GB2143506A - Container of thermoplastic material - Google Patents

Abstract

A container of thermoplastic material has a bottom 20 and a side wall 10 formed from a foil blank connected along two opposing edges. A stacking rim has an area A of constant cross section bounded by areas of relatively sharp taper, the lower part B of the container tapering to a much lesser degree. The container is preferably produced by forming the blank into a tube and heat shrinking it over a core prior to attachment of the bottom 20 by means of glue or welding. <IMAGE>

Description

SPECIFICATION Container of thermoplastic material process and apparatus for its manufacture Background of The Invention The invention concerns a container fabricated from thermoplastic material. Containers of this type are frequently used in the packaging industry whenever significance is attached, on one hand, to the visibility of the merchandise and, on the other hand, to hygienic packaging. A problem associated with these containers is that normally they must be shipped by the manufacturer to the packaging firm and/or manufacturer of the merchandise to be packaged, and that they require a relatively large shipping volume.

Therefore, it has been previously suggested to produce such containers in the form of a truncated cone so as to enable stacking.

A prior method of producing such containers provides for stamping first a suitable plastic foil blank which is then glued or welded at two opposite overlapping edges. Thereafter, a suitable bottom part is made which has an angled circular edge. This bottom part is slipped over the container cylinder, and the edge of the bottom part is glued or welded as well to the overlapped part of the container cylinder. However, this method does not permit any special shaping, for instance providing beads as a stacking rim in the container wall or similar expedient.

The manufacture of a stackable container through truncated cone shaping of a round can container wall requires defined foil blanks involving losses in the form of foil scrap.

Another widely practiced method is the hot forming (deep drawing) of the entire container. While permitting the production of containers within a certain size range, limitations do exist here as well; these are essen tialiy dictated by the ratio of container height to container diameter and/or container width.

Depending on the type of foil material used, shallow containers can normally be produced without problems, whereas deep containers involve heavy thickness fluctuations in the container walls, resulting in a limited load capacity of the container. In manufacturing stackable containers in the form of truncated cone container walls, the container cylinder requires a wall inclination of at least five percent, an inclination which is readily recognizable with the naked eye and which is not desirable for all containers. Deep drawing also makes container imprinting relatively expensive, since the printing must be conducted on finish-drawn containers. When using hard polyvinyl chloride (PVC) for clear plastic packaging it cannot be ruled out, in deep drawing, that sometimes a coloration of the PVC foil will occur which renders the container unusable for the intended purpose.

Therefore, the problem underlying the invention is to so design a stackable themoplastic container of that type that for reduction of the shipping volume several containers can be stacked smoothly and without binding and that, for another, this container is easy to manufacture and whereby, specifically, an arbitrary ratio of container diameter to container height may be provided.

Summary of The Invention This problem is solved in accordance with the invention by the provision of a container of thermoplastic material having a container bottom, the container side wall comprising a foil blank which is connected along two opposite edges, the cross section in the upper area of the container forming a stacking rim which is essentially constant while decreasing in the lower area between the stacking rim and container bottom, in the form of a truncated cone, the cross section in the area which is immediately beneath the stacking rim decreasing more severely in relation to the container bottom than in the remaining lower area, and the cross section of the stacking rim being smaller in its uppermost circumferential area than it is in the remaining area, specifically decreasing in truncated cone manner.

The design of the container from a rectangular foil blank where opposite side edges are glued or welded together has the advantage that truncated cone container walls can be made with very little side inclination, such that it cannot be readily recognized with the naked eye but nevertheless retains the stackability of the containers.

Since the cross section of the lower area immediately beneath the stacking rim decreases relative to the distance from the container bottom more severely than in the remaining area, a relatively heavy constriction is created beneath the stacking rim, forming practically a "stop" for the upper peripheral edge of the stacking rim, of the adjacent container following below, in which the top container is inserted.

Since the cross section of the stacking rim in its uppermost circumferential area is smaller than in the remaining area, a constriction is created as well on the upper edge of the stacking rim which, when stacking several containers, supports the above "stop function" and, moreover, facilitates the placement of the container lid, since it is then "guided" on the stacking rim by the tapers generated.

The process of the present invention for manufacturing a container of this type provides for forming from stretched plastic foil a container cylinder blank; this blank is slipped over a core which determines the final shape of the container cylinder, the blank is heated in the shrink range of the stretched plastic until it has at least partially assumed the shape of the core, and the container cylinder so shaped is removed from the core.

The basic idea of the invention process employs for the manufacture of packaging containers the shrink method previously known for packaging purposes (West German OLS 1,479,805). This method is employed ir large scale also for various packaging types, but always in a manner such that the plastic shrink foil envelopes the packaged goods themselves. This method has not yet been used for the manufacture of containers from thermoplastic material independently from the specific shape of the respective packing goods.

The advantages of the method of the invention include the facts that containers with any desired taper can be made, preferably also with little taper of the container cylinder, and that the desired spatial structures can be readily created, for instance a stacking rim.

If desired, it is possible also to include the container bottom in the shrink process so that container wall and container bottom can be made in one and the same operation.

Further embodiments of the process of the invention are set forth in the appended dependent claims.

Brief Description of The Drawing An embodiment of the containers of the present invention and of the process for their manufacture will be more fully explained hereafter with the aid of the accompanying drawing: FIGURE 1 shows a cross section of a container; FIGURE 2, a side elevation of two stacked containers; FIGURE 3, apparatus for the manufacture of containers according to FIGURE 1; and FIGURE 4, the finished container cylinder which upon completion of the process of the invention surrounds a core.

Initial Description The container of the invention comprises a container cylinder lo and a container bottom 20 (and a container lid not illustrated in the drawing).

For the illustrated embodiment of a round can (FIGURE 1), the container cylinder 10 consists of a rectangular foil blank rolled into circular shape and glued or welded together at the butting side edges, which blank assumes through the subsequently explained shrinking onto a core the cross sectional shape illustrated in the figures. Specifically, the cross sectional progression permits the following differentiation: An upper area A serving as stacking edge 1 Oa, its cross section being esentially constant but tapering inwardly in its uppermost circumferential area C, and a lower area B representing the major part of the container wall and having a truncated cone shape which makes it possible to nest two containers (FIGURE 2) until their stacking rims rest on each other.

The round can features for that purpose in its area of transition to the stacking rim 1 Oa relatively severe reduction of cross section, whereas the reduction of cross section is constant in the remaining area B relative to the height of the container.

FIGURE 2 shows schematically how containers of that shape can be nested; evident are the overlapping ares 60, 70 of the two containers where the cylindrical container blank is formed in an alternative embodiment by overlapping and welding and/or glueing of the rectangular foil blank.

On its other end, the container cylinder 10 has a circular flange 1 0b projecting inwardly in which the container bottom 20 is placed.

The container bottom 20 features previously known depressions 22 and/or circular grooves 21 for stabilization.

The manufacture of the containers of the invention proceeds as follows (FIGURE 3 and 4): To begin with, a blank 11 of the eventual container cylinder is made by stamping rectangular plastic foil blanks which, as the case may be, are imprinted and glued or welded so as to form a cylinder.

This blank 11 is slipped over a core 13 which determines the final shape of the container cylinder 10; FIGURE 3 shows for clarity a core 13 with a relatively large taper.

Next, the core 13 with the blank 11 is introduced into a furnace 40 featuring heating elements 41 in the form of hot air nozzles, whereafter the shrinking process of the stretched plastic foil begins, starting at the lower container end. Upon completion of the shrinking process the container cylinder 10 preferably is completely in contact with the core 13, with the projecting rim 21 of the blank 11 producing the circular flange lob of the finished container 10.

Upon completion of the shrinking process the finished container cylinder 10 is removed from the core 13. In the case of a heavily tapered conical area C of the stacking edge 1 0a the core 13 has suitably a two-part design with a gap 1 3a between the two core halves in their expanded condition. The two core halves are then caused to contract for removal of the container cylinder 10, that is, the gap 1 3a is closed, The diameter of the contracted core half should not be greater than the smallest diameter in the area C of the stacking rim 10a, i.e., the opening diameter of the container. Upon removal of the container a container bottom 20 is then introduced into the container from above until it sits on the circular bead or flange 1 orb, where it is either glued in place or welded to the bead lOb by means of conventional welding devices (for instance, "sonotrodes" (supersonic welding) or electrodes (high frequency welding).

Simple in principle, this type of manufacture can be arbitrarily varied and also automated in simple ways. The placement of the blank, introduction into the furnace 40, removal of the container cylinder, introduction and gluing and/or welding of the container bottom can be conducted by conventional process technology, with the container component handling essentially being performed with the aid of pneumatic machine components.

In a modification of the described embodiment, this process makes it readily possible to integrate the container bottom 20 with the shrinking of the blank 11, and in fact, in a way such that the container bottom has a diameter somewhat larger than the end face of the form core 13, producing then in the shrinking of the blank a bead around the container bottom which retains it in a formfitting manner. This will eliminate additional operations such as the gluing or welding of the container bottom to the container cylinder.

This process can be performed especially when the material of the container bottom 20 differs from the material of the blank 11, so that the container bottom 20 will not be affected by the shrinking operation in the furnace 40.

Specifically, this can be accomplished either by making the container bottom from cardboard or by providing for it a thermoplastic foil having a shrink range which lies above the shrink range of the plastic foil of the container cylinder 10.

With other shapes of the container cylinder 10 it may be favorable to somewhat temper the core 13 as well, and to supply heat through the core, at a temperature below the shrink range of the plastic material. For purposes of producing a particularly uniform container cylinder, specifically when it is more heavily tapered, a vacuum may be produced between the core 13 and the blank 11 during heating, thereby supporting the blank 11 in making intimate contact with the core 13.

In the framework of an automated production of the containers of the invention, the furance 40 may also be fashioned as a shrink tunnel through which the core 13 is passed with the blank 11 slipped on it.

The advantages of the container of the present invention can be summarized as follows: It consists completely (container and lid) of homogenous material without any additional aid, and the cylindrical shape of the upper container part assures an accurately fitting and close placement of the lid and thus a tight seal against environmental influences, for instance no influencing by odors.

The uniform container cylinder thickness guaranteed by the shrink process over the entire circumferential area results in a high upset load capacity, since weak areas due to localized thinning of material are eliminated.

The stackability permits a reduction of storage and shipping volume to approximately one-tenth of the volume required for containers which cannot be stacked. Automatic stacking and unstacking of several containers enables an automation and thus a considerable increase of the packing output. Also largevolume containers, for instance those which no longer can be reasonably produced by the previously described deep drawing process, can be manufactured economically by the process of the invention.

Since the container manufacture involves no scrap, a minimization of material consumption is guaranteed as well.

The container of the invention is readily able to meet legal requirements.

Claims (20)

1. Container of thermoplastic material having a container bottom, characterized in that its side wall comprises a foil blank connected along two opposing edges, that its cross section in an upper area forming a stacking rim is constant while its cross section decreases in a lower area between said stacking rim and the said container bottom in truncated cone manner, that the cross section in the lower area immediately beneath said stacking rim decreases more severely relative to the distance from said container bottom than in the remaining lower area, and that the cross section of said stacking rim is in its uppermost circumferential area smaller than in its remaining area, decreasing specifically in truncated cone manner.

2. A process for the manufacture of containers from thermoplastic material according to claim 1, characterized in that a blank of a container cylinder is made from stretched plastic foil, that the blank is slipped over a core which determines the final shape of the container cylinder, that said blank is heated in the shrink range of the stretched plastic material until the blank has assumed at least partially the shape of said core, and that the container cylinder so formed is removed from said core.

3. Process according to claim 2, characterized in that heat is supplied by means of hot air.

4. Process according to claim 2 or 3, characterized in that the application of heat to the blank begins in the area where said blank varies most from the shape of said core.

5. Process according to claim 2, characterized in that said blank includes a rim projecting beyond said core, the rim forming at least part of a container bottom when heated, or supporting said container bottom.

6. Process according to claim 2, characterized in that said blank has a rim projecting beyond said core, the rim molding itself to the end face of said core when heated and forming a circular flange for a container bottom to be inserted subsequently.

7. Process according to claim 5, characterized in that said container bottom is slipped on said core prior to heating so that the projecting rim of the shrinking plastic foil will partly wrap over said bottom.

8. Process according to claim 7, characterized in that said container bottom is a plastic foil having a shrink range lying above that of the plastic foil for said container cylinder, and in that the heating temperature lies between these two ranges.

9. Process according to claim 7, characterized in that said container bottom is a plastic foil which is not stretched, and that the melting temperature of this plastic ranges above the heating temperature.

10. Process according to claim 7, characterized in that said container bottom is made from cardboard.

11. Process according to claim 6 or 7, characterized in that said container bottom is welded to said circular flange of the container cylinder by application of pressure.

12. Process according to claim 2, characterized in that said core is heated to a temperature below the shrink range.

13. Process according to claim 2, characterized in that during heating a vacuum is generated between said core and said blank.

14. Process according to claim 2, characterized in that heat is supplied through said core.

15. Apparatus for the production of a container in accordance with the process of claim 2, characterized by a core determining the final container shape and a furnace, the inside walls of which are equipped with heating elements.

16. Apparatus according to claim 15, characterized in that said furnace is an individual furnace open toward the end face of said core, and has an inside diameter which is only slightly larger than the maximum diameter of said core.

17. Apparatus according to claim 15, characterized in that said furnace is a shrink tunnel.

18. A container of thermoplastic material substantially as herein described with reference to ana as illustrated in the accompanying drawings.

19. A container of thermoplastic material whenever produced in accordance with the process as claimed in any of claims 2 to 14.

20. A process for the manufacture of containers from thermoplastic material substantially as herein described with reference to the accompanying drawings.