JPH04264520A - Production of liquid crystal optical element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal optical element which is highly uniform in the adhesiveness between substrates with electrodes on both sides and a cure compsn. contg. a liquid crystal material therebetween. CONSTITUTION:The photosetting compsn. is prepd. by mixing a nematic liquid crystal, urethane acrylate, 1, 6-hexandiol acrylate, and a photopolymn. initiator. This setting compsn. is applied on the surface inclusive of the electrodes of the transparent polyester film substrate (PET substrate with ITO) which consists of a transparent conductive film made of In2O2-SiO2 and is provided with the electrodes. The surface including the electrodes of the same PET substrate with the ITO is superposed on the surface coated with this compsn. The substrates are irradiated with UV rays for 30 seconds from both upper and lower sides with a high-pressure mercury lamp to photoset the compsn., by which the liquid crystal optical element is produced. This liquid crystal optical element is cloudy and opaque at voltage off and transparent at voltage on. The layer of the cured compsn. induces the breakdown of flocculation in the tensile peeling test of the two substrates. The adhesiveness between the two substrates and the cured compsn. is uniform and excellent.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing liquid crystal optical elements used in displays, optical shutters, etc.

0002

[Prior Art] Light transmission (
Liquid crystal optical elements that control a transparent state) and scattering (a cloudy, opaque state) are known. Conventionally, this type of liquid crystal optical element generally has a photocurable composition containing a liquid crystal substance interposed between opposing transparent substrates with electrodes, and this is placed on, for example, a belt, above the substrates, i.e. It is manufactured by curing a photocurable composition by irradiating light from one outer side (see, for example, JP-A-62-2231 and JP-A-64-62615).

0003

[Problems to be Solved by the Invention] As described above, the method of photo-curing the composition by irradiating light has a faster curing speed than the thermosetting method, so the productivity of the composition is excellent. There is an advantage of being there. However, in liquid crystal optical elements manufactured by such conventional photocuring methods, there is a difference in adhesive strength between the layer of the cured composition and both substrate surfaces. Peeling is likely to occur at the interface with the object layer. If a liquid crystal optical element has such a peeled part, the part may not function even if a voltage is applied, and reliability cannot be said to be sufficient.

The present invention solves the above problems, and its purpose is to provide a highly reliable liquid crystal optical element in which the adhesive strength between the cured composition layer and both substrate surfaces is uniformly excellent. The purpose of this invention is to provide a method for manufacturing the same.

[0005]

[Means for Solving the Problems] The method for manufacturing a liquid crystal optical element of the present invention involves interposing a photocurable composition containing a liquid crystal substance between opposing transparent substrates with electrodes, and adding a photocurable composition containing a liquid crystal substance to the substrate. It is characterized in that the photocurable composition is cured by irradiating light from both outer sides, thereby achieving the above object.

In the present invention, the transparent electrode-attached substrate is generally made of transparent glass or transparent plastic such as polyester, and one side of the substrate is made of In2O2-SnO.
2 (ITO), SiO2, or the like, provided with a transparent electrode of a predetermined shape made of a thin transparent conductive film. As the liquid crystal material, nematic liquid crystals, particularly nematic liquid crystals having positive dielectric constant anisotropy, are generally used, but cholesteric liquid crystals and smectic liquid crystals can also be used. Furthermore, a mixture of nematic liquid crystal and cholesteric liquid crystal or smectic liquid crystal may also be used. The liquid crystal material is generally contained in the composition in an amount ranging from 20 to 80% by weight.

[0007] As the photocurable composition, a liquid composition is used in which an appropriate amount of a photopolymerization initiator is blended with a photopolymerizable prepolymer, oligomer, or monomer, or a mixture thereof. Examples of photopolymerizable prepolymers and oligomers include epoxy acrylate, urethane acrylate, unsaturated polyester, polyester acrylate, polyether acrylate, polyene/polythiol, and the like.

As photopolymerizable monomers, monofunctional or polyfunctional acrylic monomers are generally used. Such acrylic monomers include n-butyl acrylate, 2-ethylhexyl (meth)acrylate, 2-
Hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate Examples include acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

Examples of photopolymerization initiators include acetophenone types such as methoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone, benzoin ether types such as benzoin ethyl ether and benzoin isopropyl ether, and ketal types such as benzyl dimethyl ketal. be. Furthermore, phenyl (2-hydroxy-2
-propyl) Ketone: Other name: 2-hydroxy-2-methyl-1-phenylpropan-1-one
173: manufactured by Merck & Co., West Germany] and hydroxycyclohexylphenyl ketone. In particular, hydroxyalkylphenone-based initiators have high activity and good solubility in the composition, and are preferably used. Such a photopolymerization initiator is generally used in an amount of 0.1 to 5% by weight based on the total amount of the photopolymerizable prepolymer, oligomer, and monomer.

[0010] The above photopolymerizable composition may optionally contain a photosensitizer, an ultraviolet absorber, an antioxidant, a thickener,
Various commonly used compounding agents such as fillers and colorants may be added. In the present invention, first, a photocurable composition containing a liquid crystal substance as described above is interposed between opposing transparent substrates with electrodes. The following methods are generally adopted. That is, applying a viscous liquid of the above composition to the surface containing the electrodes of the electrode-equipped substrate,
If necessary, use microspheres as spacers between the substrates,
A method of overlapping the electrode-containing surface of a similar electrode-equipped substrate with this method, or facing each other so that the electrode-containing surface of the electrode-equipped substrate is on the inside, and using microspheres as spacers between the substrates as necessary, A method is employed in which the periphery is sealed to form a cell, the composition is injected in liquid form into the cell, and the injection hole is sealed.

[0011] Next, light is irradiated from both outer sides of the substrate to perform photocuring. As a light source, one that emits light in the ultraviolet to visible range is generally used, such as an ultra-high pressure, high pressure, or low pressure mercury lamp or halogen lamp. Additionally, electron beams are also used. When using an electron beam, the photopolymerization initiator can be omitted. By irradiating with such light, the photocurable composition is rapidly polymerized and crosslinked and cured. The light intensity is generally adjusted to 1 by adjusting the distance to the irradiated object and the voltage.
It is set in the range of 000 to 4000 mJ/cm2. Generally, an irradiation time of several seconds to several minutes is sufficient. Light irradiation may be performed at a constant light intensity, but it may also be irradiated with the light intensity changed in two stages, for example, by first lowering the light intensity and then increasing the light intensity. In this way, a liquid crystal optical element is manufactured.

0012

[Operation] A photocurable composition containing a liquid crystal substance is interposed between opposing transparent substrates with electrodes, and when light is irradiated from both outer sides of the substrate, the parts in contact with the opposing substrates are cured. The adhesive composition polymerizes and cures evenly from both sides. As a result, the adhesive strength between both substrates and the cured composition layer becomes equal, and a decrease in adhesiveness on the light irradiation side is prevented. Also, when light is irradiated from both outer sides of the board in this way,
Curing time is reduced.

[0013]

[Examples] Examples and comparative examples of the present invention will be shown below. Example Nematic liquid crystal (RIXON-4002: manufactured by Chisso Corporation) 110 parts by weight, urethane acrylate oligomer (
UN-5200: Manufactured by Negami Kogyo Co., Ltd.) 65 parts by weight, 1.6
A photocurable composition containing a liquid crystal substance was prepared by mixing 25 parts by weight of hexanediol diacrylate monomer and 3 parts by weight of phenyl (2-hydroxy-2-propyl) ketone [Darukiur 1173: manufactured by Merck & Co., Ltd., West Germany]. . This photocurable composition is in the form of a transparent, slightly viscous solution.

[0014] This photocurable composition is
A transparent polyester film substrate (PET substrate with ITO) equipped with a transparent electrode made of a thin transparent conductive film of O2 (
CEREC (manufactured by Daicel Chemical Co., Ltd.) was applied to the surface containing the transparent electrode. Furthermore, PET with the same ITO was added to this coated surface.
The surfaces of the substrates containing the transparent electrodes were placed one on top of the other, and ultraviolet rays were irradiated from both the upper and lower sides for 30 seconds using high-pressure mercury lamps (lamp output: 80 W/cm) placed above and below to photocure, thereby producing a liquid crystal optical element. In this liquid crystal optical element, the thickness of the layer of the cured composition containing the liquid crystal material was 15 microns.

[0015] This liquid crystal optical element has a voltage (AC100
When voltage (AC 100 volts, 60 cycles) is not applied, it becomes cloudy and opaque, and voltage (AC 100 volts, 60 cycles)
When applied, it becomes transparent. In order to evaluate the adhesion of this liquid crystal optical element, a tensile peel test was performed by forcibly peeling off the edges of the ITO-coated PET substrates on both sides, and the layer of the cured composition suffered cohesive failure. The adhesion of the cured composition layer was uniform and good. Comparative Example In the example, instead of the upper and lower high-pressure mercury lamps, a high-pressure mercury lamp (lamp output: 80 W/cm) was placed only in the upper part, and ultraviolet rays were irradiated from above for 60 seconds. Other than that, it was carried out in the same manner as in the example. In this case, in a tensile peel test of the liquid crystal optical element, it was peeled from the interface between the substrate on the light irradiation side and the layer of the cured composition, and the adhesive strength was about 300 g/cm2, and the layer of the cured composition and the substrate were separated. The adhesion was uneven and weak overall.

[0016]

Effects of the Invention As described above, a photocurable composition containing a liquid crystal substance is interposed between opposing transparent substrates with electrodes, and the photocurable composition is cured by irradiating it with light from both outer sides of the substrate. The composition polymerizes and hardens evenly from both sides,
The adhesive strength between both substrates and the cured composition layer becomes uniform and excellent, and a highly reliable liquid crystal optical element can be obtained.

Furthermore, since light is irradiated from both outer surfaces of the substrate, a uniform liquid crystal optical element with no variation in the thickness direction of the dispersed state of the liquid crystal material in the layer of the curing composition can be obtained, and the curing time can be shortened. This has the advantage of increasing production speed and reducing costs. Therefore, the liquid crystal optical element manufactured by the method of the present invention is suitably used as a display element (for example, a display) or a light control element (for example, an optical shutter).

Claims (1)

[Claims] 1. A photocurable composition containing a liquid crystal substance is interposed between opposing transparent substrates with electrodes, and the photocurable composition is cured by irradiating light from both outer surfaces of the substrate. A method for manufacturing a liquid crystal optical element, characterized in that: