JP4187194B2 - Liquid crystal display element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display element, and more particularly to a technique for avoiding a phenomenon in which a transparent electrode made of ITO is observed in a reflective state.
[0002]
[Prior art]
In general, ITO (indium tin oxide) is used for the transparent electrode used in the liquid crystal display element, and the electrode pattern is formed by patterning the ITO conductive film. The refractive index of ITO is about 1.9, which is larger than the refractive index of about 1.5 of the glass substrate that is the support substrate.
[0003]
Therefore, since the reflection intensity due to external light is different between the place where ITO is present and the place where ITO is not present, the ITO pattern can be seen and display quality is remarkably deteriorated. This phenomenon is so-called “ITO bone appearance”.
[0004]
As one of the means for avoiding this ITO bone appearance, it is known to optimally adjust the refractive index and film thickness of ITO, the refractive index and film thickness of the insulating film and alignment film formed on the ITO, The optimum condition can be derived by theoretical calculation. Since the ITO bone appearance phenomenon can theoretically be treated as reflection of a multilayer film with different refractive index, the characteristics can be understood by calculating the reflection of a general multilayer film. Are almost identical.
[0005]
By the way, in many cases, a TN liquid crystal in which liquid crystal molecules are twisted by 90 ° is used as a liquid crystal display. In this TN liquid crystal, there is a liquid crystal display type called MTN (modulated twisted nematic) in order to improve black and white achromaticity. This is a method of providing a distribution in the gap of the liquid crystal layer.
[0006]
As a method for providing a gap distribution in a liquid crystal layer, a method of performing an uneven frost treatment on a glass substrate is known. For example, an etching process using HF (hydrogen fluoride) can provide an unevenness level where the pitch of the peaks and valleys is about 100 μm and the depth of the peaks and valleys is about 5.5 μm. The pitch between the peaks and valleys refers to the distance between the adjacent peaks of the concavo-convex shape.
[0007]
The method of forming a film on the unevenness of the glass substrate is roughly classified into a sputtering method which is a dry process, a solvent-coated type flexographic printing method and a spin coating method. According to the former sputtering method, almost no film thickness distribution occurs in the formed film, but the apparatus is expensive, the film formation takes time, and the film formation is limited to inorganic materials. For example, it is not very practical.
[0008]
On the other hand, according to the latter flexographic printing method and spin coating method, since the apparatus is relatively inexpensive, film formation in a short time is possible, and organic materials can also be formed. However, it is known that the film thickness can be distributed along the unevenness.
[0009]
As described above, it is possible to derive the optimum film thickness of each component by theoretical calculation in order to avoid the bone appearance of ITO. However, in fact, when an insulating film or the like is formed on the liquid crystal display type concavo-convex substrate of MTN by a solvent coating method, a film thickness distribution is generated along the concavo-convex. The film thickness was not obtained, and it was difficult to reduce the bone appearance of ITO.
In addition, although the desired uniform film thickness can be obtained by the sputtering method, it is not preferable to employ the sputtering method for the reasons described above.
[0010]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to avoid the phenomenon of ITO bone appearance without incurring an increase in cost and a decrease in productivity, and in the liquid crystal display type liquid crystal display element such as MTN described above, there is no black and white. The purpose is to achieve both improvement in coloring and avoidance of the phenomenon of ITO bone appearance.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the liquid crystal display element of the present invention includes a pair of support substrates having transparent electrodes patterned in a predetermined shape, and at least the support substrate on the display observation surface side of the pair of support substrates. An insulating film is formed on the surface including the transparent electrode, and the insulating film is formed on the transparent electrode forming surface side of the support substrate on the display observation surface side in order to avoid the pattern appearance of the transparent electrode observed in a reflective state. Concavities and convexities having a depth of 3 μm or more for providing a film thickness distribution are formed on the display observation surface side , and the difference in the refractive index of the transparent electrode is 0. The film has a refractive index of 15 or less and a film thickness distribution within an area of a radius of 500 μm having a distribution of ± 500 mm or more.
[0012]
Na us, in the liquid crystal display device of the type that do not require insulation film, it is sufficient to have the refractive index and the film thickness distribution in the alignment film.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
First, the ITO bone appearance phenomenon will be described in more detail, and then embodiments of the present invention will be described. FIG. 3 shows the components of a general liquid crystal display element separately.
[0014]
The liquid crystal display element 1 includes a transparent substrate 10 on the display observation surface side and a transparent substrate 20 on the back surface side as a pair of support substrates. Both the transparent substrates 10 and 20 are made of, for example, a glass substrate (may be a synthetic resin substrate), and transparent electrodes 11 and 21 made of ITO are formed in a predetermined electrode pattern on the inner surfaces facing each other.
[0015]
Alignment films 13 and 23 are formed on the transparent electrodes 11 and 21 via insulating films 12 and 22, and a liquid crystal 30 such as TN is sealed between the alignment films 13 and 23. Although not shown, a silica film (SiO ₂ ) as an undercoat layer is formed on the transparent electrode forming surfaces of the transparent substrates 10 and 20.
[0016]
The liquid crystal display element 1 illustrated here is a transmissive type, and polarizing films 14 and 24 are provided on the transparent substrate 10 and 20 on the display observation surface side and the back surface side, respectively, and the back surface side of the transparent substrate 20 on the back surface side. The backlight 40 is disposed in the front.
[0017]
In this configuration, when external light enters the liquid crystal cell from the display observation surface side, the light enters from the upper polarizing film 14, but when there is a difference in refractive index between the layers, the light is reflected at the interface. To do. If the entire display unit is in the same state, the entire display unit is reflected, so that no partial difference occurs and no problem occurs.
[0018]
However, in order to achieve a desired display, the ITO is patterned and the transparent electrode is only partially present. Therefore, reflection of external light is different where ITO is present and absent. When this difference is large, an “ITO bone appearance” in which an ITO (transparent electrode) pattern can be seen occurs, and the display quality is remarkably lowered.
[0019]
For example, the refractive index of the liquid crystal is 1.628, the refractive index of the alignment film is 1.700 and the thickness is 300 mm, the refractive index of ITO is 1.900 and the thickness is 450 mm, and the refractive index of the undercoat layer (SiO ₂ ) is 1.460. When the external light is a C light source when the thickness is 300 mm, the refractive index of the glass is 1.520, the refractive index of the insulating film is 1.900 and the thickness is 700 mm, the color difference between the reflected light where ITO is present and where it is absent is About 7 Under this condition, some ITO bone appearance occurs. The above calculation is for the case where light is vertically incident and vertically emitted.
[0020]
Here, when the refractive index of the insulating film is 1.900, FIG. 4 shows the color difference when the film thickness is changed. It can be seen that the color difference in the vicinity of 500 mm is small, but large in other film thicknesses.
[0021]
Next, FIG. 5 shows what the ITO bone appearance level is when the refractive index of the insulating film remains 1.900 and the insulating film has a film thickness distribution. FIG. 5 shows color differences when the film thickness distribution is ± 0 mm, ± 300 mm, ± 400 mm, ± 500 mm, ± 600 mm with respect to the center. Here, the film thickness distribution of, for example, ± 300 mm means that the difference between the maximum film thickness and the minimum film thickness is 600 mm within an area having a radius of 500 μm.
[0022]
According to this, it can be understood that the level of ITO bone appearance decreases as the film thickness distribution increases. In order for the color difference to be 9 or less, it can be understood that the film thickness distribution should be ± 450 mm or more. In addition, it can be understood that the film thickness distribution should be ± 600 mm or more in order for the color difference to be 6 or less.
[0023]
When the refractive index of the insulating film is 1.800 in FIG. 6 and when the refractive index of the insulating film is 1.700 in FIG. Indicate. 4 to 7, there are good points for reducing the color difference, but the color difference increases when the central film thickness of the insulating film changes or the film thickness distribution changes. That is, the ITO bone appearance level deteriorates.
[0024]
Therefore, it can be seen that it is necessary to increase the film thickness distribution in order to maintain a good level even if there is a change in the center film thickness. FIG. 8 collectively shows the maximum color difference when the refractive index of the insulating film is changed from 1.9 to 1.7 and the film thickness distribution is changed in a range from 100 to 1000 mm.
[0025]
According to this, it is understood that the condition that the color difference is 9 or less is sufficient if the thickness distribution of the insulating film is ± 500 mm or more and the difference between the refractive index of the insulating film and the refractive index of the transparent electrode is within 0.15. it can. It is said that the color difference that cannot be discerned by the human eye is 3 or less. Therefore, it is preferable that the color difference is 6 or less as a range in which the ITO bone appearance is acceptable. In order to achieve a color difference of 6 or less, the refractive index of the insulating film is substantially equal to the refractive index of the transparent electrode, and the film thickness distribution is in the range of ± 600 mm to ± 700 mm.
[0026]
As a result, if the thickness distribution of the insulating film is ± 500 mm or more and the difference between the refractive index of the insulating film and the refractive index of the transparent electrode is within 0.15, any film thickness is centered. ITO bone appearance level is small. In the case of a model that does not include an insulating film, the refractive index of the alignment film is within 0.15 of the refractive index of ITO, and the film thickness distribution may be ± 500 mm.
[0027]
Next, as shown in FIG. 1 as an example, the insulating film has a film thickness distribution. As an example, the glass substrate 10 is provided with irregularities, and the insulating film 12 is applied and baked by flexographic printing. The peaks can be thin and the valleys can be thick. When the liquid of the insulating film is applied on the uneven surface, it flows so as to be flattened between the uneven peaks and valleys, and if this is baked as it is, the insulating film 12 having a film thickness distribution is formed.
[0028]
HF etching, sand blasting, etc. can be applied to the method of making the glass substrate uneven. Alternatively, a resin layer may be formed on the glass substrate and the surface thereof may be uneven. In any case, in order to prevent the unevenness from being identified by the human eye, it is necessary to reduce the pitch of the peaks and valleys.
[0029]
For this purpose, the pitch of the valleys is preferably 500 μm or less. More preferably, it is 300 μm or less, and if it is 100 μm or less, it can be hardly recognized. In addition, when irregularities are arranged in a regular repetitive pattern, interference and moire may occur. Therefore, random arrangement is preferable. The pitch between the peaks and valleys is a distance between adjacent peaks as indicated by p in FIG.
[0030]
【Example】
Next, a specific embodiment of the liquid crystal display element 1A according to the present invention will be described with reference to FIG. In FIG. 2, the same reference numerals are used for portions that are considered to be the same as or the same as the components of FIG. 3 described above.
[0031]
As the transparent substrate 10 on the display observation surface side and the transparent substrate 20 on the back surface side, 1.1 mm thick glass substrates were used. The inner surface of the glass substrate 10 on the display observation surface side was frosted by HF etching to form irregularities having a pitch between the peaks and valleys of about 100 μm and a depth of the valleys of about 5.5 μm.
[0032]
On this uneven surface, SiO _{2 is formed} to a thickness of 300 と し て as an undercoat layer, and an ITO conductive film is formed to a thickness of about 300 に よ り by sputtering, followed by patterning to form a transparent electrode 11 having a predetermined shape. did.
[0033]
And the liquid of the insulating film was apply | coated to the surface containing the transparent electrode 11 by the flexo method, and after baking, it baked at 300 degreeC and formed the insulating film 12. FIG. The film thickness of the insulating film 12 reflects the unevenness of the glass substrate 10, and the peak part is about 200 mm thick and the valley part is about 3000 mm thick, and a very large film thickness distribution was obtained. In addition, it became an intermediate | middle film thickness between a peak and a valley.
[0034]
An alignment film 13 was printed on the insulating film 12 by a flexographic method. The film thickness of the alignment film 13 is less affected by the unevenness of the glass substrate 10, and the film thickness distribution is about 200 mm thick at the peak and about 400 mm thick at the valley. The alignment film 13 was rubbed to have an alignment function.
[0035]
On the glass substrate 20 on the back side, an SiO ₂ film having a thickness of 300 mm is formed as an undercoat layer without frosting, and an ITO conductive film is formed on the glass film 20 by sputtering to a thickness of about 300 mm, followed by patterning. A counter electrode 21 was formed. Then, an insulating film 22 was formed on the surface including the counter electrode 21 to a thickness of about 700 mm, and subsequently an alignment film 23 was formed to a thickness of about 300 mm. The alignment film 23 was also rubbed to have an alignment function.
[0036]
The refractive index of each component is about 1.941 ITO, about 1.945 insulating film, about 1.746 alignment film, about 1.520 glass substrate, and about 1.460 SiO _{2 with} respect to a wavelength of 590 nm. . As the liquid crystal 30, a liquid crystal having a major axis refractive index of about 1.628 and a minor axis refractive index of about 1.498 was used.
[0037]
These two glass substrates 10 and 20 were overlapped in an arrangement in which the rubbing directions were orthogonal to each other with an in-plane spacer of 9.5 μm interposed therebetween, and a liquid crystal cell was produced by pressure bonding through a peripheral sealing material. And after injecting the liquid crystal from the injection hole by a vacuum injection method, the injection hole was sealed with a sealing material. The liquid crystal layer was 90 ° twisted TN and Δnd was about 1.6 μm.
[0038]
Polarizing films 14 and 24 were disposed outside the glass substrates 10 and 20, respectively. At that time, the liquid crystal was arranged so that the major axis direction (direction in which the refractive index is high) of the adjacent liquid crystals and the absorption axis of the polarizing film were the same. The display mode was a negative mode (normally black mode) that turned black when no voltage was applied. In addition, a backlight 40 is disposed on the back surface of the back glass substrate 20.
[0039]
When the display was observed with external light incident, the ITO bone appearance was hardly visible. As a comparative example, a liquid crystal cell was fabricated in the same manner as in the above example except that the refractive index of the insulating film was about 1.754, and the appearance of ITO bone was observed. Even when the refractive index of the insulating film was about 1.945, the appearance of ITO bone was observed when the film thickness distribution was about ± 100 mm.
[0040]
In addition, this invention is not limited to embodiment mentioned above, A various change is possible as needed. For example, in the above-described embodiment, the concavo-convex substrate is the display observation surface side, but the concavo-convex substrate may be disposed on the back surface side. Further, a dichroic dye may be contained in the liquid crystal material.
[0041]
【The invention's effect】
As described above, according to the present invention, a liquid crystal display element including a pair of support substrates having transparent electrodes patterned into a predetermined shape, and having an insulating film formed on the liquid crystal side of at least one of the transparent electrodes In this case, the insulating film has a refractive index within 0.15 with respect to the refractive index of the transparent electrode, and a film thickness distribution within an area having a radius of 500 μm has a distribution of ± 500 mm or more. By using a film, it is possible to avoid the phenomenon of ITO bone appearance without incurring an increase in cost or a decrease in productivity, and at the same time, both improvement of black and white achromaticity and avoidance of the phenomenon of ITO bone appearance are achieved. be able to.
[0042]
The liquid crystal display element of the present invention exhibits high functionality in combination with its good visibility and expressive power, particularly when used in a vehicle, a clock, an indicator, and the like.
[Brief description of the drawings]
FIG. 1 is a partially enlarged cross-sectional view showing one support substrate used in a liquid crystal display element of the present invention.
FIG. 2 is a schematic cross-sectional view showing an embodiment of a liquid crystal display element of the present invention.
FIG. 3 is a schematic cross-sectional view showing a configuration of a conventional general liquid crystal display element.
FIG. 4 is a graph showing the color difference when the film thickness is changed when the refractive index of the insulating film is 1.900.
FIG. 5 is a graph showing the color difference when the thickness distribution is changed when the refractive index of the insulating film is 1.900.
FIG. 6 is a graph showing a color difference when the film thickness distribution is changed when the refractive index of the insulating film is 1.800.
FIG. 7 is a graph showing a color difference when the film thickness distribution is changed when the refractive index of the insulating film is 1.700.
FIG. 8 is a graph showing the color difference when the refractive index of the insulating film is changed from 1.900 to 1.700 and the film thickness distribution is changed.
[Explanation of symbols]
10 Display observation side transparent substrate (one support substrate)
20 Back side transparent substrate (other support substrate)
11, 21 Transparent electrodes 12, 22 Insulating films 13, 23 Alignment films 14, 24 Polarizing film 30 Liquid crystal 40 Backlight

Claims (2)

Including a pair of support substrates having transparent electrodes patterned into a predetermined shape, and an insulating film is formed on a surface of the pair of support substrates including the transparent electrodes of at least the support substrate on the display observation surface side ; In order to avoid the pattern appearance of the transparent electrode observed in
Concavities and convexities having depths of 3 μm or more for giving a film thickness distribution to the insulating film are formed on the transparent electrode forming surface side of the support substrate on the display observation surface side, The insulating film is a film having a refractive index within a difference of 0.15 with respect to the refractive index of the transparent electrode, and a film thickness distribution within an area of a radius of 500 μm of ± 500 mm or more. There is a liquid crystal display element. The liquid crystal display element according to claim 1, wherein an alignment film is used instead of the insulating film.

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