JPH10148835A - Liquid crystal alignment layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal alignment layer which obviates the deterio ration in its electrical characteristics in photoirradiated parts in spite of irradia tion of the surface of this liquid crystal alignment layer with light, is free from the problem of after images and has good visual field angle characteristics. SOLUTION: The liquid crystal alignment layer which has aligned liquid crystal molecules used in an liquid crystal display element has the parts which are formed by irradiating the prescribed points of its surface with the light and are different in the capability to incline the liquid crystal molecules from the non-irradiated parts. The internal offset voltage (Vcdc shift value) generated when the photoirradiated parts and the non-irradiated parts are disposed to face each other and voltage is impressed thereon is specified to >=100mV. The Vcdc shift value of >=l00mV is attained by adding a suitable amt. of UV absorbents, such as a benzophenone based UV absorbent, benzotriazole based UV absorbent and the metal salt of dialkyl dithiocarbamic acid, to the liquid crystal alignment layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal alignment film which is manufactured so that the alignment of liquid crystal molecules is partially different, has no problem such as an afterimage, and has a good viewing angle characteristic.

[0002]

2. Description of the Related Art A liquid crystal alignment film is generally used for a liquid crystal display device, in which liquid crystal molecules are aligned in a certain direction, that is,
It is provided because it needs to be oriented. Liquid crystal display elements are conventionally used for displays such as watches, calculators, computers, word processors, and the like, and the structure is usually
The basic structure is such that two substrates each having a liquid crystal alignment film formed on a transparent electrode are combined with the liquid crystal alignment film inside, and a liquid crystal is sealed between them.

As such a liquid crystal display element, a display in a twisted nematic (TN) mode in which a nematic liquid crystal has a twisted structure or a super twisted nematic (STN) mode is known. In addition, as the driving of the liquid crystal display element, a matrix display in which electrodes are formed in a display pattern such as a stripe or a grid on a substrate, and a method using a thin film transistor (TFT) are known. Something comparable to a normal CRT has been realized. However, these liquid crystal display elements have a disadvantage that the viewing angle is narrow.

[0004] In order to improve the disadvantage of a narrow viewing angle, several methods have been proposed. For example, a double rubbing method in which the liquid crystal alignment film is rubbed and patterned with a resist and then rubbed in the opposite direction, or a method in which the liquid crystal alignment film has a two-layer structure (94 latest LCD technology, page 91),
Further, a method of irradiating the surface of the liquid crystal alignment film with ultraviolet light, visible light, infrared light or laser light to improve the viewing angle characteristics (JP-A-6-281937, JP-A-7-36047, JP-A-7-36047, 209,651).

[0005]

However, the above-mentioned double rubbing method and the method of forming the liquid crystal alignment film into a two-layer structure involve a patterning step using a resist, so that the manufacturing cost is high and the conventional method is difficult. The alignment film material has a problem of solvent resistance. JP-A-6-281937 and JP-A-7-281
The methods proposed in JP-A-36047 and JP-A-7-209651 can improve the viewing angle characteristics and provide a liquid crystal display device at low cost. In addition to the deterioration of the characteristic, there is a problem of an afterimage. An object of the present invention is to solve the above-mentioned problems of the prior art, and to irradiate the surface of a liquid crystal alignment film with light, without causing a problem of deterioration of electric characteristics and an afterimage of a light irradiation portion, and of viewing angle characteristics. An object is to provide a good liquid crystal alignment film.

[0006]

Means for Solving the Problems The present inventors have paid attention to the fact that the deterioration of the electrical characteristics and the problem of the afterimage occur in the light-irradiated portion due to the light irradiation. It has been found that it is important that the internal offset voltage (hereinafter, also simply referred to as “Vcdc shift value”) generated when a voltage is applied by facing a portion not irradiated with light is 100 mV or less. 100
The inventors have found that a Vcdc shift value of mV or less can be achieved by adding an appropriate amount of an ultraviolet absorber to a liquid crystal alignment film, and thus completed the present invention. That is, the present invention is the following liquid crystal alignment film. (1) A liquid crystal alignment film for aligning liquid crystal molecules used in a liquid crystal display element. The film is formed by irradiating a predetermined portion of the surface with light, and has a non-irradiation ability to tilt the liquid crystal molecules. A liquid crystal alignment film having a portion different from the portion and having an internal offset voltage (Vcdc shift value) of 100 mV or less when a voltage is applied with the light-irradiated portion and the non-light-irradiated portion facing each other. . (2) A liquid crystal alignment film for aligning liquid crystal molecules used in a liquid crystal display element, the film containing an ultraviolet absorber, and formed by irradiating a predetermined portion of the film surface with light. A liquid crystal alignment film having portions with different ability to tilt liquid crystal molecules. (3) the ultraviolet absorber is a benzophenone-based ultraviolet absorber,
The liquid crystal alignment film according to the above (2), which is one or more selected from a benzotriazole-based ultraviolet absorber and a metal salt of a dialkyldithiocarbamic acid. (4) The content of the ultraviolet absorber is equal to the resin amount of the liquid crystal alignment film 1
The liquid crystal alignment film according to any one of the above (2) and (3), wherein the content is 0.01 to 5.0 parts by weight based on 00 parts by weight.

Generally, the ability of a liquid crystal alignment film to tilt liquid crystal molecules is represented by an angle (pretilt angle) formed between the liquid crystal alignment film and the liquid crystal molecules. The Vcdc shift value is measured by the following method. [Measurement of Vcdc shift value] ITO (Indium Tin Oxid
e) Substrate with transparent electrode (size: 3cm x 4cm)
The substrate having a liquid crystal alignment film formed thereon was irradiated with light of a predetermined intensity, and the substrate having a liquid crystal alignment film as described above and having not been irradiated with light was moved in the rubbing direction. Are assembled so as to face each other at 90 ° with a gap of 5 μm, the periphery is sealed with an epoxy adhesive, and the liquid crystal ZLI-4792 is added to the test liquid crystal cell at room temperature.
(Vcdc shift value measurement cell) was sealed therein, heated at 130 ° C. for 60 minutes in advance, and then a rectangular wave of ± 3 V and a frequency of 30 Hz was applied at 70 ° C. for 1 hour. The accumulated DC voltage is measured by the flicker cancellation method, and is set as a Vcdc shift value.

When the Vcdc shift value exceeds 100 mV,
Afterimages tend to occur not only when the display is long but also when the display is short. Also, this value is preferably as small as possible.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The ultraviolet absorbent used in the present invention is a compound that strongly absorbs ultraviolet light having a wavelength of 250 to 400 nm and re-radiates the energy mainly as heat energy. The absorption intensity is 250n
When expressed as a molar extinction coefficient (ε) at the maximum absorption wavelength from m to 400 nm, it is approximately 5 × 10 ⁶ (cm ² / mol;
(In chloroform). Such compounds include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-
4-octoxybenzophenone, 2-hydroxy-4-
Dodecyloxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- Benzophenone-based compounds such as 5-benzoylphenyl) methane,

2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-ter
t-butylphenyl) benzotriazole, 2- (2 ′
-Hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2-
(2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole, 2-
(2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- {2'-hydroxy-3'-(3 ", 4", 5 ", 6"- Tetrahydrophthalimidomethyl) -5'-methylphenyl {benzotriazole, 2,2-methylenebis} 4- (1,1,
Benzotriazole-based compounds such as 3,3-tetramethylbutyl) 6- (2H-benzotriazol-2-yl) phenol {2- (2'-hydroxy-4'-octylphenyl) benzotriazole;

Salicylic acid compounds such as phenyl salicylate, p-tert-butylphenyl salicylate and p-octylphenyl salicylate;

2-ethylhexyl-2-cyano-3,
3'-diphenyl acrylate, ethyl-2-cyano-
Cyanoacrylate compounds such as 3,3′-diphenylacrylate,

Metal salts of dialkyldithiocarbamic acids such as nickel dibutyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, potassium dimethyldithiocarbamate, and terium diethyldithiocarbamate. These compounds may be used as a mixture of two or more kinds.

The amount of the ultraviolet absorber used is such that the Vcdc shift value is 100 mV or less, or the added ultraviolet absorber does not seep into the liquid crystal layer and impair the reliability of the liquid crystal display device. Is preferably 0.01 to 5.0 parts by weight based on 100 parts by weight of the resin.

In the present invention, as a polymer material of a liquid crystal alignment film serving as a base, many kinds of organic polymer materials usually used as a liquid crystal alignment film can be used. Examples of such organic polymer materials include polyimide resins such as polyimide resins, polyamide imide resins, polyester imide resins, and polyether imide resins, as well as polyamide resins, polystyrene resins, epoxy acrylate resins, polyurethane resins, and the like. There are resins and the like as components. The polyimide resin is used to include a polyimide precursor in addition to polyimide. Examples of the polyimide precursor include polyamic acid, a polyamic acid in which polyamic acid is partially imidized, and polyisoimide. The polyimide resin can be produced by reacting a tetracarboxylic dianhydride (including a derivative) and a diamine compound (including a derivative).

The liquid crystal alignment film of the present invention is prepared by dissolving both the organic polymer material and the ultraviolet absorber in an organic solvent capable of dissolving the same, and forming the film on a suitable electrode substrate such as a glass substrate on which a transparent electrode such as ITO is previously formed. It is applied and heated and dried to produce. Here, the application method is not particularly limited, but a method such as spin coating, dipping, printing, or spraying can be used. The temperature for heating and drying is not particularly limited, and is appropriately selected depending on the organic polymer material and the organic solvent used. Usually at the temperature at which the organic solvent evaporates,
The reaction is performed at a temperature of 50 to 250 ° C, preferably 150 to 230 ° C.

When a polyimide precursor such as polyamic acid is used as the organic polymer material of the liquid crystal alignment film, the temperature for heating and drying is set to a temperature not lower than the temperature at which the polyimide precursor such as polyamic acid is closed to an imide. For that purpose, the heating and drying temperature is 150 to 250 ° C, preferably 180 to 250 ° C.
250 ° C. The heating / drying time varies depending on the heating / drying temperature and is not particularly limited, but usually, an optimal time is appropriately selected in the range of 1 minute to 6 hours. In order to improve the adhesion between the substrate and the liquid crystal alignment film, a coupling agent such as a silane coupling agent or a titanium coupling agent may be used between the substrate and the liquid crystal alignment film.

The type of light used here is, for example,
UV, Deep UV, etc., these lights are high pressure mercury lamps,
It can be obtained by using a lamp such as a mercury-xenon lamp, a low-pressure mercury lamp, and a metal halide lamp. Also, an excimer laser which is a high-power ultraviolet laser can be used. The intensity (amount) of the light to be irradiated is such that the difference between the pretilt angle of the liquid crystal alignment film / liquid crystal molecules not irradiated with light and the pretilt angle of the liquid crystal alignment film / liquid crystal molecules irradiated with light is preferably 3 degrees or more. More preferably, the strength is set to be 4 degrees or more. Such light intensities are typically in the range of 0.1 to 30 Joules (J) / cm ² . 0.1J /
If it is smaller than ² cm ^2, it is difficult to produce a pretilt angle difference of 3 degrees or more, and if it exceeds 30 J / cm ² , the alignment film is deteriorated, causing problems in reliability and the like. The time of light irradiation is not particularly limited. It may be any time, such as after applying polyimide on the substrate, after drying, or after rubbing.

A liquid crystal alignment film is formed on an electrode substrate such as a glass plate provided with a transparent electrode of ITO or the like, and a pair of the substrates is opposed to each other, and a liquid crystal is held between the electrode substrates to form a liquid crystal holding substrate. Can be. In this case, the liquid crystal alignment film formed on the other electrode substrate of the liquid crystal holding substrate has the same ability to tilt the liquid crystal molecules (pretilt angle) over the entire surface, and the ability (pretilt angle) is the same as that of the non-irradiated light. It may be a film having a value between the irradiated one. A liquid crystal display device having a liquid crystal holding substrate can be obtained by a known method using the above liquid crystal holding substrate.

[0020]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Synthesis Example 1 16.0 g of N-methyl-2-pyrrolidone was placed in a four-necked flask equipped with a stirrer, a nitrogen inlet tube, a drying tube, and a thermometer.
And 0.242 g of paraphenylenediamine (2.24 mm
ol) and stirred. The flask was immersed in a water bath, and 1.56 g (2.98 mmol) of decamethylene bistrimellitate dianhydride was added while introducing nitrogen. After stirring in a water bath for 30 minutes, paraphenylenediamine 0.242
g (2.24 mmol) and 0.591 g (2.98 mmol) of 4,4'-diaminodiphenylmethane, and 5 minutes later, 3,3'4,4'-bicyclohexyltetracarboxylic dianhydride. 37g (4.47mm
ol) and stirred for 5 hours to obtain a polyamic acid solution.

Examples 1 to 15 and Comparative Examples To a certain amount of the polyamic acid solution obtained in Synthesis Example 1,
Various ultraviolet absorbers shown in Table 1 were added to various concentrations,
They were mixed and diluted with N-methylpyrrolidone so that the solid content was 5% by weight. These diluted solutions (hereinafter referred to as “additive-containing liquids”) are spin-coated on two glass substrates with ITO transparent electrodes, preliminarily dried at 70 ° C. for 1 minute, and then one of them is coated with a mercury-xenon lamp. Was irradiated at a light irradiation amount of 1 J / cm ² , then heated at 180 ° C. for 60 minutes to perform full curing, and then rubbed to obtain a liquid crystal alignment film.

The rubbing directions of the two substrates are set to 9
The polyimide layers are combined so as to face each other at 0 ° and a gap of 5 μm.
The c shift value was determined.

On the other hand, the pretilt angle measuring cell is prepared by spin-coating the above-mentioned “additive-containing liquid” onto four (2 × 2) glass substrates with ITO transparent electrodes and pre-drying at 70 ° C. for 1 minute. Two of them were not irradiated with light, and the other two were irradiated with a light irradiation of 1 J / cm ² , then heated at 180 ° C. for 60 minutes for full curing, and then rubbed to obtain a liquid crystal alignment. The two substrates are rubbed in antiparallel directions with a gap of 25.
Polyimide layers were combined so as to face each other so as to have a thickness of μm, and the periphery thereof was sealed with an epoxy-based adhesive to produce the same. After heating the pretilt angle measuring cell at 130 ° C. for 60 minutes, the pretilt angle was measured by a crystal rotation method.

Table 1 shows the measurement results. The pretilt angles of the UV absorber addition group were 1 J /
4.9 to 6.5 degrees as compared with that irradiated with light of cm ² , and a large difference of 6.6 degrees in the pretilt angle value (difference between both) without the addition of an ultraviolet absorber (comparative example). There is no. On the other hand, the Vcdc shift value of the UV absorber-added group was 0 to 90 mV, which was 220 mV when the UV absorber was not added (Comparative Example).
It can be seen that it is significantly smaller than V.

[0023]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ No. Additive Additive amount Pretilt angle (degree ) Vcdc shift value (parts by weight *) 0 J / cm ² 1J / cm ² (mV) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━━1 2- (2'-hydroxy-5'-methyl 0.2 6.5 1.0 80 phenyl) benzotriazole 2 〃 0.5 6.3 0.8 90 3 〃 0.1 6.5 0.7 904 4 ４ 1.0 6.5 0.6 90 5 2,4 -Dihydroxybenzophene 0.2 6.7 0.5 70 Non 6 〃 0.5 6.5 0.8 40 7 2,2'-Dihydroxy-4,4'-di 0.2 5.9 1.0 0 Methoxybenzophenone 8 〃 0.5 6.3 1.2 50 9 2-Hydroxy-4'-n -Octy 0.2 6.3 0.5 30 Luoxybenzophenone 10 〃 0.5 6.7 0.6 0 11 N, N-dibutyldithiocarba 0.05 7.0 0.5 80 Nickel mate 12 〃 0.1 6.8 0.5 30 13 〃 0.2 6.2 0.3 0 14 〃 0.5 6.0 0.5 70 15 〃 1.0 5.5 0.3 70 Comparison None − 7.0 0.4 220 ━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ * parts by weight with respect to the polyamic acid solid content 100 parts by weight

[0024]

When the liquid crystal alignment film of the present invention is used, even if the liquid crystal alignment film surface is irradiated with light, there is no problem that the electrical characteristics of the light-irradiated portion are deteriorated, there is no problem of afterimage, and there is no problem of viewing angle characteristics. Is good.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshihiko Kato 48 Wadai, Tsukuba, Ibaraki Prefecture Within Tsukuba Development Laboratory, Hitachi Chemical Co., Ltd.

Claims (4)

[Claims] 1. A liquid crystal alignment film for aligning liquid crystal molecules used in a liquid crystal display device, the film being formed by irradiating a predetermined portion of a surface with light, and having a capability of tilting the liquid crystal molecules. It has a portion different from the non-irradiated portion, and an internal offset voltage (Vcd) generated when a voltage is applied with a portion irradiated with light and a portion not irradiated with light.
(c shift value) is 100 mV or less. 2. A liquid crystal alignment film for aligning liquid crystal molecules used in a liquid crystal display element, the film containing an ultraviolet absorber, and formed by irradiating a predetermined portion of the film surface with light. Liquid crystal alignment film having portions having different ability to tilt the liquid crystal molecules. 3. The liquid crystal alignment film according to claim 2, wherein the ultraviolet absorber is one or more selected from a benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and a metal salt of dialkyldithiocarbamic acid. 4. The liquid crystal alignment film according to claim 2, wherein the content of the ultraviolet absorber is 0.01 to 5.0 parts by weight based on 100 parts by weight of the resin of the liquid crystal alignment film.