US2917391A - Organic coating composition - Google Patents

Description

United States Patent C ORGANIC COATING COMPOSITION Thomas L. Canuifr and Alfred E, Balocca, Wheaton, Ill., assignors to American Can Company, New York, N.Y., a corporation of New Jersey No Drawing. Application May 28, 1953 Serial No. 358,170

6 Claims. (Cl. 99-181) The present invention relates to a novel, economical and effective coating composition. More particularly the present invention pertains to a modified styrene-diolefin copolymer coating composition for sheet metal, and especially containers fabricated from ferrous metal sheets.

The use of organic coatings on sheet metal as a protection therefor is old and well known. However due to the unique problems in can manufacture, relatively few of theknown coating compositions are applicable to can making. The maximum thickness of the coating on metal cans is but a fraction of the usual thickness of the coatings on other metal surfaces. This extremely thin coating must be hard so as to resist marring during abuse in fabrication and handling of the cans; it must be flexible in order to form a continuous adherent film over can parts that have been fabricated by drawing or bending; and. it must be substantially impervious to chemical attack. In relation to the last requirement, such a variety of products are packed in cans each presenting its own corrosive problem. Heretofore there has been no single organic coating composition that is effective against the different types of chemical attack. Therefore it is necessary "to develop and use a different coating to resist each particular type of corrosion. Obviously such an operation is costly and troublesome.

During recent years this situation has been aggravated by the tremendous increase in the use of organic coatings over tin coatings. Previously most, if not all metal containers were made from sheet steel having a protective coating of tin on its surfaces. This involved a tremendous'consumption of tin in view of the fact that billions of metal containers are manufactured each year. Due tothe growing scarcity of tin, aconstant effort has been made by the container manufacturing industry to develop substitute coating compositions and methods by which to conserve tin or obviate its use entirely. In relation to protective coatings for steel plate, one method Q ti c nse t on has b e t duce ras c ly the weight of tin deposited on sheet steel and provide supplemental protection by the use of organic coatings thereover, Another method has been to eliminate entirely the use of tin coating and obtain corrosion protection solely by the use of organic coatings.

We have discovered that by modifying a particular styrene-diolefin copolymer with a. small amount of an acidic phosphorus compound and thereafter applying this novel composition to the surface of a ferrous metal plate and treating the coated plate we produce a thin, hard, adherent, flexible film thereon which protects the metal substrate from atmospheric and other chemical corrosion.

Therefore an object of this invention is to provide a substantially universal organic coating for metal containers.

Another object of this invention is to provide a sub stantially universal organic coating for metal containers that is equivalent in quality and protective value to tin coated containers and which is more readily available and less costly than tin.

, Another object of this invention is to provide a substantially universal organic coating for ferrous metal containers and many other ferrous products that is more coonomical and in many respects superior to organic coatings presently in use.

, A further object'of this invention is to provide a substantially universal, tough and flexible organic coating for all types of fabricated sheet metal products which in the course of manufacture have to undergo considerable bending and shaping operations.

The particular copolymer useful in the present invention is a synthetic drying oil. In its preparation, to parts by weight of butadiene and 25 to 15 parts of styrene, preferably 80 parts of the former with 20 parts of the latter are copolymerized in the presence of metallic sodium and a reaction diluent at a temperature below the melting point of the catalyst. Temperatures from 25 C. to C. are operable with temperatures between 40 C. and 80 C. particularly preferred. The quantity of catalyst is about 0.5 to 5 parts and preferably from 1 to 3 parts of finely divided sodium per parts of monomer.

While styrene yields the best product, it is possible in some instances to substitute for all or part of the styrene its paraor metalower alkylated homologues, e.g. para-methyl styrene, meta-methyl styrene, dimethyl styrene, and the corresponding ethyl-substituted homologues. Alpha-substituted styrenes are useless and inoperative because of their poisoning effect on the polymerization reaction.

As with styrene, butadiene produces the best results. However, here also in some instances the butadiene may be replaced in whole or in part by isoprene, 2,3-dimethyl butadiene-1,3-piperylene, or Z-rnethyl pentadiene-l,3.

The diluent used in the reaction is important. Inert diluents having a boiling range between 20 C. and 200 C. may be used with aliphatic hydrocarbons being preferred, e.g. solvent naphtha, mineral spirits such as Varsol (boiling range about C. to 200 C.), Solvesso (boiling range about 95 to 200 C.). Aromatic solvents such as benzene, toluene and Xylene may also be used but are not as desirable as the aliphatic solvents due to their toxicity. These hydrocarbon diluents are used in amounts ranging from 100 to 500, preferably 200 to 300 parts per 100, parts of monomers. An improvement in the polymerization rate and production of a colorless copolymer can be obtained by using with the aforementioned hydrocarbon diluent, a substantial amount of a C to C aliphatic ether, a nonaromatic cyclic ether or a polyether other than those having an -OC0- grouping. Particularly effective among these is dioxane-L4. Other examples of ethers producing favorable results are the diethyl ether of ethylene glycol, diethyl ether of dietbylene glycol and diethyl ether. Still other ethers useful to a lesser extent are diethyl acetal, vinyl isobutyi ether, dihydropyrane, and isopropyl ether. In general the ethers tried and found to beprcferred are cyclic diethers of 4 to 8 carbon atoms wherein the two oxygen atoms ar separated by at least two carbon atoms, and also saturated aliphatic ethers having the formula C H O(C H O),,C H wherein n is an integer from 0 to 2 inclusive. The ether co-diluent is used in amounts ranging from about 10 to 45, and preferably from 25 to 35 parts per 100 parts of monomers. For easy recovery from the reaction mass, the ether should have a boiling point at least 10 C. below the lower limit of the hydrocarbon diluent boiling range.

As a catalyst promoter, especially when using a coarser catalyst dispersion, it is advantageous to use about l%, ,to 50% by weight of catalyst, of a C to C aliphatic alco,-. hol, preferably a secondary or tertiary aliphatic alcohol. Weight percents of 10% to 20% of the catalyst, or about 0.1 to 1 Weight percent based on the monomers is preferred. Examples of such alcohols are isopropanol, secbutanol or tert-hutanol or in some instances n-propanol or n-pentanol.

In the preferred method of carrying out the reaction, an autoclave equipped with a mechanical agitator is used. The autoclave is charged with the butadiene feed in a portion of the diluent and with the sodium catalyst. It is desirable to operate with a catalyst particle size of about 1 to 100 microns, preferably about to 50 microns. The catalyst is usually fed to the reaction as a slurry of metal particles dispersed in 2 to 200 parts of a hydrocarbon diluent. This feed is then brought up to reaction temperature thereby initiating the polymerization of the butadiene. The styrene in the remainder of the liquid diluents is then fed into the autoclave. The lapse of time between the butadiene feed and styrene feed is usually from 10 to 60 minutes. The copolymerization reaction time varies with the reaction temperature and catalyst particle size, i.e. about 40 hours at 50 C. with a coarse catalyst to about minutes at 95 C. with a catalyst particle size of less than 100 microns. At the end of the reaction, the catalyst is destroyed by treating the reaction mass with a slight excess of an acid such as glacial acetic acid. The mass is then neutralized as with ammonia and the neutralized product is filtered. The filtered mass is subjected to distillation to concentrate the product to a solution of 50% to 70% non-volatile matter in hydrocarbon solvent.

The resulting produce is a clear, colorless to light yellow composition having a viscosity of about 0.5 to poises preferably 1 to 10 poises at 50% non-volatile con-- tent. The Staudinger molecular weight of the non-volatile content or polymeric product falls between 1500 and 5000, preferably about 1800.

The addition of from 0.01% to 2.5%, preferably from 0.05 to 0.50% of unsaturated anhydride, such as maleic, chloromaleic, or citraconic anhydride to the copolymer improves its properties as a vehicle for pigments. This anhydride may be added to the reaction mass during the formation of the copolymer or may be blended with the finished copolymer in a suitable well-known manner.

The above described copolymers are more fully described in copending US. patent application Serial No. 102,703, filed July 1, 1949, now Patent 2,652,342, and application Serial No. 176,771, filed July 29, 1950, now Patent 2,762,851.

The above described copolymer, while showing promise as an organic coating for metal containers is deficient in that regard in many important factors, e.g. blistering. discoloration, adhesion and especially flexibility. This last deficiency results in the corrosion of container parts fabricated from plate having the unmodified copolymer as a coating thereon due to fracture of the coating at points where the substrate metal was subjected to stress or bending. We have discovered the surprising and unexpected fact that the addition of a small amount of an acidic phosphorus compound to the copolymer alleviates these deficiencies yielding a composition having in all respects exceptional properties as a metal container coat-- ing. It is believed that this remarkable improvement is due to the acidic phosphorus compound inhibiting oxidative polymerization of the cross-linking type during the curing of the film thereby yielding a less brittle, more adherent and more fiexible film. However, since these theoretical considerations form no part of the present invention, we do not Wish to be bound thereby.

The term acidic phosphorus compound used herein designates phosphorus acids, phosphorus acid derivatives having at least one replaceable acidic hydrogen atom and mixtures thereof. Included in the phosphorus acids are ortho-, meta-, hypo-, and pyrophosphoric acid, phosphosphorous acids, polyphosphoric acid and any phosphorus compound that will yield a Phosphoric acid in aqueous solution, e.g. hydrates of orthophosphoric acid,

anhydrous phosphoric acid, phosphorus pentoxide, phosphoric oxide, phosphoric anhydride, P 0 and P 0 Of the phosphorus acid derivatives we include: inorganic salts of phosphorus acid such as zinc acid phosphate and ammonium acid phosphate; organic esters of phosphorus acids such as alkyl phosphates, e.g. n-amyl phosphate and dibutyl phosphate; and organic salts of phosphorus acids such as amine phosphates, e.g. mono- (dibutylamine) pyrophosphate, dianiline phosphate and dibenzylamine phosphate. Of the acidic phosphorus compounds disclosed, the unsubstituted phosphorus acids are preferred.

In accordance with the invention the acidic phosphorus compound is dissolved in a suitable solvent. An amount of this solution is slowly added to an already prepared solution of the copolymer so that the resulting product contains a major portion of copolymer and a minor portion of acidic phosphorus compound. Based upon the weight of copolymer in the composition, between 0.1% and 10% of acidic phosphorus compound and preferably between 0.50% and 4.0% is incorporated in the composition. These limits are critical since an amount of acidic phosphorus compound less than the minimum limit fails to give the desired result and an amount thereof greater than the upper limit inhibits curing of the film to an excessive degree causing it to be soft and tacky. If the acidic phosphorus compound solution is insoluble in the copolymer solution, the addition must be accompanied by vigorous agitation of the mass so that the former is uniformly dispersed throughout the latter yielding a homogeneous product. However, with certain acidic phosphorus compounds, e.g. some organic phosphates, a solvent compatible with the resin solution can be used so that a clear solution of acidic phosphorus compound solution in copolymer solution can be obtained. With other acidic phosphorus compounds, it may be advantageous to add them as a solid or in the form of a thick slurry. This may be accomplished by milling the acidic phosphorus compound into the copolymer. The time of mixing or temperature of the ingredients is not critical varying over a wide range. The only limitation as to time of mixing is that sufficient time be allowed to insure uniform and intimate contact of the ingredients. In general 5 to 15 minutes should be suflicient. As to temperature, it is necessary only that the solutions be liquid, i.e. above their freezing points.

Solvents such as water, lower aliphatic alcohols, normally liquid ketones and combinations thereof can be used as solvents for the acidic phosphorus compound. As a solvent for the copolymer, the hydrocarbon diluents described hereinbefore are satisfactory. In the acidic phosphorus compound modification of the copolymer the selection of a proper solvent is not critical depending merely upon the degree of solubilities of the respective ingredients therein.

In the coating operation, the metal sheet may be either spray, dip or rolled coated. The procedure generally used in metal container manufacture is the roller coating of flat, metal sheets as by an apparatus similar to that disclosed in United States Patent 1,848,856 issued to C. Wagner et al. on March 8, 1932. The resin coating is then cured at an elevated temperature usually by means of a device similar to that shown and described in United States Patent 1,293,261, issued to C. Wagner et al. on February 4, 1919.

In applying the coating composition of the present invention by the roller coating process, the liquid coating composition should have a viscosity of between and 315 centistokes and preferably between and 250 centistokes and a solids content of not less than 20 percent by weight of the total, liquid composition. In actual operation the solids content is in the range of 40 percent to 60 percent by weight of the total. To effect a cure, the resin coating is baked at a temperature of from 375' F. to 420 F. for 10 to 15 minutes. The cured film approximately from 2.5X- to 8.5)(10' cm. thick ranging upward therefrom t5 unsatisfactory. rating Over the t sub ra a d has w sh approximately at abo t e n tt l a ac y- Table l v ilumpk .0m

Coating Metal Substrate f v Process Flexib. Process Flexib.

Resist. Resist.

unmodified copolymer CMQ 12. 3 23. 4 7. 3 15. 0 Do low weight tin plate 4. 1 5. 6 6. 3 6. 4 comm'l corn can matin CM D low eight tin plate 5.3 6. 0 6. 3 5. 6 high weight tin plate- 8.3 6. 3 7. 3 6. 4 CMQ low weight tin plate.- 5. 0 6. 9 comml pumpkin. high weight tin plate. 3.0 6.0 modified copolyme CMQ 3. 0 5. 6 0. 3 6.3 Do low weight tin plate 3. 7 5.6 3. 9 6. 3

1 Unsatisfactory.

of from 2 mg. per square inch to 5 mg. per square inch respectively of metal plate surface.

The following tabulation will serve to illustrate specific While the novel composition of the present invention has been described specifically as a metal can coating, it has utility of much greater scope. This copolymer forms embodiments of the present invention but are in no way an excellent protective coating on all metal substrates,

intended as limitations thereon. In each of the following examples, the major constituent of the composition is a styrene-butadiene copolymer as described hereinbefore:

particularly ferrous metal substrates, where a tough, flexible, adherent, corrosion resistant, continuous film is desired.

Examples Percent Percent Viscosity No. Modifier Modifer Solvent Solid of in Centiadded 1 Compostokes sition 1 o-phosphoric acid 1, 2, 4 Butanol Toluene. 235 phosphorous acid 1, 2, 4, 6, 8, 10 d0 40 235 polyphosphoiic old. 1, 2. 4 40 235 dibutylphosphate 1, 2, 4 235 mono-(dibutylaminel-pyrophos 1ate 1, 2, 4 .do 40 235 zinc dlhydrogen phosphate Zn( 1104); l, 2, 4 Mineral-Spirits.-- 40 235 dianiline phosphate 1, 2, 4 Buttimlol mineral- 40 235 51) r t5. mono-dihenzylamine phosphate 1, 2, 4 do 40 235 diammonium hydrogen phosphate 1, 2, 4, 6, 8, 10 isopropanol tolu- 40 235 4):HPO4. ene wetting agent water.

Each num her represents a different composition having that percent by weight of copolymer of the particular acidic phosphorus compound designated.

8 This represents percent by weight of total composition.

Small amounts of other substances may be incorporated into the novel composition of the present invention depending upon the result desired. Included in these are It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes pigments such as aluminum oxide and titanium oxide; 55 may be made in the matter of the ingredients, their idenwaxes as internal lubricants; inhibitors; and drying oils.

The data tabulated below shows the superiority of the coating of the present invention over all the other coatings rated on the products shown thereby illustrating its value as a single replacement for the different coatings tity and their proportions without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

We claim:

1. A package comprising a comestible enclosed within a container, said container having a tubular metal body coated on its inside surface with a solid protective film comprising a substantially colorless sodium catalyzed copolymer consisting essentially of from 15 to 25 parts by weight of a monoaryl vinyl hydrocarbon and from 85 to 75 parts by weight of an aliphatic diolefin having 4 to 6 carbon atoms, and from 0.1 to 10% by weight based on said copolymer of an acidic phosphorus compound, said copolymer having a molecular weight of tainer parts and contacted with the products designated from 1500 to 5000.

below, each coating receiving identical treatment in its contact with the respective products. The coated metal can part was then removed from the product and evaluated, the results of which are shown in Table I below.

2. The package set forth in claim 1 wherein said monoaryl vinyl hydrocarbon is styrene and said aliphatic diolefin is butadiene.

3. The package set forth in claim 1 wherein said In the numerical ratings given in Table 1, zero is perfect monoaryl vinyl hydrocarbon is styrene, said aliphatic diolefin is butadiene and said acidic phosphorus compound is selected from the group consisting of an unsubstituted acid of phosphorus, a phosphorus acid salthaving at least one replaceable acidic hydrogen atom, and mixtures thereof.

4. The package set forth in claim 3 wherein the unsubstituted acid of phosphorus is ortho phosphoric acid.

5. The package set forth in claim 3 wherein the unsubstituted acid of phosphorus is phosphorus acid.

References Cited in the file of this patent 6. The package set forth in claim 3 wherein the unsub- 10 2,741,397

stituted acid of phosphorus is polyphosphoric acid.

V -UNITED STATES PATENTS Rothrock Aug. 12, 1941 Frolich et a1 Mar. 21, 1950 Hunter Feb. 26, 1952 Kalafus Nov. 25, 1952 Crouch Mar. 10, 1953 Gleason July 6, 1954 Shotton Apr. 10, 1956

Claims (1)

1. A PACKAGE COMPRISING A COMESTIBLE ENCLOSED WITHIN A CONTAINER, SAID CONTAINER HAVING A TUBULAR METAL BODY COATED ON ITS INSIDE SURFACE WITH A SOLID PROTECTIVE FILM COMPRISING A SUBSTANTIALLY COLORLESS SODIUM CATALYZED COPOLYMER CONSISTING ESSENTIALLY OF FROM 15 TO 25 PARTS BY WEIGHT OF A MONOARYL VINYL HYDROCARBON AND FROM 85 TO 75 PARTS BY WEIGHT OF AN ALIPHATIC DIOLEFIN HAVING 4 TO 6 CARBON ATOMS, AND FROM 0.1 TO 10% BY WEIGHT BASED ON SAID COPOLYMER OF AN ACIDIC PHOSPHORUS COMPOUND, SAID COPOLYMER HAVING A MOLECULAR WEIGHT OF FROM 1500 TO 5000.