US2797023A - Container - Google Patents

Description

June 25, 1957 R. w. KAERCHER Erm. 2,797,023

CONTAINER Filed Oct. l1, 1954 FIG CONTAINER Ralph W. Kaercher, Lombard, and Lehman E. Hoag, Cary, lll., assignors to American Can Company, New York, N. Y., a corporation of New Jersey Application Gctoher 11, 1954, Serial No. 461,482 5 Claims. (Cl. 220-64) The present invention pertains to a a novel coating on its inside surface. More particularly it pertains to a sheet metal container having its interior surface coated with a plurality of resinous films, one of which has an ion exchange resin incorporated therein.

A problem which has long confronted the canning industry is the migration of metal ions from the inner wall of a sheet metal container into the product packed in the can. Although these ions impart no `toxicity to the product, they do tend to impart an olf liavor and some discoloration thereto. Malt beverages, such as beer and ale, are especially sensitive to this tiavor and color deterioration.

In recent years this problem has been aggravated by the trend away from tin coated sheet steel and the substitution of plain sheet steel, so called black iron, for the manufacture of metal container parts. Black iron surfaces are observed to be more susceptible to corrosion than the more passive tin surface of tin plate and thus have a greater tendency to contribute ferrous ions to the product. The electrochemical protection of the base steel by the tin Vcoating on tin plate is of course completely lacking in plain steel plate. The use of suitable organic materials as an inside coating for the black iron cans has reduced visible corrosion to where it is no longer a serious problem. However, because of the very slight corrosion that still exists, it has heretofore -been impossible to reduce the amount of ferrous ion migration from black iron surfaces into sensitive product contents such as beer or ale to an extent that no deterioration of the flavor or color of the product occurs.

Careful investigation of this problem and extensive experiments resulted in the discovery that there is a variation over the inside surface of the metal container walls of the tendency to release iron ions, i. e. a varying metal ion release potential. It has been found that `.because of the many can making operations involved in the creation of a nished container, i. e. slitting, bending, draw ing, fluxing, soldering, welding, etc., the metal constituting certain areas of the inside walls of the container is subjected to severe treatment and conditions are created in the metal of these portions of the can which tend to liberate ferrous ions more readily than that from thc lesser disturbed or substantially undisturbed portions of the can body. For instance the annular ridge formed on the inside of a can end during countersinking has a higher ferrous ion release potential than does the at portion of the end. Also, it has been found that the container having nited States Patent side seam area of a Ablack iron can body has a considerably higher ferrous ion release potential than the remainder of the body wall and is a major source of ferrous ions, due at least in part to the soldering or welding operation performed thereon.

The application of inside organic coatings, either in single or multiple layers, has failed to reduce the ferrous` ion pickup by the product to a completely satisfactory degree. One explanation for this failure is that the thin resin tilm, even when considered perfectly continuous tory results can be obtained by omitting the in a macroscopic sense, contains sub-microscopic voids or pores. The thin resin film although applied in an apparently continuous condition has an appreciable and measurable permeability for water vapor and gases such as oxygen and carbon dioxide. This permeability of the film results in underlilm corrosion with production of ferrous ions in solution which ultimately find their way into the product.

It is therefore an object of the present invention to provide a sheet metal container having a resin Vfilm on its inside surface which resists the passage of ferrous ions from the metal wall of the container into the product.

Another object of the instant invention is the provision of an inside coating for a ferrous metal container which prevents the occurrence of olf iavor or discoloration of the canned product upon extended storage.

A further object of the present invention is to provide a sheet metal container for beer and other carbonated beverages, which container has an inside coating that protects the delicate color and flavor of the product from deterioration by the metal of the can.

Still another object of the invention is the provision of a can fabricated at least in part from black iron which imparts no olf flavor or discoloration to products such as beer and the like due to ferrous ion pickup by the product. v y

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which, taken in connection with the accompanying drawings, discloses a preferred ernbodirnent thereof.

We have discovered that these objects may be accomplished by lining a sheet metal container with a plurality of resin films at least one of which contains an ion exchange resin capable of adsorbing ferrous ions. Since a significant source of the deleterious ferrous ions is the side seam area of the can it is preferred that the ion exchange resin containing film cover at least this portion of the inside of the can body. If desired, the ion exchange resin containing iilm can extend over the entire inside surface of the ca The position of the ion exchange resin containing film in relation to the product is of great importance. Although the ion exchange resin is incorporated into the coating film to adsorb ferrous ions, it also has Vthe capacity to adsorb or tie up other ions. For this reason, the ion exchange resin should not be in direct contact with the product, especially sensitive products such as beer; otherwise the ion exchange resin'may remove flavorgiving or other essential ions from the product or exchange any adsorbed ferrous ion for these ions of the product thereby causing off-flavors and defeating the purpose of its use.`

It is also preferred to interpose va film between the ion exchange resin containing film and the bare metal wall of the container. The interposed lrn acts as a screening barrier to prevent at least a portion of the ferrous ions available at the metal surface from reaching the ion exchange resin. If such a barrier is not interposed the ion exchange resin comes into contact with an excess of ferrous ions whereby its capacity to adsorb ions is soon reached and thereafter it will not function effectively tokremove additional ferrous ions. This is because at equilibrium, i. e. when the full capacity of the resin is reached, the adsorption reaction allows the release of an equivalent amount of already adsorbed ions for any additional ions taken up'. Although the disposition of a barrier film between the can body wall and the ion exchange' resin containing film produces the best results and is the preferredconstruction, satisfacbarrier film and increasing the thickness of the ionv exchange resin containing .lilm and/ or the .concentration of ion exchange resin therein- Any of the well known ion exchange resins, both cationic and/ or anionic, may be incorporated in a resin iilm for'the'purpose of the present invention. Examples fotj cation exchange resins are fthosecontainingfSOsH and -COOH functional igroups. These. functional groups may :be linked Vto any suitable .polymeric matrix .such as phenol-,aldehyde resins, .polystyrenefdivinylbenzene V`copolymers and the like. y y

The cation exchange resins function by factual adsorbtion of ferrous ions. The anion exchange resins may function :by adsorption vof complex .ferrous Yanions or iby exchanging the corrosive anionsof the residues -frorn prior chemical treatments .or flnxing for hydroxyl ions which will precipitate ferrous ions. Includedin ftlie'anion exchange resins A`are those having the Vtanot-ional groups ofra quaternary ammonium hydroxide, anuaminogroup, a guandyl group, a dicyaiidiamidine Agroup andi-the like.

Among the polymeric matrices to which the functional plish this end the ion .exchangepamiclesshould be as tine Y as possible and must not be so 'large that they cause the film `to be rough or .proiectaboye vthesurface ofthe lm whereby direct contact with the productv lmight result.

The Word hlm-7 isjused herein in the accepted sense as describing a thin layer of material in the order-of 0.05 to 0.5 mils thick. The .ion exchange resin may be incorporated into the film in any :suitable manner. For

example the ion exchange resin may be ground toa tine particle size and then dispersed :uniformly in a solution of the lm forming .resin dissolved in a volatile solvent, Deposition .of this solution having the ion exchange resin dispersed therein ona surface :and evaporation-of the `solvent produces a continuous ilm having 'the solid ion'exchange resin uniformly distributed therethrough.

The accompanying drawingv discloses Va preferred and exemplary l.embodiment o'f the present invention in a. sheet metal container. Y i

Referring 'to the drawings: Y

Figure 1 is'a perspective` view of a side seemed container v,ha-ying a lprotective interiorY lining, part of the'body wall being broken away to Ashow the linterior lining;

Fig.. 2 is an enlarged fragmentary section taken substantially along `the line lf2-.of fFig. 1` and illustrating a cross section .of the lined canrbodyiatits bonded side seam;

Fig. 3 is a longitudinal fragmentary section taken through the, side seam at the bottom of the -can as indicated by lines 3T3 in Fig. 2; and

Fig. 4 is a view similar tolFigQZ illustrating acontainer which has a lap Welded side-seam.

The metallic container illustrated Vin vthe drawing and lined -or coated in accordance with .our invention, includes a -metal can `body 1:1 havingtwo of its edges joined together in a side .seam 12. This side seam may be lof the usual soldered 0r compound vfbondedlock and lap type such as illustrated in Figs. l, A2. and 3 of the drawing wherein two edges are hooked.1and interlocked along certain sections of the seam andare lapped'in other sections, all sections `being further soldered or otherwise bonded as with an organic adhesive to provide'a tight, preferably Yhermetic vjoint.

According to the usual Scan manufacturing practice, a

4 the inner body wall surface a prime or base coating 13 vis applied. This ^coating -is -usually applied -to dat-metal sheets by a well known roller coating process after which the coating is cured to form a hard, resistant iilm or lining by baking at an elevated temperature.

Base coat 13 may be of any suitable resnous material, the exact kind depending -upon the contents to be packed into the can. It is necessary that the coating be of such a nature as to properly adhere to -the metal surface to which .it is applied and that it will forma proper foundation for subsequent superposed linings. In addition to forming a base coat for the superposed linings, prime coating 13 functions'as a barrier iilrn between the inside wall of the metal can Abody 11 andthe ion exchange -resin containing lm 14, more fully described hereinafter.

Following the prime coating procedure, it is usual to form the hooks -or interengaging sections `of the can body to produce the side seam 12. The can body is thereafter brought into cylindrical or otherY tubular form and the intenengaging hook and lapped 4Aparts brought into tinal position'in vthe side seam for bonding 'as with solder or an organic adhesive to form an hermetic seal.

When the side seam is Vto be 'ihermet-ically sealed by means of solder, Vthe marginal edges of the can body blank must be .free of the base coat 13 so that solder zwill wet the interfolded `,layers of metalv in the side seam and securely bondthem together. Upon applicationv of the molten solder, a joint is formed in which the solder 15 extends into and around the can body hooks and forms a thin line or llet of solder 16 on lthe insideof the can. As seen in Fig. 2, the line of solder 16 and a can body inside wall immediately -on either side-thereof lis not covered by the base .coat 13 yenabling the ion exchange resin containing film 14 to contact -the metal directly. However .this gap in base coat 13 is maintained as small as possible andthe ilm 14 V4is thickest at this point.

When :the side Vseam of .the container is bonded by an organic adhesive this situation does not prevail. The organic adhesive will :adhere `tofbase coat 13 thereby obviating the necessity of leaving la fbare vmetal margin as with solder. Also any lletgof adhesive formed alongthe inside of the seam corresponding to solder line 16, is non-metallic and therefore presents 'no problem.

According tothe preferred :embodiment of the present invention, the container is provided with Ian additional lining .strip 1d :(Figs. 2 Sand 3) which is situated on the inside ofthe can body Vand locallyiconiined in the area of the sideseam .12.and 'extending-a short distancetoneach side of the seam 12. vLining strip 14 iscomposed of any suitable rres'mons material, .such as a stabilized vinyl chloride-vinyleacetate copolymer, throughout'which is uniformly distribntedan .ion exchange resin `active to Iadsorb or ztie-.up ferrous fions, for example the cationic active'sulfonic or lcarboxylic types, orv the lanionic active nitrogen containing :types intentioned 'hereinbefore This ion exchange resinicontaining iilrn may be applied inany suitable manner, as :by spraying 'or brushing. Inactual practice it has been `found `advantageous to spray a solution of the film forming :resin ina volatile organic solvent-having the ion exchange resin luniformly dispersed therein ontorthe-portion ofthe can .bodyto lbe coated, i. e. atleast the side seam area. of .the vinsidie -of the can, and thereafter evaporate the `volatile solvent by residual Aheat of the. soldering roperation. for the external application of heat wherebya solid strip of ion exchange resin containing iilin is deposited. By'this means the 7lining strip 14 merges withV .the final Vcoat:andextends laterally :from 4the side edges offthe .side seam ;a.suicient-1distance -oneither side to `provide'acomplete..coverage Lof the can Abody wall at least atthe seangrf Y Over both the base coat 13 and lliningfstrip -14 isdisposed the tonen-final 'coatll which separatesorisolates the ionzexchange.resin-containing film-141mm the packed product. ThisitopV coat may also be Varesin, -usuallyjdifferent frombasecost 4113. The'propertiesloftop coat 17 depend upon the product contents of the can and must impart no oft fiavor or clouding effect upon the contents. For example, a well known copolymer of vinyl chloride and vinyl acetate may be used for the top coat 17. As is the side seam stripe 14, the top coat 17 is usually applied by spraying the inside of the can with a solution fo the resin in a volatile solvent. A solid continuous film is then produced by the evaporation of the solvent by the application of heat. To prevent softening of the bonding agent, i. e. solder or organic adhesive, the drying of films 14 and 17 must be done at moderately elevated temperatures which are below the melting point of the bonding agent and are usually below the temperature used to cure base coat 13.

A satisfactory container for holding beer, ale or other products which have a tendency to attack raw metal such as the iron base of the can may be made by joining the marginal edges of the can body 11 into a welded side seam 21 (Fig. 4) as an alternative form. ln the welded side seam, the marginal edges of the body blank are overlapped rather than interfolded by means of hooks as in the soldered or cemented side seam. The overlapped portions are then welded or fused by means of heat to form an integral joint along the marginal edges of the body.

When such a Welded side seam is used instead of a soldered seam, the interior surface of the welded body is covered with a prime or base coat 22 which may be similar to base coat 13 in its method of application and nature. This prime coat may cover the entire inner surface of the blank prior to the Welding operation, although a better welding bond is produced where the lapped edges of the blank are left free of any lining. In either case the welding of the side seam produces an exposed metallic surface on the inside of the can which is not satisfactorily covered by the base coat 22.

According to the preferred embodiment of the present invention, a protective ion exchange resin containing film 23 is applied on the inside of the can body along the welded portion and extends laterally a suflicient distance on both sides of the side seam to protect fully or cover the entire side seam area. As with the soldered side seam, the gap in base coat 22 at the welded side seam is maintained at a minimum and film 23 is thickest at the places where it contacts bare metal. The container is then subjected to a further lining step so that there is produced a continuous top or final coat 24 completely covering the inside of the can body.

With the can body properly jointed at its side seam as by soldering, welding or cementing with an organic adhesive and fully lined as described hereinbefore, a flanged can end or bottom 31 may be secured in the usual manner to the anged can body as by a conventional double seam 32. The can may then be lled with the contents in any suitable manner after which a top end 33 (Fig. 1) is secured to the opposite open end of the can as by the usual double seam 34. To provide a hermetic joint in the top and bottom end seams 32 and 34, a rubbery gasket or end lining compound 35 is disposed in the double seam in a well known manner.

The can ends 31, 33 also have a suitable protective lining on their inner surfaces, as for example, a double coating consisting of a base or prime coat 36 and a final or top coat 37 which may be similar to the base coat and top coat on the interior of the can body. If desired the can ends 31, 33 may also have coated on the interior surface thereof an ion exchange resin containing film situated beneath the top coat 37. Further, the can'ends 31, 33 may be fabricated from the same type of metal as the can body 11 or may be of a different type of metal, e. g. a tin plate body with black iron ends.

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 may be made in the form, construction and arrangement of the parts 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:

l. A container comprising a tubular body member and end members, each of said end members being joined to said body member by an end seam, at least one of said members being metallic, said metallic member having a varying potential to release metal ions into a product in said container, an organic base coating substantially completely covering the inside surface of said metallic member, a solid organic film covering at least that portion of the inside of said metallic member having the greatest metal ion release potential, an ion exchange resin uniformly distributed throughout said film to adsorb any released metal ions coming into contact with said ion exchange resin, and an organic top coating covering the entire inside surface of said film whereby said film is interposed between said base coating and said top coating to separate said film from said product and substantially from the metal surface of said metallic member.

2. The container defined in claim l in which -at least one of said end members is black iron.

3. The container defined in claim l in which said body member is black iron.

4. The container defined in claim l in which each of said members is black iron.

5. A can body for holding beer and other products comprising a tubular sheet metal body having a longitudinally extending side seam, an organic base coating covering substantially the entire inside metal surface of said can body, a solid organic film superposed on said base coat and covering said side seam, an ion exchange resin distributed uniformly throughout sa'id film to adsorb metal ions liberated by said sheet metal can body and coming into contact with said ion exchange resin, and a continuous organic top coating covering said base coating and said film whereby said film is interposed between said base coating and said top coating to separate said film substantially from the metal wall of said can body and from said product.

References Cited in the file of this patent UNITED STATES PATENTS

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