KR20020036311A - Fabrication of Quarter-wave Films Using a Liquid Crystal and Application to the CLC Polarizer - Google Patents

Abstract

PURPOSE: A method of fabricating a birefringence film using nematic liquid crystal and a cholesteric liquid crystal polarizer formed using the fabricating method are provided to mass-product films having desired degree of retardation through sequential processes. CONSTITUTION: A birefringence film is fabricated in such a manner that nematic liquid crystal(20) is coated in a desired thickness using a film on which an alignment film is coated. The nematic liquid crystal is aligned and the aligned state is fixed by irradiating ultra-violet rays on the coated nematic liquid crystal. The alignment film is coated on a polymer film such as PET or TAC in order to align the nematic liquid crystal.

Description

Fabrication method of birefringent film using nematic liquid crystal and cholesteric liquid crystal polarizing film using the same {Fabrication of Quarter-wave Films Using a Liquid Crystal and Application to the CLC Polarizer}

The present invention relates to a method for producing a birefringent film using a nematic liquid crystal and a cholesteric liquid crystal polarizing film using the same, in particular using a PET film coated with an alignment film, the curable nematic liquid crystal is coated and oriented to a desired thickness and then UV light By fixing the reparation state by irradiation, it is possible to manufacture a variety of films from the horizontal orientation to the vertical orientation, and apply it to the cholesteric liquid crystal polarizing film to correct the sudden decrease in brightness and color change according to the angle It relates to a birefringent film production method using a nematic liquid crystal and a cholesteric liquid crystal polarizing film using the same.

In general, birefringent retardation films have been used to compensate for viewing angles in liquid crystal displays (LCDs) and in particular for the color of LCDs driven in STN mode.

Many conventional birefringent films can be stretched uniaxially or biaxially to achieve the desired birefringence, as in the US5136635 patent.

In addition, the US5743980 patent discloses polymer materials such as polycarbonate (PC), polyvinyl alcohol (PVA), polystyrene, and polymethyl methacrylate dissolved in alkyl (Alkyle), followed by spin coating on a glass plate, and heating to arrange molecules. Drying made a retar dation film.

However, this method is not only difficult to obtain the desired retardation value, but also difficult to mass production by a continuous process. In addition, there is a problem in that it is impossible to manufacture a retaration film having a larger refractive index in the thickness direction of the film due to the properties of the material.

On the other hand, in the US5853801 patent, a discotic liquid crystal dissolved in an organic solvent is continuously coated on a transparent plastic film coated with an alignment layer, and then the solvent is dried, whereby the discotic liquid crystal is aligned and fixed in a predetermined direction of the alignment layer to form a retardation film. .

However, when the discotic liquid crystal is coated on the alignment film coated PET film in a continuous process as in the US5853801 patent, there is a problem in that it is impossible to produce a film having positive retardation due to the characteristics of the discotic liquid crystal.

The present invention is to solve the above problems,

Using a photo-alignment material that can be coated on a plastic substrate, a thin film is coated on the surface of the PET film, and the alignment angle of the alignment film is adjusted by UV light irradiation, whereby nematic liquid crystals are arranged in the same direction as the alignment film and the coating thickness is adjusted. It is an object of the present invention to provide a method for mass production of a film having a retardation of a size in a continuous process.

In addition, since the nematic liquid crystal is used as the retardation film material in applying the present invention, the refractive index distribution of the film according to the orientation angle is easily provided.

In other words, when the nematic liquid crystal is applied to the present invention, if all the nematic liquid crystals are aligned in the same direction, the refractive index becomes the same as the refractive index of the liquid crystal molecules. Therefore, only the angle of the alignment layer and the thickness of the film are designed to have the necessary retardation. You will be able to make a film.

In addition, compared to conventional retardation film using a plastic film provides the advantage of producing a thinner film with the same retardation.

1 is a film Nz value change in accordance with the alignment angle of the liquid crystal.

Figure 2a is a structure of the nematic liquid crystal film oriented horizontally in the drawing direction on the PET film.

Figure 2b is a structure of the nematic liquid crystal film vertically oriented on the PET film coated with a vertical alignment layer.

2C is a tilted oriented nematic liquid crystal film structure diagram.

Figure 3a is an illustration of applying a QWP made of nematic liquid crystal to the actual CLC poloiser.

Figure 3b is an illustration of applying a QWP and compensation film made of nematic liquid crystal to the actual CLC poloiser.

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

10: PET film 20: nematic liquid crystal

30: CLC film 40: LC QWF

50: linear poloizer

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to a method of continuously producing a desired retardation film by coating and orienting nematic liquid crystals on an alignment film coated PET film, and a technique of using the prepared retardation film as a λ / 4 film when manufacturing a CLC polarizer.

For reference, a nematic liquid crystal applied to the present invention will be described.

In general, nematic liquid crystal molecules are rod-shaped and are birefringent materials having a positive refractive index in the rod direction than the refractive index in the cylindrical direction.

The nematic liquid crystal molecules have different refractive index distributions of the entire system depending on how the liquid crystal molecules are arranged, and various applications are possible.

For example, if the bar directions of liquid crystal molecules are all aligned in the same direction and parallel to the plane, a retardation film having nx> ny = nz can be made. If the bar directions of the liquid crystal molecules are randomly arranged in parallel to the plane, nx = ny> nz A retardation film can be made.

And when the bar direction of the liquid crystal character is arranged perpendicular to the plane it is possible to produce a vertical alignment phase difference film of nx = ny <nz.

In addition, when the bar directions of the liquid crystal molecules are all aligned in the same direction but are not aligned horizontally or vertically to the plane, the liquid crystal molecules may be inclined and oriented to form a retardation film having nx> ny> nz or nz> nx> ny.

The correlation of the refractive index of the film which changes according to the orientation degree of a liquid crystal can be seen by Nz value. Where Nz is expressed as follows, where Nz = (nx-nz) / (nx-ny), where nx and ny are the refractive index values measured in the direction parallel to the film surface, respectively, nz is a refractive index value measured in a direction perpendicular to the film surface.

1 illustrates a change in Nz value according to the alignment angle of the liquid crystal character. In particular, as the orientation angle exceeds 45 °, the Nz value has a negative value, which is a technique that is difficult to be produced by the film stretching method that is generally used.

In the present invention, the alignment angle of the alignment layer can be easily adjusted using a photo-alignment material, and nematic liquid crystals coated on the alignment layer are also arranged in the same direction by the alignment layer, so that the Nz value becomes easily negative. It can manufacture.

2A, 2B and 2C schematically show the nematic liquid crystals 20 arranged on the PET film 10 according to the present invention, and FIG. 2A shows the PET film 1 without the alignment film coated thereon). The nematic liquid crystal 20 is arranged above in the drawing direction of the film, and the Nz value of the film is 1.

2b shows that the nematic liquid crystals 20 are vertically arranged on the film surface on the PET film 10 coated with the vertical alignment layer, and the film 10 can be used to compensate for retardation according to the viewing angle of the CLC film. have.

FIG. 2C is an advantage of coating the vertical alignment layer and inclining the alignment angle by irradiating polarized UV light, thereby allowing the Nz value to be varied in accordance with the alignment angle to the film 10 having nematic liquid crystals arranged thereon. have.

3 is an example of actually applying the film produced through the present invention to the CLC Polarizer, Figure 3a is a horizontal wave-oriented film of about 1㎛ thickness as shown in Figure 2a as a QWP (quarter wave plate).

The liquid crystal (LC) QWP 40 is attached to the short wavelength side of the CLC film 30, and a linear polarizer 50 is attached thereto. At this time, the drawing direction of LC QWP and the transmission axis of the linear polarizer should be at an angle of 135 °.

When the CLC Polarizer is manufactured with the structure as shown in FIG. 3A, the luminance rapidly decreases and the color changes in the square due to retardation according to the viewing angle of the CLC film.

FIG. 3B is a structure for solving the problem according to the viewing angle, and a vertically oriented film may be inserted between the CLC film and the LC QWP as shown in FIG. 2B to correct a sudden decrease in luminance and color change according to the angle.

That is, by restoring the retrdation value of the negative retardation according to the angle of the CLC film to the vertically oriented positive retardation film, there is no change in the retardation value according to the angle.

The production of LC QWP and vertical alignment compensation film described above was carried out through mass production process using PET film roll as base film and roll coater.

First, the PET film is mounted on the coater's unwinder, and the film is connected to the rewinder by passing through the dryer and the UV irradiator.

Set the dryer's temperature and wind speed according to the conditions, and pour the prepared nematic liquid crystal solution into the pan to lock the coating roll. Operate the coater and adhere the PET film to the coating roll to transfer the solution to the PET film.

The PET film is continuously buried as it passes the coating roll, the solvent is dried as it passes through the dryer, and the liquid crystals are polymerized as they pass through the UV irradiator and are fixed on the PET film in the form of a film.

And when using a liquid crystal film actually, what is necessary is just to coat an adhesive agent and an adhesive on the liquid-crystal film surface, and to laminate with another film, and to remove the PET film used as a base material.

Example 1

A clean PET film prepared by uniaxial stretching and no treatment was prepared, and a nematic liquid crystal material was applied thereon by a roll coating method. At this time, a curable nematic liquid crystal material (BASF) was used as the nematic liquid crystal material.

First, a solution was prepared by dissolving a curable nematic liquid crystal material and a photoinitiator (LG184, Ciba.Geigy) in MEK. The solution concentration was 20 wt% and the photoinitiator dose was 5 wt%.

The thin film is applied onto the PET film by the roll coating method, and the solvent is dried and removed by passing through a dryer to horizontally align the nematic liquid crystal material, and then the polymerization is progressed by UV light to fix the horizontal orientation. A film was prepared.

At this time, the coating speed was 7 m / min, the drying conditions were 80 ℃, UV light irradiation was used 300W (center wavelength 360nm) lamp.

The thickness of the horizontally aligned nematic liquid crystal film prepared as shown in FIG. 2a was 1 μm, and it was confirmed that the liquid crystals were horizontally aligned by using a refractive index measurement and a polarimeter.

The measured refractive index obtained the result of Ny = Nz = 1.535 which is the same value in the extending direction of PET film in Nx = 1.660, the perpendicular direction of extending | stretching, and the vertical direction of a film plane.

This result was in good agreement with the retardation value of the film measured from the polarimeter, R = 125 nm, and can serve as a λ / 4 retardation plate of 500 nm in the visible region. The prepared λ / 4 film is positioned between the CLC film and the linear polarizer instead of the polycarbonate (PC) material λ / 4 film used in the manufacture of the cholesteric liquid crystal polarizer (CLC Polarizer). Confirmed.

Example 2

The solution was prepared to have a concentration of 2wt% in the MEK to the optical alignment material, coated by a roll coating method on a clean PET film made by uniaxial stretching and not treated, dried and solvent-coated and then squared through UV light irradiation. I got orientation.

At this time, the drying condition was 75 ℃ and UV light irradiation used a 300W Lamp with a central wavelength of 360nm.

A solution having a concentration of 35wt% was prepared by dissolving a curable nematic liquid crystal and photoinitiator (IG184, Ciba-Geigy) in 3-pentanone, wherein the photoinitiator content was 5w%.

The thin film is coated on the PET film coated with the alignment layer by a roll coating method, and the solvent is dried and removed by passing through a dryer to vertically align the nematic liquid crystal material, and then proceed with polymerization by UV light irradiation. To fix the vertical alignment state to prepare a film.

At this time, the coating speed was 7m / min, the drying conditions were 80 ℃, UV light irradiation used a 300W Lamp with a central wavelength of 360nm.

The thickness of the vertically aligned nematic liquid crystal film prepared as shown in FIG. 2b was 5 μm, and it was confirmed that the film was vertically aligned by using a refractive index measurement and a crossed polariler.

The measured refractive index of the vertically oriented film was uniform as Nx = Ny = 1.535 in the surface direction of the film, and the largest value was Nz = 1.668 in the vertical direction of the film.

The vertically oriented film thus prepared can be used to compensate for negative birefringence of the CLC film in the CLC Polarizer.

Example 3

The solution was prepared to have a concentration of 2wt% in the MEK to the optical alignment material, coated by a roll coating method on a clean PET film made by uniaxial stretching and not treated, dried and solvent-coated and then squared by UV light irradiation. I got orientation.

At this time, the drying condition was 75 ℃ and UV light irradiation used a 300W Lamp with a central wavelength of 360nm.

A solution having a concentration of 35wt% was prepared by dissolving a curable nematic liquid crystal and photoinitiator (IG184, Ciba-Geigy) in 3-pentanone, wherein the photoinitiator content was 5w%.

The thin film is coated on the PET film coated with the alignment film by the roll coating method, and the solvent is dried and removed by passing through a dryer. The nematic liquid crystal material is oblique aligned and then subjected to UV light irradiation. The polymerization was carried out to fix the alignment state to prepare a film.

At this time, the coating speed was 6m / min, the drying condition was 80 ℃, UV light irradiation used a 300W Lamp with a central wavelength of 360nm.

The thickness of the rectangular alignment nematic liquid crystal film prepared as shown in Figure 2c was 4㎛, it was possible to obtain the orientation angle of the film by using the refractive index measurement and the Crossed Polariler. The measured refractive index in addition to the rectangular alignment film was Nx = 1.549 in the surface direction of the film, Ny = 1.535 and Nz = 1.650 in the vertical direction of the film.

From this value, it can be seen that the orientation of the nematic liquid crystal of the film produced is tilted about 20 degrees from vertical. In addition, the retardation value of the film calculated from the refractive index and the thickness was R = 56 nm, which was not enough to be used as the λ / 4 film in the visible region and could not be confirmed by the polarimeter.

The rectangular alignment film thus prepared may be used to compensate for negative birefringence (negatlwebirefringence) of the CLC film in the CLC Polarizer, or may be used as a compensation film having a λ / 4 film role by adjusting the coating thickness.

When the present invention is used as described above, the curable nematic liquid crystal is coated to a desired thickness by using a PET film coated with an alignment layer, and then aligned, and then the compensation state is fixed by UV light irradiation. There is an effect that can produce a variety of films.

Claims (10)

A method of manufacturing a birefringent film, comprising coating a curable nematic liquid crystal to a desired thickness using a film coated with an alignment film and incubating the same, and then fixing the alignment state by UV light irradiation. The method of claim 1, A birefringent film production method characterized by coating an alignment film on a polymer film such as PET or TAC in order to orient the nematic liquid crystal. The method of claim 1, In order to orient a nematic liquid crystal, the birefringent film manufacturing method characterized by extending | stretching the polymer film, such as PET and TAC, in one direction with large draw ratio. The method of claim 1, A birefringent film production method using a nematic liquid crystal having a birefringence (Δn = n _e -n _o ) of 0.01 to 0.2. The method of claim 1, A method for producing a birefringent film, characterized in that the Nz = (n _x -n _z ) / (n _x -n _y ) value of the film is made less than or equal to 1 by adjusting the tilt of the alignment layer. In this case, n _x is a refractive index value on the film surface in the direction in which the nematic liquid crystal is aligned, n _y is a refractive index value in the direction perpendicular to n _{x on the} film surface, and n _z is a refractive index value in the direction perpendicular to the film surface. The method of claim 1, A method for producing a birefringent film, characterized in that it is used as a λ / 4 (quarter wave) film of a CLC polarizing film by adjusting the thickness of a birefringent film. The method of claim 6, A method for producing a birefringent film, wherein the retardation of the λ / 4 film is 100 to 200 nm. The method according to claim 1 or 5, A method for producing a birefringent film, characterized in that the nematic liquid crystal is vertically oriented so as to be inclined at 90 ° to be used as a compensation film of a CLC polarizing film. The method according to claim 1 or 5, A method of producing a birefringent film, characterized by producing an inclination of the alignment film at 90 ° to 45 ° so that the Nz value of the nematic liquid crystal becomes a negative value and the film satisfies the λ / 4 film and the compensation film of the CLC polarizing film at the same time. A cholesteric liquid crystal polarizing film, which is prepared by inserting a birefringent film produced by the method of claim 1.