JP2520682Y2 - Liquid crystal display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] The present invention relates to a TN type liquid crystal display device.

[Conventional technology]

For example, a TN type dot matrix liquid crystal display element used in a liquid crystal television receiver or the like has a structure as shown in FIG. That is, in FIG. 2, 1,2
Is a pair of upper and lower transparent substrates. On the inner surface of one substrate, for example, the upper substrate 1, a large number of stripe-shaped transparent signal electrodes 3 extending in the vertical direction are formed in parallel, and on the other substrate (lower substrate) 2. On the inner surface, a large number of stripe-shaped transparent scanning electrodes 4 are formed in parallel along the lateral width direction. Liquid crystal molecule alignment films 5 and 6 made of a horizontal alignment material such as polyimide are formed on the electrode formation surfaces of both the substrates 1 and 2, and the film surfaces of the alignment films 5 and 6 are subjected to alignment treatment by rubbing. It has been subjected. The substrates 1 and 2 are adhered to each other via a frame-shaped sealing material 7, and a nematic liquid crystal material LC is sealed between the substrates 1 and 2. Further, 8 and 9 are a pair of polarizing plates provided on the outer surfaces of both substrates 1 and 2, respectively.

FIG. 3 shows the alignment treatment directions (rubbing directions) of the alignment films 5 and 6 on both sides of the substrates 1 and 2 and the polarization axis directions of the upper and lower polarizing plates 8 and 9 in the conventional liquid crystal display device. Among them, 5a is the alignment treatment direction of the upper alignment film 5 on the upper substrate 1 side, 6a is the alignment treatment direction of the lower alignment film 6 on the lower substrate 2 surface, 8a is the polarization axis direction of the upper polarizing plate 8, and 9a is the lower polarizing plate. 9 is the polarization axis direction, and the upper alignment film 5
The crossing angle ψ between the alignment treatment direction 5a of the above and the alignment treatment direction 6a of the lower alignment film 6 is about 90 °. And both boards 1,
The liquid crystal molecules of the liquid crystal material LC enclosed between the two are aligned along the alignment treatment direction 6a of the lower alignment film 6 on the lower substrate 2 surface, and the alignment treatment direction 5a of the upper alignment film 5 on the upper substrate 1 surface.
As a result, the liquid crystal molecules aligned in the layer thickness direction of the liquid crystal layer between the two substrates 1 and 2 are aligned with each other, so that the twist angle of about 90 ° in the chain line arrow T direction from the lower substrate side to the upper substrate side. It is a twisted array. In addition, the TN type liquid crystal display element,
Polarization axis direction 8a of upper polarization plate 8 and polarization axis direction 9a of lower polarization plate 9
There are those that are parallel to each other and those that are orthogonal to each other, but generally in a dot matrix liquid crystal display device for displaying a television image or the like, the polarization axis directions 8a and 9a of the upper and lower polarizing plates 8 and 9 are mutually It is parallel and this polarization axis direction is 8
a and 9a are aligned with the alignment treatment direction 6a of either one of the alignment films, for example, the lower alignment film 6. It should be noted that A indicates the viewing direction in which the display of the liquid crystal display element 10 can be seen in the state of the best contrast.

This liquid crystal display element in which the polarization axis directions B1 and B2 are parallel to each other is called a normally black type, and each pixel display section where the electrodes 3 and 4 of both substrates 1 and 2 face each other is the electrode 3 ,
OFF that does not transmit light without applying drive voltage between 4
Then, when the drive voltage is applied, the light is transmitted and the image is displayed in the ON state.

By the way, the dot matrix liquid crystal display device,
Since it is driven at a high duty in a time division manner, the sharpness of the operation characteristic (threshold characteristic), that is, the γ characteristic and the contrast C _{R in} the time division driving are the main factors that determine the display characteristic. It becomes a problem.

FIG. 4 shows the electro-optical characteristics of the liquid crystal display device. The contrast C _R is the brightness B _ON at the time of ON at a certain applied voltage (effective voltage applied to the liquid crystal layer) V, and OFF.
This is the maximum value of the brightness B _OFF ratio B _ON / B _OFF , and the larger the brightness ratio B _ON / B _{OFF, the} better the contrast. Also γ
The characteristic is that the applied voltage V50 at which 50% brightness B50 is obtained when the difference between the maximum brightness Bmax and the minimum brightness Bmin is B100.
And 10% brightness B10 is obtained, the ratio of applied voltage V10 is V50 / V10
The smaller the voltage ratio V50 / V10 is (the closer it is to 1), the better the γ characteristic, that is, the operating characteristic when performing time division driving. The contrast C _R and γ characteristics are the twist angle of the liquid crystal molecule alignment (intersection angle between the alignment treatment directions 5a and 6a of the upper and lower alignment films 5 and 6) ψ, the anisotropy Δn of the refractive index of the liquid crystal material LC, and the liquid crystal. Depending on the product Δn · d of the layer thickness d and the layer thickness d, the twist angle ψ of the liquid crystal molecule alignment is set to about 90 ° and the polarization axis directions 8a and 9a of the upper and lower polarizing plates 8 and 9 are oriented in one direction. In the conventional liquid crystal display device in which the alignment treatment direction 6a of the film 6 is parallel, if the value of Δn · d is selected to be about 1.1, the γ characteristic and the contrast C
It is said that both _R can be satisfied.

That is, the following [Table 1] shows that the values of Δn · d of the above-mentioned conventional and liquid crystal display devices are selected to be 0.5, 1.1 and 1.4, respectively, and the contrast C _R and γ characteristics of the devices are shown for the wavelength light of λ = 580 nm. The result of the examination is shown.

As shown in [Table 1], the twist angle ψ of the liquid crystal molecule alignment is set to about 90 °, and the polarization axis directions 8a and 9a of the upper and lower polarizing plates 8 and 9 are set to the alignment treatment direction 6a of one alignment film 6. In a conventional liquid crystal display device that is parallel, the γ characteristic is Δn · d.
When it is set to 0.5, it becomes the best (close to 1), but the contrast [C _R ] is best when Δn · d = 1.1,
In addition, the γ characteristic when Δn · d = 1.1 is not significantly different from the case where Δn · d = 0.5, so the overall evaluation is Δn · d.
Ideally, the value of should be around 1.1.

[Problems to be solved by the device]

However, in the conventional liquid crystal display device, even if the satisfactory both [Delta] n · d value of about choose if γ characteristic 1.1 and the contrast C _R, its contrast had a problem that it is still insufficient.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a liquid crystal display device having a satisfactory γ characteristic and a significantly improved contrast.

[Means for solving the problem]

According to the present invention, in order to achieve the above-mentioned object, the alignment treatment directions of the alignment films respectively formed on the opposing surfaces of the pair of substrates are substantially orthogonal to each other as in the conventional case, and the refractive index of the liquid crystal material enclosed between the pair of substrates is substantially the same. Product Δ of anisotropy Δn and layer thickness d of the liquid crystal layer
The value of n · d is selected in the range of approximately 1.3 to 1.5, and the polarization axis direction of one of the pair of polarizing plates disposed on the outer surface side of the pair of substrates is set to the pair of substrate surfaces. The alignment treatment direction of one of the alignment films is shifted by about 2.5 ° in the twist direction of the liquid crystal molecule alignment, and the polarization axis direction of the other polarizing plate is set to the alignment treatment direction of the one alignment film. As a reference, the liquid crystal molecules are displaced by approximately 2.5 ° in the direction opposite to the twist direction of the alignment.

[Action]

With such a configuration, the γ characteristic is better than that of a conventional liquid crystal display element (having a Δn · d value of about 1.1), and the contrast [C _R ] is significantly better than that of a conventional liquid crystal display element. Therefore, it is possible to satisfy the γ characteristic and significantly improve the contrast.

〔Example〕

 An embodiment of the present invention will be described below.

FIG. 1 shows the alignment treatment directions of the upper and lower alignment films of the liquid crystal display element 10 and the polarization axis directions of the upper and lower polarizing plates. In the figure, 5a indicates the alignment treatment direction of the upper alignment film 5 of the upper substrate surface. , 6a is the alignment treatment direction of the lower alignment film on the lower substrate surface, 8a is the polarization axis direction of the upper polarizing plate disposed on the outer surface of the upper substrate, and 9a is the polarization axis direction of the lower polarizing plate disposed on the outer surface of the lower substrate. , The crossing angle ψ between the alignment treatment direction 5a of the upper alignment film and the alignment treatment direction 6a of the lower alignment film is about 90 °, and therefore liquid crystal molecules aligned in the layer thickness direction of the liquid crystal layer are Similarly, the twist arrangement is performed from the lower substrate side to the upper substrate side in the direction of the chain line arrow T at a twist angle of about 90 °. On the other hand, the polarization axis directions 8a and 9a of the upper and lower polarizing plates 8 and 9 are basically the directions along one of the alignment films, for example, the alignment treatment direction 6a of the lower alignment film. 8a and 9a are not parallel to the alignment treatment direction 6a of the lower alignment film, and the polarization axis direction 9a of the lower polarizing plate is about 2.5 in the twist direction T of the liquid crystal molecule array with the alignment treatment direction 6a of the lower alignment film as a reference. And the polarization axis direction 8a of the upper polarizing plate is an angle β of about 2.5 ° in a direction opposite to the twist direction T of the liquid crystal molecule array with reference to the alignment treatment direction 6a of the lower alignment film. Only shifted.
It should be noted that A indicates the viewing direction in which the display of the liquid crystal display element 10 can be seen in the state of the best contrast.

Further, in this liquid crystal display element, as the liquid crystal material LC sealed between both substrates, the product Δnd of the anisotropy Δn of the refractive index and the layer thickness d of the liquid crystal layer is in the range of about 1.3 to 1.5, for example, 1 .
I'm using 4

Therefore, in this liquid crystal display element, the crossing angle with the alignment treatment directions 5a and 6a of the upper and lower alignment films, that is, the twist angle ψ of the liquid crystal molecule alignment is approximately 90 as in the conventional liquid crystal display element.
However, the value of Δnd is set to 1.4, and the polarization axis direction 9a of the lower polarizing plate is shifted by an angle α of about 2.5 ° in the twist direction T of the liquid crystal molecule alignment with reference to the alignment treatment direction 6a of the lower alignment film. Since the polarization axis direction 8a of the upper polarizing plate is shifted by an angle β of about 2.5 ° in a direction opposite to the twist direction T of the liquid crystal molecule alignment with reference to the alignment treatment direction 6a of the lower alignment film,
The γ characteristic of this liquid crystal display element is
・ The value of d is about 1.1), and the contrast [C _R ] is much better than the conventional liquid crystal display device.

That is, Table 2 below shows Δ of the liquid crystal display device.
the value of n · d, are shown the results of examining the 0.5 and 1.1 and 1.4 Pick respective contrast C _R and γ characteristics and lambda = 580 nm wavelength light.

As shown in [Table 2], the twist angle ψ of the liquid crystal molecule alignment is set to about 90 °, and the polarization axis directions of the upper and lower polarizing plates are set.
In the above liquid crystal display device in which 8a and 9a are offset by approximately 2.5 ° in opposite directions with respect to the alignment treatment direction 6a of one alignment film 6, if Δn · d is set to 0.5 or 1.1, the contrast [C _R ] And γ characteristics are the same as those of conventional liquid crystal display panels (Δn · d
Is about 1.1), but Δn · d
If it is 1.4, the contrast [C _R ] is 21.4, which is 1 (when Δn · d is 1.1) of the conventional LCD panel.
8.5), and the γ characteristic is 1.120.
This is better than the conventional liquid crystal display device in which n · d is 1.1.

Therefore, according to this liquid crystal display element, the contrast [C _R ] can be significantly improved as compared with the conventional liquid crystal display element while sufficiently satisfying the γ characteristic.

In the above embodiment, the value of Δn · d is 1.4, but the value of Δn · d may have a difference of about ± 0.1, and the value of Δn · d is about 1.3 to 1.5. For example, Δn · d
It is possible to obtain a γ characteristic and a contrast [C _R ] which are almost the same as those in the case of 1.4.

In the above embodiment, the polarization axis directions of the upper and lower polarizing plates are set to 8
Although a and 9a are offset from the twisting direction T of the liquid crystal molecule alignment and the opposite direction with reference to the alignment processing direction 6a of the lower alignment film, the polarization axis directions 8a and 9a of the upper and lower polarizing plates are upwardly aligned. It may be shifted in mutually opposite directions with respect to the alignment treatment direction 5a of the film, in short, the polarization axis direction of one of the polarizing plates is the alignment treatment direction of any one of the alignment films of the pair of substrate surfaces. As a reference, it is shifted by about 2.5 ° in the twist direction of the liquid crystal molecule array, and the polarization axis direction of the other polarizing plate is shifted by about 2.5 ° in the direction opposite to the twist direction of the liquid crystal molecule array with reference to the alignment treatment direction of the one alignment film. You can leave it.

[Effect of device]

According to the liquid crystal display device of the present invention, the γ characteristic is better than that of the conventional liquid crystal display device (the value of Δn · d is about 1.1), and the contrast [C _R ] is remarkably higher than that of the conventional liquid crystal display device. Since it is improved, the γ characteristic can be satisfied and the contrast can be significantly improved.

[Brief description of drawings]

FIG. 1 is a plan view showing an alignment treatment direction of an alignment film and a polarization axis direction of a polarizing plate in a liquid crystal display device of the present invention, FIG. 2 is a vertical side view of the liquid crystal display device, and FIG. 3 is a conventional liquid crystal display device. FIG. 4 is a plan view showing the alignment treatment direction of the alignment film and the polarization axis direction of the polarizing plate in FIG. 4, and FIG. 4 is an electro-optical characteristic diagram of the liquid crystal display element. 10: Liquid crystal display element, 5a: Alignment direction of the upper alignment film,
6a ... Alignment treatment direction of lower alignment film, 8a ... Polarization axis direction of upper polarization plate, 9a ... Polarization axis direction of lower polarization plate, ψ ... Alignment treatment direction 5a, 6a and crossing angle (liquid crystal molecular alignment Twist angle), T
…… Twisting direction of liquid crystal molecule alignment, α, β …… Shift angles of polarization axis directions 8a, 9a of the upper and lower polarizing plates with respect to the alignment treatment direction 6a.

Claims (1)

(57) [Scope of utility model registration request] 1. In a TN type liquid crystal display element, the alignment treatment directions of the alignment films formed on the facing surfaces of a pair of substrates are substantially orthogonal to each other, and the refractive index of the liquid crystal material enclosed between the pair of substrates is anisotropic. The value of the product Δn · d of the property Δn and the thickness d of the liquid crystal layer is selected in the range of about 1.3 to 1.5, and among the pair of polarizing plates respectively disposed on the outer surface sides of the pair of substrates,
The polarization axis direction of one of the polarizing plates is shifted by about 2.5 ° in the twist direction of the liquid crystal molecule alignment with reference to the alignment treatment direction of one of the alignment films of the pair of substrate surfaces, and the other polarizing plate A liquid crystal display device, wherein the polarization axis direction is shifted by about 2.5 ° in a direction opposite to the twist direction of the liquid crystal molecule alignment with reference to the alignment treatment direction of the one alignment film.