JPH10123542A - Liquid crystal display element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of a liquid crystal material and to embody a good display grade over the entire part of a liquid crystal display element by adding a UV absorptive material to the liquid crystal material adjacent near the sealing material for sealing liquid crystals formed by using a UV curing resin at the time of assembling the liquid crystal display element, such as a liquid crystal display panel. SOLUTION: This liquid crystal display element has the liquid crystal display panel constitution formed by adding a UV absorbent to the liquid crystals of part of the panel at the time of assembling the liquid crystal panel. A benzotriazole based UV absorbent or cyanoacrylate based UV absorbent is used as the UV absorbent. The amt. of the UV absorbent to be added to the liquid crystal material (32) adjacent near the sealing material for sealing liquid crystals is specified to 0.5 to 1.5wt.%. The unevenness in the threshold voltage drop which heretofore occurs in the display area near the liquid crystal sealing part for which the UV curing resin is used or the sealing part of the injection port is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having good display quality, which eliminates threshold voltage unevenness near a pixel display area of a liquid crystal display panel and near an injection port for injecting a liquid crystal material, and a method of manufacturing the same. About.

[0002]

2. Description of the Related Art A method of manufacturing a liquid crystal display panel can be roughly divided into two types.

The first method is a dropping method in which a liquid crystal material is sandwiched between two glass substrates. According to this method, when assembling a liquid crystal display element, a seal made of an ultraviolet curable resin is printed on an outer portion of a pixel on an alignment treatment surface of one substrate, and then a liquid crystal material is dropped inside the seal. On the other alignment treatment surface, spherical beads are uniformly dispersed in order to maintain the gap thickness between glass substrates. The substrates are bonded together in a vacuum with the alignment-treated surface of the substrates inside, and the pressure is returned to the atmospheric pressure. Then, ultraviolet rays are applied to the sealing portion to seal the liquid crystal material between the glass substrates. In this dripping method, the liquid crystal material in the vicinity of the seal is also slightly irradiated with ultraviolet rays, so that deterioration of the liquid crystal material in that portion has been recognized.

[0004] A second method is a vacuum injection method in which two glass substrates are bonded together with a certain gap thickness, and the air inside is replaced with a liquid crystal material in a vacuum. In this method, when assembling a liquid crystal display element, a seal made of a thermosetting resin is printed on the outside of the pixel on the alignment processing surface of one substrate, and the gap thickness between the glass substrates is printed on the other alignment processing surface. In order to maintain the uniformity, spherical beads are dispersed. Laminate each substrate with the alignment treatment surface inside,
The thermosetting resin is cured by a hot press to complete the empty panel. Thereafter, the liquid crystal is replaced with air in the empty panel. When the liquid crystal material is uniformly injected, the injection port is sealed with an ultraviolet curable resin and cured by irradiation with ultraviolet light.
In this vacuum injection method, deterioration of the liquid crystal material near the ultraviolet curable resin used for sealing was recognized.

In the above first and second methods, the liquid crystal sealing seal constituting the liquid crystal display panel plays an important role in controlling the gap thickness and also in weather resistance.

[0006]

However, in the prior art, when the liquid crystal material is irradiated with ultraviolet light, the molecular structure is split or decomposed, and the various physical properties originally held by the liquid crystal material are not maintained. There was a problem. In particular, there has been a problem that the retardation of the liquid crystal panel is deviated from the optical compensation configuration due to a decrease in the birefringence Δn, and a decrease in the threshold voltage due to an impurity ion component occurs. In particular, the deterioration of the liquid crystal near the seal of the dropping method and the vicinity of the injection port of the vacuum injection method, in the pixel portion to which voltage is applied,
The threshold was lowered. Further, when the deterioration of the liquid crystal material further progressed, it was recognized that the color tone was abnormal even when no voltage was applied. The deterioration of these liquid crystal materials is remarkable when ultraviolet rays are irradiated into liquid crystal molecules having an ester bond. Since the bonds in the liquid crystal molecules are broken and the length of some of the liquid crystal molecules is shortened, the birefringence is lowered and the threshold value is lowered. Further, when the degree of deterioration of the liquid crystal material is large, there is a problem that the liquid crystal material is visually recognized.

An object of the present invention is to provide a liquid crystal display element which prevents deterioration of a liquid crystal material and realizes good display quality over the entire surface of a liquid crystal display panel, and a method of manufacturing the same, in order to solve the conventional problems. Aim.

[0008]

In order to achieve the above object, a liquid crystal display device of the present invention comprises a thin film transparent electrode on the inner surface,
And a liquid crystal display panel having liquid crystal sandwiched between respective glass substrates on which a liquid crystal alignment treatment thin film is applied. When assembling the liquid crystal display panel, the liquid crystal display panel is adjacent to a liquid crystal sealing seal material using an ultraviolet curable resin. Characterized in that an ultraviolet absorbing material is added to the liquid crystal material.

Next, a method for manufacturing a liquid crystal display element according to the present invention is as follows.
In a liquid crystal display panel in which liquid crystal is sandwiched between each glass substrate having a thin film transparent electrode and a liquid crystal alignment treatment thin film on the inner surface, a liquid crystal sealing seal made of a thermosetting resin is first formed, and the liquid crystal is sealed in vacuum. In the process of exchanging air and liquid crystal material inside the cell, most of the liquid crystal material is injected first, and then the remaining liquid crystal material is added with an ultraviolet absorbing material and injected, and then sealed using an ultraviolet curable resin. It is characterized by doing.

In the liquid crystal display device and the method of manufacturing the same according to the present invention, the ultraviolet absorbing material may be a benzotriazole-based ultraviolet absorber represented by the above formula (1) or a benzotriazole-based ultraviolet absorber represented by the above formula (2). It is preferably at least one ultraviolet absorber selected from an ultraviolet absorber and a cyano-acrylate ultraviolet absorber represented by the above formula (Formula 3).

In the liquid crystal display device and the method of manufacturing the same according to the present invention, the amount of the ultraviolet absorber is preferably in the range of 0.5 to 1.5% by weight based on the liquid crystal material. Here, the addition amount of the ultraviolet absorber is 0.5 to only the liquid crystal material adjacent to the vicinity of the liquid crystal sealing material.
It is in the range of 1.5% by weight. When the amount of the ultraviolet absorber is less than 0.5% by weight, the effect of protecting the liquid crystal material from ultraviolet light (UV light) is low, and when the amount is 1.5% by weight or more, the effect of protecting the liquid crystal material is only saturated. However, crystallization of the liquid crystal material at a low temperature becomes a problem.

In the method of manufacturing a liquid crystal display device according to the present invention, most of the liquid crystal material initially injected is 95% by weight.
It is preferable that the content of the liquid crystal material to which the ultraviolet absorbing material is added is about 5% by weight.

In the above, the thin film transparent electrode refers to an indium-tin oxide alloy (ITO) thin film electrode or the like. Curing of the ultraviolet curable resin is initiated by radicals generated by cleavage of a photoinitiator that initiates a polymerization reaction. Therefore, it is necessary to irradiate light in an absorption wavelength band necessary for cleavage of the photoinitiator. Further, the absorption wavelength band differs depending on the material, and it is necessary to select a material suitable for the application. Usually, a material system in which this absorption wavelength band is broadly spread to the maximum wavelength region of the ultraviolet wavelength is easy to use as a sealing resin for a liquid crystal display panel.

On the short wavelength side of the ultraviolet wavelength band, since the photopotential energy is high, the cleavage rate of the photoinitiator is high, and curing by efficient ultraviolet irradiation can be expected. However, deterioration of the liquid crystal material in contact with the sealing resin is also expected. Occurs at the same time. For this reason, when irradiating with ultraviolet rays, it is necessary to cut on the short wavelength side.

However, such separation of the ultraviolet wavelength band reduces the probability that the photoinitiator will be cleaved, and thus reduces the time efficiency of the seal curing. Therefore, when actually producing a liquid crystal display panel, it is necessary to perform a wavelength cut operation in an ultraviolet wavelength region in which the curing efficiency of the seal and the time efficiency are balanced.

Therefore, when a liquid crystal sealing seal made of an ultraviolet curable resin is cured, the liquid crystal material in the display region where the ultraviolet wavelength is close to the ultraviolet light is simultaneously absorbed when it is irradiated. Is added. The ultraviolet wavelength light does not reach the display area liquid crystal material due to the presence of the ultraviolet absorbing material. In addition, after the liquid crystal display panel is completed, by performing a heat annealing treatment, the ultraviolet absorbing material localized in the peripheral area of the display area is sufficiently diffused by heat and the final concentration is reduced by one digit. Does not adversely affect display defects.

In the structure of the present invention, the liquid crystal material has a thickness of 400 nm.
By adding one or more UV absorbers having absorption bands at the following wavelengths, it is possible to minimize the deterioration of the liquid crystal material due to the UV light radiated during panel production, and to provide good display quality over the entire LCD panel. It has a configuration realized by:

[0018]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. (Example 1) First, a test cell used for optical response evaluation will be described. As a pretreatment, two substrates were prepared in which a thin indium-tin oxide thin film electrode (ITO electrode) was formed on a glass substrate so as to be perpendicular to each other. An aromatic polyamic acid solution (PSI-A-2201 manufactured by Chisso Petrochemical) was applied onto each of the substrates by spin coating so as to have a thickness of 800 Å (80 nm). After temporary hardening heat treatment at 80 ° C for 15 minutes, 220
A thermosetting treatment was performed at 1 ° C. for 1 hour to form a polyimide alignment film. Next, the direction of the long axis of the liquid crystal material is rotated by 250 ° between the surfaces of the alignment films of the first substrate and the second substrate by the ordinary rubbing method on the surfaces of the alignment films of the respective substrates (the first substrate and the second substrate). An orientation process was performed so as to obtain a twist angle configuration (substrate pre-process).

Next, 0.1% by weight of a grease fiber having a predetermined diameter is mixed with an ultraviolet curable resin for sealing a liquid crystal outside of the ITO electrode pixel of the first substrate, and the screen is formed with a predetermined line width. Printed. A required amount of a liquid crystal material was dropped inside the sealing resin, and a considerable amount of plastic beads for ensuring a required gap thickness was sprayed on the rubbed surface of the second substrate. The first glass substrate and the second glass substrate were bonded together in a vacuum such that the rubbed surfaces faced each other, and ultraviolet rays were linearly irradiated from outside the glass substrate to the sealing resin portion in the atmosphere. Thereafter, a heating annealing treatment was performed at a temperature equal to or higher than the liquid crystal-isotropic phase transition temperature of the liquid crystal material for a predetermined time or more to form an experimental cell (1) (FIGS. 1 and 2). 1 and 2, reference numerals 1 and 5 denote ITO electrodes, 2 denotes an ultraviolet curing resin (seal resin), 3 denotes a glass substrate, 4 denotes a first glass substrate, 6 denotes plastic beads, 7
Is glass fiber, 8 is ultraviolet curing resin, 9 is ITO electrode,
Reference numeral 10 denotes a second glass substrate, and reference numeral 11 denotes a liquid crystal material.

In a similar manner, the liquid crystal material was changed to a liquid crystal material in which an ultraviolet absorber was added to one row near the liquid crystal sealing resin as shown in FIG. 5 (C). (2) was obtained (FIG. 5 (B)). In FIG. 5B, 25 is a liquid crystal material portion, and 26 is a portion to which an ultraviolet absorber is added. In FIG. 5C, reference numeral 27 denotes a liquid crystal material at a dropping point, and reference numeral 28 denotes a portion to which an ultraviolet absorber is added at the dropping point.
As an ultraviolet absorber, a benzotriazole-based ultraviolet absorber represented by the above formula (Formula 1) was added so as to be 1.0% by weight with respect to a liquid crystal material adjacent to a sealing material for sealing a liquid crystal.

FIG. 6 shows the results of measurement of the threshold voltages of the experimental cells (1) and (2) from the liquid crystal sealing seal toward the inside of the pixel (FIG. 5A). In FIG. 5A, reference numeral 23 denotes a normal threshold voltage, and reference numeral 24 denotes a portion where the threshold voltage decreases. From the evaluation results, it was clearly confirmed that the threshold voltage drop was suppressed when the ultraviolet absorber was added to the liquid crystal material near the seal. Due to the suppression of the threshold voltage,
The display unevenness due to the decrease in the threshold voltage near the seal was not completely recognized.

(Embodiment 2) Using the first glass substrate and the second glass substrate which were performed up to the substrate pre-process in the first embodiment,
A 0.1% by weight of a grease fiber having a predetermined diameter was mixed in a thermosetting resin outside the ITO electrode pixels of the first substrate, and screen printing was performed with a predetermined line width. Further, on the rubbed surface of the second substrate, a considerable amount of plastic beads for guaranteeing a required gap thickness was sprayed. Then the first
The substrate and the second substrate were bonded together such that the surface subjected to the rubbing orientation treatment was on the inside, and vacuum-packing using a heat-resistant film was performed, followed by heat-curing treatment under predetermined conditions to obtain empty cells. When the air in the empty cell and the liquid crystal material were vacuum-replaced to a predetermined gap thickness, the injection port was closed with an ultraviolet curable resin, cured by ultraviolet irradiation, and sealed. Thereafter, the liquid crystal material is higher than the liquid crystal-isotropic phase transition temperature for a predetermined time,
An experimental cell (3) was obtained by heat annealing (FIGS. 3 and 4). 3 and 4, 12 is an ITO electrode, 13 is an ultraviolet curing resin (seal resin), 14 is a glass substrate, 15
Is an ultraviolet curable resin, 16 is a first glass substrate, 17 is IT
O electrode, 18 is a plastic bead, 19 is an ultraviolet curing resin, 20 is an ITO electrode, 21 is a second glass substrate, 22
Is a liquid crystal material.

In the same manner, an ultraviolet absorber was added to the liquid crystal material near the injection port. Specifically, immediately before the completion of the injection of the liquid crystal material, the liquid crystal material was replaced with a liquid crystal material to which an ultraviolet absorber was added. As an ultraviolet absorber, a benzotriazole-based ultraviolet absorber represented by the above formula (Formula 1) was added so as to be 1.0% by weight with respect to a liquid crystal material adjacent to a sealing material for sealing a liquid crystal. Thus, an experimental cell (4) was obtained (FIG. 7B). In FIG. 7B, 3
1 is a liquid crystal material portion, 32 is an ultraviolet absorber added portion, 3
Reference numeral 3 denotes an ultraviolet irradiation lamp, and reference numeral 34 denotes an ultraviolet shielding mask.

Regarding the experimental cells (3) and (4), from the injection port sealing resin portion toward the inside of the pixel (FIG. 7 (A)),
FIG. 8 shows the result of the threshold voltage measurement. In FIG. 7A, reference numeral 27 denotes a liquid crystal material at a dropping point, and reference numeral 28 denotes an ultraviolet absorber-added portion at the dropping point. When an ultraviolet absorber is added to the liquid crystal material in the vicinity of the sealing resin clearly from this evaluation result,
It was confirmed that the threshold voltage drop was suppressed. However, in the vacuum injection method, since a polar molecule and an impurity ion component in the liquid crystal material are adsorbed in the vicinity of the injection port, a slight voltage difference is generated from the first embodiment including the difference in the method. Due to the suppression of the threshold voltage, display unevenness due to a decrease in the threshold voltage in the vicinity of the seal is not completely recognized.

Example 3 In Example 3, a benzotriazole-based UV absorber (Formula 1) was prepared in an experimental cell configuration (2), and the threshold voltage was measured by changing the amount of the UV absorber added. went. FIG. 9 shows the measurement results. When the amount of the benzotriazole-based ultraviolet absorber added was 0.5% by weight or more, the threshold value could not be recognized as lowering. Further, the threshold voltage drop suppressing effect was saturated at an addition concentration of 1.5% by weight or more. In addition, after the liquid crystal display panel is completed, by performing a heat annealing process, the ultraviolet absorbing material localized in the peripheral area of the display area is sufficiently diffused by heat and the final concentration is reduced by one digit, so that the display state is changed. Has no adverse effect. The cyano-acrylate-based UV absorber of the above formula (Chem. 3) had the same effect.

[0026]

As described above, according to the present invention, when assembling a liquid crystal display element such as a liquid crystal display panel, a liquid crystal material adjacent to a liquid crystal encapsulating seal material using an ultraviolet curable resin is provided with an ultraviolet absorbing material. By adding, the deterioration of the liquid crystal material can be prevented, and good display quality can be realized over the entire surface of the liquid crystal display element. Further, the manufacturing method of the present invention can efficiently and rationally manufacture the liquid crystal display device of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an experimental cell (1) manufactured by using a dropping method according to one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a cross section of an experimental cell (1) manufactured by using the dropping method.

FIG. 3 is a schematic plan view showing an experimental cell (3) manufactured by using a vacuum injection method according to another embodiment of the present invention.

FIG. 4 is a schematic diagram showing a cross section of an experimental cell (3) manufactured using the vacuum injection method.

FIG. 5A is an experimental cell (1) of one embodiment of the present invention.
FIG. 2 is a schematic diagram showing a threshold voltage measurement path of FIG. (B) is a schematic diagram showing the distribution of the ultraviolet absorbent-added liquid crystal in the liquid crystal display area before the heat annealing treatment of the experimental cell (2). (C) is a liquid crystal material added with an ultraviolet absorber in the experimental cell (2),
And a schematic diagram showing a state where only a liquid crystal material is dropped.

FIG. 6 shows experimental cells (1) and (2) according to one embodiment of the present invention.
FIG. 5 is a diagram showing a result of measuring a threshold voltage of FIG.

FIG. 7A is a schematic diagram showing a threshold voltage measurement path of an experimental cell (3) according to another embodiment of the present invention. (B) is a schematic diagram showing the distribution of the ultraviolet absorber-added liquid crystal in the liquid crystal display area before the heat annealing treatment of the experimental cell (4), and a schematic diagram showing the ultraviolet irradiation on the ultraviolet curing resin at the injection port. .

FIG. 8 shows an experimental cell (3) according to another embodiment of the present invention.
The figure showing the threshold voltage measurement result of (4).

FIG. 9 is a diagram showing the relationship between the amount of the ultraviolet absorber added and the decrease in threshold voltage according to one embodiment of the present invention (the measurement portion is at a position 10 mm from the seal position).

[Explanation of symbols]

 1,5,9,12,17,20 ITO electrode 2,13 UV curable resin (seal resin) 3,14 Glass substrate 4,16 First glass substrate 6,18 Plastic bead 7 Glass fiber 8,15,19 UV curable Resin 10, 21 Second glass substrate 11, 22 Liquid crystal material 23, 29 Normal threshold voltage 24, 30 Threshold voltage lowering portion 25, 31 Liquid crystal material portion 26, 32 UV absorber added portion 27 Dropping liquid crystal material 28 Dropping point UV absorber addition part 33 UV irradiation lamp 34 UV shielding mask

Claims (5)

[Claims] 1. A liquid crystal display panel having a liquid crystal sandwiched between respective glass substrates having a thin film transparent electrode and a liquid crystal alignment treatment thin film formed on an inner surface thereof. A liquid crystal display device characterized by adding an ultraviolet absorbing material to a liquid crystal material adjacent to a used liquid crystal sealing material. 2. A liquid crystal display panel comprising a liquid crystal sandwiched between respective glass substrates provided with a thin film transparent electrode and a liquid crystal alignment treatment thin film on an inner surface thereof, first comprising a liquid crystal sealing seal made of a thermosetting resin. Then, in the process of exchanging the air inside the cell with the liquid crystal material in a vacuum, most of the liquid crystal material is injected first, and then the remaining liquid crystal material is added with the ultraviolet absorbing material and injected, and then cured by ultraviolet light A method for manufacturing a liquid crystal display element, which comprises sealing with a resin. 3. An ultraviolet absorbent comprising a benzotriazole-based ultraviolet absorber represented by the following formula (Chem. 1), a benzotriazole-based ultraviolet absorber represented by the following formula (Chem. 2), and a compound represented by the following formula (Chem. 3). The liquid crystal display device according to claim 1 or 2, which is at least one ultraviolet absorber selected from the cyano-acrylate-based ultraviolet absorbers described above. Embedded image Embedded image Embedded image 4. The liquid crystal display device according to claim 1, wherein the amount of the ultraviolet absorber added is in the range of 0.5 to 1.5% by weight based on the liquid crystal material. 5. A method according to claim 1, wherein most of the liquid crystal material to be initially injected is 95%.
3. The method according to claim 2, wherein the amount of the liquid crystal material is about 5% by weight, and the amount of the liquid crystal material to which the ultraviolet absorbing material is added is about 5% by weight.