JP2560905B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device in which characters and figures are visible.

[Prior art]

Small flat-panel liquid crystal display devices are widely used in the fields of watches, calculators, testers, etc., or as devices for displaying figures and characters on a plane or cylinder for decoration and POP. Particularly in the latter, there is a demand for a lightweight device capable of displaying a large area. The oldest technology for increasing the area of a liquid crystal display device uses a dynamic scattering mode. This is an oriented nematic liquid crystal layer sandwiched between glass with transparent electrodes in a state where it is doped with a dielectric substance, and usually exhibits a transparent state, but when an AC electric field is applied to this, the liquid crystal moves due to the movement of the dielectric substance. It utilizes the phenomenon that the orientation is disturbed and the liquid becomes cloudy. This is a current consuming type, and it is very expensive to use a large amount of liquid crystal in a large area, but the contrast is not as high as expected and it is not used today.

A switchable substance having self-supporting property is desired for inexpensively manufacturing a light-weight large-area shutter, but this self-supporting property is not provided because liquid crystal itself has high fluidity. However, it is known that a liquid crystal in which a liquid crystal is randomly dispersed in a droplet shape or an arbitrary shape in a polymer matrix can electrically switch between cloudy and transparent while maintaining its self-supporting property. (Polymer dispersed liquid crystal film, hereinafter abbreviated as PDLC, JWDOANE et al., Mol.Cryst.Li
q.Cryst., Vol165, 533 (1988)).

In this method, a shutter is created by electrically inducing a transparent / white turbidity change based on the matching / mismatching of the average refractive indices of the polymer binder and the liquid crystal droplets. No polarizing plate is required, and the substrate is not only glass but also film. Can also be used. The liquid crystal display device shown in FIG. 2 schematically shows this principle. Liquid crystals are dispersed in the polymer binder (14) as droplets (16) having a diameter (submicron to micron order) approximately the wavelength of light. In a normal state, the major axis direction of the liquid crystal molecules (18) inside the droplet (16) can be regarded as (director) random (see FIG. 2 (a)). In this case, letting the average refractive index of the droplets be n _LC , Can be approximated. Here, n _″ is the refractive index in the major axis direction of the liquid crystal molecule, and _n⊥ is the refractive index in the direction perpendicular to it. Typical values are n _″ = 1.7 and _n⊥ = 1.59. If the refractive index of the polymer binder (14) is n _P = 1.5, the light (24) transmitted through this film will be scattered and appear cloudy due to spatial fluctuations in the refractive index. When an electric field is applied, the liquid crystal molecules exhibiting positive dielectric anisotropy are aligned inside the droplet (16) so that the direction of the director is aligned with the direction perpendicular to the substrate (see FIG. 2 (b)). In this case, the refractive index of the droplet (16) is approximately n _⊥ , and the transparent state is obtained, which is substantially the same as the refractive index n _P of the polymer binder (14).

As a method for producing a solid composite material in which liquid crystal droplets (16) are dispersed in a polymer binder (14),
The compatibility of the liquid crystal and polymer binder is reduced, and the liquid crystal spontaneously precipitates.

(1) The binder precursor and the liquid crystal are sufficiently mixed, and the precursor is polymerized by ultraviolet light or heat.

(2) A polymer binder and liquid crystal are dissolved in a common solvent to form a cast film, which is dried.

(3) The polymer binder and the liquid crystal are heated to a high temperature to make them compatible with each other and then cooled.

In any of the methods, when the combination of the liquid crystal / polymer binder system and the mutual amount are adjusted, liquid crystal droplets are precipitated in the binder and shutter property can be imparted. However, depending on the production method, the liquid crystal part deposited in the polymer binder may have a structure in which the liquid crystal part is randomly intertwined with the binder. Even in this case, the electro-optical response is the same. After forming a smooth film consisting of a liquid crystal / binder mixed system with a thickness of 10 μm to 20 μm on a film or glass substrate by printing or spin coating, irradiate with light or dry cure and attach the counter electrode by an appropriate means. The device is obtained.

[Problems to be Solved by the Invention]

The PDLC film thus obtained surely causes a cloudiness-transparency change, but in order to increase the contrast, it is necessary to increase the film thickness to form a cloudy state of 100 haze or more. When thickened, a high AC voltage is inevitably required to obtain a transparent state.

In order to blink letters and figures in a uniform background for home decoration or POP, low voltage operation and high contrast are required for safety and durability. It is difficult with the conventional method.

[Means for solving the problem]

To this end, the present invention provides a polymer binder in which a nematic liquid crystal exhibiting a positive dielectric anisotropy of an arbitrary shape is dispersed between electrodes facing each other and a negative dielectric anisotropy of an arbitrary shape. The polymer binder having the nematic liquid crystal dispersed therein is sandwiched in a specific pattern.

[Detailed Description of the Invention]

For decoration and POP, a specific figure or character is displayed and erased in a certain background, but in the present invention, the part of the specific figure or character is, for example, the ABCD character part (100) shown in FIG.
Is formed with a polymer binder in which a nematic liquid crystal exhibiting a positive dielectric anisotropy of an arbitrary shape is dispersed, and the remaining base portion (101) is a nematic liquid crystal exhibiting a negative dielectric anisotropy of an arbitrary shape. It shall be formed of a polymer binder in which is dispersed. These are sandwiched between the electrodes facing each other (it is arbitrary where to place the binder parts having different dielectric anisotropies).

The response of the binder part (100) in which the liquid crystal exhibiting positive dielectric anisotropy is dispersed is as already described with reference to FIG. That is, when a voltage is not applied, a white turbid state is exhibited, and when applied, it becomes transparent. Unlike this, the response of the negative part (101) is cloudy when no voltage is applied, but when an AC voltage is applied, the direction of the director in the droplet becomes parallel to the substrate surface (Fig. 1 ( See b)). In this case, the degree of white turbidity is increased as compared with the white turbid state where no voltage is applied. The reason for this can be understood from the average refractive index of the liquid crystal droplets and the refractive index of the polymer binder. As described above, if it is vertical, the difference in refractive index becomes small and the transparency increases, but it is considered that the difference becomes large as a result of being parallel to the substrate.

If the liquid crystal inside the droplet becomes almost parallel to the substrate by the application of voltage, the average refractive index n _LC will be about (n _⊥ · n _″ ) ^1/2 , which is larger than the value randomly aligned inside the droplet. This has the effect of increasing the difference in the refractive index with the binder and increasing the degree of white turbidity.Therefore, the transparency is the same as when the same binder / liquid crystal system is used, but different dielectric anisotropy is exhibited. The contrast increases as the voltage increases due to white turbidity, which allows it to be thinner to obtain the same contrast as the unique combination, and thus operate at lower voltages.

 The present invention will be specifically described below with reference to examples.

[Example 1] Thermosetting resin (A) Liquid crystal (B) 5CB (Product name of Merck) …… 0.50 parts by weight Liquid crystal (C) ZLI1623 (Merck) …… 0.50 parts by weight When the thermosetting resin has a refractive index n _P = 1.53, it slightly decreases. . Regarding the physical properties of the liquid crystal, the refractive index of 5CB is n _″ = 1.71 n _⊥ = 1.53, the dielectric anisotropy Δε> 0 ZLI1623 The refractive index is n _″ = 1.71 n _⊥ = 1.51, the dielectric anisotropy Δε <0. A mixture of the above thermosetting resin (A) and liquid crystal (B) was added to a polyether sulfone (hereinafter simply referred to as PE) with a transparent electrode.
A film having a predetermined pattern was screen-printed on the film (referred to as S) to a thickness of 10 μm. This was heated from room temperature to 110 ° C. in 1 hour and then cured for 3 hours. After cooling to room temperature, the mixture of the thermosetting resin (A) and the liquid crystal (C) was screen-printed so as not to overlap the already printed portion on the remaining portion, and cured under the same conditions. A PES film as a counter electrode was coated on this cloudy film with a 1-μm-thick room temperature curing type epoxy resin and then laminated to obtain a liquid crystal shutter in which the resin portion was sandwiched between PESs having transparent electrodes. 2
When a voltage of 0 Vpp was applied, the liquid crystal (C) was opaque with 100 haze, and the liquid crystal (B) was completely transparent.

[Example 2] Ultraviolet light curable resin (D) When it is cured at a refractive index n _P = 1.54 of the ultraviolet light curable resin (D), it slightly decreases.

A mixture of the UV-curable resin of the ultraviolet light curable resin (D) and the liquid crystal (B) was screen-printed on the PES film with a transparent electrode to a thickness of 10 μm using a screen having a predetermined pattern. This was irradiated with ultraviolet light of about 640 mJ / m ² using an ultraviolet light exposure device and cured. Screen-printing a mixture of the ultraviolet light curable resin (D) and the liquid crystal (C) so as not to overlap with the portion already printed on the remaining portion,
Exposure was performed under the same conditions. A PES film as a counter electrode was coated on the thus obtained cloudy film with a 1 μm-thick room temperature curable epoxy resin and then subjected to a laminating treatment to obtain a liquid crystal shutter in which the resin portion was sandwiched between PES films with transparent electrodes. When a voltage of 40 Vpp was applied, the liquid crystal (C) was opaque with 100 haze, and the liquid crystal (B) was completely transparent.

<Effects of the Invention> The present invention is as described above, and according to the present invention, since it operates at a low voltage and is lightweight, it is easy to increase in size, and therefore a large-sized display of characters and figures is possible. Is provided.

[Brief description of drawings]

FIG. 1 (a) is a plan view showing an embodiment of the arrangement of two kinds of liquid crystal-containing polymer binders in the liquid crystal display device of the present invention, and FIG. 1 (b) is a negative dielectric anisotropy. FIG. 2A is an explanatory view schematically showing the direction of a director in a liquid crystal-containing droplet when a voltage is applied, and FIG. 2A is a liquid crystal display having a liquid crystal-containing droplet having positive dielectric anisotropy. It is an explanatory view schematically showing the state of the device when a voltage is applied,
FIG. 2B is an explanatory view schematically showing a state when no voltage is applied. 100 …… Part containing liquid crystal showing positive dielectric anisotropy 101 …… Part containing liquid crystal showing negative dielectric anisotropy 10 …… Transparent film 12 …… Transparent electrode 14 …… Polymer binder 16 …… Liquid crystal Droplet 18 …… Liquid crystal molecule 20 …… Power supply 24 …… Incident light 26 …… Scattered light 28 …… Transmitted light

Claims (1)

(57) [Claims] 1. A polymer binder in which a nematic liquid crystal exhibiting a positive dielectric anisotropy of an arbitrary shape is dispersed is sandwiched in a specific pattern between electrodes facing each other, and a negative dielectric constant of an arbitrary shape is formed. A liquid crystal display device, characterized in that a polymer binder in which a nematic liquid crystal exhibiting directionality is dispersed is sandwiched between the remaining portions of the specific pattern.