JP-7856606-B2 - Image display device

Inventors

• 荻野 真悠子
• 中原 歩夢

Assignees

• 日東電工株式会社

Dates

Publication Date

20260511

Application Date

20230529

Claims (1)

1. The device comprises a polarizing plate and a flexible image display panel in this order. The polarizing plate is Polarizer and, The polarizer comprises a protective layer disposed on at least one side thereof, The elongation at break of the protective layer at 25°C, measured by the method described below, is 20 mm or more. The ratio of the thickness of the protective layer to the thickness of the image display panel is 1 to 2, for the image display device: <Method for measuring elongation at break> The protective layer was cut into a dumbbell shape (10 mm wide, 100 mm long) to be used as a test sample; The aforementioned test sample was subjected to a tensile test using a tensile testing machine with a chuck spacing of 10 mm and a tensile speed of 60 mm/min, and the stress-strain curve was determined; The strain at which the aforementioned test sample breaks is determined and defined as the elongation at break.

Description

This invention relates to polarizing plates and image display devices. Image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), are rapidly becoming widespread. Typically, image display devices use polarizing plates comprising a polarizer and a protective layer (see, for example, Patent Document 1). In recent years, the applications of image display devices have diversified, and the flexibility and bendability of image display devices are being considered. However, when the polarizing plate described in Patent Document 1 is applied to a bendable or foldable image display device, the flexibility of the image display device may be insufficient. Japanese Patent Publication No. 2018-200339 Figure 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.Figure 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention.Figure 3 is a schematic cross-sectional view of the image display device equipped with the polarizing plate shown in Figure 2. The following describes representative embodiments of the present invention, but the present invention is not limited to these embodiments. Furthermore, for the purpose of clarifying the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments; however, these are merely examples and do not limit the interpretation of the present invention. (Definitions of terms and symbols) The definitions of terms and symbols used in this specification are as follows: (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the refractive index is maximum in the plane (i.e., the slow phase axis direction), "ny" is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., the fast phase axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be calculated using the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Phase difference in the thickness direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be calculated using the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). A. Overall structure of the polarizing plate Figure 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. As shown in Figure 1, the polarizing plate 100 comprises a polarizer 2 and a protective layer 1. The protective layer 1 is located on at least one side of the polarizer 2. The protective layer 1 is typically flexible. The elongation at break of the protective layer 1 at 25°C is 20 mm or more. The elongation at break can be measured, for example, in accordance with JIS K 7127. If the elongation at break of the protective layer is 20 mm or more, sufficient bending durability can be provided to the polarizing plate equipped with the protective layer and polarizer. Such a polarizing plate can be applied to bendable image display devices (e.g., liquid crystal display devices, organic EL display devices, inorganic EL display devices), preferably foldable image display devices, and more preferably foldable organic EL display devices. The elongation at break of the protective layer 1 is preferably 25 mm or more, more preferably 30 mm or more. If the elongation at break of the protective layer is above this lower limit, the bending durability of the polarizing plate can be further improved. On the other hand, the elongation at break of the protective layer 1 is, for example, 150 mm or less, preferably 130 mm or less, more preferably 100 mm or less, and even more preferably 50 mm or less. If the elongation at break of the protective layer is below this upper limit, deformation of the protective layer can be suppressed. The loss tangent tanδ of the protective layer 1 at 85°C and 85% RH (relative humidity) is, for example, 15 × 10⁻² or less, preferably 13 × 10⁻² or less, more preferably 10 × 10⁻² or less, and even more preferably 7.0 × 10⁻² or less. On the other hand, the lower limit of the loss tangent tanδ of the protective layer 1 at 85°C and 85% RH (relative humidity) is typically 4.0 × 10⁻² . The loss tangent tanδ of the protective layer 1 at 100°C is, for example, 15 × 10⁻² or less, preferably 13 × 10⁻² or less, more preferably 10 × 10⁻² or less, even more preferably 8.0 × 10⁻² or less, and particularly