JP3070119B2 - Nematic liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nematic liquid crystal composition useful as an electro-optical display material, and a liquid crystal display using the composition.

[0002]

2. Description of the Related Art A typical TN-LCD is a liquid crystal display cell.
(Twisted nematic-liquid crystal display)
It is used in watches, calculators, electronic organizers, pocket computers, word processors, personal computers and the like. In recent years, the amount of information displayed on one screen has been increasing with the increase in the processing information of OA equipment. It is no longer possible to meet the demand for split drive.

[0003] Under such circumstances, Schefer (Sche
ffer) etc. [SID '85 Digest, P.120 (1985)] or Kinukawa et al. [SID '86 Digest, P.122 (1986)]
(Super Twisted Nematic)-LCDs have been developed and have begun to spread widely in displays for high information processing such as word processors and personal computers.

[0004]

However, TN-LCD
And STN-LCD have problems in terms of the chemical stability of the liquid crystal material, low-voltage drivability and response characteristics of the liquid crystal display device, and the like.

In the STN-LCD, the control of the angle between the alignment plane and the liquid crystal molecules, that is, the control of the pretilt angle is an important factor that greatly affects display performance, yield, and the like in manufacturing a liquid crystal display cell.

As the orientation method, a method of controlling the pretilt angle to a high tilt angle of about 20 ° by oblique deposition of SiOx is known. More practically, for example, “Sun Ever” manufactured by Nissan Chemical Industries, Ltd. is used. A method of controlling the pretilt angle to about 5 ° by rubbing an organic film such as 150 ”is known. In addition, various organic films have been developed and are used by controlling the pretilt angle to 5 to 10 ° by a rubbing method.

In general, it is known that the higher the pretilt angle is, the more difficult it is to generate a stripe domain and the better the yield at the time of manufacturing a liquid crystal display cell. At present, it is extremely difficult to form a stable and stable alignment film.

In addition, STN-LCDs with a large amount of information, such as word processors and personal computers, are required to have high time-division driving characteristics. However, an increase in the number of time divisions causes an increase in the drive voltage, which greatly affects the drive circuit. In order to respond to this, it is necessary to lower the driving voltage of the liquid crystal material. At the same time, in order to prevent the occurrence of stripe domains, it is necessary to optimize the physical constants of the elastic constant and the dielectric constant of the liquid crystal material, which are important for controlling the driving voltage.

However, at present, it is extremely complicated and difficult to control the elastic constant and the dielectric constant that can satisfy both the driving voltage and the display performance for a large amount of information.

[0010] Further, the STN-LCD requires a backlight as an auxiliary light source because the image quality becomes dark due to an increase in the amount of information. Therefore, a liquid crystal material used for a backlight type STN-LCD is required to have chemical stability such as heat resistance and light resistance.

On the other hand, it is known that a conventional liquid crystal material which can be driven at a low voltage has a low resistance value at the initial stage of manufacture or after an accelerated test. When the non-selection time is prolonged due to an increase in the number of images, flickering of the display screen, reduction in contrast, and the like are likely to occur.

The problem to be solved by the present invention is, in particular, ST
Prevents the generation of stripe domains by forming a pretilt angle that can be formed with a practical and stable alignment film using a rubbing method from a quality aspect as a liquid crystal material for N-LCDs. It is possible,
In addition, it is an object of the present invention to provide a nematic liquid crystal composition which has chemical stability, can be driven in a high time-division manner, can be driven at a low voltage, and can be used in a wide temperature range.

[0013]

The present invention has been made in order to solve the above problems. (1) General formula (A)

[0014]

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(Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms, m represents an integer of 0 or 1,
X ¹ represents H or F;

[0016]

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## EQU1 ##

[0018]

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In the formula, n represents an integer of 2 to 5,

[0020]

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In the above, n represents an integer of 1 to 5. However,
When X ¹ is H, n represents 2-5. A) a compound represented by the general formula (B):

[0022]

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(Wherein R ² represents a linear alkyl group having 1 to 10 carbon atoms, p represents an integer of 2 to 5,
² represents H or F. And a compound represented by the general formula (C)

[0024]

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(Wherein, R ³ is a linear alkyl group having 1 to 10 carbon atoms, Y and Z are each independently a single bond,
— Or —CH ₂ CH ₂ —, and X ³ represents H or F. The present invention provides a nematic liquid crystal composition containing a compound selected from the group consisting of compounds represented by the following formula: 2. 2. A super twisted nematic liquid crystal display device using the nematic liquid crystal composition according to the above item 1 and forming a pretilt angle higher than 5 °. 3. General formula (A)

Embedded image (Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms, m represents an integer of 0 or 1, X ¹ represents H or F,

Embedded image Represents

Embedded image In the formula, n represents an integer of 2 to 5,

Embedded image In the formula, n represents an integer of 1 to 5. A) a compound represented by the general formula (B):

Embedded image (Wherein, R ² represents a linear alkyl group having 1 to 10 carbon atoms, p represents an integer of 2 to 5, X ² represents H or F
Represents And a compound represented by the general formula (C)

Embedded image (Wherein, R ³ is a linear alkyl group having 1 to 10 carbon atoms, Y and Z are each independently a single bond, —C00— or —CH ₂
CH ₂ - represents, X ³ represents H or F. A super twisted nematic liquid crystal display device having a pretilt angle higher than 5 ° and a Δd / p of 0.17 or more, using a nematic liquid crystal composition containing a compound selected from the group consisting of compounds represented by the following formula: I will provide a.

Typical examples of the compounds represented by the general formulas (A), (B) and (C) according to the present invention and their phase transition temperatures are shown in Tables 1 to 3.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

(In the table, C represents a crystalline phase, S represents a smectic phase, N represents a nematic phase, and I represents an isotropic liquid phase.) The nematic liquid crystal composition of the present invention has the general formula (A) 5) to 70% by weight, and (2) a compound selected from the group consisting of compounds represented by formulas (B) and (C) in an amount of 20 to 60% by weight. preferable.

Examples of the liquid crystal compound which can be used by mixing with the compound represented by formula (A), (B) or (C) according to the present invention are shown below.

[0032]

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[0033]

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(In the above general formula, R4 represents an alkyl group, R5 represents an alkyl group or an alkoxyl group, and X4
Represents H or F. Table 4 shows the mixing ratio of the liquid crystal composition No. 33 containing the compounds represented by formulas (A), (B) and (C) according to the present invention, the nematic phase-isotropic liquid phase transition temperature. (T _NI ), physical property value of anisotropy of refractive index (Δn), and sealed in a liquid crystal display cell known to be capable of forming a pretilt angle of about 5 ° when a known liquid crystal composition is sealed. In this case, the obtained pretilt angle is indicated. For comparison, in the liquid crystal composition No. 33,
Instead of the compound represented by the general formula (A), a mixed liquid crystal (a) having a structure similar to that of the general formula (A) and obtained by mixing currently used compounds is prepared. Various properties are listed in Table 5.

[0035]

[Table 4]

[0036]

[Table 5]

From Tables 4 and 5, it can be seen that the liquid crystal composition No. 33 according to the present invention can form a pretilt angle 1 ° or more higher than the mixed liquid crystal (a) containing a compound having a similar structure. Can understand. Due to the difference of 1 ° in the pretilt angle, the stripe domain is hardly generated,
The yield during the fabrication of STN liquid crystal display cells was improved.

Further, the compound represented by the general formula (A) according to the present invention, the known compound of the formula (g) characterized by effectively increasing TN-I, and useful for improving the response speed. A mixed liquid crystal (i) comprising the known compound of the formula (h) was prepared, and the mixing ratio and the measurement results are shown in Table 6.

[0039]

[Table 6]

The compounds of the formulas (g) and (h)
Each

[0041]

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Is a compound represented by the formula: It is apparent that the mixed liquid crystal (i) has a smaller pretilt angle than the liquid crystal composition No. 33 according to the present invention. When an STN-LCD was fabricated using the mixed liquid crystal (i) in the same manner as described above, the drive voltage characteristics could be improved, but stripe domains were generated, and the yield could not be improved.

As described above, the nematic liquid crystal composition of the present invention is characterized in that the pretilt angle is made higher than when a conventional liquid crystal composition is encapsulated, and when the known liquid crystal composition is encapsulated. However, the present invention is not limited to a liquid crystal display cell capable of forming a pretilt angle of about 5 °.

Next, the liquid crystal composition No. 33 according to the present invention was prepared.
And a chiral substance “S-811” (manufactured by Merck) was added to the mixed liquid crystal (a) for comparison, and an organic film “San-Eva-150” was rubbed on the opposed flat transparent electrode. Each liquid crystal composition was injected into a display cell for STN having a formed alignment film and having a twist angle of 220 °, and various characteristics were measured.

The chiral substance is such that the intrinsic helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell by adding the chiral substance are Δn · d = 0.85 and d / P = 0.53. Was added.

[0046] Here, Δd / P is, the thickness of the wedge-shaped cell of the boundary stripe domain does not occur d ₁ and d
₂ (d ₁ > d ₂ ),

[0047]

(Equation 1)

The larger value is superior. When the voltage when the transmittance of light perpendicular to the display cell surface is 10% is Vth and the voltage when the light transmittance is 80% is Vsat, the steepness γ of the electro-optical characteristics is Vsat / Vth. Defined, and the closer this value is to 1, the better the high time division characteristics.

[0049] S using the liquid crystal composition No. 33 according to the present invention
Vth of TN-LCD was 1.50V. On the other hand, Vth when the mixed liquid crystal (a) was used was 1.89V.
From these results, it is clear that the nematic liquid crystal composition of the present invention is an excellent liquid crystal composition having a drastically reduced driving voltage.

Furthermore, the liquid crystal composition of the present invention has a strong dielectric anisotropy (△ ε) in order to show that it is also excellent in chemical stability. A mixed liquid crystal (b) was added to the liquid crystal (a) to improve the driving voltage characteristics. Table 7 shows the mixing ratio of the mixed liquid crystal (b) and the measurement results.

[0051]

[Table 7]

When an STN-LCD enclosing the mixed liquid crystal (b) was prepared in the same manner as described above, the Vth was 1.58 V and the driving voltage was improved, but the liquid crystal composition according to the present invention was improved.
As compared with No. 33, the pretilt angle was low, and the occurrence of stripe domains could not be prevented.

The following experiment was conducted on the deterioration of the liquid crystal material due to heat and light. Liquid crystal composition according to the present invention
No. 33 and 2 g of the mixed liquid crystal (b) for comparison were each put into an ampoule tube, degassed under vacuum, and then sealed with nitrogen substitution. For these, the heating acceleration test (150
C., 1 hour), or after the UV irradiation promotion test "Suntest" (Original Hanau Co., Ltd., 10 hours), the specific resistance of each mixed liquid crystal was measured, and the results are shown in Table 8.

[0054]

[Table 8]

Table 8 shows that the liquid crystal composition N according to the present invention
It is clear that o.33 has better heat resistance and light resistance than the mixed liquid crystal (b). Further, a compound having a similar structure to the compound represented by the general formula (A)

[0056]

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A compound represented by the formula (c) or (d) represented by the formula or a compound having a similar structure to the compound represented by the formula (B)

[0058]

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The compound represented by the formula (e) or (f), which is used in a wide temperature range, such as a decrease in TN-I and a loss of liquid crystallinity even at room temperature under nitrogen-substituted storage conditions. It is an unsuitable compound to mix with the composition.

Further, most of the compounds represented by the general formulas (A), (B) and (C) do not show uniform vertical alignment on a glass surface in a nematic state, but they are obtained by mixing these. It was confirmed that many of the resulting mixed liquid crystals exhibited uniform vertical alignment on the glass surface or the ITO electrode surface.

The flickering of the display screen in the STN-LCD is caused by a longer non-selection time due to an increase in the number of time divisions.
There is a method for measuring the frequency dependence of th, and it is known that a method in which the fluctuation of Vth at a low frequency is small is particularly excellent. Using the liquid crystal composition No. 33 according to the present invention and the mixed liquid crystal (b) to produce a TN-LCD and an STN-LCD,
The frequency dependence of Vth was measured. As a result, in the liquid crystal composition No. 33 of the present invention, the fluctuation of Vth was smaller than that of the mixed liquid crystal (b), and the display screen did not flicker at a frequency of 32 Hz.

As described above in detail, the nematic liquid crystal composition of the present invention eliminates the trouble of optimizing the physical properties of the mixed liquid crystal and can form a high pretilt angle. It can prevent and improve the yield of STN-LCD. Furthermore, the nematic liquid crystal composition of the present invention is excellent in low-voltage driving properties and does not adversely affect a driving circuit due to an increase in the number of time divisions.
It is a liquid crystal composition suitable for STN-LCDs with a large amount of information, excellent in heat resistance and light resistance, and particularly useful for liquid crystal display devices used in various environments.

[0063]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

In the following Examples and Comparative Examples,
"%" Represents "% by weight". (Comparative Example 4)

[0065]

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A mixed liquid crystal was prepared. The nematic phase-isotropic liquid phase transition temperature (T _NI ) of this mixed liquid crystal,
The threshold voltage (Vth) and the anisotropy (Δn) of the refractive index in the TN-LCD manufactured using this mixed liquid crystal were as follows.

[0067] _{T NI: 90.5 ℃ Vth: 1.31V} Δn: 0.089 The liquid crystal mixture, the alignment film and the organic film is formed by rubbing of Nissan Chemical Industries, Ltd. "Sunever 150" in the vertical antiparallel The cell was sealed in the combined cell, and the pretilt angle was measured by a magnetic field potential method. As a result, it was 6.3 °.

Also, 2 g of the mixed liquid crystal was placed in an ampoule tube, vacuum-degassed, and then subjected to a process of purging with nitrogen and sealed.
C., the specific resistance of the liquid crystal composition after a 1-hour heating acceleration test and a 10-hour ultraviolet irradiation acceleration test "SUNEST" (manufactured by Original Hanau) was measured. The results were as follows.

Specific resistance after heating acceleration test: 6 × 1
0 ¹¹ Ω · cm Specific resistance after UV irradiation acceleration test: 3 × 10 ¹¹ Ω · cm (Example 2)

[0070]

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A mixed liquid crystal was prepared, and each physical property was measured and each test was performed in the same manner as in Comparative Example 4. The results were as follows. _{T NI: 82.1 ℃ Vth: 1.39V} Δn: 0.099 pretilt angle: 6.8 ° heating acceleration test after resistivity: 6 × 10 ¹¹ Ω · cm ultraviolet irradiation accelerated testing after Resistivity: 4 × 10 ¹¹ Ω · cm (Example 3)

[0072]

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A mixed liquid crystal was prepared, and its physical properties were measured and each test was carried out in the same manner as in Comparative Example 4. The results were as follows. _{T NI: 77.0 ℃ Vth: 1.29V} Δn: 0.106 pretilt angle: 7.1 ° heating acceleration test after Resistivity: 9 × 10 ¹¹ Ω · cm ultraviolet irradiation accelerated testing after resistivity: 5 × 10 ¹¹ Ω · cm (Example 4)

[0074]

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A mixed liquid crystal was prepared, and each physical property was measured and each test was performed in the same manner as in Comparative Example 4. The results were as follows. _{T NI: 76.7 ℃ Vth: 1.27V} Δn: 0.103 pretilt angle: 7.0 ° heating acceleration test after resistivity: 5 × 10 ¹¹ Ω · cm ultraviolet irradiation accelerated testing after resistivity: 1 × 10 ¹¹ Ω · cm (Comparative Example 1)

[0076]

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A mixed liquid crystal was prepared, and each physical property was measured and each test was performed in the same manner as in Comparative Example 4. The results were as follows. _{T NI: 83.5 ℃ Vth: 1.70V} Δn: 0.099 pretilt angle: 5.0 ° heating acceleration test after Resistivity: 8 × ¹⁰ 10 Ω · cm ultraviolet irradiation accelerated testing after resistivity: 3 × 10 ¹⁰ Ω · cm (Comparative Example 2)

[0078]

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A mixed liquid crystal was prepared, and each physical property was measured and each test was performed in the same manner as in Comparative Example 4. The results were as follows. _{T NI: 88.0 ℃ Vth: 1.45V} Δn: 0.118 pretilt angle: 5.1 ° heating acceleration test after resistivity: 5 × ¹⁰ 10 Ω · cm ultraviolet irradiation accelerated testing after Resistivity: 8 × 10 ⁹ Ω · cm (Comparative Example 3)

[0080]

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A mixed liquid crystal was prepared, and its physical properties were measured and each test was performed in the same manner as in Comparative Example 4. The results were as follows. _{T NI: 74.9 ℃ Vth: 1.47V} Δn: 0.140 pretilt angle: 5.1 ° heating acceleration test after resistivity: 1 × 10 ¹¹ Ω · cm ultraviolet irradiation accelerated testing after resistivity: 5 × 10 ¹⁰ Ω · cm All of Examples 2 to 4 were able to form a pretilt angle higher by 1 ° or more than Comparative Examples 1 to 3. (Examples 5 to 8 and Comparative Examples 5 to 7) A mixed liquid crystal obtained by adding a chiral substance “S-811” (manufactured by Merck) to each of the mixed liquid crystals used in Examples 2 to 4 and Comparative Examples 1 to 4. Prepared and injected into a wedge-shaped cell with a twist angle of 220 ° and a display cell, each having an alignment film formed by rubbing an organic film of “Sun Ever 150” on the opposing flat transparent electrode, and measuring various characteristics .

The chiral substance is adjusted so that the intrinsic helical pitch P of the mixed liquid crystal by the addition of the chiral substance and the cell thickness d of the display cell are Δn · d = 0.85 and d / P = 0.53. Was added.

[0083] Here, Δd / P is, the thickness of the wedge-shaped cell of the boundary stripe domain does not occur d ₁ and d
₂ (d ₁ > d ₂ )

[0084]

(Equation 2)

The larger value is superior. When the voltage when the transmittance of light perpendicular to the display cell surface is 10% is Vth and the voltage when the light transmittance is 80% is Vsat, the steepness γ of the electro-optical characteristics is Vsat / Vth. Defined, and the closer this value is to 1, the better the high time division characteristics.

Table 9 shows the measurement results of the display characteristics of the super twisted nematic liquid crystal obtained by adding a chiral substance to each of the mixed liquid crystals prepared in Examples 2 to 4 and Comparative Examples 1 to 4.

[0087]

[Table 9]

Each of the display cells using the mixed liquid crystal of any of Examples 2 to 4 and Comparative Example 4 has a Δd / P value larger than each of the display cells using the mixed liquid crystal of Comparative Examples 1 to 3. Significantly improved, stripe domains are less likely to occur. In addition, the driving voltage was also greatly reduced, and the steepness γ was close to 1, and the nematic liquid crystal composition of the present invention exhibited liquid crystal display characteristics excellent in high time division characteristics.

[0089]

The nematic liquid crystal composition of the present invention can form a pretilt angle higher than 5 ° when sealed in a liquid crystal display cell capable of forming a pretilt angle of about 5 ° when a known nematic liquid crystal is sealed. Things. Therefore, the nematic liquid crystal composition of the present invention has a remarkably low occurrence rate of stripe domains, is chemically stable, and
It is extremely useful as a material for STN-LCDs with good yield during fabrication.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-63621 (JP, A) JP-A-58-180465 (JP, A) JP-A-58-59956 (JP, A) JP-A-2- 245089 (JP, A) JP-A-3-2137 (JP, A) JP-A-2-311461 (JP, A) JP-A-3-39934 (JP, A) JP-A-2-244120 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C09K 19/30 C09K 19/42

Claims (2)

(57) [Claims] (1) General formula (1) (Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms, m represents an integer of 0 or 1, X ¹ represents H or F, And In the formula, n represents an integer of 2 to 5, In the formula, n represents an integer of 1 to 5. Provided that when X ¹ is H, n represents 2-5. And (2) a compound represented by the general formula: (Wherein, R ² represents a linear alkyl group having 1 to 10 carbon atoms, p represents an integer of 2 to 5, X ² represents H or F
Represents And a compound represented by the general formula: (Wherein, R ³ is a linear alkyl group having 1 to 10 carbon atoms, Y and Z are each independently a single bond, —COO— or —C
X ₂ represents H ₂ or F ₂ , and X ³ represents H or F. A nematic liquid crystal composition containing a compound selected from the group consisting of compounds represented by the following formula: 2. A super twisted nematic liquid crystal display device using the nematic liquid crystal composition according to claim 1.