KR100503898B1 - A method for (anti)fabricating ferroelectric liquid crystal display device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal display device including ferroelectric liquid crystal, wherein the rubbing treatment of the surface of the alignment film by applying an alignment film to the upper substrate and the lower substrate and rubbing the rubbing cloth with the rubbing cloth comprises: By setting the width of the rubbing mark to be 11 mm to 18 mm, a ferroelectric liquid crystal display device having good alignment can be produced.

Description

A method for (anti) fabricating ferroelectric liquid crystal display device}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device including an (semi) ferroelectric ferroelectric liquid crystal (FLC).

In general, liquid crystal displays have low power consumption, light weight characteristics, and are widely used as display devices such as word processors, personal computers, and navigation systems.

The liquid crystal display device includes an upper substrate on which transparent electrodes are formed, a lower substrate on which switching elements and pixels are formed, and a liquid crystal filled between the upper substrate and the lower substrate. There are many kinds of liquid crystals, and among them, a kind used for manufacturing a liquid crystal display device is a twisted nematic liquid crystal (TN), a super twisted nematic liquid crystal (STN) and a collet. And cholesteric liquid crystals.

However, the liquid crystal display device using the STN liquid crystal is insufficient in response speed and has a very narrow viewing angle. In order to solve such a problem, improvement for viewing angle expansion using a retardation film or the like has been studied, but it is not yet possible to obtain a sufficient viewing angle. In addition, the liquid crystal display device using the TN liquid crystal can be almost satisfied with respect to the response speed, but it is still insufficient in manufacturing a large liquid crystal display device such as SVGA or XGA or more.

  In order to solve the problems of the liquid crystal display, recently ferroelectric liquid crystal (FLC), anti-ferroelectric liquid crystal (AFLC), twisted helical anti-ferroelectric liquid crystal (DHF) ) Is attracting attention.

Such ferroelectric liquid crystals are also called chiral smetic C liquid crystals, and the reaction rate of the liquid crystal molecules is very fast at 1 m / sec or less. In general, each layer of chiral smetic C liquid crystals (smetic C ^* ) consists of molecules that are arranged at an angle to the layer. When the dipole moments are aligned in one direction by applying an electric field to the Schematic C liquid crystal, the orientation of molecules is also uniform and remains even after the electric field is removed.

In addition, when the electric field is applied in the opposite direction, it can be reversed at a high speed while being oriented in the other direction. This means that the molecular orientation of the ferroelectric liquid crystal is different depending on the polarity of the electric field, and shows fast response characteristics.

1 is a cross-sectional view showing a cross section of a general liquid crystal display device.

As illustrated, a general liquid crystal display device 11 includes a color filter 7 including a black matrix 6, an upper substrate 5 having a common electrode 18 formed on the color filter 7, and The lower substrate 21 is spaced apart from the upper substrate by a predetermined distance.

The lower substrate 21 is an array substrate and includes a pixel region and a pixel electrode formed on the pixel region and a switching element.

Finally, an alignment layer 23 is formed on surfaces of the upper substrate 5 and the lower substrate 21 that face each other.

The upper substrate 5 and the lower substrate 21 are bonded to each other with an adhesive 35, and the polarizing plates 25 and 27 are attached to respective surfaces of the upper and lower portions of the bonded liquid crystal panel. Complete (11).

The liquid crystal display 11 is an apparatus in which an image is expressed by transmitting or absorbing light of the backlight 31 or adjusting the amount of light by the arrangement characteristic of the liquid crystal having the optical anisotropy.

The arrangement characteristic of the liquid crystal molecules 33 has a great influence on the optical characteristics of the liquid crystal display 11. Therefore, controlling the alignment characteristics of the liquid crystal is a very important problem. In particular, the alignment layer 23 has the greatest influence on the molecular arrangement of the liquid crystal.

In general, in the above-described configuration, the alignment layer 23 is subjected to rubbing to give a groove to the surface, and this rubbing process refers to rubbing the surface of the alignment layer in a predetermined direction by using a rubbing cloth wrapped around a roller.

When rubbing the surface of the alignment layer 23, the surface of the alignment layer is shaped to have fine grooves.

At this time, the liquid crystal molecules are aligned according to the alignment angle. The rubbing cloth uses a fabric of soft fiber, and the rubbing equipment including the roller is relatively simple. The most basic in setting the rubbing process conditions is to set the rubbing conditions of the appropriate strength and to make the rubbing strength uniform over a large area.

If the rubbing is not uniform, the alignment of the liquid crystal molecules is not spatially constant, resulting in a defect that shows locally different optical properties.

The alignment layer 23 is formed on opposite surfaces of the upper substrate and the lower substrate, respectively, and the initial alignment state of the liquid crystal molecules may be fixed by the alignment layer.

In detail, the alignment layer 23 is in direct contact with the upper substrate 5 and the lower substrate 21. The reason for forming the alignment layer is that the liquid crystal material is homogeneous by simply sandwiching between the substrates. This is because it is difficult to obtain the arrangement state.

The physical properties of the liquid crystal 33 change depending on the molecular arrangement state, and a difference also occurs in response to an external force such as an electric field. The arrangement control of the liquid crystal molecules 33 is an essential technique not only for the study of liquid crystal properties but also for the configuration of the liquid crystal display device. The relative positional relationship between the elongated liquid crystal molecules and the substrate can be expressed by the angle rising from the surface of the substrate and the orientation of the projection on the surface of the substrate, and the alignment control force received by the liquid crystal molecules 33 on the surface of the alignment layer 23 is described. The degree of force is closely related to the stability of the orientation.

The material of the alignment layer 23 may be classified into an inorganic alignment layer, an organic alignment layer, and the like.

For example, the inorganic alignment film is formed by SiO tetradeposition. In the SiO evaporation deposition method, inorganic materials such as metals, oxides, and fluorides are deposited inclined with respect to a substrate, and SiO is generally used as a deposition material. If the deposition conditions such as deposition angle, deposition rate, vacuum degree, substrate temperature, film thickness, and the deposition material and liquid crystal material are different, the orientation of the liquid crystal molecules also changes. In order to achieve an equilibrium orientation, the surface of the substrate is mechanically rubbed in one direction using diamond paste or the like. The film's orientation mechanism is thought to be due to a fine groove in the rubbing direction and the pretilt angle is almost 0 degrees.

The formation process of the alignment film as described above will be described with reference to Figs. 2A to 2G.

2A through 2D are cross-sectional views illustrating a process of forming a general alignment layer. (At this time, the formation process of the alignment film which has the orientation in a different direction is demonstrated for example.)

First, as shown in FIG. 2A, an alignment film 53 such as the polyimide described above is coated on the substrate 51.

Next, as shown in FIG. 2B, the surface of the alignment film 53 is rubbed using a predetermined means such as a rubbing cloth so that the surface of the alignment film 53 has a curved shape with fine grooves.

Next, as shown in FIG. 2C, a photoresist 55 is coated on the rubbed alignment layer 53.

Next, as shown in FIG. 2D, after exposing the photoresist 55, part of the photoresist 55 is removed with a developer to expose the partial alignment layer.

Next, as shown in FIG. 2E, the surface of the exposed alignment layer 53a is rubbed again to have microgrooves in the opposite direction to the previous step.

Next, as shown in FIG. 2F, the alignment layer in which the photoresist 55 pattern remains is exposed. Through this process, alignment layers 53a and 53b having different microgrooves are formed.

The alignment film formed through the process as described above is an important factor in the initial arrangement of the ferroelectric liquid crystal, the ferroelectric liquid crystal is significantly affected by the surface state of the rubbed alignment film compared with other liquid crystals.

This will be described with reference to FIG. 3.

3 is a cross-sectional view of the roller 63 and the alignment film 65 on which the rubbing cloth 61 for rubbing the alignment film is wound.

As shown, the roller 63 wound around the rubbing cloth 61 having a predetermined thickness l is rolled in contact with the surface of the alignment layer 65, thereby forming the weft and warp yarns of the rubbing cloth 61. The surface of the alignment layer 65 is bent so as to have a fine groove by the surface form formed by alternation.

The fine shape of the surface of the alignment film 65 is deformed by the contact width L of the alignment film 65 and the rubbing cloth 61, and the contact width is generally referred to as a mark width.

At this time, when the radius of the roller is d, and the thickness of the rubbing cloth wound around the roller is l, the mark width can be obtained by the formula L = 2 (d + l) sinΘ.

At this time, the value of Θ is the midpoint of the oblique line 65 and the roller 63 drawn in the middle of the portion (b) (c) in contact with the rubbing cloth 61 and the alignment layer 65 at the midpoint of the roller 63. Is the angle formed by the diagonal lines 67 and 69 drawn to the right (c) or left (b) where the rubbing cloth 61 and the alignment layer 65 abut.

In this case, the torsional nematic liquid crystal generally used in the liquid crystal display device is not significantly affected by the mark width, but the ferroelectric liquid crystal is greatly affected by the mark width, and the alignment layer affects the initial alignment state of the liquid crystal molecules. Crazy

4 is an enlarged cross-sectional view of A of FIG. 1.

As described above, the liquid crystal 73 is filled in the upper substrate (not shown) and the lower substrate 71 subjected to the rubbing treatment on the alignment layer 72 using the rubbing cloth.

After coating the alignment film 72 to an appropriate thickness, a ferroelectric liquid crystal 73 having parallel alignment property is positioned on the surface of the alignment film 72 surface-treated to have a low inclination angle.

At this time, since the surface of the alignment layer 72 is rubbed without considering the mark width, an irregular surface state is caused, and at this time, anchoring energy generated between the alignment layer 72 and the liquid crystal 73 is obtained. Due to the lowering of, the orientation of the ferroelectric liquid crystal layer 72 grows without regularity.

As a result, there is a disadvantage in that a liquid crystal display device having unstable optical characteristics is manufactured.

Even commercially available ferroelectric liquid crystal materials, which exhibit much improved orientation, have poor initial alignment and exhibit many problems, such as a decrease in contrast.

In order to solve these problems, the orientation stability of the alignment layer, the dependence of the thickness of the alignment layer, the consideration of the rubbing direction of the upper and lower substrates, the orientation of the surface state of the substrate, etc. Various research and development has been carried out, such as the consideration of processes such as the approval of external fields such as intestines.

Despite these efforts, there is still a problem in the orientation of the Smatic C liquid crystal, which is one of the reasons that has made it difficult to emerge a high-quality (semi) ferroelectric.

Accordingly, in order to solve such a problem, the liquid crystal display device according to the present invention has an object of manufacturing a wide viewing angle liquid crystal display device having stable optical characteristics.

Method for manufacturing a ferroelectric liquid crystal display device according to the present invention for achieving the above object comprises the steps of preparing a first, a second substrate; Forming an alignment layer on the first and second substrates; Using a rubbing cloth wound around rollers of the alignment film surfaces of the first and second substrates, treating the surface of the alignment film such that the mark width between the rubbing cloth and the alignment film is 11-18; Bonding the first substrate and the second substrate on which the alignment layer is formed; Injecting liquid crystal between the two bonded substrates.

The mark width is characterized in that it is adjusted by the height of the rubbing cloth.

The height of the rubbing width is adjusted by the formula L = 2 (d + l) sinΘ. (Where d is the radius of the roller, l is the height of the rubbing cloth, Θ: the right or left of the right or left side where the oblique line continues from the center of the roller to the intermediate point where the rubbing cloth meets the alignment film and the middle of the roller. Angle formed by the diagonal lines leading to the point of contact)

The liquid crystal is characterized in that the ferroelectric liquid crystal.

The liquid crystal is characterized in that the semi-ferroelectric liquid crystal.

The ferroelectric liquid crystal is characterized in that the smear phase.

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

5 is a cross-sectional view showing the configuration of an alignment film and liquid crystal molecules treated according to the present invention in which A of FIG. 1 is enlarged.

After the alignment film is coated to an appropriate thickness, the rubbing treatment is performed such that the mark width L, which is a width in which the rubbing cloth and the alignment layer 112 abut in the configuration of FIG. 3, is rubbed when the upper and lower substrates are rubbed.

At this time, the desired mark width L can be obtained by changing the value of l, which is the height of the rubbing width, which can have a variable value in the above-described equation of L = 2 (d + l) sinΘ.

Then, as shown in the drawing, regularity occurs in the growth direction of the smectic layer which is the ferroelectric liquid crystal 113 due to the smoothness of the surface state and the provision of the optimum surface regulating force, thereby showing a good orientation direction.

Accordingly, it was concluded that the horizontal orientation of various smectic liquid crystals, which are ferroelectric liquid crystals 113, had the best characteristics when the mark width was 11 mm-18 mm.

Therefore, when rubbing the surface of the alignment film for alignment of the smectic liquid crystal, which is a ferroelectric liquid crystal, the alignment film having a stable surface state can be obtained by setting the width between the alignment film and the rubbing cloth to be 11 mm-18 mm. Since the anchoring energy of the liver can be increased, there is an effect that can stabilize the alignment characteristics of the liquid crystal.

1 is a cross-sectional view of a general liquid crystal display device.

2A through 2G are cross-sectional views sequentially illustrating a process of forming an alignment layer on upper and lower substrates of a liquid crystal display device;

3 is a cross-sectional view showing the configuration of a roller wound with an alignment film and a rubbing cloth,

4 is a cross-sectional view showing a state of a conventional surface-treated alignment film and liquid crystal molecules,

5 is a cross-sectional view showing a state of the alignment film and the liquid crystal molecules surface-treated according to the present invention.

<Description of the symbols for the main parts of the drawings>

112: alignment film 113: liquid crystal

L: Mark width

Claims (2)

Preparing a first and a second substrate; Forming an alignment layer on the first and second substrates; Using a rubbing cloth wound around rollers of the alignment film surfaces of the first and second substrates, treating the surface of the alignment film so that the mark width between the rubbing cloth and the alignment film is 11 mm-18 mm; Bonding the first substrate and the second substrate on which the alignment layer is formed; Injecting liquid crystal between the two bonded substrates Liquid crystal display device manufacturing method comprising a. The method of claim 1, And the mark width is controlled by the height of the rubbing cloth.