JP-7856133-B2 - Liquid crystal display device and polarizing plate

Inventors

• 村田 浩一
• 佐々木 靖
• 向山 幸伸

Assignees

• 東洋紡株式会社

Dates

Publication Date

20260511

Application Date

20241111

Priority Date

20141125

Claims (5)

1. A liquid crystal display device having a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, The backlight light source has peaks in its emission spectrum in the wavelength regions of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to 780 nm, respectively, and the full width at half maximum of each peak is 5 nm to 80 nm . In at least one of the polarizing plates, a polyester film is laminated on at least one surface of the polarizer. The polyester film has in-plane retardation between 1500 nm and 30000 nm, the ratio of in-plane retardation (Re) to retardation in the thickness direction (Rth) (Re/Rth) is between 0.6 and 2.0, and the NZ coefficient is 2.5 or less. An anti-glare layer is laminated on the surface of the polyester film opposite to the surface on which the polarizer is laminated , and an anti-reflective layer is laminated on top of the anti-glare layer . The anti-glare layer comprises cellulose acetate propionate, In a laminate comprising the polyester film, the anti-glare layer, and the anti-reflective layer, the surface reflectance at a wavelength of 550 nm, measured at an incident angle of 5 degrees from the surface of the laminate on the anti-reflective layer side, using a spectrophotometer with the surface opposite to the surface on the anti-reflective layer side of the laminate shielded with black light, is 2.0% or less. LCD display device.
2. A liquid crystal display device having a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, The backlight light source has peaks in its emission spectrum in the wavelength regions of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to 780 nm, respectively, and the full width at half maximum of each peak is 5 nm to 80 nm. In at least one of the polarizing plates, a polyester film is laminated on at least one surface of the polarizer. The polyester film has in-plane retardation between 1500 nm and 30000 nm, the ratio of in-plane retardation (Re) to retardation in the thickness direction (Rth) (Re/Rth) is between 0.6 and 2.0, and the NZ coefficient is 2.5 or less. An anti-glare layer is laminated on the surface of the polyester film opposite to the surface on which the polarizer is laminated , and a low-reflection layer is laminated on top of the anti-glare layer . The anti-glare layer comprises cellulose acetate propionate, In a laminate comprising the polyester film, the anti-glare layer, and the low-reflection layer, the surface reflectance at a wavelength of 550 nm, measured at an incident angle of 5 degrees from the surface of the low-reflection layer side of the laminate using a spectrophotometer with the opposite side of the laminate shielded with black light, is less than 5%. LCD display device.
3. The liquid crystal display device according to claim 1 or 2, wherein the backlight light source includes a light source that emits excitation light and quantum dots .
4. The liquid crystal display device according to any one of claims 1 to 3, wherein at least one of the polarizing plates has a polyester film laminated on at least one surface of the polarizer such that the angle between the transmission axis of the polarizer and the phase-advancing axis of the polyester film is between -15 degrees and 15 degrees.
5. The liquid crystal display device according to any one of claims 1 to 4, wherein the anti-glare layer further comprises acrylic-styrene copolymer particles .

Description

This invention relates to a liquid crystal display device and a polarizing plate. More specifically, it relates to a liquid crystal display device and a polarizing plate in which the occurrence of rainbow-like color spots is reduced. Polarizing plates used in liquid crystal displays (LCDs) typically have a structure in which a polarizer, made of polyvinyl alcohol (PVA) or similar material dyed with iodine, is sandwiched between two polarizer protective films. In most cases, triacetylcellulose (TAC) film is used as the polarizer protective film. In recent years, with the miniaturization of LCDs, there has been a demand for thinner polarizing plates. However, reducing the thickness of the TAC film used as the protective film results in insufficient mechanical strength and poor moisture permeability. Furthermore, TAC film is very expensive, and while polyester film has been proposed as a cheaper alternative (Patent Documents 1-3), it has the problem of exhibiting iridescent color variations. When a birefringent oriented polyester film is placed on one side of a polarizer, the polarization state of linearly polarized light emitted from the backlight unit or polarizer changes as it passes through the polyester film. The transmitted light exhibits interference colors characteristic of retardation, which is the product of the birefringence and thickness of the oriented polyester film. Therefore, when discontinuous emission spectra such as cold cathode tubes or hot cathode tubes are used as light sources, the transmitted light intensity varies depending on the wavelength, resulting in a rainbow-like color patch (see: Proceedings of the 15th Micro-Optical Conference, pp. 30-31). As a means of solving the above problem, it has been proposed to use a white light source with a continuous and broad emission spectrum, such as a white light-emitting diode, as the backlight source, and to use an oriented polyester film with a certain retardation as the polarizer protective film (Patent Document 4). White light-emitting diodes have a continuous and broad emission spectrum in the visible light region. Therefore, by focusing on the envelope linearity of the interference color spectrum due to transmitted light passing through a birefringent material, it has been proposed that by controlling the retardation of the oriented polyester film, a spectrum similar to the emission spectrum of the light source can be obtained, thereby suppressing iridescence. By orthogonal or parallel to the orientation direction of the oriented polyester film and the polarization direction of the polarizer, linearly polarized light emitted from the polarizer will pass through the oriented polyester film while maintaining its polarization state. Furthermore, by controlling the birefringence of the oriented polyester film to increase its uniaxial orientation, light incident from an oblique direction will also pass through while maintaining its polarization state. When the oriented polyester film is viewed from an oblique angle, a shift occurs in the direction of the principal orientation axis compared to when viewed from directly above. However, high uniaxial orientation reduces this shift in the direction of the principal orientation axis when viewed from an oblique angle. Therefore, the shift between the direction of linear polarization and the direction of the principal orientation axis is reduced, making changes in the polarization state less likely. Thus, by controlling the emission spectrum of the light source, the orientation state of the birefringent, and the direction of the principal orientation axis, changes in the polarization state are suppressed, preventing the occurrence of rainbow-like color patches and significantly improving visibility. Japanese Patent Publication No. 2002-116320Japanese Patent Publication No. 2004-219620Japanese Patent Publication No. 2004-205773WO2011/162198 This example shows the case where multiple peaks exist within a single wavelength range.This example shows the case where multiple peaks exist within a single wavelength range.This example shows the case where multiple peaks exist within a single wavelength range.This example shows the case where multiple peaks exist within a single wavelength range. Generally, a liquid crystal display device has a rear module, liquid crystal cells, and a front module, arranged in the order from the side where the backlight light source (also called the "backlight unit") is located to the side where the image is displayed (viewing side). The rear module and front module generally consist of a transparent substrate, a transparent conductive film formed on its surface facing the liquid crystal cells, and a polarizing plate positioned on the opposite side. In other words, the polarizing plate is positioned on the side facing the backlight light source in the rear module, and on the side where the image is displayed (viewing side) in the front module. The liquid crystal display device