,000 atoms as a guide.

Example (A-4): In the case where a polyamide is formed using an amine, the same effect as in the case of using the above caprolactam can be expected, so only one example is shown here.
Hexamethylenediamine in which CF ₃ is substituted at one position in the main chain and adipic acid are subjected to polycondensation to obtain about 10,000
The average molecular weight in atomic units was used. This was applied to a glass substrate in the same manner as in the above (A-1), dried, and then rubbed to sandwich a liquid crystal exhibiting a nematic phase. The tilt angle at this time was about 15 degrees.

The polymer exemplified above is a polymer resin having a polyamide bond represented by the general formula shown in FIG. These have an advantage in handling in that they are soluble in a solvent and can be used in a polymerized state, as compared with a polymer resin having a polyimide bond as exemplified below.

However, as shown in the prior art of the above-mentioned aligning agent, a polymer resin having a polyimide bond is effective for alignment similarly to a polyamide resin, though it must be polymerized on a substrate. .

For example, [B-0]: FIG.
The polyimide resin represented by the following general formula was able to obtain a more stable orientation. An example having a polyimide bond is described below.

Example [B-1]: A polyimide resin is formed by condensing a carboxylic acid (FIG. 8B) with FIG. 8A having a fluoroalkyl chain in a diamine. In operation, such a resin material is printed and applied on a substrate, baked, and then rubbed in one direction. The rubbing direction is orthogonal and the twist angle is 270
Degree achieved. At this time, in the measurement by the magnetic field method, the tilt angle could be controlled to 5 to 30 degrees according to the amount of the fluoroalkyl chain.

In the above example, the measurement of the tilt angle has been described as the magnetic field method, but there are two reasons.
This is usually based on an optical method for measuring the tilt angle in a liquid crystal display, but it is extremely difficult to measure in the present invention. However, according to the comprehensive analysis result by the optical method, the tilt angle in the absence of an electric field is 3 to 4 degrees. On the other hand, the magnetic field method utilizes the fact that a liquid crystal exhibiting a positive dielectric anisotropy when a magnetic field above a threshold is applied is rearranged by aligning the major axis (optical axis) of the molecule in the magnetic field direction. It is detected as a capacitance. Conditions in the measurement of the tilt angle described above, the magnetic field 30~60K gauss, capacity measurement voltage 0.5V _rms, a capacitance measurement frequency 1 KHz. From these facts, it can be analyzed that in the present invention, the tilt angle is low when there is no electric field, but the tilt angle suddenly increases when a little electric field is applied.

In the above example, the tilt angle and the alignment film have been mainly described. However, selection of a liquid crystal material is one of the effective conditions for achieving a better display. What is characteristic with reference to the above description is that the substituted fluoroalkyl group mainly causes an interaction with the polar group of the liquid crystal molecule, and the tilt angle is changed by increasing or decreasing the substitution density or the number of carbon atoms of the fluoroalkyl group. It is possible to control, more preferably, the central skeleton of the liquid crystal molecule increases the stable alignment and the high-speed response.

The skeleton of the liquid crystal molecules will be described. Liquid crystals are used in a mixture, but are roughly classified into two sets. It has a liquid crystal composition with a large number of liquid crystal molecules, which has an almost rigid bond and the volume occupied by the molecule does not increase even when rotated, and a relatively flexible bond having a cyclohexyl ring, which increases the volume occupied by the molecule due to rotation. Having a liquid crystal composition. In these groups, in the present invention, when there are many rigid liquid crystal molecules, the tilt angle in the absence of an electric field is 3 degrees + -0.
The tilt angle at a weak electric field of 4 degrees was about 14 degrees, and the maximum torsional angle for stable orientation was 230 degrees. When an electric field higher than the threshold was applied, defective domains were generated. On the other hand, if the liquid crystal having a flexible skeleton exceeds 30 mol.%, The tilt angle in the absence of an electric field is 4 degrees + -0, 4 degrees, and the tilt angle in a weak electric field is approximately 18 degrees.
The maximum torsional angle for stable orientation was 275 degrees, and exhibited a monodomain. As described above, the tilt angle itself is affected by the polar group depending on the liquid crystal material, but the uniformity of the alignment is also affected. In addition to the problem of whether there is a mono-domain or a defective domain, the uniformity of the orientation also involves a problem of whether or not a predetermined orientation state is reproducible even when an electric field higher than the threshold voltage is applied. Here, the liquid crystal having a flexible skeleton refers to a liquid crystal molecule having a structure in which the volume occupied by the molecule is increased by rotation of a bond between carbon atoms, and examples thereof include a liquid crystal material illustrated in FIG. When the amount of the liquid crystal molecules having such a flexible skeleton exceeds 30 mol.%, A monodomain is formed even in a suddenly large area (for example, 100 mm × 150 mm or more). However, occasionally, when a high voltage is applied, a light-scattering domain is generated, and then, even when the voltage is raised to a saturation voltage, a contrast cannot be obtained. Such a symptom does not occur when the amount of liquid crystal molecules having a flexible skeleton exceeds 50 mol%.

The display mode having such a large twist angle is as follows.
It is used in two types of display modes determined by the arrangement of the polarizers, which are called blue mode and yellow mode because of their color. The blue mode shows deep purple in the unselected state, the background color in the selected state, and the yellow mode shows It shows a bright yellow color when not selected and a dark blue color when selected. In any case, the present invention has a weak electric field, and in the case of high time division driving, in a state where a non-selection voltage is applied, the tilt angle of liquid crystal molecules increases. It shows characteristics that are not inferior to those given. In other words, in the above literature, the contrast when the polarizing plate is rotated based on the superiority of the reflection type is described in relation to the orientation axis of the liquid crystal molecules, but in the present invention, in any display mode, The high contrast and the high-speed response and the uniformity of the display were obtained.
In a display mode having a twist angle of not less than 360 degrees and not more than 360 degrees, by selecting the angle with the orientation direction so that the polarization axes of the polarizing plates disposed on both outer sides as shown in FIG. This means that a high-contrast transmissive liquid crystal display can be provided.

For example, it has been confirmed that the response speed to the selection signal at 1/200 duty 1/15 bias and frame frequency of 128 Hz gives a response which is practically no problem at about room temperature. In addition, even with a large display capacity capable of obtaining a good contrast, a contrast exceeding the conventional 90 ° twist contrast was obtained with 40 or more scanning lines. The viewing angle dependency is 1 /
100 duty (good viewing angle 20 degrees with 90 degree twist orientation)
At this time, in the present invention, the good viewing angle is approximately 60 degrees. The twist angle of the liquid crystal can be represented by the steep rising edge of the effect of blocking transmitted light with respect to the applied voltage (the ratio of the voltage for reaching the 80% light-shielding amount to the saturation amount and that of 20%). From this point, the indicator in the present invention is 250
At a twist angle of more than degree, the display becomes superior to the display of the 90-degree twist orientation, and the steepness is about 1.06. However, even with such a combination of the alignment film and the liquid crystal, if the twist angle is large, reverse orientation occurs, so that the twist angle is more preferably 290 degrees or less in order to obtain stable alignment.

In the above-described embodiment, color display cannot be performed because display has a specific color in both the blue mode and the yellow mode. However, in the liquid crystal, for example, Merck's ZLI3093 (a mixture of three types of dichroic dyes in a total amount of 1.0 to 3.1% by weight and containing a large amount of liquid crystal having a flexible skeleton) is used. Is added in an amount of 2.0% by weight, a black color can be exhibited in the non-selection state in the transmission type blue mode. Therefore, color display can be performed by arranging three color filter layers outside the liquid crystal layer 2 and arranging, for example, a surface illuminating means on the back surface as a transmissive display mode.

[0027]

As described above, since a linear polymer oriented film can be used, a simple manufacturing method such as printing and coating can be applied, and the productivity is good. The tilt angle is high at least in a weak electric field or a residual electric field because the Van der Waals force and the volume exclusion effect that affect the alignment are sufficiently taken into account. Is good. Since a uniform and stable orientation can be obtained over a wider display area, even in the transmission type, in this display mode having a large twist angle,
A liquid crystal display having a large display surface with high productivity and high contrast and high display quality can be obtained without impairing the advantages of high time division driving and little dependence on viewing angle.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a molecular formula of ε-caprolactam used in the present invention.

FIG. 3 is a characteristic diagram of orientation in an example of the present invention.

FIG. 4 is a characteristic diagram of orientation in an example of the present invention.

FIG. 5 is a characteristic diagram of orientation in an example of the present invention.

FIG. 6 is a molecular formula diagram of a polyamide composition applied to the present invention.

FIG. 7 is a molecular formula diagram of a polyimide composition applied to the present invention.

FIG. 8 is a molecular formula diagram of a precursor a and a carboxylic acid b of the composition used in the present invention.

FIG. 9 is a molecular formula diagram of an example of a liquid crystal composition applied to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 11 Transparent electrode 12 Alignment film 2 Liquid crystal 3 Sealant 4 Polarizing plate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshifumi Nakanishi 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd. (56) References JP-A-59-21818 (JP, A) 52-108838 (JP, A) JP-A-60-107020 (JP, A)

Claims (1)

(57) [Claims] 1. A substrate having an alignment film for homogeneously aligning liquid crystal molecules, a nematic liquid crystal in contact with the alignment film of the substrate, wherein the liquid crystal molecules are helically twisted and pinched at a predetermined angle in the absence of an electric field. A liquid crystal display comprising a polarizer disposed outside a liquid crystal layer.
Alignment treatment is applied to make liquid crystal molecules homogeneously aligned.
Fluoroalkyl chain side chain so as to have a predetermined tilt angle to the liquid crystal molecules with are _{(C n H m F 2n +} 1-m: n is a natural number, m is 0 or 2n following a natural number) linear with The liquid crystal is made of a polymer, and the liquid crystal is 18
Has 0 degrees 360 degrees or less of a given twist angle, said polarizer alignment direction predetermined alignment film polarization axes are close to have a high contrast with respect to the transmitted light In the both outer sides of the liquid crystal layer A liquid crystal display characterized by being arranged so as to have an angle of.