Packing container

The invention relates to packing containers formed from shrinkable plastics material of the type in which a plastics blank is shrunk onto a mold to produce a form having a bottleneck shape. The portion so given bottleneck shape has longitudinal and relatively parallel surface pleats. The plastics material so used has a relatively thick base layer of shrinkable foamed plastics material and an outer layer of homogeneous, relatively non-shrinkable plastics material.

The present invention relates to a packing container manufactured from a 
shrinkable plastic material and comprising an end portion in the shape of 
a bottleneck of a substantially smaller cross-sectional area than the 
remainder of the packing container, the said container being of the type 
which is given the desired shape by forming a blank of plastic laminate to 
a cylinder of arbitrary cross-section, whereupon at least parts of the 
said cylinder are induced with the help of heat to shrink to the said 
bottleneck shape. 
In the technology of packing, glass bottles are often substituted by the 
corresponding containers made of plastic material. Naturally, these 
containers do not have to be given the traditional bottle shape, but it 
has been found that for certain products, such as e.g. wine and beer, the 
traditional bottle shape on the one hand is practical, and on the other 
hand is so customary among the consumers, that for the said products 
bottlelike containers are preferred instead of e.g. parallelepipedic 
containers. For both beer and wine and for a series of other liquid 
products, glass bottles have been replaced by blown plastic bottles of in 
particular polyvinyl chloride, an in many cases the traditional bottle 
shape has been retained to such an extent that in principle only the glass 
material has been exchanged for plastic material, which brings about the 
advantage that the bottles are not breakable in the same way as glass 
bottles. 
Glass bottles containing beer and wine are often provided with a cap and 
with a seal covering the bottleneck, which in most cases consists of metal 
foil which by folding can be made to adhere closely to the cap and to the 
bottleneck. It is the object of these metal foil seals to protect the cap 
and the pouring opening against contamination, to constitute evidence that 
the bottle has not been opened and not least to enhance the appearance of 
the package, and these metal foil seals are therefore often coloured so 
that they present a gold or silver lustre. 
It is of course also possible to provide plastic bottles with the 
abovementioned metal seals, but since these seals are manufactured from a 
relatively expensive material, and because the application of the seals is 
relatively expensive, it has been considered that metal foil seals can be 
used only for certain special, expensive luxury products, such as export 
beer and quality wines. It is possible, however, to provide in a simple 
manner plastic bottles with a pleating reminiscent of the said metal 
seals, provided the plastic bottles are of the type which is manufactured 
by shrinkage forming, and these plastic bottles are characterized in that 
the portion in the shape of a bottle neck has longitudinal, substantially 
parallel surface pleats which have been formed during the shrinkage 
forming of the container, and in that the plastic laminate from which the 
container is manufactured comprises a relatively thick base layer of 
shrinkable foamed plastic material and at least one outer layer of a 
homogeneous plastic material which during the shrinkage deformation of the 
laminate does not shrink, or which experiences a shrinkage only to a 
substantially smaller degree than the base layer, the said homogeneous 
plastic layer being attached to the base layer with such good adhesion 
that no delamination will occur during the shrinkage of the base layer, 
and that the homogeneous plastic layer is so thin and flexible that it 
does not to any appreciable extent counteract the shrinkage deformation of 
the base layer.

As mentioned in the introduction, packing containers are manufactured in 
accordance with the invention by shrinkage forming of a shrinkable packing 
laminate of the type which is shown in a strongly enlarged cross-section 
of FIG. 1. The packing laminate comprises a base layer 1 of an extruded 
plastic foam, preferably polystyrene foam, whereby the plastic foam 
material, directly after the extruding operation, is subjected to 
stretching which brings about a reduction of thickness of the material but 
also an extension of the closed cells 3 of the material, which in the 
manner as shown in FIG. 1 are given a lenticular or elongated form. The 
stretching can take place either in one direction or in two directions 
perpendicular to one another, and if the stretching takes place only in 
one direction the material will be shrinkable only in that direction, 
since the shrinkage characteristic is based on the fact that the cells 
which have been extended during the stretching will endeavour on renewed 
heating of the material to re-assume spherical shape. The laminate 
material shown in FIG. 1 also has an outer homogeneous plastic covering 2 
which may consist of polystyrene, acrylic material, polyvinylidene 
chloride or acrylonitrile compounds of the type marketed under the trade 
name BAREX. The laminate may also be provided with an inside coating of a 
homogeneous plastic material of the same type as the homogeneous plastic 
layer 2. 
It is important, however, that at least the outer plastic layer 2 should 
have good mechanical adhesion to the base layer 1 so that no delamination 
occurs between the plastic layer 2 and the base layer 1 when the laminate 
material is subjected to shrinkage deformation in connection with the 
heating of the laminate to such an extent that the foamed plastic material 
is made to soften and the cells in the base layer revert to their 
spherical shape. Moreover, the outer plastic layers 2 and 4 must not be so 
thick or so rigid mechanically as to counteract appreciably or prevent the 
shrinkage of the foamed plastic material. As a general rule it can be said 
that the outer plastic layers 2 and 4 shall have a thickness which is less 
than 10% of the thickness of the base layer, and preferably have a 
thickness of only approx. 5% of the thickness of the base layer. 
The blanks for packing containers in accordance with the invention are 
manufactured from a laminate of the type which has been described above 
and the plane cut-out blanks of this laminate are first formed to a 
cylinder in the manner as shown in FIG. 2. In FIG. 2 is shown how the 
package blank is given the shape of a circular-cylindrical cylinder 5 by 
joining together the edge zones of the blanks in a longitudinal joint 6. 
The cylinder need not necessarily have a circular cross-section, but in 
principle any cross-section would be conceivable. 
The cylinder formed is further processed in that it is threaded onto a 
mandrel 7, as shown in FIG. 3, whose shape corresponds to the inner 
contour of the desired packing container. As can be seen from the figure, 
a part of the previously formed cylinder will adhere to the walls of the 
mandrel whilst other parts 10 of the cylinder are not in contact with the 
mandrel when the cylinder 5 is threaded onto the mandrel 7. When the 
cylinder 5 has been placed onto the mandrel 7, at least the parts 10 of 
the cylinder 5 which do not adhere to the surface of the mandrel 7 are 
heated with the help of infrared radiation elements 9 and/or hot air which 
is blown against the parts 10 of the cylinder 5 with the help of blowing 
nozzles 8. When the parts 10 of the cylinder 5 have been heated to such an 
extent that the foamed plastic material in the base layer 1 has softened, 
the base layer 1 is caused to shrink, when, as can be seen in FIG. 4, the 
parts 10 of the cylinder 5 are induced to adhere to the shaped part 11 of 
the mandrel 7, so that the cylinder is shrunk to a bottleneck 12 whose 
cross-section is substantially smaller than the cross-section of the 
non-shrunk parts 13 of the cylinder. 
After the shrinkage operation the container body formed is removed from the 
mandrel 7, and, as can be seen from FIG. 5, the shrinkage formed container 
body has a multitude of surface pleats 14 along the shrunk part 12 in the 
shape of a bottleneck, whilst the remaining parts 13 of the container body 
do not have such surface pleats. 
The reason for the formation of the said surface pleats 14 is that the 
homogeneous plastic layer 2 in the packing laminate does not shrink, or 
shrinks to a lesser degree than the base layer 1, when the part 10 of the 
cylinder is heated. Owing to the homogeneous plastic layer 2 being 
relatively thin and flexible, the same is made to follow the base layer 1 
during the shrinking of the latter, but since the surface layer 2 itself 
does not shrink to the same extent as the base layer 1, a multitude of 
mutually parallel surface pleats 14 are formed along the surface of the 
homogeneous plastic layer 2, the preferred direction of which coincides 
with the axial direction of the cylinder. These surface pleats 14, which 
are shown in FIG. 5, resemble in an astounding manner the metal foil seals 
described in the introduction which are used in connection with glass 
bottles, among other things with the object of enhancing the appearance. 
For a further enhancement of the appearance of the bottle body formed, and 
for the imitation of the said metal foil seals, it is appropriate to 
metallize the part 12 of the packing container in the shape of a 
bottleneck presenting surface pleats 14. This metallization may be carried 
out before the shrinkage operation, but may also be carried out after the 
shrinkage has been accomplished, and the metallization may be done with 
the help of so-called vacuum metallization or in that the bottleneck part 
12 is sprayed or dipped in conventional manner in metallic lustre paint. 
After this treatment, the packing container is finished, and the finished 
packing container is shown in FIG. 6. The bottlelike packing container 
shown in FIG. 6 has been provided with a base 16 which may be realized in 
optional manner, but which is appropriately realized so that a disc of 
plastic material is sealed to the bottom edge of the container body 13. 
After filling, the packing container is provided with a cap of optional 
type, whereupon the packing container is ready to be distributed. 
It has been found that packing containers in accordance with the invention 
obtain an appearance which surpasses corresponding bottlelike containers 
which have been manufactured by blowing of a plastic tube, and it has also 
been found that the surface pleats 14 formed on the part of the packing 
container shaped like a bottleneck have a reinforcing effect on the 
bottleneck portion, and that the pleated portion moreover acts to some 
extent as a drip catcher. 
The shrinkage forming process shown in FIGS. 3 and 4 is only intended to 
illustrate the principle of shrinkage forming and it has been found that 
shrinkage forming can be carried out without applying an inner mandrel as 
shown in the embodiment. The choice of heating sources for the realization 
of the shrinkage depends upon the characteristics of the packing material 
and upon the mechanical equipment that is available, and it is thus 
possible to modify within wide limits the choice of heat sources as well 
as their placing. 
The said plastic material which is intended to form the outer homogeneous 
plastic layer has proved particularly suitable for being applied in 
connection with packing containers in accordance with the invention, but 
it is also possible to use other thermoplastic material in the homogeneous 
surface layer, and preferably such material that has greater toughness 
than the plastic foam.