Two-layer protective coating system for LCD glass

Abstract

Two-layer protective coating system for glass surfaces is disclosed. The base coating comprises at least one polysaccharide, and the top coating has a lower solubility in water than the base coating. The coating system provides good protection against contaminants and glass chips, good removability in mild cleaning condition, and extra water resistance during process steps where water is used as a cooling agent.

Description

FIELD OF THE INVENTION [0001] The present invention relates to the protection of glass surfaces, and in particular, to the temporary protection of the surfaces of glass sheets used in producing liquid crystal displays (LCDs). The invention is useful, for example, in protecting the glass sheets from being contaminated by ambient dirt or glass chips produced during the processing of the sheets, such as cutting, grinding, packing and transportation. In addition, the invention is useful in protecting the glass sheets from scratching. BACKGROUND OF THE INVENTION [0002] Many uses of glass, including glass for producing LCDs, require a very clean glass surface that is substantially free of dust and other organic and / or inorganic contaminants. When exposed to the environment, glass surface can quickly become contaminated with dust and other inorganic and / or organic ambient contaminants, with contamination being observed within a few hours. [0003] Current procedures used to cut and grind gla...

AI Technical Summary

Benefits of technology

[0133] A further advantage of the invention is that the surface of the glass sheet after removal of the coating has substantially the same chemistry and smoothness as it had prior to application of the coating. For example, the glass surface preferably has a RMS surface roughness less than or equal to 0.40 nanometers as measured by atomic force microscopy (AFM) after removal of the coating.

[0134] Moreover, the present invention makes it possible for the glass sheets to be packed closely to each other without or with minimal spacing material therebetween, because of the robust protection provided by the protective coating system of the present invention. And the extra second coating layer compared to a mono-layer coating increases the scratch resistance of the coating system.

[0135] The following examples provide further illustration of the present invention, and are not intended to limit the scope of the present invention to the specific embodiments described therein. E. EXAMPLES

[0136] In the following examples, glass sheets used for the testing were 1737 LCD glass samples (5″×5″×0.7 mm) produced by Corning Incorporated, Corning, N.Y. Each sheet was covered on one side with a polymer film attached with an adhesive, and the other major surface had a film attached by static charge. Both coatings were removed from glass sheets followed by pre-cleaning. All glass sheets were pre-cleaned before application of the coating compositions. Pre-cleaning of the glass sheets in the examples were carried out in accordance with the following procedure: (1) 2% SEMICLEAN KG was sprayed on the substrates or coatings and hand-scrubbing performed using a clean-room cloth; (2) the substrates or coatings were subjected to ultrasound cleaning (40 kHz, 2% SEMICLEAN KG, about 40° C.) for 15 minutes; and (3) the substrates or coatings were subjected to brush cleaning with 2% SEMICLEAN KG and deionized water, and spin-drying using a brush cleaner (ULTRATECH 605 Photomask / Substrate Cleaner).

[0137] Water contact angles were measured to evaluate cleanness of the glass surface and removability of coatings in the examples. It has the advantages of being quick and easy. The coatings of the present invention have lower surface energies than glass surface, thus higher water contact angle are observed when coating residues are present on the glass surface. For a substantially clean glass surface free of polymer residues and contaminants, the water contact angle should be extremely low due to the high surface energy of the clean glass surface.

[0138] In the following examples, the first coating compositions used were all Crystal Tex 627, which is a starch-containing aqueous product available from National Starch & Chemical Company, with 0.1% boric anhydride added. Thus the first protective coatings consisted essentially of starch. The first coating composition was sprayed onto a surface of a glass sheet pre-cleaned and pre-heated to about 200° C.

Problems solved by technology

When exposed to the environment, glass surface can quickly become contaminated with dust and other inorganic and / or organic ambient contaminants, with contamination being observed within a few hours.

Some of these particles irreversibly adhere to the clean glass surface, rendering the glass useless for many applications.

This is particularly a serious problem for LCD glass surfaces.

Although the adhesive-backed film protects the surface from scratching by the handling equipment, it causes other problems.

Another problem with this film is that it may leave an adhesive residue on the glass surface.

A further problem with the film approach is glass breakage during peeling of the film from the glass surface, especially for large and / or thin glass sheets.

However, few of them can be completely removed in a cleaning solution at a temperature as low as 40° C. in a typical manufacturing process.

However, the high water solubility of polysaccharides, especially starches, constitutes a potential drawback of this method.

Due to their high solubility in water, the polysaccharide coatings may be diminished during such stages, leading to reduced particle protection and scratch resistance.

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