US2699413A - Coating composition for containers and closures therefor - Google Patents

Description

United States Patent O COATING COMPOSITION FOR CONTAINERS AND CLOSURES THEREFOR No Drawing. Application May 20, 1952, Serial No. 288,998

8 Claims. (Cl. 148-31.5)

This invention relates to the art of resinous coatings for containers for foods and beverages and closures therefor, in particular containers and closures made of sheet steel or black plate as it is commonly called.

Tin plate has'been conventionally employedbut the lighter coating weights of tin now commonly used do not always provide sufficient protection for certain foods and beverages and resinous coatings have been applied to tin plate to provide the necessary protection.

The requirements of such resinous coatings are very severe. Those requirements include adhesion and the flexibility necessary to maintain that adhesion during and after the deformation encountered in fabrication of the coated plate, e. g. into can ends and screw caps plus the inertness necessary to avoid imparting any undesirable.

flavor or toxic ingredient to the food or beverage contents of the container and to avoid any substantial impairment of the resinous film by the action of the container contents or water or steam at the high temperatures encountered in processing the containers and their contents.

The following are some of the more important tests which have been developed to measure the requirements of resinous can and closure coatings or enamels:

Dry adhesion Process wet adhesion Process blush resistance Process blistering resistance Process spotting resistance Chemical and organic-solvent resistance Unfdeiglfilm corrosion resistance to oxygen-containing acid Stain resistance to sulphur-bearing products Fexibility and fabrication (dry and after pocessing) Flavor and odor freedom Because of the increasing scarcity and unreliability of tin sources, the art for many years has tried to develop satisfactory coatings for direct application to the surface of sheet steel or black plate, thus eliminating the need for the surface coating of tin, as it is present on tin plate.

It has been found, however, that the elimination of tin with its accompanying electrochemical protective action on iron creates an additional problem because the conventional types of coating well-known in the art, which meet the above requirements when applied to tin plate, are not adequate when applied directly to plain sheet steel or black plate because of the susceptibility of plain steel to corrosion, particularly under the coating, when exposed to steam and hot water, and the lack of stability of coatings in direct contact with a surface of plain steel. Therefore a coating for direct application to iron or steel must have additional properties to compensate for the loss in electrochemical protection which results from the elimination of tin.

The more discriminatory tests for judging whether a coating (i. e. lacquer or enamel) is satisfactory as applied directly to sheet steel or black plate for use in the manufacture of cans and closures for food and beverage products are as follows: The oxygenated spinach test, which measures the resistance of the coating to peeling and loosening and also the underfllm corrosion resistance of the metal; the meat staining test which measures the stain resistance to sulfur-bearing products; the process blush test which measures the resistance of the coating to steam or water at elevated temperatures such as 250 F.; the solvent resistance test which given an indication of the insolubility and chemical inertness of the coating. These tests of course are run only on coatings which show 2,699,413 Patented Jan. 11, 1955 satisfactory fabrication properties, which is a prime requirement for a can or closure enamel.

These tests are described briefly as follows:

The oxygenated spinac test: This is an accelerated test indicative of the resistance of the coating to foods, particularly the mildly acid ones, and demonstrates in a few days rather than many months of normal shelfaging, the effectiveness of the coating in preventing the attack of the steel substrate by these food chemicals, shows the resistance of the coating to blush or whitening on contact with the water in the food product, and shows the retention of flexibility and good adhesion upon exposure of the coating to the food, heat and pressure to which the coated article is subjected during the processing operation. In this test a can, the inside surface of which is provided with the coating to be tested, is filled with spinach, evacuated, and the air replaced by pure oxygen. The container thereupon is sealed and processed in steam at 240 F. for 60 minutes. After allowing to stand for several days the container is opened and the coated metal examined for deterioration and attack by the food mixture. If the coating is not processable the coating may have turned white (blushed) or have lost adhesion or both. If the coating has not protected the steel substrate from underfilm corrosion, numerous areas or the total area will have corroded or rusted. If the coating protects the steel substrate from under-film corrosion there will be no rust or corroded areas. An estimate of the resistance of the coating in the oxygenated spinach test is made by visually observing and determining the percentage area of coated metal surface unattacked. A perfect rating of 100 is obtained when none of the coated surface shows attack. A rating of signifies that 90% of the coated area shows no signs of corrosion. A minimum rating of 75 on certain products will be acceptable to the metal can or closure manufacturing industry, though naturally as high a rating as possible is preferred.

The meat staining test: This test demonstrates the protection the coating affords the steel substrate against staining by sulfur-bearing bodies present in food products, such staining being due to the formation of iron sulfides or other iron compounds. In this test, coated sheet steel panels are placed in a synthetic meat mixture comprised usually of edible oils, organic acids, carbohydrates, proteins, esters, salts and moisture and the whole subjected to steam processing (autoclaving) for two hours at 250 F. Atthe conclusion of the processing, the panels are removed, cleaned of adhering food product, and rated visually for degree of staining or blackening. A perfect rating of means no blackening of the coated steel while may be acceptable to the container manufacturing industry, though naturally as high a rating as; possible is preferred.

The solvent resistance test: In this test the effect of methyl ethyl ketone (MEK) on the coating baked on a sheet steel substrate is determined and an indication of the insolubility, chemical inertness and degree of thermosetting of the organic coating is obtained. In this test the baked coating on a steel substrate is rubbed ten times with a cloth saturated with methyl ethyl ketone. At the end of the manipulation the coating is visually examined for softening or solution by the ketone solvent. A perfect rating of 100 indicates that the coating is neither softened nor dissolved by the methyl ethyl ketone and is to that extent chemically inert. A rating of 50 means that the coating is softened by the solvent and is not as chemically inert or thermoset. A zero rating indicates the coating to be dissolved by the solvent and thus to possess a low order of insolubility, chemical inertness and thermoset properties.

The term process blush resistance is well known and relates to a test wherein the coated material is subjected in an autoclave to steam at about 15 lbs. pressure for about 30 minutes. The perfect rating of 100 means that the coating does not lose gloss, transparency and does not whiten or blush, while a rating of 0 means that the coating has lost gloss completely and/or becomes whitened or'opaque. A rating of -70or less indicatesu-nsatisfactory performance.

It is also necessary that the coating shall behave satisfactorily when subjected to the *fabrication" test. In that test a steel panel is provided 'with the coating and after the baking operation is drawn and curled "into the shapenecessary for a can end or is formed into a screw closure by imparting a thread, curl and knurl, using appropriate dies and other machinery. A satisfactory coating shows no substantial separation of the coating from the steel'substrate as a result of these forming operations. The fabrication behavior ofthe coating is made readily apparent by immersin'g'the coated can endor closure in an acidifieil'copper'sulfate solution for about -1 minute.

A principal object of the invention is to provide a lacquer or enamel coating for ca'ns or closures used for 'food products, beverages and other packaged products, where that lacquer or enamel is applied as a single coat directlyto steel or black plate, in the form of sheets or in the. form of partially or completely fabricated containers or closure.

'A further object is tozprovide such ail-acquer or enamel coating which meets all the mentioned tests including the more important oxygenated spinach, meat staining,

"process blush "and solvent resistance tests.

A'further'object is to provide a coating material which may be applied directly to steel or black plate (preferably a lighter'coating'weight than when used as asingle enamel coat) .to 'serve as a primer or base'coaton the metal, "which'is'subsequently to be over-'coatedwith one 'orzmore additional'coats of lacquer, enamel inkor coating of 'a chemical type different from that of the present invention.

'Inaccordance with theinvention, a resinous composiition consisting essentially of three components is provided, cthose components being (a) a particular kind of polyep'oxide resin, (5) a particular kind of phenolic resin, aand-'(c) 'from 5-20% of phosphoric acid:(HsPO4) based on -thetotal weight of resinous components (a) and (b).

Polyepoxide resins are well'known as such. They are 'polyethers'containing recurring hydroxy-ether groups and having terminal 'epoxide groups.

They are commonly made by reacting a compound having two reactive hydrogenxa'toms, .e. g. apolyhydric phenol or a polyhydric al- 'coh'ol, with epichlorhydrin or'a dichlorhydrin. Bis-phenol is frequently used as the compound supplying reactive hydrogenatoms. When that is reacted with epichlorhydrin the general formula of the resulting polyepoxide resin is where n varies with molecular weight from .a value of 4 toia value of 24.

The properties of the polyepoxide resins vary with variations of the molecular size. 'The average molecular "weight is readily determinedby ebulliometry or cryoscopy.

-'In this'invention polyepoxide resins are used which are polyglycidyl ethers of dihydricphenols having a molecular 'weight'of 1500 to 7200.

Atypical procedureytoillustrate the above'defin'ition,

"as described inthe art for making such-polyglycidyl'ethers =(polyepoxide 'resins) is as follows:

-'A relatively lowmole'cular weight product. ('polyglycidyl ether 1") may be made by reacting 1 mol ofbisphenol in 1:1iter of watercontaining in'excess ofx2;mols of NaOH and 2.05 mols of *epichlorhydrin which is then dissolved inithat solution by addition thereto at40 C. with stirring.

. A11" exothermic'reaction ensues which raises'the temp erature of"the.-react1on mixture to 65 C; in about thirty minutes. "As soon' as' the. reaction subsides,theat'isapplied 'to'bring the mixture to *the boiling :point, in about thirty to settle and is washed by decantation to remove'salt, excess jN'aOH, epichlorhydrin, *an'd'other impurities. Upon subsequent vacuum dehydration, a balsamic solid resin is obtained with a melting'point ofabout 45 C. and -a molecular weight of about 5 OO-to 600.

The higher molecular weight polyepoxide resins mequired in this invention arethen-o'btainedby heating the polyglycidyl "ether 1 'producedasdescribed withadditional bisphenol, with or without an alkali catalyst, for several hours at 200C. The following table shows the proportions of reactants which may be used to give the higher molecular weight polyglycidyl ethers or polyepoxide res- 1n:

Grams polyglycidyl ether 1 ggig 2 18 50 1, 800-1, 900 35 3, non-4,000 30 5, GOO-'7, 200

In the above typical procedure, instead of bis-phenol, dihydric phenols in general may be used, for example, resorcinol or hydroquinone.

In accordance with the present invention the solids of the coating composition consist essentially of two resin components, resin A and resin B, and a proportion of orthophosphoric acid of .5 to 20% by weight of the total :resin solids. Resin A is :a polyepoxide resin as above defined. Resin :B is a particular kind of phenolic resin :compatible with polyepoxide resin A and is an organic solvent-soluble alkali-condensed condensation product of formaldehyde and a/phenolof the group consisting of a 2,3 dialkyl phenol, 2,5 dialkyl phenol, 3-,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, and 4 monoalkyl "phenol, where the alkyl group has from one to five carbon atoms. Also commercial mixtures composed principally of .any two or more of the above substituted phenols .may be used, for example, certain selected phenolic mixtures composed principally of the members of thegroup described, .such as mixed xylenols, cresylic acid, cresols and butyl phenols of commerce Where the substituents on the benzene nucleus are alkyl groups.

Atypical procedure, to illustrate the-above definition, for making a phenolic resin (resin B) suitable for this invention is as follows:

Charge into a resin reactor, 610 parts of mixed xylenols, 546 parts of aqueous 37% formaldehydeand 61 parts of aqueous 28% ammonia; heat with agitation to about 82 C. in a period of onehour and hold with continuing agitation at this temperature for an additional period of one hour; stop the heating and agitation and decant the water layer; distill under about 24 inches of vacuum at a temperature of about 93 C. for about 3 hours -to remove moisture and unreacted ingredients. This yields a hard friable resin, which is suitable for this invention.

The .two resins are used in'the ratio by weight of from 50% gesin -A and 50% resin B to 80% resin A and 20% 'IBSll'l The resins and phosphoric acid are dissolved in volaitile solvents to provide a liquid coating composition having a'prop'ortion of non-volatile coating solids of about .25 to 40% by weight, and having a viscosity of 25 to iIOOseconds asmeasured ma #4 Ford Cup at 80 F.

"Epoxide resin A is not per se thermosetting and phenolic resin B per'se'mayor may not be thermosetting. However, the combination of the three components, *epoxide resin, phenolic resin, and phosphoric acid, provides a thermosetting"composition and the liquid coating 'compoundwhen'baked'at 300 F. to 400 F. as a coating on sheet steel, yields an 'infusible, relatively insoluble, thermoset'coating, which m'eets'all'the required tests, and in particular the :tests for underfilm corrosion which are especially important for can coatings on sheet steel and which are herein designated as the oxygenated 'spinac fm'eat'stainingf process blush, fabrication and solvent resistance tests.

Purely for purposes TOf illustration the following example .issubmitted, showing a preferred liquid coating composition in accordance with the invention:

Solids Parts Percent by by weight weight Solvent Percent by weight Ethoxyglycol acetate 26 Isophorone 17 n-Butanol 14 Xylol 43 The solids in this particular example are dissolved in the solvent in the proportion of 34% by weight of solids and 66% by weight of solvent and the resulting solution is applied to steel sheet by roller-coating to yield a film weight (of the dry film) of 4 mgms. per square inch and baked at 375 for 10 minutes. The resulting coating when subjected to the oxygenated spinach test gave a rating of 90.

While this example represents a typical solvent composition suitable for roller-coating application, it is understood that other active solvents and compatible diluents may also be used in place of those mentioned above, as required to adjust such properties as the flowout rate of the wet coating, and the rate or speed of dry, so that the coating may be suitable for varying speeds of roller-coating application or application by other means such as spraying, dipping, slushing or brushing.

The importance of all three components, (a) epoxide resin A, (b) phenolic resin B, and (c) phosphoric acid, in obtaining a coating composition which meets the requirements of a satisfactory can and closure enamel is shown by the data in Tables I and II below.

Table I Film Epox- Pheiggg ide nolic HaPOi Metal Bake Resin Resin 8 q. In

A 80 20 15 Steel 3. 9 10 375 F. B 80 20 do 3.6 Do. 0 80 0 15 do 3. 9 Do. D 80 0 0 do 3.8 Do. E 0 20 15 do 4.9 Do. F 0 20 0 ..-do 3.7 Do. G 0 0 15 do 0.25 Do. 11 0 0 0 do J oleoresinous do 3.9 15 400 F.

S a n i t a r y C Enamel. Kn"... do Electro- 3.9 Do.

I y t i c '1 i n plate.

SHOWING RESULTS OF TESTS ON THE COMPOSL TIONS IDENTIFIED BY THE CODE LETTERS Oxygen- Meat Steam Solvent Code Letter ate Stain- Process Resist- Fabrication pinach ing 2 Blush 3 ance 4 85 100 100 100 Satisfactory. 25 100 0 D0. 00 90 40 100 D0. 5 0 0 0 Do. 0 O 30 100 Unsatisiactory (brittle). 25 80 100 100 Do.

0 0 0 0 10 0 100 40 Satisfactory. 90 50 100 20 Do.

1 Processed 00 minutes 240 F. Stored 4 days at room temperature. fR aitiug indicates percent coating remaining. 100=pertect; 0=complete a1 ure.

2 Strips processed 2 hours 250 F., in meat mixture. Examined when 0001]]. Rating indicates degree of staining. l00=no staining; 0=complete sta ling.

Action of steam at lbs. pressure. A rating of less than 70 shows unsatisfactory performance.

4 Rating indicates degree of softening after 10 rubs with MEK soaked rag. 100=no softening; 0=complete solution or removal.

5 Can ends drawn and curled and behavior of lacquer on the fabrics.- tion test noted as satisfactory or unsatisfactory.

The compositions indicated by code letters A to F,

inc. of the above data (Table I) were deposited from indicated by code letters A, B, E, and F was the same and was a condensation product of formaldehyde and mixed xylenols condensed to an alcohol soluble condition in the presence of an alkali. The figures indicating proportions of the various components mean parts by weight. In the case of code letters I and K, the same oleoresinous enamel was applied in both instances, in one case to steel and in the other case to tinplate; the solvent in this enamel is a mixture of conventionally employed liquid hydrocarbons; solvents of this type, while suitable and economical for use in oleoresinous enamels, are entirely unsuited for use in the compositions of codes A to F; neither would the solvent mixture used in the latter mentioned be suited for use in the oleoresinous enamel. Solvents are selected primarily for their ability to dissolve the solid constituents of the enamel, and once evaporated (as for example by baking) do not further influence the final baked film properties.

Referring to Table I, the diiferent compositions are designated by the code letters A-G, with H representing untreated uncoated steel, and J and K used as control examples.

The composition of code A embodies the present invention and contains all three essential components of the solids of the coating composition, i. e. polyepoxide resin, phenolic resin, in the proportion of parts polyepoxide and 20 parts phenolic resin by weight and 15 parts phosphoric acid. It provides satisfactory performance on all five important tests.

The composition of code B contains only two of the essential components of the present invention, that is, polyepoxide resin and phenolic resin in the proportion of 80 parts epoxide resin and 20 parts phenolic resin by weight, and no phosphoric acid. While satisfactory on the fabrication and the steam process blush tests, it is unsatisfactory on the oxygenated spinach, meat staining and solvent resistance tests.

The composition of code C shows the properties obtained when only the epoxide resin and phosphoric acid are used (80 parts of the former to 15 parts of the latter). No phenolic resin is present in this composition. While satisfactory for fabrication and for solvent resistance, it is slightly inferior in meat staining and grossly inferior in oxygenated spinach and steam process blush, to the composition containing all three components.

The composition of code D shows the results obtained for steel coated solely with the epoxide resin without the effect of the other two essential components of this invention, namely, the phenolic resin and phosphoric acid. It is satisfactory only in fabrication and is completely defficient in the four other properties requisite for a satisfactory can coating.

The composition of code E shows the effects on steel when it is coated with a composition containing only phenolic resin and phosphoric acid components in the ratio of 20 parts of the former to 15 parts of the latter. This composition has no polyepoxide resin present. This composition while possessing satisfactory solvent resistance properties, is grossly deficient in the other four principal properties required, including fabrication.

The composition of code F describes the properties obtained for steel coated with a composition containing solely the phenolic resin component of this inven tion, without any polyepoxide resin and phosphoric acid. While satisfactory for steam process blush and solvent resistance, this composition does not yield preferred meat staining resistance, fails on fabrication and is deficient in oxygenated spinach resistance.

Code G shows the results for steel that has been coated only with phosphoric acid. Since there is no organic film, steam process blush, solvent resistance and fabrication tests are inapplicable but it is completely unsatisfactory for oxygenated spinach and meat staining.

Code H shows the properties of untreated uncoated steel when subjected to the appropriate tests. The same remarks apply as to code G.

In codes I and K, the compositions illustrate the results obtained by using a conventional oleoresinous sanitary can and closure enamel on steel (code J) and on tinplate (code K). This oleoresinous enamel, comprising a heat-bodied unsaturated vegetable oil and an unsaturated hydrocarbon resin is typical of enamels widely used today as coatings for tin plate. When applied to tinplate, it satisfactorily passes the oxygenated spinach, steam process blush and fabrication tests herein described,

as-shown by :code K, but when applied tested as shown in :code I, Bit-:is satis'factoryaonly on steam "process blush and fabrication tests and is completely unsatisfactory on the .other three principal tests.

'The data of the-above Table I shows the necessity of using all three of the'essential componentspolyepoxide resin, phenolic resin and phosphoric acid-toobtain a composition which provides a coating that satisfactorily passes the principal test .requirements as described :in the specification when .applied directly to sheet steel.

A comparison'of the example of .code A with .code K. shows :that the composition of this invention provides a zcoating when applied directly to :sheet steel which is even superior to 'the conventional oleoresinous coating on tin :plate, particularly with respect .to meat staining and solvent resistance.

ilThetexamp'les of codes B tOIG, where omission=of one or two of :the essential components occurs, show :that the resulting'compositions each lack one .or more of the properties necessary to qualify the composition 'as an acceptable coating .for containers and closures made from sheet steel for food and other products where thc coatingv is applied directly to the steel surface.

Table II EP QXIDE RESIN PLUS PHENOLIC RESIN 'PL'UB PHOS- PHORIC ACID Parts Parts Parts oxygenated Epoxide Phenolic Phosphoric Spinach -'Resin :Resin Acid Rating '80 20 25 '80 20 '5 7 .80 20 80 80 1'5 85 80 i 20 20 "80 80 2O 60 v70 0 r 30' 70 30 5 80 70 "30 10 85 70 30 15 90 $70 30 2O 85 '70 '30 25 65 The above data (Tablell') shows the'compositions (in parts byweig'ht) of coatings deposited on sheet steelfrom the same'solvent and under the same 'baking conditions and at the same coating weight,the solvent'beinga mixed solvent composed of 'ethoxy-glycol acetate 26% by weight, isophorone 17% by weight, -n-butanol 14% by weight,

The baking time 'was "10 :minutes at 375 'F., and=the coating weight was 4 milligrams of dry film-forming composition per square inchof sheet steel. The epoxide resin was the same in each 'of the abovelisted compositions and was a polyepoxide polyglycidyl ether of bisphenol having a molecular weightof 5000 to 6000. The phenolic resin was'also the same in each of .the'said compositions and was a condensation product of formaldehyde and miXed xyleuols condensed to an alcohol soluble condition in the presence of an alkali.

The values in Table -II show that proportions "of phosphoric acid'from'Sto 20% by weight-'of thetotal weight of phenolic and .epoxide resins give results, :as measured "by the oxygenated spinach'test rnu'ch-superior'to those .obtained by proportions of phosphoric acid beyond ithe "stated 'range, as used withproportions of 'epoxide resin to phenolic resin varying from 70% of epoxide resin and 30% of phenolic resin to 80% epoxide resin and 20% of phenolic resin 'and'it has been found that sub- .stantiallythe same results are obtained with compositions where the proportions of epoxide to phenolic rcsinextends'down to and including'50% of epoxide resin and 50% of phenolic resin.

Although the examples given herein illustrate clear (undye'd and unpigmented) resinous films, applied by roller-coating to flat sheets of steel 'baked and subsequently fabricated into container ends, bodies and other parts and closures, it'is understood that the scope -.of the invention also includes the addition of dyes, pigments, colorants and fillers to the liquid-composition; also that with or without changes in the composition of=the solvent .portion of the liquid coating, the coating maybe applied by any convenient means in addition 'to roller coating, such as by dipping, spraying, knifing, flushing, p slushing, wiping .or brushing; also. that although .con-' tainers and closures made of .sheet steel are usually coated and baked inflat sheets prior to any fabrication, the coating of this invention may also be applied to the sheet steel article that is, the container or closure, and baked thereon after the article has been partially or completely fabricated from the uncoated sheet stock.

What is claimed is:

1. A liquid coating composition adapted for direct application to sheet steel in the manufacture of containers and closures therefor consisting essentially of a resinous composition dissolved in a volatile organic solvent, said resinous composition being composed essentially of two resins, resin A and resin B, and from 5 to 20% by weight of orthophosphoric acid'based on the total weight of said resins, resin A being a polyepoxide polyglycidyl ether of bisphenol having a molecular weight of 1500 to 7200, and resin B being an alkali catalyzed condensation product of formaldehyde and a phenol reactant of the group consisting of 2,3 dialkyl phenol, 2,5 dialkyl phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, 4 monoalkyl phenol, and mixtures thereof, where the akyl group has from one to five carbon atoms, condensed-to the organic solvent-soluble condition, the proportionby weight of resin A to resin B varying from resin A and 50% resin B to 80% resin A and 20% resin "B, 'and the proportion by weight of said resinous composition in said liquid coating composition varying from 25 to 40%.

'2. A liquid'coating composition adapted for direct application to sheet steel in the manufacture of containers and closures therefor consisting essentially of a resinous composition dissolved in a volatile organic solvent, said resinous composition being composed essentially of two resins, resin A and resin B, and 15% by weight of orthophosphoric acid based on the total weight of said resins, resin.A being a polyepoxide polyglycidyl ether of bisphenol having a molecular 'Weight of 1500 to 7,200, and resin B being an alkali catalyzed condensation product of formaldehyde and-a phenol reactant of the group consisting-of 2,3 dialkyl-phenol, 2,5 dialkyl phenol, 3,4 dialkyl .phenol,.3,5 dialkyl phenol, ,2 monoalkyl phenol, 4 monoalkyl phenol, and mixtures thereof, where the alkyl group has-from .one to five carbon atoms, condensed to the organic solvent-soluble condition, the proportion by weight of resin A to resin B being of resin A and 30% of resin .B, and the proportion -by weight of said resinous composition in said liquid coating compositionbeing about 34%.

3. A coated sheet steel article adapted for the manufacture of containers and closures therefor, said sheet having on at least one of its surfaces a baked-on coating of a resinous complex initially composed essentially o'f res'inAand resin B andorthophosphoric acid, said coating resulting from the application to said steel surface of a coating ofsaid resinous complex in an organic solvent-soluble, 'thermosetting condition and containing resins A and B inthe proportion of from 50% by weight of resin Axand 50% .by weight of resin B to by weight .of resin A and 20% by weight of resin B, and from5 'to 20% by weight of orthophosphoric acid based on the combined amount of resins A and B, and there after fheatingsaid coated sheet to 3'50-400 F. and converting said resinous complex to the thermoset condition, resin LA in said soluble thermosetting resinous complex being a polyepoxide polyg'lycidyl ether of bisphenol having a molecular weight of 1500 to 7200, and resin 'B' in said soluble thermosetting complex being an alkali cat-alyzed'condensation product of formaldehyde and a .phenol reactant of the group consisting of 2,3 dialkyl phenol, 2;5 dialkyl phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, .2 monoalkyl phenol, 4 monoalkyl 'phenol, and mixtures thereof, where the alkyl group has from one to five carbon atoms, condensed to the organic solvent-soluble stage.

4. A'coated'sheet steel article adapted for the'manufacture .of containers and closures therefor, said sheet having on atleast one of its surfaces 21 baked-on coating of a resinous complex initially composed essentially of resin A and resin B and orthophosphoric acid, said coatingresulting from the application to said steel surface .of a solution ofsaid resinous complex in an organic solvent-soluble thermosetting condition and containing resins .A .and'B in the proportion of 70% byweight of resin A.and.3'0% .by weight of resin B, and 15%by weight oforthophosphoric acid based on the combined amount of resins A and B, and thereafter heating said coated sheet to 350-400 F. and converting said resinous complex to the thermoset condition, resin A in said organic solvent-soluble, thermosetting resinous complex being a polyepoxide polyglycidyl ether of bisphenol having a molecular weight of 1500 to 7200, and resin B in said organic solvent-soluble thermosetting complex being an alkali catalyzed condensation product of formaldehyde and a phenol reactant of the group consisting of 2,3 dialkyl phenol, 2,5 dialkyl phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, 4 monoalkyl phenol, and mixtures thereof, where the alkyl group has from one to five carbon atoms, condensed to the organic solvent-soluble stage.

5. A liquid coating composition adapted for direct application to sheet steel in the manufacture of containers and closures therefor, consisting essentially of a resinous composition dissolved in a volatile organic solvent, said resinous composition being composed essentially of two resins, resin A and resin B and from 5 to 20% by weight of orthophosphoric acid based on the weight of said resins, resin A being a polyepoxide polyglycidyl ether of a dihydric phenol having a molecular weight of 15004200 and resin B being an alkali catalyzed condensation product of formaldehyde and a phenol reactant of the group consisting of 2,3 dialkyl phenol, 2,5 dialkyl phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, 4 monoalkyl phenol, and mixtures thereof, where the alkyl group has from one to five carbon atoms, condensed to the organic solvent-soluble condition, the proportions by weight of resin A to resin B varying from 50% resin A and 50% resin B to 80% resin A and 20% resin B, and the proportion by weight of said composition in said liquid coating varying from 25-40%.

6. A liquid coating composition adapted for direct application to sheet steel in the manufacture of containers and closures therefor, consisting essentially of a resinous composition dissolved in a volatile organic solvent, said resinous composition being composed essentially of two resins, resin A and resin B, and by weight of orthophosphoric acid based on the total weight of said resins, resin A being a polyepoxide polyglycidyl ether of a dihydric phenol having a molecular weight of 1500-7200, and resin B being an alkali catalyzed condensation product of formaldehyde and a phenol reactant of the group consisting of 2,3 dialkyl phenol, 2,5 dialkyl phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, 4 monoalkyl phenol, and mixtures thereof, where the alkyl group has from one to five carbon atoms, condensed to the organic solvent-soluble condition, the proportion by weight of resin A to resin B being 70% of resin A and 30% of resin B, and the proportion by weight of said resinous composition in said liquid coating composition being about 34% 7. A coated sheet steel article adapted for the manufacture of containers and closures therefor, said sheet having on at least one of its surfaces a baked-on coating of a resinous complex initially composed essentially of resin A and resin B and orthophosphoric acid, said coating resulting from the application to said steel surface of a solution of said resinous complex in an organic solvent-soluble, thermosetting condition and containing resins A and B in the proportions of from by weight of resin A and 50% by weight of resin B to 8 0% by weight of resin A and 20% by weight of resin B, and from 520% by weight of orthophosphoric acid based on the combined amount of resins A and B, and thereafter heating said coated sheet to 350400 F. and converting said resinous complex to the thermoset condition, resin A in said soluble thermosetting resinous complex being a polyepoxide polyglycidyl ether of a dihydric phenol having a molecular weight of 1500-7200 and resin B in said soluble thermosetting complex being an alkali catalyzed condensation product of formaldehyde and a phenol reactant of the group consisting of 2,3 dialkyl phenol, 2,5 dialkyl. phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, 4 monoakyl phenol, and mixtures thereof, where the alkyl group has from one to five carbon atoms, condensed to the organic solventsoluble stage.

8. A coated sheet steel article adapted for the manufacture of containers and closures therefor, said sheet having on at least one of its surfaces a baked on coating of a resinous complex initially composed essentially of resin A and resin B and orthophosphoric acid, said coating resulting from the application to said steel surface of a solution of said resinous complex in an organic solvent-soluble thermosetting condition, and containing resins A and B in the proportion of by weight of resin A and 30% by weight of resin B and 15% by weight of orthophosphoric acid based on the combined amount of resins A and B, and thereafter heating said coated sheet to 350400 F. and converting said resinous complex to the thermoset condition, resin A in said organic solvent-soluble thermosetting resinous complex being a polyepoxide polyglycidyl ether of a dihydric phenol having a molecular weight of 1500-7200, and resin B in said organic solvent-soluble thermosetting complex being an alkali catalyzed condensation product of formaldehyde and a phenol reactant of the group consisting of 2,3 dialkyl phenol, 2,5 dialkyl phenol, 3,4 dialkyl phenol, 3,5 dialkyl phenol, 2 monoalkyl phenol, 4 monoalkyl phenol, and mixtures thereof, where the alkyl group has from one to five carbon atoms, condensed to the organic solvent-soluble stage.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A LIQUID COATING COMPOSITION ADAPTED FOR DIRECT APPLICATION TO SHEET STEEL IN THE MANUFACTURE OF CONTAINERS AND CLOSURES THEREFOR CONSISTING ESSENTIALLY OF A RESINOUS COMPOSITION DISSOLVED IN A VOLATILE ORGANIC SOLVENT, SAID RESINOUS COMPOSITION BEING COMPOSED ESSENTIALLY OF TWO RESINS, RESIN A AND RESIN B, AND FRON 5 TO 20% BY WEIGHT OF ORTHOPHOSPHORIC ACID BASED ON THE TOTAL WEIGHT OF SAID RESINS, RESIN A BEING A POLYEPOXIDE POLYGLYCIDYL ETHER OF BISPHENOL HAVING A MOLECULAR WEIGHT OF 1500 TO 7200, AND RESIN B BEING AN ALKALI CATALYZED CONDENSATION PRODUCT OF FORMALDEHYDE AND A PHENOL REACTANT OF THE GROUP CONSISTING OF 2,3 DIALKYL PHENOL 2,5 DIALKYL PHENOL, 3,4 DIALKYL PHENOL, 3,5 DIALKYL PHENOL, 2 MONOALKYL PHENOL, 4 MONOALKYL PHENOL, AND MIXTURES THEREOF, WHERE THE AKYL GROUP HAS FROM ONE TO FIVE CARBON ATOMS, CONDENSED TO THE ORGANIC SOLVENT-SOLUBLE CONDITION, THE PROPORTION BY WEIGHT OF RESIN A TO RESIN B VARYING FROM 50% RESIN A AND 50% RESIN B TO 80% RESIN A AND 20% RESIN B, AND THE PROPORTION BY WEIGHT OF SAID RESINOUS COMPOSITION IN SAID LIQUID COATING COMPOSITION VARYING FROM 25 TO 40%.