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JP-2026076246-A - Laminated films and their applications

JP2026076246AJP 2026076246 AJP2026076246 AJP 2026076246AJP-2026076246-A

Abstract

[Problem] To provide a foldable display that is easy to mass-produce and does not risk causing distortion of the image displayed at the folded part after repeated folding, the objective is to provide a laminated film for protecting the organic EL module of a foldable display that does not develop cracks at the folded part. [Solution] A laminated film for protecting an organic EL module of a foldable display, comprising a polyester film with an adhesive layer on at least one side thereof, wherein the polyester film satisfies the following conditions. (1) Refractive index in the bending direction is 1.590 to 1.620 (2) The refractive index in the direction of the folding part is 1.670 to 1.700 (3) Refractive index in the thickness direction is 1.520 or less (4) Density is 1.380 g/ cm³ or more (Here, the bending direction refers to the direction perpendicular to the fold when folding the polyester film.) [Selection Diagram] Figure 1

Inventors

  • 河合 究
  • 西尾 正太郎
  • 清水 亮

Assignees

  • 東洋紡株式会社

Dates

Publication Date
20260511
Application Date
20260121
Priority Date
20190528

Claims (8)

  1. A laminated film for protecting an organic EL module of a foldable organic EL display, comprising a polyester film with an adhesive layer on at least one side thereof, wherein the polyester film satisfies the following conditions. (1) Refractive index in the bending direction is 1.590 to 1.620 (2) The refractive index in the direction of the folding part is 1.670 to 1.700 (3) Refractive index in the thickness direction is 1.520 or less (4) Density is 1.380 g/ cm³ or more (5) Polyester film is polyethylene terephthalate film (6) Polyester film thickness of 10 to 300 μm (Here, the bending direction refers to the direction perpendicular to the fold when folding the polyester film.)
  2. The laminated film for protecting the organic EL module of a foldable organic EL display according to claim 1, wherein the thickness of the adhesive layer is 1 to 50 μm.
  3. A laminated film for protecting an organic EL module of a foldable organic EL display according to claim 1 or 2, wherein the elastic modulus of the polyester film in the bending direction is 2.7 GPa or less, and the elastic modulus of the polyester film in the folding direction is 4.5 GPa or more.
  4. A laminated film for protecting an organic EL module of a foldable organic EL display according to any one of claims 1 to 3, wherein the polyester film has a total light transmittance of 85% or more, a haze of 3% or less, and a maximum thermal shrinkage rate of 6% or less.
  5. A laminated film for protecting an organic EL module of a foldable organic EL display according to any one of claims 1 to 4, having an easily adhesive layer on at least one side of the polyester film.
  6. A laminated film for protecting an organic EL module of a foldable organic EL display, having a hard coat layer with a thickness of 1 to 50 μm on a polyester film opposite to the side having the adhesive layer of the laminated film for protecting an organic EL module of a foldable organic EL display according to any one of claims 1 to 5.
  7. A foldable organic EL display comprising a laminated film for protecting an organic EL module of a foldable organic EL display according to any one of claims 1 to 6, as a protective film for an organic EL module, wherein the foldable organic EL display includes a protective film for a single organic EL module that is continuous through the folded portion of the foldable organic EL display.
  8. A portable terminal device having a foldable organic EL display as described in claim 7.

Description

This invention relates to a laminated film for an organic EL module in a foldable display, a foldable display, and a mobile terminal device, and more particularly to a laminated film for an organic EL module in a foldable display, a foldable display, and a mobile terminal device that uses a polyester film that is less prone to image distortion due to film deformation even after repeated folding. The thinning and weight reduction of mobile devices has progressed, leading to the widespread adoption of mobile devices such as smartphones. While mobile devices are required to have various functions, convenience is also paramount. Therefore, popular mobile devices need to be small, around 6 inches in size, as they are designed for simple one-handed operation and to be easily stored in clothing pockets. On the other hand, tablet devices with screen sizes ranging from 7 to 10 inches offer high functionality, being designed not only for video content and music, but also for business use, drawing, and reading. However, they cannot be operated with one hand, have poor portability, and present challenges in terms of convenience. To achieve these goals, a method has been proposed to make the display more compact by connecting multiple displays together (see Patent Document 1). However, because the bezel remains, the image is cut off, resulting in reduced visibility, which has prevented its widespread adoption. Therefore, in recent years, mobile devices incorporating flexible displays and foldable displays have been proposed. This method allows for uninterrupted image display and convenient portability as a mobile device with a large screen. In conventional displays and mobile devices without a folding structure, the display surface could be protected with non-flexible materials such as glass. However, in folding displays, where the folding mechanism forms a single display surface, it is necessary to use a flexible hard-coat film or similar material that can protect the surface. However, in folding displays, certain areas of the display are repeatedly folded, causing the film in those areas to deform over time, leading to problems such as distortion of the image displayed on the screen. Furthermore, in addition to the surface protection film, folding displays utilize films in various parts, including polarizing plates, phase difference plates, touch panel substrates, substrates for display cells such as organic EL (electroluminescent) displays, and back protection components. These films also require durability against repeated folding. Therefore, methods for partially varying the film thickness have been proposed (see Patent Document 2), but these have the problem of poor mass production capabilities. Furthermore, methods for adjusting the refractive index of polyester film in the bending direction have been proposed (see Patent Document 3). However, as the refractive index in the bending direction decreases, the pencil hardness during hard coat application decreases, leading to a problem of reduced surface protection function for displays. Additionally, while decreasing the refractive index in one direction improves deformation during folding, it increases uniaxial orientation in the folding direction, leading to problems such as crack formation or breakage at the folded portion. Japanese Patent Publication No. 2010-228391Japanese Patent Publication No. 2016-155124International Publication No. 2018/150940 This is a schematic diagram illustrating the bending radius when the foldable display according to the present invention is folded.This is a schematic diagram showing the bending direction of the polyester film that constitutes the laminated film for protecting the organic EL module of the foldable display in the present invention.This is a schematic cross-sectional view of an example of an organic EL module according to the present invention. (display) In this invention, "display" refers to display devices in general. Types of displays include LCDs, organic EL displays, inorganic EL displays, LEDs, and FEDs, but LCDs with a bendable structure, organic EL displays, and inorganic EL displays are preferred. Organic EL displays and inorganic EL displays, which can reduce the number of layers, are particularly preferred, and organic EL displays with a wide color gamut are even more preferred. (Foldable display) A foldable display is a single continuous display that can be folded in half or in other ways for portability. Folding reduces the size by half, improving portability. The bending radius of the foldable display is preferably 5 mm or less, and more preferably 3 mm or less. A bending radius of 5 mm or less allows for a thinner design when folded. A smaller bending radius is generally better, but a smaller bending radius makes it more prone to creases. A bending radius of 0.1 mm or more is preferred, but it may also be 0.5 mm or more, or even 1 mm or more. Even with a bending radius of 1 mm, a sufficiently thin design