JP3154142B2 - Method of forming alignment film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an alignment film, and more particularly to a method for forming an alignment film for a liquid crystal display (hereinafter, referred to as an LCD).

[0002]

2. Description of the Related Art FIG. 11 is a sectional view showing the structure of an LCD.

That is, two glass substrates 1 and 2 face each other,
On these opposing surfaces, the transparent conductive films 3 and 6 and the alignment films 8 and 8 are applied in this order, and the liquid crystal cell 9 is disposed between the alignment films 8 and 8.
Are sandwiched, and the liquid crystal cell 9 and the alignment films 8 and 8 are
The LCD is constructed by being surrounded by a glass spacer 10 for setting the thickness of the LCD to a predetermined size. The alignment film 8 is subjected to a rubbing process prior to liquid crystal injection, so that the arrangement of molecules is aligned in a predetermined direction, whereby the molecules of the liquid crystal are aligned.

[0004] The shape of the transparent conductive films 3 and 6 is changed to XII- in FIG.
FIG. 12 is an enlarged sectional view taken along the line XII and FIG. 14 is an enlarged sectional view taken along the line XIII-XIII.

The transparent conductive film 3 is composed of a large number of pixel electrodes 4 arranged regularly and the same number of signal electrodes 5 connected thereto, and the terminal portions 5 a of the signal electrodes 5 are connected to the glass substrate 1 outside the spacer 10. It is extended above.

The other transparent electrode 6 has a portion surrounded by a spacer 10 serving as a common electrode 7, and its terminal portion 7a serves as a spacer.
It extends on the glass substrate 2 outside 10.

In display, a voltage is applied to the selected pixel electrode 4 by selectively inputting an electric signal to the signal electrode 5, and the liquid crystal cell portion corresponding only to this pixel electrode becomes translucent. It is done by things.

In addition to the above-mentioned shapes, the transparent conductive film has electrodes X ₁ , which are formed in stripes on one glass substrate and the other glass substrate along directions orthogonal to each other, as shown in FIG. X ₂ ,..., X _m and Y ₁ , Y ₂ ,.
_{There is a case where n} is set as _n and a number of intersections of both electrodes are pixels. In the LCD having this structure, the electrodes X ₁ , X ₂ ,.
By selectively inputting electric signals to _Xm and Y ₁ , Y ₂ ,..., Y _n , a liquid crystal cell portion corresponding to a pixel is selectively translucent to perform display. .

As a method of forming an alignment film on a transparent conductive film, there are a method of obliquely depositing an inorganic alignment film material and a method of applying an organic alignment film material. The oblique deposition method has an advantage that a subsequent rubbing step for orientation is unnecessary, but the deposition requires a long time. Among the coating methods, the spin coating method is particularly advantageous because the working time is short.

As a material for the alignment film, polyimide is generally used. However, to apply polyimide by spin coating, the application is completed in a short time.
It is necessary to make the viscosity of the paint sufficiently small. However, there are few types of solvents that can meet this demand, and therefore, it is difficult to obtain a uniform film thickness, and thus the orientation is insufficient.

[0011]

Therefore, instead of directly spin-coating the polyimide, it is necessary to spin-coat a polyamic acid which is a precursor of the polyimide, and then imidize the coating film of the polyamic acid to form a polyimide film. Conceivable. Since polyamic acid is an acid, it has good compatibility with many kinds of solvents, has a large degree of freedom in selecting a solvent, and therefore, it is easy to adjust the viscosity of a coating material.

However, the coating of polyamic acid has poor wettability to the transparent conductive film and is hardly adsorbed.
It is difficult to completely apply on the transparent conductive film. For this reason, as shown in FIG. 15, the region 31 where the paint is applied and the region 32 where the paint is not applied appear in a fan shape around the rotation center O during spin coating. Since the surface of the region 31 to which the polyamic acid paint is applied becomes bluish and transparent, it can be distinguished from other regions 32.

As a result of intensive studies, the inventor of the present invention illuminated the transparent conductive film with light in a specific wavelength range prior to the above-mentioned coating to thereby improve the wettability and adsorptivity of the polyamic acid paint on the transparent conductive film. It has been found that a good coating film which is improved and has no coating unevenness can be obtained. The present invention has been made based on the above findings.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for forming an alignment film capable of uniformly forming an alignment film on a transparent conductive film. And

[0015]

According to the present invention, in forming an alignment film on the surface of a substrate, the step of forming a conductive film on the surface of the substrate includes the step of forming a conductive film on the substrate surface in a range of 0.5 to 6.0 μm in the spectral distribution. To reach with energy of 10mW / cm ² or more,
At least a step of irradiating the conductive film with light, a step of coating the light-irradiated surface of the substrate with a precursor of the alignment film, and a step of heat-treating the precursor to form the alignment film. And a method for forming an alignment film.

In the present invention, it is advantageous from the viewpoint of productivity that the coating with the precursor is carried out by a spin coating method, and the light irradiation is carried out when the component having a spectral distribution within the range of 0.5 to 3.0 μm is 50 mW / cm ^2. It is even more desirable to do so with the above energy. In the present invention, it is even more desirable to perform spin coating immediately after light irradiation.

[0017]

The above-mentioned light irradiation is performed prior to coating the conductive film with the precursor of the alignment film, so that the above-mentioned coating is performed in a favorable state. This is considered to be due to the fact that the surface of the conductive film is activated by the light irradiation, and the surface activation improves the wettability of the coating material coating on the conductive film.

In addition, by performing the above-described coating immediately after the light irradiation, the coating is performed while the activated state of the conductive film surface is sufficiently maintained and good wettability is exhibited, and a good result is obtained. It is considered something.

[0019]

Embodiments of the present invention will be described below.

Example 1 Indium tin oxide (ITO), which is widely used as a transparent conductive film material, is formed on a glass substrate surface.
The coating of de) was applied by a customary evaporation method.

As shown schematically in FIG. 1, an infrared lamp 13 was disposed at a position 17 cm away from the glass substrate 11 on the side of the ITO film 12. In the figure, reference numeral 14 denotes a mounting table on which the glass substrate 11 is mounted. The dimensions of the glass substrate 11 are 43 mm × 50 mm × 1 mm, and the ITO film 12 is formed on the entire surface of one main surface of the glass substrate 11 without patterning. As the lamp 13, an R100 / 110V 250WRH infrared lamp manufactured by Iwasaki Electric Co., Ltd. was used. This infrared lamp has a spectral distribution shown in FIG. 2, and has a near infrared component as a major component.

FIG. 3 is a graph showing the relationship between the irradiation time by the infrared lamp 13 and the power per unit area received by the ITO film 12 using the apparatus of FIG.

As can be seen from FIG. 3, the power reaches about 500 mW / cm ² about 30 seconds after the power is turned on, and thereafter, the power is saturated without any apparent increase. Therefore, in order to apply stable power, it is appropriate to set the irradiation time to 1 to 3 minutes. However, if necessary, the wettability can be adjusted by adjusting the distance between the infrared lamp 13 and the ITO film 12 and / or the irradiation time.

The infrared irradiation time is set to 2 minutes. Immediately after the irradiation, the glass substrate is transferred to a rotating table (not shown).
0.14 ml of a polyamic acid (polyimide precursor) solution is dropped on the TO film 12. The dropping position is the glass substrate 11
Above the position of the center of gravity. This solution was obtained by adding Nissan Chemical Co., Ltd. type 21 thinner as a solvent to Nissan Chemical Industries, Ltd. Sun Ever RN-721 (0621) containing 5.97% by weight of polyamic acid and the balance being a solvent. The addition amount of the type 21 thinner is adjusted so that the amount of the polyamic acid is 3.75% by weight based on the polyamic acid solution.

After the above-mentioned dropping of the polyamic acid solution, the rotary table is rotated by a driving means (not shown), and the glass substrate 11 is rotated about the center of gravity at 1000 rpm for 4 seconds and then at 3500 rpm for 30 seconds on the main surface. . The fixation of the glass substrate 11 to the turntable during this rotation can be easily performed by vacuum suction, as in the usual spin coating. Due to this rotation, the solution is centrifuged to cause I
Spread over the TO film to cover it.

Next, the glass substrate was heated to 80 ° C. in a thermostat.
A heat treatment of heating at 240 ° C. for 1 hour for 15 minutes is performed to imidize the polyamic acid into polyimide, and the solvent is evaporated and removed.

A general reaction scheme for this imidation is shown in the following formula. The polyamic acid 1 undergoes a dehydration and ring closure in a heat treatment step to form a polyimide 2.

(Equation 1) Here, the structure of the portion represented by R ¹ and R ² greatly affects the characteristics of the polyimide to be formed. It is necessary to make a choice. For example, materials having a structure as shown in Table 1 below have been disclosed.

[0028]

[Table 1]

The area ratio of the polyimide film coated on the ITO film as described above (the ratio of the area of the polyimide film to the area of the ITO film) and the thickness of the polyimide film are as follows:
It is as shown in Table 1 below. For comparison, Table 2 also shows the values obtained when the infrared irradiation was not performed and the other conditions were the same as in the above example (Comparative Example).

[0030] From Table 2, it can be understood that, by irradiating infrared rays prior to the spin coating, a polyimide film is formed over substantially the entire surface of the ITO film, and the thickness of the polyimide film becomes uniform.

It is to be noted that the ITO film is not deposited on the entire surface of the glass substrate but is patterned in the shape of a large number of pixel electrodes 4 and signal electrodes 5 shown in FIGS. Then, an alignment film of a polyimide resin showing the same results as in the example of Table 2 was formed.

In this example, by changing the distance between the ITO film and the infrared lamp and / or the type of the infrared lamp (providing the same spectral distribution characteristics as in FIG. 2 but having different spectral line intensities), the ITO film is changed. Was changed, the results shown in Table 3 below were obtained.

[0033]

[0034] Note) × indicates area ratio of about 50%, △ indicates 60 to 75%, ○
The mark indicates 75 to 85%, and the mark ◎ indicates 85 to 95%, and the numerical value in parentheses indicates the conditions and results of the specific examples.

As can be seen from Table 3, the infrared irradiation power is
When the irradiation time is longer than 50 mW / cm ² , the effect of increasing the adhered area is not remarkable, and when the power is 50 mW / cm ² or more, the above effect is clearly recognized.

For example, FIG. 4 shows the relationship between the power and the area ratio when the infrared irradiation time is 2 minutes.

<Embodiment 2> In this embodiment, as schematically shown in FIG. 5, an infrared stove (VF840 FST type manufactured by Hitachi Hometech) 15 is used in place of the infrared lamp 13 of FIG. In the infrared stove 15, infrared heating wires 16A and 16B (400 W in one) of two quartz glass tubes are horizontally arranged in parallel with each other, and a fan 17 for circulating hot air is interposed therebetween.
Is arranged. However, in this example, the infrared heat ray is
Only 16A is used. The glass substrate 11 is made of an ITO film 12
Side is directed to the infrared heating wire 16A, and is supported by supporting means (not shown) so that the distance between the two is about 20 cm.

The infrared heat ray 16A has a spectral distribution characteristic (estimated spectral distribution) shown in FIG. 6, and contains both near infrared and far infrared components.

FIG. 7 is a graph showing the relationship between the irradiation time of the infrared heat ray 16A and the power per unit area received by the ITO film 12 using the apparatus of FIG.

As can be seen from FIG. 7, the above power reaches about 38.5 mW / cm ² about 3 minutes after the power is turned on, and thereafter, the power is saturated without any apparent increase. Therefore, in this example, the infrared irradiation time is suitably on the order of 10 minutes.

Immediately after performing infrared irradiation for various times (irradiation time will be described later), a polyamic acid solution is spin-coated on the ITO film in the same manner as in Example 1 and heat treatment is performed to form a polyimide film. Formed.

In this example, the infrared irradiation time and the area ratio of the polyimide film (the same area ratio as in Example 1) are as shown in Table 4 below.

[0043]

When the patterning of the ITO film was carried out in the same manner as in Example 1 when the infrared irradiation time was set to 10 minutes and 20 minutes, substantially the same results as in Table 4 were obtained.

The following can be understood from Table 4. In this example as well, the effect of increasing the polyimide film area ratio by infrared irradiation is observed, but it takes 20 minutes of irradiation time to obtain a coating result of about 100%.

In this example, as in the first embodiment, an experiment was conducted in which the distance between the ITO film and the infrared ray and / or the power of the infrared ray was changed. The results are as shown in Table 5 below.

[0047]

[0048] Note) × indicates area ratio of about 50%, △ indicates 60 to 75%, ○
The mark indicates 75 to 85%, and the mark ◎ indicates 85 to 95%, and the numerical value in parentheses indicates the conditions and results of the specific examples.

In this example, the infrared irradiation power is 10
If it is less than mW / cm ² , the effect of increasing the adhered area is not remarkable,
When the power is 10 mW / cm ² or more, the above effect is clearly recognized.

For example, FIG. 8 shows the relationship between the power and the coverage area ratio when the infrared irradiation time is set to 10 minutes.

The following can be understood from the results of Examples 1 and 2 described above. Assuming that the above effects of infrared irradiation depend on the amount of integrated energy that reaches the ITO film, if the irradiation time is set to less than 20 minutes, components within the range of 0.5 to 6.0 μm of the spectral distribution are obtained from the infrared source. 10mW / cm minimum
^At a rate of ² (Example 2), it is necessary that components within the range of 0.5 to 3.0 μm reach the ITO film at a rate of at least 50 mW / cm ² (Example 1). In particular, it is preferable to use an infrared source exhibiting the latter spectral distribution characteristic.

<Embodiment 3> Even when the infrared heat ray (16A in FIG. 5) used in Embodiment 2 is used, the distance between the infrared heat ray and the ITO film is shortened to shorten the infrared irradiation time (Example 1). ).

Table 6 below shows the relationship between the irradiation time and the polyimide film area ratio with respect to the power corresponding to the distances between the infrared heat ray and the ITO film of 15 cm, 16 cm and 20 cm. It is a similar table.

[0054]

Although the embodiments of the present invention have been described above, a transparent plastic such as a transparent acrylic resin can be used as a substrate material in addition to glass. The material of the transparent conductive film is ITO
Besides, for example, indium oxide or tin oxide can be used.

In order to manufacture an LCD through the steps according to the method of the present invention, a flowchart shown in FIG. 9 is followed.

A laminate in which a transparent conductive film and an alignment film are formed on a substrate in this order is manufactured separately for one LCD, one pair at a time, and as shown in FIG. Each of the laminates 18 can be manufactured in such a manner as described above, and cut by a large number of cutting lines 19 and 20 orthogonal to each other to form individual laminates 18. By doing so, the number of steps for depositing and patterning the transparent conductive film and forming the alignment film can be reduced.

[0058]

According to the present invention, since at least the transparent conductive film is coated with the alignment film precursor in forming the alignment film, the degree of freedom in selecting a solvent is high and the coating operation is easy.

Further, since light irradiation is performed on at least the transparent conductive film so that components having a spectral distribution within the range of 0.5 to 6.0 μm reach with an energy of 10 mW / cm ² or more, the transparent conductive film of the alignment film precursor is irradiated. The wettability and adsorptivity to the film are improved, and the coating is ensured. Therefore, the alignment film formed by heat-treating the precursor also has no coating unevenness and is highly reliable.

[Brief description of the drawings]

FIG. 1 is a schematic front view of an infrared irradiation device according to a first embodiment.

FIG. 2 is a graph showing a spectral distribution of the infrared lamp.

FIG. 3 is a graph showing the relationship between infrared irradiation time and power.

FIG. 4 is a graph showing the relationship between the power of irradiation infrared rays and the area of a polyimide film.

FIG. 5 is a schematic perspective view of an infrared irradiation device according to a second embodiment.

FIG. 6 is a graph showing the spectral distribution of infrared heat rays.

FIG. 7 is a graph showing the relationship between infrared irradiation time and power.

FIG. 8 is a graph showing the relationship between the power of irradiation infrared rays and the area of a polyimide film.

FIG. 9 is a flowchart of an LCD manufacturing process according to the first and second embodiments.

FIG. 10 is a plan view illustrating a procedure for forming an alignment film according to another embodiment.

FIG. 11 is a schematic sectional view of an LCD.

FIG. 12 is an enlarged sectional view taken along line XII-XII of FIG. 11;

FIG. 13 is an enlarged sectional view taken along line XIII-XIII of FIG. 11;

FIG. 14 is a plan view showing a transparent conductive film pattern of another LCD.

FIG. 15 is a schematic plan view of an alignment film precursor film formed without performing infrared irradiation.

[Explanation of symbols]

 1, 2, 11 Glass substrate 3, 6, 12 Transparent conductive film 4 Pixel electrode 5 Signal electrode 7 Common electrode 8, 18 Alignment film 9 Liquid crystal 13 Infrared lamp 16A, 16B Infrared heat ray 19, 20 Cutting line

Claims (4)

(57) [Claims] When forming an alignment film on the surface of a substrate, a step of forming a conductive film on the surface of the substrate includes the step of forming a film having a spectral distribution within a range of 0.5 to 6.0 μm by 10 mW /
irradiating at least the conductive film with light so as to reach with an energy of ² cm2 or more; coating the light-irradiated surface of the substrate with a precursor of the alignment film; and Heat treating to form the alignment film. 2. A method for forming an alignment film on a surface of a transparent substrate, comprising the steps of: forming a transparent conductive film on the surface of the transparent substrate; and providing a component having a spectral distribution within a range of 0.5 to 6.0 μm at 10 mW /
At least a step of irradiating the transparent conductive film with light so as to reach with an energy of ² cm or more, and a spin-coating method using a precursor of a constituent material of the alignment film on a surface of the transparent substrate on which the light irradiation is performed. And a step of heat-treating the precursor coating layer to form the alignment film. 3. The formation of an alignment film according to claim 1, wherein light irradiation is performed so that components having a spectral distribution within a range of 0.5 to 3.0 μm reach with an energy of 50 mW / cm ² or more. Method. 4. Immediately after the light irradiation, the substrate is coated with a polyimide precursor while being rotated at a high speed around the center of gravity of the substrate in the plane of the substrate, and then the polyimide precursor is imidized by heating. The method for forming an alignment film according to claim 1, wherein the body covering layer is an alignment film.