US 3623929 A
Description (OCR text may contain errors)
Nov. 30, 1971 T. M. WANNAMAKER ETAL 3,623,929
METHOD FOR PRODUCING SPIRAL WOUND CONTAINER Original Filed Oct. '7. 1966 6 Sheets-Sheet 1 III, HUHUHHR lllli ll Nov. 30, 1971 T. M.WAN NAMAKER E 3,623,929
METHOD FOR PRODUCING SPIRAL WOUND CONTAINER Original Filed Oct. 7. 1966 s Sheets-Sheet 2 2/6 21B 2m 2m I 20F 22A 205 M c 206' 2/ 27 20A 79 79F 21B Nov. 30, 1971 T. M.WANNAMAKER ETAL 3,623,929
METHOD FOR PRODUCING SPIRAL WQUND CONTAINER Original Filed Oct. 7, 1966 6 Sheets-Sheet e3 I Nov. 30, 1971 T. M.WANNAII\AAKER ETAL 3,623,929
METHOD FOR PRODUCING SPIRAL WOUND CONTAINER Original Filed Oct. 7, 1966 6 Sheets-Sheet &
II v 'IIIIIII Nov. 30, 1971 T. M. WANNAMAKER ETAL 3,623,929
METHOD FOR PRODUCING SPIRAL WOUND CONTAINER 6 Sheets-Sheet 5 Original Filed Oct. 7. 1966 Nov. 30, 1971 T. M.WANNAMAKER ETAL 3,623,929
METHOD FOR PRODUCING SPIRAL WOUND CONTAINER Original Filed 001:. v, 1966 6 Sheets-Sheet 6 US. Cl. 156-190 United States Patent 01 hce 3,623,929 Patented Nov. 30, 1971 3,623,929 METHOD FOR PRODUCING SPIRAL WOUND CONTAINER Thomas M. Wannamaker, Bastrop, La., and Charles I. Carter and Rupert 0. Rogers, Mobile, Ala., assignors to International Paper Company, New York, N.Y. Original application Oct. 7, 1966, Ser. No. 585,174, now Patent N 0. 3,428,239. Divided and this application Dec. 19, 1968, Ser. No. 813,347
Int. Cl. B65h 81/08 7 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for producing spiral wound containers in which a plurality of plies, coated on at least one surface with a thermoplastic coating with the inner ply coated on its inner surface with a slip or sanitary coating, are overlapped along adjoining edges and spirally wound onto a mandrel heated and adhesively secured with a thermoplastic coating to form a multi-ply spirally wound tube and the spirally wound tube is cut into can length units, the ends of the units are flared and can ends are attached.
The present application is a division of application Ser. No. 585,174, filed Oct.7, 1966, now Pat. No. 3,428,239. The present invention relates to method and apparatus for producing spiral wound containers.
Spiral wound containers have been available for many years and a variety of methods and apparatus have been devised for making such containers, for example as described in US. patents to Robinson Nos. 2,623,443 and 2,623,445, issued Dec. 30, 1952.
Spiral wound containers and particularly spiral wound cans have a number of advantages, the principal one of which is that the cost of such cans is less than the cost of conventional metal cans. As a result, spiral wound cans have been developed for the packaging of a wide variety of products. However, spiral wound cans previously available have been unsatisfactory for the packaging of products which must be maintained under substantial pressure, e.g., malt beverages such as beer and ale. Cans of beer and ale must not only be able to resist loss of internal gas pressure, which typically may be about 85-95 p.s.i. during pasturization, but also must be able to withstand considerable external abuse, such as immersion in ice water for extended periods and while such cans have been used successfully for packaging products such as refrigerated dough products, they have not been wholly satisfactory for this purpose.
A principal object of the present invention has been the provision of a novel and improved spiral wound can and in particular such a can which can be used to package beer and ale without substantial loss of gas pressure over extended periods of time.
Still another object of the invention has been the pro vision of such a can which can withstand the substantial external abuse to which cans of beer and ale are customarily subjected.
Another object of the invention has been the provision of such a can which can be used with conventional filling and closing equipment, suitably modified.
A further object of the invention has been the provision of a novel and improved can for beer and ale which is seamless so that the can body can be decorated around the full circumference thereof.
Still another object of the invention has been the provision of a can for beer and ale which is insulated so that it will not warm up as rapidly at room temperatures as metal cans.
Still another object of the invention has been the provision of a spiral wound can in which the paper walls have a lower moisture content than is customary for such cans, e.g., 4% as compared to 8%.
A further object of the invention has been the provision of a spiral wound can having a higher crush-resistance, both axially and radially, than is customary for conventional spiral wound cans of comparable weight.
Still another object of the invention has been the provision of a spiral wound can especially adapted for packaging products required to be maintained under moderate pressures, e.g., low carbonated soft drinks, soluble coffee, refrigerated dough products and pressure-packed snack foods.
A feature of the invention has been the provision of a novel and improved laminate construction for spiral wound can bodies.
Another feature of the invention has been the provision of a novel and improved end closure construction for spiral wound can bodies and which is especially adapted to retain the end closures in pressure-tight 'association with the can bodies despite substantial external impact forces.
Another object of the invention has been the provision of a novel and improved method of making spiral wound cans.
Another object of the invention has been the provision of a novel and improved apparatus for making spiral wound cans.
Another object of the invention has been the provision of a novel and improved spiral wound can and method and apparatus for making spiral wound cans suitable for in-line operation with can filling equipment.
Other and further objects, features and advantages of the invention will appear more fully from the following description of the invention taken in connection with the appended drawings, in which:
FIG. 1 is a top plan view, partly diagrammatic, illustrating a method and apparatus in accordance with the invention for making spinal wound can bodies;
FIG. 2 is a vertical sectional view taken along the line 22 of FIG. 1;
FIG. 3 is a vertical sectional view taken along the line 3-3 of FIG. 1;
FIG. 4 is a cross-sectional view of an outside laminate layer for a can body embodying the invention;
FIG. 5 is a cross-sectional view of an intermediate laminate layer or body ply for a can body embodying the invention;
FIG. 6 is a cross-sectional view of another intermediate laminate layer or body ply for a can body embodying the invention;
FIG. 7 is a cross-sectional view of an internal laminate layer or barrier ply for a can body embodying the invention, FIGS. 4-7 being intended to be generally to practical scale as to Width but being substantially enlarged as to thickness to better illustrate the construction of the various plies;
FIG. 8 is a side elevational view of a can body as produced by the method and apparatus of FIG. 1;
FIG. 9 is an enlarged cross-sectional view of the can body wall taken along the line 9-9 of FIG. 8;
FIG. 10 is a cross-sectional view of a typical can end closure element constructed in accordance .with the invention;
FIG. 11 is a partial longitudinal sectional view of a can body showing the flared edge provided prior to assembly of the end closure element to the can body;
FIG. 12 is an enlarged partial cross-sectional view of the end closure element of FIG. processed so as to have a rolled in edge and an annular layer of caulking;
FIG. 13 is an enlarged partial sectional view illustrating an intermediate point in the operation of assembling the can body and end closure;
FIG. 14 is a view similar to FIG. 13 at a more advanced point in the operation;
FIG. 15 is a view similar to FIG. 14 at a still more advanced point in the operation;
FIG. 16 is a view similar to FIG. 15 at a still mor advanced point in the operation;
FIG. 17 is a view similar to FIG. 16 but showing the completely assembled can body and end closure;
FIG. 18 is a partial vertical sectional view showing the end construction of a modified can body embodying the invention; and
FIG. 19 is a view similar to FIG. 17 but embodying the construction of FIG. 18.
While the invention will be described primarily in connection with cans for packaging beer and ale, it should be understood that the the the principles of the invention may be applied to cans for packaging other products.
Referring now to the drawings and more particularly to FIG. 1, there is shown a spiral tube winding machine basically of ordinary construction but with certain modifications in accordance with the invention.
In FIG. 1 a four ply or layer tube 10 is wound on a cylindrical manderl 11 by a winding belt 12. Motion is imparted to belt 12 by winding belt pulleys 13 and 14 which are suitably driven in a conventional manner. In FIG. 1 the tube 10 advances along mandrel 11 toward the left, as shown by arrow 15. Successive lengths of the tube 10 are cut off at predetremined locations by a suitable saw or knife, indicated diagrammatically at 16, to provide individual can bodies 17. One tube length or a plurality of tube lengths may be cut off simultaneously, and the cutting operation will be effected so that the usual printed matter on the outside ply of each can will be in proper registry, as is well known in the art.
The four plies which make up the tube 10 are designated 18, 19, 20 and 21, respectively. These plies are fed from conventional rolls (not shown). The ply 18 is the first to be Wound on the mandrel 11 and serves as the barrier ply of the can bodies. The ply 19 is the second to be wound and, as shown, overlies the barrier ply 18. The ply 20 is the third to be wound and, as shown, overlies the ply 19. The plies 19 and 20 are the can body plies and provide the principal structural strength for the can bodies. The ply 21 is the final ply to be wound and overlies the body ply 20. The ply 21 serves as the outside of the can bodies and usually will be provided with decorative or advertising matter on its outer surface, as is customary. The ply 21 thus forms the can label and will be referred to as the outer or label ply.
The construction of the barrier ply 18 is best shown in FIG. 7. The barrier ply 18 is formed as a laminate of three layers, inner layer 18A being a slip and sanitary coating, intermediate layer 18B being a metal foil, preferably aluminum foil, and outer layer 18C being a heat sealable thermoplastic, preferably a low density polyethylene. By low density polyethylene is meant a polyethylene having a density in the range of about .910 to .925 gram per cubic centimeter. A medium density polyethylene would have a density in the range of about .925 to .945, while a high density polyethylene would have a density above about .945. The term sanitary, as used herein, is intended to mean not only clean but also tasteless and odorless; in other words, a coating which will not impart a flavor or odor to the packaged product.
While polyethylene has been found to be particularly well suited for use as the heat sealable thermoplastic material for the layer 18C and similar layers of the other plies, other materials can be used. The most practical extrusion coatings at the present time are polystyrene and polymers or copolymers of the lower olefins (ethylene, propylene and butylene). Hot melt coatings of low molecular weight polyethylene, ethylene-vinyl acetate or wax blends of either resin would be suitable.
The layer 18B should be a self-supporting film free of pinholes. This layer serves as a principal moisture and gas seal for the can body and affords the structural basis for the barrier ply 18 as it is wound on mandrel 11. The layer 18B should be thin, but not to thin that wrinkling problems will interfere with winding. An aluminum foil thickness of 1 mil (.001) has been found well suited for the purpose. From the standpoint of a pinhole free layer, aluminum foil down to about .5 mil could be used, but wrinkling problems make a somewhat thicker foil more desirable with present handling techniques.
While aluminum foil has been found preferable, other foils could be used, e.g. a 2 mil tin plated steel foil. It is believed that the layer 18B could be made of plastic provided it was compatible with the rest of the can, would hold gas under pressure and would not cause sticking to the mandrel. So far no suitable plastic has been found.
The slip and sanitary coating forming layer 18A has three principal functions. These are facilitating sliding relative to the mandrel surfaces, i.e., reducing friction and avoiding sticking of ply 18 to the mandrel 11, a sanitary coating preventing direct contact between the metal layer 18B and the contents of the can and the sealing of such tiny holes as may exist or may be formed in layer 18B. In this regard, while layer 18B should be pinhole free, as a practical matter complete avoidance of pinholes is not reasonably possible in a practical commercial operation with equipment and materials available so that it is desirable to afford a sealing layer which will seal such tiny holes as may exist.
The coating forming layer 18A will be quite thin. Typically it may be applied in a weight of about 0.5 to 2.5 pounds per ream, a ream being 3000 square feet. The material used for the coating might be, for example, one of the commercially available vinyl materials in a nontoxic solvent system. The vinyl polymer material sold by Adcote Chemical Company under the name Adcote 501 is a specific example of a suitable slip coating. The coating may be applied in any convenient manner, as by spraying, rolling or brushing.
The polyethylene layer 18C is preferably extrusion coated onto the aluminum foil surface. The polyethylene layer 18C is used for heat sealing, as will be described, and also to serve as a moisture and gas barrier supplementing the aluminum foil layer 18B. The polyethylene further assists in sealing any tiny holes which may exist or which may be formed in the aluminum foil. The polyethylene coating weight can be selected as desired, a typical low value being about 3.6 pounds per ream which will yield a coating thickness of approximately one quarter mil. The thickness of the polyethylene layer should be sufiicient to afford a good heat seal. In many cases a polyethylene thickness of three quarter mil may be desired.
A free metal foil coated with polyethylene can be heat sealed directly to itself, with polyethylene contacting the slip coating. And since in such a construction there is no exposed paper edge as commonly encountered in the barrier layers of spiral wound cans, there is no necessity for forming a tucked seam or taped joint. Use of a kraft paper backed barrier seal requires a tucked seam or taped joint and produces a small area which may be about 4 to 5 mils thicker than the remainder of the barrier. While such thicker areas do not interfere unduly in making a can body pressure-proof, they tend to allow small openings to form at the contact areas with the metal end closures, making it difficult to obtain leakproof and pressureproof end closure attachments.
The moisture and pressure barrier properties of the polyethylene coated metal foil barrier ply described have been found well suited to cans for beer and ale.
As shown in FIGS. 1 and 2, the barrier ply 18 is wound onto mandrel 11 so that a complete barrier ply layer is formed. The leading edge of the ply 18 first contacting mandrel 11 at any instant (the left edge in FIG. 1) overlaps the trailing edge of the preceding barrier ply turn, affording an overlap as shown in FIG. 9. In this overlap the underlying surface is polyethylene of layer 18C while the overlying surface is the slip coating of layer 18A.
That portion of the polyethylene layer 18C which is included in the overlap, i.e., which contacts the slip coating layer 18A of the succeeding turn, is heated by a flame 22 directed thereon by a burner 23. The flame 22, which may be a gas flame, preferably contacts the polyethylene surface of the barrier ply in the region of the trailing edge on the mandrel just prior to contact thereof by the slip coating at the leading edge of the next turn. The flame heats and softens the contacted polyethylene surface so that it will heat seal to the slip coating.
The barrier ply supply or web is maintained under substantial tension so that the barrier ply turns will be tightly wound and so that the contacting polyethyleneslip coating surfaces will be forced together under substantial pressure to form a firm lap seam. The webs for the other plies are likewise maintained under substantial tension.
While it has been found preferable to provide the polyethylene coating 18C laminated on the metal foil layer 18B, the contacting polyethylene layer of the first body ply can be relied upon in case it should be desired to eliminate the coating 18C. However, in such case an adhesive joinder of the overlapping portions of the barrier ply should be provided to form a gas tight seal. A hot melt adhesive could be used for this purpose, e.g., a low molecular weight polyethylene or polyamide. Such a hot melt adhesive could be applied to the metal foil surface in the overlap region and could be activated by the flame 22 as described above in connection with the polyethylene coating 18C.
The construction of the two body plies 19 and 20 are preferably identical and comprise can stock layers, designated 19A and 20A, respectively, and polyethylene layers, designated 19B and 20B, respectively, extrusion coated to the can stock layers.
The can stock layers of the body plies afford the principal structural strength for the can bodies and hence should be made from relatively strong materials, kraft paper can stock having been found particularly well suited for this purpose. The minimum usable paper weight for the can stock layers is dependent, in part, on the paper tensile strength. Thus, it has been found that to resist failure of the cans by creeping under long-term loading, the can stock paper in the finished can should not be subjected to a long-term load exceeding about 40 to 50% of its ultimate tensile strength.
Another factor which influences the can stock paper weight is the winding angle of the body plies. The winding angle is measured, as is customary in the tube winding art, between the longitudinal axis of the ply in question as it approaches the mandrel and a line normal to the axis of the mandrel. This angle is shown for ply 19 as the angle in 'FIG. 1. The winding angle is important with respect to strength because most =Fourdrinier board has more strength in the direction in which it is made than in a cross direction. Hence it is desirable to take advantage of the greater machine direction strength of the paper by using as small a winding angle as practical. For a pressure can, a winding angle of about 27 has been found most advantageous. It should be noted that the circumferential (hoop) stress in a cylindrical vessel such as a beer can is twice that of the longitudinal stress and hence it is desirable to maximize the can body strength around the circumference of the can. It is desirable that the same winding angle be used for the barrier and label plies, e.g., 27.
For a pressure can expected to have to withstand a pressure of 85-95 p.s.i., which would be expected when 6 beer is pasteurized at F., the can stock layers for the body plies may conveniently be about 210 pounds per ream, assuming a winding angle of 27. Such a board would have a thickness of about 17 mils.
Because of the slight increase in tube diameter caused by the presence of the first body ply 19, the second body ply 20 should be slightly Wider than the first ply. For example, a 2ll-size can (12 ounce) might have a ply 19 with -a width of 4 inches while the ply 20 might have a width of 4 inches.
In general it is desirable that the can stock layers 19A and 19B have relatively smooth surfaces. One reason for this is that a smooth paper surface reduces the weight of polyethylene coating required for heat sealing the body plies. Another reason is that on the outside body ply 20 a smooth surface provides a smooth base for the label ply which greatly improves the appearance of the cans.
The polyethylene layers 19B and 20B of the body plies afford some moisture and gas sealing properties, but their principal use is in heat sealing. The polyethylene layers 19B and 20B are preferably low density polyethylene and the weight of each layer typically might be about 10.8 pounds per ream. While it is preferable to provide both of the polyethylene layers 19B and 20B, so long as polyethylene layer 18C is provided on barrier ply 18, the polyethylene layer 19B on inner body ply 19 could be eliminated.
An important feature of the pressure can of the invention has been the use of skived joints in forming the body plies. Sk iving contributes to the strength of the body plies by affording large contact areas at the joints. If butt joints were to be used, a gap of several thousandths of an inch would occur in commercial winding. Such a gap would allow a crevice to form and the high pressure in the can would force the barrier ply into this crevice, eventually causing a leak at the end seam.
lIn order to provide a sklived joint for each of the body plies, each of the body ply webs supplied to the mandrel 11 is passed through a skiving unit 24 which tapers the body ply edges as shown at 19C, 20C and 201). The skiving unit 24 may contain sanding wheels or other suitable devices for skiving the body ply edges.
The polyethylene coating on the body plies may be relied upon to join the skived ply edges to form respective tubes on the mandrel 11. However, it is preferable to provide hot melt adhesive to assist in the joining because the resulting seam will be stronger. For this purpose parallel beads of hot melt adhesive may be provided on the polyethylene coatings 19B and 20B adjacent the skived edges 19C and 20C. These parallel beads of adhesive are shown at 19B and 20B, respectively, and may conveniently be deposited on the can stock webs in skiving unit 24, although they may be deposited in a separate operation.
The can body ply webs 19 and 20 are passed under mandrel 11 from the opposite side shown for barrier ply web 18 and are wound on the mandrel in the usual way with the respective plies each forming complete tubes. The ply 19 overlies ply 18, while ply 20 overlies ply 19. The polyethylene layers 19B and 20B face upward in FIG. 1, causing these plies to be wound with the polyethylene layers facing the inside of the can body.
A series of burners 25, 26, 27 and 28 is positioned over the can stock ply Web 19 .just prior to the Web 19 reaching mandrel 11. Each of the burners 25-28 directs a gas flame downwardly onto the polyethylene layer 193 and completely across the width of the layer to heat the entire polyethylene surface to a heat sealing temperature. The last one of the burners, designated 28, preferably directs its flame onto the polyethylene surface at the point of contact of that layer and the barrier ply 18 on mandrel 11. The flame from burner 28 will thus not only heat the polyethylene layer 19B but will also heat the underlying polyethylene layer of the barrier 7 ply, affording a maximum heat sealing action. As shown at 1913' in FIG. 9, softened polyethylene from layer 19B will enter the tiny space at the lap of ply 18.
The burners 25-28 will also melt the hot melt adhesive beads 19E so that the hot melt adhesive will assist in forming the seam.
A set of burners 29, 30, 31 and 32, which may be identical to the burners 2528, is similarly positioned over can body ply web so that the latter forms a tube as described in connection with ply 19. In this case the polyethylene layer 20B will be heat sealed to the cam stock paper layer 19A.
The skived joint between the trailing edge of one turn of ply 19 and the leading edge of the next turn of ply 19 on mandrel 11 is shown at 19F in FIG. 9. The hot melt adhesive layer formed by melting the hot melt adesive beads 19B is shown at 196. The layer 19C adhesively joins the skived edge 19D to the polyethylene surface adjacent the edge 19C. Hence the skived edge 19C faces upward in FIG. 9. The corresponding skived joint 20F for ply 20 is similarly formed with the hot melt adhesive layer being shown at 20G.
It is important that the entire inner surface of each of the body plies to adhesively attached to the underlying ply so that the entire can body will act as a unit. This adhesive attachment occurs by heat sealing polyethylene and, in the skived joint areas, is preferably supplemented by the hot melt adhesive as described. The use of adhesive is particularly desirable when the skived surfaces 19D and 2013 are rough. If the weight of the polyethylene coatings 19B and 2013 should be increased substantially, the need for a hot melt adhesive would be reduced.
The label ply 21 is shown in detail in FIG. 4. The label ply is formed from four layers laminated together. These are an inner polyethylene layer 21A, a kraft paper layer 21B, a polyethylene layer 21C and a metal foil layer 21D. The principal strength for ply 21 is provided by layer 218 which might be, for example, a 25 pound (per ream) natural machine-glazed kraft paper. The kraft paper weight preferably lies in the range of about 25 to pounds. The polyethylene layers 21A and 21C may be laminated or coated on the opposite sides of the paper 21B in the usual way. The outer layer of metal foil may also be laminated to the polyethylene as is Well known in the art.
The foil layer 21D is preferably aluminum foil and may be as thin as desired so long as it is strong enough to be laminated to the paper. Typically the foil layer 21D might to 0.00035", although satisfactory results have been achieved with 0.000285" aluminum foil.
The polyethylene layers 21A and 21C might each be coated, for example, at a weight of 10.8 pounds per ream. The outer polyethylene layer 21C is preferably medium density to make the label more resistant to wrinkling on the can line. The inner polyethylene layer 21A is preferably low density to facilitate heat sealing to the outer body ply 20.
The label ply web 21 is fed to the tube on mandrel 11 from the same side as is barrier ply web 18, but at an advanced or downstream location relative to the previous plies 18, 19 and 20. It is desirable that the label ply 21 be wound on the mandrel after the tube has been contacted by the belt 12 so that the latter will not mar the appearance of the label. The web 21 is fed over the mandrel 11, as shown in FIGS. 1 and 3. A burner 33 is positioned under web 21 in advance of the web 21 contacting the tube on mandrel 11. Burner 33 directs a gas flame onto polyethylene layer 21A to heat the entire width of the layer 21A to a heat sealing temperature.
The outer paper layer 20A of the tube on mandrel 11 prior to contact with ply 21 is heated by a gas flame directed thereon from a burner 34. It is desirable that burner 34 heat the entire outer surface of layer 20A to facilitate heat sealing thereto of the heated polyethylene layer 21A. For this purpose the length of burner 34 should be correlated with the speed of rotation of the tube on mandrel 11. If desired, additional burners may be provided peripherally spaced to heat the entire surface of layer 20A. The tension maintained on label ply web 21 should be sufiicient to cause the same to be tightly bonded to the paper surface 20A of ply 20.
The leading edge of web 21 (left in FIG. 1) overlaps the trailing edge of the preceding turn of Web 21 to provide a simple lap seam, as shown in FIG. 9. Polyethylene from layer 21A fills this lap seam, as shown at 21A, affording a good sealing action similar to that of the polyethylene at 19B in the barrier layer lap seam.
It should be remembered that the thickness dimensions in FIG. 9 is tremendously exaggerated. Hence while the label ply lap seam looks large in FIG. 9, actually this lap seam is so thin as to be hardly noticeable in the final can body.
Each of the plies of the can body of the invention has been described as having one or more layers or coatings of polyethylene. So far as is presently known, polyethylene is the most suitable material for this purpose in view of factors such as cost, heat sealability, moisture vapor barrier properties and ease of extrusion lamination. Other plastics may, however, be found to have suitable qualities for these purposes and polyethylene could be replaced in one or more of the layers with such a plastic. In general, the polymers and copolymers of the lower olefins (propylene, ethylene and butylene) which can be extruded in molten form and laminated to paper or metal and which can be heat sealed would be usable in place of polyethylene. However, at the present time it is not believed that any such material would be as desirable as polyethylene.
It is desireable that the moisture-vapor barrier properties of the various polyethylene layers be as high as possible. Attention is directed in this regard to the processes and products of US. Pat. 3,161,560 and 3,196,063 issued Dec. 15, 1964 and July 20, 1965, respectively, to Leon J. Paquin et al.
An important advantage of the can body of the invention is the low moisture content which results from the absence of moisture containing adhesives commonly used in making spiral wound cans. Because of this low moisture content the can bodies may be made in an in-line operation with the can filling and closing equipment without the need for any intermediate drying period.
The individual can body 17 (FIGS. 1 and 8) cut off from the tube 10 is a simple cylinder in shape. It is desirable that both ends of the can body he flared outwardly, as shown at 35 in FIG. 11, before end closure are applied to the can body ends. The can end flare may be produced with any convenient apparatus as is well known in the art. Typically, if the internal diameter of the can body were 2.570 inches, the internal diameter of the flared ends might be 2.588 inches. In the usual operation, one end closure will be applied at the time the can is made and the other end closure will be applied at some later time, e.g., at a brewery after the can is filled with the product.
The types of can end closure and end seam construction usually adopted for metal cans have been used with satisfactory results in non-pressure spiral wound cans. However, such end closures and seam constructions have not yielded a pressure tight can suitable for products such as beer. Accordingly, a further aspect of the invention has been concerned with the provision of an end closure and end seam construction especially adapted for retention of pressure.
Proper design and attachment of the end closure is a very important aspect of the invention, particularly with respect to overcoming two major problems. One of these problems is a tendency for the can body end hook to unroll and allow the can end to blow off. The other problem is a tendency for the can end to deform permanently or peak under load, allowing the end to buckle outwardly and either blow off or lose pressure.
The techniques and constructions used with metal cans are not suitable for a spiral wound paper can intended to hold pressure. In this regard, it is common in metal cans to use a simple double seam with the end closure skirt held in a hook at the can end. This works well with metal cans because the metal can body wall is highly ductile and relatively thin, typically 6.6 to mils, allowing formation of a good hook section and a tight seam. Also the shear strength of a metal can body is extremely high so that there is little or no tendency for the end hook to cut through the can wall. Also a metal can body is essentially incompressible and will not spring back, resulting in a tight, mechanically strong seam.
In the cae of a spiral wound can, the sidewall is relatively thick, being of the order of 40 mils, making formation of a true body hook difficult, so that with a high pressure the body hook will tend to unroll. The principal structural features of the end closure of the invention which overcome this tendency to unroll are the use of an extended flat and an extended skirt on the end closure. The tendency of the end closure of the invention to peak is controlled primarily by deep drawing of the end closure, as will be described.
FIG. 10 shows a can end closure 36 embodying the invention with certain dimensions marked for ready reference. The end closure 36 has a skirt 37, a flat 38, a shoulder 39, a panel draw 40 and an end panel 41. The shoulder, flat and skirt form the end closure chime area. The skirt 37 corresponds to dimension D, and should be longer than conventional ends, typically to mils longer.
The dimension referred to herein will, of course, vary with can sizes, wall thicknesses and other factors. The dimensions are intended as typical examples for a can having an internal diameter of about 2.573 inches (which corresponds to a mandrel diameter of 2.570 inches), a height of 4.875 inches, a body wall thickness of approximately 40 mils and a maximum internal gas pressure of 85 p.s.i. The can body height will, of course, be reduced by the fianging operation, e.g., to 4.860". A typical value for the can body internal diameter at the flanged end would be 2.687. The end closure 36 might typically be made from 12.3 mil tinplate, which is thicker than customary for can ends.
The flat 38 corresponds to dimension B and typically might be 30 mils longer than a customary flat length. The shoulder 39 corresponds to the dilTerence between the chime height (dimension C) and the skirt height, dimension D. The shoulder 39 should be quite steep, the shoulder angle 0 typically about 4 to 6", which is approximately one-half the usual value. The height of panel draw 40 is dimension E and is substantially greater than usual, e.g., 50 mils greater.
Typical values for the dimensions shown in FIG. 10 for a nominal can body internal diameter of 2.573 inches are as follows:
A-2.5 88 inches B0..221 inch C-O.245 inch D0.087 inch E0.152 inch 0-4 to 6 degrees Before the can end 36 is joined to the can body the skirt 37 is rolled to have a rounded cross section and an inturned edge 42, as shown in FIG. 12. An annular layer of caulking material 43, which may be of any suitable type, is also applied to the inner surface of the can end. It is desirable that as much of the caulking as possible, preferably the entire quantity, be confined to the can end area between about the middle of fiat 38 and about the middle of shoulder 39. With the end seam construction of the invention, caulking located beyond about the middle of fiat 38 does no sealing and takes up space that should be filled with paper, while caulking located beyond about the middle of shoulder 39 does no sealing.
In joining the can end 36 to the can body 17, the can end, inthe condition shown in FIG. 12, and the flared open end of the can body, as shown in FIG. 11, are forced together. The internal diameter of can body 17 is smaller than dimension A of the can end so that the can body must be stressed substantially in forcing the can end onto the can body. For the typical dimensions given above this difference in diameter would be 2.5'88-2.573" or 0.015". This stressing occurs before the seam is started. The flame sealing to which the can body has been subjected during tube winding, particularly the flame sealing actions directly affecting the body plies, result in a can body which is substantially stiffer than is usual in spiral wound cans and this stiffness permits the can to withstand the stressing 'to which it is subjected when the can body and can end are forced together. FIG. 13 illustrates the can body and can end forced together, the can body being stressed so as to contact not only the shoulder surface 39 but also a portion of the fiat 38.
In FIG. 13, and also in FIGS. 14-17, the actual seam area extends outwardly from about the middle of shoulder 39, the start of the seam area being approximately at the point designated 44.
Since the chime height (dimension C) is relatively great and the shoulder is steep (small angle 0), there is a substantial area of contact between shoulder 39 and the inner surface of can body 17 inwardly of the end seam, i.e., inwardly of point 44. The extent of this contact, which is from about point 44 to point 45 might typically be about 50 mils. And since the can body is stressed in this region of contact, the frictional force between the can body and the shoulder below the seam area assists in retaining the can end 36 in place and in pressure tight relationship with the can body.
FIG. 14 shows a further rolling in of the can end rim and a slight separation of the can wall body plies 19 and 20. This separation occurs primarily because the respective body ply ends travel through different length paths in the rolling and seaming operation. FIG. 15 shows a continued rolling in of the can end rim and a reverse turning of the separated end of outer body wall ply 20. In FIG. 16 the rolling of the can end rim is almost complete. FIG. 16 also shows a tight lapping over of the separated ends of body wall plies 19 and 20.
Finally in FIG. 17 there is shown the completely rolled can end with all of the layers of the can wall tightly compressed between the skirt 37 and shoulder 39 and between skirt 37 and flat 38. It will be observed in FIG. 17 that skirt 37 and flat 38 form a smooth curved hook without a sharp angle at the juncture of the skirt and flat. Also the can body end completely fills the space between skirt 37 and flat 38. The smooth curved metal hook configuration and the complete filling of the metal hook with the can body material greatly decrease the tendency for the metal hook to unroll under pressure and hence increase the internal gas pressure which can be retained and also increase the period of time during which such high pressures can be maintained. This construction also reduces the tendency for the sharp metal hook to damage or shear off the can body wall hook which extends into the seam. The extended flat and skirt sections referred to previously are important in obtaining the good seam construction referred to. Careful rolling of the can end rim to achieve the seam of FIG. 17 is also important in obtaining a good seam.
As is evident from FIG. 17, the can body end is distorte'd in the rolling or crimping operation in which the can body and end are sealed. This distortion includes a separation of the ends of the two body plies 19 and 20. There is a tendency for the end of the outer body ply 20 to push the end of the inner body ply 19 out of the metal hook. In some cases this tendency may make it diflicult to obtain the most desirable seam construction. To minimize this problem the can body end may be cut or skived, as shown at 46 in FIG. 18, so that the ends of the body plies will be at the same elevation in the completed seam, as shown in FIG. 19. The skiving referred to should be effected before the can body end is flanged and may conveniently be done in a sanding or grinding device. It is desirable that the skiving be done so as to leave an uncut shoulder 47 at the inner surface of the inner body ply 19. This shoulder may have a width of approximately onehalf the thickness of the inner body ply.
With the skived can body end, as in FIG. 18, the ends of the body plies come to the same level in the can end seam because their initial lengths are different. This difference in length should as closely as possible equal the difference in the length of the paths through which the respective body ply ends travel. It is desirable that each ply fills an equal amount of space in the end hook.
For a can having the typical dimensions described above the difference in length of the body ply paths might be typically about 0.031". Hence the vertical height between shoulder 47 and the middle of body ply (at surface 46) should be about 0.031". The corresponding angle between the skived surface 46 and the horizontal will be approximately The various dimensions referred to herein are given only by way of example and should not be considered as limitations on the can construction of the invention.
While the invention has been described in connection with specific embodiments thereof and in specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.
What is claimed is:
1. The method of making spirally Wound can bodies having an inner barn'er ply formed as a laminate of a self supporting, substantially pinhole free, thin metal foil, a thin, continuous layer of a slip and sanitary coating on the inner surface of said foil and a continuous layer of a heat sealable thermoplastic material coated on the outer surfaces of said foil, at least one body ply overlying said barrier ply and comprising a first outer paper can stock layer and a continuous layer of a heat sealable thermoplastic material coated on the inner surface of said first outer paper can stock layer, and a label ply formed as a laminate having an inner heat sealable thermoplastic layer; said method comprising the steps of:
(a) winding a strip of said barrier ply on a mandrel to form a first continuous tube with said slip and sanitary coating contacting said mandrel and with a leading edge portion of each turn overlapping a trailing edge portion of the previous turn;
(b) heating the thermoplastic layer of said trailing edge portion of said barrier ply strip to a heat sealing temperature after said strip contacts said mandrel but prior to contact therewith of said leading edge portion of the succeeding turn;
(c) winding a strip of said body ply on said mandrel and over said barrier ply tube to form a second continuous tube, said thermoplastic coating of said body ply being disposed to contact said barrier ply;
(d) skiving the side edges of said body ply prior to winding thereof on said mandrel to provide tapered paper surfaces at each edge of said body ply, the winding of said body ply being conducted so that the thermoplastic coating at the leading edge portion of said body ply overlies the tapered paper surface at the trailing edge portion of the preceeding turn of said body ply;
(e) heating the entire width of said thermoplastic layer of said body ply to a heat sealing temperature just prior to contact thereof with the underlying tube on said mandrel thereby to heat seal substantially the entire width of said body ply to said barrier ply and to heat seal said leading edge portion of said thermoplastic coating of said body ply to said underlying tapered paper surface;
(f) winding a strip of said label ply on aid mandrel to form a third continuous tube as the outermost ply of said can body, said label ply being disposed with said inner heat sealable layer thereof disposed toward said mandrel; and
(g) heating substantially the entire width of said inner thermoplastic layer of said label ply to a heat sealing temperature just prior to contact thereof with the immediately underlying tube on said mandrel thereby to heat seal said label ply to said immediately underlying tube across substantially the entire width of said label ply.
2. The method of making spirally wound can bodies having an inner barrier ply formed as a laminate of a self supporting, substantially pinhole free, thin metal foil, a thin, continuous layer of a slip and sanitary coating on the inner surface of said foil and a continuous layer of a heat sealable thermoplastic material coated on the outer surface of said foil, at least first and second body plies overlying said barrier ply and each comprising a first outer paper can stock layer and a continuous layer of a heat sealable thermoplastic material coated on the inner surface of said first outer paper can stock layer, and a label ply formed as a laminate having an inner heat sealable thermoplastic layer; said method comprising the steps of:
(a) winding a strip of said barrier ply on a mandrel to form a first continuous tube with said slip and sanitary coating contacting said mandrel and with a leading edge portion of each turn overlapping a trailing edge portion of the previous turn;
(b) heating the thermoplastic layer of said trailing edge portion of said barrier ply strip to a heat sealing temperature after said strip contacts said mandrel but prior to contact therewith of said leading edge portion of the succeeding turn;
(c) winding a strip of said first body ply on said mandrel and over said barrier ply tube to form a second continuous tube, said thermoplastic coating of said first *body ply being disposed to contact said barrier P y;
(d) winding a strip of said second body ply on said mandrel and over said second tube to form a third continuous tube, said thermoplastic coating on said second body ply being disposed to contact said second tube;
(e) skiving the side edges of said body plies prior to winding thereof on said mandrel to provide tapered paper surfaces at each edge of said body plies, the winding of said body plies being conducted so that the thermoplastic coating at the leading edge portion of each of said body plies overlies the tapered paper surface at the trailing edge portion of the preceding turn of the corresponding body ply;
(f) heating the entire width of said thermoplastic layer of each of said body plies to a heat sealing temperature just prior to contact thereof with the underlying tube on said mandrel thereby to heat seal substantially the entire width of said first body ply to said barrier ply, to heat seal substantially the entire width of said second body ply to said first body ply and to heat seal said leading edge portions of said thermoplastic coatings of said body plies to the corresponding underlying tapered paper Surfaces;
(g) winding a strip of said label ply on said mandrel to form a fourth continuous tube as the outermost ply of said can body, said label ply being disposed with said inner heat sealable layer thereof disposed toward said mandrel, a leading edge portion of said label ply being arranged to overlap a trailing edge portion of the preceding turn of said label ply; and
(h) heating substantially the entire width of said inner thermoplastic layer of said label ply to a heat sealing temperature just prior to contact thereof with the immediately underlying tube on said mandrel thereby to heat seal said label ply to Said immediately underlying tube across substantially the entire Width of said label ply, said heating of said inner thermoplastic layer of said label ply also serving to heat seal together said overlapping edge portions of said label ply.
3. The method set forth in claim 2 comprising the additional step of applying hot melt adhesive to the edge portions of each of said body ply strips which, upon winding, are to overlie the tapered paper surfaces at the trailing edge portion of the preceding turn of the corresponding body ply.
4. The method set forth in claim 2 in which the winding angle for each of said body plies is about 27 5. The method set forth in claim 2 comprising heating substantially the entire outer paper surface of the outermost one of said body plies just prior to contacting thereof by said label ply strip thereby to improve the bonding of said inner thermoplastic layer of said label ply to said outer body ply and to reduce substantially the moisture content of the paper in said outer body ply.
'6. The method set forth in claim 5 in which said step of heating substantially the entire outer paper surface of the outermost one of said body plies is efiected by contacting said outer paper surface With a gas flame.
7. The method set forth in claim 2 in which each of said heating steps is effected by contacting the surface to be heated with a gas flame.
References Cited UNITED STATES PATENTS 2,785,700 3/1957 Vovanovich 156-195 X 3,452,506 7/1969 Broerman 156-195 X 3,279,333 10/1966 Blair et a1 93-94 3,280,709 10/1966 Elam 93-94 3,366,719 1/1968 Lueders 156-187 X 3,376,180 4/1968 Larson et a1 156-195 3,400,029 9/1968 Mesrobian et al. 156-195 X 3,429,522 2/ 1969 McCleery-Cunningham et al.
156-188 X 3,430,054 3/1969 Cunningham et al. 156-195 X 3,457,130 7/1969 Morrison 156-190 3,494,812 2/1970 Cvacho 156-195 BENJAMIN R. PADGETT, Primary Examiner G. SOLYST, Assistant Examiner US. Cl. X.R. 93-94; 156-195 Col. 3,
( A Attest:
EDWARD M.FLET cHER,JR.-- Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated November 30,- 1971 Invcntor(s) Wannamaker et a1.
It is certified that error appears in the aboveidentified patent and that said Letters Patent are-hereby corrected as shown below:
line 29 "manderl" should be ma'ndrel line 41 after 19C, insert 19D,
line 50 "closure" should "be -closures line 16 "cae" should be case line 52 after typically insert being Signed and sealed this 18th day of July 1972.
ROBERT GOTTSCHALK Comissioner of Patents USC OMM- DC 60376-1 69