JP2903600B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a super twisted nematic liquid crystal display device.

[Conventional technology]

Conventionally, when a liquid crystal cell is driven in a time-division manner in a liquid crystal display device, a duty ratio of 1 / N and a bias ratio of Has been determined to be optimal. However, the reason for the optimum is to pay attention only to the fact that the contrast is best, and not to consider the driving voltage.

[Problems to be solved by the invention]

However, when the duty ratio decreases, the driving applied voltage increases, and the driving voltage required for a high-withstand-voltage IC is The following is desired. However, there is a limit to the breakdown voltage of the IC, and it is required to lower the threshold voltage of the liquid crystal cell in order to drive at an optimum bias ratio.

In super twisted type liquid crystal display devices, lowering the threshold voltage of the liquid crystal cell significantly reduces the display characteristics, It has been found that the use of in contrast causes a decrease in contrast. Further, they have found that the response speed is also slow.

Therefore, the present invention provides a driving voltage of duty ratio 1 / N (N ≧ 300). In the following, it is an object to provide a liquid crystal display device capable of improving not only the contrast but also the response speed.

[Means for solving the problem]

In order to achieve the above object, a liquid crystal display device of the present invention has the following configuration. That is, a liquid crystal cell comprising a nematic liquid crystal that is twisted and aligned in a range of 180 degrees to 360 degrees between one electrode substrate disposed opposite to each other is provided, and the liquid crystal cell has a duty ratio of 1 / N (≧ 300). In a liquid crystal display device driven in a time-division manner, Second, the drive bias ratio is Or (or further) that the drive bias ratio is Or (or further) that the drive bias ratio is Or (or further) that the threshold voltage of the liquid crystal cell is 1.8 V or more in effective voltage,
Alternatively (or further), a pair of polarizing plates are provided on both sides of the liquid crystal cell.

〔Example〕

A typical example of the liquid crystal display device of the present invention has a structure as shown in FIG. The time division driving circuit 1 drives the liquid crystal cell 2 by applying a time division signal to the liquid crystal cell 2. In the liquid crystal cell 2, an upper electrode substrate 3 and a lower electrode substrate 4 are separated at a predetermined interval by a spacer 5, and a liquid crystal 6 is sandwiched between the substrates 3 and 4. The liquid crystal cell 2 is sandwiched between an upper polarizing plate 8 and a lower polarizing plate 9. An optically anisotropic body may be interposed between the upper polarizing plate 8 and the upper electrode substrate 3.

FIG. 2 shows a typical driving waveform applied to the liquid crystal cell 2 by the time division driving circuit 1 of the liquid crystal display device of the present invention.
This is a waveform when the duty ratio is 1 / N and the bias ratio is 1 / M.

FIG. 3 shows a luminance characteristic with respect to a vertical voltage of the super twisted type liquid crystal display device. When the voltage becomes the voltage intensity in the figure is 10% V _10, 90% and V _90, the amount beta representing the time-division driving characteristic is defined as β = V ₁₀ / V _90. Β indicates a value of 1 or more, and as it approaches 1, it indicates that the time-division driving characteristic is better.

The threshold voltage Vth of the capacitance of the liquid crystal cell is the capacitance when an effective voltage of 0.1 V and 5 V are applied to the liquid crystal cell, respectively.
When _0.1 and C ₅ copies refer to the voltage capacity Cth becomes _{Cth = C 0.1 + (C 5} -C 0.1) / 10.

The β value when the threshold voltage Vth of the amount of solution of the liquid crystal cell was changed when the twist angle of the liquid crystal was 240 degrees was examined, and is shown in FIG. As is clear from FIG. 4, Vth
Is lower, the β value increases, and the time division characteristic deteriorates.
Furthermore, when Vth drops below 1.8V, the β value suddenly increases,
The time-division characteristics rapidly deteriorate. That is, it has been found that even when the liquid crystal composition is the same, a change in the composition ratio gives a large change in the time division characteristic.

[Specific Example 1] As shown in Table 1, a predetermined Vth was obtained by changing the composition ratio of the compounds in the same table.

Next, the display characteristics when the bias ratio was changed at a duty ratio of 1/400 were examined. Drive voltage Table 1 shows the optimal liquid crystal when the bias ratio was changed in Table 1.
Of the liquid crystals A to E. Table 2 shows the display characteristics at this time.

As is clear from Table 2, the conventional optimum bias ratio was set. Not only the contrast ratio but also the response speed are inferior to the bias ratios 1/17, 1/15 and 1/12. That is, the bias ratio Thus, a liquid crystal display device having excellent contrast and response speed in the range described above was obtained. Furthermore, the bias ratio Within the range, more excellent characteristics can be obtained.

[Specific Example 2] In the specific example 1, the driving voltage Liquid crystal A to H when the bias ratio is changed
Selected from Table 3 shows the display characteristics at this time.

As is evident from Table 3, the conventional optimum Aias ratio was determined. In contrast, not only the contrast ratio but also the response speed are inferior to the bias ratios 1/17, 1/15, and 1/12. That is, the bias ratio Thus, a liquid crystal display device having excellent contrast and response speed in the range described above was obtained.

[Specific Example 3] Further, as shown in Table 4, a predetermined Vth was obtained by changing the composition ratio of the compounds in the same table. However, the twist angle of the LCD is 270
I did it.

Next, the display characteristics when the bias ratio was changed at a duty ratio of 1/500 were examined. Drive voltage Table 5 shows the optimal liquid crystal when the bias ratio was changed in Table 5.
Of the liquid crystals I to M. Table 5 shows the display characteristics at this time.

As is clear from Table 5, the conventional optimum bias ratio was set. In this case, not only the contrast ratio but also the response speed are inferior to the bias ratios 1/19, 1/17 and 1/14. That is, if the bias ratio is Thus, a liquid crystal display device having excellent contrast and response speed in the range described above was obtained.

[Specific Example 4] As shown in Table 6, the composition ratio of the compounds in the table was changed to obtain a predetermined Vth. However, the twist angle of the liquid crystal is 3
00 degrees.

Next, the display characteristics when the bias ratio was changed at a duty ratio of 1/500 were examined. Drive voltage , The optimum liquid crystal when the bias ratio was changed was selected from the liquid crystals N to R in Table 6. Table 7 shows the display characteristics at this time.

As is clear from Table 7, the conventional optimum bias ratio was set. In, the contrast ratio is bias ratio 1/19, 1/17, 1/14
Inferior. That is, if the bias ratio is Liquid crystal display measures with excellent contrast and response speed were obtained in the range up to.

[Specific Example 5] Further, as shown in Table 8, the composition ratio of the compounds in the table was changed to obtain a predetermined Vth. However, the twist angle of the liquid crystal is 2
40 degrees.

Here, R _{31 to} R ₃₈ represent a linear alkyl group having 1 to 9 carbon atoms.

Next, the display characteristics when the bias ratio was changed at a duty ratio of 1/480 were examined. Drive voltage Table 8 shows the optimum liquid crystal when the bias ratio was changed in Table 8.
Are selected from among the liquid crystals S to W. Table 9 shows the display characteristics at this time.

As is clear from Table 9, the conventional maximum bias ratio was set. The contrast ratio is 1/18, 1/16, 1/14
Inferior. That is, the bias ratio Thus, a liquid crystal display device having an excellent contrast and response speed in the range up to the above was obtained.

Further, non-uniformities in the non-selection portions, which become scan electrode lines and signal electrode lines in the display screen, were examined for unevenness (hereinafter referred to as stringing). In order to check the degree of stringing, a display as shown in FIGS. 5, 6 and 7 is made on the front screen. Thus, the difference Δ in the transmittance between the points a and b in FIG.
Check T (%). In other words, the larger the value of ΔT, the easier to see the stringing. ΔT on a display screen as shown in FIG.
(Hereinafter referred to as ΔT ₁ ), ΔT on a display screen as shown in FIG.
(Hereinafter referred to as ΔT ₂ ), ΔT on a display screen as shown in FIG.
(Hereinafter referred to as ΔT ₃ ) is shown in Table 10.

As is clear from Table 10, the bias ratio In the range up to the above, a uniform display screen without stringing can be obtained from the optimum bias ratio.

[Example 6] Duty ratio 1/300, drive voltage In the same manner as in the above specific examples, the bias ratio A liquid crystal display device having excellent contrast and response speed was obtained in the range of (1).

(Comparative example)

Check for a duty ratio of 1/200. Drive voltage In Table 8, the optimum liquid crystal when the bias ratio was changed was selected from the liquid crystals S to W in Table 8. Table 11 shows the display device at this time.

From Table 11, the optimum bias ratio And bias ratio The contrast ratio is almost the same, and the response speed is better with the optimum bias. In other words, at a duty ratio of 1/200, Is not optimal.

As described above, the effect of the present invention appears at a duty ratio of 1/300 or more.

〔The invention's effect〕

As described above, according to the present invention, the duty ratio 1 /
In a liquid crystal display device driven in a time-division manner with N (where N ≧ 300), first, the driving bias ratio is By performing the following, a super twisted liquid crystal display device having an excellent contrast ratio and response speed can be obtained. Also, the drive bias ratio is Above, or (or further) the drive bias ratio is Below, or (or further) the drive bias ratio is By doing so, the effect is further enhanced. Further, by setting the threshold voltage of the liquid crystal to 1.8 V or more as an effective voltage, the time division characteristics do not deteriorate.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of the liquid crystal display device of the present invention, FIG. 2 is an explanatory diagram showing a time-division driving waveform, and FIG. 3 is luminance with respect to voltage for explaining time-division driving characteristics. FIG. 4 is a curve diagram showing characteristics, and FIG. 4 is a diagram showing a time-division characteristic β value with respect to a threshold voltage Vth of a liquid crystal cell according to one embodiment of the present invention;
FIG. 5, FIG. 6, and FIG. 7 are views showing display screens for evaluation of the present invention. DESCRIPTION OF SYMBOLS 1 ... Time division drive circuit 2 ... Liquid crystal cell 3, 4 ... Electrode substrate 6 ... Liquid crystal 8, 9 ... Polarizing plate

Claims (6)

(57) [Claims] 1. A method according to claim 1, wherein the first and second electrode substrates are arranged opposite to each other.
A liquid crystal display device comprising a liquid crystal cell sandwiching nematic liquid crystal twisted in a range of 0 degrees to 360 degrees and driving the liquid crystal cell in a time-division manner at a duty ratio of 1 / N (N ≧ 300). Ratio A liquid crystal display device characterized by the following. 2. The driving by-has ratio is 2. The liquid crystal display device according to claim 1, wherein: 3. The driving bias ratio is The liquid crystal display device according to claim 1, wherein: 4. The driving bias ratio is The liquid crystal display device according to claim 1, wherein: 5. The method according to claim 1, wherein a threshold voltage of said liquid crystal cell is an effective voltage.
The liquid crystal display device according to claim 1, wherein the voltage is 1.8 V or more. 6. The liquid crystal display device according to claim 1, further comprising a pair of polarizing plates disposed on both sides of the liquid crystal cell.