Technical Field;

The present invention relates to tier sheets for can body containers of the type which package newly formed can bodies in tiers or layers.

Background Art:

In the manufacture of aluminum beverage cans, a cup-shaped can body consisting of a cylindrical wall and a bottom, is formed by coining and drawing operations as from a metal blank. The end or top of the can is formed from sheet material by coining and drawing operations. Subsequently, the can body is filled with a beverage and the end is attached to the top rim of the can body as by a seaming operation to effect the closure. Separate machines are needed for these several operations and the filling and closing operations are at a filling plant which may be remote from the can body and end forming operations. Accordingly, the can bodies and ends are packaged in separate containers for shipment and storage until they are ready for use at the filling plant.

Can bodies are packaged as tiers or layers in the container. As they are formed, can bodies are discharged onto a conveyor which moves them tc a loading station in an

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upright position. When a charge, i.e., a sufficient number of can bodies accumulate at the loading station to form a layer or tier, they are shifted laterally into the container, onto a tier sheet. The completed container will consist of a number of such layers or tiers of closely packed, upright can bodies. A pallet forms the base of the container, tier sheets are between the tiers of can bodies thereabove and a cover frame is placed on top of the container. To complete the container, bands tie it together.

To render the container-forming oepration automatic and as efficient as possible, the loading station includes sidewall members to permit a natural movement of can bodies from the conveyor to form a closely packed charge of can bodies. A gate between the loading station and the container then opens to move the charge onto a tier sheet. Cans slide across the tier sheet and against a bounding fence about the tier sheet forming a close-packed hexagonal pattern upon the tier sheet. Next, the container is lowered with respect to the loading station and another tier sheet is placed on top of the can body layer to permit the operations above described to be repeated.

The open top can bodies are thin-wall, lightweight, delicate units and they must be handled carefully. As a charge of can bodies moves from the loading station, the can bodies will slide upon and across the tier sheet. A small frictional resistance between the can bodies and the tier

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sheets is all that can be permitted to prevent the leading cans from falling over. This is especially important as the cans first move onto the tier sheet. Other frictional effects may occur. It is possible for the movement of the charge of can bodies onto the tier sheet to push the tier sheet out of place. It is also possible for can bodies to fall out of the container during shipment and storage.

The conventional tier sheet formed of chipboard is not really satisfactory. Can bodies fall over while loading and out of completed containers creating a constant problem. Also, the overall operation is such that the tier sheets can be recovered and returned for reuse but this is not practical when chipboard tier sheets are used. In the first place, chipboard is weak and brittle' and only a few reuses are possible; also, fumigation is necessary to kill paper mites which find their way into the chipboard during shipment and storage.

Plastic tier sheets have been heretofore proposed but repeated attempts have resulted in unsatisfactory performance. When plastic sheets thin enough to be economical are used, they are either too brittle to handle or they have a tendency to warp and curl causing can bodies to be misaligned or to fall over as they move onto the tier sheet. There is also a tendency for the tier sheets to slip out of place from an aligned position over the next lowermost tier of can bodies as a charge of can bodies moves from the loading station and onto the tier sheet. As with

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4 chipboard sheets , there is a tendency for cans at the edges of a completed container to fall out of the container. Plastic, being dielectric, will cause the many can bodies to act as a condenser and build up an electrostatic charge so strong as to injure a workman handling the container. Finally, a number of plastic materials can impart an undesirable taste and odor to the beverages which fill the cans.

There is a real and definite need for an improved plastic tier sheet to overcome these disadvantages, and the present invention was conceived and developed with the foregoing and other considerations in view.

Disclosure of invention '

It is, therefore, a primary object of the present invention to provide a plastic tier sheet which is free of the aforementioned and other disadvantages.

The invention comprises, in essence: a plastic tier sheet for a can body container formed of a selected blend of polyolefin resins having a suitable range of strength, hardness and stiffness. Also, a quality of dimensional stability which minimizes the tendency for the sheet to warp or curl when lying flat. Also, anti-static properties are incorporated into the sheet. Also, its chemical stability renders it odor-free. Finally, the improved plastic tier sheet is thin, rigid but not brittle and with the under

surface and upper surface having differing frictional characteristics.

Other objects of the invention are to provide a plastic tier sheet for a can body container which (1) will lie flat and will not warp or curl when placed upon a tier of can bodies; (2) will not shift out of position when a charge, of can bodies moves onto the sheet; (3) will permit a charge of can bodies to move across the sheet without any significant number of cans falling over; (4) will effectively grip all can bodies and practically eliminate the tendency for cans to fall out of the container during storage and shipment; (5) will be free of an electrostatic charge buildup; (6) will function --properly at temperature extremes encountered in different processing plants during different seasons; (7). is a rugged unit that can be reused many times; (8) is made of material capable of being reprocessed; and (9) is a lightweight, economical unit easy to handle and to store.

Brief Description of Drawings:

With the foregoing and other objects in view, as will more fully hereinafter appear, this invention comprises certain constructions, combinations and arrangements of parts and elements and sequences and operations as now described with reference to a presently preferred embodiment, defined in the appended claims, and illustrated in the accompanyings drawing, in which:

Fig. 1 is a diagrammatic side elevational view of an apparatus for the movement of can bodies from a conveyor to a holding station and thence to a container being formed by the apparatus, with portions of the apparatus being broken away and in section to show parts otherwise hidden from view.

Fig. 2 is a diagrammatic plan view of the apparatus shown in Fig. 1, with a charge of can bodies accumulating at the holding station for movement onto a tier sheet at the container and with a portion of the tier sheet being removed to show a layer of can bodies beneath the sheet.

Fig. 3 is a side elevational view of a completed co.n.tainer. similar to the* contai.ner being formed» in» Fig. 1 but on an enlarged scale, the view also showing the manner in which a can body may fall out of the container.

Fig. 4 is a fragmentary sectional view as taken from the indicated line 4-4 in Fig. 3 but on a further enlarged scale.

Fig. 5 is a fragmentary sectional detail as taken from the indicated line 5-5 in Fig. 4 but on a greatly enlarged scale and the thickness of the parts being exaggerated to better illustrate their construction and function.

Best Mode for Carrying out the Invention:

Referring first to Fig. 3 of the drawing, the completed can body container is carried upon a pallet P. Tiers or layers L of can bodies C are stacked upon the pallet P with

the improved plastic tier sheets T upon the pallet, between each can body layer and on the top layer L. A cover frame F tops the stack and the container together during shipment and storage. It is to be noted that can bodies may fall out of the container as indicated by the can C' . It is desirable to keep such mishaps to a minimum.

A container is formed one layer at a time by apparatus shown in Figs. 1 and 2. A conveyor M receives can bodies C from a forming machine, not shown, and directs a flow of can bodies to a holding station H. The holding station H is suitably fenced and is as wide as a tier sheet T and long enough to hold more than a charge of can bodies sufficient to constitute a layer L of the container. The excess* space is to receive' can bodies from the conveyor after a charge of can bodies is formed and before the charge can be moved to the container. A container-forming elevator E is positioned alongside the discharge end of the holding station H to support the pallet P holding layers of can bodies. The elevator E lowers a partially formed container so that the can body layers L are moved below the surface of the holding station and with a tier sheet T on the top layer L being level with the surface of the holding station H.

The surface of the holding station H is of smooth, slick material such as polytetrafluoroethylene to permit can bodies to easily slide across it to the discharge end. A finger-type gate G normally closes this discharge end to bring about a build-up of a can body charge as illustrated.

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8 When a can body charge is formed, the gate G opens and a short, wide conveyor belt N, forming part of the holding station surface, moves the can body charge en masse from the holding station and onto the tier sheet T of the partially completed container to form another layer L. A fence F about the tier sheet holds the can bodies thereon, and any can bodies which may fall over are placed upright to complete the layer L. When the charge is properly positioned upon the tier sheet, the gate G is closed. Another tier sheet T is placed on the newly formed layer L and the elevator lowers the partially completed container to repeat the above-described operation.

^* It ^' was found that several- factors had to be considered in developing a -comparatively thin plastic tier sheet T. The charge of lightweight can bodies must move onto the tier sheet smoothly and if possible without any cans falling over. It is almost impossible to avoid tipping cans over but such mishaps should be minimized. The aparent frictional resistance between the tier sheet and the sliding can bodies must be small. It is especially important that the static frictional resistance encountered momentarily when the can bodies first move onto the tier sheet also be small. If this resistance is at all significant, a whole row of can bodies can fall over requiring an operator to shut down the apparatus. Another factor involving friction is the drag against the plastic tier sheet caused ^' by the charge of moving can bodies onto the tier sheet. This drag

should not be such as to cause the tier sheet to slide out of place. Another friction factor, and a more serious problem, is the loss of can bodies from completed containers as in the manner illustrated by can body C' at Fig. 3. The tops and bottoms of the can bodies must be gripped by the tier sheets above and below them. If the can bodies are to stay in place between the tier sheets T in the container C, frictional resistance must be imparted by this gripping action.

In addition to problems related to friction, other factors must be considered in selecting a suitable plastic for a tier sheet T. Economy is one factor and many materials, such as polycarbonates, are simply too expensive. For good economy, the tier sheet must be a thin, lightweight member having a thickness of not more than 1.27 mm and preferably not more than 0.76 mm. When the sheets are extruded (the usual mode for the manufacture of plastic sheets), they must be absolutely flat and remain flat when in use. Can bodies are very lightweight members, each weighing approximately one-half ounce, and any irregularity in the surface of a tier sheet, such as would not even be onjectionable in other uses of the sheet, will cause can bodies to tip over or move out of place. Certain types of plastic materials can not be used because they could impart an odor or taste to a beverage subsequently put into the can. Finally, the plastic material must be strong, hard but not brittle, and have suitable properties at temperature

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extremes which might be encountered.

A number of synthetic plastic resins were considered including the following which are indicative of sheet materials available but which are not suitable for the purpose at hand. They include:

Polystyrene - odor and taste objectionable A.B.A. - odor and taste and expensive High density polyethylene - dimensionally unstable and too slippery Low density polyethylene - too flimsy and soft Polypropylene homopolymer - too brittle A random copolymer of ethylene and propylene was found to be generally suitable except for its frictional characteristics which were physically altered as hereinafter described. This material is available as a proprietary product, such as

NORCHEM NPP 7300, from Northern Petrochemical Co. at

Des Plaines, Illinois; also,

SHELL POLYPROPYLENE 6313 S.M. , from Shell Chemical Co. at Houston, Texas.

Also it was found that the addition of ethylene propylene rubber may be desirable to increase toughness. The addition of this ethylene propylene rubber can be achieved by direct compounding or by the inclusion of a rubber modified propylene with a selected ethylene-propylene copolymer. A suitable rubber modified propylene is SHELL POLYPROPYLENE 7328.

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The formulation of these products are trade secrets and they are generally described by their physical properties. However, for the purpose at hand, studies indicated that a variation from 2 to 10 percent ethylene (all percentages given herein being by weight) to 98 to 90 percent propylene was suitable. A lower percentage of ethylene produced a harder product more suitable for use in hot weather while a higher percentage of ethylene produced a softer product more suitable for use in cold weather. If ethylene propylene rubber is included the amount used should not exceed 20 percent; otherwise the blended resin will be too flexible.

The selected resin blend is treated with an antistatic agent such as:

ATMDL 84 from I.C.I. Americas; at Wilmington, Delaware. This proprietary product is ordinarily blended into the resin by the supplier and only a small amount, less than 1 percent, is required.

A tier sheet formed with the selected resins may have a thickness of 0.38 to 1.27 mm, with a preferred thickness being in the range 0.51 to 0.76 mm. The desirable physical properties were found to be:

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Tensile strength: 218 to 246 kgf/c , ASTM D638

Flexure Modulus: 9845 to 13362 kgf/cm , ASTM D790 Notched Izod Impact Strength: §22.78°C, 1.0 to 2.0

§-17.78°C, 0.5 to 0.8 ASTM D256 Hardness, Rockwell R: 80 to 90 ASTM D785

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Density: 0.89 to 0.91 ASTM D1505

As heretofore mentioned the frictional quality of the selected material was not entirely suitable with a smooth surfaced sheet as it is normally extruded. Three friction factors must be considered: (a) that can bodies easily slide on the upper surface of a tier sheet, requiring a comparatively low friction coefficient on the upper surface, (b) that the lateral movement of can bodies across the tier sheet will not move the sheet which rests upon a lower tier sheet of can bodies, requiring a somewhat higher friction coefficient on the under surface of the sheet and, (c) that the sheets above and below a can body have a sufficient frictional grip as to prevent the cans from falling out of place as shown by C in Fig ^* . 3.

Fig. 5 shows a fragment of the upper can body C resting upon a tier sheet T and a fragment of the lower can body C supporting the tier sheet. It is to be noted that the bottom of the upper can body contacts the top surface of the tier sheet at a gently rounded annular base 20 and that the top of the lower can body is flanged as at 21 and contacts the under surface of the tier sheet at a sharp circular edge 22.

It was found that the upper can body would slide across a smooth top surface of a tier sheet with a higher frictional resistance than it would if the surface were roughened as indicated at 23. On the other hand the sharp top edge of the lower can body would better resist sliding

13 of the sheet if the under surface of the sheet were smooth, as shown at Fig. 3.

Accordingly, the roughening of the top surface of the tier sheet solved the required differential frictional resistance between the top surface and under surface of the sheets. It was found that the degree of roughness could vary from 0.76 to 1.52μm.

This friction differential between the top and under surfaces can also be controlled by laminating the under surface of the tier sheet with a thin layer of compatible material having a selected higher coefficient of friction such as a polymer of ethylene and vinyl acetate.

The frictional differential need not be great and it must be boςne in mind that the top surface must not be too slippery for there must be sufficient friction at both the top and under surfaces to hold the can bodies in place after the container is completed.

Tests indicate that suitable and desirable frictional coefficients between the upper and lower can bodies and the respective top and under surfaces of the tier sheet are as follows:

Desirable Frictional Coefficients Top Surface Under Surface maximum 0.33 no upper limit minimum 0.29 0.35

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Insofar as can be ascertained, it appears that the difference of frictional coefficients between the upper and under surfaces should be at least 0.02.

I have now described my invention in considerable detail. However, it is apparent that others skilled in the art can devise and build alternate and equivalent constructions which are within the scope and spirit of my invention. Hence I desire that my protection be limited only by the scope of the appended claims.

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