JP3003606B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device utilizing a twisted nematic effect.

[0002]

2. Description of the Related Art Twisted nematic type (hereinafter referred to as "twisted nematic type")
It is called "TN type". ) The liquid crystal display element is a laptop
It is widely used as a display element of a notebook computer, an information portable terminal, and the like, and further higher image quality is required.

In a transmittance-applied voltage curve (VT curve) of a TN type liquid crystal display element, a phenomenon in which the transmittance is not proportional to the applied voltage generally occurs near a saturation voltage (hereinafter referred to as "tailing"). (Fig. 1). When this tailing occurs, it becomes difficult to obtain a predetermined amount of transmitted light in the tailing portion during element driving. That is, if a voltage is applied at regular intervals ignoring such tailing, a gradation shift occurs in a high gradation liquid crystal display element. In addition, in order to obtain a predetermined amount of transmitted light, a driving circuit that applies a voltage at very small intervals at equal intervals must be used. Alternatively, in order to obtain a predetermined transmittance, it is necessary to design a drive circuit so that the interval between applied voltages is changed only in the tailing portion. This complicates the drive circuit and places a heavy burden on the liquid crystal display element, such as light weight, small size, and low cost.

With respect to the relationship between the elastic constant of the nematic liquid crystal composition used in the conventional TN type liquid crystal display device and the device characteristics, the relationship between the elastic constant ratio, the threshold value, and the contrast is known. For example, in Japanese Patent Application Laid-Open Nos. 2-8 or 2-55319, the elastic constant ratio K ₃₃ / K ₁₁ (K ₃₃ : bend elastic constant, K ₁₁ : spray elastic constant) is described in Japanese Patent Laid-Open No. 2-8. In Japanese Patent Application Laid-Open No. 2-55319, it is described that excellent contrast and steep threshold can be realized by setting the value to 0.8 or less.

However, in Japanese Patent Laid-Open No. 2-8,
The steepness of the threshold is represented by a voltage change when the transmittance changes from 50% to 5%, and does not give any suggestion about the solution of tailing. Also, JP-A-2-55
In Japanese Patent Publication No. 319, regarding the relationship between the elastic constant ratio and the viewing angle, K ₃₃ / K ₁₁ ≦ 1.2 and Δnd (Δn: birefringence of the liquid crystal composition, d: thickness of the liquid crystal layer). It is shown that the display characteristics can be improved by satisfying the condition of 0.5 to 0.6, but it does not give any suggestion about the solution of tailing.

[0006]

As described above, when tailing occurs in a TN-type liquid crystal display element, it becomes difficult to obtain a predetermined amount of transmitted light in the tailing portion when the element is driven. An object of the present invention is to provide a TN-type liquid crystal display element with less tailing and excellent display characteristics.

[0007]

In the TN type liquid crystal display device of the present invention, when the transmittance is T and the applied voltage is V (V), V and logT are within the range of -2≤logT≤-1. Is approximated by a straight line using the least squares method, and the slope d of the straight line
(Log T) / absolute value as the alpha of dV, when the bend elastic constant of the liquid crystal composition constituting the liquid crystal layer was set to K ₃₃ alpha /
The value of K ₃₃ ^{is, 1.3 × 10 11 V -1 N} -1 or 8.0 × 10
¹¹ V ^-1 N ^-1 or less. The value of alpha / K ₃₃ by the above range, suppressing generation of tailing of driving the device, it is possible to secure a predetermined amount of transmitted light.

In the present invention, the tailing itself is reduced by the liquid crystal composition and the structure of the liquid crystal display element, not by the driving circuit and driving conditions.
It is possible to realize a high-gradation liquid crystal display element while satisfying demands for downsizing, cost reduction, and the like.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a TN-type liquid crystal display device is defined as having a rubbing direction of the upper and lower substrates of the display device of 80-80.
There is no particular limitation as long as the liquid crystal is shifted by 100 degrees and a liquid crystal having a nematic phase is sealed in the display element. Also,
The transmittance is determined, for example, with respect to the intensity of the emitted light relative to the intensity of the incident light at each applied voltage in a state where the polarizing plate is arranged on the incident light side and the emission light side of the TN type liquid crystal display element so as to obtain the best contrast or transmittance. It is measured as an intensity ratio. Further, the elastic constant of the liquid crystal composition is measured by an electric field method or a magnetic field method (for example, described in Liquid Crystal Fundamentals, pages 216 to 220, Motoharu Okano, Shunsuke Kobayashi, Baifukan) and the like.

A liquid crystal composition for achieving the objects and effects of the present invention can be obtained, for example, by adding a compound having a bend at the skeleton center to an existing liquid crystal composition. As the compound having a bend at the skeleton center, for example,

[0011]

Embedded image Organic silicon compounds such as

[0012]

Embedded image And the like.

In the TN type liquid crystal display device of the present invention, the value of the bend elastic constant K ₃₃ of the liquid crystal composition constituting the liquid crystal layer is not less than 5.0 × 10 ⁻¹² N and not more than 1.5 × 10 ⁻¹¹ N. Preferably, there is. The value of K ₃₃ by the above range, it is possible to further reduce the tailing is because it is possible to reduce the driving voltage.

Further, by setting the chiral pitch (p) of the liquid crystal composition to 60 μm or more and 300 μm or less, tailing can be further reduced, and the driving voltage can be reduced.

The thickness d (μm) of the liquid crystal layer of the liquid crystal display element is
m) and the chiral pitch p (μm) of the liquid crystal composition (d)
/ P) is preferably 0.01 or more and 0.12 or less.

Also, the refractive index anisotropy (Δn) of the liquid crystal composition
Is preferably 0.06 or more and 0.15 or less. This is preferable from the viewpoint of the thickness (d) and transmittance of the liquid crystal layer, and the tailing can be reduced.

[0017]

EXAMPLES Hereinafter, the present invention will be further described with reference to Examples, but the present invention is not limited thereto. The TN type liquid crystal display device in the following examples is a device in which polyimide is applied as an alignment film, two transparent electrodes that are rubbed on the surface and subjected to a 90 ° twist alignment process are adhered, and a nematic liquid crystal composition is vacuum-sealed. It is.

Example 1 Using a liquid crystal composition obtained by adding an organic silicon compound to a liquid crystal compound having a fluorine substituent,
An N-type liquid crystal display device was manufactured. Bend elastic constant K ₃₃ of the liquid crystal composition is 10.9 × 10- ¹² N, the refractive index anisotropy △ n is 0.074, chiral material was not used. The thickness d of the liquid crystal layer was 5 μm. FIG. 7 is a transmittance-voltage (VT) curve of the TN type liquid crystal display device. This VT
The curve of the transmittance from 0.01 to 0.1 was logarithmically calculated, and the absolute value α of the slope was determined. As a result, α = 2.2 (FIG. 8). The value of α / K ₃₃ is 2.0 × 10
¹¹ V ^-1 N ^-1 .

Example 2 A TN type liquid crystal display element having a liquid crystal layer thickness d = 5 μm was prepared by adding a chiral material to the liquid crystal composition of Example 1 and using a liquid crystal composition having a chiral pitch of 120 μm. did. The transmittance-voltage (VT) curve of this TN type liquid crystal display element was measured, and the transmittance was 0.01 to 0.5.
The part 1 was logarithmically calculated, and the absolute value (α) of the slope was obtained. As a result, α = 2.0 (FIG. 9). Also, α
The value of / K ₃₃ was 1.8 × 10 ¹¹ V ⁻¹ N ⁻¹ .

Example 3 The liquid crystal composition of Example 1 was
A liquid with a chiral pitch of 120 μm by adding lal material
Liquid crystal layer thickness d = 3 μm using crystalline composition
A display element was manufactured. The transmittance of this TN type liquid crystal display device
A voltage (VT) curve was measured, and the transmittance was 0.01 to 0.1.
Logarithmize the part of 1 and calculate the absolute value (α) of the slope
As a result, α = 2.1 (FIG. 10). Also,
α / K₃₃Is 1.9 × 10¹¹V ^-1N^-1Met.

Example 4 Using a liquid crystal composition in which an organic silicon compound was added to a liquid crystal compound having a fluorine substituent, T
An N-type liquid crystal display device was manufactured. The bend elastic constant K ₃₃ of the liquid crystal composition was 11.8 × 10 ⁻¹² N, the refractive index anisotropy Δn was 0.076, and no chiral material was used. The thickness d of the liquid crystal layer was 5 μm. FIG. 11 is a transmittance-voltage (VT) curve of the TN type liquid crystal display device. This V-
The logarithm of the part of the transmittance of 0.01 to 0.1 of the T curve was calculated, and the absolute value α of the slope was obtained. The value of α / K ₃₃ is 2.1 × 1
0 ¹¹ V ⁻¹ N ⁻¹ .

Example 5 The liquid crystal composition of Example 4 was
A liquid with a chiral pitch of 120 μm by adding lal material
Liquid crystal layer thickness d = 5 μm using crystalline composition
A display element was manufactured. The transmittance of this TN type liquid crystal display device
A voltage (VT) curve was measured, and the transmittance was 0.01 to 0.1.
Logarithmize the part of 1 and calculate the absolute value (α) of the slope
As a result, α = 2.3 (FIG. 13). Also,
α / K₃₃Is 1.9 × 10¹¹V ^-1N^-1Met.

Example 6 The liquid crystal composition of Example 4 was
A liquid with a chiral pitch of 120 μm by adding lal material
Liquid crystal layer thickness d = 3 μm using crystalline composition
A display element was manufactured. The transmittance of this TN type liquid crystal display device
A voltage (VT) curve was measured, and the transmittance was 0.01 to 0.1.
Logarithmize the part of 1 and calculate the absolute value (α) of the slope
As a result, α = 2.4 (FIG. 14). Also,
α / K₃₃Is 2.0 × 10¹¹V ^-1N^-1Met.

Comparative Example 1 Using the liquid crystal compound having a fluorine substituent of Example 1, a liquid crystal composition was prepared without adding an organic silicon compound. No chiral material was used. This liquid crystal composition has a bend elastic constant K ₃₃ = 18.8 × 10
^-12 N and refractive index anisotropy Δn = 0.075. Using this liquid crystal composition, a TN type liquid crystal display element having a liquid crystal layer thickness d = 5 μm was produced. FIG. 2 was obtained when the transmittance-voltage (VT) curve of this TN type liquid crystal display element was measured. The portion of the VT curve having a transmittance of 0.01 to 0.1 was logarithmically calculated, and the absolute value (α) of the slope was obtained. As a result, α = 1.9 (FIG. 3). The value of α / K ₃₃ was 1.0 × 10 ¹¹ V ⁻¹ N ⁻¹ .

Comparative Example 2 The liquid crystal composition of Comparative Example 1
Liquid crystal with chiral pitch of 40μm
Using a composition, a TN type liquid crystal display having a liquid crystal layer thickness d = 5 μm
An indicator element was manufactured. The transmittance of this TN type liquid crystal display element
The voltage (VT) curve was measured, and the transmittance was 0.01 to 0.1.
And logarithmically calculate the absolute value (α) of the slope
As a result, α = 1.7 (FIG. 4). Also, α /
K₃₃Is 0.9 × 10¹¹V^-1N ^-1Met.

Comparative Example 3 Using the liquid crystal compound having a fluorine substituent of Example 4, a liquid crystal composition was prepared without adding an organic silicon compound. No chiral material was used. This liquid crystal composition has a bend elastic constant K ₃₃ = 18.1 × 10
^-12 N, refractive index anisotropy Δn = 0.094. Using this liquid crystal composition, a TN type liquid crystal display element having a liquid crystal layer thickness d = 5 μm was produced. When the transmittance voltage (VT) curve of this TN type liquid crystal display element was measured, FIG. 5 was obtained. The portion of the VT curve having a transmittance of 0.01 to 0.1 was logarithmized, and the absolute value (α) of the slope was determined. As a result, α = 1.2 (FIG. 6). The value of α / K ₃₃ was 0.7 × 10 ¹¹ V ⁻¹ N ⁻¹ .

Example 7 Even when a compound having a CH ₂ group at the skeletal center and the skeletal center bent was added to the composition of Comparative Example 1, the same effect as in the above example was obtained.

Example 8 When a compound having a CH ₂ group at the skeleton center and having a bent skeleton center was added to the composition of Comparative Example 2, the same effect as in the above Example was obtained.

[0029]

As described above, according to the present invention,
Tailing can be reduced by the structure of the liquid crystal composition and the liquid crystal display element instead of the driving circuit and driving conditions. Therefore, it is possible to realize a liquid crystal display device with a high gradation while satisfying the demands for light weight, small size, low cost, etc. of the liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a diagram showing tailing in a VT curve of a TN type display element.

FIG. 2 shows a VT curve in Comparative Example 1.

FIG. 3 shows a transmittance of a VT curve in Comparative Example 1 of 0.01.
The log plot of the part of ０．１0.1 is shown.

FIG. 4 shows a transmittance of a VT curve in Comparative Example 2 of 0.01.
The log plot of the part of ０．１0.1 is shown.

FIG. 5 shows a VT curve in Comparative Example 3.

FIG. 6 shows the transmittance of the VT curve in Comparative Example 3 0.01.
The log plot of the part of ０．１0.1 is shown.

FIG. 7 shows a VT curve in Example 1.

FIG. 8 shows a transmittance of a VT curve in Example 1 of 0.01.
The log plot of the part of ０．１0.1 is shown.

FIG. 9 shows a transmittance of a VT curve in Example 2 of 0.01.
The log plot of the part of ０．１0.1 is shown.

FIG. 10 shows transmittance of a VT curve in Example 3 of 0.0.
The log plot of the 1-0.1 part is shown.

FIG. 11 shows a VT curve in Example 4.

FIG. 12 shows transmittance of the VT curve of Example 4 being 0.0.
The log plot of the 1-0.1 part is shown.

FIG. 13 shows transmittance of a VT curve in Example 5 of 0.0.
The log plot of the 1-0.1 part is shown.

FIG. 14 shows transmittance of the VT curve in Example 6 being 0.0.
The log plot of the 1-0.1 part is shown.

Continuation of the front page (72) Daisaku Nakata, Inventor, 5-7-1, Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Masaharu Sato, 7-7-1, Shiba, Minato-ku, Tokyo NEC Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/137 C09K 19/02 G02F 1/13 500

Claims (5)

(57) [Claims] 1. Twisted nematic liquid crystal display
In the device, the transmittance was T, and the applied voltage was V (V).
Sometimes, V and logT in the range of −2 ≦ logT ≦ −1
Is approximated by a straight line using the least squares method, and the slope of the straight line
When the absolute value of d (logT) / dV is α, the liquid crystal layer is formed.
The bend elastic constant of the liquid crystal composition ₃₃Α
/ K₃₃Is 1.3 × 10¹¹V^-1N^-1 8.0x
10¹¹V^-1N^-1A twist
De-nematic liquid crystal display device. 2. The liquid crystal composition constituting the liquid crystal layer has a bend elastic constant K ₃₃ of not less than 5.0 × 10 ⁻¹² N and 1.5 × 1.
2. The twisted nematic liquid crystal display device according to claim 1, wherein the value is 0 ^-11 N or less. 3. The liquid crystal composition has a chiral pitch of 60 μm.
3. The twisted nematic liquid crystal display device according to claim 1, which is not less than 300 μm. 4. The thickness of a liquid crystal layer of a liquid crystal display element is defined as d (μ
The twisted nematic liquid crystal according to any one of claims 1 to 3, wherein the value of d / p is 0.01 or more and 0.12 or less, where m) and the chiral pitch of the liquid crystal composition is p (μm). Display element. 5. A liquid crystal composition having a refractive index anisotropy Δn of 0.0
The twisted nematic liquid crystal display device according to any one of claims 1 to 4, wherein the number is 6 or more and 0.15 or less.