AU723597B2

AU723597B2 - Method for manufacturing flexible containers made of thermoplastic plastics

Info

Publication number: AU723597B2
Application number: AU17825/97A
Authority: AU
Inventors: Cornelius Nittel
Original assignee: Nittel & Co KG GmbH
Current assignee: Nittel & Co KG GmbH
Priority date: 1996-05-07
Filing date: 1997-04-10
Publication date: 2000-08-31
Anticipated expiration: 2017-04-10
Also published as: AU1782597A

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Nittel GmbH Co. KG ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Method for manufacturing flexible containers made of thermoplastic plastics The following statement is a full description of this invention, including the best method of performing it known to me/us:-

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5* la The invention relates to a method for manufacturing flexible containers made of thermoplastic plastics by means of swaging or blow molding, having edges running rectangularly.

Such methods have been known for a long time and when manufacturing small containers, as a rule no problems occur. This is also true for the manufacture of large containers of cubic shape when applying blow molding and swaging methods as far as in doing so, rigid containers are produced having a large wall thickness. However, if the wall thickness is minimized S.in order to thereby form flexible foldable containers, particularly at the corners thin portions occur. This frequently results in leakages which cannot be permitted.

For blow molding, it has to be attempted to blow up the molding from a preform or parison out of the ring nozzle of the extruder. In this case, the wall thickness only permits a minimization for favorable form relationships. Otherwise here too, weak portions result with the danger of leakage.

There is a possibility for the traditional swaging to apply male molds.

However, they can only be used for open trough-shaped dies.

In the so-called twinsheet method, as described for example in EP-O 579 737 Al, molding is realized in the two die molds substantially by using a vacuum. The closed die does not permit auxiliary molding devices such as male molds. Therefore, for larger moldings the swaging depth is limited.

P:\OPERCAE1782-97-I1spe.d -29A)/O -2- At the lowest portions, it can only be achieved with a general minimization of the wall thickness as compared to other portions of the wall of the container. The problem, that it is extremely difficult to obtain a uniform wall thickness over the total area of a cubic container, mainly concerns the corner regions.

Therefore, in DE-40 22 591 Al, it has been attempted to limit the weak portions at least in that the sheet material used is subjected, with its molecular orientation, to a particularly calculated curvature in the region of the corners. However, the apex also remains only in an approximately crowned corner mold and is limited to relatively large wall thicknesses for safety reasons already for smaller containers having a maximum content of up to liters.

o• *The invention may advantageously provide a design for the corner region to be sufficiently o thick mainly for larger containers, also for generally smaller wall thickness of the container, and to adjust it to the rest of the sheet appearance.

According to the invention, there is provided a method for manufacturing flexible containers made of thermoplastic plastics comprising rectangularly running edges, by oooomeans of swaging or blow molding processes, wherein the edges are molded into the internal of the container contrary to their final arrangement. According to a further aspect of the invention, there is provided a flexible container made of thermoplastic plastics, having rectangularly running edges, manufactured by means of swaging or blow molding processes, wherein the edges contrary to their final arrangement, are molded into the interior of the container. When manufacturing cuboid-shaped containers, the corners of the cuboid are molded towards the inside. That means from the molding technology point of view, the corner regions are molded in the hollow of the container opposite to its arrangement according to the method of manufacturing. The corners can be formed in a pyramid shape, whereby the edges of the pyramid can comprise roundings, the radii of which can preferably be 10 mm and more. Generally, the edges can comprise curvatures.

The pyramid shaped indents are, as a rule, formed symmetrically/diagonally into the cavity of the mold and are provided with suitable radii. The corners can also be formed in the P:NOPER\CAEI782-97-180)p.dc29A)( AXI -3shape of ball segments, the radii of which can be 10 mm and more. The suitable radius depends on the size of the container.

With the inventive method, advantageously the forming of the corners is displaced to the center of the mold. Thereby, a larger amount of swagable thicker sheet material at this point hits the molding displaced towards the inside. With a suitable selection of the transition zones in the wall of the mold, a very uniform distribution of sheet mass is possible. It has to be noted that all corners of the container are formed in the same way and that the radius of the curvature of the surfaces resulting with the corner region directed towards the inside substantially have the same radius of curvature.

o S•After removal from the mold, the shape of the container is obtained by excrescensing the corners. The entire container manufactured according to the invention including its corner regions comprises a substantially uniform wall thickness. Thereby it is achieved that for the Procedure of Permission for the transport of fluids according to UN standards on rails, roads and by sea, no problems occur.

9*o* 9 The inventive method is suitable for the manufacture of containers of any size. However, it is particularly suited for the manufacture of large containers, particularly containers with a content of more than 50 liters, preferably with a content of more than 100 liters. The 9..containers can be particularly used for the transport of fluids or powders in a supporting casing, but also without it. The method is particularly suited for the manufacture of flexible plastic containers which can be inserted into foldable and collapsible pallet containers and which store and transport liquid products. In a known way, paperboard constructions as well as supporting structures consisting of wood, metal or rigid plastics or the like are used as casing. A casing made of woven polypropylene material (FIBC) can also be used.

With the inventive method, the edges of cylindrical containers can also be molded correspondingly.

P:\OPER\CAE\7825-97-8sp.ds -29)6/O -4- Further details and advantages of the invention can be derived, by way of example only, from the embodiment represented in the drawing. It shows: Fig. 1 a side view of an inventively manufactured container; Fig. 2 a plan view of the container according to Fig. 1; Fig. 3 an enlarged view of the corner marked with a circle in Fig. 1; Fig. 4 an embodiment of the corner corresponding to Fig. 3 of another container; and Fig. 5 a further embodiment of the corner as well as the associated insert in a swaging mold.

The container shown in Figs. 1 and 2 is manufactured according to the so-called twinsheet -method by swaging two thermoplastic sheets by means of a pressure difference in a known manner. In this method, the position of the seam 2 of the two halves 1A and 1B of container 1 is thermoplastically welded after the swaging process. At least one insert 3 is 15 introduced in the top surface of the container, by means of which filling of the container 1 can be performed. The insert 3 can be formed as a fill-in socket having thread.

Corresponding members can be inserted at the top side of the container as vent openings toe* and in the bottom part as discharging sockets. The shown container used for testing

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purposes was cuboid-shaped and had a content of 750 liters. Its length was 1080 mm, its width 930 mm and its height 765 mm. The weight of the container was 4.5 kg, its minimum wall thickness was 0.4 mm. As material, LDPE was used.

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0Oo In the following, one inventive embodiment of the eight corners of such a container is described. The upper corner marked with a circle in Fig. 1 is represented in Fig. 3 with enlarged scale. It can be seen from this figure that the edge 4 of the container 1 is running perpendicularly upwards is flattened in the form of a flat surface 5 in the region of the corner, followed by the edge 6 of the top surface of the container. When manufacturing the container, this flattened edge 5 is drawn inwardly in the shape designated by reference numeral 5A and is brought into the final shape only after the thermoplastic connection of the two container halves 1A and lB and the removal from the manufacturing mold.

P:\OPER\CAE\ 7825-97.-1 80spedo-29/i6A) Fig. 4 shows another embodiment for forming the corners of a container. This embodiment has the form of a ball segment which is, when manufactured, drawn inwardly from the edged formed by the surfaces 4 and 6 according to the surface 7A and which is only brought towards the outside afterwards into the final shape designated with reference numeral 7.

Fig. 5 shows an embodiment corresponding to Fig. 4 together with the mold member 8 inserted into the corners of the swaging mold when manufacturing the container.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge of Australia.

o Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. Method for manufacturing flexible containers made of thermoplastic plastics, comprising rectangularly running edges, by means of swaging or blow molding processes, wherein the edges, contrary to their final arrangement, are molded into the interior of the container.

2. Method according to claim 1 for manufacturing cuboid-shaped containers, wherein the corners of the cuboid are molded towards the inside.

S3. Method according to claim 2, wherein the corners are molded pyramidally. to t o t o

4. Method according to claim 3, wherein said edges of the pyramidal molding are rounded and/or flattened.

5. Method according to claim 4, wherein the radii of the pyramidal molding are equal to or larger than 10 mm.

6. Method according to claim 2, wherein the corners are formed in the shape of ball segments.

7. Method according to claim 6, wherein the radii of the ball segments are equal to or larger than 10 mm.

8. Method according to one of the preceding claims, wherein the container is manufactured by a swaging method of a double sheet made of thermoplastic plastics, the edges of which are preferably thermally connected to each other.

9. Flexible container made of thermoplastic plastics, having rectangularly running edges, manufactured by means of swaging or blow molding processes, wherein the R AL,4 edges, contrary to their final arrangement, are molded into the interior of the A ii 1 P:\OPER\CAE17825-97-180spe.doc-29A)/J i -7- container.

Container according to claim 9, wherein for a cuboid shape, the corners of the cuboid are molded towards the inside.

11. Container according to claim 10, wherein the comers are molded pyramidally.

12. Container according to claim 11, wherein the edges of the pyramidal molding are rounded and/or flattened.

13. Container according to claim 12, wherein the radii of the pyramidal molding are equal to or larger than

14. Container according to claim 10, wherein the comers are formed in the shape of ball segments.

Container according to any one of claims 9 to 14, wherein the thickness of the walls is approximately constant also in the region of the corners.

16. A flexible container and/or a method of manufacturing same substantially as hereinbefore described with reference to the drawings. S. DATED this 29 th day of June 2000. Nittel GmbH Co. KG by DAVIES COLLISION CAVE Patent Attorneys for the applicant (s)