JP2641370B2 - Manufacturing method of liquid crystal display device - 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 manufacturing a liquid crystal display, and more particularly to a novel method for manufacturing a liquid crystal display capable of improving display quality by reducing the occurrence of defects in the manufacturing process.

[0002]

2. Description of the Related Art FIG. 3 schematically shows a sectional structure of a liquid crystal cell of a conventional liquid crystal display device. In a conventional method of manufacturing a liquid crystal display device, a sealing material 33 made of a thermosetting resin material or the like is provided on one peripheral portion of two glass substrates 31 and 32 that have been subjected to an alignment process.
Is applied by printing or the like, and two glass substrates 31,
32, the gap control material 34 is sandwiched therebetween, and then the two substrates 31 and 32 are heated in a state where pressure is applied by sandwiching both substrates by a press (not shown), and the sealing material 33 is baked. Glue each other.

[0003] Thereafter, the substrate is removed from the press, a liquid crystal material 35 is injected between the glass substrates from an injection port, and then the injection port (not shown) of the liquid crystal material 35 is sealed to form a liquid crystal cell.

Further, in a liquid crystal display device in which uniformity of the liquid crystal cell thickness is particularly required, after the liquid crystal is injected, the liquid crystal cell is again pressed by a press to apply a pressure to make the cell thickness uniform. Is performed.

After the sealing material is fired and before the liquid crystal is injected, the cell gap of the liquid crystal cell (empty cell) is generally such that the central portion of the glass substrate surface expands as shown in FIG. It is known that it becomes larger than the peripheral part (near the sealing material).

In the manufacturing method according to the prior art, no pressure was applied to the empty cells at the time of injecting the liquid crystal.
After the injection, the thickness of the cell gap was thicker in the central part than in the peripheral part as before the injection.

In order to obtain the uniformity of the thickness of the liquid crystal layer, after the liquid crystal is injected, the liquid crystal cell is pressed again by applying pressure to make the cell thickness uniform, and then the injection port is sealed.

[0008]

However, when a new method of manufacturing a liquid crystal display device has been developed, such a new manufacturing method cannot be used in the above-described conventional method of uniforming the cell thickness. In some cases, it became impossible to respond. Hereinafter, the new manufacturing method will be briefly described, and problems will be pointed out.

In a conventional method of manufacturing a liquid crystal display device, a static electricity generated during a rubbing process for forming an alignment film causes a short circuit between electrodes of a liquid crystal driving element such as a TFT, a disconnection between lines, or a failure of the element itself. In some cases, point defects or line defects occur due to destruction or changes in characteristics.

[0010] This is because the insulation between the electrode of the element and the line of the matrix composed of the signal line and the gate line is insulated by a very thin insulating film, so that the dielectric breakdown easily occurs due to static electricity. For example, when a high electric field is applied due to the use of an amorphous silicon or polysilicon semiconductor and electric charges are accumulated in an insulator, transistor characteristics, for example, a threshold value may change.

For this purpose, the applicant of the present application
Japanese Patent Application No. 4-47322, filed on April 4, proposes an invention in which liquid crystal molecules are aligned by controlling the temperature of the liquid crystal by utilizing the phase transition of the liquid crystal by a thermo-optic effect.

In the proposed invention, the alignment process can be performed only on one of the substrates (especially, only on the substrate side where the driving element such as the substrate forming the common electrode is not formed). With respect to generation of static electricity on the substrate due to processing, destruction of elements on the substrate, short-circuiting of electrodes and disconnection of lines can be prevented, and point defects and line defects of the display device can be eliminated.

[0013] Further, in the same manner as in
Japanese Patent Application No. 4-236652 filed on Sep. 4, 1998 proposes an invention of a liquid crystal display element in which an alignment film and an alignment process are not required by appropriately selecting a gap size of a liquid crystal cell.

The invention disclosed in the above-mentioned prior application can be said to be a method of manufacturing a liquid crystal display device having high practical value because no alignment film is required or only one substrate is required. According to these new manufacturing methods by the present applicant, nematic
The isotropic liquid crystal injected while being heated at or above the isotropic phase transition temperature (NI point) is gradually cooled from the isotropic phase. The twist angle corresponding to the spontaneous pitch of the liquid crystal molecules is determined by the cell thickness.

For this reason, if there is a portion having a different cell gap thickness in one cell, the twist angle changes according to the portion and becomes non-uniform. This could not be improved even if it was corrected by a press after the injection of the liquid crystal. Therefore, when such a liquid crystal cell is used for a display device, display unevenness occurs.

Therefore, the liquid crystal injection method according to the prior art is not optimal for the new manufacturing method disclosed in the specification of the above-mentioned prior application by the present applicant. An object of the present invention is to provide a method for manufacturing a high-quality liquid crystal display device with less occurrence of defects and less display unevenness without significantly complicating the manufacturing process.

[0017]

In the method of manufacturing a liquid crystal display device according to the present invention, the step of injecting a liquid crystal material is performed while applying pressure to the substrate.

That is, both of the manufacturing methods use liquid crystal molecules.
Interposing a sealant between the periphery of the first substrate and the second substrate having no positively oriented structure with respect to
In a state where external pressure is applied to the surfaces of both substrates,
A step of injecting a liquid crystal material between the two substrates, a step of gradually cooling the liquid crystal material after the step of injecting the liquid crystal material, and a step of gradually changing the phase from an isotropic phase to a liquid crystal phase while applying the pressure. Sealing the hole into which the liquid crystal material is injected.

[0019]

The liquid crystal material is injected while applying pressure to the surfaces of the first substrate and the second substrate. Therefore, the liquid crystal display device having a uniform cell thickness in a relatively short time without complicating the working process. Can be manufactured. After injection, the liquid crystal changes from the isotropic phase to the liquid crystal phase
By the transfer, the alignment state of the liquid crystal is adjusted.

Therefore, the display quality of the liquid crystal display device is also improved. This also works in the manufacturing process of a liquid crystal display device by a new method that can omit the alignment treatment by utilizing the thermo-optic effect of the liquid crystal.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a liquid crystal display according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a process flow for explaining a method of manufacturing an active matrix type liquid crystal display device using a twisted nematic liquid crystal.
FIG. 2 is a view for explaining a liquid crystal material injecting step in the manufacturing steps according to the present invention.

In FIG. 1, in step 1, on a transparent glass substrate (12 in FIG. 2), a driving element such as a TFT for applying an electric field to a pixel portion in accordance with a gate signal, and an electrode of the driving element are connected. And the pixel electrodes connected to the driving elements are formed. No alignment film is formed on this glass substrate (driving elements, electrodes, electrode lines,
The pixel electrodes are simplified in FIG. 2 and are collectively indicated by 14).

A common electrode (17 in FIG. 2) is formed on another transparent glass substrate (13 in FIG. 2). An alignment film (1 in FIG. 2) is provided on the surface of the common electrode in contact with the liquid crystal layer.
8) may be formed. In that case, a rubbing treatment is performed to give an orientation direction.

Incidentally, the aforementioned Japanese Patent Application No. 4-236652.
No alignment film is required in the liquid crystal display device disclosed in the above publication. In some cases, a color filter layer and a light-shielding film called a black mask for preventing light transmission outside a pixel display portion and improving contrast may be formed. Both of the above substrates can be manufactured by utilizing a conventional substrate manufacturing technique.

After the two substrates are manufactured, in step 2, a sealing material (15 in FIG. 2) such as a thermosetting resin is screen-printed on one of the edges of the two substrates. Is applied. At this time, the liquid crystal injection port (19 in FIG. 2)
Do not apply the sealing material.

Next, in step 3, a gap control material (20 in FIG. 2) is uniformly dispersed and adhered to the substrate. Further, in step 4, the two substrates are arranged so as to face each other, sandwiched by a press machine 21, and the substrates are stacked so as to have a predetermined gap thickness while applying pressure between the substrates. In this case, when the gap thickness is set to a value corresponding to the chiral pitch of the liquid crystal as disclosed in Japanese Patent Application No. 4-236652, an alignment film becomes unnecessary. For example, if the chiral pitch is p when the gap thickness is d, the condition may be 0.15 <d / p <0.75.

In step 5, the substrate is heated while the substrate surface is flattened by pressurizing with the press machine 21, and the sealing material is fired to bond the substrates together. At this time, the liquid crystal injection port 19
Are left as openings. The heating may be performed by external heaters 22 and 23, or may be performed by a hot press in which the press 21 itself is provided with heaters 22a and 23a.

Subsequently, in step 6, while the pressure is applied to the two glass substrates 12 and 13 by the press machine 21, the substrates 12, 13 are placed in the liquid crystal material 11 in the container 16 as shown in FIG. 13 are immersed. The liquid crystal material 11 is a liquid in which a chiral molecule is mixed with a nematic liquid crystal material. The liquid crystal material 11 is described in Japanese Patent Application No. 4-4732.
No. 2 can be used.

The liquid crystal material 1 is heated from both sides by heaters 22 and 23 or heaters 22a and 23a in a hot press.
1 is heated. The heating temperature of the liquid crystal material is higher than the phase transition temperature (NI point) of the liquid crystal. Therefore, the liquid crystal material 1
The direction of one liquid crystal molecule 10 is random and is in an isotropic state.

For controlling the temperature of the liquid crystal, a temperature control technique such as adjusting the current amount of the heaters 22 and 23 while monitoring the temperature by inserting a temperature detector (not shown) in the liquid crystal material 11 can be used. Temperature control can be manual or automatic.

In this heating step, the above-mentioned Japanese Patent Application No.
As disclosed in the specification of US Pat.
It is also preferable that the layers 2 and 13 are heated to a phase transition temperature or higher.

The heated liquid crystal material 11 is injected into the gap between the substrates 12 and 13 from the injection port 19 by capillary action. In this state, the liquid crystal molecules 10 are isotropic and are not aligned. The method of injecting the liquid crystal material 11 may be any method, and may be a method other than the capillary phenomenon, for example, a vacuum injection.

After injecting the liquid crystal material, in step 7, the heaters 22 and 23 or the heater 22 in the hot press machine are used.
The liquid crystal material 11 is gradually cooled while reducing the amount of heat generated by a and 23a. The cooling rate is controlled so as to be in the range of 0.1 to 10 ° C./min, for example, 0.5 ° C./min.

When the liquid crystal material 11 is gradually cooled to the phase transition temperature (NI point) at this rate, the liquid crystal material 11 first becomes the isotropic state (I).
Gradually changes to a nematic liquid crystal state (N).

In the slow cooling process, the liquid crystal molecules 10 near the alignment film 18 are aligned in the alignment direction, and the direction of the liquid crystal molecules 10 near the opposite glass substrate 12 is not particularly determined. However, since the cooling rate is low, the directions of the liquid crystal molecules 10 which are different from each other also gradually become aligned in the alignment direction.
Is aligned so as to be aligned with the direction of alignment from the vicinity of. In this way, all the liquid crystal molecules between the substrates are regulated.

Further, since chiral molecules are mixed in the liquid crystal material 11, the liquid crystal molecules 10 are twisted in a certain direction during the cooling process, and take a helical structure in the optical axis direction. By adjusting the mixing amount of the chiral molecules and the distance between the substrates, the twist angle can be set to a desired angle such as 90 °, and a TN liquid crystal display device can be obtained.

Next, in step 8, the injection port 19 is sealed (end-sealed). This step 8 is preferably performed with the same press 21 pressurized. Note that the sealing timing is determined in consideration of volume shrinkage of the liquid crystal due to heat.
Is desirably carried out after the temperature has dropped to substantially the same temperature as room temperature.

Note that the baking treatment of the sealing material in step 5 may be performed by changing the order of injection of the liquid crystal material in step 6 or simultaneously. Even when the liquid crystal injection step comes before the sealing material firing step, the heat generated for heating the liquid crystal can be used as it is as the heat for the sealing firing in the next step, so that economical energy can be used in the manufacturing step.

Next, in another embodiment of the present invention, FIG.
It is possible to eliminate the heating device 22 on the glass substrate 13 side on which the common electrode 17 is formed. A second embodiment will be described with reference to FIG.

In the case of heating with a hot press machine, FIG.
The heating function of the heater 22a on the left side of the press machine 21 is stopped. That is, in the second embodiment, the method of cooling the liquid crystal material 11 after heating is different from the method of the first embodiment.

The second embodiment is the same as the first embodiment until the liquid crystal material 11 is heated above the dislocation temperature point. Thereafter, in a slow cooling step 7, the liquid crystal material 11 is gradually cooled while giving a temperature gradient between the glass substrate 12 side and the glass substrate 13 side.

More specifically, the liquid crystal temperature on the glass substrate 12 on which the driving elements 14 are formed is maintained at a temperature higher by several to several tens of degrees than the liquid crystal temperature on the glass substrate 13 on which the common electrode 17 is formed. Cool slowly. By providing the temperature gradient in this manner, first, the liquid crystal material on the common electrode substrate 13 side becomes N-
Reach I temperature.

Subsequently, the liquid crystal material on the substrate 12 side is gradually changed to N.
Reaching the -I temperature. If the substrate 13 has an alignment structure, the liquid crystal material will be in a liquid crystal state while being gradually aligned from the substrate 13 side.

The manufacturing method of the present invention can be applied to both a simple matrix liquid crystal display device and an active matrix liquid crystal display device. In addition, TFT as a driving element
However, the present invention can be applied to a liquid crystal display device using any of the MIM diodes. Further, the present invention can be applied to a liquid crystal display device other than the TN type liquid crystal.

The manufacturing method of the present invention can be applied to the inventions disclosed in the aforementioned Japanese Patent Application Nos. 4-47322 and 4-236652 filed by the applicant of the present invention. However, it is needless to say that the present invention can be applied to a manufacturing process of a liquid crystal display device using a conventional technique.

The materials, numerical values, and the like of the embodiments described above are merely examples, and the present invention is not limited to these, and it will be apparent to those skilled in the art that various changes and improvements can be made.

[0047]

In the method of manufacturing a liquid crystal display device according to the present invention described above, the step of injecting the liquid crystal material is performed while the pressure is applied to the substrate, so that the cell thickness is uniform and high quality without display unevenness is obtained. Can be manufactured.

Further, since the liquid crystal cell can be manufactured continuously in the same pressing process, the manufacturing process can be simplified and the time can be shortened. Furthermore, since the heat required for firing the sealing material and the heat required for injecting the liquid crystal can be used mutually, energy can be saved in the manufacturing process.

The same effect can be obtained in the manufacturing process of the liquid crystal display device by a new method that can omit the alignment treatment by utilizing the thermo-optical effect of the liquid crystal.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a liquid crystal injection step in a manufacturing process according to an embodiment of the present invention.

FIG. 3 is a sectional structural view of a liquid crystal cell according to a conventional technique.

[Explanation of symbols]

1 to 8 steps of the embodiment of the manufacturing method according to the present invention 10 liquid crystal molecules 11 liquid crystal materials 12, 13 glass substrates 14 ························ Driving element, electrode, etc. 19: Injection port 20: Gap control material 21: Press machine 22, 23: Heater

Claims (7)

(57) [Claims] 1. Both have a positive alignment structure for liquid crystal molecules.
A step of baking with a sealing material interposed between the peripheral edges of the first substrate and the second substrate not having, and applying a pressure to the surfaces of both substrates from the outside,
A step of injecting a liquid crystal material between the two substrates; a step of gradually cooling the liquid crystal material after the step of injecting the liquid crystal material, and a step of gradually changing the phase of the liquid crystal material from an isotropic phase to a liquid crystal phase; Sealing the hole into which the liquid crystal material is injected in a state in which the liquid crystal material is injected. 2. In the step of injecting the liquid crystal material,
Injecting liquid crystal in an isotropic phase having a phase transition temperature or higher, and gradually cooling the liquid crystal material, a temperature is set so that the temperature on the first substrate side is higher than the temperature on the second substrate side by a predetermined temperature. 2. The method for manufacturing a liquid crystal display device according to claim 1, wherein cooling is performed with a gradient. 3. In the step of injecting the liquid crystal material,
2. The method according to claim 1, wherein the liquid crystal material is injected while maintaining the two substrates at a predetermined temperature equal to or higher than a liquid crystal phase transition temperature.
3. The method for manufacturing a liquid crystal display device according to any one of claims 1 to 2. 4. The method for manufacturing a liquid crystal display device according to claim 1, wherein the firing step and the step of injecting the liquid crystal material are performed substantially simultaneously. 5. The method according to claim 1, wherein one of the firing step and the step of injecting the liquid crystal material is continuously performed after the other step. The manufacturing method of the liquid crystal display device according to the above. 6. The method according to claim 1, wherein the sealing step is performed after the temperature of the substrate becomes substantially equal to room temperature.
6. The method for manufacturing a liquid crystal display device according to any one of items 1 to 5. 7. The method according to any one of claims 1 to 6, wherein said liquid crystal material is that a mixture of chiral molecules.