Method for protecting glass sheets

Glass manufacturing – Processes – With coating

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C065S028000, C427S154000, C427S164000, C427S165000, C427S168000

Reexamination Certificate

active

06233972

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to protective coatings for glass sheets. More particularly, the present invention relates to a method for applying and removing a temporary protective coating to a glass sheet during manufacture of the sheet.
BACKGROUND OF THE INVENTION
Protection of sheet glass during the manufacturing process is necessary to prevent scratches and damage to the major surfaces of the glass. Scratching and damage to the glass sheet typically is inflicted by handling equipment or during cutting and edge grinding steps. Damage also occurs as a result of particles or chips contacting the surface of the sheet during initial cutting and handling of the sheet. One known method of protecting the glass sheet is to apply a polymer film on both major surfaces of the glass sheet. One major surface has a polymer film attached to the sheet with an adhesive, and this sheet is removed after the edge finishing of the sheet is completed. The other major surface has a film which is attached by static charge. This film is removed prior to the finishing process.
While the adhesive backed film does protect the surface from scratching induced by the handling equipment, it causes other problems. One problem associated with the adhesive backed film is the build up of glass chips during the edge finishing process which causes scratching of the glass near the edge due to chips entrapped in polymer caught in the finishing equipment. Another problem with the adhesive backed polymer film is adhesive residue.
It would be desirable to provide a temporary protective coating early in the glass sheet manufacturing process that could easily removed after processing of the glass. It would be useful if the coating could be applied at a point during the manufacturing process wherein a separate, additional manufacturing step was not required. Finally, it would be advantageous to have a coating that is not environmentally harmful.
PRIOR ART
Canadian Patent No. 811,098 describes the use of hydroxyethyl cellulose and polyvinyl alcohol (PVA) to produce temporary coatings on glass. This patent specifically teaches that when solutions of these polymers are applied by spraying, the glass should be at a temperature of below about 95° C. to avoid flash evaporation of the water and consequent formation of a film of poor properties. That is, the patent teaches that the glass should have a temperature less than the boiling point of water.
In direct contrast, in accordance with the present invention, it has been found that the temperature of the glass needs to be substantially above the boiling point of water to produce coatings which are able to withstanding washing with water whose temperature is less than 20° C.
As shown in Example 6 below, a PVA solution applied to glass at room temperature resulted in a coating that could be removed using water having a temperature of 10° C. As shown in Examples 4-5, when the same PVA solution was applied to glass having a temperature above 200° C., the coating was not removed by washing with 10° C. water, but was removed with water having a temperature of 90° C. The following table summarizes these results which distinguish the present invention from the disclosure of Canadian Patent No. 811,098:
Removal of coating with
Removal of coating with
water whose
water whose
temperature is less than
temperature is above
Glass Temperature
20° C.
60° C.
Above about
No
Yes
200° C.
Below 100° C.
Yes
Yes
SUMMARY OF INVENTION
Accordingly, the present invention generally provides a method of protecting a glass sheet from scratching, abrasion and the deposition of glass chips and other contaminants comprising depositing a solution of water and a polymer onto at least one major surface of the glass sheet after formation of the glass sheet. Preferably, during the deposition step, the sheet is at a temperature sufficient to crosslink the polymer and form a protective layer that is generally insoluble in water at a temperature below about 10° C., preferably below about 20° C. It is also preferred that the protective layer is soluble in water at a temperature above about 60° C., preferably above about 80° C., so that the protective layer can be rinsed from the glass sheet at a point in the production process in which the protect layer is not required. This can be done immediately before final inspection of the glass. Alternatively, if desired, the protective layer can remain on the sheet during shipping and rinsed off in water after shipping.
In a preferred embodiment, the solution is deposited by spraying and the polymer consists of polyvinyl alcohol. Preferably, the solution is deposited immediately after forming the glass sheet and the temperature of the glass sheet is above about 200° C. and below about 450° C.
Several important advantages will be appreciated from the foregoing summary. One advantage of the present invention is that temporary protective coatings can be provided for glass sheets that protect the glass sheets from scratches, abrasion, chips and contaminants during the glass manufacturing process, particularly during cutting and edge grinding. Another advantage is that the coating can be relatively easily removed by rinsing in water above about 60° C., preferably above about 80° C. Additional features and advantages of the invention will be set forth in the description which follows. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
DETAILED DESCRIPTION
The present invention is directed to providing a protective layer on a sheet of glass. Preferably, the protective layer is provided early in the manufacturing process so that the sheet is protected from scratching, abrasion, chips and contamination during subsequent processing steps. For example, in a process in which the sheet of glass is drawn by a drawing apparatus, it is preferred that the solution is deposited immediately after drawing.
It is essential that the solution is deposited at a temperature to form a protective layer that can subsequently be removed by rinsing with hot water, but can not removed by warm or cold water. As used herein, hot water is water that is at a temperature greater than about 60° C., preferably about 80° C., and warm or cold water is water that is at a temperature below about 10° C., preferably below about 20° C.
The solution of water and polymer can be applied to the glass sheet in any convenient way. For example, the solution can be rolled, brushed, or applied by a doctor blade. In experiments in which a glass sheet was dipped into solutions of polyvinyl alcohol and water, the coatings in these experiments were all soluble in 10° C. water within 1 minute. In a preferred embodiment, the coating is sprayed on in solution form.
Applicants experimented with several materials in an effort to provide a temporary protective coating on flat glass sheets that could be removed without damage to the glass or without the use of pernicious chemicals. Inorganic materials were excluded because the reactive nature of inorganic coatings attacked the surface of the glass. Also materials containing sodium were excluded because sodium causes problems for certain end uses of flat glass, for example, thin film transistors. Experiments were performed with simple and complex sugars and starches, but these materials either decomposed at higher temperatures, or were soluble in water at temperatures below about 10° C.
The following non-limiting examples serve to illustrate the principles of the present invention. In each of the examples a Binks spray gun attached to an air line was used to deposit a polyvinyl alcohol (PVA) solution onto a heated glass substrate. The glass substrates were Corning 1737 glass samples. In each of the examples the solutions were made up of 3 weight percent PVA in deionized water. The glass samples were heated to the temperatures indicated in each example.
Three different hydrolyzed grades of PVA were utilized

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Method for protecting glass sheets does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method for protecting glass sheets, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for protecting glass sheets will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-2557218

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.