JP2000155320A - Active matrix liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit abnormal alignment around spacers and to suppress the leakage of light, the reduction of contrast and the occurrence of unevenness in display in a normally black mode by heating a vacant cell to stick organic fine particles as spacers to a TFT substrate and a counter substrate and then sealing a liquid crystal. SOLUTION: Organic fine particles as spacers 15 for maintaining a gap are disposed on a TFT substrate 1 or a counter substrate 2. Fine particles of a polydivinylbenzene or acrylic resin material are suitable for use as the spacers 15. The TFT substrate 1 and the counter substrate 2 are stuck together while holding the spacers 15 between them to assemble a vacant cell. The periphery of the vacant cell is sealed with a sealing material and the cell is heated to stick the spacers 15 to the substrates 1 and 2. The heating temperature is preferably in the glass transition temperature region of the spacers 15. A liquid crystal is then sealed in the cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IPS active matrix liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, a super twisted nematic (STN) has been used as an active matrix liquid crystal display device.
A method employing a normally black mode in an in-plane switching (IPS) method is widely known. However, there is a problem that light leakage due to abnormal alignment occurs around a spacer used for controlling a gap of a liquid crystal substrate in black display. In particular, this tendency is remarkable in the IPS system in which liquid crystal molecules are aligned using a lateral electric field, and it is difficult to remove the cause of the abnormal alignment.

As a method of improving light leakage in the STN mode, Japanese Patent Application Laid-Open No. Hei 6-11719 discloses a method of regulating the alignment state of liquid crystal molecules by subjecting a spacer to a surface treatment. This will be described with reference to the plan view shown in FIG.

An organic fine particle spacer (hereinafter, spacer) 15 for holding a gap between a TFT substrate and a counter substrate on which a CF (color filter) is formed is disposed. Here, as the spacer 15, a spacer having a hydrophobic group on the surface of organic fine particles such as polydivinylbenzene and acrylic is used. At this time, since the surface of the spacer 15 has been subjected to the hydrophobic treatment, alignment of the liquid crystal molecules along the outer periphery of the spacer 15 due to the surface tension of the spacer hardly occurs, and the liquid crystal layer 16 is in contact with the pixel electrode in the rubbing direction of each substrate. The liquid crystal molecules are aligned in parallel, so that bright spots and dark spots can be eliminated, which is effective in preventing light leakage.

However, at this time, since the surface of the spacer 15 is a hydrophobic group, the adhesive force between the spacer 15 and the surface of the alignment film does not increase. The spacers 15 move due to vibrations caused by the above-mentioned operations, and the spacers are charged with static electricity by friction with the alignment film. Since the lines of electric force are emitted radially from the spacers 15 charged with static electricity, the liquid crystal molecules around the spacers 15 are affected by the lines of electric force, causing abnormal alignment over a wide area as shown in FIG. The light leakage causes a decrease in contrast and uneven display.

In Japanese Patent Application Laid-Open No. 07-333621, as a technique for suppressing abnormal alignment in a liquid crystal substrate of the TN mode or the STN mode, a hydrophobic group having a terminal alkyl group or terminal acyl group structure and a terminal OH group are provided. There is disclosed a liquid crystal display spacer composed of fine particles having both hydrophilic groups. According to this publication, for example, there is a description that abnormal orientation of the liquid crystal occurs during energization, and the range of the abnormal orientation expands with energization time. It is presumed to be due to the interaction between the liquid crystal molecules and the surface of the spacer.

However, in the case of the IPS system, the liquid crystal molecules are designed so as to be arranged substantially parallel to the TFT substrate, and only the spacer moves due to an external pressure applied in a process of attaching a polarizing plate or the like. Causes abnormal orientation. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 07-333621, merely adjusting the type of functional group on the spacer surface to improve the affinity with the liquid crystal molecules and suppress the interaction does not allow the movement of the spacer. It cannot be suppressed, and as a result, the abnormal orientation in the IPS method is suppressed,
This is not enough to obtain good display characteristics.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention suppresses the abnormal orientation around the spacer, and suppresses light leakage in a normally black mode, reduced contrast, and reduced display unevenness. It is an object of the present invention to provide an active matrix liquid crystal display device.

[0009]

According to the present invention, there is provided an active matrix liquid crystal display device of the IPS type having both a pixel electrode and a common electrode on a TFT substrate.
After forming an empty cell in which an FT substrate and an opposing substrate opposing the TFT substrate are bonded via an organic fine particle spacer, the empty cell is subjected to a heat treatment so that the organic fine particle spacer is bonded to the TFT substrate and the opposing substrate. The present invention relates to an active matrix liquid crystal display device manufactured by fixing a liquid crystal to a substrate and then sealing the liquid crystal between the TFT substrate and the counter substrate.

In particular, in the IPS system, as described above, an abnormal orientation is generated only by the movement of the spacer due to the application of the external pressure in the step of attaching the polarizing plate or the like. Therefore, improvement of only the interaction between the surface of the spacer and the liquid crystal molecules cannot solve the problem.

As a result of diligent studies, the present inventor has found that when an organic fine particle spacer is used, this spacer is fixed to an alignment film provided on a substrate by heating. It has arrived.

[0012] This fixation is sufficient if the spacers are adhered to such an extent that the spacers do not move during the sticking step of the polarizing plate after enclosing the liquid crystal, during transportation, and during actual use, regardless of chemical bonding or physical bonding. .

Specifically, after the spacers are scattered and the TFT substrate and the opposing substrate are bonded with a certain gap, heating is performed in an empty cell state before the liquid crystal is filled. On this occasion,
The heating temperature is preferably a temperature near or higher than the glass transition temperature of the organic fine particle spacer. At this temperature, rearrangement of the surface molecules of the spacer occurs, and the spacer becomes more stable with respect to the surface of the alignment film, and develops a stronger intermolecular force. As a result, a comparison between the spacer and the alignment film occurs. A strong fixing force is developed. The upper limit temperature is preferably 250 ° C. or lower, which is lower than the temperature at which thermal decomposition of the alignment film such as polyimide starts.

The glass transition temperature range in the present invention means a temperature range in which the state of the organic polymer constituting the organic fine particle spacer is in a transition state that is neither a glass state nor a rubber state. The usually used organic fine particle spacer is a polydivinylbenzene-based material having polydivinylbenzene as a main chain skeleton, or an acrylic resin-based material obtained by polymerizing acrylic acid or acrylate, and is subjected to heat treatment at 100 to 150 ° C. It is preferred to do so.

The heating time needs to be long enough to fix the organic fine particle spacer, and can be determined by experiment as appropriate depending on the material of the alignment film and the organic fine particles. For example, when the organic fine particle spacer is a polydivinylbenzene-based or acrylic resin-based material and the alignment film is polyimide, for example, a temperature of 130 ° C. or more and 150 ° C. or less for about 2 hours is appropriate.

In a preferred embodiment of the present invention, the organic fine particle spacer has a hydrophilic group on its surface. This is firstly because the present invention has a hydrophilic group on the surface, thereby improving the intermolecular interaction with the alignment film and increasing the fixing force. Second, the introduction of a hydrophilic group makes it difficult to generate static electricity itself.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the active matrix liquid crystal display device of the present invention will be described with reference to the sectional view shown in FIG. 1 and the plan view shown in FIG.

First, a method of manufacturing the TFT substrate will be described. On a transparent substrate 1 such as glass, a gate electrode 5 and a common electrode 11 made of a single layer or a multilayer film of a metal such as Cr or ITO are formed by sputtering and a photoresist process. As described above, in the active matrix liquid crystal display device of the present invention, both the gate electrode and the common electrode
This is a so-called IPS active matrix liquid crystal display device formed on the side of the T substrate.

A gate insulating film 6 composed of two layers of silicon oxide and silicon nitride is formed thereon by CVD. Further, amorphous silicon (a-Si, n ⁺ a-
A semiconductor layer 9 made of Si) is formed as an upper layer by a CVD and a photoresist process, and a drain electrode 7 and a pixel electrode 8 made of a single layer or a multilayer film of a metal such as Cr and ITO are formed by a sputtering and a photoresist process. I do. Through the steps so far, the drain wiring and the gate wiring and the switching element existing at the intersection thereof are formed.

Next, a single-layer or multilayer insulating film 1 made of an organic film such as an acryl, benzocyclobutene polymer, polysilazane compound, or an inorganic film such as silicon nitride.
An organic film (not shown) made of O and polyimide is laminated.

Next, the configuration of the opposing substrate disposed on the opposing side will be described. On a transparent substrate 2 made of glass or the like, an organic film such as an acryl or polyimide compound mixed with a light-shielding material such as carbon black or metal oxide is formed by spin coating and baking. Alternatively, a single-layer or multilayer metal film of a metal such as Cr is formed by sputtering. The black matrix 12 is formed from these films by a photoresist process. When color display is performed, a color layer 13 is formed in the upper layer. Next, an overcoat layer 14 made of a transparent film is formed. The overcoat layer 14 is preferably formed by spin-coating and baking a transparent organic film of acrylic, polyimide, or the like so as to block transmitted light and not reduce the display area. On the uppermost layer of this substrate, an alignment film (not shown) made of an organic film such as polyimide is formed.

Next, both the TFT substrate and the counter substrate are subjected to an alignment treatment such as rubbing in a direction parallel to the pixel electrodes.

Next, on the TFT substrate 1 or the counter substrate 2
Organic fine particle spacer 15 for holding a gap above
Place. Here, as the spacer 15, for example, a polydivinylbenzene-based or acrylic resin-based material can be suitably used.

Further, when the spacer has one or more kinds of hydrophilic groups such as hydroxyl group, carboxylic acid, sulfonic acid and amino group on the surface, the fixing force to the alignment film is increased and the abnormal alignment is further prevented. Is possible, so that it can be used as a more suitable spacer.
Such spacers are commercially available as those produced by a method of copolymerizing a monomer having a hydrophilic group with divinylbenzene or acrylic acid, or by coupling an already synthesized organic fine particle spacer. .

By the presence of the hydrophilic group on the surface of the spacer as described above, an intermolecular force and a hydrogen bond between polar groups with the alignment film are developed, and the fixing force is further increased.
Further, there is an advantage that the presence of the polar group makes it difficult for the spacer itself to generate static electricity itself.

The TFT substrate and the counter substrate are bonded together with the spacer interposed therebetween, and an empty cell is assembled. Further, the periphery of the empty cell is sealed with a sealing material. In this sealing step, heat treatment is involved, but due to a mismatch in the coefficient of thermal expansion between the TFT substrate, the counter substrate, and the sealing material, the central portion of the portion surrounded by the sealing material is deformed in a direction to increase the gap. In the heat treatment in the sealing step, the spacer does not adhere to the alignment film. In a normal actual process, in consideration of productivity, a panel in which a TFT substrate and a counter substrate are bonded has a multi-panel layout of a plurality of cells. Particularly in the case of such a multi-panel layout, the panel tends to be deformed by a sealing process. , And the spacer is more difficult to adhere to the alignment film.

After the sealing step, a heat treatment for fixing the spacer is performed. At this time, in the multi-panel panel, heat treatment is performed after separation into individual empty cells. This heat treatment is most effectively performed immediately before liquid crystal injection.

The temperature of the heat treatment is most preferably in the glass transition temperature region of the organic fine particle spacer. In this temperature range, rearrangement of the surface molecules of the organic fine particle spacer occurs, and the most stable state in relation to the alignment film. Therefore, the fixing force is large. In addition, since the heat treatment temperature itself can be performed at a relatively low temperature, stress concentration due to a difference in the coefficient of thermal expansion of the members constituting the cell hardly occurs,
Cell reliability is also improved.

At a temperature higher than the glass transition temperature range, the organic fine particle spacer is in a rubber state, and rearrangement itself of the spacer surface molecules is manifested, so that a fixed fixing force can be secured. Furthermore, when the temperature is increased, the temperature of the alignment film itself cannot be increased to 250 ° C. or more because the alignment film itself starts to thermally decompose.

As the organic fine particle spacer, a polydivinylbenzene-based material or an acrylic resin-based material is often used in many cases. In this case, the material is heated at 100 to 150 ° C., more preferably 130 to 150 ° C. for 2 hours or more. By the treatment, a sufficient fixing force can be obtained.

More specifically, a sufficient intermolecular force is developed between the surface of the organic fine particle spacer and the surface of the alignment film, and has such a fixing force that abnormal alignment does not occur in a vibration test after liquid crystal sealing. As can be determined by experiment.

Next, the liquid crystal is sealed by a usual method,
The cell of the active matrix is completed.

The active matrix liquid crystal display device thus manufactured was subjected to a vibration tester,
When the liquid crystal layer 16 was vibrated under the vibration conditions of 0 Hz and 5 G, the abnormal alignment of the liquid crystal was examined. As shown in FIG.
The liquid crystal molecules are oriented in parallel with the pixel electrode, which is the rubbing direction of each substrate, but around the spacer 15, the liquid crystal molecules are oriented along the outer periphery of the spacer 15 due to surface tension. When a voltage is applied between the pixel electrode 8 and the common electrode 11 in this state, the liquid crystal molecules are arranged in a direction perpendicular to the pixel electrode 8 and the common electrode 11, but around the spacer 15, as in the case where no voltage is applied, The liquid crystal molecules are aligned along the outer periphery of the spacer 15. Therefore, the abnormal alignment of the liquid crystal molecules around the spacer 15 remains only in the surface layer around the spacer, and does not cause a problem such as light leakage or a decrease in contrast. As described above, the movement of the spacer generates static electricity, and the alignment direction of the liquid crystal molecules can be regulated more stably as compared with the related art in which alignment abnormality occurs over a wide area around the spacer.

Next, optical films 3 and 4 as polarizing plates are attached to the outer surfaces of the TFT substrate 1 and the counter substrate 2. At this time, they are arranged such that the absorption axes of the polarizing plates attached to the respective substrates are orthogonal to each other. For example, the absorption axis of the polarizing plate 3 on the TFT substrate side is parallel to the pixel electrode 8 and the common electrode 11, and the absorption axis of the polarizing plate 4 on the CF substrate side of the substrate 2 is orthogonal to the pixel electrode 8 and the common electrode 11. Deploy.

[0035]

According to the present invention, a polarizing plate adhering step,
Since the spacer is fixed to the surface of the alignment film in response to an external force generated during transport, generation of static electricity due to movement of the spacer in the pixel can be suppressed. Therefore, it is possible to suppress a decrease in contrast and display unevenness in a normally black mode, which is noticeably generated in an IPS type active matrix liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an IPS type active matrix liquid crystal display device of the present invention.

FIG. 2 is a plan view showing an embodiment of an IPS type active matrix liquid crystal display device of the present invention, and also schematically shows a state of alignment of liquid crystal molecules.

FIG. 3 shows a plan view of an IPS type active matrix liquid crystal display device manufactured by a conventional technique,
The state of abnormal alignment of liquid crystal molecules is schematically shown.

[Brief description of reference numerals]

Reference Signs List 1 TFT substrate 2 Counter substrate 3 Polarizing plate (optical film) 4 Polarizing plate (optical film) 5 Gate electrode 6 Gate insulating film 7 Drain electrode 8 Pixel electrode 9 Semiconductor layer (a-Si, n ⁺ a-Si) 10 Insulating film DESCRIPTION OF SYMBOLS 11 Common electrode 12 Black matrix 13 Color layer 14 Overcoat layer 15 Organic fine particle spacer 16 Liquid crystal layer

Claims (7)

[Claims] An active matrix liquid crystal display device of an IPS system having both a pixel electrode and a common electrode on a TFT substrate, wherein the TFT substrate and a counter substrate facing the TFT substrate are interposed via an organic fine particle spacer. After producing an empty cell bonded by heating, the empty cell is subjected to a heat treatment, so that the organic fine particle spacer is attached to the TFT.
The liquid crystal is fixed to the substrate and the counter substrate,
An active matrix liquid crystal display device manufactured by being enclosed between a T substrate and the counter substrate. 2. The active matrix liquid crystal display device according to claim 1, wherein a polyimide alignment film is formed on a surface of the TFT substrate and the counter substrate on a side in contact with the liquid crystal. 3. The active matrix liquid crystal display device according to claim 1, wherein said organic fine particle spacer is an organic fine particle spacer made of a polydivinylbenzene-based or acrylic resin-based material. 4. The active matrix liquid crystal display device according to claim 1, wherein said organic fine particle spacer is an organic fine particle spacer having a hydrophilic group on its surface. 5. The active matrix liquid crystal display device according to claim 4, wherein said hydrophilic group is at least one functional group selected from a hydroxyl group, a sulfonic acid group, a carboxylic acid group and an amino group. . 6. The method according to claim 1, wherein the heat treatment of the empty cell is performed at a temperature equal to or higher than the glass transition temperature of the organic fine particle spacer and at a temperature of 250 ° C. or less. Active matrix liquid crystal display device. 7. The heat treatment temperature of the empty cell is set to 100 to 1
The active matrix liquid crystal display device according to claim 3, wherein the temperature is set in a range of 50 ° C. 6.