JP2002365650A - Method for manufacturing liquid crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a liquid crystal display panel with excellent liquid crystal response by preventing viscosity of a liquid crystal from varying in filling the liquid crystal and using a low viscosity material. SOLUTION: Patterns 11, 12 of a sealing material are formed by applying the sealing material for example on a CF (color filter) substrate 10 in a frame shape. Subsequently a low viscosity liquid crystal 13 is dropped thereon. While cooling the substrate 10 so as not to make volatile components of the liquid crystal 13 vaporize, the CF substrate 10 and a TFT (thin film transistor) substrate are superposed on each other under an atmosphere of the reduced pressure and the sealing material is hardened with ultraviolet rays irradiation or the like.

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 display panel by a drop injection method.

[0002]

2. Description of the Related Art Liquid crystal display panels are advantageous in that they are thin and lightweight, can be driven at a low voltage, and consume little power, and are widely used in various electronic devices. A general liquid crystal display panel used for a television or a personal computer has a structure in which liquid crystal is sealed between two substrates. On one substrate, a number of pixel electrodes arranged in a matrix and a number of thin film transistors (TFTs) connected to the pixel electrodes are provided. The other substrate is provided with red, green, and blue color filters and a common electrode facing the pixel electrode. Note that a region where the pixel electrodes are arranged in a matrix is referred to as a display region.

Conventionally, liquid crystal is sealed between two substrates by the following method. That is, a sealant is applied in a frame shape so as to surround the display area of one substrate. However, in order to inject the liquid crystal between the substrates in a later process, a portion where the sealant is not applied is provided in a part of the frame as a liquid crystal injection port. Thereafter, a spacer for maintaining a constant gap (cell gap) between the two substrates is arranged, and the two substrates are joined with a sealant to form a liquid crystal display panel. The liquid crystal display panel before liquid crystal injection is called an empty panel.

[0004] Then, after sufficiently hardening the sealant,
The container containing the liquid crystal and the empty panel are placed in a vacuum chamber. Then, after the inside of the chamber is evacuated, the liquid crystal injection port of the empty panel is put into the liquid crystal in the container, and the inside of the chamber is returned to the atmospheric pressure. As a result, the liquid crystal enters the panel due to the difference between the atmospheric pressure and the pressure in the empty panel. After the panel is sufficiently filled with liquid crystal, the panel is sandwiched between flat plates and pressurized to discharge excess liquid crystal to make the cell gap constant. Then, a resin is filled into the liquid crystal injection port, and the resin is cured. Thereby, the enclosing of the liquid crystal is completed.

In the above-described conventional liquid crystal sealing method (dip injection method), the liquid crystal is injected by the difference between the pressure in the panel and the atmospheric pressure. Therefore, it takes a long time until the liquid crystal is sufficiently filled in the panel. Is required. Then, in order to improve workability, a method called a dropping method has been developed. In the drop-injection method, for example, a sealant is applied on one substrate so as to surround a display region, and liquid crystal is dropped on the substrate. Then, in a vacuum atmosphere, the other substrate is placed on one of the substrates with a spacer interposed therebetween, and after pressure bonding, the liquid crystal is diffused between the substrates, the sealant is cured, and a liquid crystal sealing step is performed.

Note that it is not always necessary to drop liquid crystal on a substrate coated with a sealant, and liquid crystal may be dropped on a substrate not coated with a sealant. Further, as the sealant, either a photo-curable or a thermo-curable sealant may be used, or a combination thereof may be used.

[0007]

The conventional injection method has the following problems. That is, in the conventional injection method,
Liquid crystal with low volatility was used, and a series of steps were performed at room temperature even under reduced pressure. However, in recent years, a high-speed response of a liquid crystal display panel has been required, and accordingly, use of a liquid crystal having a small rotational viscosity γ1 is expected. However, a liquid crystal having a small rotational viscosity γ1 has high volatility, and the volatile component in the liquid crystal disappears under reduced pressure by the conventional drop injection method, and the rotational viscosity γ1 of the liquid crystal increases. Therefore, even if a liquid crystal having a small rotational viscosity γ1 is used,
The effect of improving responsiveness cannot be obtained.

It is an object of the present invention to provide a method of manufacturing a liquid crystal display panel having excellent responsiveness while preventing a change in liquid crystal viscosity when liquid crystal is sealed.

[0009]

According to a method of manufacturing a liquid crystal display panel of the present invention, a low-viscosity liquid crystal is dropped by a dropping method into an injection substrate, and particularly, the liquid crystal is cooled and the substrates are bonded together under a reduced pressure atmosphere. Is performed. In this case, the liquid crystal is volatile and has a rotational viscosity γ at 20 ° C.
It is preferable to use one having 120 mPa · s or less. However, in the present invention, the volatile liquid crystal is
When left at room temperature for 30 minutes under reduced pressure of 10 ^-3 Torr, the weight after standing is 98% or less of that before standing.

[0010] A liquid crystal display panel having excellent high-speed response is required to display a moving image, and a liquid crystal having a small rotational viscosity γ1 (specifically, a liquid crystal display panel) is required to realize a liquid crystal display panel having excellent high-speed response. Specifically, it is necessary to use a liquid crystal having a rotational viscosity γ1 at 20 ° C. of 120 mPa · s or less. However, a liquid crystal having a small rotational viscosity γ1 is
It can also be said that the liquid crystal has volatility. In addition,
The rotational viscosity γ1 is related to the ease of movement of liquid crystal molecules, and is different from general viscosity (flow viscosity).

The liquid crystal used in the liquid crystal display panel is a mixture of a plurality of liquid crystal compounds, but a neutral material having no polarity (a liquid crystal compound having a neutral dielectric anisotropy).
However, when a highly volatile component is mixed, the rotational viscosity of the liquid crystal can be reduced. For example, when the rotational viscosity γ1 is 13
By mixing a neutral material with a liquid crystal of 5 mPa · s, a liquid crystal having a rotational viscosity γ1 of 82 mPa · s can be obtained. However, when this liquid crystal is sealed in a panel at room temperature and under reduced pressure by an injection method, the volatile component in the liquid crystal disappears and the rotational viscosity γ1 becomes 135 or more. In this case, a liquid crystal display panel having excellent responsiveness cannot be manufactured.

Since the volatilization of the components in the liquid crystal is governed by the temperature of the atmosphere in which the liquid crystal material is present, it is possible to minimize the amount of volatilization at a low temperature. For example, even if the above liquid crystal is cooled to 0 ° C. or less and the pressure is reduced, the composition of the liquid crystal hardly changes. Therefore, if the liquid crystal is sealed in the panel in a cooled state, a liquid crystal display panel with even better responsiveness can be manufactured.

[0013]

Embodiments of the present invention will be described below. A method for manufacturing a liquid crystal display panel (liquid crystal display device) by the drop injection method will be described with reference to FIG. First,
A substrate provided with a color filter and a common electrode (hereinafter, referred to as a CF substrate) and a substrate provided with a TFT and a pixel electrode (hereinafter, referred to as a TFT substrate) are formed by a known method.
In this embodiment mode, glass substrates each having a size of 500 mm × 400 mm are used as these substrates.
A substrate of this size is a so-called two-chamfered substrate for forming two 15-inch liquid crystal display panels. Note that a vertical alignment film (for example, polyamic acid type / manufactured by JSR) is formed on the CF substrate and the TFT substrate.

Then, as shown in FIG. 1, a first frame-shaped pattern 11 surrounding the display area of the CF substrate 10 and a second frame-shaped pattern A sealing agent is applied in a pattern 12. The width of each of the patterns 11 and 12 is 1 mm. And each frame pattern 1
Liquid crystal (N-type liquid crystal / manufactured by Merck Japan) 13 is dropped in a required amount determined from the seal outer dimensions and the panel thickness in 1,
The CF substrate 10 and the TFT substrate (not shown) are bonded in a vacuum.

After that, the liquid crystal is diffused almost entirely in the display area and then returned to the atmospheric pressure, and 2,000 mJ of ultraviolet light is irradiated from above the substrate (CF substrate side) to cure the sealant. After heating this bonded substrate at a temperature of 120 ° C. for one hour, it is divided along a scribe line. Thus, a liquid crystal display panel can be formed. Furthermore,
This will be described with reference to FIGS. 2 is a plan view showing a cell structure of the liquid crystal display panel, FIG. 3 is a cross-sectional view taken along line AA of FIG. 2, and FIG. 4 is a view showing a process of dropping liquid crystal after applying a sealant on a substrate. FIG. 5 is a schematic view showing a step of superposing a TFT substrate and a CF substrate, and FIG. 6 is a schematic view showing a curing step of a sealant. In the present embodiment, a method for manufacturing an MVA (Multi-domain Vertical Alignment) type liquid crystal display panel is described.

First, the TFT substrate 20 and the CF substrate 30 are manufactured. In manufacturing the TFT substrate 20, a gate bus line 22, an auxiliary capacitance bus line 23, a data bus line 24, a TFT 25, and a pixel electrode 26 are formed on a glass substrate 21 by using a known film forming method and a photolithography method. To form In this case, the pixel electrode 26
A slit 26a for orientation division is provided. The pixel electrode 26 and the source electrode of the TFT 25 are electrically connected via a contact hole. After that, the pixel electrode 26
Vertical alignment film 27 is formed so as to cover the top of the substrate (FIGS. 2 and 3).
reference).

In manufacturing the CF substrate 30, a black matrix 32 and a color filter 3 are formed on a glass substrate 31 by using a known film forming method and a photolithography method.
3. A common electrode 34 and a projection (bank) 35 for alignment division are formed, and a vertical alignment film 36 is formed so as to cover them (see FIG. 3). In FIG. 3, by using a protrusion (bank) layer as a fixed spacer, a narrow cell gap can be achieved without adding a step (only the step of forming a protrusion layer), and high-speed response can be achieved. In this case, a fixed spacer is arranged outside the opening at an appropriate density. Thereby, a liquid crystal display panel having a cell gap of 4 μm or less can be efficiently obtained, and high-speed response can be realized.

Next, as shown in FIG.
A sealant 28 is applied to surround the display area. Then, using the drop dispenser 41, the TFT
N (negative) liquid crystal 40 is dropped at several places on the substrate 20. In this case, the drop amount of the liquid crystal 40 is determined according to the area of the display area and the target panel thickness. The drop injection is suitable for manufacturing a small panel having a cell gap of 3.0 μm or the like. When the cell gap is 3.0 μm, an extremely high-speed liquid crystal display panel can be obtained from the square effect of the cell thickness.

Next, as shown in FIG. 5, the TFT substrate 20 and the CF substrate 30 are put in the chamber 42 of the bonding apparatus, and the TFT substrate 20 is cooled to 0 ° C.
2 is evacuated to a pressure of, for example, about 10 ^-3 Torr. Then, after the CF substrate 30 is overlaid on the TFT substrate 20, as shown in FIG. 6, the sealant 28 is cured by UV irradiation. TFT substrate 20 and CF substrate 30
When superimposed, the liquid crystal 40 spreads over the entire area surrounded by the sealant 28, and the liquid crystal is sealed in the panel. The curing of the sealant may be performed under reduced pressure (in vacuum), in air (in air), or in an atmosphere of an inert gas such as N ₂ .

Thereafter, a polarizing plate is attached to each of the front and back surfaces of the panel. Thus, the MVA type liquid crystal display panel is completed. According to the present embodiment, since the substrate temperature is cooled to 0 ° C. when the liquid crystal is sealed, the disappearance of the volatile components of the liquid crystal is almost completely avoided even under reduced pressure. As a result, a liquid crystal display panel having a small liquid crystal rotational viscosity γ1 and excellent responsiveness can be obtained. The liquid crystal having a low rotational viscosity is more suitable for the drop injection process than the conventional dip injection method because the time during which the pressure is reduced is shorter in the drop injection process. Further, it is extremely difficult to reduce the viscosity of an N (negative) liquid crystal material used for an MVA type liquid crystal display panel even if it is composed of only a material having low volatility. Therefore, the low-viscosity liquid crystal and the manufacturing method using the same are used in an MVA type liquid crystal display panel.
The effect is particularly large.

In the above embodiment, the case where the present invention is applied to the manufacture of the MVA type liquid crystal display panel has been described. However, the present invention is not limited to the method of manufacturing the MVA type liquid crystal display panel. The present invention relates to TN (Twis
ted Nematic) and other types of liquid crystal display panels. Further, the liquid crystal material is not limited to the N (negative) liquid crystal material, and the same effect can be obtained when a P (positive) liquid crystal material is used.

Further, in the above embodiment, the liquid crystal was dropped on the TFT substrate and the CF substrate was superimposed on the TFT substrate. However, the liquid crystal was dropped on the CF substrate and the TFT was placed on the CF substrate.
The FT substrates may be overlapped. Hereinafter, a result of manufacturing a liquid crystal cell for evaluation according to the present embodiment and examining the response characteristics thereof will be described in comparison with a comparative example.

A liquid crystal cell for evaluation was prepared by the above-described dropping injection method. On the first glass substrate on which a transparent electrode made of ITO (Indium-TinOxide) is formed, a resist A
(Manufactured by Shipley) was applied by spin coating to form a resist film, and the pattern for forming projections was transferred to the resist film using a photomask. Then, after developing and patterning the resist film, it was baked at a temperature of 120 ° C. for 40 minutes and at a temperature of 200 ° C. for 40 minutes. As a result, protrusions for alignment division having a height of 1.4 μm made of resist were formed on the substrate.

Next, a second glass substrate on which a transparent electrode made of ITO was formed was prepared, and the transparent electrode was patterned by a photoresist method. Area without ITO is first
(See FIGS. 2 and 3). Next, a vertical alignment film (polyamic acid type / manufactured by JSR) was formed on each of the first substrate and the second substrate. Further, a fixed spacer was formed in a predetermined position on the second substrate by a resist using a resist, and a sealant was applied in a frame shape on the first substrate side (FIG. 4).
reference).

Example 1 shows a liquid crystal A having no volatility.
(Merck Japan), and as Example 2, liquid crystal B having volatility was used, and liquid crystal was dropped on the first substrate with a drop dispenser. In Table 1 below, the liquid crystal A,
The physical properties of B are shown.

[0026]

[Table 1]

[0027] placed in the chamber of the first and second alignment bonded substrate device, while cooling to 0 ℃ in the chamber 10 ^-3
After evacuation to Torr, the second substrate was overlaid on the first substrate. At this time, the protrusions of the first substrate and the I
In such a way that the areas without TO are arranged alternately (MV
The first substrate and the second substrate were bonded together to form a panel (so as to form an A cell) (see FIG. 3). Then, after the sealing agent was cured by UV irradiation, polarizing plates were attached to the upper and lower sides of the panel in crossed Nicols.

Similarly, a liquid crystal A having no volatility (manufactured by Merck Japan) was used as Comparative Example 1, and a liquid crystal B having volatility was used as Comparative Example 2. It was dropped. Then, these substrates are put into a chamber of a bonding apparatus, and while the substrate temperature is room temperature (23 ± 1 ° C.), the inside of the chamber is evacuated to 10 ⁻³ Torr, and the second substrate is placed on the first substrate. Superimposed. Thereafter, after the sealant was cured by UV irradiation, polarizing plates were attached to the upper and lower sides of the panel in crossed Nicols. Further, a similar MVA liquid crystal evaluation cell was manufactured by a conventional injection method (dip method) instead of the drop injection method. That is, in the same manner as in the above-described method, a first glass substrate having projections and a second glass substrate having a patterned region without ITO were prepared, and a vertical alignment film was formed on each substrate.
All the substrate formations up to this point are manufactured in the same process.

Thereafter, a sealing agent (thermosetting seal, XN-21F /
(Mitsui Chemicals). Then, the first substrate and the second substrate are bonded so as to form an MVA cell (see FIG. 3),
It was left in an oven at 135 ° C. for 90 minutes. Thus, an empty cell was produced. In this empty cell, a liquid crystal A having no volatility (manufactured by Merck Japan) was used as Comparative Example 3.
As Comparative Example 4, volatile liquid crystal B (Merck Japan) was injected by vacuum dip. The vacuum of the injection device is
The pressure was 10 ^-3 Torr, and the evacuation time was 40 minutes. At this time, the temperature in the vacuum chamber was not controlled, and a series of injection steps were performed at room temperature.

After the injection, the liquid crystal injection port was sealed with a commercially available UV curable resin (manufactured by Three Bond) so that a cell gap could be obtained. Further, polarizing plates were stuck on the upper and lower sides of the panel in crossed Nicols to complete a liquid crystal cell. The electro-optical characteristics of the liquid crystal cells of Examples 1 and 2, Comparative Examples 1 and 2, and Comparative Examples 3 and 4 were examined. Table 2 shows the results. In addition, the responsiveness was obtained from a 90% variation characteristic of the light transmittance. That is, the time required for the light transmittance of the liquid crystal cell to reach 90% of the saturated transmittance when a pulse voltage was applied to the liquid crystal cell was examined.

[0031]

[Table 2]

As is clear from Table 2, in the liquid crystal cells of Examples 1 and 2 in which the liquid crystal was sealed in the panel while cooling the liquid crystal, Comparative Examples 1 and 2 in which the same liquid crystal was sealed in the panel at room temperature.
The liquid crystal cell had better response characteristics. In particular, the response of the liquid crystal cell of Example 2 using the volatile liquid crystal B was 20 msec, and it was confirmed that a liquid crystal display panel having extremely good high-speed response could be manufactured.

From the results of Comparative Examples 3 and 4 and the above,
Compared with the conventional injection method (dip method), it is also found that the drop injection method has a great effect on improving the response characteristics. This is because the vacuum defoaming process is completed in an extremely short time in the drop injection method as compared with the conventional injection method. In the case of a 15-inch liquid crystal display panel, the exhaust time is several hours in the conventional injection method, but is reduced to several minutes or less in the drop injection method. When making a large liquid crystal display panel,
This difference becomes noticeable.

In the response of Comparative Examples 3 and 4, the liquid crystal B
Is that the high-volatility component in the liquid crystal B at the time of vacuum evacuation volatilizes, and as a result, the liquid crystal viscosity γ
This is because 1 has risen from 82. The degree of volatilization of the liquid crystal B could be determined by disassembling the completed liquid crystal display panel, collecting the liquid crystal, and analyzing it by gas chromatography or the like. The liquid crystal component contributing to low viscosity was greatly reduced.

(Modification) In the above-described method for manufacturing a liquid crystal display panel, the entire substrate on which the liquid crystal was dropped was cooled to 0 ° C., but the liquid crystal 40 was dropped instead of the entire substrate 20 as shown in FIG. Even if only a part is partially cooled by the cooling body 45, the same effect as in the above embodiment can be obtained.

In the step of curing the sealant after the TFT substrate and the CF substrate are overlaid, as shown in FIG. 8, the display areas of the substrates 20 and 30 are heated by the heater 46,
Only the vicinity of the sealant 28 may be cooled by the cooling body 47. By doing so, the liquid crystal 40 spreads uniformly inside the panel to suppress the variation in cell thickness, and the spreading speed of the liquid crystal 40 is reduced in the vicinity of the sealant 28. Can be obtained. Thereby, a liquid crystal display panel with less display unevenness can be manufactured.

(Supplementary Note 1) A sealant is provided on the first substrate or the second substrate, and liquid crystal is dropped on one of the first substrate and the second substrate. A method of manufacturing a liquid crystal display panel, comprising the steps of: laminating a substrate and the second substrate; curing the sealant; and laminating the first substrate and the second substrate. And superposing the first substrate and the second substrate under reduced pressure.

(Supplementary Note 2) The method for producing a liquid crystal display panel according to Supplementary Note 1, wherein a liquid crystal having volatility and a rotational viscosity γ1 at 20 ° C. of 120 mPa · s or less is used. (Supplementary Note 3) The method for manufacturing a liquid crystal display panel according to Supplementary Note 1 or 2, wherein the temperature of the liquid crystal is set to 0 ° C. or less in the step of cooling the liquid crystal.

(Supplementary Note 4) In the step of cooling the liquid crystal, the liquid crystal is cooled by cooling only a region of the first substrate or the second substrate where the liquid crystal is dropped. Alternatively, the method for manufacturing a liquid crystal display panel according to supplementary note 2. (Supplementary Note 5) The manufacturing of the liquid crystal display panel according to Supplementary Note 1 or 2, wherein the liquid crystal is heated and the vicinity of the sealant is cooled after the first and second substrates are overlapped. Method.

[0040]

As described above, according to the liquid crystal display panel manufacturing method of the present invention, the liquid crystal is sealed in the panel by the drop injection method in a state where the liquid crystal is cooled. Even so, the disappearance of volatile components is avoided. This makes it possible to obtain a liquid crystal display panel having excellent responsiveness.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an application pattern of a sealant.

FIG. 2 is a plan view showing a cell structure of the liquid crystal display panel.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a view showing a step of dropping liquid crystal after applying a sealant on a substrate.

FIG. 5 is a schematic view showing a step of superposing a TFT substrate and a CF substrate.

FIG. 6 is a schematic view illustrating a curing step of a sealant.

FIG. 7 is a view showing a modification of the method of manufacturing the liquid crystal display panel.

FIG. 8 is a view showing another modification of the method of manufacturing the liquid crystal display panel.

[Explanation of symbols]

 10, 30: CF substrate, 11: first frame pattern, 12: second frame pattern, 13, 40: liquid crystal, 20: TFT substrate, 21, 31: glass substrate, 22: gate bus line, 23 ... Auxiliary capacitance bus line, 24 ... Data bus line, 25 ... TFT, 26 ... Pixel electrode, 26a ... Slit, 27,36 ... Vertical alignment film, 28 ... Sealant, 32 ... Black matrix, 33 ... Color filter, 34 ... Common electrode, 35: Projection for orientation division, 42: Chamber.

Claims (2)

[Claims] A sealing agent provided on a first substrate or a second substrate; a liquid crystal is dropped on one of the first substrate and the second substrate; And the second
A method of manufacturing a liquid crystal display panel, comprising: laminating a substrate; and curing the sealant and laminating the first substrate and the second substrate. The first substrate and the second substrate
A method for manufacturing a liquid crystal display panel, comprising superimposing the liquid crystal display panel on a substrate. 2. The liquid crystal has a volatility and a temperature of 20 ° C.
2. The method for manufacturing a liquid crystal display panel according to claim 1, wherein a rotational viscosity γ1 of 120 mPa · s or less is used.