US3439590A - Method for heat sealing - Google Patents

Description

A r l 22, 1969 R B R ET A; 3,439,590

METHOD FOR HEAT SEALING Sheet Filed Dec. 15, 1964 INVENTORS' WILLIAM ROSENBERG CHARLES J. F DOUGLAS JOHNSON GRAFTON ROSS W. HOHMAN FIG. 2.

ATTORNEY April 22, 1969 w. ROSENBERG ET AL METHOD FOR HEAT SEALING Sheet Filed Dec. 15, 1964 FIG. 4.

PAPER STOCK} FIG FIG. I6.

INVENTORJ WILLIAM ROSENBERG CHARLES J. GRAFTON F. DOUGLAS JOHNSON ROSS W. HOHMAN ATTORNEY April 22, 1969 W. ROSENBERG ET AL METHOD FOR HEAT SEALING Sheet Filed Dec. 15, 1964 INVENTORS WILLIAM ROSENBERG ATTORNEY CHARLES J. GRAFTON F. DOUGLAS JOHNSON ROSS. W. HOHMAN GEM:

Sheet 4 of 4 w. ROSENBERG ET AL METHOD FOR HEAT SEALING INVENTORS April 22, 1969 Filed Dec I 500 2. Me E T ROSS w. HOHMAN wig/{WW ATTORNEY United States Patent M 3,439,590 METHOD FOR HEAT SEALING William Rosenberg, Charles J. Crafton, Frederick Douglas Johnson, and Ross W. Hohman, Baltimore, Md., as-

signors to Maryland Cup Corporation, Owings Mills, Md., a corporation of Maryland Filed Dec. 15, 1964, Ser. No. 418,434 Int. Cl. C09j /10; B32b 31/20; B31b 17/60 US. Cl. 9355.1 2 Claims This invention relates to paper cups; and it is more particularly concerned with the manufacture of such cups.

A popular form of paper cup in wide, general use is known in the industry as the fiat bottom cup. It is made, generally, of a circular bottom wall having a downwardly extending flange and a frustoconical side wall the bottom of which fits around the flange of the bottom wall. A marginal extension of the side wall is bent around the flange of the bottom wall and securely fitted to it by a bottom expander. These two parts, so arranged relative to each other, are glued together, the glue being applied at a convenient step in the assembly of the blanks which form these parts.

In recent years, the industry has developed many improvements in these cups. A significant improvement is the coating of the inside surfaces of the cups with a plastic material to form a barrier against hot liquids, like coffee, and cold liquids to prevent them from coming into contact with and being absorbed by the porous paper. In many instances, these coatings are applied to the cup after their manufacture.

It has been suggested that the plastic coating might be applied to the surface of the blank members before they are assembled and that the paper coating be utilized as the sealing agent in lieu of the conventional glue.

Attempts to carry out this procedure have met with many difiiculties. An important difficulty resides in the fact that the plastic material must be heated to the point of tackiness in order for it to be available as a bonding agent. However, in this tacky condition, it is diificult to handle the blanks on the assembly machinery. Slippage necessary to position the blank sections relative to each other is markedly reduced. Also, the surface of the mandrels are exposed to the tacky plastic causing the machinery to become fouled and requiring frequent stoppage and cleaning of the parts affected.

Also, it has been a problem to produce cups of this kind from laminated sheets, such as paper cup stock laminated with aluminum foil, a formidable difficulty being the partial delamination or separation of the plies from each other under the heat required to soften the plastic coating. As a result, partial separation of the plies is encountered.

The general object of the present invention is the provision of an improved method of manufacturing flat bottom cups from plastic-coated blanks.

A specific object of the invention is the provision of such an improved method which is adaptable to commercial automatic cup-making machinery and by means of which the plastic coating does not interfere or adversely affect the operation of the machinery.

Another object of the invention is the provision of such a method which is highly effective and reliable in commercial operations.

A further object of the invention is the provision of 3,439,590- Patented Apr. 22, 1969 such a method which is applicable to the production of cups from laminated sheet material, such as sheets of ordinary paper cup stock laminated with aluminum foil.

These and still further objects, advantages, and features will appear more fully from the following description together with the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic plan view of a rotatable turret forming part of a typical cup-making machine including the radial mandrels with modifications in accord ance with this invention and illustrating the series of steps in the formation of the cups.

FIGURE 2 is a perspective view of a blank member used in forming the side wall of the cup.

FIGURE 3 is a perspective view of a blank member used in forming the bottom wall of the cup.

FIGURE 4 is a cross-sectional view along the line 4-4 of FIGURE 2.

FIGURE 5 is a view similar to FIGURE 4 showing a modified form of the blank.

FIGURE 6 is a schematic longitudinal cross-sectional view of the blank members of FIGURES 3 and 4 at one station in the series of assembly operations apart from the machine as a whole.

FIGURE 7 is a schematic longitudinal cross-sectional view of the same blank member in a subsequent step in the method of assembly designated as the initial heating station and showing in section a fragmentary portion of the unit used to direct controlled hot air to the blank members.

FIGURE 8 is a longitudinal cross-sectional view of the same blank members in a subsequent step of the method showing diagrammatically the member used to curl the end marginal portion of the wall blank about the flange of the bottom blank.

FIGURE 9 is a schematic view of the same blank parts in a subsequent step of the process illustrating the condition at the second heating stage.

FIGURE 10. is a longitudinal sectional view showing the relation of the parts at a subsequent step generally referred to in the art as bottom expansion.

FIGURE 11 is a side elevational view of one ofthe hot air units partly broken away.

FIGURE 12 is an end elevational view of the unit of FIGURE 11.

FIGURE 13 is a sectional view along the line 13--13 of FIGURE 11.

FIGURE 14 is a cross-sectional view along the line 1414 of FIGURE 11.

FIGURE 15 is a longitudinal sectional view on an enlarged scale of a fragmentary portion of a cup made in accordance with this invention by the use of plasticcoated blank members.

FIGURE 16 is a view similar to FIGURE 15 by the use of blank members plastic-coated on one side and metal foil laminated on the opposite side of the side wall part.

Referring with more particularity to the drawing, the rotary turret shown in FIGURE 1 comprises a conventional hub member 21 having frustoconical mandrels 22 secured thereto and extending radially outwardly therefrom. The turret is conventionally rotated intermittently by means (not shown), whereby the mandrels are successively positioned adjacent stations at which various steps in the process of forming the cups are carried out.

The sequence comprises, generally, placing on each mandrel at station A a blank 23 that is to form the bottom section of the cup and then at subsequent station C a blank 24 that is to form the side wall. The blank 23 is disposed at the outer end of the mandrel and the blank 24 is disposed around the circumference of the mandrel. The ends 25 and 26 of the blank 24 are lapped and secured together on the mandrel at station C by conventional means not shown. At subsequent stations, these blanks are secured together to form the cup which is finally discharged from the mandrel.

In the process of forming cups from ordinary paper stock, the blank 23 forming the bottom of the cup is secured to the side wall by gluing. When plastic-coated blanks are used, it is possible to dispense with the glue by heating the parts of the blanks to be joined together to the point of tackiness of the plastic coating. One method of accomplishing this is described in US. Reissue Patent 25,302, wherein the blanks are heated to render the plastic tacky and then are moved relative to each other to position the members in proper relation to each other.

A problem is involved in heating the plastic to the point of tackiness. A substantial amount of heat is required and the intervals of rest or dwell times of the mandrels at each station are quite short. Short dwell periods on the order of 0.3 to 0.5 second are necessary in order to achieve an economical production capacity.

When the blanks are in their final position, heat is difficult to penetrate the layer of paper, paper being a substantial heat insulator. Consequently, in prior methods, the heat is applied directly to the plastic layer or to both sides of the paper stock where the plastic is to be heated to a point of tackiness in order to achieve the condition of tackiness in the short interval of time available. In accordance with the present invention, controlled heat is applied at two separate stations. At the first or preheating station D, the heat is applied in an amount just sutficient to bring the plastic coating to a condition of impending tackiness. For polyethylene coatings, a temperature of about 750 F. is preferred when a dwell period of about 0.3 to 0.5 second is used. The heat is applied through the medium of hot air. At the second heating station F, the temperature is increased and an added quantity of heat is supplied to bring the coating to a condition of tackiness. For polyethylene plastic, a temperature of about 850 F. for the same dwell period has been found satisfactory for this purpose.

Between the station D and the station F, the blank parts 23 and 24 are subjected to a conventional operation known as curling, whereby an annular marginal portion 25 of the blank 24 is bent around the flange 26 of the blank 23 in preparation of a final forming step known as bottom expansion. Consequently, as the heating station F is reached, the blank parts are in position for the final forming operation and the heating is provided to effect or to cause the plastic to become tacky. The final forming step takes place at station G and consists of the conventional bottom expansion (see FIGURE whereby the curled portion 25 is pressed into final position. This is diagrammatically illustrated in FIGURE 10 by means of an inside roller 27 and an exterior anvil 28. However, in actual commercial operations, a more elabo rate mechanism is used. See US. Patent No. 2,842,033.

At the succeeding station H, the completed cup is discharged from the mandrel by directing a blast of air through an axial passageway 31 of the mandrel to a difiuser 32 having openings 33 at the periphery. In passing from the station H to station A, the mandrel is subjected to a cooling operation by continuing the blast of air to bring its temperature to a point below the softening tem erature of the plastic. Unless this were done, the blanks placed on the mandrel at the start of the cycle of operation would have their plastic coating become tacky. Hence, it would be difiicult, if not impossible, to manipulate the blank members on the mandrel. Also, the tacky plastic would foul the mandrel and require wasteful stopping of the operation to clean them. The efficiency of the operation from the standpoint of heat flow can be sharply controlled by adjusting the amount of heat extracted at this point so as to prevent the plastic from becoming tacky and subsequently adding only that amount of heat required to supplement the residual heat in the mandrels at the station D.

The use of the preheating station D is especially important in the manufacture of cups from laminated materials, such as paper stock, having a laminated metal foil 34 on one side of the paper stock 35 and the plastic coating 36 on the opposite side (see FIG. 5). Adhesive materials 37 used to secure the laminates together soften under the temperatures used to soften the plastic coating and may, in fact, be the same material. Consequently, it is important that heat applied to the laminated sheets be such as to avoid separation of these laminates. This is effectively accomplished in accordance with the present invention where the final heating step to soften the coating is not applied until the blanks are in their final relative positions except for the bottom expansion step. The latter step, however, does not adversely affect the laminate bonding but, in fact, increases it under the pressure applied. Hence, the tendency of the laminates to separate is eifectively negated and overcome.

The preheating station D and the final heating station F are each equipped with a heater 38. These heaters at both stations are of substantially the same construction but operated at different temperatures. Each comprises a cylindrical shell 39 of stainless steel or other oxidation resisting material, adapted to be disposed at the stations in alignment with the mandrels 22 as they come to rest at these stations. The adjacent end of the cylinder is provided with a plate 40 having a circular groove 41. The groove is provided with two radially spaced circular rows of apertures 42 and 43 on either side of the center 44 of the groove. The center of the groove has substantially the same diameter as the bottom edge 45 of the cup so that the apertures 43 on the inner row are directed toward the inside of the cup while the outer row 42 is directed toward the outside. The plate 40 is secured to an inner flange 46 of retaining rings 47 of an outer cylinder 48 by means of bolts 49.

On the interior of the cylindrical shell 39, there is mounted a cylindrical core 50 of a diameter less than the inside diameter of the shell 39 so that it is disposed coaxially therewith in spaced relation to the shell. The core is held in the axial position by means of set screws 51 passing through the shell and contacting the core.

The core is provided with a series of radial slots 52 that extend longitudinally from one end of the core to the other end through which air to be heated is directed from an outside source (not shown) into the shell through an opening 53 of an end wall 54 at the opposite end of the shell. The core is also provided with a pair of longitudinal bores 55 and 56 in which there are embedded electrical heating elements 57 and 58, respectively. A third longitudinal bore 59 is provided with a thermocouple 60 for connection to a temperature gauge and regulator (not shown).

The shell 48 is provided with mounting lugs 61 and a sheet of insulation 62 about the outer surface to reduce heat radiation losses.

Having described our invention, we claim.

1. A method of joining a closure disc having a peripheral flange to the end wall of a frustoconical shaped body to form an open-ended paper container comprising supporting said disc within the said body with the peripheral flange extending toward the end wall and the inside surface of the body and the surface of the flange adjacent said inside surface having a thermoplastic coating therein, blowing hot air at one station into the hollow end against the parts to be joined until the coating is preheated to a physical state of impending tackiness, causing the flange of the disc and the end Wall to contact, rolling the edge of the end wall over the flange of the disc, said disc being in a position adjacent said end wall while the coating remains in a physical state of impending tackiness, then blowing air at a higher temperature at a subsequent station against the said parts until the coating becomes tacky and adhesive, then pressing the parts together, then cooling the parts to restore the polyethylene to its initial physical condition.

2. The method as defined by claim 1 in which the thermoplastic coating is a polyethylene resin.

References Cited UNITED STATES PATENTS Bergstein 156227 Brown 9336.1 Wills 156497 Von Hofe.

Olson et al.

Cummings 93-36.1 Harrison et al.

Monroe et al 156-497 X EARL M. BERGERT, Primary Examiner.

C. B. COSBY, Assistant Examiner.

US. Cl. X.R.

Claims (1)

1. A METHOD OF JOINING A CLOSURE DISC HAVING A PERIPHERAL FLANGE TO THE END WALL OF A FRUSTOCONICAL SHAPED BODY TO FORM AN OPEN-ENDED PAPER CONTAINER COMPRISING SUPPORTING SAID DISC WITHIN THE SAID BODY WITH THE PERIPHERAL FLANGE EXTENDING TOWARD THE END WALL AND THE INSIDE SURFACE OF THE BODY AND THE SURFACE OF THE FLANGE ADJACENT SAID INSIDE SURFACE HAVING A THERMOPLASTIC COATING THEREIN, BLOWING HOT AIR AT ONE STATION INTO THE HOLLOW END AGAINST THE PARTS TO BE JOINED UNTIL THE COATING IS PREHEATED TO A PHYSICAL STATE OF IMPENDING TACKINESS, CAUSING THE FLANGE OF THE DISC AND THE END WALL TO CONTACT, ROLLING THE EDGE OF THE END WALL OVER THE FLANGE OF THE DISC, SAID DISC BEING IN A POSITION ADJACENT SAID END WALL WHILE THE COATING REMAINS IN A PHYSICAL STATE OF IMPENDING TACKINESS, THEN BLOWING AIR AT A HIGHER TEMPERATURE AT A SUBSEQUENT STATION AGAINST THE SAID PARTS UNTIL THE COATING

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