JPH04296719A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display element which is decreased in the hysteresis of the threshold voltage at the time of driving and can be formed to a larger area. CONSTITUTION:This liquid crystal display element is constituted by crimping a mixture composed of polymerizable compds. and a liquid crystal material between a pair of substrates having electrodes and photosetting the mixture to form the liquid crystal parts independently from the mixture. The mixture composed of the polymerizable compds. and the liquid crystal material of the above-mentioned element contains at least one kind of the liquid crystalline polymerizable compds. Compds. having the dimer or trimer structure of the liquid crystal material are used for the liquid crystalline polymerizable compds.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display element in which liquid crystal is dispersed in a polymer support and transmitted light is controlled by applying a voltage.

0002

[Prior Art] Conventional liquid crystal devices include those using twisted nematic liquid crystals, and liquid crystal displays using ferroelectric liquid crystals to improve the responsiveness of these conventional liquid crystal devices. However, in order to increase the area of these liquid crystal elements, the process becomes complicated and there are many technical problems.

[0003] Furthermore, since these liquid crystal elements require a polarizing plate, there is a problem in that the efficiency of light utilization is low.

0004

[Problems to be Solved by the Invention] In contrast, phase change type liquid crystal display elements using cholesteric liquid crystals and display elements that utilize the dynamic scattering effect of nematic liquid crystals do not require polarizing plates, so the light utilization rate is low. Although it is superior in that it has a high value and a wide viewing angle, it has problems in that it requires a high driving voltage and is difficult to fabricate into a large-area display element.

[0005] In order to improve the above-mentioned problems, for example, a display element applying a nematic liquid crystal capsule proposed by Ferguson (Published Patent Publication No. 58-501)
631) and a light modulating material in which liquid crystal droplets are dispersed in epoxy resin (Published Patent No. 502128/1982), these are advantageous in terms of increasing the area, but the driving voltage is high. There was a problem with this.

[0006] Furthermore, a liquid crystal display element using a photocurable compound as a support (Japanese Unexamined Patent Publication No. 63-271233,
JP-A-63-278036, JP-A-1-1987
No. 25, etc.) have been proposed to reduce the driving voltage. However, even in these devices, it is difficult to obtain a good threshold because the alignment regulating force by the interface is insufficient, there is hysteresis in the threshold voltage, and there is a difference in the refractive index between the support material and the liquid crystal droplet. There has been a problem in that it is necessary to improve the transmittance when transmitting light due to.

The present invention has been made to solve these problems, and can reduce the hysteresis of the threshold voltage during driving, and particularly reduce the influence on color tone during gradation driving. The object of the present invention is to provide a liquid crystal display element that can be reduced in area and increased in area.

[0008]

[Means for Solving the Problems] That is, the present invention involves sandwiching a mixture of a polymerizable compound and a liquid crystal material between a pair of substrates having electrodes, and making the liquid crystal part independent from the mixture by photo-curing. The liquid crystal display device thus formed is characterized in that the mixture of the polymerizable compound and the liquid crystal material contains at least one type of liquid crystal polymerizable compound.

The present invention will be explained in detail below. The present invention provides a so-called polymer-dispersed liquid crystal display element using a photocurable polymerizable compound as a support, in which a liquid crystalline compound is added as a component of the polymerizable compound to a mixture of the polymerizable compound and the liquid crystal material. It is characterized by using a polymerizable compound, particularly a liquid crystal material containing a component having a dimer or trimer structure.

The photocurable polymerizable compound used in the present invention is not particularly limited, and commonly used compounds can be used. Specifically, monomers having unsaturated double bonds, monomers having unsaturated double bonds, For example, styrene and its derivatives; acrylic acid and its ester derivatives; methacrylic acid and its ester derivatives; vinyls such as vinylpyridine, N-vinylpyrrolidone, and N-vinylimidazole; vinylbenzene, dialkyl acrylates and dialkyl methacrylates of dibasic acids. divalent monomers such as; trivalent or tetravalent acrylics, and other known monomers.

Further, it is preferable to use oligomers derived from these monomers because the reactivity and viscosity can be selected.

[0012] Furthermore, in order to improve reactivity, it is preferable to add a photopolymerization initiator or a sensitizer. The photopolymerization initiator can be selected from known benzoin ethers, benzophenones, acetophenones, benzoyl oximes, and the like. The amount of the photopolymerization initiator added is preferably 5% by weight or less based on the polymerizable compound.

[0013] The present invention uses a liquid crystalline polymerizable compound, particularly one containing at least one component having a dimer or trimer structure of a liquid crystal material, as a constituent component of the above polymerizable compound. do. By incorporating the above liquid crystalline polymerizable compound into a mixture of a polymerizable compound and a liquid crystal material, the effect of the liquid crystal droplet interface is improved, and as a result, the hysteresis of the threshold voltage is reduced. It is. The effect of the liquid crystal droplet interface is not necessarily elucidated, but it is thought that a certain effect can be produced by making the interface of the polymerizable compound used similar to that of the liquid crystal material.

Examples of the above-mentioned liquid crystalline polymerizable compounds include those represented by the following general formula (I) or (II).

[0015]

[Chemical formula 1] A-U-B-V-C-W-D
(
I)

[0016]

[Formula 2] B: Flexible group such as alkylene group and oxyalkylene group,

[0017]

[Chemical formula 3]

[0018]

[C4]

D: Straight chain or branched alkyl group, carboxyl group, cyano group, nitro group, halogen group such as Cl, Br, F, etc., U: Bonding group such as ester, thioester, carbonate bond, etc., V, W: Ester , ether, thioester, a bonding group such as a single bond, respectively. )

0
020]

[Chemical formula 5] A-U-B-V-(C-W-D-X)n
-C-Y-E (II)

0021
]

[Chemical formula 6] B, D: flexible groups such as alkylene groups and oxyalkylene groups,

[0022]

[C7]

[0023]

[Chemical formula 8]

E: Straight chain or branched alkyl group, carboxyl group, cyano group, nitro group, halogen group such as Cl, Br, F, etc. U: Bonding group such as ester, thioester, carbonate bond, etc., V, W, X , Y: each represents a bonding group such as ester, ether, thioester, or single bond. Indicates n=1 or 2. ) Furthermore, it is also possible to use a homopolymer that exhibits liquid crystallinity or one that does not exhibit liquid crystallinity.

Next, specific examples of liquid crystalline polymerizable compounds include the following compounds.

[0026]

[Chemical formula 9]

[0027]

[Chemical formula 10]

[0028]

[Chemical formula 11]

Among these, the compound of general formula (II) is more preferred in that it improves the effect of the liquid crystal droplet interface.

These liquid crystalline polymerizable compounds are used in an amount of 1 to 60% by weight, preferably 5 to 50% by weight, based on the photocurable polymerizable compound. If it is less than 1% by weight, no improvement effect can be seen by adding it, and if it exceeds 50% by weight, the mechanical strength of the support itself will decrease, and stability will especially decrease when creating display elements using plastic substrates. do.

In the present invention, it is possible to use a liquid crystal material that can change its transparent state or scattering state by applying or not applying an electric field, such as a nematic liquid crystal having positive dielectric anisotropy, Examples include cholesteric liquid crystal and smectic liquid crystal.

The amount of liquid crystal material used is 10 to 10% of the total mixture.
90% by weight, preferably in the range of 20-70% by weight.

The substrate used in the present invention may be glass, plastic film, etc., but it is preferable to use a plastic film since it provides a large-area and flexible liquid crystal element. Specific examples of the plastic film include polyethylene terephthalate film,
Polycarbonate film, polyimide film, polymethyl methacrylate film, methyl methacrylate-styrene copolymer film, polystyrene film, styrene-acrylonitrile copolymer film, polypropylene ferm, low-density polyethylene film, high-density polyethylene film, polyvinyl chloride film , polytetrafluoroethylene film, polychlorotrifluoroethylene film, fluorinated ethylene-propylene copolymer film, polyarylate film, polysulfone film, cellulose film, polyether ether ketone film, and the like.

The liquid crystal display element of the present invention can be prepared, for example, by coating a mixture of the polymerizable compound and liquid crystal material in a thickness of several μm to several tens of μm on a substrate with electrodes, bonding a counter substrate, and then exposing it to ultraviolet rays. It is created by photocuring by irradiation or the like. At that time, the above-mentioned mixed liquid crystalline polymerizable compound component having a dimer or trimer structure migrates to the interface with the liquid crystal droplet and becomes integrated with the support during polymerization. The liquid crystal droplets can be in a dispersed state or in a continuous state in the support.

[0035] A dye, a light stabilizer, a light absorber, etc. can be added to the mixture of the polymerizable compound and the liquid crystal material, if necessary.

[0036]

[Examples] The present invention will be explained in more detail below with reference to Examples. Example 1 A liquid crystal display element was produced by the method shown below using a mixture having the composition shown below. 2-(2-hydroxymethyl-1,1-dimethyl)
-4-ethyl-5-hydroxymethyl-1,3-dioxane-diacrylate

10 parts by weight Compound (1)
4 parts by weight 1-hydroxycyclohexyl phenyl ketone 0.4 parts by weight Z-1625 (
Manufactured by Merck & Co., nematic mixed liquid crystal) 2
6 parts by weight of the above mixture was applied to a solid ITO transparent electrode (thickness 1
300 Å) on a glass substrate with a diameter of 20 Å.
After spraying micrometer glass spacers, the same substrates as above were pressed against each other and irradiated with ultraviolet rays from a distance of 20 cm for 5 minutes using a 500 W water-cooled ultra-high pressure mercury lamp. A voltage was applied to the obtained element, and the transmittance at that time was measured. The results are shown in Table 1 below.

[0037]

[Table 1]

Example 2 A liquid crystal display element was produced in the same manner as in Example 1 except that compound (1) was replaced with compound (2). A voltage was similarly applied to the produced liquid crystal display element, and the transmittance at that time was measured. The results are shown in Table 2 below.

[0039]

[Table 2]

Comparative Example 1 A liquid crystal display element was prepared in the same manner as in Example 1 except that compound (1) was omitted. A voltage was similarly applied to the produced liquid crystal display element, and the transmittance at that time was measured. The results are shown in Table 3 below.

[0041]

[Table 3]

[0042]

[Effects of the Invention] As explained above, according to the present invention,
In a so-called polymer-dispersed liquid crystal display element that uses a photocurable polymerizable compound as a support, a liquid crystalline polymerizable compound, particularly a dimer or trimer structure of a liquid crystal material, is used as a component of the polymerizable compound. By using a mixture containing a liquid crystal component, it is possible to reduce the hysteresis of the threshold voltage during driving, and in particular, it is possible to reduce the effect on color tone during gradation driving, allowing for large-area displays. It becomes possible to improve the characteristics of the device.

Claims (2)

[Claims] 1. A liquid crystal display element in which a mixture of a polymerizable compound and a liquid crystal material is sandwiched between a pair of substrates having electrodes, and a liquid crystal portion is independently formed from the mixture by photocuring. A liquid crystal display element, wherein the mixture of a polymerizable compound and a liquid crystal material contains at least one type of liquid crystal polymerizable compound. 2. The liquid crystal display element according to claim 1, wherein the liquid crystal polymerizable compound has a dimer or trimer structure of a liquid crystal material.