Base Film of Modified Polyvinyl Alcohol and Its Preparation Method and Polarizer

Abstract

The present invention provides a base film of modified polyvinyl alcohol as well as a method for preparing the base film of modified polyvinyl alcohol and a polarizer made from the base film. The method includes steps of: (1) executing surface graft modification of nano-silicon dioxides with fluorinated silane to obtain modified nano-silicon dioxide powders; (2) adding the modified nano-silicon dioxide powders obtained from the step (1) to an aqueous solution of polyvinyl alcohol polymers, in order to prepare a composite solution of polyvinyl alcohol polymers; and (3) pouring the composite solution of polyvinyl alcohol polymers prepared from the step (2) onto a surface of a casting substrate to obtain a base film of modified polyvinyl alcohol (PVA). The present invention enhances the heat and humidity resistances and the stability of the PVA base film, and improves its mechanical performance and sticking-resistance.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of Invention[0002]The present invention relates to a base film, of polyvinyl alcohol and more particularly to a base film of modified polyvinyl alcohol as well as its preparation method and a polarizer prepared from the base film of modified polyvinyl alcohol.[0003]2. Related Art[0004]Polarizer is one of the essential important components in a liquid crystal display (LCD), and its function is to convert natural light into polarized light, in order to cooperate with liquid crystal molecules twisted to control light passing and presentation of color signals. An existing polarizer used in a LCD is mostly made of a highly oriented high polymer such as a base film of polyvinyl alcohol (PVA) as its substrate, dyed with various types of dichroic dyes, extended under a certain humidity and temperature, and then a layer of triacetate cellulose (TAC) film with high light transmission rate, excellent waterproof characteristic and a certain degree of me...

AI Technical Summary

Benefits of technology

[0049]In existing processes, in order that the PVA base film is protected because of its hydrophilic property, a protective film of triacetate cellulose (TAC) with high light transmission rate, excellent waterproof characteristic and a certain degree of mechanical strength is composited on each of two sides of the PVA base film. However, the size of this type of protective film can easily be changed under high temperatures and humidity, and thus its mechanical performance is weakened and its protective performance is also affected. The present invention can substantially enhance the heat and humidity resistances as well as the mechanical strength of the PVA base film, even that the TAC film can be omitted (i.e. the PVA base film can be directly used as a polarizer). Furthermore, a certain degree of roughness can be formed on the surface of the PVA base film by controlling the sizes of nano-silicon dioxides, and thus images are diffused and reflected by the concave and convex shapes thereof, in order to prevent the light from being overly-concentrated to cause discomfort in viewing, as a result, an anti-glare function is achieved.

Problems solved by technology

Nevertheless, iodine polarizers are comparatively less resistant to heat and water.

Therefore, modification of PVA base films for development of polarizers with excellent optical and durability performances for LCDs is a technical difficulty encountered currently.

Furthermore, iodine molecular structure is easily damaged under high temperatures and humidity, so that iodine polarizers are less humidity and heat resistant with poor mechanical performance.

Generally, they may only meet testing conditions of 80° C.×500 hrs or 60° C.×90% RH×500 hrs, and may easily become warped and peeled off, resulting in limiting their application range.

And a structure of iodine molecules 2 may be easily damaged under high temperatures and humidity.

Therefore, the PVA base film of the iodine polarizer is relatively less stable under high temperatures and humidity.

Nevertheless, boric acids increase the toughness of the PVA base film which will limit its extension percentage during a stretching process.

Others use vacuum coating or ion sputtering method to have silicon dioxides (SiO2) plated on the PVA base film in order to improve its heat and humidity resistances, but costs for both coating methods of silicon dioxide film are relatively high, and a problem with compatibility between silicon dioxides and the PVA base film also arises.

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