Method and apparatus for wrapping a film around an object

Abstract

An object is first wrapped with a strip of thermoplastic film such that upper edges of the strip project upward past a top face of the object and fold inward onto outer edge regions of the top face of the object. Then a cover sheet is laid on the top face over the folded-in edges of the strip with outer edges of the cover sheet projecting outward past and hanging down around the wrapped object outside the film strip. A heated plate is then pressed down against the cover sheet and hot air is blown against the strip on the side faces so as to shrink the strip against the side faces and such that the hot air rises and welds the outer cover-sheet edges sheet to the strip around upper regions of the side faces.

Claims

1. A method of shrink packaging an object having outwardly directed side faces and an upwardly directed top face, the method comprising the steps of sequentially: wrapping a strip of thermoplastic film around the side faces of the object such that an upper edge of the strip projects upward past the top face of the object and folds inward onto outer edge regions of the top face of the object; laying a cover sheet of thermoplastic film on the top face of the object over the folded-in upper edge of the strip with an outer edge of the cover sheet projecting outward past and hanging down outside the film strip along upper edge regions of the side faces of the object; forming a downwardly open and downwardly extendable shrinking chamber between a vertically shiftable heated plate having outer edges and a plurality of vertically extendable side walls movable independently of the plate, extending downward from the outer edges along and spaced horizontally outwardly from respective side faces of the object, and having lower ends carrying an annular shrink frame vertically displaceable with the walls; moving the plate, walls, and shrink frame down over the object wrapped in the strip of film and cover sheet to enclose the top face and to press the heated plate down against the cover sheet to flatten same and the folded-in upper edge of the strip against the top face; maintaining the plate at a temperature sufficient to soften the cover sheet but below a melting point of the cover sheet such that the cover sheet is heated by the plate only to a temperature sufficient to soften the cover sheet but not to melt and weld the cover sheet to the top face; and thereafter, while holding the cover sheet down on the top face with the heated plate, blowing hot air from the shrink frame between the side faces and the side walls of the chamber while the walls are moving downward from an upper position with the shrink frame level with the upper regions of the side faces so as to first lift the outwardly projecting edge of the cover strip, then, as the walls and shrink frame move downward to a lower position with the shrink frame level with lower edges of the side faces, cause the lifted outwardly projecting edge to drop back against the strip at upper regions of the side faces and shrink against and weld to an outer face of the strip around the upper regions of the side faces with the hot air trapped between the side walls and side faces while pressing and shrinking the strip against the side faces of the object as the shrink frame moves into the lower position, the walls laterally closing the chamber between the shrink frame and plate when in and between the upper and lower positions.

2. The method defined in claim 1, wherein the strip is wrapped in overlapping turns around the object starting from a lower end thereof such that each turn overlaps the turn immediately below.

3. The shrink-packaging method defined in claim 1, further comprising the step of: pressing the plate down onto the cover sheet so as to force out air between the cover sheet and the top face.

4. The shrink-packaging method defined in claim 1, wherein in the upper position the hot air is blown against the side walls of the object below the upper edge regions of the side faces such that the air rises up around the object in the shrinking chamber to the upper edge regions and there heats the outer edges of the cover sheet.

5. The shrink-packaging method defined in claim 1, further comprising the step of: heating the air to such a temperature as to shrink the strip and outer edges of the cover sheet inward against the side faces.

6. The shrink-packaging method defined in claim 1, further comprising the step, after starting to blow the hot air against the side faces, of lowering the frame from the upper position to the lower position.

7. The shrink-packaging method defined in claim 6, further comprising the step, after commencement of lowering the frame from the upper position, of: lifting the press plate upward off the top face while the hot air is blown against the side faces such that the rising hot air is trapped above the cover sheet on the top face to heat the cover sheet.

8. An apparatus for shrink packaging an object having outwardly directed side faces and an upwardly directed top face, the apparatus comprising: a support for holding the object with the side faces vertical and the top face horizontal; means for wrapping a strip of thermoplastic film around the side faces of the object such that an upper edge of the strip projects upward past the top face of the object and folds inward onto outer edge regions of the top face of the object; means for laying a cover sheet of thermoplastic film on the top face of the object over the folded-in upper edge of the strip with outer edges of the cover sheet projecting outward past and hanging down outside the film strip along upper edge regions of the side faces of the object; a vertically displaceable heat-controlled plate above the upper face and having an outer edge projecting horizontally outward past the side faces of the object; respective vertically extendable side walls projecting downward from the outer edge of the plate, movable vertically independently of the plate, each spaced horizontally outward from a respective one of the side faces of the object, and forming with the plate a downwardly open and downwardly expandable shrink chamber spacedly surrounding the object; an annular shrink frame carried on lower ends of the side walls; means for maintaining the plate at a temperature below a melting point of the cover sheet but sufficient to soften the cover sheet; means for downwardly moving the heated plate, side walls, and shrink frame from an upper position with the shrink frame level with the upper regions of the side faces toward a lower position with the shrink frame level with a lower edges of the side faces while the walls laterally close a space between the shrink frame and the plate to press the heated plate down against the cover sheet to flatten same and the folded-in upper edge of the strip against the top face while the heated plate softens the cover sheet without welding it to the top face; and means for blowing hot air between the side walls and the side faces while the plate is pressed down against the cover sheet so the hot air is trapped in the shrink chamber between the side walls and the side faces and first lifts the outer edge of the cover lift with the hot air and then as the walls and shrink frame move to the lower position lets the lifted outer edge drop back against and weld to an outer side of the strip around upper regions of the side faces while pressing the strip against the side faces.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

(2) FIG. 1 is a side view of an apparatus according to the invention t the start of the wrapping process;

(3) FIG. 2 is a side view of the apparatus toward the end of the wrapping process; and

(4) FIG. 3 is a perspective top view of the wrapped object.

SPECIFIC DESCRIPTION OF THE INVENTION

(5) As seen in FIGS. 1 and 2 an apparatus according to the invention shrinks a film 1 onto an object or product stack 2 that in the illustrated preferable form is rectangular with a top face 3, four side faces 3, and a bottom face 3. A heat-shrinkable film strip 4 is first wrapped around the side faces 3 of the stack 2. The strip 4 is wound so that edges 6 project up past top edge regions 16 of the side faces 3 of the stack 2, where they fold of their own accord over onto outer edge regions 5 of the top face 3. A film cover sheet 7 is then placed on the top face 3 of the stack 2 over the folded-over edges 6 of the strip 4. The cover sheet 7 here itself has edges 8 that project laterally outward past the top edge region 5 of the stack 2 and hang down by gravity along upper side edge regions 16. Here the strip 4 is preferably shrunk onto the stack 2 or onto the side faces 3 of the stack 2 by use of a hot-air shrink frame 9. As shown, the shrink frame 9 may comprise a plurality of heaters 20 that are distributed around its perimeter and heat the strip 4 to shrink it tightly onto the stack 2.

(6) Preferably here the method according to the invention comprises first moving the shrink frame 9 vertically to a center position as shown in FIG. 1, roughly vertically midway between the top face 3 and bottom face 3. This action presses a temperature-controlled press plate 10 down onto the top face 3 of the stack 2 or onto the film cover sheet 7 lying thereon.

(7) Advantageously the press plate 10 is heated or heated in controlled fashion to a temperature that is below the melting temperature of the plastic of film cover sheet 7 but above its softening temperature. Preferably, the press plate 10 is pressed onto the film cover sheet 7 in such a way that air is forced out laterally from between the sheet 7 and the top face 3 of the stack 2, exiting from the folded-over edges 6 of the strip 4, or this air is forced out from between the edges 6 and the cover sheet 7. Preferably, the press plate 10 has an all-around outer edge region 11 that projects on all four sides of the stack 2 beyond the upper edges 5 of the stack 2.

(8) Advantageously, the press plate 10 and its edge regions 11 form a closed top wall of a substantially upwardly and laterally closed shrink chamber 12 that has side walls 13 that each extend parallel to a respective side face 3 of the stack 2. Preferably, these side walls 13 are each formed by at least two vertically telescoping side-wall parts 14 and 15. The upper wall parts 14 here advantageously extend up to the press plate 10, and the lower wall parts 15 of the side walls 13 preferably are connected to the shrink frame 9 and can be moved together with it. This enables the shrink chamber 12 to be variably adapted to product stacks 2 of different heights.

(9) Hot air is generated in the center position of the shrink frame 9 as shown in FIG. 1 so that this hot air rises inside the chamber 12 along the four side faces 3 of the stack 2. The position here of the shrink frame 9 is such that the downwardly hanging film edges 8 of film cover sheet 7 are also heated by the rising hot air in the same way as upper portions of the strips 4 that contact the sides 3 of the stack 2, with the result that the film edges 8 along the sides 3 of the stack 2 are welded or bonded at upper regions 16 of the side faces 3 to the strip 4. The cover-film edges 8 are therefore welded all around to the film 4 covering the side faces 3 of the object 2 so that the object 2 is completely enclosed and, in fact, waterproof from above.

(10) Preferably, the shrink frame 9 is then moved downward on the stack 2 as shown in FIG. 2. The shrink frame 9 here is moved down at sufficiently high speed for air to be pressed down and out of the space between the strip 4 and the side faces 3 of the stack 2. The drawing further shows that the stack 2 is preferably sitting on a pallet 17. Preferably, welding is effected between the strip 4 and another thermoplastic floor film 19 that lies between the pallet 17 and the stack 2 (the so-called undershrink) in the lower position shown in FIG. 2 for the shrink frame 9 with in fact outer edges of the floor film 19 hanging down like the edges 8 to be pressed against and bond inwardly to side faces of the pallet 19 and outwardly to the windings or winding of the film 4. The shrink frame 9 then travels back upward to effect a shrinking-on or secondary shrinking-on of the strip 4 along the sides 3 of the stack 2. The shrinking-on of the strip 4 can, however, also occur only as the shrink frame 9 travels down along the stack 2. The shrinking-on of the strip 4 onto the sides of the stack 2 is also referred to as side shrink.

(11) Preferably, the press plate 10 that was pushed down onto the top face 3 of the stack 2 is moved upward (FIG. 2) during the undershrink, that is the movement downward from the middle position of FIG. 1 to the lower position of FIG. 2. A space 18 is thus created between the press plate 10 and film cover sheet 7 that has been previously brought to temperature by the press plate 10, into which space 18 the rising heated air can penetrate. As a result, the film cover sheet 7 is heated further. Heating of the film cover sheet 7 is advantageously effected with such low heat that no welding occurs of it to the folded-over edges 6 of the strip 4. During the subsequent cooling, the film cover sheet 7 is tensioned relatively tautly over the top face 3 of the stack 2, thereby creating an advantageous flat surface on which no detrimental accumulations of water or water puddles can form.

(12) A width b of the edges 6 of the strip 4 may preferably range between 50 mm and 400 mm. A width B of the film edges 8 of the film cover sheet 7 may range between 100 mm and 300 mm.