JP2008083148A - Optical film and optical transfer sheet using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film for organic electroluminescence which has a structure for improving light taking efficiency of an organic electroluminescence element used as a display or the like of lighting, a mobile phone and a digital camera, and to provide an optical transfer sheet that uses the film. <P>SOLUTION: The optical film has a fine rugged structure layer, on a base material and a surface protection layer is formed on a ruggedness formation surface of the fine rugged structure layer, and the optical transfer sheet that uses the optical film is also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic EL, and relates to an organic EL optical film having a structure that improves the light extraction efficiency of an organic EL element, and an optical transfer sheet using the same.

  The organic EL element is expected as a display or illumination because it has a wide viewing angle by self-emission, a high-speed response, and is thin and light. In recent years, it has been put into practical use as a display for mobile phones and digital cameras and has been actively developed.

  An organic EL element generally has a structure in which a hole transport layer, a light emitting layer, and an electron transport layer are sandwiched between electrodes. An electric field is applied between the electrodes, electrons and holes are injected, excitons are generated in the light emitting layer, and light is emitted by recombination. The exciton has a singlet state and a triplet state, the generation probability of the singlet state and the triplet state is 1: 3, and even when a phosphorescent material using triplet state light emission is used. The luminous efficiency is 75% at the maximum. Further, since the refractive index is about 1.7 for the organic layer, 2.0 for the transparent electrode, and 1.0 for air, total reflection occurs at the element interface, and light that can actually be extracted outside the element is 20 of the emitted light. When combined, the upper limit is 15% as the energy conversion efficiency.

As a method for improving the extraction efficiency, there is a method of forming a reflection surface on the side surface of the element and reflecting light traveling forward in the direction of the element side surface by total reflection, for example, Patent Document 1, but it is difficult to form a large area. It is not practical. In addition, there is, for example, Patent Document 2 that uses a diffraction grating or a zone plate to change the traveling direction of light by refraction and diffraction. However, although there is some effect, total reflection cannot be completely prevented. . Therefore, the light extraction method of the organic EL is still insufficient, and further improvement of the extraction method is indispensable for high efficiency.
JP 2005-327522 A Japanese Patent No. 2911183

  The present invention has been made in consideration of the above technical background, and provides an organic EL optical film having a structure for improving the light extraction efficiency of an organic EL element, and an optical transfer sheet using the same. This is a problem.

As a solution to the above problems,
The invention according to claim 1 is an optical film having a fine relief structure layer on a substrate,
A surface protective layer is formed on the unevenness forming surface of the fine unevenness structure layer.

  The invention according to claim 2 is the optical film according to claim 1, wherein the refractive index of the surface protective layer is smaller than the refractive index of the fine concavo-convex structure layer.

  The invention according to claim 3 is the optical film according to claim 1 or 2, wherein the surface protective layer is made of a fluororesin.

The invention according to claim 4 is the optical film according to any one of claims 1 to 3, wherein a cross-sectional area decreases in a direction in which the fine concavo-convex structure moves away from the base material. .

  The invention according to claim 5 is the optical film according to any one of claims 1 to 4, wherein the pitch of the fine concavo-convex structure is 50 nm to 350 nm.

  The invention according to claim 6 is the optical film according to any one of claims 1 to 5, wherein a difference in height of the fine concavo-convex structure is from 50 nm to 5 μm.

The invention according to claim 7 is the optical film according to any one of claims 1 to 6, wherein the substrate film has a fine uneven structure on both surfaces thereof.
The optical film is characterized in that an adhesive layer and a protective film are sequentially laminated on one surface of the optical film, and a planarizing layer, a barrier layer, and a transparent electrode layer are sequentially laminated on the other surface.

The invention according to claim 8 is an optical transfer sheet using the optical film according to any one of claims 1 to 6 having a fine uneven structure only on one side of the base film,
An optical transfer sheet, wherein an adhesive layer is formed on both sides of the optical film, and protective films are further arranged on both sides.

  The light extraction efficiency can be easily improved by attaching the optical film of the present invention or using the substrate. In addition, by setting the concave / convex pitch optimally according to the emission wavelength of the EL, it is possible to extract the light optimal for the light. Furthermore, when the extraction efficiency is increased, the same brightness can be obtained by using the optical film of the present invention to extend the life without applying a load with low power, and the use of a material with low brightness. Being able to contribute to the problems of high brightness and long life from other than the light emitting material, and being able to reduce power consumption is attractive and extremely effective as a device.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. In the optical film of the present invention, the pitch of the fine concavo-convex structure is changed from 50 nm to 350 nm, which is smaller than the wavelength of visible light, and the cross-sectional area decreases in the direction away from the base film 4, thereby clearly showing visible light. An interface having a difference in refractive index is eliminated, and a state in which the refractive index continuously changes in the film thickness direction can be created, and total reflection can be suppressed. Since the protective films 1 and 6 are peeled off during actual use, the surface of the optical film of the present invention is the surface protective layer 2 having a low refractive index laminated on the fine concavo-convex structure or the fine concavo-convex structure layer. The surface protective layer 2 is used to add antifouling properties and chemical resistance to protect the fine concavo-convex structure, and the fluororesin has good characteristics and is a transparent, low refractive index material and suitable. By using a material having a refractive index as low as possible, total reflection hardly occurs at the interface between the surface protective layer and air, and the effect of protecting the surface can be obtained without greatly reducing the extraction efficiency. Furthermore, by forming fine concavo-convex structures on both sides, not only the refractive index continuously changes from the base film to the air, but also the refractive index continuously changes from the organic EL element using this optical film as a substrate to the air. Thus, the extraction efficiency is improved. The fine concavo-convex structure on both surfaces of the base film may be the same shape or different. Since the organic EL element is affected by unevenness, a planarization layer is introduced. In addition, since the organic layer is affected by oxygen, a barrier layer is provided. As the barrier layer, SiN, SiO, SiO ₂ or the like is effective, but is not particularly specified.

  FIG. 1 shows the structure of an optical film having a fine relief structure. The base film must be transparent and have good adhesion to the material for forming the microstructure. Further, when UV or heat is used for forming the fine concavo-convex structure, UV transparency and heat resistance are required. The closer the molding resin and the base film are to the refractive index, the less the reflection and refraction at the interface, and the greater the extraction effect. For the structure, the pitch should be narrower than visible light, and at least narrower than 350 nm. Conversely, if it is narrower than 50 nm, the unevenness for continuously changing the refractive index must be increased, the aspect ratio becomes large, and molding is difficult and impractical. The height is required to be at least 50 nm in order to continuously change the refractive index, and is preferably 5 μm or less in view of moldability and practicality. Actually, it is necessary to determine the optimum optimally according to the emission wavelength of the organic EL. Since the fine concavo-convex structure continuously changes the refractive index, the cross-sectional shape is preferably such that the convex portion decreases from the bottom toward the top and the cross-sectional area decreases, and a cone is desirable, but is not particularly limited. Also, there is no particular designation for the in-plane arrangement. About an adhesive material and a protective film, it is necessary for the adhesive material to have good releasability, the adhesive material has a fine structure, and the base film has no adhesive residue. Regarding the surface protective layer, the refractive index is continuously changed from that of the microstructure layer and total reflection is suppressed, but total reflection occurs at the interface with air, so that the refractive index is as close to air as possible. A material with a low refractive index is required.

  Hereinafter, the present invention will be described with specific examples.

The fine concavo-convex structure was a structure having a pitch of 200 nm and a height of 300 nm, and a Ni original plate was produced by electroforming from a resist plate formed by electron beam drawing. Using the easy-adhesive PET film A4300 manufactured by Toyobo as a base film, an acrylic UV curable resin was sandwiched between the base film and the Ni original plate, and the fine concavo-convex structure was transferred onto the base film by irradiation with UV. The protective film used was R-100 manufactured by Nitto Denko, and was attached to the film to which the fine concavo-convex structure was transferred.
When this optical film was attached and evaluated on an organic EL element of SiN barrier layer / ITO transparent electrode / organic layer (red light emission, wavelength 620 nm) / Ag alloy electrode / glass, the external quantum efficiency was compared with the state without the optical film. Improved twice.

It is sectional drawing which shows a part of example of the optical film of this invention. It is sectional drawing which shows a part of other example of the optical film of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Protective film 2 Surface protective layer 3 Fine uneven structure layer 4 Base film 5 Adhesive material layer 6 Protective film 7 Fine uneven structure layer 8 Planarizing layer 9 Barrier layer 10 Transparent electrode

Claims (8)

An optical film having a fine relief structure layer on a substrate,
An optical film, wherein a surface protective layer is formed on an uneven surface of the fine uneven structure layer.   The optical film according to claim 1, wherein a refractive index of the surface protective layer is smaller than a refractive index of the fine concavo-convex structure layer.   The optical film according to claim 1, wherein the surface protective layer is made of a fluororesin.   The optical film according to any one of claims 1 to 3, wherein a cross-sectional area decreases in a direction in which the fine concavo-convex structure moves away from the substrate.   The optical film according to any one of claims 1 to 4, wherein a pitch of the fine concavo-convex structure is 50 nm to 350 nm.   The optical film according to any one of claims 1 to 5, wherein a difference in height of the fine concavo-convex structure is from 50 nm to 5 µm. The optical film according to any one of claims 1 to 6, wherein the optical film has a fine uneven structure on both surfaces of the base film,
An optical film, wherein an adhesive layer and a protective film are sequentially laminated on one surface of the optical film, and a planarizing layer, a barrier layer, and a transparent electrode layer are sequentially laminated on the other surface. An optical transfer sheet using the optical film according to any one of claims 1 to 6, wherein the optical film according to any one of claims 1 to 6 has a fine concavo-convex structure only on one side of the base film,
An optical transfer sheet, wherein a pressure-sensitive adhesive layer is formed on both sides of the optical film, and protective films are further arranged on both sides.