JP2001125108A - Method of manufacturing for alignment layer and method of manufacturing for liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing for an alignment layer which attains lowering of temperature in a process for forming the alignment layer and controlling the alignment property of the layer over a wide range and a method of manufacturing for a liquid crystal display device having excellent contrast and display quality. SOLUTION: The surfaces of plastic film substrates 11, 12 on which transparent electrodes 11a, 12a are formed are coated with a polymer solution for alignment so as to form polymer solution films 11b1, 12b1 for alignment. Subsequently the films are dried with heating under the reduced pressured so as to form polymer films 11b2, 12b2 for alignment. In this case, it is desirable to dry the polymer solution films 11b1, 12b1 for alignment with heating up to 80-120 deg.C while reducing the pressure to <=133 Pa. Subsequently the alignment layers 11b, 12b are formed by subjecting the polymer films to alignment treatment by a rubbing method or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an alignment film and a method for manufacturing a liquid crystal device, and more particularly to a method for manufacturing an alignment film using an alignment polymer solution in which a soluble alignment polymer is dissolved in a predetermined solvent. And a method for manufacturing a liquid crystal device.

[0002]

2. Description of the Related Art FIG. 3 is a schematic sectional view of a general simple matrix type liquid crystal device 100, and the structure of the liquid crystal device will be briefly described.

[0003] As shown in FIG. 3, a substrate 101 and a counter substrate 102 are sealed with a sealing material 1 at the periphery of each substrate.
A liquid crystal cell is formed by adhering a liquid crystal between the substrate 101 and the opposing substrate 102 at predetermined intervals via the substrate 04. Transparent electrodes 101a and 102a are formed on the inner surfaces of the substrate 101 and the counter substrate 102, respectively. Substrates 101, 102 on which transparent electrodes 101a, 102a are formed
Alignment film 10 for further aligning the liquid crystal on the inner surface of
1b and 102b are formed. Further, a spherical spacer 103 made of glass, plastic, ceramic, or the like for keeping the distance between the substrate 101 and the counter substrate 102 constant is disposed between the substrate 101 and the counter substrate 102. The liquid crystal injected into the liquid crystal cell is aligned according to the alignment of the alignment films 101b and 102b, and the liquid crystal layer 105 is formed. Although illustration is omitted,
A polarizing plate and the like are attached to the front and back of the liquid crystal cell.

Conventionally, in a liquid crystal display device such as a TN (Twisted Nematic) mode or an STN (Super Twisted Nematic) mode, a transparent electrode 101 is used as a method of forming an alignment film for aligning liquid crystal molecules in a predetermined direction.
After forming an oriented polymer film such as a polyimide film having orientation on the substrates 101 and 102 on which the a and 102a are formed, the surface of the oriented polymer film is subjected to a certain direction with a cloth such as rayon or nylon under a load. A method of performing an alignment treatment by a rubbing method of rubbing (rubbing) or a method of irradiating ultraviolet rays from a predetermined direction above an oriented polymer film is known.

As a method of forming an oriented polymer film,
An oriented polymer solution in which a soluble oriented polymer such as a soluble polyimide having orientation is dissolved in a predetermined solvent is applied to the transparent electrode 101 by a method such as spin coating or printing.
a and 102a are uniformly coated on the substrates 101 and 102 to form an oriented polymer solution film.
A method of forming by drying at a temperature of 00 ° C. to remove the solvent and drying is generally performed.

According to the above method, it is possible to control the orientation direction and pretilt angle of the orientation film by combining the molecular structure of the oriented polymer to be used and the orientation treatment by rubbing or ultraviolet irradiation. Can be controlled.

[0007]

By the way, in particular, the substrate 1
A plastic film substrate having a thickness of 0.2 mm or less in which one or more protective layers are laminated on at least one surface of a polycarbonate, polyacrylate, polyethersulfone, or polyethylene terephthalate substrate film as 01 and 102. When used, the heat-resistant temperature of the plastic film substrate is a maximum of 120 ° C., which is lower than the normal processing temperature (150 to 200 ° C.) of the step of drying the oriented polymer solution film. This is achieved by increasing the proportion of the low-boiling solvent in the solvent of the solution and changing the molecular structure of the polyimide so that the polyimide can be dissolved in a solvent having a high proportion of the low-boiling solvent.

For example, in the case of a substrate made of a heat-resistant material such as glass, a polyimide solution containing a main solvent having a boiling point of about 220 ° C., such as N-methyl-2-pyrrolidone or γ-butyrolactone, and ethylene glycol mono- A mixture of a low-boiling solvent having a boiling point of about 80 ° C. such as ethyl ether or ethylene glycol monobutyl ether at a ratio of 8 to 2 or the like and a polyimide dissolved in a solvent having a boiling point of 150 to 180 ° C. is used.

However, when the above-mentioned plastic film substrate is used, the proportion of a solvent having a low boiling point such as ethylene glycol monoethyl ether or ethylene glycol monobutyl ether in the solvent must be increased. The structure becomes limited. As a result, there is a problem that the alignment of the obtained alignment film is limited due to the restriction of the molecular structure of the polyimide.

Further, in the drying process of the oriented polymer solution film according to the prior art, the solvent is not completely removed, and the residual solvent affects the orientation of the oriented film, thereby limiting the orientation. Since the alignment of the liquid crystal is controlled by the alignment of the alignment film, when the alignment of the alignment film is limited, the display performance of the obtained liquid crystal display device is limited. In particular, since a high pretilt angle cannot be obtained in the alignment film, there is a problem that the display performance is limited in the STN mode requiring a high pretilt angle in the alignment film.

For example, in the STN mode, the liquid crystal is twisted by 240 °, and in order to obtain good display characteristics, the pretilt angle of the alignment film is set to 5 to 6 °, and the liquid crystal is twisted by 250 to 255 ° to obtain good display characteristics. It is necessary to set the pretilt angle of the alignment film to 7 to 8 ° in order to obtain the above. However, in the case of using a polyimide solution having a high ratio of a low boiling point solvent, the limit of obtaining a pretilt angle of 4 to 5 ° is the limit even when combined with an alignment treatment such as a rubbing method or ultraviolet irradiation which is the next step. Yes, as a result
The limit is to make it twist by 40 °.

It is also possible to forcibly twist up to 240 ° or more, but in that case, there is a problem that the influence of the cell thickness distribution on the display quality becomes large.

In the STN mode liquid crystal display device,
Δn · d value (where Δn is the refractive index of the liquid crystal and d is the cell thickness)
It is known that the transmittance of light is changed by the change of .DELTA.n.d value, that is, if the distribution of the cell thickness d is large, a distribution occurs in the light transmittance, that is, the brightness, so that the contrast is lowered. . If the change in the Δn · d value, that is, the distribution of the cell thickness d is large, in the STN mode, the unique yellow or blue coloration is eliminated by the phase difference plate to compensate for black and white, but at this time, the optical characteristics deteriorate. However, color unevenness occurs on the display. Also, if the cell thickness d has a distribution, the sharpness of the liquid crystal deteriorates, and the contrast decreases. As described above, in the STN mode liquid crystal display device, it is known that if the distribution of the cell thickness d is large, the contrast is lowered and color unevenness is generated in the display, so that the display quality is deteriorated. This problem occurs when the distribution of d is ± 0.1 to 0.2 μm or more. However, 24
In the case of twisting up to 0 ° or more, the display quality is good only when the distribution of the cell thickness d is ± 0, that is, when there is no distribution of the cell thickness, but it is practically impossible to eliminate the distribution of the cell thickness. Since it is impossible, the resulting liquid crystal display device has poor contrast and poor display quality.

Therefore, the present invention solves the above-mentioned problems, and comprises a step of forming an oriented polymer solution film by applying an oriented polymer solution on a substrate on which a transparent electrode is formed, followed by drying. Production of alignment films that realizes an alignment film with a high pretilt angle and enables a wide range of control over the alignment of the alignment film by enabling the temperature to be lowered and allowing the solvent to be completely removed. It is an object of the present invention to provide a method and a method for manufacturing a liquid crystal display device having excellent display quality with good contrast.

[0015]

Means for Solving the Problems A first means taken by the present invention to solve the above problems is to form an alignment film for aligning liquid crystal in a predetermined direction on a substrate. The method is characterized in that an oriented polymer solution in which a soluble oriented polymer is dissolved in a predetermined solvent is applied thereon to form an oriented polymer solution film, and then heated under reduced pressure.

The substrate is characterized in that one or more protective layers are laminated on at least one surface of a substrate film of a polycarbonate, polyacrylate, polyethersulfone or polyethylene terephthalate.

After forming the oriented polymer solution film, it is desirable to heat the film to 80 to 120 ° C. while reducing the pressure to 133 Pa or less.

A second means taken by the present invention to solve the above-mentioned problem is that an alignment film for aligning a transparent electrode and a liquid crystal in order on an inner surface of two opposing substrates sandwiching a liquid crystal layer. In a method for manufacturing a liquid crystal device, a soluble polymer having an orientation polymer dissolved in a predetermined solvent is applied on the surface of the substrate on which the transparent electrode is formed, and a high alignment property is obtained. After forming the molecular solution film, the film is dried by heating under reduced pressure to form the alignment film.

The substrate is characterized in that one or more protective layers are laminated on at least one surface of a substrate film of a polycarbonate, polyacrylate, polyethersulfone or polyethylene terephthalate.

After forming the oriented polymer solution film, it is preferable to form the oriented film by heating to 80 to 120 ° C. while reducing the pressure to 133 Pa or less.

According to the above means, even when a plastic film substrate is used, in the step of drying the oriented polymer solution film, it can be dried at a low temperature of 80 to 120 ° C. by heating while reducing the pressure. As it can be used, an oriented polymer solution using a high boiling point solvent can be used, so the molecular structure of the oriented polymer used is not limited, and the solvent existing in the deep part can be completely removed by drying under reduced pressure. Therefore, an alignment film having a high pretilt angle can be realized, and the alignment of the alignment film can be controlled in a wide range. In addition, since the alignment of the liquid crystal is controlled over a wide range by controlling the alignment of the alignment film over a wide range, a liquid crystal display device with good contrast and excellent display quality can be provided.

[0022]

Next, an embodiment according to the present invention will be described in detail. FIG. 1 shows a process chart illustrating a method for manufacturing a liquid crystal display device 10 according to an embodiment of the present invention, and the process is described.

As shown in FIGS. 1 (a) and 1 (b), transparent electrodes 11a, 12a are provided on the surfaces of a substrate 11 and a counter substrate 12, respectively.
a is formed. As the substrate 11 and the counter substrate 12, at least one protective layer is laminated on at least one surface of a polycarbonate, polyacrylate, polyethersulfone, or polyethylene terephthalate base film and has a thickness of 0.2 mm or less. A plastic film substrate is used. Although only two 11a and one 12a are shown in the drawings for simplicity, a number (for example, several tens to several hundreds) corresponding to the number of pixels required for an actual liquid crystal display device is shown. ) 11a and 12a are formed.

Next, as shown in FIGS. 1 (c) and (d), an oriented polymer solution obtained by dissolving a soluble oriented polymer such as a soluble polyimide having an orientation in a predetermined solvent is spin-coated. The orientation polymer solution film 11 is uniformly coated on the surface of the substrate 11 on which the transparent electrodes 11a and 12a are formed and the counter substrate 12 by physical printing and by physical adsorption.
b1 and 12b1 are formed. At this time, the film is formed so that the final film thickness after drying is about 50 to 100 nm.

Next, as shown in FIGS. 1 (e) and 1 (f), the oriented polymer solution films 11b1 and 12b1 are heated under reduced pressure to remove the solvent and then dried, whereby the oriented polymer solution film is dried. The films 11b2 and 12b2 are formed. At this time, it is desirable to dry by heating the oriented polymer solution films 11b1 and 12b1 to 80 to 120 ° C. while reducing the pressure to 133 Pa or less.

Next, as shown in FIGS. 1 (g) and 1 (h), the surface of the orienting polymer films 11b2 and 12b2 is subjected to an alignment treatment by a rubbing method, ultraviolet irradiation, or the like, thereby forming the alignment film 11b.
b and 12b are formed.

Next, as shown in FIG.
a spherical spacer 1 made of glass, plastic, ceramic or the like on the surface of the substrate 11 on which
3 are scattered, the substrates 12 on which the alignment films 12b are formed via the spacers 13 are placed so that the alignment films face each other, and the peripheral portion is fixed with the sealing material 14 to manufacture a liquid crystal cell. When liquid crystal is injected into this liquid crystal cell, the liquid crystal is aligned with the alignment film 1.
1b and 12b, and the liquid crystal layer 15
Is formed. Finally, although not shown, the liquid crystal display device 10 is manufactured by attaching polarizing plates and the like to the front and back of the liquid crystal cell.

According to the present invention, even when a plastic film substrate is used, the process of drying the oriented polymer solution film is performed at a low temperature of 80 to 120 ° C. by heating the oriented polymer solution film while reducing the pressure to 133 Pa or less. , The range of choice of the oriented polymer solution to be used is widened, and the solvent can be completely removed, so that it is possible to produce an oriented film having a high pretilt angle of 6 ° or more. The orientation of the film can be controlled over a wide range. In addition, since the orientation of the alignment film can be controlled over a wide range, the twist angle of the liquid crystal can be controlled over a wide range, and a liquid crystal display device with good contrast and excellent display quality can be provided.

Next, a specific example of an electronic apparatus including the liquid crystal display device 10 manufactured according to the above embodiment will be described.

FIG. 2A is a perspective view showing an example of a portable telephone. In FIG. 2A, reference numeral 200 denotes a mobile phone main body, and reference numeral 201 denotes a liquid crystal display unit including the liquid crystal display device 10 described above.

FIG. 2B is a perspective view showing an example of a portable information processing device such as a word processor or a personal computer. Fig. 2 (b)
1, reference numeral 300 denotes an information processing apparatus, 301 denotes an input unit such as a keyboard, 303 denotes an information processing main body, and 302 denotes a liquid crystal display unit provided with the liquid crystal display device 10 described above.

FIG. 2C is a perspective view showing an example of a wristwatch-type electronic device. In FIG. 2C, reference numeral 400 denotes a watch main body, and reference numeral 401 denotes a liquid crystal display unit including the liquid crystal display device 10 described above.

Each of the electronic devices shown in FIGS. 2A to 2C includes the liquid crystal display device 10 described above.
The display quality is excellent with good contrast.

[0034]

EXAMPLES (Examples 1 and 2) A polyimide solution film was formed on a substrate by using a polyimide solution STX-24 manufactured by Hitachi Chemical as an oriented polymer solution. Next, the polyimide solution film was dried by heating at 120 ° C. in Example 1 and at 80 ° C. in Example 2 for 3 hours under a reduced pressure of 133 Pa to form a polyimide film. After that, an alignment treatment was performed by a rubbing method to form an alignment film. DI as liquid crystal
A liquid crystal display device was manufactured using a product of Company C with a Δn · d value (where Δn is the refractive index of the liquid crystal and d is the cell thickness) of 0.8. Table 1 shows the performance of the obtained alignment film and the liquid crystal display device.
Shown in

[0035]

[Table 1]

(Comparative Examples 1 and 2) A polyimide solution film was formed on a substrate by using a polyimide solution STX-24 manufactured by Hitachi Chemical Co., Ltd. as an oriented polymer solution. Next, under a reduced pressure of 133 Pa, the temperature was 70 ° C. in Comparative Example 1 and 130 ° C. in Comparative Example 2.
For 3 hours, the polyimide solution film was dried to form a polyimide film. Then, Examples 1 and 2
In the same manner as described above, formation of an alignment film and fabrication of a liquid crystal display device were performed.

(Comparative Examples 3 and 4) A polyimide solution film was formed on a substrate using a polyimide solution STX-24 manufactured by Hitachi Chemical as an oriented polymer solution. Next, the polyimide solution film was dried by heating at 120 ° C. for 3 hours under a reduced pressure of 266 Pa in Comparative Example 3 and under a reduced pressure of 665 Pa in Comparative Example 4, thereby forming a polyimide film. afterwards,
As in Examples 1 and 2, formation of an alignment film and fabrication of a liquid crystal display device were performed, and the performance of the obtained alignment film and the liquid crystal display device is shown in Table 1.

(Comparative Examples 5 and 6) An alignment film was formed and a liquid crystal display device was manufactured by a conventional technique. In Comparative Examples 5 and 6, STX-24 was prepared as an oriented polymer solution by adjusting STX-24 so that the boiling point of the solvent was 120 ° C. or lower.
Using 4-9, a polyimide solution film was formed. Next, the polyimide solution film was dried by heating at 120 ° C. for 3 hours under normal pressure to form a polyimide film. At this time, heating was performed in an air atmosphere in Comparative Example 5 and in a nitrogen atmosphere in Comparative Example 6. Thereafter, similarly to Examples 1 and 2, formation of an alignment film and fabrication of a liquid crystal display device were performed, and the performance of the obtained alignment film and the liquid crystal display device is shown in Table 1.

In Table 1, the steepness values are 90% light transmittance and 10% light transmittance in relation to applied voltage and light transmittance.
% Indicates the ratio of the applied voltage, and the closer the ratio is to 1, the more excellent the steepness and the better the contrast. The value of the maximum contrast is a value when driven at 1/64 duty. The cell thickness margin indicates a distribution from the center value of the cell thickness, and indicates that a liquid crystal display device having good optical characteristics can be obtained when the cell thickness is within the range shown in the table.

The pretilt angles of the alignment films obtained in Comparative Examples 5 and 6 according to the prior art were 3 to 4 ° and 4 to 5 °, respectively, whereas the pretilt angles of the alignment films obtained in Examples 1 and 2 were Has a high pretilt angle of 6 to 8 °.
As a result, in Comparative Examples 5 and 6, the liquid crystal was 230 °, respectively.
Twisting by 240 ° was the limit, whereas in Examples 1 and 2, twisting was possible up to 255 °. In Examples 1 and 2, compared to Comparative Examples 5 and 6,
The sharpness value was close to 1 and the value of the maximum contrast was large, that is, an excellent display quality with excellent steepness and good contrast was obtained. Further, in Comparative Examples 5 and 6, the display quality deteriorates when the cell thickness distribution is ± 0.1 μm or more, whereas in Examples 1 and 2, the cell thickness distribution is ± 0.1 μm.
Since the display quality is good when the thickness is within 2 μm, a liquid crystal display device with better display quality can be obtained.

Further, even if heating was performed under the same reduced pressure as in Examples 1 and 2, a good alignment film and liquid crystal display device could not be obtained at a heating temperature of 70 ° C. or less as shown in Comparative Example 1.
In Comparative Example 2 in which heating was performed at 130 ° C., the plastic film substrate deteriorated or deformed, and a good liquid crystal display device was not obtained. Further, as shown in Comparative Examples 3 and 4, 13
Under a reduced pressure of 4 Pa or more, the polyimide solution film was not sufficiently dried, and a favorable alignment film and liquid crystal display device could not be obtained. Therefore, by drying the polyimide solution film by heating it to 80 to 120 ° C. while reducing the pressure to 133 Pa or less, it was possible to obtain a good alignment film and a liquid crystal display device.

[0042]

As described above, according to the present invention, an oriented polymer solution in which a soluble oriented polymer is dissolved in a predetermined solvent is uniformly applied on a substrate on which a transparent electrode is formed, and By heating the oriented polymer solution film while reducing the pressure after forming the polymer solution film, it is possible to lower the temperature of the drying process of the oriented polymer solution film and completely remove the solvent. Therefore, even when a plastic film substrate is used, an alignment film having a high pretilt angle is realized, and the alignment property of the alignment film can be controlled in a wide range. Can be provided. In the present invention, the oriented polymer solution film is set to 133 Pa
It is desirable to dry by heating to 80 to 120 ° C. under reduced pressure.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for manufacturing a liquid crystal display device according to an embodiment of the present invention.

FIG. 2A is a diagram showing an example of a mobile phone provided with a liquid crystal display device manufactured according to the above embodiment, and FIG. 2B.
FIG. 2 is a diagram illustrating an example of a portable information processing device including a liquid crystal display device manufactured according to the above embodiment. FIG. 2C is an example of a wristwatch-type electronic device including the liquid crystal display device manufactured according to the above embodiment. FIG.

FIG. 3 is a schematic sectional view showing the structure of a general simple matrix type liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 11 Substrate 12 Counter substrate 11a, 12a Transparent electrode 11b, 12b Orientation film 11b1, 12b1 Orientation polymer solution film 11b2, 12b2 Orientation polymer film 13 Spacer 14 Sealing material 15 Liquid crystal layer

Claims (6)

[Claims] In forming an alignment film for aligning liquid crystal in a predetermined direction on a substrate, an alignment polymer solution obtained by dissolving a soluble alignment polymer in a predetermined solvent is formed on the surface of the substrate. A method for producing an alignment film, comprising applying, forming an alignment polymer solution film, and then heating while reducing the pressure. 2. The device according to claim 1, wherein the substrate is formed by laminating at least one protective layer on at least one surface of a polycarbonate, polyacrylate, polyethersulfone, or polyethylene terephthalate base film. A method for producing an alignment film, comprising: 3. The method for producing an alignment film according to claim 1, wherein after forming the alignment polymer solution film, the film is heated to 80 to 120 ° C. while reducing the pressure to 133 Pa or less. Method. 4. A method for manufacturing a liquid crystal device, comprising: a transparent electrode and an alignment film for aligning liquid crystal sequentially formed on inner surfaces of two opposing substrates sandwiching a liquid crystal layer. On the surface of the formed substrate, an oriented polymer solution obtained by dissolving a soluble oriented polymer in a predetermined solvent is applied to form an oriented polymer solution film, and then dried by heating under reduced pressure. And forming the alignment film. 5. The substrate according to claim 4, wherein at least one protective layer is laminated on at least one surface of a substrate film of a polycarbonate, polyacrylate, polyethersulfone, or polyethylene terephthalate. A method for manufacturing a liquid crystal device, comprising: 6. The method according to claim 4, wherein after forming the oriented polymer solution film, the orientation film is formed by heating to 80 to 120 ° C. while reducing the pressure to 133 Pa or less. A method for manufacturing a liquid crystal device, characterized by: