JPH09101507A - Production of liquid crystal electro-optic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a production method of a polymer dispersion type liquid crystal electro-optical element by which deterioration in display characteristics is prevented by improving a photopolymn. process and the reliability of the element is improved by decreasing the amt. of residual monomers. SOLUTION: A soln. 9 prepared by mixing a liquid crystal and a polymer precursor is sealed between substrates 1, 8 and then, as the first step, the soln. is irradiated with UV rays of high illuminance in a short time to produce lots of polymn. starting points 50 in the soln. 9. In the second step, the soln. 9 is irradiated with UV rays of low illuminance for a long time to complete the polymn. reaction to form a liquid crystal polymer composite layer 10 having dispersion of a polymer 5 in the liquid crystal 4. By this method, the structural stability of the polymer 5 is improved and deterioration in the electro-optical characteristics with temp. can be suppressed.

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 a liquid crystal electro-optical element, and more particularly to a polymer dispersion type liquid crystal by irradiating a solution in which a liquid crystal and a polymer precursor are compatible with each other with light to photopolymerize the solution. The present invention relates to improvement of a manufacturing method for forming a liquid crystal polymer composite layer.

[0002]

2. Description of the Related Art Conventionally, in a polymer-dispersed liquid crystal electro-optical element in which a liquid crystal and a polymer are dispersed with each other, the difference in the refractive index between the liquid crystal and the polymer, which changes depending on whether an electric field is applied, is used to generate light. The scattering state (light transmission state) is changed. This liquid crystal element is different from a liquid crystal display such as a TN type.
Since it can be displayed without using a polarizing plate, it has advantages such as being bright and having a wide viewing angle.

Among these polymer-dispersed electro-optical elements, the polymer particles are dispersed in the liquid crystal, and the liquid crystal and the polymer are oriented in the same direction when no electric field is applied. Figure 2 shows the structure of the liquid crystal electro-optical element of
(A) and (b).

In manufacturing this element, transparent electrodes 2 and 7 made of ITO are formed on the inner surfaces of two transparent substrates 1 and 8 by vapor deposition, and polyimide and polyvinyl are formed on the surfaces of the transparent electrodes 2 and 7. A solution such as alcohol is applied to a predetermined thickness by a spin coating method or the like,
The alignment films 3 and 6 are formed by drying or baking at a temperature of about 150 ° C. The surfaces of the alignment films 3 and 6 are rubbed in a predetermined direction (directions A and B in the figure).

A liquid crystal and a polymer precursor (for example, a UV-curable monomer) are mixed at a predetermined ratio and are made compatible with each other to form a solution having liquid crystallinity. On the other hand, the transparent substrates 1 and 8
Is fixed in a state of being held at a predetermined interval (for example, an interval of about 5 to 10 μm), and the solution is sealed in the meantime. In this state, ultraviolet rays are irradiated from one or both of the transparent substrates 1 and 8 to polymerize and cure the polymer precursor, and at the same time, the liquid crystal and the polymer are phase-separated. In this way, as shown in FIG. 2A, the liquid crystal polymer composite layer 10 in which the particles of the polymer 5 are dispersed in the liquid crystal 4 is formed.

In the liquid crystal polymer composite layer 10, the liquid crystal 4 and the polymer 5 are aligned along the rubbing direction of the alignment films 3 and 6, and are oriented in substantially the same direction as shown by directions A and B in the figure. ing. Here, when a predetermined AC voltage is supplied between the transparent electrodes 2 and 7 and an electric field is applied to the liquid crystal polymer composite layer 10, as shown in FIG. 2B, only the liquid crystal is oriented in the electric field direction. (Direction C in the figure).

By adopting a liquid crystal having a large refractive index anisotropy, and selecting in such a manner that the liquid crystal 4 and the polymer 5 have substantially the same refractive index in the state shown in FIG. 2 (a). , Becomes transparent when no electric field is applied, but when the liquid crystal 4 is aligned in the direction of the electric field as shown in FIG.
Since the refractive index of the liquid crystal 4 is different from the refractive index of the polymer 5 and a difference in refractive index between the two is generated, a light scattering state occurs and the liquid crystal becomes cloudy.

[0008]

In the polymer-dispersed liquid crystal electro-optical element, since the polymer 5 has low heat resistance and low resistance to high-temperature energization, it cannot be stored or used in a high-temperature environment. Then, there is a problem that both the light transmittance in the transparent state and the light scattering degree in the light scattering state deteriorate due to the change in the alignment state of the liquid crystal and the polymer.

In the photopolymerization, usually, 10 to 20% of unreacted monomer may remain. In this case, the specific resistance of the liquid crystal polymer composite layer becomes small, and display failure occurs. There is also a problem that the reliability of the device is lowered.

Therefore, the present invention solves the above-mentioned problems. The problem is to improve the photopolymerization process to prevent the deterioration of display characteristics and reduce the amount of residual monomer to improve the reliability of the device. Is to improve the sex.

[0011]

Means for Solving the Problems The means taken by the present invention to solve the above problems is to store a solution in which a liquid crystal and a polymer precursor are compatibilized between two substrates, and to apply the solution to the solution. By irradiating the liquid crystal and the polymer generated by the polymerization of the polymer precursor with each other, and forming a liquid crystal polymer composite layer in which the liquid crystal and the polymer are phase-separated. In the device manufacturing method, in the step of polymerizing the polymer precursor, a first step of irradiating the solution with high-intensity light for a short time and a step of irradiating the solution with low-intensity light for a long time. And a second stage.

According to this method, a large number of reaction nuclei (polymerization initiation points) are relatively uniformly formed by irradiation with light of high illuminance in the first step, and the polymerization does not proceed deeply around the polymerization initiation points for a short time. In the meantime, the first stage is completed, and then
In the second stage, the polymerization reaction slowly proceeds by irradiation with light of low illuminance. Due to this two-stage light irradiation, a large number of relatively small polymer particles are densely formed inside the formed liquid crystal polymer composite layer,
It is easy to be connected to each other and structurally stable. Therefore, stability with respect to temperature is also improved, and deterioration of electro-optical characteristics is suppressed. Further, since the polymerization reaction proceeds slowly around the polymerization initiation point formed with high density, the amount of the remaining polymer precursor is reduced, and the deterioration of reliability is prevented.

Here, in the first step and the second step, it is preferable that the treatment is performed in a state where the solution is maintained in each predetermined temperature range.

By setting the optimum temperature in each of the first step and the second step to carry out the polymerization reaction, it is possible to prevent the deterioration of the optical characteristics while increasing the production concentration of the polymerization initiation point.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a method for manufacturing a liquid crystal electro-optical element according to the present invention will be described with reference to the accompanying drawings. 1A and 1B show main steps in an embodiment of a method for manufacturing a liquid crystal electro-optical element according to the present invention.

The following description will be made based on a liquid crystal display device of the type shown in FIG. 2 above, but in the present invention, light is applied to a solution in which a liquid crystal and a polymer precursor are preliminarily compatibilized. A polymer-dispersed liquid crystal electro-optical element configured to irradiate and photopolymerize a polymer precursor so that a liquid crystal and a polymer are mutually dispersed to form a phase-separated liquid crystal polymer composite layer. If there is, liquid crystal 4 as shown in FIG.
It is not limited to the type in which the particles of the polymer 5 are dispersed therein, and the liquid crystal layer and the polymer 5 have the same alignment direction when no electric field is applied and the liquid crystal layer is in a transparent state. The present invention can also be applied to those in which are dispersed, those in which polymers are randomly oriented, and those in a light scattering (white turbid) state when no electric field is applied.

As a result of earnest research on the manufacturing conditions of the above-mentioned polymer-dispersed liquid crystal electro-optical element, the present inventor has found that when the light illuminance during photopolymerization is increased and the polymerization reaction is carried out in a short time,
It was found that the driving voltage becomes low, but the heat resistance deteriorates, and when the polymerization reaction is carried out for a long time with low light illuminance, the heat resistance is improved, but the driving voltage becomes high. As a result of further intensive research, the present invention has been completed.

FIG. 1A shows a state in which a liquid crystal polymer composite layer 10 is enclosed between transparent substrates 1 and 8 to form a liquid crystal panel, and then the liquid crystal panel is subjected to a first polymerization step. is there. In the first polymerization step, the solution 9 in which the liquid crystal and the polymer precursor are compatible with each other is irradiated for a short period of time with light having a higher illuminance than that of the second polymerization step, which will be described later, to polymerize in the solution 9. The reaction nuclei 50, which are the starting points of the polymerization of the reaction, are generated at a high density.

The suitable light illuminance in this step varies depending on the type of light source, the liquid crystal forming the solution, and the material of the polymer, and within the light illuminance range applicable to the material used, the second polymerization step described below is performed. Select an illuminance that is sufficiently higher than the light illuminance. The upper limit of this light illuminance range is determined by whether or not the liquid crystal or polymer precursor, which is a constituent component of the solution, decomposes. When the constituent components are decomposed by light irradiation, the decomposed products remain as impurities in the layer, so that the specific resistance of the liquid crystal layer is lowered, and the display quality and reliability are deteriorated.

Further, the light irradiation time is set to be as long as possible within a range in which polymer polymerization hardly progresses with respect to the light illuminance. When the light irradiation time is short, the production concentration at the polymerization initiation point is low and the effect is reduced, as described later.
If the light irradiation time is too long, the polymerization reaction will proceed,
Heat resistance deteriorates.

In this process, the liquid crystal panel is set at 30 ° C.
~ The NI point of the solution 9 (the phase transition temperature between the nematic phase and the isotropic phase) is preferably 40 ° C to (NI point-5) ° C. Within this range, the temperature is optimized while improving heat resistance and viewing the display quality of the liquid crystal panel.
When the temperature is lower than the optimum temperature, the concentration of the polymerization initiation point is low and the effect of improving the heat resistance is low, and when the temperature is higher than the optimum temperature, the alignment property of the liquid crystal layer is deteriorated and the display contrast and scattering degree are decreased. .

In the first polymerization step, the polymerization reaction itself hardly progresses, but a large number of reaction nuclei 50 that cause the polymerization reaction are formed in the solution 9 by the energy of light. The reaction nucleus 50 serves as a polymerization starting point and serves as a starting point of the polymerization reaction in the second polymerization step described later.

Next, the second polymerization step shown in FIG. 1 (b), which is performed subsequent to the first polymerization step, will be described. In the second polymerization step, the solution 9 that has undergone the first polymerization step is irradiated relatively with light having an illuminance weaker than that in the first polymerization step for a long time to perform the polymerization reaction of the solution 9. Is to be completed.

A suitable light illuminance in this step is within the range of light illuminance applicable to the above-mentioned material to be used.
It is set to be sufficiently lower than the light illuminance in the polymerization step. The lower limit of the light illuminance range is that the amount of unreacted polymer precursor (monomer) increases even after the process,
It is determined by whether the display contrast or the light scattering degree is deteriorated and the display characteristics are deteriorated. On the contrary, when the illuminance is increased in the second polymerization step, the variation of the electro-optical characteristics of the liquid crystal element is increased, and when the light illuminance in the first polymerization step is approached, the heat resistance cannot be improved by the present invention.

In this step, the liquid crystal panel is set at 30 ° C.
~ The NI point of the solution 9 (the phase transition temperature between the nematic phase and the isotropic phase) is preferably 40 ° C to (NI point-5) ° C. The temperature in this step affects the phase separation state of the liquid crystal and the polymer, and changes the light transmittance in the transparent state and the light scattering degree in the light scattering state. Therefore, this temperature is experimentally optimized to minimize the reduction in light transmittance and light scattering due to the phase separation in order to increase the contrast of the completed liquid crystal panel.

In the liquid crystal polymer composite layer 10 thus formed, polymerization initiation points are uniformly and densely generated in the layer, and a large number of polymers 5 are formed based on these polymerization initiation points.
It is considered that the particles of (3) are likely to be formed and densely connected to each other and connected to each other. In such a state, the state of the polymer 5 in the liquid crystal 4 is structurally stable and heat resistance is improved. Due to this improvement in heat resistance, it is possible to form a liquid crystal electro-optical element in which the light transmittance and the light scattering degree are less deteriorated even when exposed to a high temperature, and the change with time is small. In addition, it is possible to form an element with less variation in electro-optical characteristics by generating a uniform polymer.

Further, according to the two-step photopolymerization process,
Since the amount of unreacted polymer precursor that finally remains can be reduced, the polymerization reaction can be smoothly started by the initial high-intensity light irradiation without using an additive such as a polymerization initiator. The amount of impurities other than the liquid crystal 4 and the polymer 5 remaining in the layer can be reduced, a decrease in the specific resistance of the liquid crystal layer can be suppressed, and a display defect can be prevented, so that the reliability of the device can be improved.

Further, by the two-step photopolymerization process,
By optimizing the temperature condition during photopolymerization, it is possible to obtain a high-quality display characteristic while suppressing an increase in driving voltage of the completed device, and it is possible to suppress variations in driving characteristics.

As described above, by carrying out the present invention, it is possible to manufacture a liquid crystal electro-optical element having high reliability with respect to various characteristics such as optical characteristics, heat resistance, durability and driving characteristics. become.

[0030]

EXAMPLES Next, specific examples according to the present invention will be described. In this embodiment, an empty reflective liquid crystal panel in which a substrate interval is set to 7 μm and an MIM (Metal Insulator Metal) element is formed for each pixel is prepared, and a liquid crystal and a polymer precursor are mixed in this liquid crystal panel. The resulting solution was vacuum sealed.

In this solution, TL- was used as the mother liquid crystal.
213 (product number, manufactured by Merck Japan Ltd.) 80 parts by weight, 5 parts by weight of the additive liquid crystal shown in Chemical Formula 1 below,
A liquid crystal obtained by adding 5 parts by weight of the compound shown in Chemical formula 2 and 10 parts by weight of the compound shown in Chemical formula 3 and further adding 0.5 part by weight of R-1011 (product number, manufactured by Merck Japan Co.) as a chiral agent. Used as.

[0032]

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[0033]

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[0034]

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As the polymer precursor to be mixed with the liquid crystal, 7 parts by weight of the biphenol acrylic ester shown in Chemical formula 4 was mixed with the liquid crystal to form a solution. The NI point of this solution is about 88 ° C.

[0036]

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The liquid crystal panel thus formed was irradiated with ultraviolet rays from the transparent substrate side of the surface using a microwave type electrodeless lamp (D bulb, manufactured by Fusion Japan). In addition to the above, various sources such as a high pressure mercury lamp and a metal halide lamp can be used as the light source for the ultraviolet irradiation.

As the first step of the photopolymerization step by irradiation with ultraviolet rays, ultraviolet rays having a light intensity of 30 mW were irradiated for 30 seconds in an environment of 40 ° C. The amount of residual monomer after this step is 93
%Met.

The intensity of ultraviolet rays in this step is 20 to 5
It is 0 mW, preferably 22 to 40 mW. If it is less than 20 mW, the concentration at which the polymerization initiation point is generated is small, and the effects such as heat resistance are small. When it exceeds 50 mW, constituent components (liquid crystal, monomer, etc.) are decomposed and remain as impurities.

The irradiation time of ultraviolet rays is 5 seconds to 5 minutes, preferably 10 seconds to 3 minutes. However, it is adjusted in consideration of the intensity of ultraviolet rays. When the time is less than 5 seconds, the concentration of the starting point of polymerization is small, and when the time is 5 minutes or more, most of the monomers are polymerized, which makes it meaningless to provide the second step described later.

Next, in the second step, 1
Ultraviolet light having a light intensity of 0 mW was irradiated for 8 minutes. The amount of residual monomer after this step was 6%. Here, the residual monomer was measured by dissolving the liquid crystal and the polymer in the layer with chloroform and quantifying them using high performance liquid chromatography. The number average molecular weight of the produced polymer was 118,000 and the weight average molecular weight was 398,000.

In this step, the intensity of ultraviolet rays is 2 to
20 mW, preferably 3 to 18 mW. If it is less than 2 mW, a large amount of unreacted monomer remains, and the contrast and light scattering of the obtained display element are lowered. When it exceeds 20 mW, the characteristic variation of the obtained display element becomes large.

The UV irradiation time is generally 5 under the above conditions.
It is ˜15 minutes and sets the time for the polymer to sufficiently polymerize and cure.

In the liquid crystal panel formed as described above, the threshold voltage between the transparent state and the light scattering state was 16.2v and the saturation voltage was 22.3v. The reflection brightness is 48 when a data voltage of 15V is applied to the MIM element.
The reflection brightness when applying cd / m ² , 24v is 315c
It was d / m ² , and it was possible to realize a uniform display as a whole.

After this liquid crystal panel was left at 80 ° C. for 10 hours, the reflection brightness when the data voltage of 15 V of the MIM element was applied was 60 cd / m ² , and the reflection brightness when 24 v was applied was 304 cd / m ² . there were.

(Comparative Example) The same liquid crystal panel as in the above example was irradiated with an ultraviolet ray having a light intensity of 25 mW for 5 minutes in an environment of 55 ° C. The amount of residual monomer was 13%.
The produced polymer had a number average molecular weight of 106,000 and a weight average molecular weight of 278,000.

In this liquid crystal panel, the threshold voltage was 15.7v and the saturation voltage was 21.1v. MIM
The reflection brightness is 5 when the data voltage of 15V is applied.
The reflection brightness when applying 0 cd / m ² and 24 v is 34
It was 0 cd / m ² .

[0048] Upon standing the liquid crystal panel 80 ° C. 10 hours, the reflection luminance in the case of applying the data voltage 15v of the MIM element is increased to 93cd / m ^2, the reflection luminance in the case of applying the 24v is 291cd / m ² Decreased to.

In the above-mentioned examples, the amount of residual monomers is greatly reduced and the uniformity of display is improved as compared with the comparative examples.
Further, the decrease in transparency and scattering degree after being left at a high temperature was significantly suppressed as compared with the comparative example.

[0050]

As described above, according to the present invention, a large number of reaction nuclei (polymerization initiation points) are relatively uniformly formed by the high-intensity light irradiation in the first step, and the polymerization initiation points are mainly formed. The first step is completed within a short time in which the polymerization does not proceed deeply, and then, in the second step, the polymerization reaction slowly proceeds by light irradiation with low illuminance. Due to the two-stage light irradiation, a large number of relatively small polymer particles are densely formed inside the formed liquid crystal polymer composite layer, so that the liquid crystal polymer composite layer is likely to be connected to each other. It will be structurally stable. Therefore, stability with respect to temperature is also improved, and deterioration of electro-optical characteristics is suppressed. Further, since the polymerization reaction proceeds slowly around the polymerization initiation point formed with high density, the amount of the remaining polymer precursor is reduced, and the deterioration of reliability is prevented.

[Brief description of the drawings]

FIG. 1 is a process sectional view (a) and (b) showing an embodiment of a method for manufacturing a liquid crystal electro-optical element according to the present invention.

FIG. 2 is vertical sectional views (a) and (b) showing a driving state of a polymer-dispersed liquid crystal electro-optical element.

[Explanation of symbols]

 4 liquid crystal 5 polymer 10 liquid crystal polymer composite layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidekazu Kobayashi 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Co., Ltd. (72) Inventor Shuhei Yamada 3-3-5 Yamato, Suwa, Nagano Prefecture Seiko Epson Incorporated (72) Inventor Eiji Chino 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation

Claims (2)

[Claims] 1. A solution in which a liquid crystal and a polymer precursor are compatible with each other is housed between two substrates, and the solution is irradiated with light so that the liquid crystal and the polymer precursor are polymerized. In the method for producing a liquid crystal electro-optical element, which comprises forming a liquid crystal polymer composite layer in which the liquid crystal and the polymer are phase-separated while dispersing molecules with each other, in the step of polymerizing the polymer precursor, A method for manufacturing a liquid crystal electro-optical element, comprising: a first step of irradiating a solution with high illuminance light for a short time; and a second step of irradiating the solution with low illuminance light for a long time. 2. The method for manufacturing a liquid crystal electro-optical element according to claim 1, wherein in the first step and the second step, the treatment is performed in a state in which the solution is kept in each predetermined temperature range.