US 3322045 A
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May 30, 1967 v. TANONA SEALING CLOSURES Filed Oct. 5. 1964 FIG! United States Patent 3,322,045 SEALING CLOSURES Robert V. Tanona, Lexington, Mass., assignor to W. R. Grace & Co., Cambridge, Mass, a corporation of Connecticut FiledOct. 5, 1964, Ser. No. 401,427 4 Claims. (Cl. 933.1)
This invention relates to the application of can ends to can bodies, and particularly to the application of metallic can ends to composite can bodies.
Composite can bodies are made from paper stock which may be wound either convolutely or spirally. If the container is to contain a fluid such as motor oil, the interior wall of the can body is liquid-proofed, sometimes with a resinous coating, but much more frequently wit-h an impervious lamination, often of aluminum foil. Making dependable and secure end closures on composite cans has always presented a problem because the composite can body presents two diificulties which do not appear in the closing of metallic cans:
(1) The cut end of the tube exposes a cross-section of the fibrous inner layers into which the liquid contents of the can can seep or be drawn by capillarity-a defect known as wicking. At best, wicking stains the label badly; at the worst, it so weakens and softens the can body that the cans distort and sometimes burst open.
(2) The soft, compressible nature of the can body makes it difiicult to seal the cans in a leak-proof manner.
I have discovered that fast and dependable can end closing can be accomplished if the exposed end and a portion, at least, of the interior wall of the flange of the can body be coated with a thermo-p-lastic sealing composition. Then, if an end, heated to well above the melt temperature of the thermo-plastic, is applied and immediately seamed on the can body, the very high pressure exerted by the seaming rolls drives the thermoplastic-now heated to melting by the can endinto the exposed interfibre spaces of the can body. The end seam is thus not only mechanically made, but its sealing material is simul taneously molded into the seam by heat and pressure.
The closing operation can be performed on ordinary can end closing machinery-the only change which is required is the addition of means to keep the feed-stack of metal ends at the correct elevated temperature.
The process may be better understood by reference to the accompanying drawings, wherein FIG. 1 illustrates one method by which the ends of the cans may be coated with the thermoplastic,
FIG. 2 is a perspective view of a portion of an endcoated can body, and
FIG. 3 is an enlarged cross-section of the completed end-seam.
In carrying out my invention, the individual can bodies, 10, after they have been cut to proper length and their ends flared or flanged, may be placed on a mandrel which rotates the body, 10, in proximity to a nozzle, N, which places a fine stream of molten thermo-plastic peripherally on the end of the body, 10, placing it as shown in FIG. 1. The mandrel, M, is rotated by the motor, P. It will be noticed (see FIG. 2) that following this operation the thermo-plastic covers the exposed fibres of the cut end and has formed a bead, 13, on the flange, 14, of the can, 10, which adheres to the exterior and interior can body walls for a slight distance along their extent. Bead, 13, completely covers the extreme end and the major part of the internal surface, 15, of the flange, 14. But preferably, head, 13, should cover very little of the exterior surface, 16, of flange, 14. If the surface, 16, carries much thermo-p-lastic, squeezing may ensue and the rolls may become dirty.
3,322,045 Patented May 30, 1967 Subsequent to the body-end coating operation, the thermoplastic is allowed to cool and to solidify. Thereafter, the end-coated can bodies are placed on the feed track of a conventional can end-closing machine which, however, is equipped with composite can type closing rolls. The stack of ends in the feed-stack of the machine is maintained at appropriate elevated temperatures, for example, between 350 and 380 F. These temperatures are generally representative of temperature values which will cause the melting and reflow of the bead, 13, of a considerable number of thermo-plastic compositions which may be placed on the can bodies. Certain compositions with high softening points may require higher (400-425 F.) temperatures. Seals can be made with a wide variety of substances-asphalt and ester-gums are examples, but for high performance and suitability for a major portion of the substances now packed in composite cans, the following are especially suitable.
These sealing compositions include polyamides, e.g. Versalon 1112, a polyamide supplied by General Mills, having a softening point of from 230 to 240 F., and a viscosity at 374 F. of 31-44 poises. Its tensile strength at F. ranges from 1900 to 2100 psi. Other materials are equally eflective, e.g. the polyamide resins formed by the reaction of diethylenetriamine and ethylenediamine reacted with dimerized linoleic acid and supplied by the Dewey & Almy Chemical Division of W. R. Grace & Co. as Hot Melt 8305 or a polyamide resin formed by the reaction of ethylenediamine with dimerized linoleic acid, supplied by the same company, as Hot Melt 6355 6H. The ball-and-ring softening points of the above resins are 270-300 F. and 226 F. respectively. These resins can be used without admixtures, but advantageously can be combined with proportions of other thermo-plastic substances, fillers, etc. Proprietary hot-melt compositions are also useful. Additionally, an amorphous copolyester resin, the major proportion of which is terephthalic acid and the minor proportion isophthalic acid, is also'useful. This material available in molar ratios of terephthalic acid to isophthalic acid ranging from 70-90 and 30-10, and having crystalline melting temperatures between 338 F. and 392 F. is available from the United Shoe Company. When the latter material is used, the temperature of the ends when applied to the can body should be raised above the lower ranges given to reach the proper melt temperatures.
Tests conducted on cans manufactured as above showed the following results:
Example I A number of #401 size, l-quart motor oil can bodies were end-coated as described above, with a thenno-plastic composition having a specific gravity of 0.99 and a viscosity as measured on a Brookfield viscometer equipped with a #3 spindle of 900 centipoises at 365 F. and 60 rpm. Its composition is approximately 50 parts rnicrocrystalline wax, MAP. 172-177,
25 parts of the resin copolymer of ethylene and vinyl acetate, softening point 243 F and 25 parts of petroleum hydrocarbon resin (Hot Melt 70631H, Dewey and Almy Chemical Division, W. R. Grace) The end coatings weighed between 300 and 400 mgs.
The temperature of the hot-melt at the moment of application was 365 F. Subsequent to coating the ends of the can bodies with the molten hot mix, the can bodies were allowed to cool. Can ends formed of #75-lb. tin plate were heated to temperatures of between 350 and 380 F., and were seamed on the can body by an Angelus seamer, #291, equipped with R11S15 seaming rolls. The temperature of the can ends just before being seamed, as determined by an Alnor Portable Pyrometer, type 4200,
3 was between 300 and 320 F. A second reading taken just after the seamed-on end was ejected from the seaming machine showed the temperature then to be 270 F. Subsequent to applying ends to the can bodies, the cans were subjected to an end blowofl test by injecting compressed air into the sealed can.
End blew ofistructural failure of can. Over 30 p.s.i Do.
The maximum pressure recordable on the blowofi pressure gauge was 30 lbs. Air-line pressure was maintained at 35 lbs. Consequently, in the table, blowotf pressures recorded as over 30 psi define a pressure greater than 30 psi, but no greater than 35 psi l-qt. motor oil cans are not designed to withstand high internal pressure. Rupture of the can body was to be expected at about 30 lbs.
Example 11 Flange Coating Blowofi Pressure Comments End did not blow olistructural failure of can.
D0. End did not blow ofi.
End did not blow oft structural failure of can.
United Shoe S179-170- 24.5 p.s.i
Example III As counter examples, plain ends seamed on to #401 l-qt. motor oil can bodies blew oft" item the can bodies at l722 lbs. In every instance, the ends blew ofl the body of the can.
Example IV One-quart #401 motor oil composite can bodies (aluminum foil lined), were flanged and the flange was covered as described with a head of Hot Melt #70631H (previously identified). The cans were filled with 10-W detergent motor oil to an inch from the top of the can. The open ends of the cans were then closed with 75-lb. tin plate ends which had been heated to temperatures of 350 to 380 F. The temperature of the can ends just prior to seaming (determined as in Example I) was between 300 and 320 F. Seaming was performed on an Angelus 29P seamer, equipped with Rll-SIS seaming rolls. Temperatures (determined as in Example I) of the ends immediately after ejection from the sealing machine were between 250 and 260 F. The cans which were completely outside labeled were stored at room temperature (test end down) for 16 hours were then carefully examined for evidence of label staining. The label was then removed and the cans were examined for wicking. No wicking was observed. The cans were then stored, test end down, at 100 F. for the following times with results as tabulated.
Days of Total Cans Cans Wicking Notes Storage lFrom Test End 1 9 2 (A) 23--- 9 1 (B) 40 8 1 (C) (A) The most heavily wicked can was removed from the test and examined. A large foil crack was found over the butt seam in the flange area of this can which extended beyond areas covered by the sealing material. The remaining wicked can was retained in the test.
(B) No additional cans had wicked.
(C) No additional cans had wicked. The test was discontinued. The double seam area of all test ends was examined. The wicked can was examined for foil cracking in the flange area. None was evident.
Example V.-Water Pack Test Time of Storage Total cans Cans Wicking at F. from Test End The test was discontinued after the 50-day storage, and the cans were examined. 10 out of 10 cans showed no leaks in the end seam area.
The above tests show that the seams formed in the manner described are dependable and substantially leak-proof, even under rigorous test conditions.
It is believed that the eflectiveness of the present method of forming the end-seam closure is due to the fact that the seam is formed under the dual conditions of heat and pressure, i.e. the thermo-plastic is raised by the heat derived from the can end to a temperature at Which it is a flowable, or at least a moldable, material, and the pressure of the closing rolls which is exerted at the same instant that the thermo-plastic reaches moldable temperatures makes What, in eiiect, is a completely remolded seal for the end. The thermo-plastic material completely coats the cut end of the can body, and the high closing pressure plus the fluidity of the thermo-plastic at that moment drives a considerable portion of the applied thermo-plastic into the fibrous inner layers of the can body. Wicking is thus successfully blocked. The high adhesion which these materials exhibit bothto the metal of the closure and to the can body not only adds to the mechanical strength of the seam,
but prevents any penetration in the seamed area of the fluid 7 contents by seepage along the interface of the sealing material and the metal closure or the can body.
Coating the cut end and flange as described is but one way of covering the exposed fibres and the interior of the flange with the thermo-plastic sealing composition. Others will suggest themselves to those familiar with this disclosure.
For example, the cans, standing upright, may be run under a roll on which a film of molten thermo-plastic, doctored to the proper thickness, is spread. Also, the ends of the can bodies can be dipped into a thin film of thermoplastic spread over a hot plate. This latter method coats both the interior and exterior Walls of the flange equally. While acceptable for a number of uses, it may cause squeezing of the thermo-plastic below the exterior margin of the metallic end closure.
When the seams are rolled under heat and pressure in the manner described, very few leaking seams will be produced, contrasting rather sharply with the results of procedures Where the cans are seamed in the cold and then are heated to cause the reflow of the sealing composition.
1. The method of sealing metallic can-end closures to composite can bodies, which includes forming a bead of thermo-plastic sealing composition on the flanged area of a flanged can body, cooling the bead to solidify it, heating a can end closure to a temperature sufficient to melt said sealing composition, applying the hot closure to a can body and roll-seaming the hot closure on said body while the closure remains at an elevated temperature, whereby heat derived from the hot closure is suflicient to cause the reflow of the thermo-plastic and the same is remolded into the seam area under the simultaneous conditions of heat and pressure.
2. The method of claim 1 wherein the thermoplastic composition is a polyamide resin having a softening point lying between 230 and 300 F., and wherein the temperature of the can end closure at the moment of closing is in excess of the said temperature.
3. The method of claim 1 wherein the thermo-plastic is the copolyester of terephthalic and isophthalic acid and the metallic can end closure, prior to seaming, is heated to References Cited UNITED STATES PATENTS 2,378,470 6/1945 Cusmo 93-39.1 X 2,802,631 8/1957 Boyd 93-391 X 3,072,517 1/1963 Gaylord.
3,202,065 8/1965 Bolcato 9339.1 X
BERNARD STICKNEY, Primary Examiner.