Optical film, method for producing optical film, polarizing plate and liquid crystal display device

Abstract

Disclosed is an optical film having improved moisture absorption, heat resistance and brittleness at the same time.  The optical film rarely causes light leakage, and has good reworkability.  Also disclosed are a method for producing the optical film, a polarizing plate and a liquid crystal display device. The optical film is characterized in that the film contains an acrylic resin (A) and a cellulose ester resin (B) at a mass ratio of from 95:5 to 30:70, that the acrylic resin (A) has a weight average molecular weight Mw of not less than 110,000 but not more than 1,000,000, that the total degree of substitution (T) of acyl groups of the cellulose ester resin (B) is not less than 2.0 but not more than 3.0, and the substitution degree of acyl groups having 3-7 carbon atoms is not less than 1.2 but not more than 3.0, that the cellulose ester resin (B) has a weight average molecular weight Mw of not less than 75,000 but not more than 300,000, that the film has a tension softening point of 105-145°C and a folding endurance of 50-100 times, and that the film is produced by melt casting.

Description

technical field [0001] The present invention relates to an optical film, a method for producing the optical film, a polarizing plate, and a liquid crystal display device, and more specifically, to an optical film, a polarizing plate, and a liquid crystal display device that are less prone to light leakage and have good rework properties. Background technique [0002] The demand for liquid crystal display devices is increasing due to applications such as liquid crystal televisions and personal computer liquid crystal displays. [0003] Generally, a liquid crystal display device is composed of a liquid crystal cell and two polarizers arranged on both sides thereof. The liquid crystal cell is formed by sandwiching a transparent electrode, a liquid crystal layer, a color filter, etc. It is formed by sandwiching a polarizer (also called polarizer, polarizing film) between two optical films (polarizer protective film). As the polarizing plate protective film, a cellulose triaceta...

AI Technical Summary

Problems solved by technology

However, it is difficult to obtain sufficient moisture resistance with cellulose ester films such as cellulose triacetate films that have been used in the past.

[0006] As a technique for improving moisture resistance, a combination of impact-resistant acrylic rubber-methyl methacrylate copolymer or butyl-modified acetyl cellulose in an acrylic resin at a ratio of 60 to 90 / 40 to 10 is disclosed. method (Patent Document 1), but in terms of this method, the acrylic resin film has remarkable brittleness and brittleness (brittleness), and fractures occur during film production or reprocessing steps, and it is particularly difficult to stably produce Optical films for large liquid crystal display devices

[0007] In addition, there are also the following problems: acrylic resin films represented by polymethyl methacrylate (hereinafter, abbreviated as PMMA) usually lack heat resistance, and their shape will change during use at high temperatures, long-term use, etc.

This method also does not sufficiently improve the brittleness

[0012] Patent Document 3 also describes an example of adding a plasticizer, but the originally necessary heat resistance is deteriorated, and brittleness and heat resistance cannot be achieved at the same time.

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