KR20120080370A - Liquid crystal display and manufacturing methof thereof - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a manufacturing method thereof are provided to easily switch a twist state and a splay state in a memory mode of a liquid crystal cell in a BCSN(Bistable Chiral Splay Nematic) mode, thereby maintaining features of a memory in a twist state. CONSTITUTION: A first insulating substrate faces a second insulating substrate. A liquid crystal layer(3) is inserted between the first insulating substrate and the second insulating substrate. The liquid crystal layer comprises a plurality of liquid crystal molecules(31) and a polymer network. The state of the liquid crystal molecules is switched between a twist state and a splay state. The polymer network is arranged around the liquid crystal molecules.

Description

Liquid crystal display device and its manufacturing method {LIQUID CRYSTAL DISPLAY AND MANUFACTURING METHOF THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display and a method of manufacturing the same, and more particularly, to a liquid crystal display and a method of manufacturing the bistable chiral splay nematic (BCSN) mode.

Among the liquid crystal display devices, the memory mode using the bistable characteristics of the liquid crystal can be driven with low power consumption and can display permanent information, thereby allowing portable liquid crystals such as e-books or personal digital assistants (PDAs). It can be applied to a display device.

The bistable chiral splay nematic (BCSN) liquid crystal mode is a new liquid crystal mode that can simultaneously implement a dynamic mode and a memory mode using a splay liquid crystal layer. The dynamic mode of the BCSN liquid crystal display can be achieved by switching between the low and high bend states, while the memory mode is the 180 ° twist state and the splay state, which is the initial alignment state. Can be implemented by switching.

In order to implement the memory mode of the liquid crystal cell of the BCSN mode, in order to properly switch from the twisted state to the splay state, the ratio (d / p) of the cell spacing (d) of the liquid crystal cell to the pitch (p) of the liquid crystal molecules is adjusted. In the range where the ratio of the cell spacing of the liquid crystal cell to the pitch of the liquid crystal molecules has a low value, it is possible to switch from the twisted state to the splay state, but the twisted state cannot be kept long, resulting in a memory state. There is a problem that can not maintain.

Accordingly, a technical problem to be solved by the present invention is to provide a liquid crystal display device and a method of manufacturing the same in which the twist state and the splay state can be easily switched and the memory state of the twist state can be maintained in the memory mode of the BCSN mode liquid crystal cell. It is.

The liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal layer injected between the first insulating substrate and the second insulating substrate facing each other, the first insulating substrate and the second insulating substrate, and the liquid crystal layer Includes a plurality of liquid crystal molecules that switch between a twisted state and a splay state and a polymer network disposed in the plurality of liquid crystal molecules.

The polymer network may be a reactive mesogen polymer network.

The liquid crystal display may further include a first electrode and a second electrode disposed on the first insulating substrate, and a third electrode disposed on the second insulating substrate.

The first electrode and the second electrode may be insulated from each other to apply a horizontal electric field to the liquid crystal layer.

At least one of the first electrode and the second electrode and the third electrode may apply a vertical electric field to the liquid crystal layer.

The liquid crystal display device includes a first alignment layer disposed on the first substrate, and

A second alignment layer may be further disposed on the second substrate, and the first alignment layer and the second alignment layer may be rubbed in directions parallel to each other.

A method of manufacturing a liquid crystal display device according to an exemplary embodiment of the present invention includes injecting a liquid crystal layer including a plurality of liquid crystal molecules and a photopolymerizable monomer between a first insulating substrate and a second insulating substrate facing each other, in the liquid crystal layer. Arranging the liquid crystal molecules in a first state by applying a first vertical electric field, arranging the liquid crystal molecules in a second state by applying a second vertical electric field greater than the first vertical electric field to the liquid crystal layer; Removing the second vertical electric field in a state where the liquid crystal molecules are arranged in the second state, and polymerizing the photopolymerizable monomer by irradiating light to the liquid crystal layer in a state where the second vertical electric field is removed. It may include.

The liquid crystal layer may further include a chiral dopant.

The photopolymerizable monomer may include a reactive mesogen monomer.

The first state may be a high bend state, and the second state may be a twisted state.

The liquid crystal display according to the exemplary embodiment of the present invention includes a reactive mesogen polymer network structure that fixes the liquid crystal alignment state of the twisted state, and thus the liquid crystal cell interval and the pitch of the liquid crystal layer for controlling switching between the twisted state and the splay state. While having a ratio, the twist state duration can be kept long, and the memory characteristic can be kept long.

1A and 1B are cross-sectional views of a memory mode of a liquid crystal display according to an exemplary embodiment of the present invention.
2A to 2E are cross-sectional views sequentially illustrating steps of manufacturing a liquid crystal display according to a method of manufacturing a liquid crystal display according to an exemplary embodiment of the present invention.
3 is a graph measuring memory time of the liquid crystal display according to the experimental example of the present invention.
4 is an electron micrograph showing a texture change that transitions from the twisted state to the splay state of the liquid crystal display according to the experimental example of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

First, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 1A and 1B. 1A and 1B are cross-sectional views of a memory mode of a liquid crystal display according to an exemplary embodiment of the present invention. Specifically, FIG. 1A shows the pie twisted state, and FIG. 1B shows the splayed state.

1A and 1B, a liquid crystal display according to an exemplary embodiment of the present invention is injected between a first display panel 100 and a second display panel 200 facing each other, and two display panels 100 and 200. The liquid crystal layer 3 is included.

The first display panel 100 is disposed on the first insulating substrate 110 and the first insulating substrate 110, and is insulated from each other to form a horizontal electric field in the liquid crystal layer 3 and the second electrode 191a and the second display panel 100. The electrode 191b and the first alignment layer 11 are included. An insulating layer 180 is disposed between the first electrode 191a and the second electrode 191b. In the illustrated embodiment, the first electrode 191a has a plate shape, but the shape of the first electrode 191a and the second electrode 191b is not limited to the illustrated embodiment, and is insulated from each other to form a horizontal electric field. It can have any shape that can be formed.

The second display panel 200 includes a second insulating substrate 210, a third electrode 270 disposed on the second insulating substrate 210, and a second alignment layer 21.

The third electrode 270 of the second display panel 200, the first electrode 191a and the second electrode 191b of the first display panel 100 may form a vertical electric field in the liquid crystal layer 3.

The first alignment layer 11 of the first display panel 100 and the second alignment layer 21 of the second display panel 200 may be rubbed in parallel with each other.

The liquid crystal layer 3 includes a plurality of liquid crystal molecules 31 and a polymer network 32. The plurality of liquid crystal molecules 31 comprise liquid crystal molecules of bistable chiral splay nematic mode and are in a memory mode state switching between a splay state and a twist state. The polymer network 32 provides an anchoring energy to the liquid crystal molecules 31 that switch between the twisted state and the splayed state, thereby increasing the retention time of the twisted state.

The polymer network 32 may be a reactive mesogen (RM) polymer network. Here, reactive mesogen (RM) means a polymerizable mesogenic compound. A "mesogenic compound" or "mesogenic material" includes a substance or compound comprising one or more rod-shaped, plate- or disc-shaped mesogenic groups, ie groups having the ability to induce liquid crystalline behavior. Liquid crystal compounds having rod-shaped or plate-shaped groups are known in the art as calamitic liquid crystals, and liquid crystal compounds having disc-shaped groups are known in the art as discotic liquid crystals. Compounds or materials containing mesogenic groups do not necessarily have to exhibit a liquid crystalline phase by themselves. It is also possible to exhibit liquid crystalline behavior only in mixtures with other compounds or upon polymerization of mesogenic compounds or substances, or mixtures thereof.

Reactive mesogen is a substance which is polymerized by light such as ultraviolet rays and is oriented according to the alignment state of adjacent materials. Examples of reactive mesogens include compounds represented by the following formula:

P1-A1- (Z1-A2) n-P2,

Here, P1 and P2 are independently selected from acrylate, methacrylate, vinyl, vinyloxy, and epoxy groups, and A1 and A2 are 1,4- Is independently selected from phenylen and naphthalene-2,6-diyl groups, Z1 is one of COO-, OCO- and a single bond, and n is one of 0, 1 and 2 .

More specifically, there may be mentioned a compound represented by one of the following formulas:

Here, P1 and P2 are independently selected from acrylate, methacrylate, vinyl, vinyloxy and epoxy groups.

Therefore, in the liquid crystal display according to the exemplary embodiment of the present invention, the twisted state and the splay in the liquid crystal display of the bistable chiral splay nematic mode of the memory mode switching between the twisted state of FIG. 1A and the splayed state of FIG. By including a reactive mesogen polymer network 32 which gives anchoring energy to the liquid crystal molecules 31 switching between states, under the conditions of the liquid crystal layer 3 capable of switching between the twisted state and the splay state. In addition, the twisted state may be maintained to maintain the twisted memory state.

Next, an operation of the liquid crystal display according to the exemplary embodiment of the present invention will be described. First, as shown in FIG. 1A, the liquid crystal molecules 31 are arranged in a twisted state by 180 °, in which the reactive mesogen polymer network 32 in the liquid crystal layer 3 is anchored to the liquid crystal molecules 31. By applying and fixing energy, the retention time of the liquid crystal molecules 31 arranged in the twisted state is increased, thereby maintaining the memory state for a long time.

Thereafter, when different voltages are applied between the first electrode 191a and the second electrode 191b of the first display panel 100, and a horizontal electric field is formed in the liquid crystal layer 3, the liquid crystal molecules 31 are formed. The memory state is released by returning to the splay state.

Through this operation, it is possible to display the image of the on / off state.

Next, a method of manufacturing a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 2A to 2E.

2A to 2E are cross-sectional views sequentially illustrating steps of manufacturing a liquid crystal display according to a method of manufacturing a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 2A, a liquid crystal layer 3 including a splay liquid crystal molecule 31 and a photopolymerizable monomer 30 is injected between two display panels 100 and 200. In this state, the liquid crystal molecules 31 are in a low bend state. The photopolymerizable monomer 30 may be reactive mesogen (RM).

Thereafter, as shown in FIG. 2B, different voltages are applied between the first electrode 191a or the second electrode 191b and the third electrode 270 formed on the two display panels 100 and 200. Thus, a vertical electric field is formed in the liquid crystal layer 3. By this vertical electric field, the liquid crystal layer 3 changes to the dynamic mode while changing to the high bend state.

Thereafter, as shown in FIG. 2C, by generating a vertical electric field larger than the vertical electric field for maintaining the high bend state, the liquid crystal layer 3 is changed into a 180 [deg.] Twist state. In such a twisted state, the vertical electric field applied to the liquid crystal layer 3 is removed and ultraviolet rays are irradiated.

By irradiating the ultraviolet light to the liquid crystal layer 3 in the twisted state, the photopolymerizable reactive mesogen monomer 30 is polymerized, thereby forming the reactive mesogen polymer network 32 as shown in FIG. 2D. Since the reactive mesogen polymer network 32 is formed in the twisted state of the liquid crystal molecules 31 of the liquid crystal layer 3, the reactive mesogen polymer network 32 is formed of the liquid crystal molecules 31 of the liquid crystal layer 3. ) To keep the twisted state.

Thereafter, as shown in FIG. 2E, even if the liquid crystal layer 3 forms a horizontal electric field, and the liquid crystal molecules 31 of the liquid crystal layer 3 change to a splay state, the polymer network 32 remains in the liquid crystal layer. It remains in (3).

Next, memory characteristics of the liquid crystal display according to the exemplary embodiment of the present invention will be described with reference to FIGS. 3 and 4. 3 is a graph measuring memory time of a liquid crystal display according to an experimental example of the present invention, and FIG. 4 is an electron microscope showing a texture change transitioning from a twisted state to a splay state of the liquid crystal display according to an experimental example of the present invention. It is a photograph. In the present experimental example, an existing liquid crystal display including a liquid crystal layer in which a liquid crystal (ZKC5085 from Chisso Co. Ltd., 91.92 wt%) was mixed with a chiral dopant (R-811 from Merck Co., 0.35 wt%) was formed. In this case, the reactive mesogen monomer (RM257 from Merck Co., 6.44 wt%), and photoinitiation are performed in the liquid crystal layer including the same liquid crystal and chiral dopant as in (a). In the case of manufacturing the liquid crystal display device according to the manufacturing method of the liquid crystal display device according to the embodiment of the present invention by using the liquid crystal layer further comprising (Irgacure651 from Ciba Specialty Chemicals, 1.29wt%), the memory time Was measured. In this case, the cell spacing d was about 5 μm in both cases (a, b), and the ratio (d / p) of the cell spacing d and the pitch p of the liquid crystal molecules was about 0.2. As described above, although the other conditions are the same in the present experimental example, two liquid crystal displays differing whether or not they contain a reactive mesogen monomer network and a photoinitiator in the liquid crystal layer. This is a comparison of the measured memory time for a twisted state.

Referring to FIG. 3, it can be seen that the memory time for maintaining the twisted state is more than twice as long as the liquid crystal display according to the exemplary embodiment of the present invention (a) compared to the conventional liquid crystal display (a). there was. In the present experimental example, the memory time for maintaining the twisted state of the conventional liquid crystal display was about 15 hours, but the memory time for maintaining the twisted state of the liquid crystal display according to the embodiment of the present invention was about 35 hours.

Referring to FIG. 4, in the case of the conventional liquid crystal display (a), a texture change that changes from the twisted state to the splay state occurs after about 15 hours, and in the case of the liquid crystal display according to the exemplary embodiment of the present invention (b). The texture change from the twisted to the splayed state occurs after a longer time, for example 30 hours.

That is, the liquid crystal display according to the exemplary embodiment of the present invention includes a reactive mesogen polymer network having a similar behavior to that of the liquid crystal molecules of the liquid crystal layer arranged in the twisted state, thereby arranging the liquid crystal molecules in the twisted state. By fixing, the memory holding time of the twisted state of the liquid crystal display device is kept long. Therefore, the retention time of the liquid crystals arranged in the twisted state is increased, so that the retention time of the memory state is long.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

100: first display panel
200: second display panel
3: liquid crystal layer
31: liquid crystal molecules
32: reactive mesogen polymer network

Claims (22)

A first insulating substrate and a second insulating substrate facing each other,
A liquid crystal layer injected between the first insulating substrate and the second insulating substrate,
The liquid crystal layer includes a plurality of liquid crystal molecules for switching between a twisted state and a splay state, and a polymer network disposed around the plurality of liquid crystal molecules.
In claim 1,
The polymer network is a reactive mesogen polymer network.
In claim 2,
A first electrode and a second electrode disposed on the first insulating substrate, and
And a third electrode disposed on the second insulating substrate.
4. The method of claim 3,
The first electrode and the second electrode is insulated from each other,
And a horizontal electric field applied to the liquid crystal layer.
5. The method of claim 4,
At least one of the first electrode and the second electrode and the third electrode apply a vertical electric field to the liquid crystal layer.
The method of claim 5,
A first alignment layer disposed on the first substrate, and
Further comprising a second alignment layer disposed on the second substrate,
And the first alignment layer and the second alignment layer are rubbed in directions parallel to each other.
4. The method of claim 3,
At least one of the first electrode and the second electrode and the third electrode apply a vertical electric field to the liquid crystal layer.
In claim 7,
A first alignment layer disposed on the first substrate, and
Further comprising a second alignment layer disposed on the second substrate,
And the first alignment layer and the second alignment layer are rubbed in directions parallel to each other.
In claim 1,
A first electrode and a second electrode disposed on the first insulating substrate, and
And a third electrode disposed on the second insulating substrate.
The method of claim 9,
The first electrode and the second electrode is insulated from each other,
And a horizontal electric field applied to the liquid crystal layer.
11. The method of claim 10,
At least one of the first electrode and the second electrode and the third electrode apply a vertical electric field to the liquid crystal layer.
12. The method of claim 11,
A first alignment layer disposed on the first substrate, and
Further comprising a second alignment layer disposed on the second substrate,
And the first alignment layer and the second alignment layer are rubbed in directions parallel to each other.
The method of claim 9,
At least one of the first electrode and the second electrode and the third electrode apply a vertical electric field to the liquid crystal layer.
In claim 13,
A first alignment layer disposed on the first substrate, and
Further comprising a second alignment layer disposed on the second substrate,
And the first alignment layer and the second alignment layer are rubbed in directions parallel to each other.
In claim 1,
A first alignment layer disposed on the first substrate, and
Further comprising a second alignment layer disposed on the second substrate,
And the first alignment layer and the second alignment layer are rubbed in directions parallel to each other.
Injecting a liquid crystal layer comprising a plurality of liquid crystal molecules and a photopolymerizable monomer between a first insulating substrate and a second insulating substrate facing each other,
Arranging the liquid crystal molecules in a first state by applying a first vertical electric field to the liquid crystal layer;
Arranging the liquid crystal molecules in a second state by applying a second vertical electric field greater than the first vertical electric field to the liquid crystal layer;
Removing the second vertical electric field in a state in which the liquid crystal molecules are arranged in the second state, and
And polymerizing the photopolymerizable monomer by irradiating light to the liquid crystal layer in a state in which the second vertical electric field is removed.
17. The method of claim 16,
The liquid crystal layer further comprises a chiral dopant.
The method of claim 17,
The photopolymerizable monomer includes a reactive mesogen monomer.
The method of claim 18,
And wherein the first state is a high bend state and the second state is a twisted state.
17. The method of claim 16,
The photopolymerizable monomer includes a reactive mesogen monomer.
20. The method of claim 20,
And wherein the first state is a high bend state and the second state is a twisted state.
17. The method of claim 16,
And wherein the first state is a high bend state and the second state is a twisted state.

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