JP3156332B2 - Display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a material of a display element in which a liquid crystal and a polymer used for a display, a light valve and the like are aligned and dispersed.

[0002]

2. Description of the Related Art In recent years, a display element in which a liquid crystal and a polymer are dispersed in each other has attracted attention. The operating principle of this display element utilizes the difference between the refractive indices of the liquid crystal and the polymer. If the refractive index of the liquid crystal and that of the polymer match when an electric field is applied, it indicates a transmission state. In this case, the scattering state is indicated. As a representative one, Tokujo Sho 58
NCAP (Nemat
ic Curvilineear Aligned Ph
case) liquid crystal or technical report of the Institute of Television Engineers of Japan,
Article No. IDY90-42, PN-LCD (Polymer Network) introduced in February 1990
Many examples have been reported, such as Liquid Crystal Display.

On the other hand, a display element of an opposite mode in which light is transmitted when no electric field is applied and scattered when an electric field is applied was announced last year. Mo
l. Cryst. Liq. Cryst. , 1991, v
ol. 198, pp. In 357-370, an element is manufactured by using an alignment substrate, curing an ultraviolet-curable bifunctional polymer precursor, and then fixing the two-phase separation as an isotropic gel to realize this mode. Also, Procedi
ng of IDRC. 45-52,
In 175-178, an element is manufactured using the same manufacturing method, but here, a liquid crystal contains a chiral component in order to improve contrast.

[0004]

However, in general, these display elements have a poor reflectivity at the time of light scattering, and in particular, display elements in a mode of scattering at the time of application of an electric field have a problem that the viewing angle is narrow. Could not be displayed sufficiently when used as.

Therefore, an object of the present invention is to make the transparent state more transparent, to improve the light scattering degree in the scattering state, and to reduce the dependence on the viewing angle.

[0006]

The display device of the present invention has a pair of substrates on which an alignment treatment for aligning liquid crystal is performed, and a mixture of a bifunctional polymer precursor and liquid crystal is used. In a display device having a layer in which a liquid crystal and a cured polymer are cured and dispersed between the substrates, at least one of the pair of substrates is subjected to an orientation treatment in two directions. Features. Also,
The liquid crystal is characterized by being mixed with a polychromatic dye.

Hereinafter, the present invention will be described in detail with reference to examples.

[0008]

In this embodiment, as shown in FIG. 1, an example is shown in which an element is used in which two-sided alignment treatment is performed on each of the two-sided substrates so as to be orthogonal to each other, and the alignment directions between the two substrates are overlapped with each other. Show. FIG. 2 shows a sectional view of the display element of the present invention. A method for manufacturing an element will be described. First substrate
The electrodes 5 and 10 were formed on the surfaces of the substrate 4 and the substrate 11 by a vapor deposition method. A 2% solution of polyimide (JIB manufactured by Nippon Synthetic Rubber Co., Ltd.) was spin-coated on the surfaces of these substrates at 2000 RPM as alignment films 6 and 9 . These substrates were fired at 150 ° C. Thereafter, the surface of the alignment film was rubbed. Further, in the direction perpendicular to the above, rubbing was performed again so as not to erase the previously rubbed orientation. The substrate 4 and the substrate 11 were fixed with a gap of 10 μm (hereinafter referred to as a cell thickness) such that the electrodes were on the inside. In this gap 4-biphenyl methacrylate

[0009]

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And a liquid crystal (PN001: manufactured by Roddick Co.) mixed at a ratio of 5:95 (W: W) at 130 ° C., cooled and sealed, and the liquid crystal / monomer mixture is aligned, and ultraviolet light is applied at room temperature. When irradiated, the liquid crystal and the polymer phase-separated, and an almost transparent device was produced.

The evaluation method is as follows. 1 cm of velvet cloth on the back side of the substrate (opposite side to the white light)
With an interval of The evaluation was performed by irradiating the substrate with white light at angles of 30, 50, and 70 ° from above and from the left, and measuring the reflectance in the normal direction to the substrate. The reflectance of white light with respect to white paper was set to 100%, and the reflectance when light was shielded was set to 0%. At the time of scattering, a reflectance of about 65% was obtained. When an electric field of 0 V was applied, a reflectivity of 4% was obtained. The viewing angle dependence was hardly observed. As a conventional example,
When an element in which substrates oriented in one direction are fixed at the same cell thickness so as to be parallel to each other is used, a reflectance of 40% is obtained, and when an electric field of 0 V is applied, the reflectance is 3%. Was. In addition, when the light source was moved in parallel with the orientation direction, the reflectivity at the time of applying the electric field was lowered, and the contrast was deteriorated.
It can be seen that the reflectance when an electric field was applied was improved and the viewing angle dependency was improved without changing the reflectance when no electric field was applied.

Embodiment 2 In this embodiment, as shown in FIG. 3, an element in which a substrate oriented at a right angle and a substrate oriented by being rotated by 45 ° with respect to the substrate are stacked and fixed is used. The same as 1 was used. As a result, an almost transparent element was produced.

When an electric field was applied, a reflectance of 70% was obtained. The reflectivity when an AC electric field of 0 V is applied is 5
%Met. There was no dependence on viewing angle. This is significantly improved as compared with the conventional example shown in the first embodiment.

Example 3 In this example, an element was manufactured using the same substrate as that in Example 2. Here, 4-benzoylphenyl methacrylate is used as the polymer precursor.

[0015]

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Using this precursor and a liquid crystal (PN001)
Were mixed at a ratio of 8:92 at 130 ° C., gradually cooled, and then sealed in a substrate at room temperature to orient the liquid crystal / polymer precursor mixture. When irradiated with ultraviolet rays at room temperature, the liquid crystal and the polymer were phase-separated, and an almost transparent device was produced.

When an electric field was applied, a reflectivity of 86% was obtained. The reflectance when an AC electric field of 0 V was applied was 7%. The viewing angle dependence was hardly observed. This is significantly improved as compared with the conventional example shown in the first embodiment.

(Embodiment 4) This embodiment shows a case where a dichroic dye is used. The same substrate as in Example 1 was used. Here, 2% by weight of liquid crystal (PN001) S-344 is used.
(Mitsui Toatsu Dye Co., Ltd.) was used.

The same polymer precursor as in Example 1 and the above-mentioned dye-containing liquid crystal were mixed at a ratio of 15:85 (W: W) at 130 ° C., gradually cooled, and sealed in a substrate at room temperature. / Polymer precursor mixture was oriented. When irradiated with ultraviolet rays at room temperature, the liquid crystal and the polymer phase-separated, and a uniform black element was produced.

When the element is driven by turning on and off the electric field, white-black display is performed. At the time of white display at the time of applying an electric field, conventionally, grayish white has low contrast and poor viewing angle dependency, but in the present embodiment, white tone with good color tone and almost no viewing angle dependency are observed. Because it was not possible, it was improved as compared with the conventional example.

In the above embodiments, the manufacturing method of the substrate, the manufacturing method of the element, and the like have been described, but the present invention is not limited to these methods.

The polymer precursors other than those used in the present embodiment can be used. That is, there is no problem as long as the liquid crystal is arranged in the same direction as that of the liquid crystal, or in a direction almost aligned even in a different direction. In addition, all functional groups which can be used as a photocurable polymerization site as a polymerization site can be used. Preferred are methacrylic acid derivatives. In addition, the polymer precursor having a polymerized portion that is cured by heat is also arranged in a direction substantially the same as the orientation of the liquid crystal, or in a roughly uniform direction even in a different direction, and the orientation does not change significantly during polymerization. If it can be used. When an aromatic ring or the like is present, it is preferably substituted at the 1- and 4-positions, and desirably, those having a linear molecular structure are easily polymerized. After polymerization, the polymer becomes a side chain polymer, and at least one of the side chains preferably has at least two or more aromatic rings. Even if these are directly bonded to the polymerization site, they are bonded indirectly. May be. Although the case of direct bonding is described in this embodiment, in the case of indirect bonding, an intervening molecule such as ester, amide, urethane, acetylene, ethylene or the like can be used. When the ester group is also present in the polymerized portion, the ester group is preferably bonded in the opposite direction. Further, the bonding position of the side chain is desirably at the 4-position, that is, at the para-position, where the position where the ester group is added is at the 1-position. Many. In the case of a polymer precursor having both an ester group and an alkyl side chain, the threshold voltage can be lowered while improving the reflectance. Here, if the length of the alkyl side chain is too long, the reflectance at the time of transparency increases, and the contrast deteriorates. Desirably, those having 1 to 6 carbon atoms may be directly bonded to the aromatic ring portion, or may be bonded via a hetero atom such as an ether or ester bond. Further, the side chain may be substituted by a substance having a large dipole moment such as a fluorine atom or a cyano molecule in some cases.

The alignment film is not limited to polyimide, but may be any material such as polyvinyl alcohol as long as it has a power to align the liquid crystal. The orientation treatment is effective even with only one side of the substrate. The orientation direction is not limited to that described in the above embodiment, and it is necessary to optimize each time regardless of the orientation process of one or both substrates. Alternatively, the electrode side of the substrate may be simply rubbed without applying the alignment film.

The liquid crystal preferably has a refractive index anisotropy Δn as large as possible. The liquid crystal may have a positive dielectric anisotropy. The content of the liquid crystal is optimally 50 to 98% based on the total weight of the polymer monomers. If the liquid crystal content is less than this, the liquid crystal will not respond to an electric field, and if it is more than this, contrast will not be obtained, or the polymer portion will move due to the electric field, and the device will easily burn. In the above examples, no chiral component was mixed, but when S-1011 (manufactured by Merck) was added as a chiral component in the range of 0.1 to 5%, the contrast and steepness in threshold characteristics were improved. .

Further, in the above embodiment, the example in which the substrate is subjected to the horizontal alignment processing is described. However, the present invention can be applied to the method of vertically aligning the substrate using liquid crystal having negative dielectric anisotropy. This is shown in Example 5.

(Embodiment 5) In this embodiment, an example using a substrate subjected to a vertical alignment process will be described. FIG. 4 shows a cross-sectional view of the display element of this example. A method for manufacturing an element will be described. First, the electrodes 16 and 21 were formed on the surfaces of the substrate 15 and the substrate 22. A vertical alignment agent (LP manufactured by Shin-Etsu Silicone Co., Ltd.) was formed on these substrate surfaces as alignment films 17 and 20.
-8T) was spin coated at 2000 RPM. These substrates were fired at 100 ° C. Thereafter, the surface of the alignment film was rubbed. Further, in the direction perpendicular to the above, rubbing was performed again so as not to erase the previously rubbed orientation. The substrate 15 and the substrate 22 were fixed to a cell thickness of 10 μm such that the electrodes were on the inside. The 4-biphenyl methacrylate used in Example 1 was filled in this gap.

[0027]

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And a liquid crystal (RDN-00775: manufactured by Roddick Co.) mixed at a ratio of 6:94 (W: W) at 130 ° C., then cooled and sealed, and the liquid crystal / monomer mixture was oriented to room temperature. When irradiated with ultraviolet light, the liquid crystal and the polymer were phase-separated, and an almost transparent device was produced.

Next, the reflectance of the device was measured. When an electric field was applied, a reflectance of 20% was obtained. When no electric field was applied, a reflectance of 5% was obtained. There was almost no dependence on viewing angle. As a conventional example, in the case of only vertical alignment treatment, a 6% reflectivity was obtained when an electric field was applied, and a 5% reflectivity was obtained when a 0 V electric field was applied. The reflectivity at the time of application could be improved without changing.

The method of manufacturing the substrate and the element described in this embodiment is not limited to this. Any alignment film may be used as long as the liquid crystal is vertically aligned, and the coating and baking methods are not limited to those described here. The orientation treatment is effective even with only one side of the substrate. The orientation direction is not limited to that shown here, and it is necessary to optimize each time regardless of the orientation process of one or both substrates.

As the polymer precursor, those having the performance or structure as described in Example 5, other than those shown here, can be used.

The liquid crystal used preferably has a refractive index anisotropy Δn as large as possible. The liquid crystal may have a negative dielectric anisotropy. The content of the liquid crystal is optimally 50 to 98% based on the total weight of the polymer monomers. If the content of the liquid crystal is less than this, no response to an electric field is caused, and if it is more than this, contrast cannot be obtained, or the polymer portion is moved by the electric field, so that the device tends to burn. In this embodiment, no chiral component is mixed, but S-101 is used as a chiral component.
When 1 (manufactured by Merck) or the like is added in the range of 0.1 to 5%, contrast and steepness in threshold characteristics are improved.

In the above Examples 1 to 5, two substrates are used, but a liquid crystal / polymer layer can be formed on one substrate. The method of mixing and enclosing the liquid crystal and the polymer precursor is not limited to the method described here. Also, the cell thickness need not be the value shown here, and may be determined according to the application.

The present invention can be applied not only to the above embodiments but also to displays, light control elements, light valves, light control mirrors, and the like.

[0035]

As described above, according to the present invention, it is possible to manufacture a display element having high reflectance and good scattering.

The present invention is considered to be effective for a polymer-dispersed liquid crystal element or a liquid crystal-dispersed polymer element, particularly a display element used as a reflection type.

[Brief description of the drawings]

FIG. 1 is a diagram showing an orientation direction of a display element substrate of Example 1.

FIG. 2 is a conceptual diagram showing a cross section of a display element of Examples 1 to 4.

FIG. 3 is a view showing an orientation direction of a display element substrate of Example 2.

FIG. 4 is a conceptual diagram showing a cross section of a display element of Example 5.

[Explanation of symbols]

 Reference Signs List 1 upper substrate surface 2 lower substrate surface 3 alignment direction 4 substrate 5 electrode 6 alignment film 7 polymer 8 liquid crystal 9 alignment film 10 electrode 11 substrate 12 upper substrate surface 13 lower substrate surface 14 alignment direction 15 substrate 16 electrode 17 alignment film 18 height Molecule 19 Liquid crystal 20 Alignment film 21 Electrode 22 Substrate

Claims (2)

(57) [Claims] 1. A liquid crystal display device comprising: a pair of substrates on which an alignment treatment for aligning a liquid crystal is performed; and a mixture of a bifunctional polymer precursor and a liquid crystal being cured between the substrates to be cured with the liquid crystal. A display device having a layer in which polymers are dispersed each other, wherein at least one of the pair of substrates is subjected to an orientation treatment in two directions. 2. The display device according to claim 1, wherein a polychromatic dye is mixed with the liquid crystal.