Patented Apr. 6, 1948 2,439,108

UNITED‘ ‘STATES ,PATENT OFFICE

coa'rmo wrrn POLYVINYL ALco'no’i." Henry C. Staehle, Rochester, N. Y., assignm- ‘to ’ Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application September 11, 1943, ' Serial No. 502,044 6 Claims.‘ (Cl. 117-62) 1 , 2 The present invention relates to a method of One object of my invention is to provide a coating with polyvinyl alcohol in which a boron polyvinyl alcohol coating solution which, may be‘ ~ ‘compound is incorporated in the coating compo quickly set upon coating the composition onto a sition and the coating resulting therefrom is surface merely by fuming with a gaseous basic fumed with a volatile base such as ammonia. material. Another object of the inventiom is to" Polyvinyl alcohol has been suggested for many provide a method of coating materials with poly and various uses as that material is of interest vinyl alcohol in which warming of the coating because of its water-solubility characteristics. composition is unnecessary and .yet setting It has been recognized in the art that it is a thereof is obtained. A further object of my in distinct advantage in the making of polyvinyl al 10 vention is to provide. a method of setting‘or gell cohol products to be able to set polyvinyl alcohol, ingcoating compositions which willallow the used in making those products, rapidly. at the toleration of gelation in those compositions with desired time. Various methods have been sug '» out'any detrimental effect to the setting proper gested for accomplishing this setting or semi ties thereof. ‘A still further object of the inven solidifying of the polyvinyl alcohol in aqueous 15 tion is to provide a method of setting polyvinyl solution after it has been formed or placed where alcohol compositions which is effective not only it was to be used. , ‘ with compositions made using high viscosity In order to thus hold the polyvinyl alcohol and polyvinyl alcohols but also compositions in which aqueous solution to the desired form, gelling low vlscosity polyvinyl alcohol is‘ employed in agents have been previously suggested.‘ Those whole or in part. - ‘ " gelling agents which have been mentioned up to I have found that by incorporating a boron now have had the effect of converting the poly compound in an aqueous solution of polyvinyl vinyl alcohol in aqueous solution into a thermo alcohol at a pH of not more than 6 that a com! reversible gel. In order to use compositions of position is obtained which may be coated out this nature, it has been necessary to warm up 25 onto a surface and by fuming the coating with the coating composition to impart ?uidity there a volatile basic material such as ammonia, meth to and, after coating out the composition upon ylamine or ethylamine the coating is almost im a surface, the coating has been chilled for the mediately set and, therefore, there is no distor purpose ‘of gelling or setting it. These previous tion or slipping. away of the coating obtained. gelling or setting agents, although found to be 30 After the polyvinyl alcohol coating has been set, useful in certain connections, have‘not gone into it may be easily cured by drying thus leaving a extensive use due to the limitations of one sort coating of substantial permanence and evenness ‘ or another met with in coating compositions de- ' thereon. My invention is characterized‘by the pending upon those prior art jelling agents to setting of. polyvinyl’ alcohol coating compositions accomplish the setting of the aqueous polyvinyl in which boron is. present, which compositions, alcohol. One of v‘the disadvantages‘of the poly . after being coated out. are fumed with ammonia vinyl alcohol coating compositions containing a or some other gaseous base. Upon drying of the gelling agent as suggested by the prior art is ‘ coating, the excess ammonia is driven off so that that it does not set as rapidly as gelatin upon a firm transparent coating is obtained. chilling. Therefore, there is more danger of 40 VMy invention’ contemplates the use of boron distortion and ?ow than in cases where gelatin compounds‘ generally for this hardening‘ opera is employed for this purpose. Another disad > tion. Some of the‘boron' compounds which have vantage of prior polyvinyl alcohol coating com been found to be suitable are borax, sodium positions is that the gelling agent therein has metaborate, sodium perborate, boric acid, or been found to lose its‘ effectiveness in the pres in . fact, any water-soluble boron compound.‘ ence of gelatin or other colloidal material. In It is’ an essential feature , of my invention working with photographicemulsions, it is‘di?i that the boron compounds are incorporated in cult to gell the polyvinyl alcohol which is em the polyvinyl alcohol'solution at an acid pH such ployed as the protective colloid when gelatin has as obtained_ by the use of ‘a slight excess of been added thereto. Another disadvantage of to acetic acid. 1 After the boron compound has the prior attempts to set coatings of emulsions ~ been incorporated in the coating composition. which employ polyvinyl alcohol as the carrier it may be coated out ‘onto a smooth surface such - for the silver halide is that low viscosity poly \as paper, metal, glass, Celluloid, cellulose acetate vinyl alcohols employed in ‘this connection give sheeting or the like andpimmediate setting is. ob weak gels. , 55 tainedby the fuming operation without the ne 2,439,108 3 4 cessity of any change in temperature. "The acetic‘ acid so as to be just acid to litmus. The‘ polyvinyl alcohol sets into a rigid, non-tacky, resulting composition was of slightly higher vis clear gel which can be dried in any position, the cosity than before the addition of the borax but coating drying down to a clear, transparent, it was sufficiently ?uid ‘to be readily suitable for tough ?lm. » coating. The composition was thinly coated on a The proportion of boron compound‘ which is ,i glass surface and the~layer was then subjectcd I necessary to impart setting characteristics to the to the action of ammonia vapor. The coating polyvinyl alcohol solution is rather small. Pro liquid immediately set and was then dried by portions of 1% ' or even less of boron compound treatment with a current of warm dry air. A based on the weight of polyvinyl alcohol have 50' clear transparent coat of polyvinyl alcohol was been found to be suitable. I have found that obtained, proportions of boron compounds within‘ the range My invention contemplates the use of poly a. of 1‘ to 6%, based on the weight of the polyvinyl vinyl alcohols of various viscosities as the set alcohol have exhibited satisfactory properties and ting e?ect is ‘useful on low viscosity polyvinyl ordinarily the amount of boron compound added alcohols as well as those-of high viscosity. Where will be within this range. My inventiomhow _, low viscosity polyvinyl alcohols are employed, ever, is only limited to an amount of boron com the concentration may be less or it may be pound which will give a. setting e?ect when a , greater than in cases‘ where the higher viscosity coating thereof is fumed with ammonia vapors. polyvinyl alcohols’ are employed. If desired, If desired, larger quantities of boron compounds 20 other agents, such as gelatin, may be mixed with than those‘ speci?ed may be employed but ordi the polyvinyl ‘alcohol as the gelatin has little, narily the use of too great an amount of boron if any effect upon the setting action of the borax compound with the polyvinyl alcohol is not pre ammonia treatment. \ ferred because of the formation ,of‘a' thermore- ‘ ' Coatings in accordance with my invention may versible gel thereby. This necessitates warming 25 be employed for various purposes where a. thin of the polyvinyl alcohol coating composition, in’ . transparent layer is desired. For instance, poly ‘ use, which is not necessary where the proportion vinyl alcohol is suitable for use in light ?lters but of boron compound is restricted to that which up to now the di?iculties involved in the manu will not have this e?ect upon the polyvinyl alco facture have precluded its use therefor. Also' hol. I have noted that the addition of the boron 30 other instances where a very thin transparent compound does increase the viscosity of the poly coating would be desirable would lit in with my vinyl‘ alcohol solution some but if the proportion invention. , of boron compound used is kept to a minimum, My invention contemplates not only the use this increase in viscosity is of little in?uence on of polyvinyl alcohol but also the use of hydrolyzed the process. My‘ invention. however, contem ‘polyvinyl esters in which the major portion is ' plates both the use of proportions of boron com / polyvinyl alcohol. The description herein of the pound which will not appreciably affect the vis use of polyvinyl alcohol is to be understood as cosity of the polyvinyl alcohol and also higher applicable to both partially hydrolyzed polyvinyl proportions which do exhibit that effect. The pH esters, the major portion of which is polyvinyl of the resulting polyvinyl alcohol coating compo 40 alcohol, and to the substantially completely hy sition should be on the acid side and should pref drolyzed polyvinyl esters. erably be 6 or less. If’ the pH is not kept down, I claim: _ an undesirable viscosity increase will be obtained 1. A method of applying a coatingv of a poly which interferes with coating operations. vinyl ester, which has been hydrolyzed until a The setting e?ect, in accordance with my in 45 large portion thereof is polyvinyl alcohol, to the vention, is accomplished \by fuming the coating surface of a sheet which comprises forming a obtained with a volatile organic base. The most composition by dissolving in an aqueous solution commonly known compounds characterized by a thereof 1-6% of a water-soluble boron compound this designation are ammonia, methylamine and selected from the group consisting of the alkali ethylamine and any one of these materials would 50 metal borates and boric acid, coating out the be suitable in that connection. The setting _ composition thus formed at a pH of not more. action is most effective when the coatings or than 6 in a layer having a- thickness less than layers resulting from the coating composition are .005 inch upon the sheet, fuming the coating with ‘thin, preferably less than .005" in thickness. ammonia gas and drying the coating thus ob For instance, if a coating of .001" is applied to a tained. I surface" the setting of the coating takes place 2. A method of applying‘ coatings which com 7 almost immediately upon fuming with the vola prises dissolving in an aqueous solution of a poly tile base or ammonia. ' My invention is also ap vinyl compound selected from the group consist plicable when thicker coatings or layers are ap ing of the partially hydrolyzed polyvinyl esters, , plied. .However', a little more time is necessary 60 the major portion of which is polyvinyl alcohol, to assure even distributionv of the ammonia or and polyvinyl alcohol, approximately .1—6%, based base into the coating layer thus-resulting in set on the weight of the, polyvinyl compound, of a ting. In ordinary manufacturing operations water-soluble boron compound selected from the where speedy coating is desirable, it would be group consisting of the alkali metal borates and preferable to apply the polyvinyl alcohol coating boric acid, coating out the composition thus composition as a rather thin layer. ' formed at a pH of not more than 6 in a layer The following example is illustrative of my in having a thickness of less than .005 inch, fuming vention: '1- i - the coating with a, nitrogen base selected from A polyvinyl alcohol coating composition was the group consisting of ammonia, methylamine prepared by adding to 100 cc. of a 10% aqueous 70 and ethylamlne gas, and drying the coating thus solution of polyvinyl alcohol having a viscosity of obtained. ' 60 seconds. one cc. of a 4% solution of borax 3. A method of applying polyvinyl alcohol coat which has been just acidi?ed with acetic acid. ings upon the surface of a ShGLJ which comprises Before addition of the acidi?ed borax the poly dissolving approximately l-6%, based on the vinyl alcohol solution was also acidi?ed with 75 weight of the polyvinyl alcohol, of a water-soluble

I 2,489,108 boron compound selected from the group consist mately 1-6%, based on the weight of the ‘poly ing of the alkali metal borates and boric acid in vinyl alcohol, of a water-soluble boron compound an aqueous solution of polyvinyl alcohol, coating selected from the group consisting‘ of the alkali out the composition thus formed at a pH ,of not metal borates and borlc acid coating out the com- ‘ more than 6 in a layer having a thickness of less position thus formed at a pH of not more than than_;_l.005 inch upon the sheeting, fuming the 6 on the surface 'of the glass in a layer having a coating with a volatile base selected from the thicknessv less than_.005 inch, fuming the coating group consisting of ammonia, methylamine'and with ammonia gas and drying. ethylamine gas, and drying the coating thus ob—' . HENRY C. STAEHLE. tained. ' 10 4. A method of applying a‘ polyvinyl alcohol IqtEFERENCES CITED coating to the surface of sheeting which com: The following references are of record in the prises applying an aqueous solution of polyvinyl ?le of this patent: alcohol, approximately 1-6%, based on the weight of the polyvinyl alcohol,- or borax and 15 ‘ UNITEDYSTA'I’ES PATENTS su?lcient acetic acid to assure a pH of not more Number Name Date than 6, to form a layer having a thickness less 1,920,564 ‘ Jochum ______Aug. 1,‘ 1933 than .005 inch, fuming the coating with ammonia 1,998,544 Jochum et al ______Apr. 23, 1935 gas and drying. 1 ' ' 2,251,296 Shipp ______“Aug. 51, 1941 5. A method of applying a polyvinyl alcohol 20' 2,278,902 Spanagel ______- Apr. '1, 1942 coating to the surface of sheeting which com 2,300,074 Strain _-.______Oct. 27, 1942 prises dissolving approximately 1-6%, based on ' 2,324,601 ‘ Spanagei ______July 20, 1943 > the weight of the polyvinyl alcohol, of boric acid 2,330,314 Schwartz ______Sept. 28, 1943 in an aqueous solution of polyvinyl alcohol, coat ing out the composition thus formed at a pH of , FOREIGN PATENTS . not more than 6 in a layer having a thickness less Number Country Date than .005 inch upon the surface of the sheeting. 399,905 Great Britain ..... __ Oct, 19, 1933 fuming the coating with ammonia gas and dry ing the coating thus obtained. 4 OTHER REFERENCES 6. A method of applying a polyvinyl alcohol 30 R. 8: H. Technical Bulletin, Polyvinyl Acetate, coating to glass which comprises dissolving in an Mar. 1941. aqueous solution of polyvinyl alcohol, approxi Rubber Age, Nov. 1943, (page 133).