IL26063A - Coating composition for a can body - Google Patents

Description

26063/2 COATING COMPOSITION FOR. A CAN ΒΟΡΪ The American Caa Company The present invention relates to a novel can body; and, in particular, relates to a sheet metal can body having a longitudinally extending lap side seam securely bonded with an organic adhesive.

Cemented, as opposed to soldered, side seam bodies are known in the art. Cans produced from' such bodies have found a substantial degree of commercial success for the packing of products which generate no substantial internal pressure, such as frozen citrus concentrate, household cleaners and polishes, and the like. One of the major selling features of such can bodies is that it is possible to provide printed decorations, as opposed to paper labels, completely around the external surface of the can body. However, such prior art cemented side seam can bodies do not have a high degree of bursting strength, particularly when the can is subjected to conditions necessary to process certain products such as the sterilization cooking for fruits and vegetables, or pasteurization of beer.

The very high strength adhesives known to the art have not been heretofore sucessfully used in the manufacture of cemented side seam can bodies for any one of anumber of reasons. Some of the major reasons are that although these adhesives have excellent cohesive strength they have been woefully deficient in their adhesion to a. metal surface or even to the coatings applied to sheet metal for making can bodies. Another drawback is that these high strength adhesives require a relatively prolonged setting time, in the order of minutes or even hours, which time periods are completely unsuitable for high speed can making operations where sufficient bonding strength to hold the can body together must be achieved within seconds or less.

It is therefore an object of the present invention to . Ί provide a lap side seacn can bod having exceptionally high bursting or hoop strength.

Another object is to provide a lap side se m can body vhich main tains its high bursting or hoop strength oven af er it is subjected to prolonged conditions of naois heato Tot another object is to provide a lap side seam can body which can be made apidly on high speed automatic eqnij/fiien .

A further ohjoet is to provide a can body blank from which a high strength lap sode seam ca body cart be made · Yet a further object is to provide a coating cotaposi-» tion for sheet metal from which a lap side s am can body is made, hich coating adheres tenaciously to the sheet metal under widely diverse ambient conditions and to which a high strength adhesive adheres tenaciously under those same condi tionso 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 embodiment thereof..

The above objects are accomplished by providing a tubular sheet metal, lap side seaaa can body having as a coating on at least the opposed surface of the longitudinal margins thereof included in the lap side seam, the reaction product of a polyvinyl acetal resin, a normally solid epoxide resin, a phenol-aldehyde resin and an acidic aliphatic amine phosphate, the opposed coated surfaces being bonded together with a linear superpolyamide adhesive. This can body is formed from a flat blank having its margins coated in the manner described and these marginso The isethdd and apparatus for the aali nfr of this can body blank is described in Israel Patent Specification No. 26319.

Referring to the drawings : Pig. 1 is a perspective view of a can body blank of the instant invention; Fig. 2 is a perspective view of a can body of the instant invention; Fig. 3 is a fragmentary enlarged sectional view taken substantially along line 3-3 of Fig. 2; and Fig. 4 is a modified form of the can body blank shown in Fig. 1.

As the preferred or exemplified embodiment of the instant invention. Fig. 1 shows a' substantially rectangular .can body blank generally designated 10 having for the metal component thereof thin gage sheet metal.11 in the order of magnitude of ten thousandths of an inch. This sheet metal, which may be thicker or thinner than the numerical value given, may be aluminum or low carbon steel, with or without an external plating of al!uminum, chromium, nickel or tin. Completely covering the opposed, extensive flat surfaces 12 and 14 is a particular organic coating composition 13 which will be defined more fully hereinafter. Tenaeiouslycadhered to the coating 13 along the upper surface of one longitudinal margin 16 of the blank 10 is an organic cement or adhesive 18, which will also be defined, more fully hereinafter. The adhesive 18 extends the full length of the margin 16 and inwardly from the edge of this margin, i.e. has a width of, from 7/32" to 9/32" and preferably 1/4", and upwardly from the coated surface of this margin, i.e. has a thickness of, from .003" to. .006" and preferably about .005".

The blank 10 is formed into an open ended tubular can body, generally designated 20 (Fig.2), on a high speed, automatic, the adhesive 18 to a semi-fluid, tacky condition and pressing the coated lower surface of the opposite blank margin 17 into Intimate contact with the tacky adhesive. Immediately thereafter the bonded side seam is chilled to set the adhesive and to secure the lapped margins together to form the can body.20 having a lap side seam generally designated 22 , including an inner lap 24 (from the margin 16 ) and an outer lap 26 (from the margin 17 ) . Bonding of the lapped margins is .accomplished in less than one second, c^- As best shown in Fig. 3 * the adhesive 18 does not bond directly to the sheet metal 11 of the. can body but rather to the opposed surfaces of the organic coating 13 included within the side seam 22. In other words, the high strength bond of the lap side seam 22 is a result of the tenacious adherence of the coating 13 to the sheet metal 11 and to the organic adhesive 18 interposed between the coated faces of the margins 16 , 17 .

As stated previously, the coating 13 extends over the entire flat surfaces 12 and 14 of the sheet metal 11 and as a result thereof over the entire inside and outside surface of the can body 20. However, it 3s to be understood that to form the high strength bond of the instant invention it is necessary onl that the coating 13 be present on the inner surface of the other lap 26 and: on the outer surface of the inner lap 24; or stated in another way, that the coating 13 be present on the opposed faces of the margins 16 , 17 included within, the lap seem 22 ... However, the coating 13 not only provides a highly adherent intermediate layer between the adhesive 18 and the sheet metal 11 , it also provides a protective coating for the metal over its exposed surface. For this reason it is preferred that the coating 13 extend over the entire inside and outside surface of the can body 20.

The coating 13 also provides an adherent base upon which to apply printing or other decorating for the outside surface of the can body 20. This decoration (not shown) is most conveniently applied in the flat, i.e. to that surface of the '· blank 10 or of a larger sheet from which the blank is cut which will later form the outside surface of the can body 20. This decorative coating does not extend into the margin 16 to which the adhesive 18 is adhered so as to Insure that the adhesive 18 is bonded directly to the coating 13. However, when the blank is formed into the tubular can body 20, this gap in the decorative coating is taken up by the overlap in the lap side seam 22 to provide substantially full circumferential decoration on the external surface of the can body.

Fig. 4 shows the modified form of the can body blank generally designated 10A. The can body blank 10A is similar to can body blank 10 previously described in all respects except that both the upper surface of the margin 16 and the lower surface of the' margin 17 have adhered thereto a strip of adhesive.18. In this manner when the blank is rolled into tubular configuration to form the can body 20 there will be an adhesive-to-adhesive seal in the lap side seam 22 rather than an adhesive-to-coating seal as in the preferred embodiment. The thickness of each strip of adhesive 18 on the blank margins is preferably less in the modified form shown in Pig. 4 than in, the preferred embodiment of Fig. 1 so that, upon overlapping and bonding the marginal edges, the adhesive thickness between the lapped margins will be substantially the same as or only slightly greater than in the preferred embodiment.

The coating 13 mentioned hereinbefore, consists essentially of, by weight, the heat reaction product of from 1 to 8 and preferably about 4 parts of a polyvinyl acetal resin; from 50 to 90 and preferably about 70 parts of a 1,2-eppxide resin; from 5 to 50 and preferably about 25 parts of a methylol phenol resin; and from 0.2,; to 2.0 and preferably about 0.6 parts of an aliphatic amine phosphate acid salt. The coating 13 is applied as a solution or dispersion of the above described Ingredients, before their inter-reaction, in a fugitive liquid. The solution method is preferable, and the particular liquids, whether solvents or dispersants, are not especially critical. It is necessary, however, that the liquid be volatile at baking temperatures which may be as low as 350°F. or as high as 650°P. At the lower temperature a baking period of about 20 minutes may be required and at 650°F. a time of 15 seconds may suffice. For the preferred solvent solution, the solvent must also be compatible with all the ingredients in their useful concentrations, so that precipitation, stratification or other separation does not occur. Due to the presence of vinyl polymers in the compositions, only very small, amounts of aliphatic hydrocarbons can be tolerated. Suitable solvents comprise aryl or aralkyl hydrocarbons blended with alcohols, ketones, ethers or esters and mistures thereof. Alcohols, ketones, ethers and esters or mixtures thereof can be used without the aryl or aralkyl hydrocarbons. Solvent systems comprising a mixture of aryl or aralkyl hydrocarbons and alcohols yield solutions having optimum viscosity for application and for this reason are preferred.

Examples of the aromatic hydrocarbon solvents are xylene, toluene, and petroleum fractions having a high proportion of aromatic hydrocarbons and having a boiling range of about 230°F. to 4l5°F. Examples of suitable oxygen containing solvents are butanol, di-acetone alcohol, isophorone, methyl isobutyl ketone, nitropropane , butyl Cellosolve, tetrahydrofuran, cyclohexanone, amyl acetate, methyl Cellosolve acetate, dissobutyl ketone and cyclohexanol .

The polyvinyl resins that are useful are polyvinyl formal, polyvinyl acetal, and polyvinyl butyral, each containing some free hydroxyl groups. The maximum useful polyvinyl alcohol content is about 22% . Mixtures of these polyvinyl resins can also be employed. The preferred resin is a polyvinyl acetal having a polyvinyl alcohol content of from about 8 to 21%, and specifically preferred in this class is polyvinyl butyral .

The 1 , 2-epoxide resin present in the coatings belongs to the class of complex polymeric epoxy-hydroxy ethers resulting from the catalyzed reaction of a polyhydric phenol with an excess of an epoxide, e.g. epihal chydrins and alkylene oxides, as described in U.S. Patents #2, 45β, 4θ8 and 2, 592, 560. The principal product of this reaction is a resinous epoxy glyceryl polyether comprising epoxy glyceryl radicals or hydroxyl substituted glyceryl radicals alternating with the divalent residue of the polyhydric phenol, which radicals are united in a chain through ether oxygen atoms. Prom this class of polymeric epox -Ayd oxy ethers only those that are solid at room temperature, about 65°P. have an epoxide equivalent, i.e. number of grams of resin containing one gram-equivalent of epoxide, of about 425 to 6, 000 and having a number- average molecular weight of from 1 , 000 to 4, 000 are operable. , The 1 , 2-epoxide resin preferred for use in the instant invention is the glyceryl polyether of 4, -dihydroxy-diphenyl -dimethyl methane (bisphenol) having an epoxide equivalent of from 2 , 000 to 2, 500 and a £gQ^Br average molecular weight of about 3> 000 .

The methylol -phenol resin is a methyl ol phenyl ether in which the H of the hydroxyl group attached to the phenyl group is substituted by an alkyl,. alkenyl, or cycloalkyl' group, or by an aralkyl or aralkenyl group, as well as the halogenated derivatives thereof. These resins are A-stage methyl ol -phenol resins, i.e. soluble and fusible, and are disclosed and described in U.S. Patent # 2, 579^ 330. The preferred resin from this class is amounts of the mono- and dimethylol phenyl allylether.

As the aminophosphate acid salt may be used ortho, meta and pyrophosphate salts of primary, secondary and tertiary aliphatic amines and mixtures thereof wherein the amine moiety contains 3 to 15 carbon atoms. The expression "acid salt" is meant to connote that one or more acidic hydrogen atoms, e.g. 3> from the phosphoric acid remain in the molecule of the salt. Phosphate acid salts found suitable include monodibutylamine pyrophosphate, triethylammonium metaphosphate, tertiaryoctylamine metaphosphate, laurylamine metaphosphate, allylamine metaphosphate, triamylamine pyrophosphate and dicycl ohexylamine metaphosphate. In the amounts used in the instant coating composition these amine phosphate salts are soluble in the volatile organic liquid system of the coating composition.

After application of the fluid coating composition described immediately above and during the baking of the thus coated sheet described hereinbefore, the non-volatile ingredients are inter-reacted and the volatile organic liquid is driven off so that upon completion of the baking ■ operation and subsequent cooling the solid inert adherent coating 13 remains on the metal sheet 11. At the elevated temperature of the baking operation the amine phosphate salt provides a multiplicity of functions some of which are not completely understood. It is believed that at the elevated temperature, the salt breaks down into an acid phosphate moiety and an amine moiety. The acid phosphate moiety apparently treats the surface of the metal sheet 11 in some manner to make it more adherent to the coating 13 and to passify the surface to make it corrosion resistant. It also provides acid functionality to catalyze the polymerization of the phenol -aldehyde resin toward, if not to, its thermoset condition. The amine moiety reacts with the 1,2- its polyvinyl alcohol component enters into reaction possibly with the 1,2-epoxide resin to provide the finished coating vith better flexibility, adhesion and moisture resistance .

A specific example of a fluid composition for application t.o; the sheet metal 11 to provide the finished coating 13 is as follows: Ingredient Parts by Weight E on 1007 70.0 1-all loxy-2,4,6,trimethylol-benzene 26.0 polyvinyl butyral containing about 12% polyvinyl alcohol 4.0 monodibutylaraine jjyrophosphate 0.5 toluone 100.0 butanol 70.0 Epon 1007 sot forth above is the trade name for a 1,2-epoxido resin meeting the definition of the preferred 1,2-epoxide resin. The first four ingredients were dissolved in the toluene and butanol through a homogenous solution which was uniformly applied to one large flat surface of sheet aluminium. The thus coated sheet was passed into an oven and baked at a temperature of about 400°P. for 10 minutes and thereafter cooled to provide the coating 13.

In addition to the above described coating, other types of epoxy based coatings also been found to be suitable for use as the coating 13 in promoting a tenacious bond within; the side seam and for providing a protective coating for the surface of the metal body 11. One such other coating which may be thus substituted is an epoxy-urea-formaldehyde coating, wherein the epoxy component is substantially similar to the 1,2-epoxide Tho linear superpolyaaiide adhesives useful in the instant invention are generally characterized by having recurring aliphatic amido groups separated by alkylene grops having at least two carbon atoms and having an intrinsic viscosity of at loast Ge o These superpolyaraides and the definition of* intrinsic viscosity are disclosed in U.S.Patent 2,130,948. Among th© superpolyamides %h ich are useful in the present invention are polypentaraethylene sebacamide, polyhexamethylene adiparaide, polyhexamethylene sebacamide, polydec methylene adipaciide, polydecamethylene sebacamide, poly-cj-phenylene sebacamide, 6-atnino-eaproic acid polymers, 7-amino-heptanoic acid polymers, 11-amino undecanoic acid polymers and 12-amino stearic acid polymers, with poly-ll-ataino-undecanoic being preferred.

It is believed that the tenacious bond between the epo.gr coatings and these su er-polyamide adhesives is produced as the result of a reaction product between the 1,2-epoxide resin and the adhesive.

It is thought that the invention and many of its attendant advantages will bo understood froa the foregoing description r and it will be apparent that various changesniay be made in the matter of ingredients, the identity and the proportions of the formulation, and the changes may be tnad© in the form, construction and arrangement of the parts of the article without departing from tho spirit and scope of the invention or sacrificing all of its material advantages, th© form herein before described being merely a preferred embodiment thereof.

Claims (1)

1. 1 A tabular sheet can body having longitudinall extending lap side the opposed surfaces of said sheet metal included said side having adhered thereto an organic and an organic adhesive securing the opposed surfaces of said coating comprising the reaction product of a polyvinyl an resin of the class of complex polymeric resultin from the catalyzed reaction of polyhydric phenol with an excess of an a and an acidic aliphatic ataine phosphate having carbon said adhesive a linear having an intrinsic viscosity of at least The can body set forth in claim 1 wherein said coating covers the entire inside surface can body set forh in ciaia 1 vh rein said coating covers entire inside and outside surfaces of said The can body set forth in claim 1 wherein said polyvinyl acetal resin contains roia 6 to polyvinyl alcohol and is selected from the consisting of polyvinyl polyvinyl butyrai and mixtures can body set forth in claim 1 wherein said resin is a glyceryl polyether having terminal radicals united with the divalent residue of a polyhydric phenol through ether oxygen atoms has epoxide of 425 to 12 The can body set forth in claim 1 wherein said aldehyde rosin an ether of a poiymethyol The can body forth claim 6 wherein said aldehyde resin is The can body set forth in 1 wherein said phosphate is pyrophosphate salt of an aliphatic amine the group consisting of tertiary amines and mixtures The can body set forth in claim wherein said is polymer of A blank for a tubular sheet metal can body havin a longitudinally extending lap side a organic coating on both sides of the longitudinal margins of said blank comprising the reaction product of a polyvinyl acetal resin of the class of complex polymeric ethers resulting froia the catalyzed reaction of a polyhydric phenol an excess of an a an acidic aliphatic amine phosphate having carbon and an adhesive comprising a linear having an viscosity of at least adhere to said coating on one side of one of said 1 he set forth in claim wherein said adhesive in the form o a strip extending the full length of said margin and is about wide and about e blank set forth in claim 10 said coating covers the entire surface of both sides of said 12α coating composition for application to sheet metal adapted to formed into a tubular can said composition polyvinyl resin polyvinyl alcohol content of 6 to by a normally solid resin having terminal glyceryl radicals united with the divalent residue of a pelyhydric phenol through ethor oxygen and having an epoxide equivalent of from 425 a soluble polymethylol phenol and a phosphate acid salt of an aliphatic amino having 3 to carbon The composition set forth in claim 13 wherein said resinous are dissolved and dispersed in a volatile organic 15 The composition set forth in claim 13 wherein said polyvinyl acetal resin has a number average molecular weight of from 21 000 to 000 and is selected from the group consisting of polyvinyl polyvinyl polyvinyl butyral and mixtures The composition set forth in claim 13 wherein said resin is a glyceryl polyether of 4 diphenyl and has an epoxide equivalent of from 000 to The composition set forth in claim wherein said polymethylol phenol resin is The composition set forth in claim 13 wherein said phosphate salt is 19 The composition set forth in claim 13 containing by weight 1 to 8 parts of said acetal 50 to parts of said epoxide 5 to parts of said phenol and 2 to 2 0 parts of said acid Dated this 24th day of ON BEHALF OF APPLICANTS insufficientOCRQuality