Plastic film for optics, polarizing plate, and image display device

A plastic film with controlled slow axis direction variations and specific retardation values addresses rainbow unevenness and blackout issues in image display devices, enhancing mechanical strength and suitability for curved or foldable designs.

JP7700674B2Active Publication Date: 2025-07-01DAI NIPPON PRINTING CO LTD
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Patent Information

Application Number
JP2021522845
Authority / Receiving Office
JP · JP
Patent Type
Patents
Current Assignee / Owner
Priority Date
2019-05-30
Filing Date
2020-05-28
Publication Date
2025-07-01
Estimated Expiration
2040-05-28

AI Technical Summary

Technical Problem

Existing plastic films for image display devices suffer from rainbow unevenness and blackout issues when viewed with polarized sunglasses, particularly when the polarizer and stretched plastic film are arranged in specific configurations, and they often require high in-plane retardation, leading to mechanical weaknesses.

Method used

The solution involves a plastic film with controlled variations in the direction of the slow axis and specific retardation values, ensuring an average in-plane retardation of 600 nm or less, a difference in slow axis directions of 5.0 degrees or more, and a ratio of in-plane to thickness retardation of 0.10 or less, without increasing overall retardation.

Benefits of technology

This approach effectively suppresses rainbow unevenness and blackout while maintaining mechanical strength, even under bending stress, making it suitable for curved or foldable display devices.

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Abstract

Provided is a plastic film for optical applications that, without increasing an in-plane phase difference, makes it possible to suppress iridescent unevenness when viewed with the naked eye and blackout when viewed with polarized sunglasses. The plastic film for optical applications has an average in-plane phase difference of 600 nm or smaller and satisfies the following condition. A difference between a maximum value among angles D1-D5 and a minimum value among the angles D1-D5 is equal to or larger than 5.0 degrees, where: a sample having a size of 50 mm in length × 50 mm in width is cut out from the plastic film; a direction of a slow axis is measured at each of a total of five locations of the sample, including four locations at 10 mm from the four corners toward the center section of the sample, and a center portion of the sample; and angles between any one side of the sample and the directions of the slow axes of the measurement locations are defined as D1, D2, D3, and D4, and D5, respectively.
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Citation Information

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