Packing containers of laminated material having venting means

A packing container e.g. for sterile milk is manufactured from laminated material which is folded and sealed to the desired container shape. In the seal, cut surfaces facing towards the inside will occur which have to be sealed so as to prevent the central paper layer of the material from absorbing some of the contents. Usually this is done by means of a strip of a plastic material which is impermeable to liquid. When the packing material is sterilized and exposed to high temperatures these strips are often damaged, because the moisture present in the paper layer of the laminate is converted into vapor and penetrates the strip softened by the heat. In accordance with the invention the seal is now ventilated with the help of ducts extending through the seal in such a manner that the vapor can escape to the surrounding air without affecting the sealing strip which thus remains intact and can fulfil its intended sealing function.

BACKGROUND AND SUMMARY OF THE PRESENT INVENTION 
The present invention relates to a packing container of laminated material 
comprising a seal wherein a first edge area of the laminate is sealed to a 
second edge area, the side of the seal facing towards the inside of the 
packing container being covered by means of a liquid-tight material strip. 
The invention also relates to a packing laminate web for production of the 
container. 
Packing containers for liquid foodstuffs are generally manufactured from 
the laminated material which comprises a central carrier or base layer of 
paper or cardboard which is covered on both sides with a thermoplastic 
material, e.g. polythene. The paper layer in this case has a carrying 
function, whilst the thermoplastics on the one hand makes the material 
impermeable to liquid and on the other hand makes possible a heat-sealing 
of the material without a supplementary adhesive. 
A known packing container for milk is manufactured in that a laminated 
material of the aforementioned type is fed to a packing machine in the 
form of a web. In the machine the material web is converted to tubular 
shape, in that the longitudinal edge portions of the material web are made 
to overlap one another, whereupon they are heated so that the 
thermoplastic layers reach their softening temperature and are compressed 
to a longitudinal liquid-tight overlap joint. The filled tube is then 
converted to a line of connected, cushion-like containers in that the tube 
at uniform intervals is compressed and sealed in transverse zones. The 
cushions formed, wholly filled with contents, are subjected moreover to a 
forming process in the course of which forming jaws give the desired 
shape, e.g. parallelepipedic shape, to the packages. 
The longitudinal overlap joint mentioned above is formed in a known manner 
in that the two edge areas of the material are placed on top of one 
another and are heated and compressed to a liquid-tight seal. One edge 
area will then be located inside the finished container, which means that 
the cut edge remains unprotected so that the central paper layer of the 
laminate will come into contact with and absorb some of the contents. To 
prevent this, the seal is generally provided with a so-called longitudinal 
joint strip, that is to say, a liquid-tight material strip of the same 
material as the plastic layer of the laminate, e.g. polythene, which 
strip, after the sealing is applied over the edge area situated inside the 
packing container in such a manner that the cut edge itself is sealed off 
from the interior of the package. 
When the packing container described is to be used for the packing of 
sterile contents, the packing laminate is sterilized with the help of a 
sterilizing agent, e.g. hydrogen peroxide, which is applied to the packing 
laminate. After a certain time in contact with the packing laminate the 
sterilizing agent is removed again, which is done among other things by 
heating the inside of the packing material tube so such a temperature that 
the sterilizing agent is evaporated and can be drawn off by ventilation. 
Since the outside of the material tube during the heating is exposed to a 
certain amount of cooling by the surrounding air, the packing laminate 
will not be heated to temperatures which are harmful for the laminate. In 
the area of the longitudinal joint of the tube, however, where the edge 
zones overlap one another, the material is so thick that the cooling will 
be appreciably impaired. This means that the sealing zone is subjected to 
such a high temperature that the sealing strip commences to melt at the 
same time as the natural moisture of about 6% enclosed in the paper layer 
of the laminate is made to evaporate, which is true in particular for the 
edge area located close to the centre of the material tube. Since the cut 
edge of the edge area is enclosed underneath the sealing strip, the space 
underneath the strip will be filled with expanding vapour until the 
sealing strip, softened up by the heat, is deformed or breaks, so that the 
vapour can escape from the space between the sealing material strip and 
the laminate. 
Up to now it has been tried to eliminate the difficulties described by 
designing the sealing material strip in such a manner that the vapour 
cannot penetrate the same. In a known solution a laminated strip is 
proposed which had an enclosed core of heat-resistant material, e.g. 
HD-polythene. This strip has certainly proved to function relatively well, 
but the manufacture of the strip is complicated and the strip becomes 
relatively expensive. 
It is an object of the present invention to overcome the abovementioned 
problem and to provide a solution which allows the utilization of an 
uncomplicated and inexpensive longitudinal joint strip. 
This object has been achieved in principle in accordance with the invention 
in that the longitudinal seal is designed in such a manner that the vapour 
can be drawn off by ventilation without affecting the sealing strip, and 
more particularly, the abovementioned object has been achieved in that a 
packing container of the type described in the introduction has been given 
the characteristic that ducts are arranged to connect a space present 
between the material strip and the laminate with the outside air. The 
ducts make possible a ventilation of the previously closed space 
underneath the sealing longitudinal strip, as a result of which the vapour 
produced can directly escape so that no significant vapour pressure is 
capable of building up. 
A preferred embodiment of the arrangement in accordance with the invention 
has been given the further characteristic that the ducts extend between 
the surfaces lying against one another in the sealing area. 
A further embodiment of the arrangement in accordance with the invention 
has been given the further characteristic that the ducts in a seal of the 
overlapping type are in the form of depressions provided in the edge area 
of the laminate. 
A further embodiment of the arrangement in accordance with the invention 
has been given the further characteristic that the depressions comprise 
grooves, extending transversely in relation to the longitudinal direction 
of the seal, which are of a length slightly exceeding the width of the 
seal. 
According to the invention a packing laminate web for production of the 
packing container has been given the characteristics that one edge area of 
the web is provided with a series of depressions. 
Further embodiments of the packing laminate web in accordance with the 
invention have been given the characteristics which are evident from 
reading the specification and claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The packing container shown in FIG. 1 is of substantially parallelepipedic 
shape with front and back faces 1, side faces 2 and end faces 3 in 
parallel pairs, only one of which is apparent in the figure. The two end 
faces 3 have transverse sealing fins 4 which are folded down so as to rest 
substantially against the respective end face. Between the end faces 3 and 
the narrow side faces 2 there are substantially triangular corner lugs 5 
of surplus material which for geometric reasons arise when the packing 
container is converted from cushion shape to parallelepipedic shape. All 
corner lugs 5 are folded in against the small side faces and end faces and 
joined to the same. The packing containers finally have a vertical seal 6 
of the overlap type extending longitudinally over parts of the end faces 
3. Adjointing the seal 6 can be seen a large number of depressions of 
ducts 7 which are formed in the packing laminate and whose function will 
be described in more detail in the following with special reference to 
FIG. 2. 
FIG. 2 shows on a larger scale a section through part of the seal and the 
side face 1 of the packing container according to FIG. 1. The figure 
clearly shows how the packing laminate is composed of different layers, 
namely a central layer 8 which is relatively thick and consists of paper, 
and relatively thin layers 9, 10 of homogeneous thermoplastic material, 
e.g. polythene, applied on both sides of the same. The figure also shows 
how the longitudinal seal 6 is formed as an overlapping joint in that the 
edge areas 11 and 12 of the packing laminate have been brought together to 
overlap one another, whereupon the two thermoplastic layers 9 resting 
against one another are heated and pressed together. 
The cut edge 13 of the edge area 12 is situated inside the packing 
container and is covered by a sealing material strip 14 which runs along 
the whole length of the seal. The sealing strip 14 is made of the same 
material as the sealing layer of the laminate, that is to say, polythene, 
and can therefore be simply joined to the layer 9 by thermosealing. The 
grooves 7 are constituted of indentations or depressions in the surface of 
the packing laminate in the edge area 12 which faces towards the edge area 
11. The depressions 7 extend substantially at a right angle from the cut 
edge 13 and are of such a length that they reach with their opposite end 
beyond the sealing zone of the edge areas 11 and 12. As a result the 
grooves 7 together with the edge area 11 form ducts which extend from the 
elongated space 15 which is delimited by the edge area 11, the cut edge 13 
and the sealing material strip 14 to the outside of the packing container. 
The grooves 7, as mentioned earlier, consist of depressions or indentations 
in the material surface. The grooves are made preferably by passing the 
material through a roller whose peripheral surface is provided with ribs 
of dimensions corresponding to the grooves 7. In a typical packing 
material with a total thickness of approx. 0.5 mm the grooves may have a 
depth of approx 0.1 mm. The length of the grooves exceeds by a few 
millimeters the width of the sealed area and as a typical value with a 
sealing width of 7 mm, a groove length of 9 mm has proved appropriate. 
The manufacture of the packing containers in accordance with the invention 
may take place e.g. in the known type of machine described earlier which 
for the purpose is additionally provided with a wheel or a roller so as to 
achieve the desired pattern. The material is made to pass the roller 
before conversion to tubular form, so that the edge area 12 of the 
material web 1 has been provided with depressions 7 when the longitudinal 
seal 6 is formed. During the subsequent heating of the material with the 
object of eliminating superfluous sterilizing agent and ensuring a good 
sterilization effect the moisture included in the paper layer 8 of the 
material will, as mentioned previously, commence to boil and be converted 
to vapour. The moisture in the edge area 12 will escape via the cut 
surface 13 and fill the elongated space 15. Owing to the presence of the 
depressions or ducts 7 in accordance with the invention the vapour can 
then escape to the surrounding air via the ducts 7 without any major 
pressure being created in the space 15. The sealing material strip 14 
warmed up by the heat to its softening temperature thus fails to be 
subjected to any pressure from the expanding vapour in the space 15 and as 
a result the risk of the material strip being penetrated or deformed has 
been fully eliminated. Since the material strip remains intact and thus 
ensures complete tightness of the sealed area, the ducts 7 do not bring 
about any disadvantage from a point of view of tightness. 
The embodiment described with ducts in the form of pressed, transverse 
recesses in the material has proved very suitable, since it provides a 
good ventilation for the vapour formed whilst the depressions can be 
produced at very low cost without any appreciable changes in the machine 
for the manufacture of packing containers of the present type. Naturally, 
the ducts may also be given a different shape and it is even conceivable 
to give the ducts the form of a series of holes which penetrate through 
the outside edge area 11 in front of the space 15. However, such an 
embodiment in most cases does not represent an advantage over the 
embodiment described, which provides perfectly satisfactory ventilation 
without any kind of weakening of the packing material. 
Finally, it is also possible to provide one edge area of the packing 
laminate web with a series of depressions at an earlier stage, i.e. in 
connection with the production of the laminate. Such a laminate can be 
used in presently existing packing machines without any alterations of the 
machines, which can be advantageous in certain cases. Such a laminate is 
preferably given the same preferred form of indentations or depressions as 
earlier described, i.e. a series of grooves extending transversely from 
the edge of the web. The grooves should of course be placed on that 
surface of the laminate, which is intended to form the outside of the 
finished packing container.