JPS6237766B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display panel capable of displaying good image quality and having a long life.

Various types of liquid crystal display panels have been proposed that utilize the electro-optic effect of liquid crystals, and they are classified according to the alignment treatment of the substrate and the type of liquid crystal material. The substrate alignment process is roughly divided into a vertical alignment process in which nematic liquid crystal molecules are aligned perpendicular to the substrate surface, and a parallel alignment process in which nematic liquid crystal molecules are aligned parallel to the substrate surface. Ordinarily, an alignment process that forms an alignment that is tilted within about 10 degrees from perpendicular or parallel is also called a vertical alignment process or a parallel alignment process, respectively. Liquid crystal materials are classified into nematic liquid crystals, cholesteric liquid crystals, and smectic liquid crystals depending on the type of liquid crystal phase they exhibit. In this classification, so-called chiral nematic liquid crystals are also included in the cholesteric liquid crystal classification. As mentioned at the beginning, various types of liquid crystal display panels can be obtained by combining these alignment treatments and liquid crystal materials. For example, currently widely used
A TN (twisted nematic) liquid crystal display panel is composed of two electrode substrates subjected to parallel alignment treatment and a nematic liquid crystal. Nematic GH is attracting attention as a color display method.
The (guest-host) system consists of two rotating substrates that are both vertically aligned or parallelly aligned, and a nematic liquid crystal to which dichroic dye is added. It consists of two electrode substrates and a cholesteric liquid crystal containing a dichroic dye. Furthermore, the CNT (cholesteric nematic transition) method, which is promising for character displays, consists of two vertically aligned electrode substrates and a cholesteric liquid crystal. Among these display methods, the cholesteric GH method has superior features compared to the same color display method, the nematic GH method, such as a brighter display because it does not require a polarizing plate, and no viewing angle restrictions. have. Also
The CNT method also has excellent features compared to the TN method used for character display, such as being able to use a larger number of electrodes and not having viewing angle limitations. The cholesteric GH method and CNT method, which have these excellent features, are actually basically applications of the same operation mode called phase transition electro-optic effect, and the difference between the two is that dichroic dye is added to the cholesteric liquid crystal. The only difference is whether you do it or not. In other words, it can be said that the operation mode called phase transition type electro-optic effect is an operation mode that has extremely excellent features. This phase change type electro-optic effect can be realized by vertically aligning the two electrode substrates and using cholesteric liquid crystal having positive dielectric constant anisotropy as the liquid crystal material. In a liquid crystal display panel that combines such an alignment treatment and a liquid crystal substance, when no voltage is applied, liquid crystal molecules are aligned perpendicular to the substrate surface over the entire surface of the panel near the electrode substrate, and both In the center portion away from the electrode substrate, the electrode is oriented parallel to the substrate surface and forms a helical structure. Such an orientation state of liquid crystal molecules is called a spiral structure, and is an almost transparent state (a colored state when a dichroic dye having an absorption axis in the direction of the long axis of the molecule is added). On the other hand, when a voltage is applied, the liquid crystal molecules only in the area where the display electrode is located transform into a homeotropic structure in which all of the liquid crystal molecules are oriented perpendicular to the substrate surface. This homeotropic structure is still transparent, and remains uncolored even when the above-mentioned dichroic dye is added. Therefore, when dichroic dye is added (cholesteric GH method), the voltage on/off
Color display can be performed by switching between a non-colored state and a colored state depending on the off state.

On the other hand, the driving method when no dichroic dye is added (CNT method) is a little complicated. This is because, as mentioned above, both the homeotropic structure and the spiral structure, which correspond to on/off voltages, are in a transparent state, and no display can be performed in these two states. The CNT method displays the voltage required for transition to the homeotropic tissue mentioned above when the voltage is turned off.
This is achieved by applying a voltage _V2 lower than _V1 .

In other words, when the voltage is changed from V ₁ → 0, it returns to the original spiral structure, but when it is changed from V ₁ → 0 → V ₂ → 0, it transitions to another focal structure, and this focal structure changes. Since the Nik tissue is in a cloudy state that exhibits light scattering, it can be displayed in combination with a transparent spiral tissue.

The above is the principle of the phase transition type electro-optic effect. As mentioned above, this phase change type electro-optic effect has excellent features, and this is largely due to the spiral structure obtained without applying any voltage.
That is, as mentioned above, in a spiral structure, liquid crystal molecules form a helical structure, and since the helical axis is perpendicular to the substrate surface (liquid crystal molecules are parallel to the substrate surface), it has the effect of optically rotating incident light. As a result, when used as a cholesteric GH system, there is no need for a polarizing plate, resulting in brightness and a wide viewing angle. In addition, in the spiral structure, the liquid crystal molecules are vertically aligned near the electrode substrate surface, which has the advantage that the transition time to the homeotropic structure when voltage is applied, that is, the response time when voltage is applied, is short. There is. However, in addition to the above advantages, the phase change electro-optic effect also has some disadvantages. This is because the response time when voltage is cut off is relatively long, and when voltage is continued to be applied for a long time, the area around the display electrode that should originally be a transparent spiral structure transforms into another structure that scatters light. , the display image quality gradually deteriorates, etc. The latter phenomenon, called "seepage phenomenon," occurs because the light-scattering tissue that is once generated remains without disappearing even after the display electrode voltage is cut off, resulting in a shortened lifespan of the liquid crystal display panel when it is energized. This is considered to be a major drawback in segment display type liquid crystal display panels, which have a smaller display area. As a result of conducting experiments and studies using various types and processing methods of orientation treatment for electrode substrates, the inventor found that the above-mentioned drawbacks can be removed by a novel orientation treatment, and the present inventors This led to the invention.

An object of the present invention is to provide a long-life liquid crystal display panel capable of displaying good image quality.

The liquid crystal display panel of the present invention has two substrates sandwiched between each other, each having a display electrode forming a display pattern and a lead electrode for guiding an electric signal to the display electrode formed on the inner surface, and a liquid crystal substance being filled in the gap between the two substrates. In particular, as the liquid crystal substance, a liquid crystal substance containing at least one type of liquid crystal substance exhibiting a cholesteric phase is used, and the inner surface of one of the two substrates is at least a display electrode portion. is subjected to vertical alignment treatment, and the other parts are subjected to parallel alignment treatment, and the inner surface of the other substrate is the display electrode portion at the portion facing the vertical alignment treatment of the one substrate. It is characterized in that the other parts are subjected to parallel alignment treatment, and the other parts are subjected to vertical alignment treatment or parallel alignment treatment.

Next, the present invention will be explained in detail with reference to the drawings.
FIG. 1 is a sectional view showing an embodiment of the liquid crystal display panel of the present invention. 1 and 1' are In ₂ O ₃ display electrodes that constitute the display pattern, 2 and 2' are In ₂ O ₃ lead electrodes that guide electrical signals to the display electrodes 1 and 1', respectively, and 3 and 4 are glass substrates. be. A portion 5 of the inner surface of the glass substrate 3 including the display electrode 1 is subjected to vertical alignment treatment using Teflon.
The other portions 6 are subjected to parallel alignment treatment using a lavender. Further, on the inner surface of the glass substrate 4, a portion 7 opposite to a portion 5 of the glass substrate 3 other than the display electrodes 1' is subjected to a parallel alignment treatment by rubbing, and a portion 8 of the other portions is subjected to parallel alignment treatment. is subjected to vertical alignment treatment using Teflon, and the other portion 8' is subjected to parallel alignment treatment using rubbing. For these alignment treatments, first, the entire inner surface of both glass substrates 3 and 4 is rubbed with absorbent cotton, and then parts 6, 7, and 8' of each substrate are covered with a mask, and the exposed portions 5 and 8 are sputtered. This can be achieved by forming a Teflon film using the method described above. In the area covered by the Teflon film, the underlying rubbing treatment remains ineffective, and the nematic liquid crystal molecules are aligned perpendicular to the substrate surface. 9 in Figure 1 is the thickness to keep the distance between the two glass substrates 3 and 4 constant.
15 μm film spacer, 10 is epoxy adhesive for bonding glass substrates 3 and 4, 1
1 is BDH (British Drug House)
E8, a nematic liquid crystal manufactured by the company, and cholesteryl chloride (abbreviated CC) as a cholesteric liquid crystal were mixed in a weight ratio of 9:1, and then the Japan Photosensitive Pigment Research Institute
This is a liquid crystal material containing 0.4% by weight of dichroic dye GR-17 manufactured by Co., Ltd.

When the liquid crystal substance 11 is vertically aligned on the inner surfaces of both substrates, the liquid crystal molecules are vertically aligned near the surfaces of both substrates, as shown in FIG. A so-called spiral structure is formed parallel to and spirally structured.

In addition, if the inner surface of one substrate is vertically aligned and the inner surface of the other substrate is parallelly aligned, as shown in Figure 2b, the area near the vertically aligned substrate is Only in this case, the liquid crystal molecules are vertically aligned, and in other cases, the liquid crystal molecules form a so-called striped structure that is parallel to the substrate surface and has a helical structure. Furthermore, if the inner surfaces of both substrates are subjected to parallel alignment treatment, all liquid crystal molecules are parallel to the substrate surfaces and form a so-called Grangian structure with a helical structure, as shown in Figure 2c. . Therefore, in the liquid crystal display panel of this embodiment, the liquid crystal material 11 is used as the display electrodes 1 and 1' in FIG.
A spiral structure is formed in the display area where the two are facing each other.
In other non-display areas, a grunge texture is formed on the left side of the display area, and a striped structure is formed on the right side of the display area. The response time of the liquid crystal display panel in this example is that the rise time when voltage is applied is 320 ms;
The fall time when the voltage was cut off was 240 ms. It was also confirmed that even if voltage was continued to be applied, the liquid crystal structure other than the display area did not change at all, and that the energization life did not deteriorate at all due to the above-mentioned "seepage phenomenon." On the other hand, for comparison, we created and measured a liquid crystal display panel with the same structure as this example, except that the entire inner surface of the two substrates was subjected to vertical alignment treatment using a Teflon coating, and the response times were the same. However, as the voltage was continued to be applied, it was observed that the spiral structure of the liquid crystal material around the display area gradually changed from the periphery of the display electrode, and a light scattering region was formed. The speed at which this light scattering region expanded was 6 μm/hour. The light scattering area formed by this "seepage phenomenon" remains even after the voltage is cut off, so when the cumulative power-on time reaches about 300 hours, the light scattering area due to "seepage" will not be visible for a display electrode with a width of 4 mm. It reached a total width of about 4 mm on both sides of the electrode, and it must be said that the energizing life has come to an end.
It is clear that the smaller the area of the display electrode, the more pronounced the reduction in the current life due to the "bleed-out phenomenon." In addition, even if the energization life has not been reached, the light scattering area due to the "seepage phenomenon" becomes noticeable to the naked eye after several hours have passed, and it is inevitable that the display quality will deteriorate. In this way, the "bleeding phenomenon" was a fatal flaw in conventional liquid crystal display panels that utilized the phase change electro-optic effect, but in the liquid crystal display panel of this example, this flaw was completely eliminated. It has become clear that it is possible to display good image quality and have a longer energized life.

That is, the "bleeding phenomenon" occurs when the liquid crystal in the region adjacent to the display electrode forms a spiral structure, and the "seepage phenomenon" occurs when the liquid crystal in the region adjacent to the display electrode forms a spiral structure. "Seepage phenomenon" occurs in liquid crystal display panels.
does not occur.

FIG. 3 is a sectional view showing another embodiment of the liquid crystal display panel of the present invention, and the numbers in the figure correspond to those in FIG. 1. This second embodiment differs from the first embodiment in that the inner surface of the display electrode 1' of the glass substrate 4 is subjected to parallel alignment treatment by rubbing. In this case, the liquid crystal material in the display electrode portion forms a striped structure, resulting in a display in an operating mode different from the conventional phase change type electro-optic effect that uses a spiral structure. However, when we measured the response characteristics of the liquid crystal display panel of this example, we found that the rise time was
The display time was 350ms, and the fall time was 150ms, and the characteristics were recognized to be comparable to those of conventional liquid crystal display panels. Also in the liquid crystal display panel of this embodiment, since the liquid crystal material in the non-display area adjacent to the display area forms a grunge-yan structure or a striped structure, the liquid crystal display panel of the first embodiment is similar to the liquid crystal display panel of the first embodiment. There were no problems such as deterioration of image quality or shortening of energized life due to "bleeding phenomenon".

FIG. 4 is a sectional view showing another embodiment of the liquid crystal display panel of the present invention, and the numbers in the figure correspond to those in FIG. 1. In this embodiment, the first and second points are that the inner surface of the glass substrate 3 is all subjected to a vertical alignment treatment using Teflon, and the inner surface of the glass substrate 4 is all subjected to a parallel alignment treatment by rubbing. This is different from the example. That is, of the two left and right regions adjacent to the display electrodes 1 and 1', the left region is vertically aligned on glass substrate 3 and parallelly aligned on glass substrate 4, which means that both glass substrates are parallel. This is largely different from the first and second embodiments, which involve orientation treatment. This example is the same as the second example in that the liquid crystal material in the display electrode portion forms a striped structure, and therefore the liquid crystal display panel of this example has exactly the same good response as the second example. The characteristics were shown. Also in the liquid crystal display panel of this embodiment, since the liquid crystal substance in the non-display area adjacent to the display area forms a striped structure, the liquid crystal display panel of the first and second embodiments has the same characteristics as the liquid crystal display panel of the first and second embodiments. There were no problems such as deterioration of image quality or shortening of energized life due to "bleeding phenomenon".

In addition, in the examples, only the case where a liquid crystal material containing a dichroic dye is used is described, but as mentioned earlier, the presence or absence of a dichroic dye has no bearing on the basic electro-optic effect, so this topic is not covered here. It goes without saying that the liquid crystal display panel of the invention has similar features even when the liquid crystal substance does not contain a dichroic dye.

As described above, according to the present invention, a liquid crystal display panel capable of displaying good image quality and having a long life can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of the liquid crystal display panel of the present invention, FIG. 2 is a diagram for explaining the alignment state of liquid crystal molecules, and FIGS. 3 and 4 are the liquid crystal display of the present invention. FIG. 7 is a cross-sectional view showing the structure of another example of the panel. In FIGS. 1, 3, and 4, 1 and 1' are display electrodes, 2 and 2' are lead electrodes, 3 and 4 are glass substrates, 5 and 8 are vertically aligned parts, and 6 , 7 and 8' are parts subjected to parallel alignment treatment, 9 is a spacer, 1
0 is an adhesive, and 11 is a liquid crystal substance. In FIG. 2, 12 is a substrate subjected to vertical alignment treatment, 13
14 is a substrate subjected to parallel alignment treatment, and 14 is a liquid crystal molecule.

Claims (1)

[Claims] 1. In a liquid crystal display panel formed by filling a gap between two substrates, each of which has a display electrode forming a display pattern and a lead electrode that guides an electric signal to the display electrode formed on the inner surface, with a liquid crystal substance, as the liquid crystal substance,
A liquid crystal substance containing at least one type of liquid crystal substance exhibiting a cholesteric phase is used, and the inner surface of one of the two substrates is arranged such that liquid crystal molecules are aligned perpendicularly to the substrate surface at least in the display electrode portion. The liquid crystal molecules are aligned parallel to the substrate surface (parallel alignment process) in other areas.
In addition, the inner surface of the other one substrate is a portion opposite to the vertically aligned portion of the one substrate, and a portion other than the display electrode portion is subjected to parallel alignment treatment, and the other portions are subjected to vertical alignment treatment. Or a liquid crystal display panel characterized by being subjected to parallel alignment treatment.