JPH03217819A - High polymer/liquid crystal complex - Google Patents

Abstract

PURPOSE:To obtain the high polymer/liquid crystal complex with which a high change in light transmittance is obtainable by low-voltage driving by irradiating a mixture formed by mixing a liquid crystal of a nematic type of a cyanobiphenyl system, bifunctional polyester oligomer and acrylic acid monomer at specific ratios with UV rays and causing phase sepn. CONSTITUTION:The liquid crystal of the nematic type of the cyanobiphenyl system is used as the liquid crystal. The bifunctional polyester is used as the oligomer and the monomer of the acrylic acid system is used as the monomer. The uniform soln. prepd. by mixing at the ratios of the liquid crystal: (oligomer +monomer)=65 to 75:35 to 25(weight %) and the oligomer/monomer=7/3 to 6.5/4.5 or 4/6 to 2/8 (by weight) is irradiated with the UV rays to cause the phase sepn. The high polymer/liquid crystal complex with which the high change in the light transmittance and the good contrast are obtd. by the low-voltage driving and which is low in viscosity, is easy to handle and is good in productiv ity is obtd. in this way.

Description

Detailed Description of the Invention [Industrial Field of Application 1] The present invention relates to a polymer/liquid crystal composite in which liquid crystal is dispersed and held in a polymer matrix. It is related to the improvement of

[Prior Art] A polymer/liquid crystal composite is one in which very fine liquid crystals are dispersed and held in a polymer matrix, and the alignment state of the liquid crystals changes depending on the presence or absence of an electric field. For example, when there is no electric field, the liquid crystal is in a random state, so a spatial difference in refractive index occurs and light is scattered. On the other hand, when an electric field is applied, the liquid crystals become aligned in the direction of the electric field. As a result, the refractive index of the liquid crystal portion and the polymer matrix portion match, resulting in a transparent state allowing light to pass through.

Such polymer/liquid crystal composites do not require polarizing plates, so light transmission is very good, and they can be made into large areas, so they are suitable for use in photosensitive films and various display devices. Applications are being extensively considered.

By the way, methods for manufacturing such polymer/liquid crystal composites include: (1) solvent evaporation from an emulsified state, and (2) phase separation by solvent evaporation. ■Phase separation by quenching. ■Phase separation due to polymerization is known. Above all, structural stability. Productivity.
Phase separation by polymerization (2) is attracting attention because of the possibility of structural control. In addition, the types of liquid crystals and polymer matrices include liquid crystals, monomers, and oligomers.
It is attracting attention for reasons such as the stability of the structure mentioned above (
Proceedings of the 38th Polymer Symposium P 2 1 5 1;
Polymer Prints Japan Vo
1.38 No. 7 (see 19891 "Polymer one-component composites (■) to (II)").

For this, BDH's product name E-8 (cyano biphenyl type) was used as the liquid crystal, 2-ethylhexyl acrylate was used as the monomer, and bifunctional urethane acrylate (molecular weight 2000) was used as the oligomer. A polymer/liquid crystal composite is disclosed in which a homogeneous solution of 12-year-old oligomers = 6:2.4:1.6 (weight ratio) is polymerized and phase-separated by ultraviolet irradiation.

[Problems to be Solved by the Invention] The relationship between the driving voltage and the light transmittance of such a conventional polymer/liquid crystal composite film is as shown in FIG. As is clear from this figure, the driving voltage is as high as about 20 V, and the change in transmittance with respect to this driving voltage is about 70%, making it impossible to obtain a fully satisfactory contrast. Furthermore, since the viscosity of the homogeneous solution obtained by mixing the liquid crystal, monomer, and oligomer is high, it is not easy to handle, and there are also disadvantages in that productivity is poor.

The present invention has been made in view of these points, and it is possible to obtain a high change in light transmittance and good contrast with a low driving voltage, as well as a polymer/liquid crystal that has a low viscosity, is easy to handle, and has high productivity. The purpose is to provide a complex.

[Means for Solving the Problems] The present invention combines a cyanobiphenyl-based nematic type liquid crystal, a bifunctional polyester oligomer, and an acrylic acid-based mobmer into a liquid crystal. (oligomer + monomer) = 65
~75: 35 to 25 (wt%), and oligomer/monomer 7/3 to 6.5/4.5 or 4/
It is characterized in that a homogeneous solution mixed at a ratio of 6 to 2/8 (weight ratio) is irradiated with ultraviolet rays to cause phase separation.

[Function] In the present invention, a cyanobiphenyl-based nematic quib is used as the liquid crystal. Furthermore, a bifunctional polyester is used as the oligomer, and an acrylic acid type oligomer is used. The homogeneous solution of these mixtures was then irradiated with ultraviolet rays to homopolymerize the bifunctional polyester oligomer. Homopolymerization of acrylic acid monomers. Alternatively, copolymerization of both may be caused to obtain a polymer matrix in which these homopolymers and copolymers are mixed. At this time, phase separation occurs between the polymer matrix and the liquid crystal, and a polymer-liquid composite is produced.

The light transmission characteristics of this polymer-liquid crystal composite are extremely low, with a driving voltage of about IOV, as shown in Examples below. Further, the change in light transmittance with respect to this driving voltage is as large as about 95% or more, and the contrast is also high.

Note that when the mixing ratio of liquid crystal in the above-mentioned homogeneous solution is more than 75% by weight, the driving voltage becomes high and the change in light transmittance with respect to this driving voltage becomes small. Further, since the alignment state of the liquid crystal does not change satisfactorily, the contrast is also poor. The viscosity is also too high. The mixing ratio of liquid crystal is 6
The same applies when the amount is less than 5% by weight, and therefore, in the present invention, the mixing ratio of the liquid crystal is limited to 75 to 65% by weight.

Regarding the blending ratio of the oligomer and the monomer at this time, if the weight ratio of the oligomer/monomer is greater than 7/3, the viscosity of the homogeneous solution will be too high, and conversely, if the weight ratio is less than 2/8, the viscosity will be too high. The action of the molecular matrix is not good. Furthermore, the characteristics deteriorate even near the middle 5/5, as shown in the examples described later. For this reason, in the present invention, the blending ratio of Sairigoma and monomer is set to 7/3 to 6.5/4.
5 or 4/6 to 2/8 (weight ratio).

In addition, the particle size of the liquid crystal is determined by a low driving voltage. In order to obtain characteristics such as high contrast, the thickness is preferably about 2 to 3 um.

In addition, the molecular weight of the oligomer is 1000 or less in order to cause the above-mentioned homopolymerization and copolymerization to occur well and to obtain a good polymer matrix. Preferably << is 650
It is preferably about 850 to 770, particularly about 770.

[Example] <First Example> As a cyanobiphenyl-based nematic type liquid crystal, BDH Co., Ltd.'s trade name E-9 (which exhibits a nematic phase at room temperature) was used. As the bifunctional polyester oligomer, HX-620 (trade name) manufactured by KAYARAD (molecular weight 768) was used. Furthermore, 2-ethylhexyl acrylate was used as the acrylic acid monomer.

These liquid crystals, oligomers, and monomers are called liquid crystals: oligomers. Monomer = 7: t. 8: 1.2 (weight ratio), and 3% by weight of Darocur 1 1 7 3 (trade name, manufactured by KAYARAD) was added as a polymerization initiator.
A homogeneous solution was prepared. Next, this homogeneous solution was injected into a glass cell with a transparent electrode having a thickness of 10 μm, and a wavelength of 400 nm. Strength 3mW/
cm" ultraviolet rays for 3 to 4 minutes. As a result, a single or copolymerization reaction of the oligomer and monomer occurs, and a mixture of polymer compounds (polymer matrix) produced by this polymerization reaction Phase separation from the liquid crystal is performed.

The light transmission characteristics of the polymer/liquid crystal composite obtained as described above are as shown in FIG. Note that the light source used at this time had a light wavelength of 633 nm, as in the case of FIG. 3 described above.

As is clear from this figure, the polymer and
According to the liquid crystal composite, driving is performed at an extremely low voltage of about IOV, and the change in light transmittance with respect to this driving voltage is as large as about 90%. Furthermore, as described above, the viscosity of the homogeneous solution before the start of the polymerization reaction can be kept low.

<Second Example> Furthermore, in the above example, the liquid crystal = (oligomer + monomer) = 70.30 (weight%) was fixed, and oligomer/monomer
When the monomer ratio was changed from 8/2 to 3/7, the light transmission characteristics changed as shown in FIG. 2. In the same figure, the ratio of oligomer/monomer is 8/2 and 7/
When changing to 316/4, the slope of the graph becomes steeper (see graphs L1, L2, and L3 in the same figure). Then, the ratio of oligomer/monomer = 6/4 is that of the first embodiment of the previous century, and the light transmission characteristics shown in FIG. 1 are exhibited. When the oligomer is reduced and the oligomer/monomer ratio is increased from 6/4 to 5/5, the slope of the graph gradually becomes smoother (see graphs L3 and L4 in the same figure). When the number of oligomers is further reduced and the ratio of oligomers = / 1,000 nomers is set to 5/5 = > 4/6 = 63/7, the slope of the graph becomes steeper again (graph L4.L in the same figure).
5yt. (See 3). As shown in this example, the oligomer/monomer ratio is preferably from 7/3 to 6.5/4.5 or from 4/6 to
By setting the range to 2/8, especially about 6/4 or 3/7, almost the same effect as in the first embodiment can be obtained. [Effects of the Invention] As explained above, according to the present invention, a cyanobiphenyl-based nematic type liquid crystal is used, a bifunctional polyester-based oligomer is used as the oligomer, and an acrylic acid-based liquid crystal is used as the oligomer. using the
By mixing them at a predetermined ratio, it is possible to obtain a high change in light transmittance and good contrast with a low driving voltage, as well as low viscosity, easy handling, and high productivity.

[Brief explanation of drawings]

FIG. 1 is a graph showing the light transmission characteristics of the first example of the polymer/liquid crystal composite according to the present invention, FIG. 2 is a graph showing the light transmission characteristics of the second example of the present invention, and FIG. 2 is a graph showing the light transmission characteristics of a conventional Q polymer/liquid crystal composite.

Claims (1)

[Scope of Claim] A polymer/liquid crystal composite in which a liquid crystal is dispersed and held in a monomer/oligomer polymer matrix, comprising: a cyanobiphenyl nematic type liquid crystal;
A functional polyester oligomer and an acrylic acid monomer are combined into a liquid crystal: (oligomer + monomer) = 65 to 75:
35 to 25 (wt%), and oligomer/monomer = 7/3 to 6.5/4.5 or 4/6 to 2/
A polymer/liquid crystal composite characterized by phase-separating a homogeneous solution mixed at a ratio of 8 (weight ratio) by irradiating ultraviolet rays.