JPH02289825A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display device for a color display which can selectively display the colors of color filters and has a large display surface with good productivity by providing means for making transmitted light approximately colorless at the time of no electric field between two sheets of polarizing plates. CONSTITUTION:Straight chain high polymer films are used for oriented films of a liquid crystal layer having a large twist angle. The color filter layers are provided under the orientat ed film 12. The polarizing plates 4 are provided to meet the negative display and the means for making the transmitted light colorless at the time of the no-electric field in the liquid crystal is provided between the polarizing plates 4. Namely, the color filter layers 13R, 13G, 13B of the three colors are provided an the outer side of the liquid crystal layer 21. Materials which are blackened at the time of the non-electric field may be provided between the polariz ing plates 4 and 4 by, for example, mixing 3 kinds of dichromatic dyes, as the means for making the light colorless at the time of non-selection. The black color is, therefore, exhibited on the outside of the polarizing plates even if the light is elliptically polarized by the arrange ment of the liquid crystal molecules while the liquid crystal is stably oriented. The chromatic display by the color filter layers is executed by making high-speed response when the electric field is impressed. The display device adequate for mass production is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application 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 color liquid crystal display with a large spiral twist angle.

(Example) Prior Art Conventionally, in order to drive a liquid crystal by an electric field effect, there is a device in which liquid crystal molecules are oriented in a 90 degree helical structure (Japanese Patent Publication No. 13666/1983). However, 90 degree iFL
The orientation display has a large viewing angle dependence and is not suitable for high time division driving.

Therefore, the twist angle of liquid crystals was reconsidered, and
Other display modes have been proposed, such as in Japanese Patent Laid-Open No. 0-107020 and Japanese Patent Application Laid-Open No. 60-50511. These are made by increasing the fold angle of the liquid crystal to 160-360 degrees and utilizing the birefringence of liquid crystal molecules, so that practical contrast can be obtained even when driving at a duty of 1/100-1/200. (c) Problems to be Solved by the Invention However, points that must be solved in this display mode include stably aligning the liquid crystal molecules and the inability to perform color display due to birefringent interference colors.

Regarding the stable alignment of liquid crystal molecules, the above-mentioned prior document uses an alignment film obtained by obliquely vapor-depositing an inorganic material onto a substrate, and uses an alignment film obtained by obliquely vapor-depositing an inorganic material onto a substrate to achieve a stable alignment of 5 degrees or more, preferably 10-30 degrees, which is required for this display mode. It achieves alignment stability with a high tilt angle.

However, since the deposition angle is an important factor in this alignment film, a uniform alignment film has a limited area, and is limited to a flat plate with a radius of about 10 cm at most. For these reasons, this oblique deposition method is not suitable for producing large-area displays or for mass-producing displays regardless of area size. And in this display mode. Changes in the degree of birefringence interference are directly used for display, so the unique coloration can be used to determine whether the display is ON or OFF.
This always occurs in either F, and color display is not intended.

(2) Means for Solving the Problems The present invention has been made in consideration of the above points, and uses a linear polymer film as an alignment film for a liquid crystal layer with a large twist angle. A color filter layer is provided below, the polarizing plates are adapted for negative display, and means is provided between the polarizing plates to achromatize the transmitted light when there is no electric field in the liquid crystal.

(E) Effect: As a result, the alignment film made of a linear polymer film can stably align liquid crystal molecules, and while the liquid crystal is stably aligned, even if the liquid crystal molecules are elliptically polarized due to the arrangement of the liquid crystal molecules, the alignment film will be able to stably align the liquid crystal molecules. It exhibits a black color, and when an electric field is applied, it responds at high distances and can perform colored display using a color filter layer.

(f) Embodiments Before describing embodiments, the basic structure of such a liquid crystal display device will be explained based on FIG. 1. In the figure, (1) (1) are substrates placed opposite each other, and transparent electrodes (11) (l1) for applying an electric field to the liquid crystal are provided on the opposing inner surfaces.
Alignment film (12) (12) that homogeneously aligns liquid crystal molecules
)have. (2) is the substrate (
1) A liquid crystal supported by (1), which exhibits a nematic phase and has a helical structure twisted by 180 to 360 degrees,
It has a chiral nematic display mode.

(3) (3) is a sealant for forming a liquid crystal container to fill and hold the liquid crystal (2) between the substrates (1). (4) (4) is a polarizing plate placed on the outside of each of the substrates (1) (1) so as to be located on both sides of the liquid crystal (2) layer, and has a polarizing effect on the substrates (1) (1) themselves. It may also be used as a polarizing substrate.

The above-mentioned liquid crystal (2) has a thickness of, for example, 7 μm and Δn of 0.
12-0. 13, and it is screwed by a luminous substance! ii
It makes the structure easier to take. The liquid crystal (2) preferably includes liquid crystal molecules in which the volume occupied by the molecules increases due to rotation of the bonds between carbon atoms, and the orientation [(12
) (I2) can use an alignment film such as.

This display mode is determined by the arrangement of the polarizing plates (selection of the angle between the polarization axis and the alignment direction of adjacent liquid crystal molecules).
It is used in different display formats, which are called blue mode (corresponding to so-called negative mode) and yellow mode (corresponding to so-called positive mode) due to their coloring. Blue mode is non-selective! ! The liquid crystal exhibits a deep purple color (when no electric field is applied) and a background color in the selected state. That is, the light transmittance increases when an electric field is applied. On the other hand, the yellow mode exhibits bright yellow in a non-selected state and dark blue in a selected state. In yellow mode, light is blocked by applying an electric field, so display color selection in this state is lol
A color filter must be placed on the observer's side,
Color display cannot be performed unless the color of the color filter is disabled in the non-selected state. On the other hand, in blue mode, it was found that by changing the deep purple color when not selected to achromatic black, it was possible to display colors depending on the background color of the selected state. The present invention provides the display device described above, as shown in FIG.
R) (13G) (13B) are arranged. As a means to make the color achromatic when not selected, for example, Me
A material that turns black in the absence of an electric field is provided between the polarizing plates (4) (4), such as a mixture of three types of dichroic dyes at a total weight percent of 1.0-3.1, such as RCK's IZLI3093. That's fine. It is difficult to make the color outside the polarizing plate transparent when selected and black when not selected, but the deep purple coloring when no electric field is applied is as shown in JP-A-60-107020. The analysis is based on the birefringent elliptically polarized light of liquid crystal molecules, that is, between two polarizing plates.
For example, the color may be rendered achromatic in the absence of an electric field by the action of the polarizing plate and the dye described above between the polarizing plates.

The alignment film and liquid crystal molecules will be explained in more detail since they are related not only to improving the productivity of the liquid crystal display device of the embodiment of the present invention, but also to the stability of display and the vividness of coloration.

Example A CH. where one hydrogen atom of ε-cabrolactam was replaced with CF. -CH. -NH and C-cabrolactam were ring-opening copolymerized in various proportions to give an average molecular weight of approximately 10,000 atomic units. This was dissolved in N-methyl-2-pyrrolidone to make an 8% solution. Then, this solution was applied and dried on a soda glass substrate having a base layer and an electrode film to form a coating of about 1,000 people. This film was rubbed in one direction with a cotton cloth to obtain an alignment film (12).

Then, the gap was adjusted so that the layer thickness of the liquid crystal (2) was 10 μm, and a liquid crystal display was formed.
Filled with 1840 (nematic phase). At this time, the rubbing directions of the substrates (1) (1'') are arranged so that they are opposite to each other with the aim of achieving the minimum twist angle of 180 degrees in order to analyze the characteristics.1CF. Substitution rate and liquid crystal The relationship with the tilt angle of the molecule (measured by magnetic field method) is that the displacement power of prolactam to make the tilt angle between 5 degrees and 40 degrees, which is suitable for this display mode, is between 20% and 60%.
It is as follows. In addition, the displacing force was reclassified according to the molar ratio of brolactam, and after applying 15VO-P, 100μsec, 30Hz alternating positive and negative pulses at room temperature for 100 hours, 18
We confirmed that there is a relationship between the amount of fluoroalkyl chains present per unit number of atoms and the stability of monodomains, using the total area of defective orientations (domains) occurring within the effective display area of 0x 220 mm as an indicator. . 5000 as a guide
More than one fluoroalkyl chain per atom was required.

General formula like this It is effective for sea urchin orientation.

For example, [B-0] In the present invention, general formula or h (n is a natural number, X, Y are linear bonding groups with one or more methylene groups, methylene ether groups, phenylene groups, phenylene ether groups) A polymeric resin having a polyamide bond shown in the formula can be used, and since it is soluble in a solvent, a polymerized version can be used. However, in addition to these, polymer resins with polyimide bonds also have polyimide resins, which are expressed in the same way as polyamide resins, although they must be polymerized on a substrate, and polyimide resins have been able to obtain more stable orientation. An example of a material having a polyimide bond will be given below.

Example [B-1 Having a fluoroalkyl chain in codiamine
OF! 1141-Il+H. N-(CHI)1-CH
-(CHI)1-NH, (n.m is a natural number) is condensed with carboxylic acid to form polyimide sugar bean. The process involves printing and coating the resin on the substrate, baking it, and then rubbing it in one direction. The rubbing directions were orthogonal to achieve a twist angle of 270 degrees. At this time, the tilt angle could be controlled within the range of 5 to 30 degrees depending on the amount of fluoroalkyl chains when measured using the magnetic field method.

Now, in the above example, the measurement of the tilt angle was explained using the magnetic field method, but there are two reasons for this.

Generally, the optical method is used to measure the tilt angle of a liquid crystal display, but in the present invention it is extremely difficult to measure, and according to the comprehensive analysis results using the optical method, the tilt angle in the absence of an electric field is 3 to 4 degrees. be. On the other hand, the magnetic field method utilizes the fact that when a magnetic field above a threshold is applied, liquid crystals that exhibit positive dielectric anisotropy realign their long axes (optical axes) of molecules in the direction of the magnetic field. It is detected as capacity. The conditions for measuring the tilt angle described above are a magnetic field of 30 to 60K Gauss, and a capacitance measurement voltage of 0. 5V rms, capacitance measurement frequency 1kHz. From these facts, it can be analyzed that in the present invention, the tilt angle is low when no electric field is applied, but the tilt angle sharply increases when even a small electric field is applied.

Now, in the above example, the explanation was centered on the tilt angle and the alignment film, but it is better to select the material for the liquid crystal in order to achieve good display. For example, the first group uses liquid crystals R-Sa1010N R -Q-Q- CN, and the second group uses R\S-{toC
NR-8! -OR'R c) c=c-Q=-R'RCH=CH
A liquid crystal called PenF}PenR' was used. In these mixed liquid crystals, the first group is liquid crystals with roughly rigid bonds, and the second group is liquid crystal molecules (hereinafter referred to as liquid crystal molecules) whose structure increases the volume occupied by the molecule by rotating the bonds between carbon atoms It can be said to be a liquid crystal that contains a large amount of liquid crystal molecules (liquid crystal molecules with flexible skeletons). These groups differ in the following characteristics.

In this way, the tilt angle is affected by the liquid crystal material, but the uniformity of alignment is also affected. Regarding the uniformity of orientation, in addition to the question of whether it is a monodomain or a defective domain,
The question is whether or not the orientation is in a predetermined orientation that is reproducible even when an electric field higher than the threshold voltage is applied. If the amount of liquid crystal molecules with such a flexible skeleton exceeds 30 mol%, the area will suddenly become larger (for example, 100 mm x 150 am or more).
Monodomains are also formed in However, sometimes when a high voltage is applied, light-scattering domains are generated, and even if the voltage is subsequently increased to the saturation voltage, contrast cannot be obtained. Such symptoms do not occur when the liquid crystal molecules having a flexible skeleton exceed 50 mo 1.%. (In the above-mentioned first group of liquid crystals, the amount of liquid crystal molecules having a flexible skeleton is 20 mol.%).

In the liquid crystal display device of the present invention, for example, when the duty is 1/1.00 (good viewing angle is 20 degrees with a 90 degree twisted orientation), the good viewing angle is approximately 60 degrees.

Furthermore, the twist angle of the liquid crystal can be expressed by the steepness of the rise of the shielding effect of transmitted light with respect to the applied voltage (ratio of the voltage required to achieve 80% light shielding amount with respect to the saturation amount and that of 20%). From this point of view, the display device in the present invention has two
A twist angle of 50 degrees or more is particularly superior to a 90 degree twist arrangement, and the steepness is about 1.06. However, even with such a combination of alignment film and liquid crystal, if the twist angle is large, the orientation will be in the opposite direction, so in order to obtain stable alignment, the twist angle is preferably 290 degrees or less.

(g) Effects of the invention As described above, even in the display mode that utilizes birefringent interference color, in the negative mode, the area between the polarizing plates, which is the cause of interference color, becomes almost black when no electric field is applied, and when an electric field is applied, 3
Since the colors of the color filters corresponding to the primary colors are selectively displayed, suitable color display can be performed in a transmissive display format. Since a linear polymer alignment film can be used, simple manufacturing methods such as printing and coating can be applied, resulting in good productivity. And, although the tilt angle is low at less than 5 degrees when there is no electric field,
Since van der Waals forces and volume exclusion effects that affect orientation are fully taken into account, the tilt angle becomes high in weak electric fields or residual electric fields, resulting in good responsiveness in display driving. Furthermore, by selecting liquid crystal molecules, stable alignment can be obtained even over a wide display area. Due to these factors, high time division drive is possible in this display mode with a large twist angle.
A color liquid crystal display with a large display surface can be obtained with good productivity without impairing the advantage of having little viewing angle dependence.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid crystal display used in the present invention, and FIG. 2 is a sectional view of a liquid crystal display in an embodiment of the present invention. (1)...Substrate, (11)(11)...Transparent electrode,
(12) (12)...Alignment film, (13R) (13G)
(13B)...Color filter layer, (2) (21)
...Liquid crystal, (3) (3)...Sealant, (4
)(4)...Polarizing plate. Applicant: Sanyo Electric Co., Ltd. (1 other person) Representative: Patent attorney Takuji Nishino (2 others)

Claims (1)

[Claims] (1) A substrate having an alignment film made of a linear polymer film arranged in parallel and homogeneously aligning liquid crystal molecules on the inner surface;
The liquid crystal molecules filled between the substrates are 180 degrees or more 36
A liquid crystal consisting of a helical nematic liquid crystal phase with a torsion angle of 0 degrees or less, and a liquid crystal arranged on both sides of the liquid crystal such that the polarization axis and the orientation direction of the liquid crystal molecules are at an angle that increases the light transmittance when an electric field is applied to the liquid crystal. a polarizing plate disposed on the substrate, a means provided between the two polarizing plates for making transmitted light substantially achromatic in the absence of an electric field, and a color filter layer provided on the inner surface of at least one of the substrates. A liquid crystal display device characterized by: