JPH09304776A - Liquid crystal display element - Google Patents

Abstract

(57) Abstract: A display quality that can be driven at a low voltage and is good for a long time when energized at a high temperature of about 50 ° C. under a low frequency driving condition in which the number of polarity reversals per second is 200 or less. Provided is a liquid crystal display element which is excellent in low power consumption. SOLUTION: The liquid crystal composition is selected so that the effective voltage of the device is 1.5 V or less, and as an alignment film material,
A high molecular substance containing fluorine such as a fluorine-containing polyimide is used.

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 device that can be driven at a low voltage.

[0002]

2. Description of the Related Art In applications such as mobile information terminals and mobile phones,
From the viewpoint of weight reduction and extension of battery life, a liquid crystal display element with low power consumption is required. Since power consumption is almost proportional to the frequency of the applied electric field and the square of the driving voltage,
There is a high expectation for an element that can be driven at a low voltage and can secure a good display even when driven at a low frequency.

In order to reduce the driving voltage of the liquid crystal display element, it is effective to adopt a liquid crystal composition having a low threshold voltage as a material for forming the liquid crystal layer. It is generally known that the threshold voltage decreases as the dielectric anisotropy of the liquid crystal composition increases.

However, a liquid crystal composition having a large dielectric anisotropy, which is effective only for lowering the threshold voltage, is applied to the conventional device specifications for the purpose of lowering the driving voltage, and the number of polarity reversals per second is 200. When the following low frequency driving was performed, there was a problem in that, when energized at a high temperature of about 50 ° C., display unevenness occurred in a few hours to a few tens of hours, making it unusable for practical use.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a liquid crystal display element which can be driven at a low voltage and does not cause display unevenness even when energized at a high temperature for a long time under a low frequency driving condition. The purpose is to provide.

[0006]

Means for Solving the Problems The inventors have found that the cause of the above-mentioned display unevenness that occurs when electricity is applied at a high temperature is due to ionic impurities common to liquid crystal compositions having a large dielectric anisotropy. We thought that it had low resistivity, and studied various ways to increase its resistivity, but we could not achieve the purpose.

Then, from a different viewpoint, as a result of conducting a study focusing on the relationship with the characteristics of the alignment film layer, surprisingly, a large full-dot display in which the conventional high pretilt property is used to achieve a high contrast is realized. In the field of devices and the like, a liquid crystal having a large dielectric anisotropy can be obtained by using an alignment film made of a polymer substance containing fluorine, which has been applied only to high frequency driving in which the number of polarity reversals per second is 500 or more. It has been found that the problem of display unevenness can be solved even when it is combined with a composition, and the present invention has been completed.

That is, the present invention is the following inventions. [1] The alignment film layers of the two substrates on which the alignment film layers are formed on the transparent electrode have a crossing angle of 80 ° to 30 between their alignment directions.
A nematic liquid crystal composition having a positive dielectric anisotropy is enclosed between them so that they face each other at 0 °, and a polarizing plate is arranged outside at least one of the substrates. In a liquid crystal display device driven at a low frequency of 200 or less, the 50% threshold voltage value is 1.5V.
A liquid crystal display device characterized by the following, wherein the alignment film layer is composed of a polymer substance containing fluorine.

[2] The liquid crystal display device according to [1], wherein the polarizing plate is arranged outside both substrates. [3] The fluorine-containing form in the polymer substance is at least one selected from the form of bistrifluoromethylmethylene and the form in which all hydrogen atoms other than the bonding site of the aromatic ring are replaced with fluorine [1] or The liquid crystal display device according to [2]. [4] The content ratio of fluorine in the polymer substance is 1 carbon atom.
5 to 70 fluorine atoms per 00 [1],
The liquid crystal display element according to [2] or [3]. [5] The liquid crystal display device according to [1], [2], [3] or [4], wherein the liquid crystal composition has a dielectric anisotropy of +19 or more. [6] The liquid crystal display device according to [2], wherein a retardation film having an optical compensation function or a liquid crystal layer for interference is provided on at least one of the polarizing plate and the substrate arranged on both sides. [7] The crossing angle of the orientation direction is 160 ° to 270 °,
The liquid crystal display element according to [1], wherein the liquid crystal composition contains an optical rotatory substance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is important to use an alignment film made of a polymer substance containing fluorine. The structure and the like of the polymer substance containing fluorine is not particularly limited, but from the viewpoint of the resistivity of the alignment film, carbon atoms of 100
Those containing 5 to 70, especially about 10 to 30, fluorine per unit, and those having a polyimide structure can be preferably used from the viewpoint of heat resistance of the film, liquid crystal resistance, film formability and the like. .

The form of fluorine contained in the polymer substance may be a form of a bonding group such as a perfluoroalkylene group, an oxyperfluoroalkylene group, a perfluoroarylene group or an oxyperfluoroarylene group, or a fluorine atom. Examples of the form of the substituents include a perfluoroalkyl group, a perfluoroalkoxy group, a perfluoroaryl group, and an oxyperfluoroaryl group. However, from the viewpoint of easy availability, film stability, etc. The form of bistrifluoromethylmethylene or the form in which all hydrogen atoms other than the bonding site of the aromatic ring are replaced with fluorine can be preferably used.

The specific resistance (25 ° C.) of the orientation film made of the above-mentioned fluorine-containing polymer substance is usually 1 × 10 ¹² Ω.
cm or less. The thickness of the alignment film layer is not particularly limited, but if it is too thin, the orientation may be defective, and if it is too thick, the contrast may be deteriorated. Therefore, it is preferably selected from the range of 20 nm to 80 nm.

In the present invention, the 50% threshold voltage means
It means the voltage at which the value of the transmittance becomes the average value of the maximum value and the minimum value when the target liquid crystal display element is statically driven. And it is important that this value is 1.5 V or less.

In order to lower the threshold voltage, it is generally effective to use a liquid crystal composition having a large dielectric anisotropy, and for example, a liquid crystal composition having a value of +19 or more is preferably used. A typical example is a composition containing a fluorocyanophenyl ester-based liquid crystal substance. The specific resistance (25
C.) is usually 7 × 10 ¹⁰ Ωcm or less.

In the present invention, the twist angle of the liquid crystal molecule between both electrodes is 80 ° to 300 °, preferably 160 ° to 2
It is set to 70 °. This is because if the twist angle is too small, the change in the state of the liquid crystal during time-division driving is small, and if it is too large, hysteresis and domains that scatter light are likely to occur.

Next, the overall structure of the liquid crystal display device of the present invention will be described. ITO (In ₂ O ₃ —SnO ₂ ) patterned into a desired pattern, plastic provided with a transparent electrode such as SnO ₂ or the like, a film of the above-mentioned fluorine-containing polymer substance is provided on the surface of a substrate such as glass, The surface is subjected to an alignment treatment by a method such as rubbing, and a liquid crystal layer of 80 ° to 300 ° twist made of nematic liquid crystal having a positive dielectric anisotropy is twisted between the substrates with the transparent electrodes on which the alignment film layers are formed. It is supposed to be pinched.

This element can be used as a transmissive type using a backlight, a reflective type using a reflecting plate, and a semi-transmissive type using a semi-transmissive reflecting plate. Furthermore, a color filter is provided on one substrate. A layer may be provided and used as a color display element.

In the case of a liquid crystal display device in which a retardation film having an optical compensation function or a liquid crystal layer for interference is provided on at least one of a polarizing plate and a substrate arranged on both sides, these are not provided. Since the display becomes more noticeable because the contrast is larger than that of the element, the effect of the present invention becomes more remarkable when applied to such an element.

FIG. 1 shows an embodiment in which the present invention is applied to a transmissive liquid crystal display device. In FIG. 1, the backlight, the light guide plate, etc. located below the lower substrate are omitted. In this example, one retardation film is used, but it may be replaced with an interference liquid crystal layer, or it may be omitted, or two retardation films may be provided above and below. FIG. 2 shows an embodiment in which the present invention is applied to a reflective liquid crystal display device. Also in this case, various modifications are possible.

The liquid crystal display device of the present invention is driven at a low frequency where the number of polarity reversals per second is 200 or less, and in order to reduce the power consumption, the polarities are reversed every frame where it becomes about 50 to 100. A driving method is preferably adopted. In an element which is driven at a high frequency with this value being, for example, 500 or more, even if the 50% threshold voltage is 1.5
Even if the problem of uneven power distribution does not occur at V or less, the purpose of reducing power consumption is not achieved.

Further, the liquid crystal display device of the present invention is preferably applicable to applications in which the duty ratio is driven at about 1/8 to 1/65. For example, a fish finder, an in-vehicle instrument panel, an information terminal, an industrial information display device (for example, an operation status display on a control panel of a copying machine or an operation display of a power device), various dot matrixes for consumer use. It can be used as a functional element having a display function of a display device (audio device, clock, game device, amusement, communication device, car navigation, camera, TV phone, calculator display).

In particular, since the liquid crystal display device of the present invention can be used with a low driving voltage and a low power consumption, portable electronic devices such as a mobile phone, an electronic notebook, an electronic book, an electronic dictionary, and a PDA (mobile phone) are used. It is effective when used for information terminals, pagers (pagers), etc. Further, the present invention can be applied in various ways within a range that does not impair the effect.

[0023]

Example A transparent conductive film having a sheet resistance of about 100 Ω / □ was provided on a glass substrate, and a stripe-shaped electrode pattern was formed by photolithography. An insulating film made of silica and titania is formed thereon to a thickness of about 50 nm, and a predetermined alignment film material is applied by a printing method and baked to give a thickness of 40 nm.
An alignment film layer having a thickness of 10 nm was formed. The surface of the alignment film layer was subjected to alignment treatment by a rubbing method. The orientation direction was set so that the crossing angle was 240 ° when the cells were assembled.

After screen-printing a sealing material made of a thermosetting epoxy resin on one of a pair of upper and lower substrates in a predetermined shape, and spraying plastic beads as spacers on the other to keep the gap between the substrates constant. The two were superposed at a predetermined position and thermocompression bonded to each other. As the spacer, the gap between the substrates when the cell is assembled is 6 μm.
Was selected.

A predetermined liquid crystal composition was injected into the empty cell thus prepared by a vacuum injection method and sealed with an epoxy resin.
Using the evaluation element prepared as described above, the combination of the enclosed liquid crystal composition and the alignment film material was changed to 1/3.
Under a driving condition of 2 duty-1 / 7 bias, the number of polarity reversals 70 per second (polarity inversion for each frame),
An energization test at 50 ° C. was performed.

Example 1 A liquid crystal composition having a dielectric anisotropy of +22 and a refractive index anisotropy of 0.147, pyromellitic dianhydride and 4 ″, 4 ″ ′-(hexa The fluorine content (the number of fluorine atoms per 100 carbon atoms) formed by using an equimolar polycondensate with fluoroisopropylidene) bis (4-phenoxyaniline) as a raw material is 16.2, and the form of fluorine content is When combined with the fluorine-containing polyimide-based alignment film material, which is bistrifluoromethylmethylene, display unevenness was not observed even after continuous energization for 200 hours, and uniform display was maintained. The 50% threshold voltage at this time was 1.39V.

Example 2 A liquid crystal composition similar to that of Example 1, 1,4-bis (3,4-dicarboxytrifluorophenoxy) -tetrafluorobenzene dianhydride and bis (2,3,3) 5,6-Tetrafluoro-4-aminophenyl) -ether and an equimolar polycondensate of the same film were used as a raw material to form a film, and the fluorine content (same as above) was 53. Even when combined with a perfluoropolyimide-based alignment film material in which all hydrogen is replaced by fluorine, no uneven display is observed even after continuous energization for 200 hours, and uniform display is maintained. Was done. The 50% threshold voltage at this time was also 1.37V.

[Comparative Example 1] When a liquid crystal composition similar to that of Example 1 was combined with a usual polyimide-based alignment film material containing no fluorine, display unevenness occurred 4 hours after the start of energization. The 50% threshold voltage was 1.45V.

[Comparative Example 2] When a liquid crystal composition having a dielectric anisotropy of +10 and a refractive index anisotropy of 0.146 and the same alignment film material as in Example 1 were combined, energization was started. 48 hours later, display unevenness became remarkable. The 50% threshold voltage was 2.06V.

[Comparative Example 3] When a liquid crystal composition similar to that of Comparative Example 2 and an alignment film material similar to that of Comparative Example 1 are combined, display unevenness occurs even after continuous energization for 200 hours. It was not observed and a uniform display was maintained. The 50% threshold voltage at this time was 2.14V.

[0031]

The liquid crystal display device of the present invention can be driven at a low voltage and the number of polarity reversals per second is 20.
Under low frequency drive condition of 0 or less, uniform display is maintained even when energized at high temperature of about 50 ° C. for a long time, and it has excellent low power consumption, and is particularly useful as a display element for portable electronic devices. is there.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment in which the present invention is applied to a transmissive liquid crystal display device.

FIG. 2 is a sectional view of an embodiment in which the present invention is applied to a reflective liquid crystal display device.

[Explanation of symbols]

 1: Substrate 2: Transparent electrode 3: Alignment film layer 4: Liquid crystal layer 5: Polarizing plate 6: Sealing material 7: Spacer 8: Phase difference film 9: Reflector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Uehara 1-2-1 Kamisakabe, Amagasaki City, Hyogo Prefecture Optrex Co., Ltd. Amagasaki Plant

Claims (7)

[Claims] 1. An alignment film layer of two substrates, each having an alignment film layer formed on a transparent electrode, having a crossing angle of 80 ° between their alignment directions.
A nematic liquid crystal composition having a positive dielectric anisotropy is sealed between them so as to face each other at an angle of ˜300 °, and a polarizing plate is arranged on the outside of at least one of the substrates. In a liquid crystal display device driven at a low frequency with the number of inversions of 200 or less, the 50% threshold voltage value is 1.
A liquid crystal display device having a voltage of 5 V or less and the alignment film layer made of a polymer substance containing fluorine. 2. The liquid crystal display device according to claim 1, wherein the polarizing plate is arranged outside both substrates. 3. The polymer containing substance has at least one fluorine-containing form selected from the form of bistrifluoromethylmethylene and the form in which all hydrogen atoms other than the bonding site of the aromatic ring are replaced with fluorine. 3. The liquid crystal display device according to 1 or 2. 4. The liquid crystal display device according to claim 1, 2 or 3, wherein the content of fluorine in the polymer substance is 5 to 70 fluorine atoms per 100 carbon atoms. 5. The liquid crystal display device according to claim 1, wherein the liquid crystal composition has a dielectric anisotropy of +19 or more. 6. The liquid crystal display device according to claim 2, wherein a retardation film having an optical compensation function or a liquid crystal layer for interference is provided on at least one of the polarizing plate and the substrate arranged on both sides. 7. The liquid crystal display device according to claim 1, wherein the crossing angle of the alignment direction is 160 ° to 270 °, and the liquid crystal composition contains an optical rotatory substance.