KR101251574B1 - Optical retardation film and Method of preparing the same - Google Patents

Abstract

The present invention relates to an optical compensation film and a method of manufacturing the same. The optical compensation film of the present invention comprises a first substrate and a second substrate each having a plasma-treated one surface; And a vertically oriented liquid crystal layer in which the first substrate and the second substrate are disposed such that respective plasma-treated surfaces face each other, and interposed between the substrates. Since the optical compensation film of the present invention does not require an alignment film or an orientation inducing agent, the optical compensation film may have a thinner form.

Description

Optical retardation film and method of preparing the same

The present invention relates to an optical compensation film and a method of manufacturing the same. More specifically, the present invention relates to a thin optical compensation film and a method for manufacturing the same, which can be economically manufactured in a simple process.

Liquid crystal displays (LCDs), which lead the information display device in the information age, are applied to portable devices such as notebook computers because they are thinner and lighter than conventional cathode ray tubes. .

However, notebook computers, which began to introduce LCDs in earnest, were personal devices, so they only needed to be seen from the front, so the viewing angle was not a big concern.

However, when LCDs are introduced into monitors and TVs, they have become larger, and as a result, many people simultaneously view the LCDs from various angles, and thus the expansion of the viewing angle has emerged as a core technology.

At present, it is well known that various retardation films are used to enlarge the viewing angle in the LCD. The retardation film is an element having optical anisotropy, and so far, the method of applying the retardation film to the LCD has generally used an external type in which the retardation film is bonded together with the polarizing film on the outside of the two glass substrates constituting the liquid crystal cell.

In recent years, in-cell retardation film is attracting attention instead of an external retardation film. An in-cell retardation film means the retardation film provided in the board | substrate of a cell, and is a system in which the retardation film was introduce | transduced into the liquid crystal cell. It is called 'in-cell' retardation film because it is installed inside the cell.

The in-cell retardation film must be able to be applied on a rigid substrate first in that it intends to impart the function of the retardation film to the substrate. Of course, since the phase difference must be expressed, it is necessary to have optical anisotropy in the film-formed state. There are several materials that satisfy these requirements. Generally, photopolymerizable liquid crystals are widely used.

A photopolymerizable liquid crystal is a compound that adds a photoreactor such as an acryl group to a mesogen and reacts like a normal liquid crystal in a monomer state, but polymerizes when UV is irradiated to fix the alignment state. An optical film having various optical anisotropy can be produced according to the alignment state of the liquid crystal, such as (planar alignment), tilt alignment (inclined alignment), homeotropic alignment (vertical alignment) or twisted alignment (disordered alignment).

A liquid crystal film with vertical alignment (homeotropic alignment) are divided into positive C plate because of the direction of the optical axis larger than the refractive index in the optical axis perpendicular to the direction of the refractive index n _z in the direction of an optical axis in a direction. Combining these positive C plates with other optical films can be used as a viewing angle compensation film in a horizontally oriented liquid crystal mode (ie, in plane switching) mode.

A remarkable advantage of the in-cell retardation film using the photopolymerizable liquid crystal is that the panel can be thinned and the patterning is effective. Like a normal liquid crystal material, a photopolymerizable liquid crystal has a high birefringence of about 0.2 at most, and realizes a thin film thickness compared with an external retardation film. In the in-cell retardation film, a film having a maximum of several hundreds of micrometers was required as the film.

The method which has been used to induce homeotropic alignment of the liquid crystal until now is to lower the surface energy of the substrate, in which case the energy of the system is minimized by having liquid crystal molecules in contact with each other rather than the surface. It is known that vertical orientation is produced due to this.

However, there is a limit to the type of substrate with low surface energy and moreover, it is not suitable for use in LCD panels. Coating the liquid crystal solution after coating the alignment film or the orientation inducing agent on the substrate to manufacture the film is a problem that the process of undesirable high temperature and additional steps such as coating, drying, heating and curing processes must be introduced. There is this.

Therefore, the problem to be solved by the present invention is to provide an optical compensation film of a thin film to be used as an in-cell retardation film.

In addition, it is to provide a manufacturing method capable of manufacturing an optical compensation film of a thin film by a simple method without the need of forming an alignment film or adding an orientation inducing agent.

In order to solve the above problems, the optical compensation film of the present invention, the first substrate and the second substrate each having a plasma-treated one surface; And a vertically aligned cured liquid crystal layer in which the first substrate and the second substrate are disposed such that respective plasma-treated surfaces face each other and interposed between the substrates.

In the optical compensation film of the present invention, the liquid crystal used in the liquid crystal layer is preferably dielectric anisotropy (negative).

In the optical compensation film of the present invention, the liquid crystal layer may have a thickness of 10 nm to 1 μm, but is not limited thereto.

In the optical compensation film of the present invention, the substrate may be a glass substrate or a polymer substrate, but is not limited thereto.

In addition, an embodiment of a method of manufacturing an optical compensation film of the present invention for solving the above problems, (a1) preparing a first substrate and a second substrate having a plasma-treated one surface; (a2) interposing spacers between the two substrates, wherein the plasma-treated surfaces of the substrates face each other; And (a3) injecting a photocurable liquid crystal between the two substrates and maintaining a liquid crystal temperature to induce vertical alignment of the liquid crystal; And (a4) irradiating ultraviolet light to cure the photocurable liquid crystal.

In addition, another embodiment of the manufacturing method of the optical compensation film of the present invention for solving the above problems, (a1) preparing a first substrate and a second substrate having a plasma-treated one surface; (a2) forming a photocurable liquid crystal layer by applying a photocurable liquid crystal to the plasma-treated surface of the first substrate; (a3) covering the second substrate on the photocurable liquid crystal layer such that its plasma-treated surface is in contact with the photocurable liquid crystal layer and maintaining a liquid crystal temperature to induce vertical alignment of the liquid crystal; And (a4) irradiating ultraviolet light to cure the photocurable liquid crystal.

The optical compensation film of the present invention can be produced very economically by simply and easily inducing vertical alignment of the liquid crystal using a plasma treated substrate. In addition, since the liquid crystal layer itself has a compensation function, it is possible to realize a thin film structure, which is very suitable for the in-cell method.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a schematic vertical cross-sectional view of an embodiment of an optical compensation film according to the present invention.
2 is a polarized light micrograph of the horizontally aligned liquid crystal film (a) and the optical compensation film (b) prepared in Example 1 of the present invention and a conoscope (c) picture of the optical compensation film according to the present invention.
3 is a phase difference measurement graph of the optical compensation film manufactured in Example 1 of the present invention.
4 is a phase difference measurement graph of the optical compensation film prepared in Example 2 and Example 3 of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

1 schematically shows an embodiment of an optical compensation film 100 according to the present invention. However, the configuration described in the embodiments and drawings described below are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, which can be replaced at the time of the present application It should be understood that there may be various equivalents and variations.

The optical compensation film 100 of the present invention includes the plasma-treated substrates 11 and 12 and the vertically aligned cured liquid crystal layer 20 on one surface thereof.

The inventors of the present invention have found that the present invention finds that vertical alignment is induced when a liquid crystal is brought into contact with a substrate on which a surface is plasma-treated. Accordingly, the optical compensation film 100 of the present invention does not need an alignment film between the substrates 11 and 12 and the cured liquid crystal layer 20 vertically aligned, or does not require a separate additive such as an orientation inducing agent.

Specifically, when plasma treatment is performed on the substrate surface, polarizability in the substrate direction increases. Van der Waals interaction increases the interaction when the direction of high polarization is placed in parallel. In the case of liquid crystal, since the direction of the dielectric constant is large, the substrate and liquid crystal have large polarization. In order to increase the van der Waals interaction between the liquid crystal, the direction of the dielectric constant is placed parallel to the substrate.

Therefore, the orientation of the liquid crystal is changed according to the difference in the dielectric anisotropy of the liquid crystal. That is, the liquid crystal (Δε> 0) whose dielectric constant in the long axis direction of the liquid crystal is larger than the dielectric constant in the short axis direction, that is, the dielectric anisotropy is positively oriented planarly on the polar substrate, while the short axis It is determined that the liquid crystal Δε <0 whose dielectric constant in the direction is larger than the major axis direction, that is, the dielectric anisotropy is negative, is oriented perpendicular to the substrate.

Therefore, the liquid crystal used in the vertically aligned cured liquid crystal layer 20 of the optical compensation film 100 of the present invention is preferably dielectric anisotropy, and may be used without particular limitations if the dielectric anisotropy is negative.

Since the vertically aligned cured liquid crystal layer 20 according to the present invention is formed by polymerizing liquid crystal molecules, the thickness thereof may be adjusted according to the coating amount, and thus, the thin film layer may be formed as a considerably thin layer. For example, the thickness may be 10 nm to 1 μm, but is not limited thereto.

In the optical compensation film 100 of the present invention, the two substrates 11 and 12 are disposed such that the plasma treated surface contacts the liquid crystal layer 20. Through this, the liquid crystal of the liquid crystal layer 20 may be induced to be vertically aligned.

The substrates 11 and 12 used in the optical compensation film 100 of the present invention may be used without limitation as long as the substrate has a polarization degree improved on its surface by plasma treatment. For example, a glass substrate or a polymer substrate may be used, but is not limited thereto.

Optionally, the optical compensation film of the present invention may be used with both substrates combined, but may be used with one or all of the substrates removed as necessary.

Preferably, the optical compensation film according to the present invention may be a compensation film of the C plate.

Hereinafter, an embodiment of the manufacturing method of the optical compensation film 100 of the present invention will be described in detail. However, the present embodiment is merely an example and is not limited to the scope of the present invention.

First, a first substrate and a second substrate each having a plasma treated surface are prepared (a1).

The plasma treatment method may be a conventionally used plasma treatment. Cleaning the substrate surface prior to the plasma treatment is desirable to better exert the plasma treatment effect. Plasma treatment may be performed a plurality of times in order to obtain a desired degree of treatment effect.

Next, a spacer is interposed between the two substrates, and the plasma treated surfaces of the substrates are positioned to face each other (a2).

The spacer used in the present invention may be used without limitation as long as it is a spacer used in manufacturing a liquid crystal cell. The thickness of the vertically aligned cured liquid crystal layer 20 may be determined according to the size of the spacer.

The spacer is spread over the plasma treated side of one of the substrates and then the other substrate is covered thereon so that the plasma treated side contacts the spacer. As a result, the two substrates are positioned such that the plasma treated surfaces of the substrates face each other with spacers interposed therebetween.

Next, a photocurable liquid crystal is injected between the two substrates and the liquid crystal temperature is maintained to induce vertical alignment of the liquid crystal (a3).

Photocurable liquid crystals are reactive liquid crystals having polymerizable functional groups at both ends. The photocurable liquid crystal that can be used in the present invention is not limited as long as photopolymerization is possible, and it is preferable that the dielectric anisotropy is negative. Commercially available as such liquid crystals include LC242 (BASF).

The method of injecting a photocurable liquid crystal between two substrates uses a capillary phenomenon. That is, when the liquid crystal is dropped at the end portion of the substrate, the liquid crystal penetrates into the space secured by the spacer between the substrate and the substrate by the capillary phenomenon.

When adding a photocurable liquid crystal, it is preferable to add a small amount of photoinitiators together. The photoinitiator according to the present invention may adopt those conventionally used in the art for polymerizing the monomer. A person skilled in the art can select an appropriate photoinitiator depending on the photocurable liquid crystal used, and commercially available ones include, for example, hydrogen peroxide, 2-hydroxy-2-methyl-l-phenylpropane-l-one (2-hydroxy). 2-methyl-l-phenylpropan-l-one (DAROCURE 1173)), 2-dimethoxy-1,2-diphenylethan-1-one (2-dimethoxy-l, 2-diphenylethan-l-one (IRGACURE 651)), l-hydroxycyclohexyl phenyl ketone (IRGACURE 184), IRGACURE 500 (mixture of IRGACURE 184 and benzophenone), IRGACURE 127, IRGACURE 2959, IRGACURE 907, IRGACURE 369, IRGACURE 379 , IRGACURE 754, IRGACURE 1300, IRGACURE 819, IRGACURE 1700, IRGACURE 1800, IRGACURE 1850, IRGACURE 1870, DAROCURE 4265, DAROCURE MBF, DAROCURE TPO, IRGACURE 784, IRGACURE OXE01, and the like. The IRGACURE and DAROCURE are Ciba Specialty Chemicals Co. Ltd is a trade name.

The injection of the photocurable liquid crystal is preferably carried out at an isotropic temperature at which the liquid crystal maintains the liquid phase or at a liquid crystal temperature at which the liquid crystal maintains the liquid crystal phase. When the liquid crystal temperature is maintained for a predetermined time after the liquid crystal is added, the photocurable liquid crystal is in a vertical alignment by interaction with the surface of the plasma-treated substrate. Typically, the vertical orientation is complete within minutes of the dosing.

Optionally, in another embodiment of the manufacturing method of the present invention, a method of applying a liquid photopolymerizable liquid crystal to one substrate surface and then covering the other substrate thereon may be adopted. This method is preferable for the production of large area cells, without using spacers. Specifically, applying a photocurable liquid crystal to the plasma-treated surface of one substrate to form a photocurable liquid crystal layer, and the other substrate so that the plasma-treated surface is in contact with the photocurable liquid crystal layer Covering the liquid crystal layer and maintaining the liquid crystal temperature may be carried out through the step of inducing vertical alignment of the liquid crystal. In this case, a conventional coating method may be used to apply the liquid crystal to the surface of the substrate. For example, the liquid crystal may be performed using a doctor blade or a knife, but is not limited thereto.

Next, when the vertical alignment of the liquid crystal layer is completed between the two plasma-treated substrates, ultraviolet ray is irradiated to cure the photocurable liquid crystal (a4).

Optionally, lowering the temperature of the liquid crystal layer below the liquid crystal temperature before the ultraviolet irradiation is preferable to maintain the vertical alignment of the liquid crystal. For example, when using LC242 liquid crystal, it is preferable to lower to 40-60 degreeC.

When photocuring is completed, a cured optical compensation film according to the present invention can be obtained.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example 1

Two glass substrates were soaked in NaOH solution, respectively, and then ultrasonically washed at 60 ° C. for 1 hour, taken out, and then sufficiently washed with distilled water. The surface of one side of the glass substrates was then treated using an atmospheric oxygen plasma apparatus. Plasma production conditions were O ₂ , 20 sccm, Ar 5 LPM, RF power 100W. Plasma was treated 10 times

-1.8, Δn = 0.14, BASF사) 액정을 기판 한 끝에 떨어뜨린 후 모세환 현상에 의해 액정이 기판 사이의 공간으로 침투되는 것을 확인하였다.The spacer was disposed on the plasma-treated surface of one of the substrates, and then the other substrate was covered so that the plasma-treated surface was in contact with the spacer. LC242 (Δε) with 1 wt% of IG-907 added as a photocuring initiator

-1.8, Δn = 0.14, BASF Co., Ltd.) After dropping the liquid crystal at one end of the substrate, it was confirmed that the liquid crystal penetrated into the space between the substrates by the capillary phenomenon.

At this time, the temperature was maintained at 80 ° C., and left for 10 minutes in this state to induce vertical alignment of the liquid crystal.

Then, the temperature was lowered to 40 ℃ and irradiated with 5Mw UV light for 5 minutes to proceed with photocuring to prepare a compensation film.

Example 2

After the plasma treatment of the two substrates, the liquid crystal layer is formed by evenly spreading the liquid crystal using a doctor blade after dropping LC242 added 1% by weight of IG-907 on the plasma-treated surface of any one of the substrates, A compensation film was manufactured in the same manner as in Example 1, except that the other substrate was covered with a plasma-treated surface to contact the liquid crystal layer. The thickness of the liquid crystal layer applied at this time was 400 nm.

Example 3

A compensation film was manufactured in the same manner as in Example 2, except that the thickness of the coated liquid crystal layer was 100 nm.

Test Example 1: Vertical Orientation Evaluation

It was confirmed through the polarization microscope between the orthogonal polarizer that the liquid crystal layer of the compensation film prepared in Example 1 is vertically aligned, the results are shown in FIG.

Specifically, when the vertically aligned liquid crystal film according to the present invention is positioned between the orthogonal polarizers and the vertically aligned liquid crystal layer is observed in the vertical incidence direction with respect to the film plane, since the phase difference does not generate phase difference, light transmission does not occur and thus appears black. Observing while tilting, the phase difference occurs, so the light transmits and appears bright.

FIG. 2 (a) is a polarized light micrograph when LC242 is not oriented on a glass substrate which is not plasma treated, and FIG. 2 (b) is a polarized light micrograph of a compensation film prepared in Example 1. FIG.

In the case of FIG. 2 (a), since the LC242 is disorderly oriented in the horizontal direction in the glass substrate without plasma treatment, it can be confirmed that light is transmitted by the birefringence property of the liquid crystal. In the case of 2 (b), the light is transmitted vertically. It is isotropic so that light does not penetrate and can be seen as black.

However, although it is difficult to distinguish between an isotropic state and a vertical alignment by using a polarizing microscope, it is possible to easily check whether the vertical alignment is performed by a conoscope, but the conoscopy image of Example 1 is shown in FIG. It can be seen that 2 (c) is the same as a typical conoscope image that appears when the liquid crystal is vertically aligned.

Test Example 2: Phase difference evaluation

The phase difference of the compensation film prepared according to Examples 1 to 3 was measured and the results are shown in FIGS. 3 (Example 1) and 4 (Example 2, Example 3).

The phase difference in this test was measured by a RETS R & D phase difference measuring device (Otsuka Electronics, Japan) in the direction of inclination at a specific angle from the vertical incident angle. The rotational analyzer method used in this apparatus sets retransmission by setting the respective transmission spectra in parallel and orthogonal nicol states and calculating the intensity contrast between parallel and orthogonal nicols for each wavelength. It is effective to measure retardation film with small retardation value (R _e ) by obtaining wavelength dispersion equation of. R _in is calculated by the following equation (1) as the phase difference value of the planar phase.

Here, n _x is a refractive index in the direction of the largest refractive index on the plane, n _y is a value perpendicular to the n _x direction, the smallest refractive index on the plane, d is the thickness of the film.

Referring to FIGS. 3 and 4, the liquid crystal molecules of the liquid crystal film are also perpendicular to the film plane because the phase difference increases as the viewing angle increases and the values in the − and + directions of the viewing angle are symmetrical to each other. It can be seen that the film is oriented to the compensation effect of the compensation film of the present invention can be effectively implemented.

Claims (6)

delete delete delete delete In the manufacturing method of the optical compensation film in the form of an in-cell retardation film interposed between the first substrate and the second substrate,
(a1) oxygen plasma treating one surface of the first substrate and another third substrate;
(a2) interposing a spacer between the first substrate and the third substrate, and positioning the oxygen plasma treated surfaces of the substrates to face each other;
(a3) injecting a photocurable liquid crystal between the first substrate and the third substrate and maintaining a liquid crystal temperature to induce vertical alignment of the liquid crystal; And
(a4) irradiating ultraviolet light to cure the photocurable liquid crystal and to remove the third substrate,
The first substrate thus produced is used as the upper plate or the lower plate of the cell substrate, the manufacturing method of the optical compensation film. In the manufacturing method of the optical compensation film in the form of an in-cell retardation film interposed between the first substrate and the second substrate,
(a1) oxygen plasma treating one surface of the first substrate and another third substrate;
(a2) forming a photocurable liquid crystal layer by applying a photocurable liquid crystal to an oxygen plasma treated surface of one of the first substrate and the third substrate;
(a3) The liquid crystal is vertically covered by covering the photocurable liquid crystal layer on the photocurable liquid crystal layer such that an oxygen plasma-treated surface of the first substrate and the third substrate on which the photocurable liquid crystal layer is not formed is in contact with the photocurable liquid crystal layer. Inducing orientation; And
(a4) irradiating ultraviolet light to cure the photocurable liquid crystal and to remove the third substrate,
The first substrate thus produced is used as the upper plate or the lower plate of the cell substrate, the manufacturing method of the optical compensation film.

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