JP2673533B2 - Liquid crystal display device - Google Patents

Description

The present invention relates to a liquid crystal display device having a multi-layer structure in which a display liquid crystal cell in which a liquid crystal is sandwiched between two transparent substrates and a phase correction liquid crystal cell are laminated. .

[Conventional technology]

Liquid crystal display devices were used in the dynamic scattering mode (DSM;
Since the wristwatch element using the Dynamic Scattering Mode was commercialized, the twist nematic mode (TN; Twist)
ed Nematic Mode) has been widely used as a mainstream display device for wrist watches and calculators because of its low voltage drive and low power operation.

Recently, liquid crystal display elements have been increasingly used in the field of information / OA-related equipment typified by various computers, word processors, data terminals, and the like, and accordingly, there has been a demand for large capacity and high quality of liquid crystal display elements.

Conventionally, in order to increase the capacity of a liquid crystal display element of a so-called simple matrix method, which has an XY matrix structure in which a liquid crystal is sandwiched between transparent substrates having two electrodes formed, the frequency of multiplex drive ( It is necessary to increase the duty ratio). However, when the duty ratio is increased, there are problems such as a decrease in display contrast and a decrease in viewing angle. After that, it was the Supertwisted Nematic Mode (STN) that solved this problem and achieved a large capacity (JP-A-60-107020). However, in this STN display mode, the transmitted light has wavelength dependence, so there are two types of display modes, yellow mode that displays black on a yellow background color and blue mode that displays blue on a white background color. Was not.

Therefore, a technical means capable of reducing the wavelength dependence of transmitted light and achieving high quality of a liquid crystal display element is disclosed in JP-A-57-96315.
No. 6,086,045.

This technical means is the first to display the power supply means arranged.
For TN liquid crystal display element (hereinafter referred to as liquid crystal cell for display),
A second TN liquid crystal display element (hereinafter referred to as a phase correction liquid crystal cell) having no power supply means is laminated, and the phase correction liquid crystal cell is used as an optical correction plate.

In the above technical means, the optical path difference of the liquid crystal layer of the phase correcting liquid crystal cell, that is, the thickness d ₁ of the liquid crystal layer and the birefringence of the liquid crystal Δn ₁ (= n _e −n _o , n _e : refraction to extraordinary light rate, n _o: the product and d ₁ · Δn _1, the optical path difference of the liquid crystal layer of the displaying liquid crystal cell, i.e. the thickness of the liquid crystal layer d ₂ and birefringence of the liquid crystal Δn ₂ (= n of the refractive index) to normal light ′ _E −n ′ _o , n ′ _e : Refractive index for extraordinary light,
n _o: equal to a product d ₂ · Δn ₂ of the refractive index) to normal light, the background color of the display liquid crystal cell, resolved by phase correction liquid crystal cell, i.e. the transmittance in the visible light region by zero , To eliminate the wavelength dependence.

[Problems of the prior art]

However, when the optical path difference is equalized as in the liquid crystal display element in which the display liquid crystal cell and the phase correction liquid crystal cell are laminated, the optical correction is sufficiently achieved in the case of no voltage application, When the liquid crystal display element is multiplex-driven at a predetermined duty ratio, the bias voltage is applied to the non-selected pixels, and the arrangement state of the liquid crystal molecules changes correspondingly. As a result, the refractive index n ′ _{e of} the liquid crystal molecules with respect to extraordinary light changes, and a difference occurs between d ₁ · Δn ₁ and d ₂ · Δn ₂ , optical correction becomes insufficient, and non-selected pixels are exposed to visible light. There has been a problem that the transmittance of light of a certain wavelength in the region is increased and the display contrast is lowered.

(Object of the present invention)

The present invention has been devised in view of the above problems, and an object thereof is to provide a liquid crystal display device having a large capacity and a high quality.

[Specific means for solving the problem]

According to the present invention, in order to solve the above-mentioned problems, in a liquid crystal display element in which a liquid crystal display cell in which liquid crystal is sandwiched between two transparent substrates and a liquid crystal cell for phase correction are stacked, the liquid crystal cell for phase correction is provided. That is, the pretilt angle of the liquid crystal layer is set larger than the pretilt angle of the display liquid crystal cell.

[Action]

By the above-mentioned concrete means, the pretilt angle of the liquid crystal layer of the liquid crystal cell for phase correction in which the alignment state of the liquid crystal molecules does not change is set to be larger than the pretilt angle of the liquid crystal layer of the liquid crystal cell for display. Even in the non-selected pixel that is plex-driven, the difference in pretilt angle between the display liquid crystal cell and the phase correction liquid crystal cell is eliminated, and the optical correction of the non-selected pixel is improved.

〔Example〕

Hereinafter, the liquid crystal display device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a structure of a liquid crystal display device according to the present invention.

The liquid crystal display device of the present invention comprises a display liquid crystal cell A in which a liquid crystal is sandwiched between two transparent substrates coated with electrodes and an alignment film.
And a liquid crystal cell B for phase correction are laminated, and polarizing plates are respectively arranged on the outer surfaces of the two transparent substrates.

The display liquid crystal cell A includes a liquid crystal layer 7, two transparent substrates 3 and 4 which sandwich the liquid crystal layer 7, and a sealant 5 which also serves as a spacer.

The two transparent substrates 3 and 4 are made of glass, translucent resin, or the like, and transparent electrodes 8 and 9 for applying an electric field to the liquid crystal layer 7 are formed in a predetermined shape on the inner surfaces thereof.

The transparent electrodes 8 and 9 have a film thickness of 500 to 2000 liters, are made of indium oxide to which tin oxide is added, and are patterned by the photolithography technique. Further, on the surface in contact with the liquid crystal layer 7, an alignment film 10 for determining the alignment of liquid crystal molecules is formed.
Are formed.

The alignment film 10 is a polyimide resin, such as Nissan Chemical Co., Ltd.
It is formed by applying the product "SE-4110" with a film thickness of about 800 to 1000Å and rubbing in a predetermined direction.

The liquid crystal layer 7 is a nematic liquid crystal having a positive dielectric anisotropy, to which is added a levorotatory optically active substance, for example, S-811 in an amount of about 0.8 wt% in order to define the twist direction.

The liquid crystal layer 7 has a pretilt angle θ of liquid crystal molecules defined in FIG. 2 of about 3.0 to 3.5 °. Further, the birefringence Δ of the liquid crystal layer 7
n is 0.125 at about 25 ° C. for light of 589 nm, and
Since the thickness d of the liquid crystal layer 7 is 6.0 μm, the optical path difference d · Δn of the liquid crystal layer 7 is set to 0.75.

Since the sealant 5 functions as a spacer, the liquid crystal layer 7
An epoxy resin mixed with a glass fiber having a diameter substantially the same as the thickness d is used.

Next, the liquid crystal cell B for phase correction is composed of the liquid crystal layer 6, the substrates 1 and 2 sandwiching the liquid crystal layer 6, and the sealant 5 also serving as a spacer.
And consists of

As the two transparent substrates 1 and 2, glass, translucent resin, or the like is used, and an alignment film 11 for determining the alignment of the liquid crystal molecules of the liquid crystal layer 6 is formed on the inner surface of the transparent substrates 1 and 2. .

The alignment film 11 is formed by applying a polyimide resin different from the polyimide resin used for the alignment film 10 of the liquid crystal cell A for display, for example, "RN-422" manufactured by Nissan Chemical Industries, Ltd. in a thickness of about 500 to 800 Å. , Is formed by rubbing in a predetermined direction.

In the liquid crystal layer 6, nematic liquid crystal having positive dielectric anisotropy is added with about 1.2 wt% of dextrorotatory optically active substance, for example, CB-15, for defining the twist direction.

The liquid crystal layer 6 has a pretilt angle θ of liquid crystal molecules defined in FIG. 2 of about 6.0 to 7.0 °. Further, the birefringence Δ of the liquid crystal layer 6
n is 0.125 at about 25 ° C. for light of 589 nm, and
Since the thickness d of the liquid crystal layer 6 is 6.0 μm, the optical path difference d · Δn of the liquid crystal layer 6 is set to 0.75.

Since the sealant 5 functions as a spacer, the liquid crystal layer 6
An epoxy resin mixed with glass fibers having a diameter substantially the same as the thickness d of is used.

The positional relationship between the display liquid crystal cell A and the phase correction liquid crystal cell B is as follows: the major axis direction of the liquid crystal molecules arranged on the inner surface of the substrate 3 of the display liquid crystal cell A and the substrate 2 of the phase correction liquid crystal cell B. Are laminated so that the long axis directions of the liquid crystal molecules arranged on the inner surface thereof are orthogonal to each other, and further, a predetermined angle, for example, −, with the long axis direction of the liquid crystal molecules arranged on the inner surface of the substrate 4 of the display liquid crystal cell A. A polarizing plate 13 is attached with a polarization axis of 45 ° to 45 °, and a predetermined angle, for example, −45 ° to 45 ° is formed with the long axis direction of the liquid crystal molecules arranged on the inner surface of the substrate 1 of the phase correcting liquid crystal cell B. Polarizing plate 12 is attached with the polarization axis formed, and preferably polarizing plate 1
2 and 13 are set to be orthogonal to each other.

FIG. 3 shows the liquid crystal display device of this embodiment with a duty ratio of 200.
It shows a transmitted light spectrum of a non-selected pixel when driven by one-half (solid line). Further, in order to clarify the effect of the present invention, although the conventional liquid crystal display element, that is, the optical path difference d · Δn and the pretilt angle are set to the same value in the display liquid crystal cell A and the phase correction liquid crystal cell B, The transmitted light spectrum of the selected pixel is also shown (broken line).

As is clear from FIG. 3, the liquid crystal display device of the present invention has a higher transmittance than that of the conventional one, that is, it has almost the same transmittance in the visible light region wavelength in the non-selected pixels of the multiplex drive which is a drive system of a high number of pixels. It can be zero, and the optical correction will be sufficiently achieved. As a result, there is no coloring phenomenon in the display liquid crystal cell and the contrast ratio is high.

 FIG. 4 is a sectional structural view of another embodiment of the present invention.

In the present embodiment, the display liquid crystal cell A and the phase correction liquid crystal cell B are composed of three substrates.

In a liquid crystal display device composed of three transparent substrates 15, 16 and 17, in the liquid crystal display cell A for display, the alignment film 20 is formed by the oblique vapor deposition film of SiO, and the pretilt angle of the liquid crystal layer 18 is about 25 °. Is. On the other hand, the alignment film 21 of the liquid crystal cell B for phase correction is also formed by the oblique vapor deposition film of SiO, but the pretilt angle of the liquid crystal layer 19 is about 30 °. The components other than the above are the same as those in the above-described embodiment.

FIG. 5 shows the liquid crystal display device of this embodiment with a duty ratio of 100.
It shows a transmitted light spectrum of a non-selected pixel when driven by one-half (solid line). Further, in order to clarify the effect of the present invention, although the conventional liquid crystal display element, that is, the optical path difference d · Δn and the pretilt angle are set to the same value in the display liquid crystal cell A and the phase correction liquid crystal cell B, The transmitted light spectrum of the selected pixel is also shown (broken line).

As is clear from FIG. 5, the liquid crystal display element of the present invention has achieved a sufficient optical correction of the non-selected pixels as compared with the conventional one.

As described above, according to the present invention, in order to make the pretilt angle of the liquid crystal layer of the phase correcting liquid crystal cell B larger than the pretilt angle of the display liquid crystal cell A in consideration of the duty ratio during the multiplex driving, the liquid crystal material is used. It is important to control the combination of and the material for the alignment film and the conditions for the oblique deposition of SiO, which is the alignment film. In addition, in order to control the pretilt angle, the manufacturing conditions of the alignment film, for example, the pressure during rubbing and the rubbing density may be appropriately changed. Furthermore, when there is a limit to the control of the pretilt angle, the birefringence Δ that is determined by the liquid crystal material
The optical path difference d · Δn of the liquid crystal layer of the liquid crystal cell for phase correction is set to be smaller than the optical path difference d · Δn of the liquid crystal layer of the liquid crystal cell A for display by appropriately combining n and the layer thickness d of the liquid crystal layer. If so, the optical correction of the non-selected pixels is more sufficiently achieved. In addition, although the transmissive liquid crystal display element has been described in the above embodiments, a reflective liquid crystal display element in which a reflecting plate is attached to the outer surface of one substrate may be used. Further, the present invention can be applied even when the twist angle of the liquid crystal layer is 90 ° to 360 °.

〔The invention's effect〕

As described above, in the liquid crystal display device of the present invention, the pretilt angle of the liquid crystal layer of the phase correction liquid crystal cell is appropriately set larger than the pretilt angle of the display liquid crystal cell in consideration of the duty ratio during multiplex driving. Therefore, it is possible to completely prevent the coloring phenomenon caused by the change in the alignment state of the liquid crystal molecules due to the application of the bias voltage generated in the non-selected pixels that are driven in multiplex. As a result, a large-capacity liquid crystal display device having a high display quality such as black and white display with a high contrast ratio can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a liquid crystal display device according to the present invention, and FIG. 2 is an explanatory view defining a pretilt angle of liquid crystal molecules. FIG. 3 is a characteristic diagram of a transmitted light spectrum showing the relationship between the transmittance and the wavelength of a non-selected pixel when the liquid crystal display element shown in FIG. 1 is driven at a duty ratio of 1/200. FIG. 4 is a sectional view of a liquid crystal display element showing another embodiment of the present invention. FIG. 5 shows the liquid crystal display device shown in FIG.
FIG. 6 is a characteristic diagram of a transmitted light spectrum showing the relationship between the transmittance and the wavelength of a non-selected pixel when driven by a factor of 1. 1,2,3,4,15,16,17 …… Transparent substrate 5 …… Sealant 6,7,18,19 …… Liquid crystal layer 8,9, …… Transparent electrode 10,11,20,21 …… Alignment film 12,13, ... Polarizing plate

Claims (1)

(57) [Claims] 1. A liquid crystal display device in which a liquid crystal display cell having a liquid crystal sandwiched between two transparent substrates and a liquid crystal cell for phase correction are stacked, and a pretilt angle of a liquid crystal layer of the liquid crystal cell for phase correction is displayed. A liquid crystal display device characterized in that it is set to be larger than the pretilt angle of the liquid crystal layer of the liquid crystal cell for use.