KR101155575B1 - A manufacturing method of optical film having planar oriented cholesteric liquid crystal layer - Google Patents

Abstract

Method for producing an optical film having a planar oriented cholesteric liquid crystal layer according to the present invention, (S1) preparing an amorphous polyethylene terephthalate film; (S2) preparing the uniaxially oriented polyethylene terephthalate film by stretching the amorphous polyethylene terephthalate film only in the uniaxial direction; And (S3) spin coating a cholesteric liquid crystal on the uniaxially oriented polyethylene terephthalate film.
According to the present invention, it is possible to induce the planar orientation of the cholesteric liquid crystal without the generation of fine particles in a simple manner, it is possible to manufacture an optical film having a cholesteric liquid crystal layer having good selective reflection characteristics.

Description

A manufacturing method of optical film having planar oriented cholesteric liquid crystal layer

The present invention relates to a method for manufacturing an optical film used for a color filter, and more particularly, to a method for manufacturing an optical film having a planar oriented cholesteric liquid crystal layer.

A cholesteric liquid crystal (CLC), also called a chiral nematic liquid crystal, is a liquid crystal having a cholesteric mesogen or a nematic liquid crystal (NLC). Is a liquid crystal mixture with a chiral substance that induces a periodic spiral structure.

The cholesteric liquid crystal is divided into the following three alignment structures according to the form in which the axial direction of the cholesteric liquid crystal is arranged. Planar orientation when the cholesteric liquid crystal spiral axes are arranged perpendicular to the substrate surface, homeotropic orientation when horizontal to the substrate, and random arrangement of the spiral axes. It is called focal conic orientation.

)과 피치의 곱인

으로 표시되므로, 평균굴절률이 다른 재료를 사용하거나 콜레스테릭 액정의 피치를 조절하면 선택 반사되는 파장 영역을 조절할 수 있다. 이러한 콜레스테릭 액정의 선택 반사 특성은 반사형 편광판, 반사형 컬러필터 및 tunable laser 필터 등의 광학필름으로 매우 유용한 응용분야를 갖고 있다.Among them, when the arrangement of cholesteric liquid crystals has a planar orientation, it exhibits a unique characteristic of selectively reflecting light depending on the twist direction of the spiral and the pitch ( p ) of the repeating structure. When the light incident on the planar oriented cholesteric liquid crystal is represented as the sum of two circularly polarized light with opposite directions of rotation, the circularly polarized light in the same direction as the twisted structure of the cholesteric liquid crystal is reflected and Circularly polarized light has the property of transmitting. The wavelength λ of the reflected light at this time is the average refractive index of the liquid crystal (

) Is the product of the pitch

Since it is represented by, it is possible to adjust the wavelength range of the selective reflection by using a material having a different average refractive index or by adjusting the pitch of the cholesteric liquid crystal. The selective reflection characteristics of such cholesteric liquid crystals have very useful applications as optical films such as reflective polarizers, reflective color filters, and tunable laser filters.

Conventionally, a method of manufacturing an optical film having a planar oriented cholesteric liquid crystal layer is a method of coating a cholesteric liquid crystal on a polymer film coated with a polyimide alignment layer. The polyimide alignment layer is a film for inducing the planar alignment of the cholesteric liquid crystal, and is produced by applying a polyimide solution on the polymer film, followed by a high temperature heat treatment and a rubbing process. Therefore, a process waiting time for a certain time occurs because of the high temperature heat treatment process for forming the polyimide alignment layer. In addition, since the polyimide film must be rubbed to form a groove for liquid crystal alignment by a physical method such as rubbing, a large amount of fine particles are generated in this process. Fine particles generated during the rubbing process act as defects in the liquid crystal alignment, leading to process defects in manufacturing facilities requiring high cleanliness.

The technical problem of the present invention was devised to solve the above problems, and a method of manufacturing an optical film having a cholesteric liquid crystal layer inducing a planar alignment of the cholesteric liquid crystal without generating fine particles in a simple manner. To provide.

In order to achieve the above object, the manufacturing method of an optical film having a planar oriented cholesteric liquid crystal layer according to the present invention,

(S1) preparing an amorphous polyethylene terephthalate film;

(S2) preparing the uniaxially oriented polyethylene terephthalate film by stretching the amorphous polyethylene terephthalate film only in the uniaxial direction; And

(S3) spin-coating a cholesteric liquid crystal on the uniaxially oriented polyethylene terephthalate film.

In the optical film production method of the present invention, the elongation of the uniaxially oriented polyethylene terephthalate film is preferably 50% or more.

The production method of the present invention uses a uniaxially oriented polyethylene terephthalate film for the planar alignment of the cholesteric liquid crystal. Accordingly, the heat treatment process required for forming the conventional polyimide alignment layer may be omitted, thereby improving productivity and preventing thermal damage of the polymer film coated with the polyimide alignment layer.

In addition, since the rubbing process for forming the alignment groove of the polyimide film is omitted, it is possible to remove the contamination by the fine particles generated by this. Therefore, since the planar orientation of a cholesteric liquid crystal can be induced favorably, the optical film provided with the cholesteric liquid crystal layer excellent in the selective reflection characteristic can be manufactured.

1 is a cross-sectional view of an optical film formed according to the manufacturing method of the present invention.
2 is a schematic cross-sectional view and a plan view of a stretching apparatus for stretching an amorphous polyethylene terephthalate film (PET) in a uniaxial direction, used in an embodiment of the present invention.
Figure 3 is a graph measuring the change in absorption peak intensity of the E7 liquid crystals according to the change in elongation of the polyethylene terephthalate film of the optical film prepared according to the Examples and Comparative Examples of the present invention.
Figure 4 is a graph measuring the change in reflectance according to the change in elongation of the polyethylene terephthalate film of the optical film prepared according to Examples and Comparative Examples of the present invention.

Hereinafter, a method of manufacturing an optical film having a planar oriented cholesteric liquid crystal layer of the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

First, prepare an amorphous polyethylene terephthalate film (S1 step). The polyethylene terephthalate polymer chain contributes to the planar orientation of the cholesteric liquid crystal by interactions such as van der Waals forces with the cholesteric liquid crystal molecules as described below. The polyethylene terephthalate film should be amorphous. The planar orientation of the cholesteric liquid crystal is good only when the polyethylene terephthalate polymer chains are uniaxially arranged in the stretching direction through the stretching process described later. It is not possible to achieve the object of the present invention.

Subsequently, the amorphous polyethylene terephthalate film is stretched only in the uniaxial direction to prepare a uniaxially oriented polyethylene terephthalate film (step S2). At the interface of the uniaxially oriented polyethylene terephthalate film, cholesteric liquid crystals spin-coated in the following process are lined up along the stretching direction of the polyethylene terephthalate film. It is preferable for the elongation of the uniaxially oriented polyethylene terephthalate film to be 50% or more in order to improve the planar orientation of a cholesteric liquid crystal. Stretching of the amorphous polyethylene terephthalate film can be carried out using a conventional stretching apparatus and process, in order to achieve sufficient stretching, the amorphous polyethylene terephthalate film is 75 ℃ or more, for example, about 80 ℃ the glass transition temperature of polyethylene terephthalate After annealing at, it is preferred to carry out stretching.

Then, spin-coating the cholesteric liquid crystal on the uniaxially oriented polyethylene terephthalate film (step S3). Of course, the cholesteric liquid crystal can be further added to the solvent, photoinitiator, leveling agent and the like as necessary. The cholesteric liquid crystal is uniformly coated on the film by spin coating, and the applied cholesteric liquid crystal layer has the cholesteric liquid crystal oriented in a planar orientation as follows.

The cholesteric liquid crystals at the interface of the uniaxially oriented polyethylene terephthalate film are lined up along the stretching direction of the polyethylene terephthalate film by interaction between molecules such as van der Waals forces. That is, according to the interaction between the cholesteric liquid crystal molecules and the polyethylene terephthalate polymer chain, the cholesteric liquid crystal molecules are lined up in the same plane direction as that of the polyethylene terephthalate polymer. On the other hand, the liquid crystal molecules that are separated from the interface of the polyethylene terephthalate film is arranged by the liquid crystal molecules are arranged along the helix axis of the direction perpendicular to the polyethylene terephthalate film by the intermolecular interaction of the chiral component and the liquid crystal molecules inducing a spiral structure, The orientation is derived.

The planar orientation-induced cholesteric liquid crystal layer can be manufactured into a final optical film through a process such as drying, light irradiation, if necessary.

As shown in FIG. 1, the optical film 10 manufactured according to this process includes a planar oriented cholesteric liquid crystal layer 11 on the uniaxially oriented polyethylene terephthalate film 12. Such an optical film can be usefully used as an optical film such as a color filter and a polarizing plate.

Hereinafter, examples will be described in detail to help understand the present invention. However, embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example

The unstretched amorphous polyethylene terephthalate (PET) film was cut into dog-bone shapes. As shown in the cross-sectional view and the plan view shown in Figure 2, the PET film is fixed to a drawing machine having two fixing frames, and after annealing (annealing) at 80 ℃ for 5 minutes in an oven 50% elongation at a rate of 11mm / min, The uniaxial stretching was performed at 100% and 200%, respectively. The middle portion of the uniaxially stretched PET film was cut out and pasted onto a glass substrate, and then the cholesteric liquid crystal mixture was spin coated at 500 rpm for 15 seconds at room temperature to prepare an optical film.

The cholesteric liquid crystal mixture used was mixed with E7, a nematic liquid crystal from Merck, and R1011, from BASF, a chiral dopant, in a ratio of 95: 5 (wt%) at 70 ° C.

Comparative example

An optical film was prepared in the same manner as in Example, except that the cholesteric liquid crystal mixture was spin coated on an unstretched amorphous polyethylene terephthalate (PET) film.

Measurement of Orientation Distribution of Liquid Crystal According to Elongation of PET Film

 The degree of planar orientation of the cholesteric liquid crystals according to the elongation of the PET film was measured through the change in absorption peak of the C≡N group.

로 나타낼 수 있는데, M은 분자 진동운동의 transition dipole, E는 IR beam의 electric field이며, α는 electric field 와 transition dipole moment가 이루는 각을 의미한다. 콜레스테릭 액정 셀을 FTIR spectrometer로 측정할 때 IR beam은 항상 기판에 수평하게 입사되므로 콜레스테릭 액정의 배열 상태에 따라 IR beam의 electric field와 C≡N 그룹 진동운동 dipole moment가 이루는 각이 달라진다. 플래너 배향된 콜레스테릭 액정은 기판과 E7 액정 축이 수평을 이루어 α값이 0°에 근접하므로 흡수피크는 최대값을 가지게 되며, 호메오트로픽 배열인 경우 α값이 90°이어서 흡수피크의 세기가 최소값을 갖게 된다. 따라서 E7 액정의 시아노기 신축운동 2226cm^-1 흡수피크의 세기 변화를 통해 액정의 배향 상태를 확인할 수 있다.Since the E7 nematic liquid crystal used has a cyano group (C≡N) attached in a direction parallel to the long axis direction of the liquid crystal molecules, the IR absorption peak of the cyano group represented by 2226 cm ⁻¹ is used for the measurement of the liquid crystal director. Absorption peak intensity of vibration

Where M is the transition dipole of molecular vibration, E is the electric field of the IR beam, and α is the angle between the electric field and the transition dipole moment. When the cholesteric liquid crystal cell is measured by FTIR spectrometer, the IR beam is always incident horizontally on the substrate, so the angle between the electric field of the cholesteric liquid crystal and the C≡N group vibration motion dipole moment depends on the arrangement of the cholesteric liquid crystal. . The planar oriented cholesteric liquid crystal has a maximum absorption value because the substrate and the E7 liquid crystal axis are horizontal and the α value is close to 0 °. In the homeotropic array, the α value is 90 ° and the absorption peak intensity is increased. Will have the minimum value. Therefore, the alignment state of the liquid crystal may be confirmed by changing the intensity of the cyano group stretching movement 2226 cm ⁻¹ absorption peak of the E7 liquid crystal.

 In order to measure the concentration distribution according to the planar orientation of the cholesteric liquid crystal of the present invention, an IR test for obtaining an IR spectrum was performed using a Perkin-Elmer system 2000 FTIR spectrometer.

FIG. 3 shows the planar orientation of cholesteric liquid crystals on a non-stretched PET film (none) and the planar orientation of cholesteric liquid crystals on a stretched PET film with three elongations (50%, 100%, 200%). The change is a graph showing the change in intensity of the cyano group absorption peak of E7. The intensity of 2226 cm ^-1 , the absorption peak of C≡N on the unstretched PET film, was found to be 0.25, but the intensity of 2226 cm ^-1 on the stretched PET film was increased with increasing elongation. In particular, the intensity of the C≡N absorption peak of the cholesteric liquid crystal on the PET film having an elongation of 200% increases to 0.37, indicating that the planar orientation is very good.

Measurement of Reflected Light Efficiency According to Elongation of PET Film

 As shown in FIG. 4, the cholesteric liquid crystal layer formed on the unstretched PET film did not exhibit selective reflection because no selective reflection occurred, and the selective reflectance of the cholesteric liquid crystal layer formed on the stretched PET film was increased in elongation. It can be seen that increases according to. In particular, it can be seen that the cholesteric liquid crystal layer on the PET film having an elongation of 200% exhibits a selective reflectance of about 36%.

Claims (2)

(S1) preparing an amorphous polyethylene terephthalate film;
(S2) preparing the uniaxially oriented polyethylene terephthalate film by stretching the amorphous polyethylene terephthalate film only in the uniaxial direction; And
(S3) Spin-coating a cholesteric liquid crystal added with a chiral component to induce a periodic spiral structure to the liquid crystal or nematic liquid crystal having a cholesteric mesogen on the uniaxially oriented polyethylene terephthalate film Comprising the steps,
A method for producing an optical film having a planar oriented cholesteric liquid crystal layer. The method according to claim 1, wherein the elongation of the uniaxially oriented polyethylene terephthalate film is 50% or more.

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