The present invention relates to a method and an apparatus for produc¬ ing a tubular container according to the preambles to the respective independent claims. By tubular container it is meant a continuous walled container which has a cross-section taken through the wall of the container being substantially arbitrary e.g. circular, elliptical polygonal, having at least one corner, one flat surface, an inwardly curved surface etc. A round, oval or polysided container form embodi¬ ments of the invented container.

In the injection moulding of tubular containers of plastic material, the maximum length which can be obtained for the tubular portion of the container is determined by the selected material and the wall thickness of the tubular portion. In addition, the wall thickness may not be less than approx. 0.5 mm irrespective of the plastic material employed in the injection moulding. This relationship is clarified further later in the body of this description.

In the injection moulding of containers, the flow length of the sup¬ plied molten plastic material and, thereby, the unit formed in the in- jection moulding process is maximized by the material thickness. In purely practical terms, it has proved that injection moulded products having a wall thickness of less than 0.5 mm cannot be produced in mass production lines. Cf., for example, the book by Menges/Mohren, "How to Make Injection Molds", 1985, Hanser Publishers (ISBN 0-19-520744-0 Oxford University Press), p. 66.

Tubular containers of plastic material have recently been adopted for use as tubes for, for example, toothpaste, handcrea s etc. However, for the reasons outlined above it has been necessary to select material thicknesses for the tubular portion to be unnecessarily large or, oth¬ erwise it has been necessary to restrict the length of the tubular por¬ tion.

The present invention relates to a technique in which, as compared with the prior art techniques, the length of the tubular portion of the con¬ tainer is extended by at most approx. 4 times, at the same time as the material thickness in the tubular portion is reduced by at most approx. 4 times. Simultaneously, the material properties of the tubular portion are improved, in particular the mechanical material properties. The ma¬ terial properties of the tubular portion of the container will be modi¬ fied, implying, among other things, that the material in the walls of the mould portion will be softer and more readily mouldable than in prior art containers. Emptying of the contents from such containers will thereby be facilitated.

This object is attained by means of the technique as disclosed in the characterizing clauses of the appended independent claims.

The present invention realizes a considerable materials saving, with the result that the costs involved in producing such containers are drastically reduced as compared with that which applies to tubular con- tainers produced according the prior art technique. Cost savings of the order of magnitude of 40% have been achieved.

Expedient embodiments of the present invention are defined below in the appended subclaims.

The present invention will now be described in greater detail hereinbe- low with particular reference to a number of drawing figures, in which:

Fig. 1 shows a blank obtained by injection moulding;

Fig. 2 shows a container formed by extension of the blank;

Figs. 3-6 are cross-sections through an apparatus, the apparatus be¬ ing illustrated in mutually subsequent production stages of the blank;

Figs. 6-9 show an apparatus for forming the blank by extending the tubular portion of the blank in different stages of the forming process; and

Figs. 8a,b show parts of the apparatus of the figs. 7-9 for extending the tubular portion of the blank.

Fig. 1 shows an axial cross-section through an injection moulded blank 1, comprising a tubular portion 13 and an adjacent portion 19 including an emptying aperture or mouth 12. As a rule, the associated portion ta¬ pers towards the mouth 12. The tubular portion and, thereby, the blank, is open at that end 10 which is opposed to the emptying aperture or mouth 12. At its other end 11, i.e. in that end which encompasses the mouth, the tubular portion 13 connects to the tapering portion 19. A closer means 14 included in the blank is shown as placed in a position where, as a rule, it sealingly abuts against material portions of the emptying aperture or mouth 12. The closure means 14 constitutes an in¬ tegrated portion of the blank and is, via a hinge-like pivot 18, con¬ nected with the remainder of the blank.

Fig. 2 shows an axial cross-section through that container 2 which is obtained once the blank illustrated in fig. 8 has been extended, in that the material thickness of the tubular portion of the blank has been reduced on the extension or prolongation of the tubular portion. The tubular portion of the container, formed by the tubular part 13 of the blank, has been given reference numeral 23. The tapering portion 19 of the blank, together with the closure means 14 pivotal ly integrated with the tapering portion is not influenced by the forming process. The end 20 which is opposed to the emptying aperture or mouth 12 is still open, while the other end 21 of the tubular portion connects integrally with the tapering portion 19. All parts which are included in the con¬ tainer 2 constitute a unit in which the parts merge into one another without any mechanical joints or seams. In other words, the material in the container forms one single material piece (an integral unit).

Figs. 3-6 show a section through an injection mould 3 for forming plas¬ tic material to the blank 1. The injection mould 3 comprises a forward

portion 30, an intermediate portion 31 and a rear portion 32. The por¬ tions of the injection mould together enclose a forming cavity 34. The Figures show the injection mould once the plastic material has been supplied into the forming cavity 34.

Figs. 7-8 schematically illustrate longitudinal sections through parts of an apparatus for extending the blank 1 formed in the injection mould 3.

Fig. 7 shows that part of the apparatus where the tubular portion 13 of the blank 1 is surrounded by heating means 50 which abut against the outer surface of the tubular portion. A mandrel 51 is generally in¬ serted into the blank so as to stabilize the blank during the heating process. In certain embodiments, the mandrel 51 is also provided with means for temperature conditioning of the blank.

Fig. 8 shows the blank 1 once the material in its tubular portion 13 has passed through a gap 4 (cf. fig. 8a) for reduction of the material thickness under simultaneous extension of the blank.

Figs. 8a and 8b show in detail portions of a drawing ring 40 and a drawing ring mandrel 61 co-operating with the drawing ring when both of these devices are displaced by drive means (not shown in the Figures) to positions in which the gap 4 is formed between the drawing ring and the drawing ring mandrel. Fig. 8a shows the gap 4 without any plastic material being located therein, and fig. 8b shows the wall of the blank 1 on passage through the gap 4 formed by the drawing ring 40 and the drawing ring mandrel 61.

In Figs. 8a,b the drawing ring 40 is shown in one embodiment in which it is composed of two part rings 42,43. Each drawing ring is provided with a channel 44,45 for conveying thermal medium. The drawing ring has a guide surface 46 facing towards the drawing ring mandrel 61, against which surface the material in the blank is pressed on passage through the gap 4. The guide surface makes an angle with the surface 60 of the drawing ring mandrel and merges into a drawing ring surface 41 located substantially parallel with the surface of the drawing ring mandrel.

The surface 41 constitutes the bounding definition of the gap in that region of the gap where this is narrowest. The drawing ring mandrel is generally provided with channels 63 for thermal medium.

Fig. 9 shows the container 2 formed from the blank once a trimming de¬ vice 52 has cut away superfluous material at the open end 10 of the ex¬ tended blank 1 (the future filling aperture).

In Fig. 3, the three parts 30,31,32 from which the injection mould 3 is constructed are united and form the inner cavity 34 of the injection mould, with a form corresponding to the contemplated form or shape of the blank. A channel 33 runs through the forward end 30, and discharges in the inner cavity 34 in the region thereof where the emptying mouth 22 of the contemplated container is formed. The inner forming cavity 34 comprises two mutually interconnected part cavities, the one 34a for forming the blank body and the other 34b for forming the closure means 14 of the blank. An injection mould nozzle 35 is shown in connection with the channel 33. An arm 36 is displaceable by means (not shown) to and from the starting position illustrated in Fig. 3.

In Fig. 4, the injection mould is shown with the forward portion 30 separated from the intermediate portion 31 interconnected with the rear portion 32. In this position the mould is open and parts of the blank 1 are exposed.

Fig. 5 shows the arm 36 displaced to a position in which the arm presses the closure means 14 against the emptying mouth or aperture 12 of the blank. During displacement from the position which is shown in Figs. 3 and 4 the arm is moved to a position causing the arm, when traveling from said position to the position in Fig. 5, to displace closure means 14 in a pivotal motion from the position assumed by the closure means in Fig. 4 to the position assumed by the closure means in Fig. 5.

In Fig. 6, the intermediate portion 31 of the injection mould has been displaced from a position in which the intermediate portion abuts against the rear portion 32. The blank 1 has been removed from the male

portion 37 which is located within the blank on injection moulding thereof. The arm 36 is moved back to its starting position.

Fig. 7 shows the blank 1 placed between one or more heating means 50. In certain practical applications, in particular in large material thickness of the tubular portion 13 of the blank, a mandrel 51 is also inserted into the blank as a rule to constitute a supplementary heat source for the material during the heating cycle. The mandrel is gener¬ ally provided with heat-conditioning means, for example channels for a thermal medium.

Fig. 8 shows the blank la once a drawing ring 40 has passed the tubular portion of the blank in the axial direction thereof and during reduc¬ tion of the material thickness of the tubular portion. The drawing ring is disposed to maintain a surface temperature in its surface 41,46 fac¬ ing towards the plastic material which is adjustable to a level within the range of between approx. 50 and 70°C.

A mandrel (drawing ring mandrel) 53 is disposed to be at least partly located within the blank 1. The drawing ring mandrel forms a gap 4 to¬ gether with the drawing ring 40. The mandrel is disposed to maintain for the surface, facing the drawing ring 40 for forming the gap 4, a temperature which is adjustable at a level within the range of between approx. 50 and 100°C.

The gap 4 has a minimum gap width which is less than the material thickness of the injection moulded blank. The gap width is within the order of magnitude of between 0.1 and 0.9 mm, preferably between 0.13 and 0.55 mm, and in special cases between 0.13 and 0.45 mm. After pas- sage of the gap, the material thickness of the tubular portion of the blank substantially corresponds with the gap width of the gap employed in the reduction of the thickness of the material in the tubular por¬ tion of the blank.

The size of the extension of the tubular portion and the size of the reduction are adapted to suit properties desired in the finished con¬ tainer. The size of the reduction is selected so as to lie within the

range of between 2.5 and 5.0 times, preferably within a range of be¬ tween 3.5 and 4.5 times.

Fig. 9 shows the finished container (cf. Fig. 2) in position in the end station once trimming has taken place of the end region of the axial ly extended tubular portion of the blank 15a. As a result of this trimming operation, a substantially uniform defining edge will be achieved in respect of the opening or aperture in the end region 20 opposed to the emptying aperture or mouth 12.

The container 2 illustrated in Figs. 2 and 9 has a thin-walled tubular portion 23 which has, in its one end 20, an opening whose size (cross- section) corresponds to the inner cross-section of the tubular portion. This facilitates the supply of contents into the container. Closure of the filled container after filling is put into effect simply by means of a welding process, for example two heat punches which heat the mate¬ rial to fusion temperature. The thin-walled material rapidly assumes the form or shape which is determined by the form of the dies, as a rule a straight form, and rapidly arrives at the temperature which is necessary for the material to fuse together and form a tight seal. At its other end 21, the container is of a form and construction which wholly correspond with that which it obtains as a blank in connection with the injection moulding. The thin wall of the tubular portion of the container entails that the material is relatively easily deformable and that emptying of the container will thereby be facilitated.

Preferred thermoplastic materials in the practical application of the above described technology are polypropylene (PP), polyethylene tere- phthalate (PET), polyolefines (PE) and certain thermoplastic elasto- mers, for example styrene elastomers (SEBS) . It will be obvious to a person skilled in the art that the technique as disclosed in the fore¬ going is generally applicable to all plastic materials which have simi¬ lar reformation properties, i.e. materials possessing properties corre¬ sponding to those required for a container to be formed in the applica- tion of the above described technology.

It has surprisingly proved that, for certain given materials, for exam¬ ple polypropylene (PP), polyethylene terephthalate (PET), and polyole- fines (PE), it is possible to produce containers whose tubular portion has so-called "dead fold" properties. To achieve such properties, a material thickness is selected for the tubular portion of the container within the range of between 0.1 and 0.15 mm. The term "dead fold" prop¬ erties is taken to signify those properties which are known from tubes of aluminium, i.e. that the tube can retain its form after compression. The resilient return action which is known from earlier tubes of plas- tic material will thereby thus be avoided.

"Dead fold" properties are wholly unique properties in thin-walled plastic tubes. This ensures an almost complete emptying of the tube on use, which also prevents oxygen/air from being drawn back into the tube in connection with its being emptied.

The above detailed description has referred to but a limited number of embodiments of the present invention, but a person skilled in the art will readily perceive that the present invention encompasses a large number of embodiments without departing from the spirit and scope of the claims.