US1994269A - Coating of glass and other objects with varnish film - Google Patents

Description

March 12, 1935. c. w. BONNIKSEN 1,994,269

COATING OF GLASS AND OTHER OBJECTS WITH VARNISH FILM Filed Aug. 4, 1952 45 fects therein.

Patented. Mar. 12, 1935 UNITED STATES PATENT OFF ICE COATING F GLASS AND OTHER OBJECTS WITH VARNISH FILM Cyril Wilfred Bonniksen, Slough, England, asv mot to Protectoglass Limited, London, Eng- Application August 4, 1932, Serial No. 627,501 In Great Britain August 13, 1931 9 Claims. (CI. 91-68) purpose which is in'view is the employment of glass so coated in connection withthe manufacture of so-called safety glass, that is to say glass combined with layers of a tough material, such as celluloid, with the object of preventing I splinters from flying in the event of fracture.

I According to the present lnventiona process for coating objects (for example of glass) with a varnish-fllmconsists in applying a fllm.; of varnish dissolved in a solvent and thereafter treating the coated object with a treating-liquid which is capable of mixingv with the solvent but not with the varnish.

The varnish may consist of a solution of a cellulose-ester (for example celluloid) dissolved in a solvent therefor (for example acetone). I

The invention comprises a process for coatin sheet material (for example glass) with celluloseester films characterized by feeding a film of viscous liquid cellulose-ester varnish downwardly upon a surface of the sheet which is moving transversely relatively to the film and thereafter immersing the sheet in a nearly horizontal positionin a bath of a treating-liquid which is capable of mixing with the solvent but not with the varnish.

The treating liquid may be one which has a boiling point markedly different from that of the solvent which it is to dissolve, and the solvent be separated from the treating liquid after its treatment of the coating by fractional evaporation, with or without re-use of the treatingliquid and/or solvent cyclically.

One great advantage of treating the film in this way for the removal of the solvent is that evaporation of vthe solvent into the atmosphere is avoided, thereby obviating the use of expensive methods of collecting the evaporated solvent. Another great advantage lies in the fact that there is no opportunity for specks o i dust out of the atmosphere to settle upon the film and cause 'de- It has been found that thepresent invention provides a means of obviating one of the defects which is most common in films of thick or heavy varnishes and particularly varnishes such as celluloid varnishes in which solvents such as .acetone are employed. This defect consists in the development of bubbles in the varnish film as it dries. It has been found that such bubbles;

are' due'to gases, particularly air; which become absorbed in the acetone or other solvent, and are released into the varnish-film as the solvent evaporates and ceases to'be able to retain them' in solution. Both acetone and the treating liquid, such as castor oil, employed according to the present process readil'ydissolve air, but if contained gases, such as air, are removed from the treating liquid by subjecting it to a vacuum before use,pthe occurrence of bubbles is greatly reduced while if gases such as air are also removed from the varnish under a vacuum the occurrence of bubbles may be entirely eliminated.

The occurrence of bubbles in thick celluloid varnish-films has hitherto been inevitable upon drying, but it is found according to the present invention that it is possible to apply films of a thickness as great as five thousandths of an inch .or more and to dry them without bubbles.

The following is a description by way of example of one form of the process according to the present invention with reference to the accompanying drawing which shows diagrammatically part of an apparatus adapted to carry the invention into effect:-

In the drawing 11 represents a hopper having a feed slot 12 in the bottom thereof through which a film 13 of cellulose-ester solution contained in the hopper 11 may descend. The film 13 descends into contact with a rotating roller 14 below the feed slot 12 except whenit meets a transversely moving sheet of glass 15 propelled by rollers 16, 17, in which case it becomes attached to the sheet and coated thereon.

The glass 15 which is fed beneath the feed slot 12 is glass which has first been carefully cleaned and rendered entirely free of grease and all foreign substances so that the cellulose film will readily adhere to it. This may be efiected bypassing it through a washing machine such as is commonly employed for washing glass for photographic plates before applying the sensitive emulsion thereto. The rate of feed of the glass by the rollers 16, 17 is arranged'to be very slight- .oil. The angle at which the sheets are caused to dip into the bath are such that the still-liquid film of cellulose-ester solution will not run appreciably down the face of the glass.

The roller 14 which receives excess cellulose film engages a doctor 20 which scrapes off the excess and this is collected and made up again into fresh solution for re-use. Covers 21, 22 are provided over the apparatus to keep out dust.

The solution in the hopper 11 may conveniently consist of celluloid dissolved in acetone. The strength of the solution will depend upon the temperature at which it is fed from the slot, but good results have been obtained by making a celluloid solution containing about 30% of celluloid and 70% acetone and cooling this to a temperature of- 8 C. before applying it to the glass. Cooling reduces evaporation of acetone prior to passage into the castor oil bath 19.

In order to prevent the production of air bubbles on the fihn it is important that the celluloid solution in the hopper ll-should be air free, and to this end it should be submitted to a vacuum in a treatment tank prior to passage into the hopper 11. The obvious precautions of filtering the solution so as to render it free of contained specks and uniform in consistency need also, of course, to be observed.

The. castor oil flows through the bath 19 in a direction opposite to the direction of passage of the glass sheets as shown by the arrows in the figure and is withdrawn through outlets 23, 24. The temperature ofthe bath is kept at about 35 C. and the length of the bath and the rate of passage of the glass through it is such that the glass is immersed in the castor oil for about forty minutes. With a rate of travel of the glass of 15 inches per minute this corresponds to a length cyclically. This is secured by passing the outflow from the outlets 23, 24 to a vacuum tank where it is subjected to reduced pressure. The reduced pressure serves to evaporate from the castor oil contained acetone as well as to remove any air which it has absorbed and the air-free, solventfree castor oil is then returned to the bath 19.

After passage out of the bath 19 the glass is preferably passed into a second and shorter bath of castor oil heated to a temperature of about C. for the purpose of extracting the final traces of acetone. Thereafter it'goes through a steam-heated oven where it attains a temperature of between 80 and C. Finally the conveyor 18 takes the glass up to a series of rubber covered squeegee rollers which remove excess castor oil. The coating of the glass is then complete. It may be used for manufacturing safety glass if desired as described in United States application No. 627,502, filed August 4, 1932.

The thickness of the film applied to the glass may be very substantial without leading to the production of bubbles and apreferred thickness for the purpose of manufacturing safety glass is 0.008 of an inch.

' hol or even water. Petrol and water tend, however, to the production of bubbles in the film, and alcohol tends to leave a flabby coating.

Castor oil is a solvent for camphor as well as for acetone and it is found that camphor in the celluloid is extracted with the castor oil in addition to its extraction of acetone. Consequently a 1. A process for coating sheet material with a cellulose-ester film consisting in preparing a solution of cellulose-ester in a solvent therefor, removing air from the solution by sub ecting it to a vacuum, feeding a film of said sol ion downwardly upon a surface of the sheet material while moving the sheet transversely relatively to'the film, thereafter immersing the sheet in a bath of a vegetable oil which has been freed of air under vacuum so as to dissolve solvent from the cellulose-ester film without producing bubbles therein and finally removing the vegetable oil.

2. A process for coating glass sheets with a cellulose-ester film consisting in preparing a solution of cellulose-ester in a solvent therefor, re-

moving airfrom the solution by subjecting it to a vacuum, feeding a film of said solution downwardly upon'a surface of the glass while moving the sheet transversely relatively to the film, thereafter immersing the sheet in a bath of a vegetable oil which has been freed of air under vacuum so as to dissolve solvent from the cellulose-ester film without producing bubbles therein and finally removing the vegetable oil.

3. A process for coating sheet material as claimed in claim 1, wherein the solvent employed for the cellulose-ester is one having a, boiling point markedly different from that of the vegetable oil and is separated from the vegetable oil after application of the latter to the sheet material by fractional evaporation.

' 4. A process for coating glass asclaimed in claim 2, wherein the solvent employed for the cellulose-ester is one having a boiling pointmarkedly different from that of the vegetable oil and is separated from the vegetable oil after application of the latter to the glass by fractional evaporation.

5. A process for coating sheet material with cellulose-ester films characterized by feeding a film of viscous liquid cellulose-ester varnish downwardly upon a surface of the sheet which is moving transversely relatively to the film and thereafter immersing the sheet in a nearly horizontal position in a bath of a treating-liquid which is capable of mixing with the solvent but not with the varnish and subjecting the treating liquid to a vacuum to remove contained ,gases, before immersing the sheet therein.

6. A process for coating glass sheets with cellulose-ester films, characterized by feeding a film of viscous liquid cellulose-ester varnish downwardly upon a surface of the glass sheet while moving said sheet transversely relatively to the filmsoastocoatthesheetwiththefilmand thereafter immersing the sheet in a nearly horizontal position in a bath. of a treating liquid which is capable of mixing with the solvent but not with the varnish and subjecting the treating liquid to a vacuum to remove contained gases, before immersing the sheet therein.

7. A process for coating objects with a varnish film consisting of taking varnish dissolved in a solvent, eliminating air therefrom by subjecting it to a vacuum, thereafter coating the object with the varnish, and finally treating the varnish with a treating liquid capable of mixing with the solvent but not with the varnish, so as to remove the solvent therefrom, the said treating liquid having the contained gases, such as air, removed therefrom by subjecting it to a vacuum before use.

8. A process for coating glass with a varnish film consisting of taking varnish dissolved in a solvent, eliminating air therefrom by subjecting it to a vacuum, thereafter coating the glass with the varnish, and finally treating the varnish with a treating liquid capable of mixing with the solvent but not with the varnish so as to remove the solvent therefrom, the said treating liquid having the contained gases, such as air, removed therefrom by subjecting it to a vacuum before use.

9. A process for coating objects with a cellulose-ester varnish consisting in first subjecting a solution of a cellulose-ester in a solvent therefor to a vaccum to eliminate air, thereafter applying the air-freed solution to the object, and finally removing the solvent by treating with a liquid capable of mixing with the solvent but not with the cellulose-ester, said liquid having the contained gases, such as air, removed from it by subjecting it to a vacuum before use.

CYRIL WILFREH) BONNIKSEN.

Images