JPH052170A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To increase a contrast by sealing a ferroelectric liquid crystal compsn. into a cell disposed with two sheets of electrode substrates formed with oriented layers consisting of specific silicon compds. in such a manner that the oriented layers exist on the inner side. CONSTITUTION:This liquid crystal display element is constituted by sealing the ferroelectric liquid crystal compsn. 30 into the cell constituted by disposing two sheets of the electrode substrates 10, 20 formed with the oriented layers 14, 24 consisting of at least one kind of the silicon compds. selected form the silicon compds. expressed by formula I on the surfaces of transparent electrodes 12, 22 on substrates 11, 21 in such a manner that the oriented layers exist on the inner side. In the formula I, R denotes CmF2m+1-or CmH2m+1(m is 5 to 25 integer); R<1> to R<3> independently denote 1 to 5C alkoxy group or 1 to 5C alkyl group; n denotes 0 to 5 integer. Both of the transparent electrodes 12, 22 are formed to stripe shapes and the transparent electrodes 12, 22 are so combined that the shapes of the stripes intersect orthogonally with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, liquid crystal display elements used in clocks, computers, word processors, etc.
As its basic structure, it is usual that two transparent electrode substrates each having an alignment film provided on a transparent electrode are arranged with the alignment film inside, and a liquid crystal is sealed between them. The transparent electrode of such a liquid crystal display device is generally formed on the substrate in the form of a display pattern such as a stripe pattern or a grid pattern, and the alignment film is formed on the transparent electrode and the exposed substrate (other than the display pattern). Is provided by coating or vapor deposition. The two transparent electrode substrates are respectively arranged with the alignment film inside, and a ferroelectric liquid crystal is sealed between them to manufacture a liquid crystal display element. Therefore, the enclosed liquid crystal is generally in contact with only the alignment film. In general, the alignment film is required to align the liquid crystal in a certain direction, that is, to align the liquid crystal,
It is provided, and the liquid crystal molecules are aligned by this.

The mainstream of such a liquid crystal display device is a display in a twisted nematic (TN) mode in which a nematic liquid crystal has a twisted structure. However, this TN type liquid crystal display element has a drawback that the response speed is slow and the limit is 20 milliseconds under the present circumstances, which is a big problem when it is used for a television panel or the like which requires high speed response. Is becoming

On the other hand, recently, a ferroelectric liquid crystal having a high-speed response has been expected and studied as a new field of display.

Ferroelectric liquid crystals not only respond rapidly to changes in the electric field, but also take one of a first optical stable state and a second optical stable state in response to an applied electric field. In addition, it also has a property of maintaining its state when no voltage is applied, that is, a memory property (also called bistability). Therefore, in the liquid crystal display device using the ferroelectric liquid crystal, it is sufficient to apply the pulse voltage only when switching between the two states, so that the power supply and the electronic circuit for maintaining the optical state as in the past are not necessary. Therefore, the power consumption is reduced as compared with the conventional liquid crystal display element. That is, it can be said that the liquid crystal display element using the ferroelectric liquid crystal is a liquid crystal display element having a simple structure and realizing high-speed response.

In order to switch the above two optical stable states at high speed and surely and to improve the memory property, it is necessary to orient the ferroelectric liquid crystal uniformly. In order to align the ferroelectric liquid crystal, it is general to use an organic thin film as the alignment film, and a film obtained by rubbing the organic thin film, or a film obtained by obliquely depositing an inorganic oxide as the alignment film.

A rubbing polyimide film is generally used as the alignment film. The rubbing polyimide film is obtained by using, for example, polyamic acid which is a polyimide precursor, pyridine, N-methyl-2-pyrrolidone, dioxane, and TH.
A solution prepared by dissolving F, a glycol derivative or the like in an appropriate solvent is prepared, and the solution is applied onto a transparent electrode by spin coating or the like, dried at room temperature to 150 ° C., and the dried coating film is then dried at 200 to 300 ° C. It is formed by heating at a temperature to form a polyimide film, and then rubbing the polyimide film with synthetic fibers such as nylon, polyester, polyacrylonitrile, etc., and natural fibers such as cotton, wool, etc.

Although this rubbing polyimide film sufficiently aligns the liquid crystal, it has a problem that a heat treatment at a very high temperature of 200 to 300 ° C. is required in the process of forming the polyimide film. In particular, in the case of a color filter type color liquid crystal display element, the color filter is provided in contact with the transparent electrode, and the color filter also has a high temperature during the high temperature heat treatment when forming the polyimide film on the transparent electrode. Since it is heated, there is a problem that the color filter is easily deteriorated. Therefore, it is desired to form the alignment film at a relatively low temperature that does not affect the characteristics of the color filter.

It is also known to use a rubbing silane film as the alignment film. For example, Proceedings of the 14th Liquid Crystal Discussion Session, p. 132 to 133 disclose that an amino silane coupling agent is used as an alignment film on a transparent electrode. However, the liquid crystal display element in which the alignment film made of an amino-based silane coupling agent is provided on the transparent electrode has a small pretilt angle and a light-dark ratio and a small contrast, as shown in a comparative example described later.

The Japanese Journal of Applied Phys
ics, Vol.29, No.9, September 1990, L1689 to L16
On page 92, 18-nonadecenyltrichlorosilane and 3 are described as alignment films for liquid crystal devices using nematic liquid crystals.
Forming a chemisorption monolayer of -bromopropylenyltrichlorosilane is disclosed. However, even when such a compound is used as an alignment film of a ferroelectric liquid crystal display device, the pretilt angle and the contrast ratio are small and the contrast is small.

[0011]

DISCLOSURE OF THE INVENTION The present invention is provided with an alignment layer which can be formed under mild conditions without adversely affecting other components of the liquid crystal display element, and has a pretilt angle and a light-dark ratio. Provided is a ferroelectric liquid crystal display device having a large size and therefore a large contrast.

[0012]

According to the present invention, a transparent electrode is provided on a substrate, and the general formula (1):

[0013]

[Chemical 2]

[Wherein R is C _m F _{2m + 1} -or C _m H _{2m + 1}
-(However, m is an integer of 5 to 25) is a group represented by R ¹ , R ² and R ³ each independently having 1 carbon atom.
To an alkoxy group having 1 to 5 carbon atoms or an alkyl group having 1 to 5 carbon atoms, and n is an integer of 0 to 5], and an alignment layer made of at least one silicon compound selected from the silicon compounds is formed. A liquid crystal display device characterized in that a ferroelectric liquid crystal composition is enclosed in a cell constituted by arranging two electrode substrates so that an alignment layer faces inside.

The preferred embodiments of the liquid crystal display device of the present invention are as follows. 1) The liquid crystal display device, wherein the contact angle of water on the surface of the alignment layer is 75 ° or more at 25 ° C, preferably 75 to 87 °.

2) The thickness of the alignment layer is 1 to 500 nm.
The above liquid crystal display device is characterized in that

3) The liquid crystal display characterized in that the alignment layer is formed by applying the solution of the above silicon compound, drying it, and then subjecting the surface of the formed film to a rubbing treatment. element.

4) The liquid crystal display device, wherein a color filter is provided between the substrate and the transparent electrode.

5) The liquid crystal display device, wherein an insulating film made of a metal oxide or a metal nitride is formed on the transparent electrode.

The structure of the liquid crystal display device of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a main part of an example of the liquid crystal display element of the present invention.

In FIG. 1, a liquid crystal display element 1 is a transparent electrode in which a transparent electrode 12 is provided on a transparent substrate 11, an insulating film 13 is provided thereon, and an alignment layer 14 is provided thereon. A transparent electrode substrate 20 in which a transparent electrode 22 is provided on a substrate 10 and a transparent substrate 21, an insulating film 23 is provided thereon, and an alignment layer 24 is further provided thereon.
And a ferroelectric liquid crystal composition 30 is enclosed in a cell formed by arranging so that the alignment layer 14 and the alignment layer 24 face each other.

The transparent electrodes 12 and 22 are both formed in a stripe shape, and the transparent electrodes 12 and 22 are combined so that the stripe shapes are orthogonal to each other to form a liquid crystal display device capable of matrix display. Further, the transparent electrode may be formed in a stripe shape only on one side. An insulating film for preventing a short circuit between the upper and lower electrodes is provided, but the insulating film may not be provided in some cases.

Examples of the material of the transparent substrate include glass such as float glass having good smoothness, polyester such as polyethylene terephthalate and polybutylene terephthalate, epoxy resin, phenol resin, polyimide, polycarbonate, polysulfone, polyether sulfone,
Heat-resistant resins such as polyetherimide, acetylcellulose, polyamino acid ester, aromatic polyamide, vinyl polymers such as polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polyacrylamide, polyethylene, polypropylene, and fluorine-containing polymers such as polyvinylidene fluoride Examples thereof include a film or sheet of a polymer compound formed of a resin and a modified product thereof.

Examples of the material of the transparent electrode include indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ) and ITO (indium tin oxide).
The transparent electrode is formed on the substrate in a stripe shape or a grid shape.

Examples of the material of the insulating film include metal oxides and metal nitrides.

Further, a color filter, a black mask or the like may be provided between the substrate and the transparent electrode.

For the production of the substrate, the formation of the transparent electrode, the formation of the insulating film, the color filter and the black mask, the techniques conventionally used for the production of the ferroelectric liquid crystal display element can be applied.

The orientation layers 14 and 24 are formed of at least one silicon compound selected from the silicon compounds represented by the general formula (1). In the general formula (1), R is C _m F _{2m + 1} − or C _m H _{2m + 1} − (where m is 5 to 5).
Is an integer of 25), for example, C
_{F 3 (CF 2) 4 -} , CF 3 (CF 2) 5 -, CF 3 (CF 2)
_{7 -, CF 3 (CF 2} ) 10 -, CF 3 (CF 2) 11 -, CF 3 (C
_{F 2) 15 -, CF 3} (CF 2) 24 -, CH 3 (CH 2) 4 -, CH
_{3 (CH 2) 10 -,} CH 3 (CH 2) 17 -, CH 3 (CH 2) 21 -,
CH ₃ (CH _{2) 24} -, and the like. R ¹ , R
² and R ³ are each independently an alkoxy group having 1 to 5 carbon atoms or an alkyl group having 1 to 5 carbon atoms, for example,
Methoxy group, ethoxy group, propoxy group, butoxy group,
Examples thereof include a pentoxy group, a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. n is 0
It is an integer of 5.

Among the silicon compounds represented by the general formula (1), the particularly preferable examples of the compounds are the following compounds. _{(S-1): CF 3} (CF 2) 7 CH 2 CH 2 Si (CH 3) (OCH 3) 2 (S-2): CH 3 (CH 2) 17 Si (OC 2 H 5) 3 (S _{-3): CH 3 (CH 2} ) 21 Si (OC 2 H 5) 3 (S-4): CF 3 (CF 2) 11 CH 2 CH 2 Si (OC 2 H 5) 3 (S-5): _{CF 3 (CF 2) 5 CH} 2 CH 2 Si (OCH 3) 3 (S-6): CF 3 (CF 2) 7 CH 2 CH 2 Si (OCH 3) 3

The above silicon compound is commercially available as a silane coupling agent or can be easily synthesized by a conventional method.

The alignment layers 14 and 24 are prepared by using the above silicon compound in a suitable solvent (eg, alcohol such as isopropyl alcohol, ethyl alcohol, methyl alcohol, etc., dimethylformamide, hexane, tetrahydrofuran, toluene, pyridine, triethylamine, water, The alignment layer coating solution is prepared by dissolving it in acetone or the like, and the substrate on which the transparent electrode and the insulating film are formed is immersed in the alignment layer coating solution, or the insulating film (insulating layer) on the substrate on which the transparent electrode and the insulating film are formed. When the film is not provided, it is formed on the surface of the transparent electrode) by a suitable coating method (for example, spin coating method), then the coating film is dried, and preferably the dried coating film is further heat-treated.

The contact angles of water on the surfaces of the alignment layers 14 and 24 are preferably 75 degrees or more at 25 ° C., and particularly preferably 75 to 87 degrees. When the contact angle of water on the surface of the alignment layer is smaller than the above range, the pretilt angle of the liquid crystal of the liquid crystal display element becomes small, and when the contact angle is too large,
The liquid crystal tends to be vertically aligned and it is difficult for switching to occur.

The contact angle of water of the alignment layer can be appropriately changed by selecting the type (one kind or a combination of two or more kinds) of the silicon compound represented by the general formula (1) which constitutes the alignment layer. In addition, when the contact angle of water of the alignment layer cannot be obtained only with the silicon compound represented by the general formula (1), and further under other conditions (for example, the rubbing property is not excellent, and the uniform alignment such as surface deterioration is caused). If necessary from the case where it is not obtained), a silicon compound other than the silicon compound represented by the general formula (1) may be added. As the silicon compound other than the silicon compound represented by the general formula (1), for example, a highly reactive group (for example, an amino group,
(Imino group, epoxy group, hydroxy group, chlorine atom, etc.)
Examples thereof include silicon compounds having a hydrocarbon group having. The compounding amount of the silicon compound other than the silicon compound represented by the general formula (1) is preferably 80% by weight or less, and particularly preferably 50% by weight or less of the total silicon compounds.

The solvent used for the alignment layer coating liquid is selected in consideration of the method for forming the alignment layer, the conditions and the like. The concentration of the silicon compound in the alignment layer coating liquid is generally 0.01 to 10% by weight.
Is preferred. Alignment layer coating liquid is generally 0
It is carried out at .about.50.degree. C., and the drying of the coating film is generally carried out at 0.about.50.degree. The dried coating film is preferably further heat-treated at a temperature of 50 to 200 ° C. By this heat treatment, the alignment layer is hydrolyzed to form a siloxane bond, and is brought into close contact with the substrate.

The layer thickness of the alignment layer is preferably in the range of 1 to 500 nm. If the layer thickness of the orientation layer is larger than the above range, the surface accuracy is poor and gap unevenness occurs, and if it is smaller than the above range, the effect of orientation cannot be obtained.

Then, it is preferable to rub the surface of the alignment layer formed as described above. The rubbing treatment of the alignment layer in the present invention can be performed by the same method as the rubbing treatment which has been conventionally performed on the polyimide alignment film. For example, the surface of the alignment layer composed of the silicon compound formed as described above, nylon,
Rubbing is performed with synthetic fibers such as polyester and polyacrylonitrile, and natural fibers such as cotton and wool.

The ferroelectric liquid crystal composition in the present invention is not particularly limited, and includes chiral smectic C layer (SmC ^* ), H
A liquid crystal having a layer (SmH ^* ), an I layer (SmI ^* ), a J layer (SmJ ^* ), a K layer (SmK ^* ), a G layer (SmG ^* ) or an F layer (SmF ^* ) may be used.

In the display device of the present invention, other components (eg, a polarizing plate, a reflection plate, a retardation plate, etc.), other structures of the display device, a driving method of the display device, etc. are known per se. Can be used.

[0039]

EXAMPLES Examples of the present invention and comparative examples will be described below. However, the present invention is not limited to this embodiment.

[Example 1] Two glass plates (25 mm x
A transparent electrode (10 Ω / □) of indium-tin oxide (ITO) is stripe-shaped (width of electrode: 300 μm, gap between electrodes: 10 μ) on each of 20 mm × 1.1 mm.
m).

SiO ₂ (manufactured by Osaka Titanium Co., Ltd.) was formed on the surface of the _two glass plates with ITO electrodes, which had electrodes.
Was sputtered to form an insulating film having a film thickness of 100 nm.

Formula: CF ₃ (CF ₂ ) ₇ CH ₂ CH ₂ Si (C
0.5 g of a silicon compound represented by H ₃ ) (OCH ₃ ) ₂ (manufactured by Toshiba Silicone Co., Ltd., trade name TSL8231), and a formula: H ₂ N (CH ₂ ) ₂ NH (CH ₂ ) ₃ Si (CH ₃ )
0.5 g of a silicon compound represented by (OCH ₃ ) ₂ (trade name: KBM602, manufactured by Shin-Etsu Silicone Co., Ltd.) was dissolved in 100 g of isopropyl alcohol to prepare an alignment layer coating solution.

The glass plate provided with the electrode and the insulating film was immersed in the alignment layer coating solution for 5 minutes and then taken out, and compressed air was blown onto the surface of the glass plate to dry it at about 25 ° C. Next, this was placed in an oven and kept at 130 ° C. for 1 hour to be heat-treated to form an alignment layer on the surface of the insulating layer. After cooling this to room temperature, the surface of the alignment layer is covered with a nylon raised cloth.
The rubbing treatment was performed under the conditions of 00 rpm, 20 seconds × 3 times.
The contact angle of water on the surface of the alignment layer was measured by the method described below.

The two substrates with electrodes manufactured in this manner are superposed with a spacer (Makoto Kabushiki Kaisha, Ltd.) so that the alignment layers face each other and the electrode patterns are orthogonal to each other. And a cell gap having a cell gap of 2 μm was prepared by bonding with an epoxy adhesive.

Ferroelectric liquid crystal having the composition and phase transition temperature shown in Table 1 was placed in this cell at 100
Inject at ℃ for 30 minutes, naturally cool to room temperature,
A liquid crystal display device was manufactured.

[0046]

[Table 1]

With respect to the obtained liquid crystal display device, the pretilt angle and the contrast ratio were measured by the methods described below. The results are shown in Table 2.

[Evaluation of Alignment Layer] 1) Water Contact Angle of Alignment Layer The contact angle of water at 25 ° C. was measured using an Elmer contact angle measuring instrument.

[Evaluation of Liquid Crystal Display Element] 1) Pretilt angle The tilt angle was measured by the crystal rotation method.

2) Bright / Dark Ratio A drive waveform of the 4-pulse method is applied to the liquid crystal display element at 35 ° C. (± 32 V, duty = 480, bias ratio = 1 /).
4) and then the microscope (Nikon OPTIPHOTO2-POL, objective lens M
The brightness of the bright frame (B) and the brightness of the dark frame (D) were measured using Plan 10) and a photodiode. The B / D ratio was measured while gradually increasing the pulse width, and the maximum value (B / D) _max of the B / D ratio was defined as the light / dark ratio.

Example 2 Instead of the alignment layer coating solution used in Example 1, 0.5 g of TSL8231 and the formula: H ₂ N (CH ₂ ) ₃ Si (CH ₃ ) OSi (CH ₃ ). (
CH ₂₎ a silicon compound represented by ₃ NH ₂ (Toshiba Silicone Co., Ltd., in addition to the product name TSL9306) was used 0.5g, an alignment layer coating liquid prepared by dissolving in isopropyl alcohol 100g is Example 1 A liquid crystal display device was manufactured in the same manner as in.

For this liquid crystal display element, the contact angle of water, the pretilt angle and the contrast ratio of the alignment layer were measured in the same manner as in Example 1. The results are shown in Table 2.

Example 3 Instead of the alignment layer coating solution used in Example 1, the formula: CH ₃ (CH ₂ ) ₁₇ Si (OC ₂ H ₅ )
Silicon compound represented by ₃ (Toshiba Silicone Co., Ltd.)
Manufactured by TSL8186), 0.5 g, and the above KB
0.5 g of M602, 100 g of isopropyl alcohol
A liquid crystal display device was manufactured in the same manner as in Example 1 except that the coating solution for the alignment layer prepared by dissolving in.

For this liquid crystal display element, the contact angle of water, the pretilt angle and the contrast ratio of the alignment layer were measured in the same manner as in Example 1. The results are shown in Table 2.

Example 4 Instead of the alignment layer coating solution used in Example 1, 0.5 g of TSL8186, 0.5 g of TSL9306 and isopropyl alcohol 1 were used.
A liquid crystal display device was manufactured in the same manner as in Example 1 except that the coating solution for the alignment layer prepared by dissolving in 00 g was used.

For this liquid crystal display element, the contact angle of water, the pretilt angle and the contrast ratio of the alignment layer were measured in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1 Instead of the alignment layer coating liquid used in Example 1, the formula: glycidyl-O (CH ₂ ) ₃ Si was used.
0.5 g of a silicon compound represented by (OCH ₃ ) ₃ (manufactured by Shin-Etsu Silicone Co., Ltd., trade name KBM403), formula: H
0.5 g of a silicon compound represented by ₂ N (CH ₂ ) ₂ NH (CH ₂ ) ₃ Si (OCH ₃ ) ₃ (manufactured by Shin-Etsu Silicone Co., Ltd., trade name KBM603) and 1 isopropyl alcohol
A liquid crystal display device was manufactured in the same manner as in Example 1 except that the coating solution for the alignment layer prepared by dissolving in 00 g was used.

For this liquid crystal display element, the contact angle of water, the pretilt angle and the contrast ratio of the alignment layer were measured in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 2] Instead of the alignment layer coating solution used in Example 1, 0.5 g of the KBM403, 0.5 g of the KBM602 and isopropyl alcohol 1 were used.
A liquid crystal display device was manufactured in the same manner as in Example 1 except that the coating solution for the alignment layer prepared by dissolving in 00 g was used.

For this liquid crystal display element, the contact angle of water, the pretilt angle, and the contrast ratio of the alignment layer were measured in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 3] Instead of the alignment layer coating solution used in Example 1, 0.5 g of KBM603 and 0.5 g of KBM602, isopropyl alcohol 1
A liquid crystal display device was manufactured in the same manner as in Example 1 except that the coating solution for the alignment layer prepared by dissolving in 00 g was used.

For this liquid crystal display element, the contact angle of water, the pretilt angle, and the contrast ratio of the alignment layer were measured in the same manner as in Example 1. The results are shown in Table 2.

[0063]

[Table 2]

As is clear from the results of Table 2, the liquid crystal display elements obtained in the examples were compared with the liquid crystal display elements having the alignment layer made of the silicon compound outside the scope of the present invention obtained in the comparative examples. Thus, the water contact angle of the alignment layer is large, the pretilt angle and the light / dark ratio are large, and an image display with a large contrast can be obtained.

[0065]

The liquid crystal display device of the present invention is provided with an alignment layer that can be formed under mild conditions, and has a remarkable effect that an image can be displayed with a large pretilt angle and a large contrast ratio, and thus a high contrast. ..

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an example of a liquid crystal display element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display element 10, 20 Transparent electrode substrate 11, 21 Transparent substrate 12, 22 Transparent electrode 13, 23 Insulating film 14, 24 Alignment layer 30 Ferroelectric liquid crystal composition

Claims (1)

Claim: What is claimed is: 1. A transparent electrode is provided on a substrate, and on the surface of the transparent electrode, a compound of the general formula (1): [In the formula, R is a group represented by C _m F _{2m + 1} − or C _m H _{2m + 1} − (where m is an integer of 5 to 25), and R ¹ ,
R ² and R ³ are each independently an alkoxy group having 1 to 5 carbon atoms or an alkyl group having 1 to 5 carbon atoms, and n is 0 to
Which is an integer of 5], a cell constituted by arranging two electrode substrates each having an alignment layer made of at least one silicon compound selected from the silicon compounds so that the alignment layer is on the inner side. A liquid crystal display device comprising a ferroelectric liquid crystal composition enclosed therein.