KR20120057519A - Liquid Crystal Element - Google Patents

Abstract

PURPOSE: A liquid crystal element is provided to use a polymer wall in a liquid crystal layer, thereby stably maintain a twisted state in a first turning direction. CONSTITUTION: Orientation treatment is performed on a first substrate(1) and a second substrate(2). The first substrate faces the second substrate. A liquid crystal layer(3) is installed between one side of the first substrate and one side of the second substrate. A plurality of polymer walls(6) are installed in a layer-thickness direction in the liquid crystal layer. The liquid crystal layer comprises a chiral agent. The chiral agent has features for twisting a liquid crystal molecule in a second turning direction opposite to a first turning direction.

Description

Liquid Crystal Element

The present invention relates to a technique for improving electro-optical characteristics in liquid crystal devices.

Japanese Patent No. 2510150 discloses a liquid crystal display in which electro-optical characteristics are improved by twisting and aligning liquid crystal molecules in a direction opposite to a direction of rotation regulated by a combination of alignment treatment directions performed on a pair of substrates arranged oppositely. An apparatus is disclosed (prior example 1). The operation mode of such a liquid crystal display (liquid crystal element) is called a reverse twisted nematic (TN) type.

In addition, Japanese Patent Application Laid-Open No. 2007-293278 discloses a turning direction (second turning direction) opposite to a turning direction (first turning direction) regulated by a combination of alignment treatment directions applied to a pair of substrates arranged oppositely. While adding a twisting chiral agent, the liquid crystal molecules are twisted and oriented in the above-described first turning direction to increase distortion in the liquid crystal layer, thereby lowering the threshold value voltage to enable low voltage driving. A liquid crystal device is disclosed (prior example 2).

Japanese Laid-Open Patent Publication No. 2010-186045 discloses a technique related to a reverse TN type liquid crystal element which is spray twisted in the initial state but stabilized in reverse twisted orientation when a longitudinal electric field is applied once (priority 3). .

By the way, in the liquid crystal display device of Japanese Patent No. 2510150, the alignment state of reverse twisting is unstable, and a reverse twisting alignment state can be obtained by applying a relatively high voltage to the liquid crystal layer. There is a problem of transition to a torsional alignment state. In addition, the liquid crystal element of JP 2007-293278 A has the advantage of lowering the threshold voltage as described above, but when the voltage is turned off (for example, several seconds), the liquid crystal element transitions to the forward twisted alignment state. Conversely, there is a problem of raising the threshold voltage. Further, the reverse TN type liquid crystal device of JP2010-186045A still leaves room for improvement in terms of electro-optical characteristics. For example, the sharpness in Japanese Patent Application Laid-Open No. 2010-186045 is about 1.7 at the most favorable time, and is expected to be further improved.

The specific form which concerns on this invention aims at providing the reverse TN type liquid crystal element which can aim at the improvement of the stability of a reverse twist orientation state, and the improvement of an electro-optical characteristic.

The liquid crystal device of one embodiment of the present invention includes (a) a first substrate and a second substrate, each of which is subjected to an alignment treatment and disposed to face each other, and (b) one surface of the first substrate and the first substrate. A liquid crystal layer provided between one surface of the two substrates, and (c) a plurality of polymer walls provided in the liquid crystal layer along the layer thickness direction, and (d) the first substrate and the second substrate are formed of the liquid crystal layer. The alignment process direction is set relatively to facilitate the generation of the first alignment state twisted in the first turning direction with respect to the liquid crystal molecules, and (e) the liquid crystal layer is formed so that the liquid crystal molecules are opposite to the first turning direction. A liquid crystal device comprising a chiral agent having a property of twisting in a second turning direction and having an alignment state twisted in the first turning direction.

According to the above configuration, by introducing the polymer wall into the liquid crystal layer, the alignment state (reverse twist state) twisted in the first turning direction is stably maintained. For the polymer wall, for example, a photocurable resin is added to the liquid crystal material at the time of forming the liquid crystal layer, the liquid crystal material is injected between the first substrate and the second substrate, and then the liquid crystal layer is initialized by applying voltage or the like. It can form easily by making a transition from the in-spray twist state to a reverse twist state, and irradiating light in that state. The reverse TN type liquid crystal device having such a polymer wall is excellent in its electro-optical characteristics (threshold, sharpness). Therefore, according to the above configuration, there is provided a reverse TN type liquid crystal device capable of improving the stability of the reverse twist alignment state and the electro-optical characteristics.

In the above liquid crystal device, it is preferable that the plurality of polymer walls are bonded to each other and have a lattice shape in plan view.

This further improves the stability of the reverse twisted state. On the other hand, such a lattice-shaped polymer wall can be easily formed by, for example, using a mask having a lattice-shaped shielding portion at the time of light irradiation with a photocurable resin.

In the above liquid crystal device, the chiral agent is preferably added in an amount such that the ratio of the chiral pitch and the layer thickness of the liquid crystal layer is 0.04 or more and 0.4 or less.

Moreover, in the said liquid crystal element, it is also preferable that some polymer wall is what polymerized the photocurable liquid crystalline monomer.

And in the said liquid crystal element, the twist angle of the said liquid crystal molecule in a liquid crystal layer is set to about 90 degrees, for example. On the other hand, the torsion angle may be around 90 °, for example, about 80 to 110 °.

1 is a schematic diagram schematically showing the operation of a reverse TN type liquid crystal element.
2 is a diagram schematically illustrating a method (polymer stabilization method) for forming a polymer network in a liquid crystal layer.
It is a figure explaining the method of forming a polymer wall in a liquid crystal layer.
4 is a cross-sectional view showing a configuration example of a reverse TN type liquid crystal element.
5 is a view for explaining the definition of the threshold voltage and the sharpness.
6 is a diagram showing the structure of a mask used for ultraviolet irradiation in Example 1. FIG.
7 is a view showing a microscope observation image of the liquid crystal device of Example 1. FIG.
8 is a diagram showing a measurement result of electro-optical characteristics of the liquid crystal device of Example 1;
9 is a diagram illustrating a structure of a mask used for ultraviolet irradiation in Example 2. FIG.
10 is a view showing a microscope observation image of the liquid crystal device of Example 2. FIG.
FIG. 11 shows measurement results of electro-optical characteristics of the liquid crystal device of Example 2. FIG.
12 is a view showing a microscope observation image of the liquid crystal device of Example 2. FIG.
FIG. 13 shows measurement results of electro-optical characteristics of the liquid crystal device of Example 2. FIG.

EMBODIMENT OF THE INVENTION Next, embodiment of this invention is described with reference to drawings.

1 is a schematic diagram schematically showing the operation of a reverse TN type liquid crystal element. The reverse TN type liquid crystal device includes, as a basic configuration, an opposingly arranged upper substrate 1 and a lower substrate 2 and a liquid crystal layer 3 provided therebetween. The surface of each of the upper substrate 1 and the lower substrate 2 is subjected to an orientation treatment such as a rubbing treatment (indicated by an arrow in the drawing). The upper substrate 1 and the lower substrate 2 are arranged relatively so that these alignment treatment directions cross each other at an angle of about 90 degrees. The liquid crystal layer 3 is formed by injecting a nematic liquid crystal material between the upper substrate 1 and the lower substrate 2. In this liquid crystal layer 3, a liquid crystal material to which a chiral agent is added is used, which generates an action of twisting liquid crystal molecules in a specific direction (right turning direction in the example of FIG. 1) in the azimuth direction. When the distance (cell thickness) between the upper substrate 1 and the lower substrate 2 is d and the chiral pitch made of chiral is p, these ratios d / p are set to about 0.4, for example. Such a reverse TN type liquid crystal device is in a twisted state in which the liquid crystal layer 3 is twisted while being spray-oriented in the initial state. When a voltage exceeding the saturation voltage is applied to the liquid crystal layer 3 in the spray twisted state, the liquid crystal molecules transition to the reverse twisted state (uniform twisted state), which is twisted in the left turning direction. In the liquid crystal layer 3 in the reverse twisted state, since the liquid crystal molecules in the bulk are inclined, the effect of reducing the driving voltage of the liquid crystal element appears. However, in general, such a reverse twist state is often unstable, and naturally transitions to the spray twist state which is an initial state with time. Therefore, the inventor of the present application considered that the alignment state of the liquid crystal layer 3 should be stabilized by introducing a polymer network into the liquid crystal layer 3.

2 is a diagram schematically illustrating a method (polymer stabilization method) for forming a polymer network in a liquid crystal layer. As shown in Fig. 2A, when the liquid crystal layer 3 is formed between the upper substrate 1 and the lower substrate 2, the liquid crystal molecules 3a and a photocurable type (for example, an ultraviolet curable type) are formed. The liquid crystal material containing the liquid crystalline monomer 3b is used. Next, as shown in FIG. 2B, a voltage is applied to the liquid crystal layer 3 using the upper electrode 4 and the lower electrode 5 provided on the upper substrate 1 and the lower substrate 2, respectively. By applying, the alignment state of the liquid crystal layer 3 is shifted to the reverse twist state. Next, as shown in FIG.2 (C), while the reverse twist state of the liquid crystal layer 3 is hold | maintained, such liquid crystal layer 3 is irradiated with light (for example, ultraviolet irradiation). As a result, the liquid crystalline monomer 3b is polymerized, and a polymer network is formed in the liquid crystal layer 3. By forming such a polymer network, the stability of a reverse twist state improves, and it becomes difficult to transition to the spray twist state of an initial state.

3 is a diagram schematically illustrating a method of forming a polymer wall in a liquid crystal layer. In addition, the same code | symbol is used about the structure common to FIG. 2, and the description about them is abbreviate | omitted. In the step of irradiating light in the method of forming the polymer network (see FIG. 2C), a mask 10 for selectively passing light is used. The pattern of the light shielding portion in the mask 10 can be arbitrarily set, for example, a pattern having a plurality of linear light shielding portions extending in one direction (line pattern), and a plurality of patterns extending in two directions. It is also possible to set it as a two-dimensional lattice pattern (matrix pattern) formed by superimposing linear light shielding portions. By irradiating light through such a mask 10, as shown in FIG. 3B, the polymer wall 6 is formed in a position corresponding to the light-transmitting portion of the mask 10 in the liquid crystal layer 3. On the other hand, after light irradiation using the mask 10, you may further irradiate light over the whole liquid crystal layer 3 without using the mask 10. FIG.

4 is a cross-sectional view showing a configuration example of a reverse TN type liquid crystal element. The liquid crystal element shown in FIG. 4 has a basic configuration in which a liquid crystal layer 59 is interposed between the first substrate (upper substrate) 51 and the second substrate (lower substrate) 55. The first polarizing plate 61 is disposed outside the first substrate 51, and the second polarizing plate 62 is disposed outside the second substrate 55. Hereinafter, the structure of the liquid crystal element will be described in more detail. In addition, illustration and description are abbreviate | omitted about members, such as the sealing material which seals the periphery of the liquid crystal layer 59. As shown in FIG.

 Each of the first substrate 51 and the second substrate 55 is, for example, a transparent substrate such as a glass substrate or a plastic substrate. As shown in the drawing, the first substrate 51 and the second substrate 55 face each other, and a predetermined gap (for example, several micrometers) is provided to be attached to each other. In addition, although illustration is abbreviate | omitted, switching elements, such as a thin film transistor, may be formed on either board | substrate.

The liquid crystal layer 59 is provided between the first substrate 51 and the second substrate 55. The dielectric anisotropy (Δε) of the liquid crystal material constituting the liquid crystal layer 59 is positive (Δε> 0). The thick line shown in the liquid crystal layer 59 schematically shows the orientation orientation of liquid crystal molecules in an initial state in which no voltage is applied to the liquid crystal layer 59. The liquid crystal layer 59 includes a polymer wall 60 formed by the above method.

The first electrode 52 is provided on one surface side of the first substrate 51, and the second electrode 56 is provided on one surface side of the second substrate 55. The first electrode 52 and the second electrode 56 are each configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example.

The alignment film 53 is provided on one surface side of the first substrate 51 so as to cover the first electrode 52. The alignment film 57 is provided on one surface side of the second substrate 55 so as to cover the second electrode 56.

FIG. 5 is a diagram for explaining the definition of the threshold voltage and the sharpness used as evaluation indexes of the reverse TN type liquid crystal element of the present embodiment. The transmittance when no voltage is applied to the liquid crystal element is 100%, and the value when the transmittance is not changed by raising the applied voltage is 0%. At this time, if the voltage value at which the transmittance is 90% is set to V ₉₀ , and the voltage value at which the transmittance is 10% is set at V ₁₀ , the threshold voltage and clarity can be expressed as follows.

Threshold Voltage = V ₉₀

Sharpness (γ) = V ₁₀ / V ₉₀

In general, the smaller the value of both the threshold voltage and the sharpness, the better the electro-optical characteristics of the liquid crystal element.

Next, some embodiments of the reverse TN type liquid crystal device as described above will be described.

(Example 1)

The liquid crystal element of Example 1 was produced under the following conditions, and the characteristics thereof were evaluated. First, two glass substrates with an ITO film were prepared, washed and dried. Next, the alignment material was applied to the surface of each glass substrate. As an orientation material, the horizontal orientation material which gives a pretilt angle of 1-2 degrees to liquid crystal molecule was used suitably. After baking the orientation material of one glass substrate, carrying out a rubbing process to this, the spacer material was spread | dispersed on this glass substrate, and the sealing material was printed again. As the spacer material, one having a particle diameter of 4 m was used. In addition, after the orientation material was fired about the other glass substrates and subjected to a rubbing treatment, the glass substrates were bonded to each other to form a cell, and a liquid crystal material was injected therein. Regarding the adhesion of the two glass substrates, the directions of the rubbing treatments on the respective glass substrates were set to 90 ° to each other. As the liquid crystal material, ZLI-2293 manufactured by Merck Co., Ltd. was used. CB15 was added to this liquid crystal material as a chiral agent. The addition amount of the chiral agent was set so that the ratio (d / p0) of the cell thickness d and the chiral agent pitch p0 became 0.2. In addition, ultraviolet curable resin was added to the liquid crystal material. The amount of the ultraviolet curable resin added was three patterns of 4 wt%, 5 wt% or 6 wt%. After injecting the liquid crystal material, the cell was sealed, and the alignment state of the liquid crystal layer was changed from the spray twist state in the initial state to the reverse twist state by voltage application, and then irradiated with ultraviolet rays with an ultraviolet curable resin. The structure of the mask used for ultraviolet irradiation is shown in FIG. In this embodiment, two ultraviolet irradiations were performed using a mask having a line-shaped pattern as shown. The mask direction at the time of one irradiation and the irradiation of two times was rotated approximately 90 degrees. In other words, the longitudinal direction of the line-shaped pattern was approximately orthogonal when irradiated once and irradiated twice. As shown, the line pattern of the mask has a line width of about 150 mu m and a line spacing of 20 mu m. The wavelength of the ultraviolet ray was 365 nm and the irradiation intensity was 40 kW / cm 2, and irradiation for 30 seconds at the irradiation intensity was performed three times before and after changing the mask direction. At this time, before each ultraviolet irradiation, a voltage for transitioning the liquid crystal layer to the reverse twisted state was applied. As the voltage application condition, for example, a voltage of about 15V was applied for 10 seconds or a voltage of about 15V was applied intermittently two or three times. As a result, a two-dimensional lattice-shaped polymer wall was formed in the liquid crystal layer.

7 is a view showing a microscope observation image of the liquid crystal device of Example 1. FIG. The illustrated liquid crystal element is a 4 wt% addition of an ultraviolet curable resin. It is the polymer wall that looks like a black lattice in the figure. In addition, a white point is a spacer material. The absorption axes of the polarizing plates P and A of the liquid crystal element were arranged in a state of forming an angle of approximately 45 ° as shown. It was confirmed that the reverse twisted state was stabilized by the formation of the polymer wall. The measurement result of the electro-optical characteristic (V-T characteristic) of the liquid crystal element of Example 1 is shown in FIG. 8 (sample which added the amount of ultraviolet-ray curable resin to 4-6 wt%). Except for 4 wt% samples showing hysteresis, 5 wt% and 6 wt% samples were compared with each other.

(Example 2)

The liquid crystal device was produced under the same conditions as in Example 1, and the characteristics thereof were evaluated. However, the following conditions are different from Example 1. In the present Example, d / p0 value was 0.2 or 0.4, and the addition amount of ultraviolet curable resin was 4 patterns of 4 wt%, 5 wt%, 6 wt%, 7 wt%. In addition, in the present Example, ultraviolet-ray was irradiated using the mask which has a grid | lattice-like (matrix-shaped) pattern. The structure of the mask used for ultraviolet irradiation in the present Example is shown in FIG. As shown in the drawing, the lattice pattern of the mask has a line width of about 180 mu m and a line spacing of 20 mu m. The wavelength of the ultraviolet ray is 365 nm and the irradiation intensity is 80 mW / cm 2. With this irradiation intensity, the exposure time was repeated four times for 1 minute, and the mask was exposed. Finally, the mask was removed and exposed for 1 minute (front irradiation). At this time, before ultraviolet irradiation, a voltage was applied to transition the liquid crystal layer to the reverse twisted state. As the voltage application condition, for example, a voltage of about 15 V was applied for 10 seconds or a voltage of about 15 V was applied intermittently two or three times. As a result, a two-dimensional lattice-shaped polymer wall was formed in the liquid crystal layer.

10 is a view showing a microscope observation image of the liquid crystal device of Example 2. FIG. In the illustrated liquid crystal element, d / p0 is set to 0.2, and 4 wt% of ultraviolet curable resin is added. It is the polymer wall that looks like a white lattice in the figure. The absorption axes of the polarizing plates P and A of the liquid crystal element are in a state of forming an angle of approximately 20 degrees as shown in the figure, and the absorption axes of one polarizing plate A are arranged substantially parallel to one of the extending directions of the polymer walls. It was. It was confirmed that the reverse twisted state was stabilized by the formation of the polymer wall. The measurement result of the electro-optical characteristic (V-T characteristic) of each sample which changed only the addition amount of the liquid crystal element and ultraviolet curable resin of such a sample is shown in FIG. Meanwhile, in FIG. 11, 'ps before rise' and 'ps before fall' are V-T characteristics of the sample before the polymer wall is formed. As shown, magnetic hysteresis is observed in the V-T characteristics in the sample before the polymer wall is formed.

12 is a view showing a microscope observation image of the liquid crystal device of Example 2. FIG. In the illustrated liquid crystal element, d / p0 is set to 0.4, and 4 wt% of ultraviolet curable resin is added. It is the polymer wall that looks like a white lattice in the figure. The absorption axes of the polarizing plates P and A of the liquid crystal element are in a state of forming an angle of approximately 10 degrees as shown in the figure, and the absorption axes of one polarizing plate A are arranged substantially parallel to one of the extending directions of the polymer walls. It was. It was confirmed that the reverse twisted state was stabilized by the formation of the polymer wall. The measurement result of the electro-optical characteristic (V-T characteristic) of each sample which changed only the addition amount of the liquid crystal element of this sample and an ultraviolet curable resin is shown in FIG. Meanwhile, in FIG. 13, 'ps before rise' and 'ps before fall' are V-T characteristics of the sample before the polymer wall is formed. As shown, magnetic hysteresis is observed in the V-T characteristics in the sample before the polymer wall is formed.

The threshold value in the liquid crystal element of Example 2 was generally equivalent to that of a conventional TN type liquid crystal element, and was specifically about 1.58 V (volts). In addition, the sharpness value of 1.32 was obtained under optimum conditions, and greatly improved compared with the conventional TN type liquid crystal device. The value of 1.32, which is obtained here, indicates that a simple matrix drive of more than 1/12 duty can be performed, and the range of use of the TN type liquid crystal device in which the conventional 1/4 duty or 1/8 duty is limited can be greatly extended. It is present. In addition, definition of sharpness and a threshold value is as above-mentioned.

In addition, this invention is not limited to the above-mentioned content, It can variously deform and implement within the range of the summary of this invention. For example, in the above, although photocurable resin was illustrated in order to form a polymer wall, you may use thermosetting resin. In addition, although the values of 0.2 and 0.4 were mentioned previously as a suitable example with respect to d / p0, d / p0 is not limited to these numerical values. Based on preliminary experiments and the like, the inventors of the present application found that the smaller the d / p0 value was, the more the sharpness tended to deteriorate, and it was confirmed that the lower limit of d / p0 that could achieve the improvement of the sharpness was 0.04.

1: upper board 2: lower board
3: liquid crystal layer 3a: liquid crystal molecules
3b: liquid crystalline monomer 4: upper electrode
5: lower electrode 6: polymer wall
10: mask 51: first substrate
52: first electrode 53, 57: alignment layer
55: second substrate 56: second electrode
59: liquid crystal layer 60: polymer wall

Claims (5)

The first substrate and the second substrate, each of which is subjected to an orientation treatment and are disposed to face each other;
A liquid crystal layer provided between one surface of the first substrate and one surface of the second substrate;
A plurality of polymer walls disposed in the liquid crystal layer along the layer thickness direction,
The orientation direction of the first substrate and the second substrate is relatively set so that the first alignment state twisted in the first pivot direction with respect to the liquid crystal molecules of the liquid crystal layer is easily generated.
The liquid crystal layer includes a chiral agent having a property of twisting the liquid crystal molecules in a second turning direction opposite to the first turning direction, and having an alignment state twisted in the first turning direction. The method of claim 1,
The plurality of polymer walls are bonded to each other, the liquid crystal device having a grid shape in plan view. The method according to claim 1 or 2,
And said chiral agent is added in an amount such that the ratio of the chiral pitch and the layer thickness of the liquid crystal layer is 0.04 or more and 0.4 or less. The method according to any one of claims 1 to 3,
The plurality of polymer walls are polymerized photocurable liquid crystalline monomers. The method according to any one of claims 1 to 4,
And a twist angle of the liquid crystal molecules in the liquid crystal layer is approximately 90 degrees.

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