JPH07301787A - Liquid crystal display element manufacturing method - Google Patents

Abstract

(57) [Abstract] [Purpose] A polymer-dispersed type that can suppress volatilization of polymerizable monomers from a mixture during encapsulation between substrates and stabilize the composition ratio of the encapsulation between the substrates. A method for manufacturing a liquid crystal display device is provided. [Structure] When a mixture 2 containing a polymerizable monomer and a liquid crystal material is enclosed between two substrates 1 and 7, the mixture 2 is mixed with
If the temperature at which the mixture 2 phase-separates at atmospheric pressure is Tc, then Tc-
It is cooled to any temperature in the temperature range of Tc + 10 ° C or lower at 10 ° C or higher, and the degree of vacuum in the vacuum chamber 8 is set to 1 to
By decompressing to an arbitrary vacuum degree of 0.1 torr or less with rr or more, the composition change of the mixture 2 due to volatilization can be reduced,
Moreover, the mixture 2 can be prevented from phase-separating into the polymerizable monomer and the liquid crystal material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a liquid crystal display element used in a projection type display or the like.

[0002]

2. Description of the Related Art In a polymer dispersion type liquid crystal display device, a mixture of a liquid crystal material and a polymerizable monomer is introduced between two substrates and irradiated with ultraviolet rays or the like to cause the liquid crystal material to undergo phase separation. Polymerize. As a result, a state in which the liquid crystal material is dispersed in the polymer is formed between the two substrates (for example, flat panel display '91 Nikkei BP.
See page 221).

The conventional method for producing a polymer-dispersed liquid crystal display element, in particular, the method for introducing a mixture of a polymerizable monomer and a liquid crystal material between substrates includes, for example, the following.

An empty panel is prepared in which two substrates are bonded together with an interval of several μm to several tens μm. In order to enclose the mixture of the polymerizable monomer and the liquid crystal material in this empty panel, an injection port and an air hole are formed in the empty panel, and the mixture is brought into contact with the injection port under normal pressure to utilize the capillary phenomenon. Then it was installed in the empty panel.

For TN (twisted nematic) type liquid crystal and STN (super twisted nematic) type liquid crystal, a vacuum injection method and a dropping method (see Japanese Patent Laid-Open No. 62-89025) have been proposed. In the vacuum injection method, only the injection port is formed in the empty panel, and the mixture of the liquid crystal material and the polymerizable monomer is brought into contact with the injection port under reduced pressure and then returned to normal pressure to use the atmospheric pressure to mix the mixture. Install in empty panel. Further, in this vacuum injection method, a method of cooling the mixture introduced into the empty panel to near the melting point has been proposed.
(See JP-A-62-8630).

In addition, in the dropping method, an appropriate amount of the mixture is dropped on one substrate without forming an empty panel in advance, and the other substrate is attached to this substrate under reduced pressure. This dropping method is characterized in that the liquid crystal is exposed to vacuum for a relatively short time.

[0007]

In the method of introducing the mixture into the empty panel by capillary action at atmospheric pressure, air bubbles tend to remain in the panel, which is not suitable for mass production.

In order not to leave air bubbles in the panel, a vacuum injection method for injecting the mixture into the empty panel under reduced pressure may be used. However, when the vacuum injection method at room temperature is used, the polymerizable monomer in the mixture is removed. Most of them volatilized, and there was a problem that the composition ratio changed significantly.

An object of the present invention is to prevent the polymerizable monomer from volatilizing from the mixture during encapsulation between the substrates and to stabilize the composition ratio of the mixture encapsulated between the substrates. It is to provide a manufacturing method of a display element.

[0010]

In order to solve the above-mentioned problems, a method for manufacturing a liquid crystal display device of the present invention is characterized in that after a mixture containing a polymerizable monomer and a liquid crystal material is sealed between two substrates, In the step of producing a liquid crystal display element in which a polymerizable monomer is polymerized to disperse the liquid crystal material in a polymer,
It is characterized in that the mixture is sealed between two substrates whose internal pressure is reduced to atmospheric pressure or less, and the mixture is cooled to a temperature of room temperature or lower during the sealing.

Further, in the method for producing a liquid crystal display device of the present invention, a mixture containing a polymerizable monomer and a liquid crystal material is sealed between two substrates, and then the polymerizable monomer is polymerized to form a liquid crystal in a polymer. In the step of manufacturing a liquid crystal display element in which the material is dispersed, the mixture is dropped onto one substrate, and the other substrate is bonded to the other substrate in a depressurized space depressurized to atmospheric pressure or less. To do.

[0012]

In general, the polymerizable monomer has a relatively high volatility, and the boiling point decreases under reduced pressure, so that the volatility becomes higher. However, it is known that lowering the temperature lowers the volatility of the polymerizable monomer. Therefore, volatilization of the monomer can be reduced by lowering the temperature of the mixture of the polymerizable monomer and the liquid crystal material.

Further, in the vacuum injection method, the mixture is exposed to the vacuum for several tens of minutes or more, but in the dropping method, the mixture is exposed to the vacuum for a very short time of tens of seconds to several minutes, which causes a problem of volatility. Considering this, it is advantageous to use the dropping method. Furthermore, by cooling the mixture in this dropping method, it is possible to improve the effect of preventing a decrease due to volatilization of the monomer.

[0014]

Embodiments of the method of manufacturing a liquid crystal display device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a liquid crystal display device manufacturing apparatus capable of carrying out a first embodiment of a liquid crystal display device manufacturing method of the present invention. In this example, the following materials were used for the mixture 2 introduced between the two substrates 1 and 7. BL035 manufactured by Merck was used as the liquid crystal material, and 2 ethylhexyl acrylate was used as the polymerizable monomer.
Both are mixed, and viscoat 828 is used as an oligomer.
(Manufactured by Osaka Organic Chemical Industry) was added, and benzyl methyl ketal (manufactured by Nippon Kayaku) was added as a polymerization initiator. The mixture 2 does not exhibit liquid crystallinity at room temperature and is a uniform isotropic liquid. By cooling this to a temperature of 0 ° C. or lower under normal pressure, phase separation occurs and it appears cloudy. This is because the liquid crystal material that was uniformly dissolved at room temperature was deposited by phase separation, and at this time, small droplets of liquid crystal were present in the solution in a dispersed state, scattering light and making the solution cloudy.

A process of enclosing the mixture 2 between the two substrates 1 and 7 and polymerizing the polymerizable monomer to disperse the liquid crystal material in the polymer will be described with reference to FIG.

An appropriate amount of the mixture 2 of the liquid crystal material and the polymerizable monomer described above is dripped on one substrate 1 in advance, and the ultraviolet curable resin 3 is seal-printed on the peripheral portion thereof. The substrate 1 is set on the setting table 4 in the vacuum chamber 8. Inside the installation table 4, ethylene glycol cooled to −5 ° C. is circulated as the cooling medium 5 by the cooling mechanism 6, whereby the substrate 1 is cooled together with the installation table 4. By cooling the substrate 1, the mixture 2 on the substrate 1 was cooled to about 1 ° C. and held. Further, the vacuum pump 8 evacuated the air in the vacuum chamber 8 and evacuated to 0.1 torr. In the depressurized space in the vacuum chamber 8, the other substrate 7 held above the substrate 1 is moved downward by the substrate moving mechanism 9 and pressed against the substrate 1 on the installation table 4, so that the substrate 1 and the substrate 7 are separated from each other. To glue. Then, the vacuum chamber 8 is opened, the inside of the vacuum chamber 8 is returned to normal pressure, and the substrates 1 and 7 in which the mixture 2 is sealed are taken out.

The bonded substrates 1 and 7 were vacuum packed and fixed, and then heat-treated at 80 ° C. to spread the mixture 2 evenly in the substrates 1 and 7. After that, the substrates 1 and 7 are heated to 50 ℃
Then, the polymerizable monomer was polymerized, and the ultraviolet curable resin 3 was cured by being held at the temperature of 1. and polymerized liquid crystal panel was produced.

In this series of processes, the time during which the mixture 2 of the liquid crystal material and the polymerizable monomer was exposed to vacuum was about 60 seconds. During this period, 1% of the polymerizable monomer was volatilized from the mixture 2. However, when the mixture 2 was prepared, the problem was not caused by adding 1% more of the polymerizable monomer than the ideal value.

In the above process, when the mixture 2 dropped on the substrate 1 was not cooled, about 5% of the polymerizable monomer was volatilized from the mixture 2. Even in this case, if a large amount of the polymerizable monomer is volatilized in advance in the mixture 2, a polymer dispersed liquid crystal panel can be manufactured, but there is a problem that the dispersion between products is slightly increased.

When the mixture 2 is cooled to room temperature or lower as described above, the amount of the polymerizable monomer volatilized from the mixture 2 is reduced. Here, in order to minimize the decrease due to volatilization of the polymerizable monomer, it is desirable to cool the mixture 2 to a temperature below the temperature at which the mixture 2 separates into the liquid crystal material and the polymerizable monomer. However, the cooling temperature of the mixture 2 is lowered below the temperature at which the liquid crystal material and the polymerizable monomer are separated, and the separation of the mixture 2 is promoted. Even if the mixture 2 in which the separated state is significantly accelerated by enclosing the mixture 2 in the substrates 1 and 7 and then heat-treated at 80 ° C. by being cooled to such a temperature is not homogenized, the liquid crystal material distribution is The unevenness occurs.
Therefore, from the viewpoint of the uniformity of the mixture 2, it is desirable that the cooling temperature of the mixture 2 be equal to or higher than the temperature at which the mixture 2 separates the liquid crystal material and the polymerizable monomer.

Therefore, the cooling temperature of the mixture 2 which satisfies the contradictory conditions of suppressing the volatilization of the polymerizable monomer and ensuring the uniformity of the mixture 2 is as low as possible, and It is desirable to use a temperature at which phase separation does not occur significantly. By cooling the mixture 2 to such a temperature, even if the mixture 2 enclosed in the substrates 1 and 7 undergoes a slight phase separation, the phase separation is such that the heat treatment at 80 ° C. sufficiently melts the liquid crystal material to diffuse. If so, there will be no practical problems.

Specifically, as a cooling temperature satisfying the above conditions, when the temperature at which the mixture 2 is phase-separated under normal pressure is Tc, it is Tc-10 ° C or higher and Tc + 10 ° C or lower at any temperature. It is sufficient if the mixture 2 on the substrate 1 is heated to Tc-10 ° C or higher and Tc + 10 ° C in the vacuum chamber 8.
By cooling to any temperature in the following temperature range, the volatilization amount of the polymerizable monomer can be minimized and the phase separation of the mixture 2 can be suppressed to such an extent that it can be sufficiently homogenized by heat treatment at 80 ° C.

When a TN type liquid crystal display device is manufactured by a known vacuum injection method, most of the polymerizable monomers are volatilized, so that it is very difficult to manufacture a polymer dispersion type liquid crystal display device. .

Therefore, in the second embodiment of the method of manufacturing a liquid crystal display device of the present invention, the mixture 2 is cooled to about 0 ° C. by the cooling mechanism in the vacuum injection method and the two substrates 1 and 7 are bonded together. Injected into the panel. As a result, the volatilization amount of the polymerizable monomer in the mixture 2 in the empty panel can be reduced to about 10%. By increasing the addition amount of the polymerizable monomer in the mixture 2 in advance, the TN type liquid crystal display can be obtained by the vacuum injection method. It has become possible to manufacture devices. Here, when the temperature at which the mixture 2 phase-separates under normal pressure is Tc, the cooling temperature of the mixture 2 of the second embodiment of about 0 ° C. belongs to a temperature range of Tc−10 ° C. or higher and Tc + 10 ° C. or lower. Is the temperature.

Further, the volatilization amount of the polymerizable monomer also largely depends on the degree of vacuum, and the degree of vacuum in the vacuum chamber 8 in the first embodiment and the substrates 1, 7 in the second embodiment.
The lower the degree of vacuum inside, the more the amount of volatilization can be reduced. However, there arises a problem that the degree of vacuum decreases and the number of bubbles generated in the mixture 2 enclosed in the substrates 1 and 7 increases. In order to solve this problem, in the first embodiment, when the mixture 2 is sealed between the two substrates 1 and 7, the decompression space in the vacuum chamber 8 is decompressed to 0.1 torr, so that the substrate 1, The mixture 2 enclosed in 7 had almost no bubbles, and the volatilization of the polymerizable monomer was suppressed to a negligible amount.

In the first or second embodiment, practically, when the mixture 2 is sealed between the two substrates, the degree of vacuum is set to 10 torr or less and 0.01 torr or more. It was possible to stabilize the volatilization amount of the monomer without causing bubbles to stand out. Further, in the first embodiment, the degree of vacuum in the vacuum chamber 8 is reduced, and in the second example, the degree of vacuum in the substrates 1 and 7 is reduced to an arbitrary degree of vacuum of 1 torr to 0.1 torr, so that the substrate 1 It was possible to almost completely eliminate the air bubbles in 7 and 7, and to make the volatilization of the monomer negligible.

[0027]

As described above, according to the method of manufacturing a liquid crystal display element described in the claims of the present invention,
Since the composition change of the mixture which is the material of the liquid crystal can be reduced and the phase separation of the mixture can be suppressed, a polymer dispersion type liquid crystal display device of stable quality can be manufactured.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a liquid crystal display element manufacturing apparatus capable of carrying out a first embodiment of a liquid crystal display element manufacturing method of the present invention.

[Explanation of symbols]

1, 7 ... Substrate, 2 ... Mixture, 3 ... UV curable resin,
4 ... Installation stand, 5 ... Cooling medium, 6 ... Cooling mechanism, 8
... vacuum chamber, 9 ... substrate moving mechanism, 10 ... vacuum pump.

(72) Inventor Junji Nakajima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Issei Inoue, 1006 Kadoma, Kadoma City, Osaka Prefecture

Claims (9)

[Claims] 1. A liquid crystal display device in which a mixture containing a polymerizable monomer and a liquid crystal material is sealed between two substrates and then the polymerizable monomer is polymerized to disperse the liquid crystal material in a polymer. In the step, a method for manufacturing a liquid crystal display device, characterized in that the mixture is sealed between two substrates whose internal pressure is reduced to atmospheric pressure or lower, and the mixture is cooled to a temperature of room temperature or lower during the sealing. 2. The method for manufacturing a liquid crystal display element according to claim 1, wherein the inside of the two substrates is depressurized to an arbitrary vacuum degree of 10 torr or less and 0.01 torr or more. 3. The method of manufacturing a liquid crystal display device according to claim 1, wherein the inside of the two substrates is depressurized to an arbitrary vacuum degree of 1 torr or less and 0.1 torr or more. 4. A step of manufacturing a liquid crystal display device in which a mixture containing a polymerizable monomer and a liquid crystal material is enclosed between two substrates and then the polymerizable monomer is polymerized to disperse the liquid crystal material in a polymer. 3. The method for manufacturing a liquid crystal display device according to, wherein the mixture is dropped on one substrate and the other substrate is attached to the one substrate in a decompressed space decompressed to atmospheric pressure or less. 5. The depressurized space is 0.01 torr at 10 torr or less.
The method for producing a liquid crystal display device according to claim 4, wherein the pressure is reduced to an arbitrary vacuum degree equal to or higher than rr. 6. The reduced pressure space is 0.1 torr at 1 torr or less.
The method for producing a liquid crystal display device according to claim 4, wherein the pressure is reduced to an arbitrary vacuum degree of r or more. 7. The liquid crystal display device according to claim 4, wherein the mixture dropped onto the one substrate is cooled to a temperature equal to or lower than room temperature and the other substrate is bonded. Production method. 8. The method according to claim 1, wherein the mixture is cooled to room temperature or lower and to any temperature higher than a temperature at which the mixture separates into the liquid crystal material and the polymerizable monomer under normal pressure. 3. A method for manufacturing a liquid crystal display element according to 3 or 7. 9. The mixture is cooled to an arbitrary temperature of Tc + 10 ° C. or lower and Tc−10 ° C. or higher, where Tc is the temperature at which the mixture separates into the liquid crystal material and the polymerizable monomer at normal pressure. The method for manufacturing a liquid crystal display device according to claim 1, 2, 3, or 7.