JPH07140460A - Color liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the color tone of the color liquid crystal display device from being spoiled even when the device is obliquely viewed by interposing a phase difference plate between the transparent substrate on a side where the rubbing direction of an oriented film provided on the transparent substrate and the direction of the axis of absorption of a polarizing plate are orthogonal to each other and the polarizing plate. CONSTITUTION:A twisted nematic type liquid crystal layer 1 is sandwiched between two transparent substrates 4 and 5, and the transparent substrate 5 is provided with a tricolor filter 10. Electrodes and oriented films are provided inside the transparent substrates 4 and 5 respectively and polarizing plates 2 and 3 are arranged outside the substrates; and the absorption axis directions C and D of the polarizing plates 2 and 3 match each other and are perpendicular to the rubbing direction B of the oriented film provided on the transparent substrate 5. Then the phase difference plate 6 is interposed between the transparent substrate 5 on the side where the rubbing direction of the oriented film and the absorption axis directions of the polarizing plates 2 and 3 are perpendicular to each other and the polarizing plate 3. Consequently, redish colors which are easy to transmit through obliquely are canceled and a view angle is varied between 0 and 40 deg. to eliminate the conspicuousness of redness even when the device is viewed in various directions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device. More specifically, the present invention relates to a color liquid crystal display device whose color tone does not change even if the viewing angle changes.

[0002]

2. Description of the Related Art A liquid crystal display device changes the state of a liquid crystal by an electric signal and converts it into optical information. Due to the difference in the mechanism, other systems such as a twist nematic system and a birefringence control system are adopted. There is. Furthermore, recently, colorization of liquid crystal display devices using color filters has been advanced.

Conventional twisted nematic type (hereinafter, T
An example of a color liquid crystal display device (referred to as N type) is shown in FIG.
5 and an example of the color filter used for this is shown in FIGS. FIG. 4 is an exploded perspective view for explaining an essential part of the TN type color liquid crystal display device, and FIG. 5 is a sectional view thereof. FIG. 6 is a plan view of the color filter, and FIG. 7 is a partially enlarged view thereof. In these figures, the liquid crystal layer 1
The front side polarizing plate 2 is arranged on the display surface side of the transparent substrate 4 made of glass or the like which sandwiches the liquid crystal layer 1, and the rear side polarizing plate 3 is arranged outside the transparent substrate 5 on the back side of the liquid crystal layer 1.
Are sandwiched between transparent substrates 4 and 5, and spacers (not shown) are studded in the liquid crystal layer 1 so that the distance between the transparent substrates on both sides is kept constant. Further, on both transparent substrates 4 and 5, a transparent electrode 9 composed of an ITO film or a SnO ₂ film, and alignment films 7 and 8 composed of polyimide or polyamic acid are provided with a thickness of about 70 to 90 nm. Rubbing is applied to 7 and 8 so that the alignment of liquid crystal molecules is fixed. In the TN type liquid crystal, the directions of the liquid crystal molecules are twisted by 90 ° at both ends of the liquid crystal layer, so that the rubbing directions A and B of the alignment films 7 and 8 provided on the two transparent substrates 4 and 5 are front as shown in FIG. The side and the rear side are formed in a direction substantially orthogonal to each other. Further, the transparent electrode 9 on the rear transparent substrate 5
For example, a red color filter 10 is provided on the R, 9G, and 9B.
One pixel is composed of a set of three color filters of R, a green color filter 10G, and a blue color filter 10B. A black mask 11 provided between each pixel by, for example, chrome plating or printing with black ink.
It is shaded by. This prevents light from the light source arranged at the rear of the rear side polarizing plate 3 from leaking from the gaps between the pixels to the display surface and lowering the contrast.

With this structure, by appropriately applying a voltage to each of the three transparent electrodes 9R, 9G, 9B constituting each pixel, the liquid crystal molecules between the transparent electrodes 9R, 9G, 9B of the colors to which the voltage is applied rise. It is possible to display a desired color.

Further, the above-mentioned front side polarizing plate 2 and rear side polarizing plate 3 are constructed such that their absorption axes C and D are substantially in the same direction when a negative type display is made. Usually, the rubbing direction A, which is the alignment direction of the liquid crystal molecules on the display surface (front surface) side of the liquid crystal layer 1, and the absorption axis C of the front side polarizing plate 2 are configured to be the same direction. Further, in this TN type liquid crystal layer, as shown in FIG. 4, the front surface of the liquid crystal layer 1 and the rear surface of the liquid crystal layer 1 are twisted by 90 ° in the arrangement direction of liquid crystal molecules. The absorption axis D of the rear side polarizing plate 3 and the rubbing direction B of the rear side alignment film 8 are substantially orthogonal to each other. By setting the absorption axis C of the front-side polarizing plate 2 and the absorption axis D of the rear-side polarizing plate 3 in substantially the same direction as in this example, linearly polarized light transmitted through the rear-side polarizing plate 3 is between the electrodes. When a voltage is not applied to the liquid crystal layer 1, the polarization direction is twisted by 90 ° by passing through the liquid crystal layer 1 and is orthogonal to the absorption axis direction C of the front side polarizing plate 2, so that the light is blocked. on the other hand,
When a voltage is applied between both electrodes, liquid crystal molecules rise and are not rotated, so that only the color filter to which a voltage is applied transmits light. Therefore, the color filters 10R, 10G, and 10B constituting the pixel are connected to the transparent electrode 9
By selecting R, 9G, and 9B, negative color display can be performed by the additive color mixing method.

On the contrary, a type in which the absorption axis directions of the polarizing plates on both sides are vertical is called a positive type.

[0007]

However, in a color liquid crystal display device having a built-in color filter, the retardation Δn · d of the liquid crystal layer (Δn is the difference in refractive index between ordinary light and extraordinary light, and d is the liquid crystal layer). Since the relationship between the thickness of the liquid crystal layer and the transmittance differs depending on the wavelength of light, a color of a certain wavelength is lost (leaks to the display surface) depending on the value of Δn · d of the liquid crystal layer. Normally, thickening the liquid crystal layer eliminates green and suppresses red and blue, and thinning the liquid crystal layer does the opposite. Therefore, Δn · d of the liquid crystal layer is set so that the transmittance of green light (wavelength λ = 550 nm) having the maximum visibility is minimized.
The red color is easily transmitted, and when viewed from an oblique direction rather than the front side, the display of the color liquid crystal display device becomes significantly reddish and the color tone is impaired. On the other hand, if you try to suppress the redness so that it does not matter even when viewed from an oblique direction, the green color when viewed from the front becomes noticeable and the color tone is also impaired.

An object of the present invention is to solve the above-mentioned problems and to provide a color liquid crystal display device which is not reddish and does not impair the color tone even when a negative type color liquid crystal display device is viewed from an oblique direction. To do.

[0009]

In order to prevent the color tone from being impaired in the color liquid crystal display device both when viewed from the front and when viewed from an oblique direction, the present inventor has conducted extensive studies, and as a result, the rubbing direction By interposing a retardation plate between the transparent substrate and the polarizing plate on the side where the absorption axis direction of the polarizing plate is vertical, the leakage of red light from the oblique direction is reduced, the contrast is improved, and the color display is improved. Was found to be clear.

The color liquid crystal display device according to the present invention comprises:
A twisted nematic liquid crystal layer is sandwiched between two transparent substrates, at least three color filters are provided on one of the two transparent substrates, and an electrode and an alignment film are provided inside the two transparent substrates. Polarizing plates are respectively arranged outside the two transparent substrates, the absorption axes of the two polarizing plates are substantially the same, and on the liquid crystal layer side of the two transparent substrates. A liquid crystal display device provided so as to be substantially perpendicular to one side of a rubbing direction formed on each of the provided alignment films, wherein the rubbing direction of the alignment film and the absorption axis direction of the polarizing plate. A retardation plate is interposed between the transparent substrate and the polarizing plate on the side where and become substantially vertical.

The retardation of the liquid crystal layer is set so that the green transmittance is smaller than the red transmittance, and the retardation is 460 to 520 nm or 980 nm.
It is preferably ˜1150 nm.

Further, it is preferable that the color filters have three colors of red, green and blue.

Here, the fact that the absorption axis directions of the two polarizing plates are substantially the same direction means that most of the linearly polarized light transmitted through one polarizing plate is transmitted through the other polarizing plate as it is. It means that the absorption axis directions are aligned to such an extent that the contrast of display by transmitted light is hardly affected. Further, the fact that the absorption axis direction of the polarizing plate and the rubbing direction of the alignment film are substantially vertical means that linearly polarized light in the rubbing direction hardly passes through the polarizing plate and does not affect the contrast of the liquid crystal display device. Saying a relationship.

[0014]

According to the present invention, the retardation plate is provided between the polarizing plate and the transparent substrate on the side where the rubbing direction of the alignment film provided on the liquid crystal layer side and the absorption axis direction of the polarizing plate are substantially perpendicular to each other. Because of the interposition, the reddish color that is easy to come out in the diagonal direction is canceled out, and not only can you see from the vertical direction of the display surface,
Redness does not become noticeable even when viewed from various directions by changing the viewing angle in the range of 0-40 °, and the strong green is also adjusted by adjusting the retardation (Δn · d) of the liquid crystal layer. Since it is suppressed, the display quality does not deteriorate due to the change in color tone. Therefore, the contrast of the negative TN liquid crystal display device is improved, and a clear color display can be obtained.

[0015]

The present invention will be described below with reference to the drawings. FIG. 1 is a perspective view for explaining a main part of an embodiment of a liquid crystal display device of the present invention, and FIG. 2 is a sectional view thereof. 1-2, reference numerals indicate the same parts as in FIGS. 4-5, and 6 is a retardation plate.

The inventor of the present invention makes the thickness (retardation Δn · d) of the liquid crystal layer not to make noticeable green color noticeable, and even when the liquid crystal display surface is viewed from an oblique angle. In order to prevent the reddish color tone change, we tried to suppress the color tone change by interposing a retardation plate. The retardation plate is a polymer material formed of, for example, polycarbonate, and a plate material that causes a phase difference between an extraordinary ray and an ordinary ray is used. ing.

Retardation R and refractive index n
_e, is in between the _{n o R = | n e -n} o | relationship × d = Δn · d is established. Here, d is the thickness of the plate, n _e is the refractive index for the extraordinary ray, n _o is the refractive index for ordinary ray.

The inventor first examined the change in color tone by changing the retardation R _L = Δn ₁ · d ₁ of the liquid crystal layer.

As shown in FIG. 1, the retardation R _P = Δn ₂ · d between the rear side polarizing plate 3 and the transparent substrate 5.
The retardation film of ₂ is 295 nm is interposed so that the optical axis direction is perpendicular to the absorption axis direction of the polarizing plate, and the retardation R _L = Δn ₁ · d _{1 of} the liquid crystal layer ₁ is 400 nm, 460 nm, 48
0nm, 520nm, 550nm, 650nm, 800nm, 900nm, 980n
Twelve kinds of m, 1050 nm, 1150 nm and 1200 nm were prepared and the color tone was examined by visual evaluation. As a result, as shown in Table 1, Δ
When n ₁ · d ₁ is 480 nm and 1050 nm, it looks very good (○) without any greenish or reddish appearance when viewed from the front or from an oblique direction, and Δn ₁ · d ₁ is 460 nm and At 980 nm, it is slightly reddish when viewed from an oblique direction, but is almost good (△ mark), at 520 nm and 1150 nm, slightly greenish when viewed from the front, but almost good (△ mark), 400 n
It was found that when the m, 550 nm to 900 nm and 1200 nm, the reddish and greenish colors became strong and the color tone deteriorated.

[0020]

[Table 1]

This result shows that the retardation of the liquid crystal layer is R _L = Δn ₁ · d ₁ and the transmittances of red, green and blue are shown in FIG. It has been shown that it is preferable to use a date. Further, it is more preferable that the transmittance of green is smaller than the transmittance of blue as well as red.

Next, using the liquid crystal layer 1 having retardation R _L of 480 nm, the phase difference of the retardation plate was changed, and the color tone change was examined by interposing the retardation plate at various places of the liquid crystal display device.

First, the transparent substrate 4 on the front side of the liquid crystal layer 1
As a result of interposing between the front side polarizing plate 2 and the front side polarizing plate 2, the direction of the optical axis of the retardation plate and the retardation R _P (value of Δn ₂ · d ₂ where d ₂ is the thickness of the retardation plate) Various investigations were conducted, but the change in color tone was not improved at all, and rather Δn ₂
・ Depending on the value of d ₂ , the reddishness became even stronger, and in some cases, it became worse. In addition, the retardation plate 6 is attached to the front side polarizing plate 2
The result of arranging it further to the front side was also the same result.

Next, the retardation plate 6 is attached to the rear side polarizing plate 3
As a result of examination by arranging further on the outer side of the optical axis and changing the direction of the optical axis and the retardation R _P variously, no improvement was observed as in the above.

Next, as a result of interposing the retardation plate 6 between the rear side polarizing plate 3 and the transparent substrate 5, the reddish color tone was clearly reduced and improved. Further, it has been found that by changing the direction of the optical axis of the retardation plate 6 and the retardation R _P , it is possible to further reduce the change in color tone, as described below. The relationship will be described in more detail.

In FIGS. 1 and 2, the liquid crystal layer 1 is a TN type liquid crystal layer as in the conventional example, and the alignment direction of the liquid crystal molecules (the rubbing direction of the alignment film) is the front side (the liquid crystal display surface) as shown in FIG. The rubbing direction A on the side) and the rubbing direction B on the rear side (the side opposite to the liquid crystal display surface) are perpendicular to each other.

In the normal case, as shown in FIG. 1, the absorption axis direction C of the front side polarizing plate 2 is formed in the same direction as the rubbing direction A on the front side, and the absorption axis direction D of the rear side polarizing plate 3 is formed. Is configured to be substantially perpendicular to the rubbing direction B of the rear side alignment film 8. The location of the retardation plate this time is also examined on the front side and the rear side under this positional relationship, but according to the backward law of light,
It goes without saying that the light source and the display surface side (front side and rear side) will be the same even if they are reversed.

In the present invention, between the rear transparent substrate 5 of the liquid crystal layer 1 and the rear polarizing plate 3, that is, on the side where the rubbing direction of the alignment film and the absorption axis direction of the polarizing plate are substantially orthogonal to each other. It is characterized in that the retardation plate 6 is interposed between the transparent substrate and the polarizing plate. Optical axis direction E of retarder 6
As a result of various changes, the most reddish color tone change occurs in the same direction as the absorption axis direction D of the rear side polarizing plate 3, and the phase difference plate 6
Is improved as the optical axis direction E of the optical axis becomes perpendicular to the absorption axis direction D of the rear side polarizing plate 3, and it is most preferable when it is set to 90 °, but significant improvement can be seen even in the range of 90 ° ± 10 °. Was given. This relationship is summarized in Table 2. The degree of color tone change was evaluated by visual judgment. The viewing angle (the angle between the viewing direction of the display surface and the normal to the display surface) is 0.
At -40 °, the retardation of the retardation plate was R = 295 nm. In Table 2, the front side means the side where the absorption axis direction of the polarizing plate and the rubbing direction are the same direction, and the rear side means the side where the absorption axis direction of the polarizing plate and the rubbing direction are perpendicular to each other. To do.

[0029]

[Table 2]

Further, when the transparent substrate 5 and the rear polarizing plate 3 are arranged so that the optical axis direction E of the retardation plate is substantially perpendicular to the absorption axis direction D of the rear side polarizing plate 3. Then, when the retardation (Δn ₂ · d ₂ ) of the retardation plate 6 was changed, a difference in color tone appeared, and the optimum value was searched for. In this case, the retardation Δn ₁ · d _{1 of the} liquid crystal layer is about
It was performed with two types, 480 nm and about 1050 nm.

Example 1 With the above-mentioned structure, the retardation Δn _{1 is used} as the liquid crystal layer 1.
・ Using TN type liquid crystal with d ₁ of about 480 nm, polarizing plates 2 and 3
As the color retarder 6, a iodine-based polarizing plate of about 0.2 mm is used, printing inks of R, G, and B three colors are adhered to about 1 to 3 μm. Value from 162 to 350n
Several kinds were prepared within the range of m, and the degree of color tone change was evaluated by visual judgment. The results are shown in Table 3. In this measurement, the viewing angle (angle with respect to the normal to the liquid crystal display surface) is 0.
Performed in the range of -40 °.

[0032]

[Table 3]

As can be seen from Table 3, if the retardation (Δn ₂ · d ₂ ) is in the range of 240 to 320 nm,
The change in color can be suppressed to a negligible level.
It was found that even in the range of 0 to 340 nm, it can be used practically without any problems.

Example 2 Further, instead of the above-mentioned liquid crystal layer 1, the retardation was about
A TN type liquid crystal of 1050 nm is used, the same as in Example 1 except that the retardation R value of the retardation plate 6 is 190 to 34.
The same change as in Example 1 was carried out in the range of 7 nm, and the degree of color tone change was evaluated by the same method as in Example 1. The results are shown in Table 4.

[0035]

[Table 4]

As shown in Table 4, the same as Example 1
Retardation (Δn₂・ D ₂) At 240-320nm
Within the range, the change in color tone can be suppressed to a negligible level.
And practically no problem even in the range of 230 to 340 nm.
I found that it can be used without.

Example 3 The liquid crystal layer 1, the polarizing plate 2, the transparent substrate 4 and the retardation plate 6 are arranged in the same manner as in Examples 1 and 2, and the display surface and the light source are reversed (Example 1). As a result of similarly examining the change in color tone with the front side and the rear side of Nos. 1 and 2 reversed), the same results as in Example 1 and Example 2 were obtained.

As can be seen from the above description, the retardation R _L of the liquid crystal layer is 460 to 520 nm or 980 to 1150 nm.
In addition, the retardation plate 6 is interposed between the transparent substrate and the polarizing plate in which the alignment direction (rubbing direction) of the molecules of the TN type liquid crystal layer and the absorption axis direction of the polarizing plate are substantially vertical. As a result, it can be seen that the change in color tone can be reduced, and even when a negative type display is made, it is clearly improved. Furthermore, its optical axis is 90 ° with the absorption axis of the rear side polarizing plate 3.
By arranging so as to make an angle of ± 10 °, preferably 90 ° ± 5 °, it is possible to further reduce the change in color tone, and the retardation of the retardation plate is in the range of 230 to 340 nm, more preferably 240 to 320 nm. When set to the range, regardless of the material of the retardation film, it is possible to greatly reduce the change in color tone, such as greenish when viewing the liquid crystal display surface from the front and reddish when viewed from an angle. The display quality is improved. Therefore, as the material for the retardation film, other than the examples given above, color display that emphasizes the redness when viewed obliquely by adjusting the location of the retardation plate and the retardation value as described above. It is possible to greatly reduce the change in color tone.

Although the number of the retardation plates is one in each of the above-mentioned embodiments, the present invention is not limited to this, and the number of the retardation plates is two if the retardation described above can be obtained. It may be more than.

[0040]

According to the present invention, the alignment direction (rubbing direction) of molecules of the liquid crystal layer of the color liquid crystal display device using the TN type liquid crystal and the absorption axis direction of the polarizing plate are substantially perpendicular to each other. Since the retardation plate is interposed between the transparent substrate and the polarizing plate, the green color when viewed from the front is suppressed, and the color change to reddish when viewed from an angle is minimal. The display quality can be significantly improved by improving the contrast, and fatigue or discomfort does not appear even when viewed for a long time.

The retardation of the liquid crystal layer is 460 to 52 so that the transmittance of green is smaller than that of red.
By adjusting the thickness to 0 nm or 980 to 1150 nm, the change in color tone can be further reduced and the display quality is greatly improved.

[Brief description of drawings]

FIG. 1 is an exploded perspective view for explaining a main part of a color liquid crystal display device that is an embodiment of the present invention.

FIG. 2 is a cross-sectional explanatory diagram of a main part of a color liquid crystal display device that is an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between retardation R _L of a liquid crystal layer and transmittance at R, G, and B wavelengths.

FIG. 4 is an exploded perspective view for explaining an essential part of a conventional color liquid crystal display device.

FIG. 5 is an explanatory cross-sectional view of a main part of a conventional color liquid crystal display device.

FIG. 6 is a plan view of an example of a color filter.

7 is a partially enlarged view of the color filter shown in FIG.

[Explanation of symbols]

 1 Liquid crystal layer 2 Front side polarizing plate 3 Rear side polarizing plate 4, 5 Transparent substrate 6 Phase difference plate 7, 8 Alignment film 10 Color filter A, B Rubbing direction of alignment film C, D Absorption axis direction of polarization plate E Phase difference Plate optical axis direction

Claims (3)

[Claims] 1. A twisted nematic liquid crystal layer is sandwiched between two transparent substrates, at least three color filters are provided on one of the two transparent substrates, and an electrode and an electrode are provided inside each of the two transparent substrates. An alignment film is provided, and a polarizing plate is arranged outside each of the two transparent substrates,
The two polarizing plates have absorption axes substantially in the same direction, and are substantially on the same side as the rubbing direction formed on the alignment films provided on the liquid crystal layer side of the two transparent substrates. A liquid crystal display device provided so as to be substantially perpendicular to the transparent substrate and the polarizing plate on the side where the rubbing direction of the alignment film and the absorption axis direction of the polarizing plate are substantially perpendicular to each other. A color liquid crystal display device in which a retardation film is interposed between and. 2. The retardation of the liquid crystal layer is set so that the transmittance of green is smaller than the transmittance of red, and the retardation is 460 to 520 nm or 980 to 980 nm.
The color liquid crystal display device according to claim 1, which is 1150 nm. 3. The color liquid crystal display device according to claim 1, wherein the color filter has three colors of red, green and blue.