US2371866A - Lacquer and like coating composition - Google Patents

Description

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LACQUER AND HIKE GOATING WMROSITION Gerald lit. Barrett, Winchester, Mass, as'signor to Monsanto Chemical Company, St. Louis, Ma, a corporation of Delaware No Drawing. Application April 16, N41,

Serial No. 383,797 1 (Cl. Mid-177) Claims.

This invention relates to improved lacquers and like coating compositions, and more particularly to cellulose ester lacquers, such as nitrocellulose coloration is believed to be caused by the corrosive action of one or more of the ingredients of the lacquer on the metal of the container in which it is stored. Thus, it is believed the discoloration of lacquers under storage conditions s due to contamination by dissolved iron or other metal or by other corrosion products of lacquer upon metals.

It isa, primary object of the present invention to prepare a lacquer which is iree of the above objection and which, upon being stored in metal containers, does not become discolored or contaminated in such a way as to result in an inferior and commercially undesirable product.

A further object of the invention is to provide a lacquer which is stable and not subject to gelation in the presence of lead containers, lead tubes, lead foil or lead pigments.

Still further objects and advantages of the invention will appear from the following description and appended claims.

The invention is in general carried out and the above objects are obtained by incorporating in the lacquer relatively small amounts of either partially or wholly neutralized oxalic acid or partially or wholly neutralized phosphorus acid, including phosphoruaortho and pyro phosphoric and alkyl phosphoric acids, the acids being neutralized to the desired extent eitherby orgrfic amines or by other alkalies or bases capable of yielding salts which are sufliciently soluble in the lacquer composition being treated to obtain the desired results. Organic amines, such as mono and diamyl amine and dibutyl amine are the most suitable bases for the purpose, since they form salts with oxalic and phosphorus acids whic'h are of ample solubility. In general amines of lower molecular weight result in salts of lower solu- ,-bility, and therefore are less desirable. However,

when ethyl phosphoric acids are used, it is even possible to employ caustic soda, as the sodium tions by incorporating therein small amounts of phosphoric acid or alkali salts thereof, such as various sodium or potassium phosphates, has been described in the patent to C. B. Gilbert lio. 2.008.641. found to be not nearly as efficient as the organic amine and like salts of oxalic and phosphorus acids which are the subject of this invention. Moreover, the sodium and potassium salts described by Gilbert are not sufiiciently soluble in the solvent mixtures generally employed in lacquers to be effective for the intended purpose.

Theeilectiveness of the salts of the present invention in arresting corrosion, and consequent discoloration, appears to depend on the formation of a thin film of insoluble metal salt, such as iron phosphate, pyrophosphate or the like, on the surface of the metal container. The resulting film, which is closely adherent to the metal surface, tends to stifie any further attack and is so thin as not to affect the original brightness of the metal. nature of the inhibitor anion and its concentration determine the degree of insolubility ofthe metal salt formed and possibly also the compactness and adhesion of the salt film, and therefore the effectiveness of inhibition. Moreover, the addition of an organic amine, or other suitable base essary for best results varies with the inhibitor,

ethyl phosphate is sufliciently soluble in lacquer "for most practical purposes.

to the lacquer, serves not only to decrease the acidity of the solution but to increase the concentration of the precipitating anion, thus favoring film formation by increasing the possibility of interaction between the anions and the metal ions and simultaneously decreasing the solubility of the protective salt formed.

The amount of addition agent or inhibitor necwith the intensity of corrosion-in the absence of inhibitor, and with the composition of the solution being treated. For example, any variation in composition may be expected. to change the solubility of the protective salt film and thereby change the concentration of anion necessary for effective and immediate formation of the protective film. As the presence of an excessive amount of water soluble material might be expected to increase the water sensitivityof the dried film solids formed by the lacquer coating, it is in general desirable to use the lowest quantity of inhibitor. adequate for continued protection. In the case of nitrocellulose lacquers, for example, from .1 to .2% of the acid. based on the weight of'the entire solution, when neutralized with a suitable base to the desired extent, is sufficientto prevent substantially all discoloration However, phosphoric acid has been 1 It has been found that both the or contamination, without detectable effect on the water resistance of the lacquer film. In the case of shellac solutions, however, it is usually necessary to employ larger amounts, e. g. from .7 to .8% of acid based on the weight of the solution, and as shellac is more water sensitive initially than nitrocellulose lacquers, these larger amounts may have a noticeable effect on the tendency of the dried shellac to whiten in water.

The amount of inhibitor necessary also depends on the previous history of the solution to be inhibited. Thus, a solution already badly contaminated with dissolved metal will consume the inhibitor by precipitation and require a correspondingly larger initial quantity. In general, however,

it is not practical to use more than about 1% of acid based on the weight of the solution.

The amount of base which should be used to neutralize the acid forming the inhibitor is variable within a rather wide range without affecting seriously the amount of inhibition. Thus it is possible to vary the amount of base from .15 to 1 equivalent of the acid. The most suitable-range, however, is from .15 to .6 equivalent, with a preferred ratio of about .3 equivalent. A lower ratio usually results in less inhibition, while higher ratios, especially when a large content of inhibitor is present, results in yellow to brown solutions. Thus, in general, decreasing the acidity of the lacquer solution tends to produce a yellowish coloration, which is irreversible and becomes intensified with time.

A further understanding of the invention will be derived from the following examples of lacquers and like coating compositions, t which small amounts of an inhibitor have been added:

Example I To a solution of one quarter second nitrocellulose having the composition:

. Per cent Nitrocellulose 40 Ethyl acetate 21.4 Butyl acetate 21.4 Denatured alcohol 17.2

v, f Example II To a solution of bleached de waxed shellac in anhydrous denatured alcohol containing 8 pounds of shellac per gallon of alcohol, was added .75% of pyrophosphoric acid'and'.6% of dibutyl amine,

dissolved in .45% of "denatured-alcohol} Tinned,

steel in contact with the solution remained bright.

In the absence of the inhibitor, however, the solution etched the tin plate rapidly and became discolored.

Example [II To a solution of colorless scrap Celluloid having the composition:

. Percent Celluloid i Butyl ace 10 Acetone Methyl ethyl ketone Denatured alcohol was added .1% of pyrophosphoric acid and .08% of mono amyl amine dissolved in .3% of denatured alcohol. The composition, when packaged in lead tubes, remained stable and fluid, whereas in the absence of the pyrophosphoric acid solution gelation occurred in a few hours.

Example IV To a solution of half second nitrocellulose having the composition:

Per cent Nitrocellulose 30 Ethyl acetate 30 Toluene 27 Denatured alcohol 13 was added .2% to 75% phosphoric acid and .07% of diamylamine. When contacted with steel or imperfectly tinned steel the solution did not discolor and the metal remained bright.

As tin plate in general is corroded by lacquer solutions less rapidly than steel, it is possible to use lower concentrations of inhibitor in solutions stored in tin containers. For example, as little as .015% of phosphoric or pyrophosphoric acid in a combination with a suitable amount of organic amine will usually give adequate protection from discoloration. Shellac solutions, however, usually require higher inhibitor concentrations, and also the use of tin or terne plate containers rather than uncoated steel.

01' the acids suitable for the purposes of this invention partially neutralized pyrophosphoric acid is preferred, as it may be employed in somewhat lower concentrations or with more corrosive solutions than-is possible in the case of orthophosphoric or ethyl phosphoric acid. Moreover, since-pyrophosphoric acid is tetra basic as well as being a stronger acid than orthophosphoric or ethyl phosphoric acid, it .is possible to employ a higher number of equivalents of organic amine or other suitable base than is the case with the other phosphoric acids'without encountering the undesirable yellow solutions obtained when acidity is too low.

Although pure pyrophosphoric acid is not ob tainable commercially, it is possible to use almost as effectively commercial syrupy tetra phosphoric acid which has been diluted to a phosphorus pentoxide content of about 79.6%, the theoretical value for pyrophosphoric acid. Contrary to expectation, the salts ofpyrophosphoric acid are relatively stable and do not form orthophosphoric acid. Thus, aminated pyrophosphoric acid, even after prolonged heating of a concentrated solution in 95% denatured alcohol, retains its greater effectiveness as compared with similar solutions of orthophosphoric acid.

The partially neutralized acids of the present inventionare primarily of value in lacquer solu- 1 lead pigments, and have a limited anti-gelling action in the presence of some reactive pigments. The efiect on pigmented lacquers is demonstrated in the following example:

Example V To a grind of 1 pounds of Chinese blue in 1 gallon of nitrocellulose solution containing 4 hol. which sets to a gel on aging, the phosphated I lose ester and a solvent therefor, said solution.

ounces oi heavy dope nitrocellulose in 1 gallon of a mixed solvent having the composition:

Ethyl acetate--. per cent by volume 20 Butyl acetate per cent 20 Toluen do 50 Denatured alcohol do was added .2% pyrophosphoric acid and .15% of dibutyl amine dissolved in .5% denatured alco- As compared with the untreated grind,

" taining natural acidic resins, particularly those I soluble in alcohols or mixtures of alcohols with other organic solvents, such as shellac, Manila containing not more than-about 1% of an 'alkyl phosphoric acid which has been at least partially neutralized by an organic amine, said neutralized acid being present in an amount suflicient to stabilize said solution against deterioration ordiscolo'ration in the presence of metals.

6. A nitrocellulose solution comprising nitrocellulose and a solvent therefor, said solution having added thereto about .14% of pyrophosphoric acid and about .11% of dibutyl amine.

7. A celluloid solution comprising colorlesscelluloid and a solvent therefor, said solution having added thereto about .'1% of pyrophosphoric acid and 118% of mono amyl amine.

8. A nitrocellulose solution comprising nitro- 'cellulose and a solvent therefor, said solution resin, pontianac resin,- kauri resin and other copal resins. Moreover, the invention isalso concerned with lacquers or solutions containing mixtures of cellulose derivatives fid resins of the above type.

It is to be unders d that the invention is not limited in its application to the details described herein, since the invention is capable of other embodiments-and of being practiced or carried out in various ways. Also it-is to be understood, that the phraseology or terminology employed herein is for the purp se of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

What I claim is:

1. A cellulose ester solution comprising a cellulose ester and a solvent therefor, said solution containing a relatively small amount of an acid of phbsphorus which has been at least partially neutralized by an organic amine.

2. A cellulose ester solution comprising a cellulose ester and a solvent therefor, said solution containing not more than about 1% by weight of an acid of phosphorus which has been at least partially neutralized by an organic amine; said neutralized acid being present in an amount suilicient to stabilize said solution against deteriora-- 4 acid being present in an amount 'sufliicent to stabilize said solution against deterioration or discoloration in the presence of metals.

4. A cellulose ester solution comprising a cellulose ester and a solvent therefor, said solution containing not more than about 1% of orthophos-' phoric acid which has been at least partially neu- ,tralized by an organic amine, said neutralized acid being present in an amount sufllcient stabilize said solution against deterioration or discoloration in the presence of metals.

' 5. A cellulose ester solution comprising acelluhaving added thereto about .2% of 75% phosphoric acid and .0'7% of diamylamine.

9. A shellac solution comprising shellac andsolvent therefor, said solution having added thereto about .75% of pyrophosphoric acid and .6% of dibutyl amine.

10. A pigmented nitrocellulose solution comprising nitrocellulose, a solvent therefor and Chinese blue, said solution having added thereto,

about .2% of pyrophosphoric acid and .15% of dibutyl amine.

11. A cellulose ester solution comprising a cellulose ester and a solvent therefor, said solution having added thereto from. .-'1 to .2% of an acid of phosphorus and from .15 to .6 equivalent of i an organic amine. l 12. A cellulose estersolution comprising a cellulose ester and a solvent therefor, said solution having added thereto not more than about 1% by weight of an acid of phosphorus which has been reacted with from .15'to 1 equivalent ofian organic amine, said reaction product being present in an amountsufllcient to stabilize said solution against deterioration or discoloration in the presenc of metals.

13. The method of stabilizing a cellulose ester solution against discoloration when contacting metal which comprises incorporating in said soluderivative which is soluble in organic solvents, a natural acidic resin which is soluble in alcohols and in-mixtures of alcohols and other organic solvents, and a solvent for said-derivative and said resin, said solution containing a relatively small amount of an acid of phosphorus which has been at least partially neutralized by an organic amine, said neutralized acid being present in an amount'suflicient to stabilize said solution against deterioration or discoloration in the presence of metals,

- GERALD R. BARRETT.